002. Chemical Factors in Hypertension (1950)

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CHEMICAL

FACTORS IN

HYPERTENSION

A collection of the papers and discussion

presented at the Symposium on Chemical

Factors in Hypertension held by the Division of

Medicinal Chemistry of the American Chemical

Society at the 115th national meeting in

San Francisco, March 28 to April 1, 1949

Number two of the Advances in Chemistry Series

Edited by the staff of I n d u s t r i a l an d E n g i n e e r i n g Chem i s t r y

Published May 23, 1950, by

AMERICAN CHEMICAL SOCIETY

1155 Sixteenth Street, N.W.

Washington, D. C.

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Copyr ight 1950 by

A M E R I C A N C H E M I C A L S O C I E T Y

A l l R i g h t s R eserv ed

American Chemical SocietyLibrary

1155 16th St., N.W.Washington, D.C. 20036


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FOREWORD

H yper t e ns i o n is tod ay one of t he ma jor an d most complex pr oblems

of medical pr actice. A s i n al l other areas affectin g h u ma n welfar e,

chemistry must p lay a part i n i t s final solut i on. W hen the chemist ,

the physiologist, the pharmacologist, and the cl in ic ian can meet oncommon ground to discuss the factors involved and can join forces i n

p lann ing new lin es of a tt ack, we ma y confiden tl y expect new advances

i n a better un derst and in g of, a n d i n methods for, contr ol of thi s

disease.

Grate fu l ackn owl edgment is made to W i l l i a m G . C l a r k , who was

p r i m a r i l y responsible for the program and who acted as chairman of

the symposium, and to H a r r y G oldbl att for the in tr oduct i on to th is

volu me. W e par ti cul ar l y appr eciat e th e fine cooperat ion of the

speakers i n par t i cipat in g i n the symposium and i n preparin g thei rmanuscr ipts for publ icat ion.

GLENN E . U L L Y O T , Secr e t a r y -T r easu re r

Di vision of M edicinal C hemistry, 1949


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Introduction

HARRY GOLDBLATT

Insti tute f o r Medical Resear ch, Cedars o f Lebanon Hospit al, a n d

Depar t ment o f Pat hology, Universit y o f Sout hern Calif ornia, Lo s Angeles, Calif .

T h i s sym po siu m is a ti mely one, for i t demonstrates clear ly that i t takes a long tim e

to establish beyon d question any single advance in medical know ledge. M or e th an 15

years have passed since the successful p r odu cti on of a persistent typ e of hy per tensio n i n

animals by interference wi th the hemody nami cs of their ki dneys. C onfi r mati on of thi s

finding came qui ck ly , but the exact mechan ism of the developm ent, a nd especially of the

maintenance, of this type of hypertension is by no means established and is still the sub

ject of much study.

F r o m what has already been published, and from what is contained in this sym

posium, it is abundantly clear that at least the early period of the hypertension which

develops after con stri ctio n of the ma i n renal arteries of anima ls is of h um or al or ig in .

T h e difficulty has been, and still is, the dir ect app li cati on of what h as been learned a bou t

experi mental renal h yp ertensi on to the pr obl em of the pathogenesis of h u ma n essential

hy per tensio n. O f the greatest imp or tance wou ld be the determi nati on of the exact cause

of the relatively long period of experimental hypertension and of human hypertension in

wh i c h , up to the present time, the existence of a humoral mechanism has not been proved.

Schroeder evidently believes in the chemical mechanism, even of arterial hypertensioni n m an ; yet he regards the in i t ia l condit ion as p r i ma r i l y of psych osomatic (sympathetic)

or ig in , with the neurogenic vasoconstriction in the vascular bed of the kidneys resulting,

i n th e in i t ia l stages, i n the release of the r enal h um or al pr essor mech ani sm an d, in the later

stages, the appearance of a var iety of pressor substances, p r obably acti ng in com bin atio n.

It is interesting that most of these pressor substances, with the exception of norepineph

r ine, are also of renal or ig in . It is clear that much remains to be learned about the

interrelationship of these pr essor substances w hi ch may h ave a com mo n or simi lar effector

substance.

It is comforting to hear Beyer say that "the various concepts of the etiology of essen

t ia l hy pertension are not mut ual ly exclusi ve" and that a combinati on of these theories may

be the corr ect id ea. H e, too, agrees that the in i t ia l vasoconstr i ct ion is pr obably motivatedby autonomic impulses, with the release of pressor substances that induce the develop

ment of vascul ar disease i n the ki dney s an d other organs. T h e weakness of B eyer 's co n

cept is that there is no unequivocal proof that hypertension per se produces arteriosclero

sis. E v e n i n the hy pertension associated w ith ph eochr omocy toma, for example, the de

velop ment of vascul ar disease i n the kid ney s or other organs, as a dir ect result of the h yp er

tension, has not been established.

Role of Adrenergic Blockade

N i c k e r s on also agrees that neurogenic factors ma y p lay a par t i n the or igin, mecha

nism, an d main tenance of essential h yp erten sio n; yet he admi ts th at th e role of adrener gic blockade (chemical sympath ectomy) i n the ther apy of hy pertensio n is sti l l obscure.

E v e n if the reni n-hyp ertensin mechani sm could be shown to pla y an imp or tant par t, at one

stage or another, in the or igin of human essential hypertension, yet the nature of the

stimulu s for the formati on or l i beration of the renin from the kidney into the blood must

sti l l be discovered. T h i s is a very im por tant gap in our knowledge, on the elucidati on of

wh i c h E r w i n H aas and the wri ter have been wor ki ng for several years.

T h e par tici pants i n this symp osiu m have not dealt to any extent with the subject of

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2 ADVANCES IN CHEMISTRY SERIES

ant irenin, but this continues to be an important matter and deserves more consideration

than it has received i n the past. I n our hands it has pr oved an interesting an d imp or tant

tool. I t is h igh ly pr obable th at hu mor al pressor substances, pro duci ng vasoconstricti on,

are concerned i n the in i t iat ion of arterial hy pertensi on i n ma n . I t ma y be, as all the au

thors have i ndi cated, that vasoconstrictor effector substances act in conju ncti on w ith

neurogenic stimuli to b r i n g about the persistence of the hy per tension. J ust wh at par tcertain hor mones of the adrenal cortex pl ay i n thi s ph enomenon is certain ly not estab

l ished. T h e fact tha t the substances r esponsible for the elevation of bloo d pressure are

present in such a small amount, and that at least some of them are h igh ly unstable, m u l t i

plies the difficulties. A s Schr oeder has stated, "T h e identi ficati on of the natur e of these

materi als is essential to the eluci dati on of the mech ani sm of thi s com mo n disease or gr oup

of diseases."

Although the development of agents capable of specifically and effectively blocking

response to sympathoadrenal activity is of the greatest importance, yet their significance

i n the treatment of cl inical hypertension wi l l certai nly depend, as N ic ker son has stated,

"up on the establishment of the part play ed by the sympath oadr enal system i n this ty pe

of h yp ert ensi on ." E xc ept in a few r are types of hy pertension , this role is sti l l obscure.T h er e is certain ly no definite simi lar ity between wh at is generally recognized as a neur o

genic type of experimental hypertension (carotid sinus hypertension) and what is usually

called essential h um an hyper tension. N ick erson admits, and the wr iter, of course, be

lieves, that hy pertension r esultin g from interference wi th renal hemody nami cs resembles

closely essential hypertension of man, and he goes so far as to state "that the develop

ment of this type of hypertension is completely independent of a nervous mechanism."

Wi t h th is the wr iter also agrees, and believes wi th h i m th at the asserti on th at nervou s fac

tors are important in the late stage of renal hypertension is far from being conclusively

established and that the crucial experiments or observations to prove this are sti l l to be

made.

T h e results of symp athectom y have not yet clearly defined the extent to w hich surg i

ca l elimi nati on of sympath etic vasoconstricti on may be expected to lower the blood pr es

sure in essential human hypertension and there is therefore no good reason for believing

that chemical (adrenergic) blockade can accomp lish more th an surgical excision. T h e u n

fortunate thing is that many of the adrenergic blocking agents have side effects that are

undesirable.

T h e par tici pants i n this symp osiu m are to be congratulated upon the restrain t th ey

have p racti ced i n the fair presentation of their own views and up on their sincere attempt

carefully to weigh the available evidence upon which they have based their cautious and

altogether reasonable, even if still debatable, conclusions. I n this pu bli cati on those inte r

ested in the subject of hypertension, from both the experimental and cl inical standpoint ,

wil l find much valuable information and food for thought.



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Humoral Pressor Substances and Their

Relation to Arterial Hypertension

HENRY A. SCHROEDER and NORMAN S. OLSEN

Depar tment of nternal Medicine, Washingt on Universit y School of Medicine, St . Louis, Mo.

Arterial hypertension, one of the most important diseases

under modern social and economic conditions, presents a

major problem to biochemistry: the discovery of specific

therapeutic measures for its alleviation. This paper discusses known humoral substances, examines each in the light

of its possible relation to hypertension, and considers other

evidence of the existence of such substances and their

chemical structure. Humoral pressor mechanisms are prob

ably initiated by neurogenic ones and therefore comprise

only one link in the chain of events that lead to chronic

hypertension.

T h e d iscovery of specific th erapeuti c measures dir ected at arterial hypertension hasbecome one of the major problems of biochemistry. Theprevalence of this condit ion in

the modern social andeconomic environment has made it one of the most impor tant d is

eases to which man is he ir . It is time, therefore, to examine the progress made d u r i n g

the past few years in the elucidat ion of the pathogenesis of this disease, especially those

factors of biochemical interest.

Arter ia l hypertension is very common. Ap pr ox imate ly 40% of the populat ion over

the age of 40 exhibit elevations of blood pressure, more than 140 mm. of mercury systol ic

an d 90 mm. diastolic (64). The incidence increases with advancing years. It appears

to be greater in negroes (2, 8, 28), the obese (83), andthose exposed to higher degrees of

c ivi l izat ion (16).

T h e effects of chroni c hypertension on the human organism are, with one exception,

of little interest to the investigator study in g pathogenesis, al thou gh of great import to

the sufferer and his ph ys ic ian. T h at except ion is fai lure of the kidneys. Disease and

failure of the heart are probably caused by chronic overstrain, often associated with an

other metabolic disease, arteriosclerosis of the coronary arter ies. T h ey account for about

two thirds of the deaths p r i ma r i l y due to hypertension. Strokes of apoplexy, or cerebral

vascular accidents, from rupture or thrombosis of a cerebral artery weakened by disease

cause another sixth, uremia about one twelfth, and other conditions the remainder (28).

E x c e p t for uremia, these events areusually the result of overwork and increased arterial

tension. O nl y rar e ly does the heart escape h y p e r t r o p h y .

Aside from major changes in organs, the only constant pathological findings concernthe ar teri oles; th eir walls are thickened, the ratios of wall to lumen being increased.

Degenerat ion of muscular coats, in t im ai thi ckening, and sometimes (in " m a l i g n a n t "

hy pertension) necrosis occu r. T hese alterations aremost marked in thekidneys, but are

found less constantly i n most other areas. Theevidence th at ar teri olar disease is second

ar y to, and is not the pr imary cause of, chronic hypertension is conclusive, although in

direct . E xper im ental ly , s imilar lesions can often be produced in the k idneys of certain

animals (56, 67), when renal hypertension is induced. In thecase of the dog, lesions ap-

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pear less readi ly , and special techniques must be used (52). I n almost half of a series of

renal biopsies taken from hypertensive patients little or no arter iolar sclerosis was seen

(11), whereas almost all the kidneys of such indiv idua ls show it at autopsy. Certainly ,

the nature of the lesions themselves suggest tha t they cause ren al isch emi a; alth ough a

result of hypertension, they probably contribute to itsmaintenance and further progress.

Therefore, arterial hypertension may begin as a generalized physiological alterationi n hemod yna mi cs, pr odu ci ng secondar y path ological changes i n arterioles. Sustain ed hy

pertension leads to cardi ac hy per trop hy an d more renal arteri olar sclerosis. F i na l l y , be

cause of overw ork , overstrain , an d thefrequent association of arteriosclerosis, theheart or

brain is permanently damaged and death ensues. The durat ion of life from onset of hy

pertension to terminus is extremely variable (6 months to over 40 years).

Psyche

Personality Defects

"Subnormal Assertiveness"

"Obsessive-Compulsive Tendencies'*

Nerves Kidneys

Renat Ischemia

Blood Vessels

Arteriolar Sclerosis

Organic«< Arteriolar Nephrosclerosis /

Neurogenic

Conflicts

Τ

Pressor Substances Hypertension

, Hypothalamus

ISympathetic Nervous System > Increased Peripheral Resistance

Tension '

Figure 1. Pathogenesis of Psychoneurogenic Hypertension

Probab le sequence of events l e a d i n g to susta ined hyper tens ion w hen accessory e t i o l og i ca l f actors are absent .Repressed emot iona l tens ion causes d i scharges of the s y m p a t h e t i c n e r v o u s s y s t e m vi a the h y p o t h a l a m u s , w h i c hl e a d to g en e r a l i z e d v a s o c o n s t r i c t i o n . T he k i d n e y s are i n c l u d e d i n the response. T he r e s u l t a n t d i s t u r b a n c e of

i n t r a r e n a l h e m o d y n a m i c s causes p r o d u c t i o n of pressor substances . H u m or a l vasocon str i c t i on l asts l onger th anthe neur ogeni c typ e . R epeated d i scharges eventu a l l y l ead to s u s t a i n e d n e p h r o g e n i c h y p e r t e n s i o n , w h i c h is

a c c o m p a n i e d by changes i n the w a l l s of the ar ter i o l es , espec ia l l y those of the k i d n e y s . T he o r g a n i c r e n a li schemia caused thereby is p a r t of a v i c i o u s c i r c le , i n w h i c h the c o n t i n u e d p r o d u c t i o n of pressor substances is

p r e d o m i n a n t . T he neurogeni c e l ement is super imp osed ther eon. Wh en organi c ren a l d i seases , i n fect i ous ,destruct i ve , metabo l i c , or a r t e r i a l , arepresent as accessory e t i o l og i ca l f actors , the course of h y p e r t e n s i o n is oftena l t e r e d . W h e n the adrena l cor tex is h y p e r a c t i v e , the v i c i o u s c i r c l e may be i n s t i t u t e d by d i r e c t a c t i o n of its

h o r m o n e s u p o n a r t e r i o l a r m u s c l e .

Effects of Psychic DisturbancesI t is becoming i ncreasingly evident that arterial hypertension in ma n is usual ly a psy

chosom atic disease. T her efore, to un der stand pathogenesis one must examine the psyche

an d theeffects of psychic disturbances upon the soma. It is not with in theprov ince of

this discussion to consider at length such disorders and their relation to hypertension.

F or purposes of orientation toward a view of thewhole picture, however, wemust scrut i

nize briefly the influences which bear on this condition inorder to direct our attention to

salient features w hi ch deserve fur ther in vesti gati on . Suffice it to say,therefore, that dis

orders ordeficiencies ofpersonality exist (SO) ; that they antedate the occurrence of hy per

tension (8) and that theemotional tension arising from their presence profoundly affectsvegetative functions, especially those concerned with blood flow and blood pressure (68).

T h e pathogenesis of neurogenic hypertension appears to be somewhat as follows:

Emo t io na l tension is discharged via thehypothalamus and the sympathetic nervoussystem.

Neurogenic (sympathetic) vasoconstriction occurs, with its well-known effects uponheart andblood vessels.

T h e renal cir culati on takes part in thegeneralized vasoconstrictive process.When renal vasoconstriction is relatively greater than the concomitant rise in blood

pressure a n d incr ease in cardiac outp ut — i.e., when total renal blood flow is lowered—the



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SCHROEDER AND OLSEN—HUMORAL PRESSOR SUBSTANCES 5

ki dneys are stimulated to release into the blood hu mor al vasoconstrictor substances w hi chhave a more prolonged action and maintain theelevation of blood pressure.

Repeated sympathetic discharges lead to repetitions of this phenomenon, causingtransient but more prolonged periods of hypertension.

T h e hypertension itself damages renal arterioles, whi ch become hypertrophied and

nar row ed. T h u s, organic renal ischemia results, in itself causing continuous production

of pressor substances.O n this organic change, functional neurogenic vasoconstriction is superimposed.

T h e whole process may take years to develop, rar ely month s, and is a dy namic one,

wi th changes constantly occur ri ng (F igur e 1). Wh en organic renal or urologie diseases ar e

present concomi tantly, orsclerosis of the larger renal arteries develops, thecourse is l ike ly

to bealtered by theassociated disturbance.

T he purpose of this report is to discuss know n h um ora l substances, to examine each

i n the l ight of its possible relation to hypertension, and to consider other evidence, both

direct and indirect, for theexistence of such substances and for their chemical structures.

Inquiry into the neurogenic influences of this condi tion an d methods for neutrali zin g them

wil l be discussed by others (6, J$). It must be remembered, however, that humoralpressor mechanisms are probably usual ly init iated by neurogenic ones, and therefore

comprise only one l ink—even though the most important one—in the cha in of eventswhich lead to chronic h ypertension.

Sixteen different substances arek n o w n or have been found in body fluids or m o d i

fications of th em, wh ic h either cause acu te hy per tensi on or lead to vasoconstriction in the

experimental animal (Table I). T h r e e of these substances areproteins, three peptides,

six amines, twonicotinel ike bases, an d one steroid. O ther un identi fied substances have

been detected. T h e pr odigali ty of N a t u r e inpro v id ing so many substances which act in

Table I. Pressor Substances Possibly Related to Hypertension*

N a m e

P r o t e i n sR e n i n

V E M

P r o l o n g e dpressorsubs.

P e p t i d e sH y p e r t e n s i nP e p s i t e n s i n

S e r o t o n i n

A m i n e s" A m i n e s ' *

N o r e p i n e p h rine

U r o s y m -p a t h i n

V o n E u l e r ' ss u b s t a n c e I

V i c t o r ' sm a t e r i a l

P h e r e n t a s i n

N i c o t i n e bases

L o c k e t t ' s

base

U r o h y p e r -t e n s i n

O t h e r sN e p h r i n

D e s o x y c o r t i -costerone

S o u r c e

K i d n e y

K i d n e y

K i d n e y a n db l o o d

o a - G l o b u l i na j - G l o b u l i n

B l o o d

B l o o d

T i s s u e

U r i n e

B l o o d an d

tissuesK i d n e y

A r t e r i a lb l o o d

U r i n e an d

b l o o d

U r i n e

K i d n e y

A d r e n a lcor tex

A c c e s s o r yC o n d i t i o n s

R e n a li s c h e m i a

R e n a li s c h e m i aa n d a n o x i a

H y p o t e n s i o n( rena li s c h e m i a )

R e n i nP e p s i n

S t a n d i n g

A n o x i a an d

i s c h e m i aN e r v o u s

s t i m u l iN e r v o u s

s t i m u l iN e r v o u s

s t i m u l iA n a e r o b i c

a u t o l y s i sH y p e r t e n s i o n

(renal )

R e n a l

i s c h e m i a



S a l t and hy

p e r t e n s i o n(?)

C h e m i c a lN a t u r e

P h a r m a co log i cA c t i o n

O b t a i n e dP u r e

F o u n d i n

H y p e r t e n s i o n

S i m i l a r i t y to

H o c h d r u c k -

stoff

P r o t e i n P r o l o n g e d N o A c u t e Y e s

P r o t e i n (?) P r o l o n g e d N o Y es U n k n o w n

P r o t e i n V e r y p r o l onged

N o (?) U n k n o w n

P e p t i d eP e p t i d e

P e p t i d e

A c u t eA c u t e

A c u t e

N oN o

Y es (?)

A c u t eN o

N o

Y e sY e s (?)

U n k n o w n

A m i n e A c u t e Y e s Y e s P r o b a b l y

A m i n e A c u t e Y es (?) Y e s (?)

A m i n e s A c u t e N o Y e s U n k n o w n

N o r e p i n e p h rine

T y r a m i n e (?)

A c u t e

A c u t e

N o

N o

N o

N o

Y es (?)

U n k n o w n

A m i n o p e p t i d e(?)

P r o l o n g e d N o Y e s U n k n o w n

C o m p l e x

a l k a l o i d

A c u t e N o E x p e r i

m e n t a lo n l yY e s (?)

U n k n o w n

N i c o t i n ebase (?)

A c u t e N o

E x p e r i

m e n t a lo n l yY e s (?) U n k n o w n

U n k n o w n P r o l o n g e d N o Y es U n k n o w n

S t e r o i d P r o l o n g e d Y es C e r t a i nt y p e s(?)

Y es (?)

α L i s t t a k e n f r o m l i t e r a t u r e . W h e r e ? i s s h o w n , c h a r a c t e r i s t i c of m a t e r i a l is i n d o u b t ,fication a n d p h a r m a c o l o g y of most of these substances have been i nsuf f i c i ent l y s tud ied .

C h e m i c a l i d e n t i -



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similar ways to maintain blood pressure andblood flow appears unjustifiable even for so

v i t a l a funct ion. The possibil ity therefore exists that the effector substances, the final

act ive pr inci p les, ofm a n y ofthese materials may be of similar chemical structur e, and that

the act iv i ty of thematerials on the c i rculat ion was by chance demonstrated during some

stage of the ir intermediary catabol ism.

In order to determine whether each of these substances might or mig ht not be theact ive agent in chronic hypertension, it is necessary first to postulate a hypothet ica l ma

ter ial wh ic h fulf i l ls the phar macologi cal requir ements to produce the hemodynamic p icture

seen in hyp ertension. F or purposes of brev i ty , wewill cal l this mater ial the H o c h d r w k -

stoff . Its char acteri stic actio n is to cause : (1) elevation ofblood p ressure ; (2) generalized

an d relatively equal vasoconstriction of all vascular beds; (3) no great change in cardiac

output or pulse rate; (4) renal vasoconstri ction, greater on efferent arterioles; and (5) no

visible sympathetic effects (sweating, p allo r , spasm of sphincters, etc.). It is not neces

sary for the substance to have a prolonged act ion, provided cont inuous product ion is

assured. When a pressor agent acts in this manner, and can occur natur al ly i n the body ,

attention is immediately given it as a possible effector substance i n h yp erten sion . U n for

tunately , we do not k no w for certai n whether per ip her al resistance is equally i ncreased inal l vascular beds, or whether some are re lat ive ly more constr i cted than others. T h i s c r i

ter ion (2) therefore cannot be absolute, but at least we can say that ep inephr ine and

epinephr inel ike substances are not the pr inc ipa l effector agents, as they do not fulfill

requirements (2), (3), and (5).

Nephrogenic Protein Pressor Substances

T h e thr ee pr otein pressor substances are renin, a prolonged pressor substance found

i n shock, and vasoexcitor mater ial . A pp ar ently they aredifferent substances. R en i n is

the best understood (10). Its react ion with a globulin substrate to form hypertensin or

ang iotonin suggests that it is a pr oteolyt ic enzyme. R eni n hasbeen considerably concent rated, bu t has not been pur i f ied. T h e stimulus for its release by the k i dney is a reduct ion

of r enal bl oo d flow; j ust how th is comes about is u n k n o w n .

C e r t a i n readjustments take place in the renal cir culati on wh en blood flow is acutely

reduced by arter ial constr i ct ion; intern al vasodi latat ion occurs s lowly and total blood

flow m ay retur n toward or to normal, although theactua l renal arteri olar resistance must

be considerably lowered (58). T h is phenomenon is seen when blood flow ismeasured by a

thermostromuhr , or when oxygen tension in the cortex is estimated by an electrode. One

measurable change does occur under these condit ions, however. A lth ou gh oxygen ten

sion and blood flow may be norm al whi le the renal artery is part ial ly constr icted, the p H

of renal cortical tissue changes in the acid d irect ion (48). Further const r ic t ion of the

renal artery , of course, per man entl y reduces r enal bloo d flow, thecortex cont in uin g to havea higher hydr ogen ion concentrat ion. A l th ough renin is released under these condit ions,

its relation to lowered pH has not been demonstrated.

T h e site of formation of renin is not know n, a l though the indi rect and cir cumstant ial

evidence favors slightly the juxtaglomerular apparatus rather than the tubules as a source

(18). C r u d e renin, however, is extracted readily from renal cortex by saline extraction,

acidif ication, andpr ecip i tat ion wi th ammon iu m sulfate andsodium chlor ide. O ther ac

t iv e pr otein substances are likewise extracted, and the ir separation from reni n is often a

matter of considerable di ff iculty. The reni n substrate, an a 2- g lo b u l in , is found in blood

seru m and is probably formed by the l ive r . I t can beeasily salted out of beef serum as a

crude p reparat ion.

U n d e r theproper st imulus renin is released into the cir culat ing blood wh ere it can beidentified, especially in that from the renal ve in. It acts rap idl y up on its specific sub

strate, splitt ing the protein into peptides, one or more of wh ich have been cal led "h y p er

t e n s i n " or "ang i o t o n i n . " H y p e r t e nsin has been concentrated but not obtained in p ur e

f o r m. It is theeffector substance of renin, constricting arterioles and raising blood pres

sure. Theact ion of hypertensin is abolished by "hypertensinase," an enzyme found in

blood and renal extracts. F or tun ately , the latter is destroyed by heat anda l k a l i n i t y .

T h e renal pressor m echani sm just described acts in a manner that fulf i l ls the require -



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 1




50

Time in Minutes

Figure 2. Oxyge n Uptake by Amine Oxidas e Preparations and

Tyramine, Hypertensin (Angiotonin), and Histamine

C o n c e n t r a t i o n s of t y r a m i n e a n d h i s t a m i n e w er e s i m i l a r ; t h a t of a n g i o t o n i n is e s t i m a t e d . T h ep r e p a r a t i o n , w h i c h c o n t a i n e d a c t i v e a m i n e o x i d a se a n d no o t h e r o x i dases, was s u p p l i e d by K a r l F o l k e r s of M e r c k a n d C o m p a n y . D a t a w er e o b t ai n e d

f r o m C. C . S t o c k , to w h o m th e a u t h o r is i n d e b t e d .

ments of theH och dr uck stoff . Demonstrable amounts of renin, however, have been found

i n renal venous blood of dogs and human beings only dur ing the acute stage of h y p e r

tension. In acute glomerulonephrit is, toxemia of pregnancy, and a few other conditions

renin is released by ischemic k i dneys (14) ; as the hypertension becomes more chronic itdisappears to a poin t lower, if anyth i ng , than in renal venous blood of normal ind iv iduals .

R e n i n is also demonstrable in other conditions, such as congestive heart failure and

shock (15). I t is found likewise only in theearly stages of exper imental hyp ertension an d

i n exper imental shock. E it h er methods for its detection are too crude, or some other

mechanism takes over its funct ion in chronic elevation of theblood pressure.

R e n i n can be antigenic; dogs wi l l produce antibodies to hog ren in . W ak e r l in (66)

an d his group found that i n a cer ta in p rop or t ion of experiments thedevelopment of " a n t i -

r e n i n " was accompanied by a lower blood pressure or pr otection against experimentally

induced renal hypertension. The reni n used, how ever, was imp ur e , andother active or

antigeni c substances were pr obabl y pr esent. Si mi lar effects against hypertension could

be caused by renal extracts, the renin of w h i c h hadbeen destroyed. Some other ant i hypertensive substance may have accounted for p ar t of his results. K i dn eys are k n o w n

to con tai n anti hy per tensiv e materi als effective in rats, dogs, and probably man, although

little attention has been paid them in recent years (44)·

T h e available evidence suggests, therefore, tha t thi s ren al pr essor mechan ism is an

important factor in themaintenance of blood pressure through vasoconstriction, without

marked effect u p o n the o ut p ut of the heart . There are several such mechanisms. The

sympathetic nervous system and chromaffin tissue exert an emergency action by way of

neurogenic vasoconstriction and cardiac st imulat ion. The renal pressor mechanism is

called in to pla y under more severe condi tions of stress— i.e., wh en cir culati on thr ough the

k idney is im pai red because of central or per iph eral c i rcu latory insuff iciency (and in local

pathological renal conditions). It requires a greater stimulus, acts longer, and disappears

more slowly. A th i rd , longer-acting and less easily evoked mechanism of wider imp l ica

tions is that whereby blood volume is increased, probably monitored in p ar t by the ad

renal cortex, and its act ion on salt andwater balance. T h ere may be other homeostatic

mechanisms which are less wel l known. In regard to t ime of act ion, it appears that the

neurogenic oneacts in seconds, the renal in minutes and hours, and the adrenal in days.

T h e r e is no dir ect evidence, how ever, t h at the last two aredisturbed inmost cases of ex

per imental or cl inical hypertension.



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 1




T h e second pr otei n mater ial to be considered is a pr olon ged pressor substance (P P S)

first obtained by Shi p ley, H elmer, and K ohl staedt ( 6 2 ) from the blood of animals dying

after a long peri od of shock, an d later obtained fro m hu man bl ood and from k id ney ti ssue.

I t has not been pur i f ied. I t is closely all ied to, but not i dentical wi th , ren in; although i t

can be demonstrated in most ren in pr eparations, it is most difficult to separate. T h e pr ep

arat ion best suited to test for its presence is a 2-day nephrectomized p i thed cat , in whi chver y pr olon ged elevation s of bloo d pr essure can be pr odu ced. I n this respect it differs

f rom all other known pressor substances. L i k e r en i n it is relatively species specific, is not

block ed by Di benami ne [iV -(2-chloroethyl )dibenzylami ne], and ma y be antigeni c. N ot

o n ly does i t come from k id ney tissue, but i s in acti vated or destroyed b y k id ney tissue, re

ma i n i n g i n the ci rc ulati on of neph rectomized anim als for some time and capable of being

transferred to other anim als whi le retain in g its acti vi ty. So far, pr olonged pressor sub

stance has not been found i n h um an beings suffering fr om h yp ertension .

A lth ou gh n ot str ict ly a pressor substance an d not defini tely established as a pr otein ,

the vasoexcitor mater i al (V E M ) of Shor r and his group ( 6 9 ) can be considered as the t h i r d

of the nephr ogenic pr otei n vasoacti ve substances, unt i l established otherw ise. I t pr obabl y

pl ays a role i n hy per tension. Vasoexcitor m ateri al is obtained from an anaerobic au tol y-

zate of r enal tissue. I t can be detected i n mi nu te amou nts wh en in jected in tr aveno usly b y

observing directly its pr inc ipa l acti on, whi ch is to potentiate the vasoconstrictor actio n of

topi cally app li ed epineph ri ne. T h e metarterioles of the rat's mesoappendix are th e

vessels comm onl y used for its determi nati on. Vasoexcitor mater ial is opposed i n its acti on

by a vasodepressor materi al (V D M ) wh ich produces an opposite typ e of response in ar

terioles, and which has been identif ied by immunological techniques as ferrit in or apofer-

r i t i n ( 4 1 ) . Vasodepressor material is obtained from an anaerobic autolyzate of l iver .

B o t h materials are inactivated under aerobic conditions by the organs in which they are

formed, presumably by enzymatic action.

I t has not been conclusively demonstrated th at potenti ation of the vasoconstri ctor ac

t ion of epineph ri ne is a specific reaction confined onl y to vasoexcitor ma teri al. O ther sub

stances, in the authors' hands at least, wi l l produce the same react ion. T h e act ion of

vasoexcitor materi al, however, lasts considerably longer th an that of hy per tensin an d

other short-acting amines, but only a l itt le longer than that of ephedrine and benzedrine.

Therefore, it is impossible to apply this test as one specific for vasoexcitor ma ter i al ; i t

may be a general reaction common to other compounds, but is extremely valuable in de

tecting minute amounts of vasoexcitor material and vasoexcitor material-like substances.

Simi la r ly , depression of the reaction of arterioles to epinephrine is a phenomenon not con

fined to the acti on of vasodepressor ma ter i al ; i n thi s labor ator y the auth or s h ave seen

definite prolonged, although less mar k ed, depression of arteri olar response caused by

adenosine tr iphosphate.R egardl ess of the lack of specifici ty of the test, vasoexcitor mater ial has been d emon

strated in incr eased amoun ts i n the blood of animals u nder the same condition s as renin i s

produced—i.e., shock, renal ischemia, and the early stages of experimental hypertension

( 6 8 ) . It has also been found in the blood of human beings suffering from shock and con

gestive cir culatory fai lur e. Wh en hyp ertension becomes ch ro ni c, how ever, vasoexcitor

material can no longer be detected. D u r i n g th is stage a change in the relative concentra

tions of vasoexcitor material and vasodepressor material has occurred, so that they have

now become equal, vasodepressor material having been formed by the liver in large

amou nts, eventual ly maskin g the acti on of vasoexcitor mater ial . F or tun ately , vasoexcitor

materi al can be destroyed by i ncu batio n wi th renal t issue under hi gh oxygen tensions,

leaving the in creased amo un t of vasodepressor mater ial to be assayed. T h e assump ti oncan therefore be made th at, in chr oni c hy per tension , vasoexcitor mater ia l is pr esent in

greatly in creased amounts i n the cir culati ng bloo d.

F r o m these very interesting observations we can speculate with reasonable assurance

th at blood pressure, or at least vasoconstr ict ion an d vasodi latati on , is contr olled by two

opposi tely actin g substances an d that i n the hy pertension of animals and h um an beings

these two substances are incr eased i n amoun ts. M os t of the wor k on identif i cation, p u r i

fication, an d ch ar acteri zatio n, usi ng the rat's mesoappendix as a bioassay, has been done



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 1




on vasodepressor material; it ishoped that the chemical identif ication of vasoexcitor ma

terial wi l l besoon forthcomi ng. T her e is nodoubt now that these twosubstances play an

important ro le inmain taini ng vasomotor tone and, furthermore, that thek idney and the

l iver are int imately identif ied with their formation a nd their in activati on. The findings of

Shorr andhisgroup have provided a newoutlook upon theregulation of blood pressure

an d of arteriolar reactions to abnormal conditions. It is notdifficult to believe that disturbances of these regulatory mechanisms, which arenaturally affected by chemical sub

stances, may lead to hypertension andmay be important when blood pressure is altered

i n theopposite direction as in shock. But to be able to understand and to alter these

disturbances inthe nor mal direction by influences under our control , wemust know their

chemical nature and theexact mechanism of their formation.

T h e r e are curi ous simil ari ties amon g these three nephr ogenic pr essor pr oteins wh ic h are

worthy ofment ion. A l l areformed by ki dneys under thestimulus ofshock, which causesrenal isch emia. P rol onged pressor substance has notbeen i dentified inrenal venous blood

of kidneys made ischemic by other means, but could conceivably bepresent. Prolonged

pressor substance andvasoexcitor material are both found closely associated with ex

tracts containing renin (although neither is renin) andcan be separated only with considerable difficulty. The pharmacologic action of each is prolonged, suggesting slow con

t inued action and breakdown, whi ch isthecase with renin. N o n e hasbeen obtained pu re.

Vasoexcitor material is found in solutions of hypertensin (24). T her e are certain chemical

differences (heat stabi l i ty , p H sensitivity), however, which suggest that they are different

substances. The question to be answered is: Ar ethese materi als di fferent aspects of the

same general homeostatic mechanism, or doth ey repr esent thr ee different mech ani sms?

Peptide Pressor Agents

O f thethree peptides, hypertensin is themost clearly under stood, resulting as it does

from theenzymatic action of renin on a specific substrate. I t has already been discussedi n tha t conn ection. H yp er ten sin is, however, considered separ ately, for wear e notcertain

that renin (being impure) produces only a single effector substance (nor are wecertain that

hypertensin is pure). It is notknown whether hypertensin is broken down into simpler

effector components (such as pressor amines) by specific enzymatic action in smooth

muscle or whether thepeptide as itself acts upon arterioles. The composite result, how

ever, fulfills therequirements wehave set for theHochd rucks to f f ; thedurat ion of action

is mu ch shorter tha n that of renin, but longer th an epin ephri ne.

Hypertens in issoluble inalcoh ol, glaci al acetic acid, phenol, and water, an d in soluble

i n ether (61). Because it is inactivated by tyrosinase it probably contains a catechol or

phenol group, and by amine oxidase, an amine group on an α-carbon atom (F igure 2).

Hypertens in is inactivated by certai n phen olic , catecholic, an d amin e oxidases, by pepsin,trypsin, chymotryps in , andcarboxypeptidase, andby "hypertensinase" found in plasma.

T h e nature of hypertensinase is unkno wn, but it is probably not an oxidative enzyme.

Because it isheat-labile, hypertensinase can be removed from blood an d renin preparations

by heatin g; hyper tensin itself is heat-stable. L a c k of pure preparations of hypertensin

has delayed its further chemical identif ication .

Consideration must be given to the protective action of hypertensin in congestive

failure, shock, andacute hypertensive states. F a i l u r e of this mechanism by depletion of

the cir cul ating substrate of renin mayaccount for certain irreversible changes. F u r th e r

investigation in to themode of action of this compound is necessary. Is this r enal pr essor

mechanism one wayby which vasoconstrictor substances maybeobtained from proteins?

Hypertensin isa peptide, onestage in pr otein breakdown, and onfurther degradation may

produce simpler pressor materials. The problem is of fundamental importance and must

be investigated.

A second peptide is pepsitensin, formed by peptic digestion of thesubstrate of renin

(18). It represents an interesting type reaction similar to that of renin. Because two

proteolytic enzymes, renin and pepsin, act on a protein to produce vasoconstrictor sub

stances, thesubstrate must h ave peculiar structur al properties condu cive to formation of

these substances when broken down. The pharmacology of pepsitensin has notbeen ex-



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0 2 . c

h 0 0 1




tensively investigated, nor has it been purif ied, but evidence available suggests a s imi lar i ty

to hyp ertensin, althou gh it is not ident ical. Therefore, we are not concerned with its re

lat ion to abnorm al vascular states, bu t only w ith the suggestion th at the ren in mechanism

m ay not be a specific one. T h e natur e of the substrate is probab ly the important specif ic

for the formation of pressor substances.

T h e t h i r d pept ide to be examined is serotonin, an in dole-containi ng substance isolated from blood, which is probably ident ical with " s p à g i f t " (46). T h i s vasoconstr ictor

appears i n shed blood as a constant source of annoyance to those performin g perfusion ex

periments, and has been recognized foryears. O n ly recently has it been isolated and p ar

t ia l ly purif ied, and its chemical constituents par ti ally identif ied. I t differs from hyper

tensin in conta in ing an indole r ing , and its pharmacology and resemblance to the H o c h -

dr uck stoff have not been thor oughl y wor ked out. T her e is no evidence that it may bei n

vo lved in hypertens ion. Again , we do notknow whether it acts directly, or whether it is

broken down by cellu lar enzym es in to sim pl er effector substances suc h as t r y p t amine , a

much neglected pressor substance.

Amine Pressor Substances

T h a t amines formed from natu ral ly occurr i ng amino acids arepartly responsible for

chron ic hypertension is a rather attractive hypothesis f irst suggested by the experiments

o f H o l t z (35). Besides the normal metabolic enzymes of amino acids, tissues, especially

k idney, l iver , an d bra in , contai n ami no aci d decarboxylases, some of them specific for cer

ta in amino acids, some less so. These are anaerobic enzymes. A fter decarboxyl ation ,

certain monoamines are deaminated by amine oxidases which are sensitive to oxygen

tension. The best k n o w n of these oxidases is the enzyme of Blaschko , R iehter , and

Schlossmann (9) } which may be a mix t ur e of three or more (29), and which is specific for

ma ny nonsu bstituted vasoactive amines found i n the body , wi th the notable exception of

histamine.Therefore, if theamount of oxygen available for thedeaminat ion of amines were cut

down sufficiently, decarboxylation would continue but deaminat ion would be incomplete,

result ing in an accumulat ion of amines. T h e most powerful pressor substances known are

amines. If an amino acid , such as p-hydr oxyp henyl alanin e, were decarboxylated but not

deaminated the result would be p-hydroxypheny le thy lamine or ty ramine , a re lat ive ly

active pressor substance. If th is same disturbance of deamination were prevalent and

affected other amines wemight expect a mixture in the cir culat ing blood, and their effects

up o n the c i rculat ion might bepr ofoun d. O ne could expect to f ind eight p r i n c i p a l vasoac

tive amines in bloo d: butylami ne, amylami ne, isoamylamine, ph enylethy lamine, tr yp ta

mine , ty ramine , hydroxytyramine , andhi stamine. T h ere migh t be others. H istami ne

dilates capillaries but constricts arterioles. I t has, however, a specific decar boxylase anddeaminase. Theothers, as far as we know, constrict arterioles, although the act ion of

t r y p t amine is not wel l known.

Presumably, vasoactive substances act upon smooth muscle cells by intimate associa

t ion with them, and aredestroyed in theprocess of st imulat ion or depression. E p i n e p h

r ine, when injected intravenously, can be recovered in much larger amounts from ar

ter ial than from venous blood ; minut e dosesgiven intraarter ia l ly may affect only the local

c irculat ion. If amines formed from the incomplete catabolism of amino acids are act ive

i n hypertension, onemu st postulate their formati on by ischemic organs in direct venous

connect ion with the heart (kidneys, brain, l iver, adrenals, etc.) or in direct arterial con

nect ion with the arter io lar bed (heart and lungs). If the former, they must not be de

stroyed in large amoun ts by the lungs. Fur thermore , arterial blood could beexpected tocontain larger quantit ies th an venous. A bsor pt io n from or formation in the intestinal

t ract or spleen of amines would notproduce vascular effects, as these substances probably

would be metabolized by the l iver .

Because cerebral andhepatic blood flow is no r ma l in hypertension and renal blood

flow is usually r educed, our atten tio n is focused on renal oxidati ve mechanisms an d their

suscept ib i l i ty to disturbances caused by lowered oxygen supp ly. F or tun ately for th is

hy poth esis, r enal amine oxidase, alth ough a slowly acting enzyme in v i t r o , is h ig h ly sus-



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 1




ceptible tomoderate changes inoxygen tension (61). Fur thermo re , B i n g and Zucker (7)

have shown, ashave others, that severely ischemic kidneys of dogs wi l l decarboxylate but

not deaminate dihydroxyphenylalanine. D O P A | ji3-(3,4-dih ydroxyp henyl)alanin e] is a

pressor substance for rats (49). Whether slight or moderate ischemia wi l l affect renal

oxidative deaminases in v iv o is not k n o w n . If amino acids are at al l metabolized by

kidneys (which have the highest resting metabolic rate of an y organ) a simple calcul ationwi l l po int out themagnitude of changes expected from slight inhibit ion of deamination.

T a k i n g 3m g. % ofα-amino nitrogen as the normal concentration in blood, and 1000

m l . of blood per minute as thenormal total renal blood flow, we can readi ly see that 30

m g. of amin o aci d nitrogen pass through theki dneys per mi nute. T o decarboxylate but

not deaminate 0.1% of this amou nt w ould lead to levels i n renal venous b lood of 30m i c r o grams of amin e nitr ogen per liter, certainly a large amount of vasoactive substance if the

nitr ogen were part of certai n amin es. A lt h ou gh the effective doseofphenylethylamine as

judged by ther at isapproximately 2mg. per liter of blood, or 100micrograms per kg. of

body weight, even this relatively weak pressor agent could beexpected toproduce vascular changes if continued accumulation of only slight degree occurred; this dose is aboutseven times thehypothetical one considered above. O bvi ously, effects could be causedby much smaller amounts of themore active compounds—for example, oneth i rd of thisamount of tyramine, one fourth of hydroxytyramine, or one three-hundredths ofarterenoi(if thelast has anamino a cid precursor) .

We may therefore take for granted that failure of renal deamination of appreciable

amounts of tyrosine, tryptophan, andphenylalanine may produce vascular effects, and

that disturbances of similar more complex mechanisms for synthesis or metabolism may

cause even greater ones. T h e eviden ce, how ever, that amin es are act ua ll y pr esent in i n

creased amounts in chronic hypertension must beexamined. M ethods for their measure

ment are on the whole un satisfactory. T her e is a strong suggestion, however, that amines

are in general present i n higher concentration s i n the blood ofhypertensives than ofnormal

subjects (57, 69). Occasionally, however, they are found in large amounts in the latter.In over half of a series of 33 samples of arterial blood of hypertensives, the amine

picrates measured in terms of isoamylamine were higher than in twelve of fifteen normalones, and innine cases were more than 10 mg. per l iter. T h e normal range was 0 to 7.0

mg., only three being greater than 3mg. In a second series, the results, expressed in termsof units of color, showed high values in two of twelve normal subjects, seven of fourteenpatients with neurogenic hypertension, and eleven of thirteen with renal hypertension.T h e color-concentration curves obtained from picr ates of var iou s amin es, however, di ffered in thei r slopes; therefore theamount of color found was no true indication of the

actual concentration of an y oneamine.

I n spite of the lack of specificity of the method, it is obvious that "am i n es" wh ic h give

a color by R ich ter 's method (48) are usually increased in chronic hypertension, especiallyi n themor e severe form s. B ecause themore highly active phenolic amines are not measured by this method, and others might bepresent in toosmall amounts tomeasure, these

results m ay betaken as amanifestation of a general disturbance ofamino acid metabolism

i n chronic hypertension w hich may inc lude theformation of pressor amines; it doesnot

prove their presence.

The pharmacology of these compounds and their s imilar ity to the H o c h d r u c k s t o f f

have not yet been investigated thoroughly. It is notkn own whether a mixture of them

wi l l produce thetrue picture of hypertension, although there aresimilarities (Table II).

One closely related substance, however, Z-arterenol or noradrenaline, which is the most

active pressor amine known, does reproduce thehemodynamic effects of the H o c h d r u c k

stoff everywhere but on thepul monar y vascular bed (26). Infusions of small amounts of

this amine wil l cause elevation of blood pressure in man wi thout affecting cardi ac ou tpu t;

the renal hemodynamic picture is also simulated, but thepu lmo nary vessels, contrary to

th e state existing in hypertension, are constricted under the conditions of the experiment.

It appears very likely that ^-arterenoi is S y mpath in E , theeffector substance of the sym

pathetic n ervous system, w hi ch again calls neurogenic factors tomind. Artereno i is found

i n theadrenal medulla along with epinephrine, and is present in U . S . P . epinephrine ob

tained from this source (25). It has not been i solated from hypertensive b lood .



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0 2 . c

h 0 0 1




Table II. Action of "Natural " Pressor Amines on Various Circulatory Functions

C o c a i n e I n h i b i t i o nP r e s s o r " V a s o c o n E r g o t o x i n P o t e n o f S m o o i

A m i n e R a t i o H e a r t L u n g K i d n e y s t r i c t i o n R e v e r s a l t i a t i on M u s c l e

H o c h d r u c k s t o f f ? 0 0 + 0 0 ?A r t e r e n o i

l - 1640 0 + + ?+

=b

+0

d - 50E p i n e p h r i n e

l - 1000 + + + + + +d - 40

+G u a n i d i n e 40 0 ? + + +H y d r o x y t y r a m i n e 20 0

T y r a m i n eP h e n y l e t h y l a m i n e

10 + + + +=fc 0 +y r a m i n e

P h e n y l e t h y l a m i n e 7 + +? + +T r y p t a m i n en - A m y l a m i n e

3+

+ + 0 0r y p t a m i n en - A m y l a m i n e 2 +n - B u t y l a m i n e 1 +I s o a m y l a m i n e 1 + + + +

β P r e s s o r r a t i o was o b t a i n e d f r o m a s t u d y of the l i t e r a t u r e of B a r g e r an d D a l e (δ), H a r t u n g (8S), an d

G u g g e n h e i m (31). T he a c t i o n on othe r const i tue nts than b lood pre ssure was o b t a i n e d f r o m these an d m a n yothe r source s .

H e a r t . +.indi cates e i the r inc re ase i n c a r d i a c o u t p u t or inc re ase i n a m p l i t u d e of c o n t r a c t i o n .L u n g . + i n d i c a t es p r o d u c t i o n of a r t e r i o l a r c o n s t r i c t i o n .

V a s o c o n s t r i c t i o n . + i n d i c a t e s c o n s t r i c t i o n i n p e r f u s i o n e x p e r i m e n t s or an a c t i o n on smooth musc le s ofa r t e r i o l e s .

E r g o t o x i n r e v er s a l . + ind icate s that p re ssor effect of the a g e n t was i n h i b i t e d or re ve rse d by the p r i o ri n j e c t i o n of e r g o t o x i n i n t o an a n i m a l .

C o c a i n e p o t e n t i a t i o n . + ind icate s that p re ssor effect was inc re ase d by the p r i o r i n j e c t i o n of c o c a i n e .I n h i b i t i o n of s m o o t h m u s c l e . + i n d i c a t e s t h a t an a c t i o n s i m i l a r to t h a t of e p i n e p h r i n e — i . e . , i n h i b i t i o n

—was obse rve d on the i so late d musc le of an o r g a n c o m m o n l y i n h i b i t e d by e p i n e p h r i n e ( v i r g i n c a t 's u t e r u s ,etc . ) .

Substances Probably of Amine Nature

F o u r substances have been described as having pressor effects, which are probably

amines or aminelik e. U r osymp ath in , described by Holtz , Credner , and K r o n b e r g (34),

is a substance found innormal ur ine inamounts per day,giv ing a pressor response equal

to 2 to 3 mg. of hydroxytyramine or 100 to 150 micrograms of epinephrine or arterenoi.I n cases of essential hypertension the amount is said to be increased three- tofourfold. Be

cause its action was intensified by cocaine and lessened by ergotoxin and yohimbine, they

believed that it represented a mixture of hydroxytyramine, epinephrine, and arterenoi.

T h e material was recovered by lead acetate precipitation of urine with subsequent acid

hydrolysis.

A substance found by v on E u l e r an d Schmiterlôw (21) inhuman and bovine blood is

believed to be ident ica l wi th Sympath in E . A l t h o u g h its pharmacology has not been

thoroughly studied to identify it w i t h the H och dr uck stoff , its s imi la r i t y to Z-arterenoi, as

judged by i ts action, is s t r i k i n g . V on E u l e r has also found a similar substance in a var ie ty

of organs, spleen being an especially r i ch source (20). While probably representing a

normal constituent, the demonstration of its frequent occurrence is of considerable interest to the problem of hypertension. No greater pressor action of hypertensive blood

extracts, however, was found than in n or ma l ones (22).

A crude pressor substance was obtained from the anaerobic autolysis of r enal tissue by

V i c t o r et a l . (65) , wh i c h was inact ivated by tyrosinase (58) andamine oxidase. I t p r o b

ably contain ed isoamylam ine, ph enylethy lami ne, and t y r a mi n e (17) released by proteo

ly ti c enzy mes. P r essor substances were not formed or were destroyed under conditions of

aerobiasis. It is difficult to a p p l y these results to in vivo pathological states except under

extreme anoxia andnecrosis of renal tissue.

Before leaving the matter of amines, we should examine some of the known s impler

ones for their effects u p o n the cir culati on, especially as to cardiac action anddurat ion of

pressor response. The former is noteworthy, as its absence is a necessary prerequisite ofth e H och dr uck stoff . Presumably an extended vasospastic action should also be a prereq

uisite. P r olon ged action can be produced in at least four ways: (1) by some proper ty

inherent in the structure of the molecule of the pressor agent which prevents its r a p i d

destruction in situ or in blood; (2) by slow l iberat ion of an effector substance from a

larger, more complex molecule or system; (3) by i n h i b i t i on of the act ion of an enzyme

system w hi ch inactivates some natur ally occur r in g pressor agent; and (4) by cont inuous

pr oducti on from par ent sources. C lear -cut examples are not evident at present, although



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 1




renin is an example of (2) and ephedrine, by in activ atin g epinephrin e oxidases, ma y be an

example of (3).

U s i n g ther at as a test object, theauthors found that of a number of aminel ike and

other pressor compounds only one,phenylethylamine, had a prolonged action (5 to 30

minutes) on blood pressure (Table I I I ). Of the others renin had only a relatively long ac

tion (5 minutes or less), while isoamylamine, tyramine, epinine, arterenoi, hypertensin,casein hydrolyzate, epinephrine, and t ryptamine hadonly a short action (2 minutes or

less). Phenylethylamine therefore may be an example of either (1) or (3). T h i s was an

unexpected result, andsuggests further the importance of certai n ami ne pressor agents.

D O P A , although not an amine, also had a prolonged action.

T h e r e is one further substance of unkno wn, but probably amine, nature, which has

been isolated from arterial blood ofhypertensive patients, and therefore probably plays a

part in thecausation of hypertension, although its pharmacological relation to the H o c h

d rucks to f f i s unk nown (67). T h i s for the moment somewhat optimi stically has been nam ed

pherentasin (φβρο = h o l d ; €ντασι$ = pressure; name suggested by H e n r y A. Schroeder,

J r .) unt i l its chemical structur e is indi cated. Ce r ta in assumptions were made in develop

ing methods for its extraction.

T h a t H o c h d r u c k s t o f f is present, and could bedemonstrated pharmacologically. The

direct appr oach seemed th e most rewarding, although eventually placing a decided bur denupon organic chemical methods.

T h a t it is present in very small amounts; otherwise it would have been discoveredb y thetechniques available.

T h a t it is rather rapi dly oxidized or otherwise destroyed by blood.

Table III. Pressor Activity of Aminelike Compounds in the Rat

C o m p o u n d * *

I s o a m y l a m i n e

T r y p t a m i n e

E p i n i n e

P h e n y l e t h y l a m i n e

M a x . R i s e T i m e of

D o s e , i n B . P . , R i s e ,

Ύ M m . H g. M i n . R e m a r k s

175 14/20 5 I n i t i a l r i se . 30/23 <1

440 8/6 5 S l i g h t i n i t i a l depress ion440

8/6

N o d e m o n s t r a b l e effect

875 28/34 **2

875 45/40 <1 10/8 at 2 m i n u t e s

100 20/20 <1100 18/20 2 60/48 in <1 m i n u t e100 39/33 <1 E t h e r e x t r a c t e d300 20/20 <1 E t h e r e x t r a c t e d100 15/12 <1

300 36/27 <1

10 45/31 <1 F a l l to n o r m a l at 2 m i n u t e s10 52/30 <1 F a l l to n o r m a l at 2 m i n u t e s (ether2/30

ex tracted )

120 22/26 30 I m m e d i a t e r i s e24 2/0 5 Immed ia te r i se a l so24 8/0 5 Immed ia te r i se a l so60 10/2 5 Immed ia te r i se a l so60 20/14 2 Immed ia te r i se a l so60 48/42 15 Immed ia te r i se a l so60 30/30 15 Immed ia te r i se a l so

M g .

100 35/24 <1 I mm ed ia te r i se f o l l ow ed by depress ion10 28/28 <1 Im med i a te r i se f o l l ow ed by depress ion90 47/30 <1 I mmed ia t e r i se f o l l ow ed by depress ion

M l .

0.2 10/13 2 I m m e d i a t e r i s e0.5 15/14 2 Immed ia te r i se a l so

0.1 5/14 3 N o r m a l at 5 m i n u t e s0.1 40/29 5 N o r m a l at 6 m i n u t e s

1 16/17 <1 14/11 at 20 m i n u t e s

1 45/39 5

C a s e i n h y d r o l y z a t e

A n g i o t o n i n

R e n i n

M i x e d p i cra tes of

b lood ex tractsP oo led p ressor b lood

ex tractsβ Of c o m p o u n d s t e s t e d i n the rat, o n l y p h e n y l e t h y l a m i n e p r o d u c e d a pro longed r i se i n b lood p ressure .

M i x e d p i c r a t e s of b lood ex tracts w ere a p r e p a r a t i o n of hyper tens i ve b lood ex tracts pur i f i ed by the f o r m a t i o nof p i c r a tes . T hese gave an im med i a te p ressor response . P oo led p ressor b loo d ex tracts i n d i ca te ex tractst a k e n f r o m a n u m b e r of samp les of h y p e r t e n s i v e a r t e r i a l b l o o d an d c o n c e n t r a t e d . P o o l e d s a m p l es f r o m n o r m a ls u b j e c t s gave no such response .



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 1




T h a t it comes f rom the k id ne y , an unnecessary assump tion.

T h a t the mater ials in blood might be amines and might therefore be unstable.

A r t e r i a l blood was used for the reasons outlined previously, about 500 ml . being obtained from each i nd iv idua l direct ly into 95% ethy l alcoh ol. A fter acid if icat ion, filtra

t ion , concentrat ion, and fur ther extract ion wi th alcohol and w ith p etroleum ether , a crude

extract wasobtained. A l l thevar iou s fractions were tested a nd discar ded if inact ive ,the

test ani mal used being the anesthetized r at. B ecause the act ive mater i al mayhave beenpresent in very small amounts, concentrated crude extracts were injected intravenously

whi le the r at's blood p ressure wasbeing continuously measured by an opt ical manometer ,

the needle of w h i c h was inserted into the femoral arter y. B lo od extracts from nor mal

ind iv idua ls were used as controls and the differences compared.

A s thi s wor k progressed it soon became obvious that there were differences in act ion

on blood pressure between normal andhy pertensive blood extracts. B ot h types of ex

tracts contained depressor materials, but on the average those from hypertensives con

tained less; these resembled adenyl compounds, both pharmacological ly and spectro-

photometr ica l ly . The extracts from hypertensive patients appeared to exert prolonged

pressor effects wh ich lasted 10 to 15 minutes, sometimes as long as 1 to 3 ho ur s . T he r e fore, a test was made available by w h i c h the act ive p r i nc ip le could be fo l lowed through

var ious pur if icat ions. The wo r k was inte r rupted by the war; after it the results were

confirmed in a second series of crude extracts. B y further pur if icat ion, formation of

picrates, and the use of specific solutes, the authors have obtained active extracts of

hypertensive b lood w hi ch conta in roughly f r om 10 to 20 micrograms of act ive mater ial

per l iter of or ig ina l b lood . I nab i l i ty to get sizable quantities, due to its extremely low

concentration in blood, has he ld up its chemical character izat ion. A l th ough h i gh ly

purif ied, 10 to 20 micr ograms per l i ter of hyp ertensive blood may or may not be the total

amoun t or ig in al ly present and may not be p ur e . The authors believe, however, that

this mater ial is amine l ike in nat ur e ; its pressor action is destroyed by i ncub at io n w i t h

amine oxidase, oxygen being taken up in the react ion. O ther chemical in act ivat i onpr ocedur es hav e failed to show that it is not an amine .

I n o rder to integrate further some of thevarious reactions mentioned, and to detect

its p resence by other methods, the vessels of the rat's mesoappendix were employed as a

test object (Chambers-Zweifach preparat ion, 12). A good cor relatio n between the

presence of a vasoexcitor material- l ike substance in the extracts and the presence of

hypertension was found. When the whole rat was used for assay, a much cruder index,

sizable quantities of active pressor material were isolated from the blood only of those

patients showing at least a degree of renal impairment (lessened ab i l i t y to concentrate

urine, etc.). In general it may be stated unequivocally that patients with severe hyper

tension have in the ir arterial blood extractable substances which arepressor for the rat;

there are less or undemonstrable amounts in blood of less severe or neurogenic h yp er

tensive pa ti ents; there is l i t t le or none in blood of normotensive subjects; a vasoexcitor

mater ial- l ike ac t iv i t y is exerted by blood from most hy pertensive pat i ents; adenyl

compounds, having a depressor action, present in extracts of blood are less prevalent in

those from hypertensive pat ients; the act ive rat pressor material (pherentasin) is p r o b

ably aminel ike in nature, is not a prote in , but may be a simple peptide or an amine .

Amine Oxidase and Amines

V a r i ou s tissues contain amine oxidases, the l iver , k id ne y , and intestines usually

h a v i n g the highest concentrations depending on species, but bra in and muscle containi ng

large amounts. T h at in bra in may be different from tha t i n k id ney . T hese oxidases actupon amines to give ammonia or methy lamine and aldehydes. If one assumes that

amine oxidase is in thebody for a purpose, and examines the amines coming from natu

ra l ly occur r i ng amin o acids, onediscovers that there is a remar kable corr elation between

pressor action and deaminat ion by amin e oxidase. T h i s enzyme acts on ly wh en the

amino g roup is on the end of a carbon chain, and when there is no substituent on th is

carbon atom (carboxyl , methyl groups, etc.). It does not act up on diamines, tr i amines,

or tetramines. H istami ne is not attacked, there being a specific histaminase in tissues.



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 1




A l t h o u g h the l ist is incom plete, T abl e I Vshows the r elative pressor effect and suscepti

bil it ies to oxidat ion of some "n at u r al " amines coming indi rect ly or direct ly f rom the

amino ac ids which are considered "bu i ld i ng blo ck s" of proteins. It is obvious that al l

the pressor amines are so in activ ated, whereas most of the iner t or depressor amines are

not attacked. L i t t le is k n o w n of the pharmacological act ions of amines result ing from

the decarboxylation of isoleucine, serine, threonine, iodogorgoic acid , or thyrox ine , butby analogy amine oxidase may well inactivate them. If it does, this group forms an

exception, as all of them, except possibly the iodine-contain ing compounds, are vascu-

la r ly iner t . The other eight amines are probably not acted upon, a lthough th is is not

k n o w n for certa in. Of course, many other aminelike compounds are synthesized in the

b o d y ; some of them may have vascular effects, but it is cur ious that amine oxidase

appears to have a predi lect ion for pressor amines rather than for others. Specific de

carboxylases arek n own on l y for hist id ine, D O P A , tyros ine , and t ryptophan (61).

Table IV. Pressor and Amine Oxida se Ratios of Naturally Occurring Amines

A m i n e

H y d r o x y t y r a m i n eI s o a m y l a m i n eT y r a m i n eT r y p t a m i n eZ -E p i n e p h r i n eB u t y l a m i n eÎ -Arterenoid - A r t e r e n o id - E p i n e p h r i n eA m y l a m i n eP h e n e t h y l a m i n eM e t h y l a m i n eE t h y l a m i n eC h o l i n eE t h a n o l a m i n e/ 3- H y d r o x y p r o p y l a m i n e

0 - A m i n o p r o p i o n i c a c i dγ-Aminobutyric a c i d-y-Amino-ô-hydroxybutyric a c i d/ 8 - M e t h y l b u t y l a m i n eT a u r i n e

£ - A m i n o e t h y l su l f i deD i - ( /S - a mi no e th y l ) d i su l f i de

3- M e t h y l m e r c a p t o p r o p y l a m i n eP u t r e s c i n eC a d a v e r i n eG u a n i d i n eO r n i t h i n e4- H y d r o x y - 3 , 5 - d i i o d o p h e n e t h y l a m i n e3,5-D i i o d o - 4 - ( 4 - h y d r o x y - 3 , 5 - d i i o d o p h e n o x y ) -

p h e n e t h y l a m i n eP y r r o l i d i n e3 - H y d r o x y p y r r o l i d i n eH i s t a m i n e

G l u c o s a m i n eα Pre ssor rat ios we re obta ine d as n o t e d i n f o o t n o t e to T a b l e I I . A mi n e ox idase rat ios we re obta i ne d

f r o m B l a e c h k o , R i c h t e r , an d S c h l o s s m a n n W h e r e + is g ive n unde r ox idase rat io , it is a s s u m e d t h a t the

a m i n e w o u l d be o x i d i z e d a c c o r d i n g to the ge ne ra l charac te r i s t i c s of the e n z y m e as d e s c r i b e d by B l a s c h k o et

a l . , a l t h o u g h t h i s has not be e n s tud ie d , as far as can be d e t e r m i n e d . ? i n d i c a t e s t h a t the a c t i o n of the e n z y m ei s d o u b t f u l i n v i e w of the presence of acce ssory groups or s u l f u r - c o n t a i n i n g c o m p o u n d s w h i c h m i g h t be i n

h i b i t o r y . T hepressor effect of 0 - m e t h y l b u t y l a m i n e is not k n o w n bu t t h e o r e t i c a l l y s h o u l d be s i m i l a r to b u t y l a m i n e . I t is not k n o w n w h e t h e r the s u l f u r - an d i o d i n e - c o n t a i n i n g a m i n e s an d those w i t h a p y r r o l i d i n e r i n ga r e a c t i v e on the v a s c u l a r s y s te m . G u a n i d i n e is the on ly p re ssor substance not a c t e d u p o n by a m i n e o x i d a s e .

Nicotine Bases

Pressor bases, closely allied to ^-nicotine, have been isolated from urine.

Lo cket t (86,87) hasdescribed twocompounds, base A an d base B. Base A occurred

i n theur ine of men (who smoked), women (whod i d notsmoke), an d bitch es. T h er e wasapproximately three times as much in the ur ine of men andbitches as of women. The

base was somewhat more active pharmacologically than ^-nicotine, and was found to exertits pressor effect through themediation of the corpus striatum and thalamus, stimulatingthe sympathetic nervous system (38). Base A could be converted to ^-nicotine by d r y i n gi n a high vacu um , with alteration of itsaction from a central to a peripheral one; therefore it must be very similar instructure to nicotine. Base Β was a different compound,also with pressor activity; both were obtained by steam di stil lation from strongly al k aline ur in e. F ur therm ore, another compoun d, wh ich she called base x, appeared in the

O x i d a s e Pre ssor

P r e c u r s o r R a t i o R a t i o *

D i h y d r o x y p h e n y l a l a n i n e 140 20

L e u c i n e 105 1

T y r o s i n e 100 10

T r y p t o p h a nD i h y d r o x y p h e n y l s e r i n e ?

87 3r y p t o p h a nD i h y d r o x y p h e n y l s e r i n e ? 65 1000

N o r v a l i n e 54 2

D i h y d r o x y p h e n y l s e r i n e ? 51 1640



N o r l e u c i n e 19 2

P h e n y l a l a n i n e 11 7

G l y c i n e 0 0

A l a n i n e 0 0

G l y c i n e 0 0

S e r i n e+

0

T h r e o n i n e +0

A s p a r t i c a c i d?

0G l u t a m i c a c i d ? 0?

H y d r o x y g l u t a m i c a c i d 0?

I s o l e u c i n e + +?C y s t e i n e 0 ?C y s t e i n e ?C y s t i n e ?M e t h i o n i n e ?A r g i n i n e όL y s i n e 0

40 *r g i n i n e 0 40 *

A r g i n i n e 0 0

D i i o d o t y r o s i n e+

?

T h y r o x i n e + ?P r o l i n e 0 0?

H y d r o x y p r o l i n e 0 0?

H i s t i d i n e 0

G l u c o s e 0 "0"



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 1



Ι ό ADVANCES IN CHEMISTRY SERIES

ur ine only after theproduct ion of uni lateral renal ischemia (89) ; it wasexcreted mainlyby the contralateral k id ney, an d was also detected in blood . C hr on ic canine hyper tensionwas accompanied by this base i n blood and u ri ne, disappearing when it regressed. Base χ

increased in blood and disappeared in urine when hypertension was made worse by the

administration of salts, especiall y potassi um . L ock ett believed th at base A an d base χ

were similar substances coming from a single compound which was transformed into the

latter by renal ischemia and into the former by alkal ine hydrolysis (40). Thefact thatthey are pressor is of considerable interest. Although their action is depressed by ergo-toxine, these bases differ from epinephr ine in certain characteristics. L ock ett's wor k has

not been confirmed.

Urohypertensin (1) was isolated from urine many years ago,and resembles in some

respects L ock ett's base A, except that it wasnot, l ike base A, precipitated with mercuri c

chloride. B a i n (4) thought that isoamylamine, which he found in human ur ine, was

urohypertensin. Lockett wasunable to find isoamylamin e in urine, although von E u l e r

and Sjostrand (22) have stated that it ispresent i n decreased amou nts inessential hyper

tensi on. T hese pressor bases are worth fur ther study, especially their relation to amines.

Other Substances

A n uni dentif ied substance, named n ephr in , was described by E n g e r (19). N e p h r i n is

a pressor material having a prolonged action, obtained from extracts of renal cortex,

bu t not present in any other tissues. I t wasalso found in ur ine and in blood and was

said tohave been present in increased amounts both in hypertensive dogs and in patients

with hypertension, eclampsia, nephritis, and other hypertensive conditions. Its action

was not intensified by cocaine nor affected by ergotoxin and it di d not act upo n the

guinea pi g uterine muscle. As it wasdialyzable, it probably was not renin. If this work

is substantiated, nephrin represents yet another renal pressor substance probably of

nonprotein nature. Its relation to hypertension has not been substantiated.

M a n y other un iden tified pressor materi als hav e been isolated from organs and fluids(see von E u l e r , 20, for discussion). Some of them were probably simple amines, others

epinephrinelike. T h ey have been given a variety of names. Because of their non

specific nature and the manner of their extraction it seems unl ikely that they are co n

cerned in the development or maintenance of chronic hu man hypertension.

A n interesting reaction to intradermal histamine has been described (65), which ,

whi le not a pressor substance, appears to reproduce certain symptom s an d signs encou n

tered in hypertensive subjects. H istam in e has a renal action similar to epinephrine

(47), constricting efferent arterioles. I n neurogenic hypertensive patients it also pro

duces the "hy per tensive diencephalic syn dr ome." Whether this reaction is direct, or

indirect through some other mechanism, is obscure.

Adrenal Cortical Hormones

One hormone, desoxycorticosterone, which comes from or is closely allied to an

adrenal cortic al steroid, has the probably unique characteristic of raising blood pressure

i n hypertensive human beings (27, 45) not shared by simi lar steroid substances. As the

acetate or more soluble glucoside it also acts as a pressor agent inno rma l dogs and rats.

Whether it sensitizes vessels to the vasoconstrictor action of other circulating agents,

or acts directly of itself, isno t kn o wn; in chronic experiments, at least, salt is necessary

for its hypertensive acti on. Desoxycorticosterone acetate also produces chronic hyper

tension an d renal vascula r disease i n rats when giv en in large doses (60). In the majority

of cases of hu man h ypertension there isno evidence of excessive adrenal cort ical act i v i ty;i n a certain cl inical group, however, sodium concentr ation of sweat is low, and other signs

of endocrine disturbances arepresent (54). Theresponse of the blood pressure to diets

low in salt is often dramatic. I n such cases theauthors believe that a different patho

genesis is operating, governed mainly by the adr enal cortex. P r obab ly the output of

salt-retaining hormone is excessive; hypertension mayhave been initiated on this basis,

leading to secondary changes in the renal vascular bed and the inst itution of a renal

pressor mechanism.



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 1



SCHROEDER AND OLSEN—HUMORAL PRESSOR SUBSTANCES

Indirect Methods for Identifying the Hochdruckst of f

B y the use of specific enzymes, studies have been made in an attempt to classify the

pressor substances in experimental hypertension. If a specific enzyme lowered blood

pressure in hypertensive animals and not in normal ones, it was assumed that the sub

strate of that enzyme was attacked, and therefore contributed to the hypertension.

Such assumptions, while not whol ly val id , nevertheless pointed to certai n substances as

possibly concerned in hypertension.

Tyrosinase obtained re lat ive ly pure was tested for its effect in rats, dogs (53), and

m an (50), an d was found to exert a specific depression of blood pressure only i n hyp erten

sive ani mal s. T yr osi nase contain s catecholase and cresolase, and has the proper ty of

Figure 3. Effect of Intravenously Administered Amine Oxidas e on Blood

Pressure and Blood Urea Nitrogen of Hypertensive DogsD o g s w e r e m a d e h y p e r t e n s i v e by the G o l d b l a t t m e t h o d . T h e h a tch e d a r e a r e p r e se nts th ee x t r e m e s of the c o n t r o l v a l u e s for 3 to 12 m o n t h s of h y p e r t e n s i o n p r i o r to the e x p e r i m e n t .

D o g 39. D a i l y i n j e c t i o n s of a c ti v e p r ep a r at i on s ( E l l , 29, 30, 34) r e su l te d i n a fa l l of b l o o dp r e s s u r e to n o r m a l l e v el s . A f t e r d i s c o n t i n u a n c e of the e n z y m e , b l o o d p r e s su r e s o o n r e t u r n e dt o f o r m e r v a l u e s. B l o o d u r e a n i t r o g e n was l i t t le a ffected.

D o g 29. A s i m i l a r r e s u l t was o b t a i n e d w i t h a n o t h e r a c t i v e p r e p a r a t i o n (E 9), the effectl a s t i n g for a week a f t e r s t o p p i n g a d m i n i s t r a t i o n of the e n z y m e , w i t h o u t e l e v a t i n g b l o o d u r e an i t r o g e n . A n o t h e r l a r g e r i n j e c t i o n , g i v e n on the 16th day, c a u s e d f u r t h e r h y p o t e n s i o n ,u r e m i a , and d e a t h .

D o g 53. T wo p r e p a r a t i o n s , of w h i c h th e e n z y m e hadb e e n i n a c t i v a t e d by a l k a l i n e h y d r o l y s is , di d not a f fe c t b l o o d p r e ssur e or b l o o d u r e a n i t r o g e n .

A m i n e o x i da se was s u p p l i e d t h r o u g h the c o u r t e s y of K a r l F o l k e r s , M e r c k an d C o m p a n y .



0 2 1 / b a - 1 9 5 0 - 0 0

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Figure 4. Prevention of Pressor Action of Renin and Hypertensin (Angiotonin) by Amine

Oxidase

P h o t o k y m o g r a p h s of the b l o o d p r e s s u r e of r a t s , u s i n g a H a m i l t o n o p t i c a l m a n o m et e r . T h e upper f iguresr e p r e s e n t the s y s t o l i c , the l o w e r the di a sto l i c p r e ssur e s i n mm. of m e r c u r y .

U p p e r two c u r v e s (rat 95). E f f ec t of a l a r g e i n t r a v e n o u s dose of r e n i n (0.1 ml .). A f t e r 4 m i n u t e s , at A.O .a s o l u t i o n of a mi ne o x i da se was i n j e c t ed i n t r a v e n o u s l y , w h i c h s l o w l y l o w e r e d the b l o o d p r e s s u r e to n o r m a l .A f t e r 12 m i n u t e s , a l a r g e r dose of r e n i n (0.15 ml.) was g i v e n , w i t h l i t t l e effect on b l o o d p r e s s u r e . R at wash y p e r t e n s i v e .

M i d d l e two c u r v e s (rat 100). E f f ec t of a s i ng l e dose of a n g i o t o n i n . At A.O.a m i n e o x i d a s e was i n j e c t e d ,w h i c h r e t u r n e d the m o d e r a t e l y e l e v a t ed b l o o d p r e ss u r e to c o n t r o l v a l u e s . A f t e r 5 m i n u t e s the same dose ofa n g i o t o n i n was g i v e n , w i t h a m o d i f i e d r e s p o n s e. R at was n o r m o t e n s i v e .

L o w e r c u r v e (rat 183). E f f ec t of a d o u b l e dose of a n g i o t o n i n m i x e d w i t h a m i n e o x i d a s e and s h a k e n for 30m i n u t e s at r o o m t e m p e r a t u r e . A n g i o t o n i n was c o m p l e t e l y i n a c t i v a t e d . A f t e r 4 m i n u t e s the same dose a l o n ep r o d u c e d a mo di f i e d p r e sso r r e sp o nse . R at was h y p e r t e n s i v e .

oxidiz ing mono- and or thod ihydroxypheno ls to quinones. U nfor tunately , the quinones

thus formed are active oxidizing agents, and therefore the effects cannot be attr ibuted

to any specific phenolic pressor substance. The least that can be said, however, is that

easily oxidizable pressor substances are present in hy per tension ; possibly they are cate

chol or cresol deriv atives. Wh en injected in traveno usly in to hy pertensive rats, no effect

was observed unt i l 5 to 15 min utes later, when blood pr essure in var ia bly fell to no r ma l

an d di d not rise again, even for as long as 2 weeks. In dogs effects were more transient,

but hypertension could be controlled by dai ly inj ections. T yr osin ase acted as a p a r a

sympathomimet ic agent in dogs, its action being observed for an hour or two after ad

min is t ra t ion , and consisting of vomi t in g, d iarr hea, and brad ycar dia, wh ich were abol ished

by atrop ine. It is probable, from the nature of the enzyme, that tyrosinase produced a

true chemical, or "enz y ma ti c" sympath ectomy. Specific enzymatic act i v i ty was detected

i n blood for 24 hours fol lowing inject ion. F ur ther mor e, urea nitrogen in blood was low

ered, and urea clearance unchanged in the face of a lowered blood pr essure. Sim il ar

effects were observed in man, which were usually not correlated with febrile episodes.



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h 0 0 1




T h e course of malignant hypertension in man was reversed readily by this agent, and

blood pressure in benign cases lowered. No hypotensive effect was noted when the

enzyme was inact ivated.

Tyros inase had other interesting actions. Pr eparati ons of old renin contained a

substrate for the enzyme and pressor activity was abol ished. T h i s pr obably occurred

through quinonic ox idat ion, for the substrate could be dialyzed from the renin. F r e s h l ydialyzed renin, not affected by the enzyme alone, was inact ivated by tyrosinase plus a

catechol-hydroquinone substrate. One sample of hypertensin (angiotonin) was i nact i

vated direct ly by tyrosinase; another was inact ivated only when serum was added as

well. P r i o r injections of tyrosinase modified the pressor actions of ang iotonin , ty rami ne ,

an d epinephr ine, but did not abol ish them. A lth ough these amines are rap i d ly ox id ized

in v i t r o , the relative rates of vasoactivity after injection (rapid) and ox idat ion in v i v o

(less rap id) probably accounted for the results; very slow infusions of epinephrine were

without effect on the blood pressure of animals havi ng cir culat ing enzyme. Vi ctor 's

renal pressor substance (65) was completely inactivated by tyrosinase. Furthermore,

renal blood flow in dogs was increased, and epinephr ine was seen to act as a renal vaso

dilator after tyrosinase had been given. A foreign (plant) protein, tyrosinase was a good

antigen, precipi t ins being formed wh ich in activated the enzyme only when it was in an

insoluble state; it did not cause anaphylactic shock. In man,however, it could not be

used for more than a few weeks because of its ant igenic i ty .

T h i s phenolic oxidase therefore seems to be a tru e anti h yp erten sive substance, affect

i ng blood pressure without deleterious effects on k idneys. There is a strong presumption,

therefore, that some phenolic substrate important for the maintenance of hypertension

Figure 5. Prevention of Pressor Action of Renin and Hypertensin by Amine

Oxidase

U p p e r two c u r v e s (rat C14). E f f ec t of i n j e c t i o n of r e n i n (0.1 ml .) u p o n b l o o d p r e s s u r e of a m a r k e d l yh y p e r t e n s i v e rat. A f t e r 8 m i n u t e s at A.O. a mi ne o x i da se was i n j e c t ed i n t r a v e n o u s l y , w h i c h wasf o l l o w e d by l i t t l e i m m e d i a t e effect but a slow fa l l of b l o o d p r e s s u r e to m u c h l o w e r l e v el s . A f t e r 33m i n u t e s a l a r g e r dose was g i v e n , w i t h l i t t l e effect on b l o o d p r e s s u r e .

L o w e r two c u r v e s (rat 94). I n d u c t i o n of t a c h y p h y l a x i s to r e n i n by a m i n e o x i d a s e w i t h o u t p r i o ri n j e c t i o n of r e n i n . A m i n e o x i d a s e was i n j e c t e d i n t r a v e n o u s l y , f o l l o w e d 75 m i n u t e s l a t e r by r e n i n(0.1 ml .) an d 80 m i n u t e s l a t e r by r e n i n (0.15 ml .). T h e r e was o n l y a s l i g h t r e n i n p r e sso r r e sp o nse ,ne v e r to h y p e r t e n s i v e l e v e l s .



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h 0 0 1




is altered. Al l suspected phenolic pressor amines and other pressor substances were

inact ivated by the enzyme. The evidence thus becomes more suggestive that some

catecholic or phenolic pressor compounds may act in hyp ertension. E nzy mes capable of

attacking theguanidine linkage in such compounds asarginine, creatinine, and guanidine

acted as pressor—not depressor—substances.

A mi ne oxidase prepar ed from hog liver and ki dney acted simi lar ly if less dramat ica l ly(51). Thepreparation used contained no other oxidase activity, but was only par t ia l ly

purif ied. It h ad a strong, but slowly developed hypotensive action on the blood pressures

of rats, much greater on elevated than on normal ones. E xper i menta l G o ldb lat t hy per

tension in dogs was controlled by injection of the enzyme usually at no expense of renal

funct ion (F igure 3). The level of blood urea nitrogen was lowered by the therapeutic

dose. O verdo ses, ho wever , caused enough depression of blood pressure to produce

renal insufficiency and death, probably lessening the head of pressure thr ough the clamped

ar tery . T en in activ ated pr eparations were wi thou t effect. T h e blood pressure of no r ma l

dogs was not lowered appreciably by theenzyme. Its imp ur i ty p r evented its parenteral

use in m a n ; by mouth it h ad no effect. So far l itt le work by qualif ied organi c chemists

has been done on the character i zation and pu r i f icat ion of this interesting enzyme.

Amine oxidase also was found to have the ab i l i ty of d imin i sh ing or abol ishing the

pressor action of renin. W he n an act ive preparat ion of the enzyme was injected i n t r a

venously into rats, subsequent injections of renin had l itt le effect (F igures 4 and 5).

Hyper tens in , however, showed only a modified response in these preparat ions, probably

because of therelative slowness of act ion of the enzyme. Sim il ar results were found wit h

other pressor agents.

Characteristics of True Antihypertensive Substances

M er ely because a substance depresses blood pressure does not make it a t rue ant i

hypertensive substance. The level of blood pressure is the resultant of several factors:

the viscosity of the blood, the cardiac output, the volume of circulat ing blood, and the

state of the arteri al an d arteriolar bed, wh ich determin es the p erip her al resistance to blood

flow, other factors being equal . T h i s discussion has indicated that peripheral resistance

through arter io lar constr i ct ion may be affected by renal blood flow and the p r o d uct io n

of ci r cul atin g pr essor agents. T her efore, a definit ion of a true antih yper tensive substance

is necessary, in order that we be not misled by depressor substances wh ic h lower bl ood

pressure at a detriment to the body's economy.

A n antihypertensive substance is one w h i c h does not affect blood volume, blood

viscosity, or the funct ion of the heart ; it lowers blood pressure to normal levels in

hypertensive states by generalized arteriolar dilatation, including those of the k idneys.Vasodilators (such as hi stamine), w hi ch lower ar terial pressure at the expense of renal

blood flow, are not ant ihyper tens ive . Fur thermore , an ideal substance should affect the

blood pressure in normal states to l i t t le or no extent. It can bepr edicted, however, that

when true antihypertensive substances are found, they wil l not increase or main ta in renal

blood flow in the face of lowered arter ial pressure wh en renal arteri oles h ave lost the

abi l i t y to dilate because of pathological changes (see F i g u r e 3).

T y r o s inase andamine oxidase appear to be true antih yper tensive substances; they

ar e useless at the present time for cl inical app l icat ion. M an y cardio tox ic and depressor

agents are k no wn wh ich wil l lower blood pressure at the expense of kidneys, heart, or

blood volume. A few newer compounds, however, are now being studied which on

pre l iminary t r ia l appear to fit the definition of antihypertensive substances. It is believedthat, in the not too distant future, a pract ical method for the control of this prevalent

condit ion will be found.

Summary and Conclusions

F r o m the evidence now avai lable it appears that arteri al hy pertension in man is

usually a psychosomatic disease, and that the effects of psych ic disturbances manifest



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themselves upon the soma by w ay of sympathetic nervous pathw ays. D ischar ges of these

nerves cause neurogenic vasoconstri ction , an d in clu de the ren al vascul ar bed. R ena l vaso

constriction wh ich is not wholly compensated by elevation of blood pressure causes the

kidneys to release pressor substances into the bl ood . Si xteen different pressor substances

or types of substance have been discover ed; ma n y others have been detected wh ic h may

or may not be similar.T h e renal pressor mechanism—renin and hypertensin—acts in acute hypertension

an d in acute renal ischemic states, but apparently not in chronic hypertension. The

other mechanisms shown to beactive in chr onic hypertension are : vasoexeitor-vasodepres-

sor m aterial relationship ; pherentasin, a pressor substance found on ly i n hu man h yper ten

sion; amines resulting from theinsufficient oxidation of ami no acids, whi ch are incr eased

i n human hypertension; and norepinephrine (Sympathin E ),wh ich largely reproduces

the hemodynamic picture of chronic hypertension. M ost of the known pressor

substances, with the notable exception of norepinephrine, come from disturbances of,

or are extracted from, theki dneys. T h e large nu mber of pressor substances which have

been obtained suggests that many may represent different stages of metabolism of certain

parent substances, and that their effectors may be fewer innumber and simpler in structure. The chemical identif ication and purif ication of most of these substances leave

m u c h to bedesired, an d their ph afmacol ogy has i n most cases been inadequately studied.

T h e whole problem, however, maysoon become simplif ied.

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UP PO RT E D by a grant-in-aid from the National Heart Institute, U. S. Public Health Service.

Discussion of Paper on Humoral Pressor Substances

and Their Relation to Arterial Hypertension

DOUGLAS R. DRURY

Depart ment of Physiol ogy, School of Medi cine, Universit y of Sout hern California, Lo s Angeles 7, Cali f .

Schroeder has very adequately reviewed the known humora l agents that i n the past have

been implicated inexperimental or clini cal hypertension. Wi th theexception ofhis own

substance isolated from the blood of hypertensive patients, these all have one or more

serious deficiencies when considered asthe causative agent ofhypertension. Schroeder's

substance is too new to have been given r igid examination i n his own an d inother labora

tories, although itpromises interesting possibilities.



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DRURY—DISCUSSION OF PAPER ON HUMORAL PRESSOR SUBSTANCES 23

T h e r e isno dearth of chemical compounds th at wil l cause a rise i n bloo d pressure wh en

injected into the exper imental ani mal. E xtr acts of pl ant an d ani mal t issues y ield several,

an d enzymes present in the tissues wil l often produce pressor substances as a result of

autolysis. F or a chemical agent then to be proved as a cause of hypertension it must be

found as such in the animal and in greater amount in the hypertensive than in the normal

an imal . The substance must be capable of p r o d uc ing a continued elevation of bloodpressure when administered continuously to thenor mal ani mal. T h e substance must be

of such a nature that the body does not make corrective or adaptive responses to it. I n

this fashion tachyphylax is or immunological react ions may reduce the act ion of certain

agents if given repeatedly.

R ecent experimental w ork indi cates that factors in exper imental hypertension make

the picture more complicated than that of a pressor substance being produced in greater

than normal amounts. I n early experimental renal hypertension the conclusion is p r a c

t ica l ly inevitable that a humo r a l agent coming from the ischemic k idney is imp l icated in

the p roduct ion of the increased arterial pressure. I n later stages of the hypertens ion,

however, another mechanism must become operative, since in an animal hypertensive

f rom uni lateral renal i schemia the causative kidney may be removed, and the high blood

pressure wi l l usually persist forweeks or months thereafter. A hum oral mechanism may

be involved in thep r o d uct io n of this residual or self-perpetuating hypertension, and it is

even possible that this substance might be produced by the remain ing unmanipulated

k i d n e y . A n d so thepressor substance found by Schroeder in the blood of hypertensive

patients might be theresult of a long cont inued condit i on, rather than the original cause.

T h e fact that he does not find it in al l cases gives some suppor t to th is not ion.

T h e mechanism of thi s r esidual hy per tensio n has been assumed by many to beneuro

genic. Theevidence for th is is not conclusive, andeven if the central nervous system

is involved (it is invo lved inmost things going on in thebody), it is not improbable that

h u mor a l factors in add it ion may act in this self-perpetuating hypertension.



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Role of Sympathetic Blockade

in the Therapy of Hypertension

MARK NICKERSON

Univer sit y of Utah Coll ege of Medicine, Sal t Lake Cit y, Ut ah

Considerable progress has been made in the develop

ment of agents capable of producing a specific and

effective blockade of responses to sympatho-adrenal

activity. Three groups of compounds show particular

promise—the β-haloalkylamines, the dihydro ergot

alkaloids, and the imidazolines. However, lack of

information regarding the role of sympatho-adrenal

factors in the etiology of essential hypertension pre

vents a definitive evaluation of their potential useful

ness in the therapy of this condition.

During the past few years considerable progress has been made in the development of

agents capable of producing a specific and effective blockade of responses to sympatho

adrenal acti vi ty. R esearch on several series of blocking agents has progressed to the

point where it is now possible to produce a c l in ical ly useful ' 'chemical sympathectomy."

Such a chemical sympathectomy hasobvious uses in thecl inical evaluation and treatmentof conditions in w h i c h a large component of sympathetically mediated smooth muscle

spasma is involved. However, anyassessment of the place whic h these agents may u l t i

mately occupy in the therapy of hypertension depends upon a more specific delineation

of therole of the sympatho-adrenal system i n hu ma n hyp ertension. In spite of extensive

laboratory and cl inical investigation and elaborate speculation, this role is still obscure.

I n his J aneway lecture of 1941 (78), Page listed 52 types of human hypertension.

These were classified with respect to etiology with two notab le exception s: essentialhypertension and mali gnant hyper tension. U nfor tun ately, about 95% of al l cases of

human hypertension fall into these two poor ly defined group s. I ndeed, it is possible

that neither of these categories is homogeneous. Inasmuch as the etiology of most cases

of hu ma n hypertension is still u n k n o w n , no rati onal basis has yet been established for the

use of adrenergic blockade in their treatment.

Neurogenic Hypertension

E xper im ental neurogenic hypertension has been known andstudied for many years.

Some of its more pr omi nent features are listed i n T ab le I. E v e n a casual appr aisal of these

characteristics indicates that human essential hypertension and uncomplicated neurogenichypertension have little incommon. H ypertension indu ced by infusion of epinephrine or

norepinephrine is inc luded for comparison. It is clear that infusion of epinephrine causes

hemodynamic changes which are different from those seen in essential hypertension and

which resemble those observed in neurogenic hyp ertensi on. I nfusion of norepinephrine

(36), on theother hand, induces changes comparable to those observed inessential hyper

tension. However, the s imi lar i ty has not been proved to be of etiological significance.

Hypertension w i th these characteristics may be dupl icated by the infusion of any agent—

24



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NICKERSON—ROLE OF SYMPATHETIC BLOCKADE IN THERAPY OF HYPERTENSION 25

e.g., angi otoni n— wh ich produces a general ized per i pheral vasoconstr i ct ion wh ich pr edomi

nates over cardiac st imulat ion.

B ecause of the m an y dissim ilar iti es between h u ma n essential hy per tensio n and ex

perimental neurogenic hypertension, studies of the latter have been relegated to the back

grou nd in recent years in favor of work o n experi mental r enal hy pertensi on, wh ic h mu ch

mor e closely resembles essential hyp erten sion (T able I ; 1 1 , 3 5 , 6 4 , 77). N ever th eless, acareful analysis of neurogenic hypertension is important as a basis for the recognition or

exclusion of neurogenic factors i n h um an hy per tension .

M a n y cl inical observations indicate that neurogenic factors in some way influence the

development an d mai ntenan ce of essential h yp erten sion . I t has lon g been recogni zed

th at stressful situati ons ma y i nduc e ma r ked increases i n bot h systolic an d diastoli c pr es

sures which persist for varying periods of t ime ( 2 1 , 3 8 ) , and that hypertensives tend to

have a characteristic typ e of personality ( 2 , 9 9 } . Such ind i v iduals usual ly exh ib i t im por

tant components of repressed antagonism and anxi ety. T h ey do not find emotional out

lets in overt acts, but rather their emotions are expressed through an increased activity of

the sym pa th o-adr enal system wi th a consequent incr ease i n blo od pr essure. R elief of

psych ic tension frequently produces salutary effects i n these pat ients. I ndiv i duals who

show hyperactive sympathetic vasomotor reflexes (as measured by the cold pressor test)

are mu ch mor e pr one tha n the average i nd iv idua l to develop hy pertension i n later l ife ( 5 7 ) .

F i g u r e 1 illustrates the pr inc ipa l nervous pathways involved in the maintenance of

blood pressure. U nd er no r mal conditi ons the afferent pathw ays from the caroti d sinus

an d aort ic arch areas carr y tonic imp ulses wh ic h depress the acti vi ty oî the vasomotor

centers. C onsequ ently , section of these moderator nerves in animals ( 5 1 , 5 6 ) or man

( 1 0 3 ) brin gs about a sustained hy pertensi on. O f more impor tance to an analysis of c l in i

cal hy per tension, however, is the fact that increased acti vi ty of the sympath o-adrenal sys

tem ma y arise on a central basis. I n animal s such hy pertension may be in duced by elec

tr ical st imulat ion of or injury to the hypothalamus ( 5 9 , 9 8 ) ; i n both ani mals ( 1 7 , 2 6 , 3 9 )an d m an ( 1 6 ) it may result fro m an incr eased i n t racran ia l pr essure, at least i n p ar t because

of the cerebral isch emia th at r esults ( 1 6 , 4 8 ) .

N eurogeni c renal vasoconstricti on, wi th consequent act ivati on of the r enin -angio-

t on i n mechan ism, is not a major factor i n most cases of neurogenic h yp ertensi on; evidence

for this is seen in the limited fall i n blood pressure wh ic h follows r enal denervati on ( 4 1 , 5 4 )

an d the failure of pr io r nephrectomy to alter the pressor response to moderator nerve

section ( 9 5 ) . H ow ever, neurogenic renal vasoconstricti on may be adequate to pr oduce a

sustained hyp ertension after other body structur es hav e been symp atheti cally denervated

( 4 2 , 4 4 ) , a n d i t is possible that neurogenic r enal vasoconstricti on may pl ay a signif icant

role i n the develop ment of essential hy per tensi on .

Table I. Cardiovascular Characteristics o f Various Types o f Hypertension

M e c h a n i s m 0

Indexes"E s s e n t i a l "

h y p e r t e n s i o nR e n a l

h y p e r t e n s i o n

N e u r o g e n i ch y p e r t e n s i o n

E p i n e p h r i n ei n f u s i o n

N o r e p i n e p h r i n ei n f u s i o n

P u l s e r a t e Ν Ν Ν or Y

C a r d i a c o u t p u t Ν Ν Ν or y

T o t a l per iphera l res i s tance Ν ΫB l o o d f low in extremities Ν Ν Y

Pressure fluctuations M a r k e d e a r l yL i m i t e d l a te

L i m i t e d M a r k e d C o n t r o l l e d C o n t r o l l e d

a N . N o r m a l . >K- I n c r ea sed . " Ϋ . D e c r e a s e d .

One of the distinguishing characteristics of uncomplicated neurogenic hypertension is

its dramatic response to sympathectomy or to chemical blockade of the sympathetic

nervou s system. C omp lete symp athec tomy results i n an imm ediate redu ction i n the

blood pressure to nor mal or to subnor mal levels wi th a grad ual r etur n to nor motensive or

slightly higher levels over a period of 1 to 2 months ( 4 1 , 4® , 5 4 ) . M oder ator nerve sec

tion or increased intracranial pressure usually fails to increase the blood pressure in com

pletely sympath ectomiz ed ani mals an d if a rise is elicited it is rela tivel y slight and develops

slowly ( 5 , 2 7 , 4 1 ) .



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Consistent lowering of the blood pressure had been observed in dogs with neuro

genic hypertension to which ergotamine, 883F (d iethylaminomethylbenzodioxan), or

933F (p iper idylmethylbenzodioxan) hadbeen administered (9, 52, 53, 59, 60). I n some

of these cases centra l inh ib i t ion of vasomotor act iv ity aswell as adrenergic block ade by

the drug was un doubtedly in volved. H owever, this does notdetract from the fact that

the reduction or e l iminat ion of sympatho-adrenal act iv ity always induces a dramat ic red u c t i on in blood pressure.

F a c t o r s invo lved in the regulat ion of the blood pressure of no r ma l (5,13, 46, 65) and

neurogenic hypertensive animals after complete removal of the sympathetic nervous sys

tem have not been clearly defined. H ow ever, these factors may inc lude renal humor al

(3, 28, 55, 97), extrarenal humoral (6) , extrasympathetic neural (4, 5, 42, 46), and local

(22) components; all are imp o r t ant in anyevaluat ion of theblood pressure response to

sympathectomy or to sympathetic blocking agents. Thedegree of fall in blood pressure

after these procedures may depend not o n ly up o n the extent to w h i c h the sympatho

adrenal system was invo lved in themaintenance of the i n i t ia l pressure, but also upon the

r a p i d i t y and the extent of compensation by other factors. F igu r e 2 i l lustrates a possible

sequence of adjustments during thedevelopment ofneurogenic hypertension and its subse

quent "cu r e" by sympathectomy or sympathetic blockade. Fewquantitat ive data are

available regarding most of these factors. H ow ever, it is clear that some such over-all

adjustment does occur .

Renal Hypertension

In contrast to neurogenic hypertension, the role of adrenergic factors in experimental

renal hypertension is obscure. The sequence of events by wh ich interference wi th renal

hemodynamics leads to elevation ofthe systemic blood pressure hasbeen carefully studied

an d has been shown to be independent of nervous mechanisms (see11, 85). Sympathec

tomy does not prevent the development of renal hy pertension an d induces onl y slight andirregular reduct ions in pressure in renal hy pertensive animals (3, 28, 55, 97) .

Prolonged administrat ion of adrenerg ic b locking agents may produce a signif icant,

but highly var iable , reduct ion in systemi c ar teri al pressure in animals with exper imental

renal hypertension. T h is hasbeen observed after the ora l administ rat ion of y o h imb ine

to dogs (58), the ora l administ rat ion of Dibenamine [iV^-(2-chloroethyl)dibenzylamine]

to rats (71), an d the intravenous admini strat ion of D ib e namine to dogs (100). I n none of

these exper iments involv ing chronic administrat ion of adrenergic blocking agents were

the pressures consistently reduced to thenor motensiv e ran ge. Sin gle in jections of 883F

an d 933F produce l i t t le or no vasodepression in dogs with chronic renal hypertension (9,

20, 61), a , response very similar to that seen in normotensive controls. I t hasbeen re

por ted that single injections ofpentobarbital , yoh imbi ne, and 883F, but not933F, producea greater depressor response in rats which have been hypertensive for more than 2 months

than in those wit h a shorter durat ion of hypertension (84, 86) ; on this basis it has been

suggested that neurogenic factors areof impor tance in late but not in ear ly r enal hyp er

tension (76, 84, 86). T h i s differential response wi th r egard to thedurat ion of therenal

hypertension was not observed with Dibenamine in chronic experiments on rats (71) ,or

w i t h various anesthetics andother procedures to reduce vasomotor ac ti vi ty in exper i

ments on dogs (68). I n general, the significance of those observations which indicate a

correlat ion between the durat ion of experimental renal hypertension and the magnitude

of theadrenergic component seemstobevery l imi ted (see70 and 71 for further discussion).

O ther evidence whi ch hasbeen adduced to suppor t the significance of neurogenic fac

tors i n renal hyp ertension is theobservation that thearter ial pressures ofnor mal and renal

hypertensive dogs and rabbits were reduced to essentially the same level after comp lete

destruction ofthe central nervous system (18,19). H owever, interpr etat ion ofthe results

obtained with this drastic procedure is difficult. O th er wor kers ha ve observ ed a sharp

fall in pressure when the spinal cord wasdestroyed below C 5 (the level of the fifth cervical

vertebra) in renal hypertensive dogs, but the pressures returned to hypertensive levels as

the acute effects of the operat ion wore off (32). O ther exper iments in volv in g e l imin at ion

of the central connections of the sympathet ics by cervi cal cord section in the region ofC7



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have demonstrated that thepressures ofearly and late neurogenic hypertensive dogsmay

fal l below those ofno rma l dogs after cor d section. T h i s is probably dueto a reduction in

nonsympatho-adrenal pressor factors inthese animals (see F i g u r e 2,B) . However, under

th e same condi tions pressures of renal hypertensive animals aremain tained signif icantly

above those of the normals {40). In addit ion, it hasbeen demonstrated that chronic

destruction of the spin al cord below C5 does not pr event the development of typica l chronicrenal hypertension (83) . I t appears that theless trauma involved in thesurgical el im in a

t ion ofthesympathetic nervous system inanimals with renal hypertension, theless effect

the procedure has on the blood pressure.

C en t r a l J i f er v oa s*Sty j& teX7x

Ws/efsl mscfe

Respiration

SympaiJheficGanglia

< Ε θ ϊ2 3 ΐ

Vesselsffesrt Terjpheral Adrenal Splanchnic

Vessels Medal/a Vessels*Figure 1. Principal Nervous and Humoral Pathways Involved in

Maintenance of Systemic Arterial Pressure

Solid lines depict nervous pathways and broken lines humoral agents

Essential Hypertension

In human essential hypertension also, sympathectomy or blockade of the sympatho

adrenal system brings about an equi vocal response. T h er e is l ittle doubt that variousdegrees of surgical sympath ectomy may produce a prolonged reduction inblood pressure

i n cer tai n selected cases (1$, 81, 82, 89), but theresponse is high ly variable and the degree

of benefit attributed tothe procedures employed may depend toaconsiderable extent up on

an evaluation ofthenatu r al course of thedisease (see 79).

I n the work of Goldenberg and co-workers (37) , who employed members of the

F ou r n e au series of adrenergic blocking agents to detect pheochromocytoma, it was ob

served th at most cases ofessential hypertension actually responded with an increase in the

resting blo od pressure. T h i s increase wasundoubtedly due tothecentr al nervou s system

stimulant effects of these drugs (see 70), but failure to respond by a fall in pressure sharp ly

distinguished cases ofessential hyp ertension fr om those i n wh ic h therise i n blo od pressure

was largely due to an excessive secretion ofepinephrine or norepinephrine. C l i n i ca l treatment of hyp ertension w it h the more effective adrenergic block in g agents hasalso produced

hi ghly vari able results, whi ch arediscussed below in connection with the i nd iv i dua l com

pounds involved.

Factors in Blood Pressure Regulation

T h e high ly var iabl e blood pressure responses to adrenergic blockade in cases of

experimental renal hypertension and human essential hypertension, particularly those



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responses obtai ned wi th single in jections ofblo ck i ng agents, are extremely di fficult to i n t e r

pr et. H owever, their mar ked ir regular i ty , wh en compared wi th the consistent depressor

response to adrenergic bloc kad e seen in neurogenic hypertension, argues against derange

ment of sympatho-adrenal funct ion as a major factor in exper imental r enal hypertension

an d most cases of established essential hypertension. In add it ion, it must be concluded

that the contention that nervous factors are of impor tance in late but not in early r enalhypertension has not received œnvincing support f rom exper iments employing sym

pathetic denervation or adrenergic block in g agents.

Although blood concentrat ions of vasoexc i tor mater i a l (V E M ) are increased in both

experimental renal and hu man essential hyp ertension (see88), studies of this mater i al have

not progressed to thepoint where its ro le in maint a in ing the elevated blood pressure can

be adequately evaluated. V E M appears to have litt le direct effect on smooth muscle

an d produces its p r i m a r y effects not direct ly , but by sensitiz ing vessels to the act ion of

epinephr ine and probab ly to that of sy mp at h in . F a i l u r e of such powerful adrenergic

block ing agents as Di benamin e consistently to reduce to no r ma l thepressure in renal and

h um an essent ial hyp ertension argues against V E M play in g a major ro le in m a i n t a i n i n g

the elevated blood pressure in these condit ions.

N o n e of the specific adrenergic blocking agents in hi bits vascular responses to angio

ton in (see70), and the mechan ism by wh ich adrenerg ic b lockade or sympathectomy br ings

about even a part ia l reduct ion in blood pressure in renal or human essential hypertension

has not been clear ly established. H ow ever , it has been definitely demonstrated that

vasomotor reflexes are sti l l active in thepresence of acute or chroni c renal hyp ertension in

animals (7, 19, 68, 97) and man (88) and in human essential hypertension (81, 88).

Consequently , itm ay beassumed that at least part of theobserved decrease in pressure is

due to thee l iminat ion of sympatho-adrenal factors. If a signi ficant element of neurogenic

renal vasoconstr ict ion is invo lved in human essential hypertension, a second factor in

the hypotensive effect of adrenergic blockade m ay bethe increase in renal bloo d flow wh ic h

cou ld be induced by the blockade. Inhib it ion of sympathetic vasoconstrictor tone by

h igh spinal anesthesia hasbeen shown to cause an increase in renal blood flow in b ot h h u

man essential hypertension and experimental renal hypertension in dogs (94), but the

relat ion of this observation to the etiology of the blood pressure elevation is not clear.

Sympathectomy may fail to alter renal blood flow and filtration in at least some casesof

essential hypertension (16). As poi nted out above, the fall i n pressure eli cited by the el im i

nat ion of neurogenic factors may not be direct ly p ropor t ional to the magnitude of these

components, but may also be dependent upon the extent to which other factors compen

sate for the deficiency.

Possible interrelationships of various hypertensive factors in renal (and perhaps

essential) hypertension are diagramed in F i g u r e 3. The highly variable response ofrenal an d essential hy pertensi on to sympathectomy or sympathetic blockade makes it i m

possible to present any diagram adequately covering al l cases.

C o l u m n C represents a case i n wh ich sympath et ical ly mediated renal vascular tone isassumed to be a significant factor in maint a in ing the elevated pressure, and co lumn Ddepicts possible changes in the few cases of human essential hypertension in w h i c h a c o n

t inued fall in pressure is noted for some t ime after sympathectomy, perhaps also on thebasis of altered r enal blood flow. C ol u m n Ε represents a common result of sympathectomy or adrenergic block ade inr enal an d essential hyp erten sion ; this result may or may

not be preceded by some early fall in pressure such as i l lustrated in co lumn C.

Sympatho-adrenal Factors in Development of HypertensionO n thebasis of theabove discussion itwould appear that therole of adrenergic block

ade in the treatment of hypertension, wi th theexception of isolated cases clearly due to

sympatho-adrenal factors, is negligible. However, the possibil ity remains that neurogenic factors may be invo lved in theearly stages of human essential hypertension. C e r tain psychic components are k now n to be in volv ed in the development ofhypertension andi t is possible that emotionally activated neurogenic factors maycause repeated episodes of

renal vasoconstriction and ischemia, which finally lead to thedevelopment of local organic



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changes capabl e ofpermanently alterin g renal hemodynam ics. T h e experimental basis for

such a conclusion is as yet incomplete, but certain points of evidence are of interest in this

connection.

I t has been observed that reflex activation ( 4 - 2 , 44) or electrical stimu lation (62, 63)

of sympathetic nerves to the k idney may cause sufficient vasoconstriction to produce a

marked hypertension. However, in experiments w hi ch invol ved stimu lation for 20 to 22hours per day for as long as 45 days, thehyp ertension persisted onl y dur ing an d for a few

hours after the end of st imulat ion. It hasalso been frequently observed that experimen

tal hypertension may itself br ing about marked changes in the renal vessels (30, 34, 50,

87, 101). In cases of un ila teral compression of the renal artery or k idn ey parenchyma,vascular changes in the contralateral kidney may alter its hemodynamics to such an ex

tent that it becomes capable of maintain ing the hypertension after surgical removal of

the kidney in it ial ly i nvo lved. It is not surprising that m an y w orkers have noted a per

sistence of hypertension after removal of a single ischemic kidney (30, 47, 80, 101).

-A 3 C jD JET

Figure 2. Possible Contributions to Maintenance of Systemic

Arterial Pressure during Neurogenic Hypertension and Its Subsequent "Cure" by Sympathectomy or Adrenergic Blockade

A. Normal

β. Neurogenic hypertension

C to E. Sequential stages in recovery of blood pressure after sympathec

tomy. Pressure may stabilize at eitherD or Ε

A similar sequence of renal changes has not been demonstrated in connection withneurogenic hyp ertension. H ow ever, hi ghly suggestive evidence for the development of

persistent hypertension on thebasis of intermittent neurogenic vasoconstriction is foundi n observations on rats subjected to repeated audiogenic stimuli (24, 66). The bloodpressures of young control and stimulated rats were found to be essentially thesame, but

i t was noted that a large percentage of the experim ental ani mals became hypertensive afterthey were oneyear of age. Hypertens ion was noted par t icular ly among those whi c h hadconsistently responded vigorously to the st imul i . It is of particular interest that these

responses arecharacterized by a mar ked sympatho-adr enal discharge inc luding mydriasis ,piloerection, etc. (23). A lth ough blood pressure was not determined in these studies, it

is reasonable to assume that a temporary elevation accompanied each response.

O ne may speculate that a similar process occurs in some humans. D u r i n g earlystages of the development of hypertension the ind iv idual may be subjected to repeated



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episodes of incr eased pr essure and r enal vasoconstr i ct ion on a pu r ely neurogenic (psychic)

basis and over a per iod of years he may secondarily develop suff icient renal hemodynamic

changes to sustain a r elatively stable, r enal hy per tension. Suc h a sequence of events

would expla in the l a b i l i t y of ear ly and the stabi l i ty of late hypertension as well as the ob

served cor relation between psyc hi c and sympatho-adrenal factors and the final develop

ment of a largely nonneurogenic hy pertension.A sequence of events by wh ich renal hemodyn amic a lterat ions induced by either

mechanical or neur al factors mi ght l ead to a persistent, self-perpetuating r enal hy per ten

sion is depicted in F i g u r e 4. Thehemodynamic changes in the k i d n e y mi g h t be depen

dent upon organic changes in a m a j o r i t y of renal vesselsor s i mp l y u p on a red is t r ibut ion of

renal blood flow leading to a r elative cor t ical ischemia (96).

I n summar iz in g evidence for the part ic ipat ion ofderanged sympatho-adrenal (' 'neuro

genic") factors in human hyper tens ion , it must be concluded that such factors have been

conclusively demonstrated only in cases of ph eochr omoc ytom a, central nervous system

t r a u ma , and increased i n t racran ia l pr essure. T h er e is presumptive evidence that neuro

genic factors may be i mp or t a n t d u r i n g the early, labile phases of essential hypertension

an d that theeffects of th is ear ly sympath o-adrenal act iv i ty may lead to a persistent hyper

tension on a r enal basis later in l i fe. H owever , the development of hypertension through

th is or any other mechanism occurs only in individuals predisposed by some completely

u n k n o w n , but probably hereditary, inf luence.

Locus of Blockade

I n the treatment of neurogenic factors in hy pertension , perip her al vascular disease,

etc., it is necessary to i n h i b i t the excitatory, vasoconstr ictor effects of sympatho-adrenal

act iv i ty . B lockade of i n h i b i t o r y effects of thesympatho-adrenal system and of other nerv

ous act iv i ty is not only unnecessary but frequently undesirable. C h emi cal blockade

may occur at many points a long the reflex arcs controlling the a c t i v i t y of the sympathoadrenal system (F igur e 1). H owe ve r , in order to achieve a desirable degree of specificity

i t is necessary to produce the blockade at the efferent neuro-effector ju nc ti on . B lo ck ade

w i t h i n the central nervo us system, along per ip her al nerves, or at autonomic ganglia i n

evi tab ly affects nervous funct ions other than excitatory act iv i ty of the sympatho-adrenal

system. Bl ock ade wi th in the central nerv ous system alters man y v i ta l regulatory re

flexes, resp i ra tory ac t iv i ty , and par tic ula r ly vagal acti vi ty , even wh en consciousness is

not impa i red. B lock ade at autono mi c ganglia indi scr i mi nately inter r upts all efferent im

pulses passing over both the sympathet ic andparasympathet ic pathways.

Adrenergic Blocking Agents

Agents which block responses of effector cells to sympatho-adrenal st imul i may be

term ed adrenergic blocki ng agents. It is on ly at these effector cells that adrenergic medi

ators are invo lved in transmission of the nerve impulse. For a number of reasons, the

f requent ly used terms "adrenolyt ic" and " s y m p a t h o l y t i c " agents are ambiguous and un

desirable (see 70).

E f fo r t s to develop pharmacological agents capable of pr eventi ng excitato r y r esponses

to symp atho-adrenal act iv i ty have led to the study of a wide var iety of compounds. The

search for new agents has been spurred by the fact that none of the current ly avai lable

agents is wholly satisfactory. U n t i l very recently their use in both research and therapy

was seriously l imited by lack of specificity, imcompleteness of block ing act ion , and h i g h

tox ic i t y . Thecharacterist ics of an adrenergic block ing agent capable of p r od u c i n g a usefu l "chemica l sympathectomy" are a high specif icity, a blockade effective against strong

st imul i , a prolonged anduni form act ion , and a hi gh therapeut ic index. M u c h has been

said and wr it ten about the potency of var ious block in g agents, but th is property seems to

be of l i t t le importance in compar ison wi th a high therapeut ic index. Some of the most

potent compounds available at the present time have the lowest therapeutic indexes, par

t i cu lar ly because of their st imulat ing effects u p o n the emetic center (70).

D i b e n a m i n e . The /S-haloalkylamines, of wh i c h D i b e n ami n e may be considered the



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prototype, are themost recently discovered and also themost effective, specific, and per

sistent of the known adrenerg ic b locking agents (70, 72, 73, 75). These compounds ap

parently b lock by a direct chemical combinat ion with some substance in the effector cell

an d ther eby pr event responses to adrenergic mediators (74)· Because of thestable nature

of this bond, these agents have a very prolonged act ion. C ertai n members of the group

block responses of smooth muscle cells to histamine (see 70). E x c e p t for this action, theblockade produced seems to be l imited almost entirely to the excitatory effects of adren

ergic stim ul i. T hese agents produce a transient stimulation of the centr al nervou s sy stem,

but this effect wears off much more rap id ly than the adrenergic blockade an d is p r i m a r i l y

associated with a high concentrat ion of the d r u g in the blood stream, such as may occur

after r a p i d intravenous inject ion (69). C entr al nervous st imulat ion can be almost com

pletely eliminated by slow administ rat ion or prior sedation—e.g., the L D 5 0 for mice is

about 50mg. per kg. when D ibenami ne isadministered intr avenously with in a few seconds,

but animals may surv ive doses ash ig h as 300 mg . per k g. wh en the inject ion ismade over

a per iod of 0.5 h o u r . Thedrugs are effective by all routes of administ rat ion, but when

administered subcutaneously, intramuscularly, or intraper itoneally the ir local i r r i tant

act ion may produce tissue necrosis.

J L . J & . C. D . X .

Figure 3. Possible Contributions to Maintenance of Systemic Arterial

Pressure during Renal (and Perhaps Essential) Hypertension

A. Normal

B. Renal (and perhaps essential) hypertension

C Immediately after extensive sympathectomy

D. Case of essential hypertension in which pressure continued to drop after sympathec

tomy, presumably because neurogenic alteration of renal blood flow was a sig

nificant factor in the original hypertension

E. Common end result of sympathectomy, which may or may not be preceded by an

initial fall in pressure such as that depicted in C

Dibenamine hasbeen employed with excellent results in the diagnosis andpreopera

t ive therapy of pheochromocytoma (90, 91). Thepressor response evoked by the hista

mine test in these patients is completely blocked and reversed, and the inject ion of D i b e n

amine at 72-hour intervals has been found to provide complete symptomatic relief. In

human essential hypertension, therapy with Dibenamine produces a very signif icant fall

i n both systolic and diastolic pressures insome patients (see 12). In severe h yp ertension,

par t icu la r ly the malignant form, the d r u g has been found to lower the blood pressure

signif icantly in most cases, but rare ly to r e t ur n it to the nor motensive range. H ow ever,



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 2




st r ik ing relief of sequelae such as hy pertensive encephal opath y and i mp air ed renal fun ctio n

was noted in most cases (102), probably due to the release of local vascular spasm.

Other workers have observed a significant depressor response to Dibenamine lasting

24 to 72 hours in man y p atients wit h early or moderately advan ced beni gn hyp ertension ,

but n ot i n patients wi th more advan ced organic cardi ovascular changes ( 4 9 ) . O n t h i s

basis it was suggested that the response to Dibenamine should be determined for prognosticpur poses pr io r to sym pa th ectom y, as a measur e of the role of the sym pat h o-adr enal sys

tem i n a given case of hypertension (49,102). O n theoretical groun ds, an agent with the

specifici ty of D i bena mi ne woul d be expected to be ideal for thi s pu r pose. I ndeed, att en

t ion has been call ed to the sim il ar it y between the over -all effects of Di benamine medicat ion

an d those of surgical sympathectomy (100). I t h as also been repor ted that D iben ami ne is

super ior to tetraethylamm oni um as a test for pr edicti ng the results of symp athectom y i n

acute peri ph eral vascular con dition s, but the same investigator questioned its prognostic

value i n hypertension ( 1 4 ) * L ac k of knowledge r egardin g the etiology of h um an essential

hyp ertension and the mu lt i p l ic i ty of factors determi ning the extent of the fall in blood

pr essure after excision or block ade of the sym pat heti c system m akes the in terp r etation of

any prognost ic test extremely hazar dous. K esults of tests with Pr isco l ine (2-benzyl-2-im idazoli ne), the ergot alkaloi ds, tetraeth yl ammo ni um , spi nal anesthesia, and bar bi tu

rates, in wh ich factors oth er th an peri ph eral blockade of the symp atho -adrenal system

are involved, would seem to have even less diagnostic specif icity than tests w i t h D i b e n

amine.

Signif icant toxi city , pr im ar il y central nervous system excitation, and the necessity for

slow in travenou s admi ni strati on or pri or sedation have considerably l im ited the study of

D iben ami ne i n the th erap y of hy pertensio n. H owever , recent reports have in dic ated that

other members of this series possess up to ten times the potency of D ibenam in e wi thou t

being more toxic ( 7 0 , 7 4 ) . T h i s increased therapeutic index, perhaps coup led wi th the

increased oral absorption of some congeners ( 2 5 ) , may largely eliminate the present diffi

culti es an d disadvan tages of the 0-ha loal ky lam in es. I t is possible th at w it h in the next

few years a truly satisfactory cl inical agent wil l be found within this series of adrenergic

block ing compounds.

Altered RenalHemodynamics

^ \Renal Vascular X

C hanges R enin(Nephrosclerosis?) -f-

ÎPlasma

GlobulinIncreased

Arterial Pressure

\Hypertensin(Angiotonin)

Figure 4. Possible Sequence o f

Events Leading to Renal Hypertension

Sympatho-adrenal factors could enter this

cycle by increasing the arterial pressure ordirectly altering renal hemodynamics

E r g o t A lk al o i ds. R ecent ly , s ignif icant advances have resulted also fr om the

study o f adrenerg ic b lock ing agents of the ergot al ka lo i d seri es. Sto ll i n B asle h as

demon stra ted that "er go tox i n e" is real l y a compl ex of thr ee alk alo i ds: ergocor ni ne,

ergocristine, and ergokryptine ( 9 2 ) . H e has also succeeded i n pr oducin g d ih ydr o der i va

tives of all these compounds ( 9 3 ) . Pharmaco log ica l tests in dic ate th at all members of th e

ergotoxine complex are more potent adrenergic blocking agents than the common ly em

ployed ergotamine, and that hydrogénation also markedly increases the potency of all



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 2




thesealkalo ids (70, 85). Me mb e r s of the ergotoxine complex differ from one another only

i n possessing different amino acids in thepolypeptide side chain of the lyserg ic acid nu

cleus. No unn atur al polyp ept ide containi ng ergot alkalo ids has yet been reported, but

the synthesis of alkaloids containing different amino acids would seem to be a p r o mis ing

l ine of approach in th is field.

A lth ou gh the ergot alkaloids are true adrenergic block in g agents, th ey unfor tunatelyalso have very potent effects up o n the central nervous system (see70). A l l k no wn n at

ura l and dihydrogenated members of this group act on the central nervous system to

depress reflexes in concentrations lower than those required to produce true adrenergic

block ade. A no th er expression of their central action is the vomit ing which they produce

i n hu mans i n total doses as low as 0.3 m g. (10, 29) ; hypertensive patients are more sensi

t ive than n ormal ind iv i duals to the emetic action of the d ih ydr o alkalo ids (10). Because

of the ser ious l im itat i on in dosage imposed by st imulat ion of theemetic center, produc

t ion of signif icant adrenergic blockade in humans with any of the natura l or d i h y d r o

genated ergot alkaloids has not yet been demonstrated.

H ow ever, even i n the absence of adrenergic blockade, the ergot alkaloids are capable

of inducing some reduct ion in blood pressure in human essential hypertension (10, 29).

T h i s fall in pressure appears to have two*components: (1) thecentral st imulan t effect of

the alkalo id on the vagal center to decrease heart rate and cardiac output, and (2) a cen

tral depression of the cardiovascular reflexes which normally compensate for changes in

body posi tion . Because of this second factor, the orthostatic hypotension caused by the

ergot alkaloids cannot be considered as evidence of a "sy mp at h o ly t i c " ac t i o n— i .e., the

product ion of adrenergic blockade. I n hy pertensive patients, r eductio n i n arterial pres

sure by these agents has been found not to paral le l the suppression of experimentally

induced vasomoto r reflexes, and in ma n y cases an i ncrease in the dose of an ergot alkaloid

causes an incr ease rath er than a decrease i n pr essure (10). T h e pulse pressure is mar kedl y

decreased d u r i n g th e fall i n blood pressure indu ced by the d ihy dr o ergot alkalo ids i n h yp er

tensive pati ents ; an u nalter ed or incr eased pu lse pr essure wo ul d be expected i f the fall were

p r i ma r i l y due to adrenergic blockade wit h resultant peri ph eral arteri olar dil atati on.

I m id az o l ine s . A t h i r d g r o up of adrenerg ic b lock ing agents w h i c h has recent ly

received attent ion is the imi dazo l ines . T hese drugs are moderately effective i n

causing adrenergic blockade, but they exhib it many important s ide effects (see 70).

Pr iscol ine, the most thoroughly studied member of the series, in add it ion to p r o d uc ing

adrenergic block ade, stimul ates almost a ll smooth muscles an d itseffects are comparable

i n one way or another to those of sympathom imetic, parasympathom imetic, an d hi sta-

minergic agents. I n the few cases of h um an hyp ertension g iven Pr iscol ine, l i t t le r educ

t ion in blood pressure wasobserved (1,0), although theagent is capable of p r o d uc ing

significant adrenergic blockade an d direct perip heral vasodilatati on i n doses tolerated byhumans (45) . T h e basis for the failure of thed r u g to reduce blood pressure is probab ly

that Pr iscol ine is a potent cardiac stim ul ant ; the increase i n cardi ac outp ut may balance

or more than compensate for the vasodi latat ion produced. E v e n a massive dose of

Pr iscol ine taken wi th sui cidal in tent caused no lower ing of blood pressure (67) . Indeed

Pr iscol ine ma y actuall y cause an alar mi ng increase i n blood pr essure in some patients (8) .

Summary

T h e r o le ofadrenergic blockade in the ther apy ofhyp ertension is sti l l obscure. P h a r

macological advances dur ing the past few years have led to the development of agents c a

pable of p r o d uc ing a clinically useful "ch emic al symp ath ectomy ." Such agents are very

effective in lowering the blood pressure in cases of neurogenic (sympath o-adrenal) h yp er

tension.

A t the present t ime, pheochromocytoma and intracranial lesions are theonly causes

of human hypertension which are definitely known to involve overact iv ity of the s y m

path o-adrenal system. H owever, pr esump tive evidence is accumulat ing to indicate that

neurogenic factors may be in vol ved i n early essential hy pertension , an d it ispossible that

adequate adrenergic blockade early in the course of such hypertension may beeffective in

abor t ing its developm ent. O nl y addi tio nal evidence regarding the etiology of essential



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 2




hypertension and further c l inical trial of adrenergic blockade can define the extent to

which this possibil i ty may be realized.

O f the compounds c ur rently employed for the production of adrenergic blockade, the

β-haloalkylamines appear to be th e most pr omisin g. T h ey are the most specific, effective,

an d persistent of the avail able agents. T h e di hy dr o ergot alk aloid s are mu ch more effec

tive th an their non hyd rogenated congeners. H owev er, at present much of the experimental work on these compounds is complicated by the marked depressant effects which

they exert upon vasomotor reflexes and the vasomotor center and by their stimu lant action

on the vagal nuclei . The cl inical administration of the dihydro compounds has been

l imited by their ver y potent emetic action . Signi ficant specific adrenergic block ade has

not yet been pr oduced in hum ans by members of the ergot series. A thi rd group ofadren

ergic blocking agents to receive recent attention, the imidazolines, appear to cause so

much cardiac st imulation that no consistent lowering of the blood pressure is observed

when they are administered to either animals or m a n .

Research in the field of adrenergic blockade need not be l im ited to members of series

now kn own to be acti ve. T h e three groups of compounds mentioned above are structur

ally unrelated, and only 4 years ago0-haloalkylamines were completely unknown as ad

renergic b lock in g agents. Thecooperation of synthetic chemists and pharmacologists in

study of series of compounds unrelated chemically tothose listed ma y pr ovid e the soluti on

i n the search for an agent producing a fully satisfactory "ch emi cal sym pat hec tomy ."

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Discussion of Paper on Role of Sympathetic Blockade

in the Therapy of Hypertension

BENEDICT E. ABREU1

Universit y of California Medical School , San Francisco, Calif .

Nickerson an d his co-workers are to be highly congratulated for their contr ibution to

the field of biochemorphology in addit ion to other fields related to chemistry and medi

cine. T h ey have pr ovid ed chemists and biologists wi th knowledge of a newparent com

pound which possesses pharmacologic properties that were otherwise unpredictable from

its structure and physicoch emical properties. T h i s lends further support to the often

repeated statement that it still is practically impossible to predict pharmacologic effects

for a given new chemical stru cture. Ni ck erson is to be commended for hismodesty and

honesty in statin g that thediscovery of the adrenergic block in g properties of Dibenamine

was pur ely accidental .

In considering paths to follow in the synthesis of agents which wil l be useful in the

therapy ofhypertension, one is faced with the necessity ofknowing more about the etiology

of what is now considered a homogeneous gro up—v iz . , the individuals considered to be

"essenti al hy per tensi ves." T h e essential hyp ertension group m ay very well bephysio logi

cal ly heterogeneous, but as yet a satisfactory delineation of subgroups is not forthcoming

other than a classification based on the grade or degree of hypertension and associated

sequelae. It still remains as a pr oblem i n whi ch the cooperative efforts of clinicians, chem

ists, physiologists, and pharmacologists must be integrated, so that a reasonable solution

wi l l be forthcoming.

Because it is considered that an important part of the symptomatic or " c u r a t i v e "

therapy of essential hypertension is concerned with vasodilation, a number of mechanisms, by which such anen d may be attained, immediately suggest themselves. These

and examples of agents which act by such mechanisms are as follows:

1. "D i r ec t" depression of vascular musculature which is nonspecific in character—nitrites and papaverinelike compounds.

2. C holi nergic facil itati on— e.g., postganglionic cholinergic stimul ants, such as

acetylcholine, other choline derivatives, and pilocarpine.3. Depression of response to excitatory sympathetic nervous system stimulation at

postganglionic adrenergic endings ("adrenergic blockade")—Dibenamine, yohimbine,933F.

4. Depression ofautonomic gangl ionic transmission—certain quaternary ammon iu m

compounds, such as tetraethylammonium salts.5. Depression of the vasomotor center or possibly stimulation of the vasodilatorcenter—certain of the ergot alkaloids, pr imar i ly the dihydrogenated ergot alkaloids.(Some of theergot alkaloids are considered also to possess adrenergic bl ocki ng pr operties,bu t innontoxic amounts inm a n ; it is difficult to demonstrate such action.)

6. C erebra l cortical depression—depression of transmission i n association pathwayswhich may be of importance in in it iat ing central sympathetic stimulant effects, such as

hypnotics, pr imar i l y thebarbiturates.

Present address, Research Department, Pitman-M oore Company, Indianapolis, Ind.



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 2



Biosynthesis and Metabolism of

Phenylethyl (Pressor) Amines

KARL H. BEYER

Sharp and Dohme, I n c . , Glenolden, Pa.

This report presents the likely pathways in the bio

synthesis of phenylethyl (pressor) amines from their

amino acid precursors, discusses the relative signifi

cance of the various modes by which they may beinactivated in the body, and considers the interplay

of these factors as they may relate to hypertension.

Γhysiological ly , hypertension may be defined as an elevation of blood pressure abovethe nor mal l im its of var iabi l i ty. T here are at least five basic factors involved in them a i n

tenance of blood pressure. Ab err ation s of any one or a combination of these factors could

produce anelevation affecting princ ipal ly systolic or diastolic pressure, or influencing both

more or less equall y. T hese factors in clu de peri ph eral resistance, elasticity of thearteries,

cardiac output (heart rate andstroke volume), blood volume, andviscosity of the blood.T h e central nervous system, theendocrine glands, and the kidney must exert their inf lu

ence onblood pressure through theabove factors.

A cl inical diagnosis of essential hypertension usually carries no connotation as to the

etiology of the condit ion, and yet the preponderance of l iterature directing attention to

the etiological role of one or another organ in the product ion of hypertension very often

influences our everyday thoughts on the subject.

Predominant ly , the immediate visceral response to stress is mediated through the

adrenergic components of the autonomic nervous system. The adrenergic components

ar e those thoracolumbar autonomic nerves whose postganglionic fibers elaborate adrena

line, or arterenoi, together with the adrenal medul l a whose chr omaffin cells are analogous

embryologically and functional ly to the adrenergic postganglionic neurones (107). The

most obvious manifestation of this overfunction, immediately andprogressively, wi l l de

pend generally on the i nd iv idua l . M anifestations of one or another imbalance of the

autonomic nervous system may take thefamil iar form of a colitis, peptic ulcer, hyp erten

sion, or certai n other aberr ations of function depending on the i nd iv idua l .

T h e im medi ate response to stress in a normotensive person may be considered to fall

i n thealarm reaction stage of what Selye (145, 147) haselected to call a general adaptation

syndrome, whose manifestations areessentially independent of the specific nature of the

stress. Thedevelopment of clinically sustained hypertension hasbeen considered by h i m

to fall into a second stage of resistance to a prolonged exposure tostress. Simi lar ly , Wolf

et a l . (166)

have presented recently an interesting discussion of hypertension as a reactionpattern to stress. Thever y readable article by White (164) also stresses the importance

of theneurogenic aspects of early hyp ertension as amajor factor that must bedealt wi th in

the management of this disease.

W h a t Selye described as the immediate response to stress in a normotensive i n d i v i

dual graduates in the l ikely candidate into what Corcoran , T a y l o r , and Page (51, 52)

have termed early essential hypertension. T h i s state is characterized by moderate,

widely fluctuant, sometimes remitting, increases of arterial pressure. It is accompanied

37



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 3




by n o change or mi ni ma l evidences of vascul ar or ren al damage (44,88) when the patient is

at rest. O utw ar dly , thesepatients may or may n ot appear to be un stable emotion all y, b u t

J acobsen ( 1 0 1 ) has stated that under stress the action potential measurements of even

their skeletal muscles become extremely high.

S t r o k e , v o l . / c c . 80

6040

B l o o d pressur e, m m . 230H g 210

190170150130110

R e n a l blood flow, +5% ch an ge 0

- 1 0- 2 0

F i l t r a t i o n f ract i on 0 .300.20

U r i n e f low, c c . /m i n . 100

ί I

Figure 1. Effect o f Unpleasant Interview on Cardiac Stroke Vol

ume, Blood Pressure, Renal Blood Flow, Filtration Fraction, a n d

Urine Flow o f Patient ( ? 66 )

Although there m ay be no demonstrable alterati on i n the fun cti on of the car di ovascu

lar system or the kidneys of such patients, other than the sustained elevation of blood pres

sure when they are at rest, the extreme responsiveness of these systems to emotional stressis rema rk able. T her e ma y be no alter ation of the in herent abi li ty of an organ or tissue to

respond to a stimu lu s. I nstead, their greater reacti vi ty is to an incr eased tran smission of

nerve impulses in response to what may be a psychogenic stimulus. Wolf, Pfeiffer, R i p

ley, Winter, and Wolff ( 1 6 6 ) have demonstrated such changes in their patients admirably,

and two of their figures from a recent publ ic ation illustrate this poi nt.

F igu r e 1 shows th e effect of "traumatic" or unpleasant interview on blood pressure,

cardiac stroke volume, renal blood flow, and the fraction of the renal blood flow that wasfiltered at the glom eru li (filtr ation fr acti on). I n response to the in terv iew bot h the systolic

an d diastolic blood pressure an d the strok e volum e of the heart inc reased. T her e was a

decrease in the flow of blood thr ough the ki dn ey, an d this decrease was due pr edomi nan tly

to an efferent ar teri olar con stri cti on since the filtration fr acti on was in cr eased somewh at.

F igu r e 2 shows th e effect of reassurance and sedation on the blood pressure and renal

function and the promptness with which this effect could be reversed by introducing a

topi c of signi fican t conflict in to the di scussion. T h e reassur ance an d sedation d ecreased

blood pr essure, increased renal blood flow a nd glomerul ar fil trati on rate, and also increased

the filtration fr ac ti on ; thi s wou ld ind ic ate th at afferent as well as efferent ar teri olar co n

striction was present i n the k id neys. A t the onset of the unpleasant part of the interview

these effects were reversed on the whole, an d i n the last por tion of the inter view a ver y i n teresting change i n ren al hemod yna mi cs m ay be seen to have occur red. A t this poi nt

there was an incr ease i n ren al pl asma flow an d a decrease in the filtration frac tion s. T o b e

sure, this change may be thought to be wi thi n anal yti cal error , an d yet it is most tempting

to interpret the increase in blood flow as being attributable to the opening of subcortical

renal shunts as descri bed by T r u eta e t a l . (157). W i l k i n s e t a l . ( 1 6 5 ) studied the effects of

symp athec tomy on the fun cti on of var iou s organs an d concluded that the r educ tion or

abol iti on of reflex vasopressor overshoots of arter ial pressure (after blood pressure-lower-



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0 2 . c

h 0 0 3



BEYER—PHENYLETHYL (PRESSOR) AMINES 39

i ng procedures) and their substitution by a more stable, or gra du al, homeostatic mech a

nism may be avery important hemodynami c effect of the operation.

F o l l ow in g repeated insults to thevascular system mediated through or at least i n i t i

ated in thenervous system thehistologic "fractures" of the integument of theblood ves

sels result in thickenin g and loss of elasticity. Since thearterioles are the vessels pr inc i

pal ly involved i n thealteration of arterial pressure they are apt tobear theb r u n t of the i n j u ry . T h u s thecondition gradually progresses to a second phase that C orc ora n and P age

(51) have called established essential h yper tension . D u r i n g this stage theblood pressure

is more sustained an d at a higher level, is less susceptible to sedation andother therapeu

ti c or surgical measures, and is accompanied by definitive evidence of cardiovascular and

renal damage. In theinstance of malignant hypertension these various phases are passed

through in a matter of months frequently, instead of years.

I f one is to admit both neurogenic and nephrogenic as well as other factors in the

pathogenesis of hypertension, then the neurogenic element probably plays its dominant

role in the init ial stages of thedisease. T h u s itwould beantici pated that medical (164) o r

surgical (72,149,150) approaches to therapy on the neurogenic basis should be the more

effective thesooner thedisease is recognized. Indeed anynephrogenic component of the

disease may be thought to follow changes in the renal blood flow usually, rather than to

initiate them. In substantiation of this point, renal function studies indicate that de

monstrable alterations of function in thecells l in ing therenal tubules follow rather than

F i l t r a t i o n f r a c t i o n +10

% change, 0 == -j- 5

0.227 0

- 5

- 10

7 / / / / Λ

G l o m . l i l t , ra te

% change,0 ο 101

+40

+30+20

+ 10

E f fect i ve p l a sma fl ow% change, 0 ο 450

V i l l i

Figure 2. Effect of Reassurance and Sedation on Blood Pressure

and Renal Functions of Hypertensive Patient

Following the period of reassurance, indicated in black, a topic of emotional con

flict to the patient was introduced into the interview {166)

precede thealterations of ren al blood flow (44, 51, 88). In this connection the review by

Smith (148) of theevidence relating urologie disease tohypertension could hardl y be cited

to substantiate thenephrogenic factor as a dominant one in theearly etiology of essential

hypertension in humans. Presenting the subject in a different perspective, Goldblatt



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 3




(80) haspublished an interesting review ofthe l iterature pertaining totherenal origin of

hypertension.

T h e chemical mediator or mediators of the neurogenic element i n hyper tension may be

considered to benoradr enaline (syn ony m: arterenol, norepi nephr ine), adrenal ine, or both .

Within recent years a certain orderliness hasevolved in this controversial field so that the

problems that remain seem better defined and approachable from an experimental standpoint. Theuncertainty as to thenature ofthe chemical mediator ofadrenergic nerves is

evident if one recalls that from a textbook standpoint adrenergic nerves are supposed to

mediate their effects through thel iberation ofsympathin . Whereas adrenaline is capable

of eliciting both excitatory and inhibitory effects, both a S y mpath in Ε (excitatory) and a

S y mpath in I (inhibitory) were postulated, and much experimentation has been carried out

to support thesympa thi n hypothesis. T h e evidence up to 1937 hasbeen summarized by

C a n n o n and R osenblueth (48,1$) whowere theearlier exponents ofthis view. O pposing

the sympathin theory ofchemical mediation were the contemporary data of Lo ew i 118)

an d of G a d d u m and his associates (76-79) that indicated adrenaline was the chemical

mediator.

I t hadbeen anticipated by Barger and D a l e (18) in their classic (1910) article thatadrenaline probably was not thechemical mediator, for this theory "involves the assump

t ion of a stricter par alleli sm between the twoactions th an actu ally exists. Ad r eni ne has,

i n common with other methylamino bases of its catechol group, theproperty of exaggerat

ing inhibitor ascompared with motor effects. The action of some other bases, part icu

lar ly of theamino andethylamino bases ofthe catechol group, corresponds more closely

k H M M A M M M U

Figure 3. Effect of Hepatic Nerve Stimulation (15 Seconds) and Intravenous Injections

of Adrenaline and Noradrenaline on Arterial Blood Pressure and Denervated Nictitating

Membrane of Anesthetized Cat

Previous injection of cocaine (75)



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0 2 . c

h 0 0 3




with that of sympathetic nerves than does that of adr eni ne." T h ey also antici pated, as

i n theabove quotation, the hypothesis proposed by B a c q (10) and reiterated by Stehle

and E l lsworth (158) an d by Gr eer, P in kston, B axter, and B ra nn on (84) that noradrenaline

(arterenoi) more closely simulated the properties of Sympathin Ε asreleased following he

patic nerve stimulation . B arger and D ale (18) gave theprincipal biological methods for

distinguishing between the action of adrenaline and its nonmethyiated counterpart.Wi th i n the past 2 or 3years many of these differences have become reconciled. T h e avai l

abi l i ty of ^-arterenoi, following its resolution in 1948 by T u l l a r (158), hasalready contr i b

uted tothe progress i n this difficu lt field.

T h e present status of the adrenaline against sympathin mediation of nerve impulses

wou ld in dicate that both adrenalin e an d arterenoi are li berated. Inthe previ ous evidence of

G a d d u m et a l . (74, 76-79) adrenaline clearly was liberated on stimulation of certain nerves.

M ore recently G add um and G oodwin (75) confirmed Cannon's (48) early experi ments t ha t

the pressor response to hepatic nerve stimulation probably was not adrenaline. Where

comparisons were made, theeffect of liver sympathin resembled those of noradrenal ine

more closely than of adrenaline. T h ey conclude that there is no evidence against the

theory that l iver symp athi n is noradrenaline (75). O ne of their i l lustrations compar in g theeffect of hepatic nerve stimulation with that of adrenaline and noradrenaline on blood

pressure and the denervated nictitating membrane of the cat is reproduced inF i g u r e 3.

T h e character of the blood pressure curve and the relative pressor effect and membrane

contraction following nerve stimulation were quite similar tothose caused by the intravenous injection of noradrenaline. West (168) confirm ed the previous observation of Dawes

(57) that therelation between doses of adrenaline producing equal rises of blood pressure

by the jugular an d by the por tal routes of admin istration differed accordin g to the amount

injected. T h i s ju gul ar /portal equipressor ratio remained constant for ^-noradrenal ine.

It would appear that this indicates a difference in the inactivation of the two compounds

by the liver where the arterenoi acts as th e principal nerve mediator.

T h i s same qual itati ve difference between adrenaline an d noradr enaline obtains for the

splenic ar ter y/spl eni c vei n equipr essor dosage-response rati os as well, and both observa

tions quite possibly may find their explanation in the recent work of E u l e r (64-70). He

has found that thepressor substance isolated from theheart, blood, l iver, and spleen has

predominantly thecharacteristics of noradrenaline. T h us, he has considered Sym path in

Ε to be identical with l-noradrenaiine.

F igu r e 4 is one of the illustrations from a recent publ ication by E u l e r . After the ad

ministration of an adrenolytic agent, Dibenamine, thepressor effect of adrenaline was in

large measure reversed whereas the pressor response to corresponding increments of l -

noradrenaline and toextracts of spleen or splenic nerve remained upr igh t an d monoph asic.

I n general the effect of hepatic nerve stimul ation is not affected by amounts of adrenolyticagents that wil l reverse the response toepinephrine (48, 75,168).

B a c q and F ischer (11) have reported that extracts of mammalian spleen contained

only noradrenaline, extracts of mammalian coronary nerves and arteries only adrenaline,

but extracts of splenic nerves andsympathetic chains yield a mixture of adrenaline and

noradrenaline. T h ey have interpreted this var iati on as being due to theprobabi l i ty that

the synthesis of adrenaline is through the transmethylation of noradrenaline as a final step

and that this takes place slowly or not atal l in some tissues.

Synthesis of Pressor Amines

T h e synthesis of pressor amines in the body may convincingly be considered to begin

with the essential amino acid, phenylalanine as i l lustrated in T able I . G u r i n and De l luv a(86) have reported that phenylalanine labeled with t r i t ium, or containing C 1 4 located both

i n the carboxyl group and in theposition adjacent thereto, wasconverted in ther at to r a

dioactive adrenaline. O nl y one C 1 4 atom was present in the side chain and it was in the

terminal group bearing the secondary amine (86). H owever the intermediate steps i n the

synthesis are by nomeans socertain , nor does this necessarily preclude other paths of sy n thesis.



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 3



Te

AtenvSmeoShsoEn

nnthB

^-C

H

2

—

C

H

—

C

O

O

H

Jk

Ph

a

a

n

-C

H

2

—

C

H

—

C

O

O

H

1NH2

OH

Ty

o

n

/T-C

H

2

—

CH—COOH

;OH

NH

2

Dihy

o

e

y

a

a

n

(D

O

PA)

y-y CH2

CH2

Γ NH2

OH

Dihy

o

e

y

e

h

am

in

^-CHOH—CH—COOH

IAH

Ph

s

n

^C

H

O

H

—

C

H

—

C

O

O

H

O

H

H

y

o

s

n

C

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O

H—

C

H

—

C

O

O

H

1NH2

JOH

O

H

Dihy

o

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y

s

n

(DOPS)

yC

—CH2

HiNH2-

OH

No

e

n

n

(s

n

a

e

n

a

e

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/C

-C

-H

+

Be

d

h

CH2—COOH

NH2

Gly

n

P u b l i s h e d

o n

J a n u a r y

1 , 1 9 4 9

o n

h t t p : / / p u b s . a c s . o r g

| d o i : 1 0 . 1 0 2 1 / b a - 1 9 5 0 - 0 0 0 2 . c h 0 0 3




The biological conversion of phenylalanine to tyrosine has been demonstrated by

M o s s and Schoenheimer (118) who administered phenylalan ine-^ to rats and recovered

tyrosine containing deuterium from their bodies. In vitro this conversion could be ac

complished in thepresence of i ron and hydrogen peroxide ( ISO) . Thedecarboxylation of

tyrosine toyield thepressor agent tyramine probably is not a step in di rect line to the sy n

thesis of epinephrine, but the compound long has played a role in investigators' thoughtsabout hypertension. T her e is a decarboxylase invarious mammalian tissues, inc luding

kidney and pancreas, capable of convertin g tyrosine to ty ramine (87, 62, 68, 71,93, 96).

Figure 4. Blood Pressure Records from Anesthetized Cat before and followingAdministration of Adrenolytic Agent

A = Before Dibenamine; β = after 5 mg. Dibenamine per kg.; time = 0.5-minute intervals (67)

The oxidation of tyrosine to 3,4-d ihydroxypheny la lan ine (D O P A ) can be shown to

take place invitr o both enzymatical ly and by noncatalytic measures (7, 8,91,181,138),

bu t the precise in vivo mechanism is less certain. The ascorbic-dehydroascorbic acid

system is capable of bringing about this oxidation inv i t ro (20), and it has been shown to

stabilize epinephr in e i n the adr enal gland (92). In unpu bl ished work it was found that po

tato phenol oxidase is capable of bri nging about theoxidation of thephenol ic to the cate

chol nucleus, as it does in the case of tyrami ne. H owever, B hagvat and K i c h t e r (81)

have surveyed a number of ani mal species and they could not demonstrate a phenol oxidase i n mam mal ia n tissues by theconventional methods. P r obabl y the most direct in v i vo

evidence is that of Medes (117) who reported the recovery of £-3,4-dihydroxyphenylala-nine from u ri ne when large amounts of tyrosine were given to a patient diagnosed as h a v

ing tyrosinosis.

A l though it is uncertain as to just what step comes next, it isprobable that either de

carboxylation or the introduct ion of the hyd roxy l group on the carbon atom adjacent to

th e r ing mu st occur, wi th tran smethylation of arterenol toadrenaline being thelast stepin

the synthesis (87). Cer ta in ly theanaerobic decarboxyl ation of D O P A to the correspond

ing 1-3,4-dih ydr oxyph enylethylam in e occurs smoothl y i n thepresence of kidney , l iver, and

other organs, as wasdescribed by H o l t z et a l . (100). B o t h he andBlaschko (85-37) have

proposed that this step takes place in thesynthesis of Z-adrenaline. Regarding thealternative pathway in volv i ng iV -methyl ation before decarboxylation, H ear d and R aper (91)

reported that theaction of tyrosinase (phenol oxidase) oniV -methy l D O P A in v itr o y ielded

adrenalone, theketone of adrenaline, but theperfusion of theketone through theadrenal

gland did not result in its reduction to adrenaline. In addit ion, Blaschko (85) reported

that D O P A decarboxylase did not decarboxylate N-methyl-3,4-dmydroxyphenylalaiune.

Whether or not the introduct ion of anhyd rox yl group into the side chain of D O P A , as by

beta oxidation, occurs before or after decarboxylation is uncerta in . It is this reviewer's



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 3




op i n i on that the h y d r ox y l g r ou p wil l be found, eventually, to be introduced into the s y n

thesis of epinephr ine at some point before decarboxylation of the amino acid precursor.

V i n e t (161, 162) has claimed that the adrenal medulla is capable of convert ing 3,4-

dihydroxyphenylethylamine, formed f rom the decarboxylat ion of D O P A in the k i d n e y ,

to epinephr ine in vi t ro , wh ich in effect completes the synthesis . According to h i m , the

adrenal medulla cannot decarboxylate D O P A . Simi la r ly , Schap i ra ( l jO ) reported thatwhereas guinea pigki dney cou ld decarboxylate D O P A , the adrenal medul la did not c on

tain the decarboxylase an d that adrenaline in hi bited the decar boxyl ation of 3,4-dihydroxy-

phenyla lan ine . J us t how the h yd r ox y l g r ou p is introduced into the side chain is not

clear, if th is is thepr inc ipa l course of thesynthesis, but it seemscertai n th at this pr ecedes

methy ia t ion (37). Recent ly du Vigneaud and his associates (160) fed C 1 4 r a d i ome t h y l -

methionine to rats and succeeded in isolat ing adrenaline bearing the radioact ive group

I P H E N Y L S E R I N E

3 0 6 0 9 0 120 160

M I N U T E 6

Figure 5. Anaerobic Decarboxylation of

Phenylserine, Dihydroxyphenylalanine

(DOPA), and D ihydroxypheny l ser ine

(DOPS) by Supernatant from 2 0 % Homoge-

nate of Dog Kidney in 0.1 M Phosphate

Buffer

Final concentration of substrates = 0.02 mM.; pH

adjusted to 6.5

f rom their adrenal g lands. T h us the transmethylation reaction in the synthesis of adrena

l ine is indi cated. T h i s would seem to complement nicely the aforementioned concepts of

E u l e r (65, 70) an d of B acq and F ischer (11) that noradr enal ine is thepr inc ipa l mediator of

adrenergic impulses and is released from those tissues that are not capable of t ransmethy l -

at ing it to adrenaline.

I n spite of the p laus ib i l i t y of the foregoing hypothesis for the synthesis of adrenaline

and ar terenoi there is a certain attractiveness to theold pr oposal of R osenmun d and D o r n -

saft (187) that has lost ground by neglect and by the strengthening of the alternat ive

scheme just presented. It wastheir v iew that thr ough the condensation of benzaldehyde,

or p -hydroxybenza ldehyde or phenylglyoxylic acid with iV-methylglyeine (sarcosine), p-

hydroxy- iST-methylphenylser ine or its p-phenolie analog would be formed. T h ey synthe

sized 0-3,4-dih ydr oxyp heny lser ine. T h e synthesis wasrepeated by Guggenheim (85) and

more recently by M a n n a n d D a l g li e sh (115). H a r t u n g (90) prepared theseries of p h e n y l -

serine, p -hydr oxyph enylser i ne, and 3,4-dihy droxy phenylser i ne.

I f the in i t ia l aldo l condensatio n between benzaldeh yde a nd glyci ne or sarcosine takes

place in thebody to form phenylser ine and/or iV-methylphenylser ine, and it is not an u n

likely reaction, then it seemspossible for the nucleus to undergo the same phenol ic oxida-



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 3




t ion that has been discussed in the conversion of phenylalanine —>• tyrosine —>-

D O P A . Actua l l y it is conceivable that phenylalanine is a precursor of phenylserine, or

that tyrosine is converted by beta oxidation to hydroxyphenylserine. I n either instance

the introduction of the hydroxyl group would be into a relatively stable compound, as

compared tothose bearing a dihydr ic nucleus. In addit i on this step would make the pat

tern of synthesis of epinephrine through the phenylserines consistent with the strongestevidence cited for the eventual form ation of th at pr essor agent from phenylalanine.

•UINEA ΡΙβ

KIDNEY

DOPA

.^DOPA+DIHYDROXY-/ PHENYLETHYL-METHYLAMINE

DOPS

D O p S φ ARTERENOL

SO 100

MINUTES

ISO

Figure 6. Inhibitory Effect of Amines on Anaerobic Decar

boxylation of DOPA and DOPS by Supernatant from 2 0 %Homogenate of Guinea Pig Kidney in 0.1 M Phosphate

Buffer

Final concentration of substrates = 0.02 mM.; pH adjusted to 6.5

In experiments not published heretofore, it was found that the oxidation of p-hy-

droxyphenylserine to 3,4-dihydr oxyphenylserin e occurs rap id ly in thepresence of phenol

oxidase. Contrary to the findings of Blaschko and his associates (89), this laboratory

found that 3,4-dihydroxyphenylserine and its pheny l andmonophenolic precursors were

decarboxylated by the kidney of guinea pigs, cats, and dogs. (When this seeming dis

crepancy wascalled to Blaschko's attention he wask i n d enough to repeat his experiment.

In correspondence with theauthor he indicated that in theretest of dihydroxyphenylser-ine wi th fresh extract of guinea pi g li ver there was avery slow formation of carbon dioxide

under anaerobic conditions, which wasscarcely significant after 1hour , but which cont in

ued wi th tim e. B ioassay of the resulting material indicated that ^-noradrenaline was

formed.) An experiment involving the decarboxylation of these three compounds and

D O P A by the anaerobic kidney of the dog is il lu strated in F i g u r e d . Inal l thr ee species the

rate of decarboxylation of the phenylserines does not seem to exceed that for D O P A .

T h e decarboxylation of 3,4-dihydroxyphenylserine was least inguinea pig kidney, as may



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 3




be seen i n F i gu r e 6. I n thi s experiment it was found that addi ti on of the corr espondi ng

amine to the vessels decreased or abolished the decarboxylation of both D O P A and d ihy

droxyp henylser ine. T h i s was i n keepin g wi th the observat ion of Schap ir a that ep i neph

r i n e in hi b ited the decarboxylat ion of D O P A (140). Since it is possible that different

stereoisomers were present i n the racemic mixtures wi th wh ich Bl aschk o and this labor a

tory have worked, there may be no real discrepancy between the two observations, although from an interpretative standpoint the difference is qualitatively signif icant.

P r ob a b l y the absolute values for c ar bon dioxide evolu tion i n the il lustration s have no de

finitive significance other th an that th ey ma y in dicate the relative concentr ation of the

single opti cal form of the phenylserine deri vative i n the r acemic mi xtur e th at was suscep

tible to decarboxy lation by the enzyme. O ne of the pr inc ipa l attraction s of this theor y is

th at on decarboxy lation of 3,4-dih ydr oxyp heny lserin e, nor adrenaline is form ed. T h i s

avoids the awk war d necessity of accounti ng for the in tr odu cti on of a h yd r ox yl grou p i nto

such a compou nd as d ih ydr oxyp heny lethyl amin e. H ere, again, transmethyl at ion of

noradrenal ine would be the final step in the synthesis of adrenaline, as was anticipated by

B laschk o (35-37).

T h e pressor amines have been im pl ic ated also i n the neph rogenic theories of hy per tension. I n 1910 E wi ns and L aid law ( 7 3 ) commented that the formation of tyramine

f r om tyr osine i n the intestine has qui te recently been r egarded as pla yi ng a par t in certain

patholog ical states i n whi ch a h ig h blood pressure is the most prominent symptom. C o n

temporar i ly , B a i n ( 1 2 ) reported that tyramine was excreted in the urine of hypertensive

patients but to a less extent th an i n pat ients ha vin g nor mal b lood pressure, the i mp l i c a

t i on being th at the elevation in blood pressure was due to the retention of tyr ami ne. T h e

urohypertensin of A belous and Bar dier ( 1 ) contained isoamylamine.

Figure 7 . Pressor Response in Anesthetized C a t following Re-establishment o f

Circulation

F o l l o w i n g th e in i t ia l repor ts by H o l tz ( 1 0 0 ) and Blaschko (35-87), B i n g ( 3 2 , 8 8 ) be

gan a series of experiments on dogs th at brou ght i nto perspective the possible relationship

between renal hypertension and the decarboxylation of D O P A i n the k i dney. H e dem

onstrated that if D O P A was injected in to a par tia lly or totally i schemic ki dney of an anes

theti zed cat an d was allowed to r emai n there for awh ile, the r e-establish ment of ci rcula

t ion thr ough that organ was accompan ied by an elevation of blood pressure. T h e logical

interpretat ion of thi s observati on finds its basis in H ol tz ' observati on ( 1 0 0 ) that in v i t r o

decarboxylation was demonstrable only when the kidney and substrate were maintained

un der anaerobic conditi ons. I n the presence of air or oxygen, oxidative deami nati on of

the amine occurred simultaneously with decarboxylation so that the carbon dioxide lib-



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 3




erat ion was not readi ly demonstrable. Wh en D O P A was injected into the ischemic l iver

or other organs and released to thegeneral c ircu lat ion of the cat,hyp ertens ion d id not oc

cur . Ne i t he r dida rise in blood pressure follow the inject ion of D O P A into the u n i m

paired k id ne y s of th is animal . The inte rpre tat ion of Bing's exper iment was that D O P A

was decarboxylated in the ischemic k idney under condit ions that would not suppor t the

aerobic deaminat i on of the resulting pressor com po un d by the amine oxidase present in the

t issue. T h u s there was an o ut p o ur ing of, presumably, 3,4-dihydroxypbenylethylamine

when blood wasallowed to circulate thr ough the k id ne y .

C A T 2.38 KG.

194 ' »9 4

1

, f ^ ^^ ™* , ,

188 176

3ASE L INE

L E F T KIDNEYUNCLAMPED

CONTROL ICCINJECTED AT

. RINGERS9J50

S 0 L N .

RIGHT KIDNEY U N C L A M P E D

I 0 M G . DOPA IN ICC. RIN GE RS S O L N

l i : 4 2 TIME , 30 S E C . 12:02

Figure 8. Blood Pressure Response Following Re-establishment of Circulation through

Kidney of Anesthetized Cat

Renal artery and vein had been clamped 2 hours previously

T h e basic experiments by B i n g ha ve been con fir med. Sch r oeder et a l . (144) have re

ported the isolation of a dialyzable pressor agent f rom the blood of hypertensive pat ients

that was not present in theblood of normotens ive ind i v iduals and w hi ch had cer tain b io

logical an d chemical characteristics th at w oul d relate it to ep inephr ine or a closely similar

co mp o und . D r i l l (62) also hasexpressed theop in i on that the pressor effects of anaerobic

ki dney extracts are due to thepresence of tyr ami ne and other pressor amines. H ol tz and

Credner (98) found that when D O P A was admini stered parenteral ly to man andto sev

eral animal species they could isolate 3,4-dihydroxyphenylethylamine as such and in a

conjugated form from theur ine. Page (124) hasdemonstrated thepresence of D O P A de

carboxylase act iv ity in the k id ne y s of man, guinea pigs, monkeys, and rabbits, but none

was found in the rat . O ster and Sork in (123) made some interesting observations on the

effect of intr avenous i njections of D O P A on the blood pressure of normotensive and hy

pertensive cats and patients. I n both instances the pressor effect of a given inject ion of

D O P A wasgreater in the hyp ertensive subject. T h i s they interp reted in the l ight of

Bing 's work asattr ibutable to impaired metabol ism of the decarboxylated pressor amine

i n the k id ne y s of the subjects. N on e of the conventional renal function studies were

mentioned by them as having been performed on the subjects to substantiate this view,

an d the observati on has not pr ovok ed substantiati on elsewhere.

A l t h o u g h the evidence presented to th is po int has been reasonably consistent, Page

an d R e ed (125) observed that the int raper i toneal or intravenous inject ion of D O P A i n t o

the rat caused a marked and sustained rise in blood pressure. T h i s wou ld not have been

ant ic ipated, for Page (124) reported that rat tissues donot conta in D O P A decarboxylase.Indeed, Page andR e e d (125) have claimed that the blood pressure response of rats to

D O P A cannot beused as a measure of the decarboxylase content of the tissues, nor as an

indicator ofdecreased intr aren al oxygen tension.

A few experiments were conducted in barbi tur ate anesthetized cats and dogs where

i n D O P A , pheny lser ine, p -hydroxyph eny lser ine (D O P S) , and 3,4-dihydroxyphenylser ine

were hr supp ly wasclamp ed tern-

1155 16th s u m .

200»



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 3




p or a r i l y . T h e results of these exper iments are shown i n F igur es7t h r o ug h 11. F i g u r e 7

i l lu strates the effect of u n c l a mp i n g the left k idn ey into wh ich 3.0m l . of R inger 's so lution h ad

been injected 2hour s pr eviously as a contro l . H ere , as i n almost all such experiments, re-

establishment of c i rculat ion was followed by a rise in blood pr essure. Wh en the blood

sup p ly to theother k idney into which 10 mg. of D O P A had been injected was re-estab

l ished, a greater an d reasonably sustained rise i n blood pressure followed. F ig ur e8 is thefirst of three illustrations taken from a single experiment on a cat. I n this case, both k i d

neys were clamped immediately following the intrarenalarterial inject ion of 3m l . of R i n g

er's solution on one side and 3 ml . conta in ing 10 mg. of dihydroxyph eny lser ine into the

k id ne y on theother side. Wh en the contro l k i dney wasreleased, theblood pressure rose

slowly over a per iod of about half an hour . When the c i rculat ion wasreleased through

t he k i d n ey i n to w h i c h D O P S was injected, the rise in blood pressure wasdramat ic and

was sustained well over an h o u r , as is i l lustrated in F i g u r e 9. F i g u r e 10 shows the effect

of the intravenous inject ion of dihydr oxypheny lser in e into the same cat after the blood

pressure had returned to a low level. The r ise in blood pressure wasgreater than when

th e dr ug was in cu bated in the ki dn ey before its r elease.

I n F i g u r es 11 and 12 thepressor effect of intravenously injected phenylserine,p-hy-droxypheny lser ine (DO P S) , and D O P A are comp ared wi th epin ephr ine in the dog. D O P A

was ina cti ve whereas all ph enylserin es caused a r ise i n blood pr essure. T h i s wou ld seem

to be good presumptive evidence that the r ise in blood pressure was due to decarboxyla

t ion of the several ph enylseri nes. A lt h ou gh the decarboxylat ion of the sample of

3,4-dihydroxyphenylser ine by the k id ne y of the dog and cat in v i t r o has been demon

strated, even a very small percentage contamination of the amino ac id wi th the corre

sponding pressor amine (noradrenaline) would give r ise to a considerable elevation of

blood pressure, though probably not assustained a durat ion ofeffect aswas present in thi s

instance. H owever , it wo uld be desirable to have a comparison of the pressor effect of

D O P A an d dih ydroxy ph enylser i ne repeated in another laboratory using other samples of

the drugs to check the p o in t .

C o n v i n c i n g as the preceding evidence may seem, there is just basis for a certain reser

vat i on concerni ng the ir s ignif icance. T h ey tend to imp ly t ha t the balance between the

decarboxylat ion of pressor amine precursors and the e l iminat ion of theamines is so deli

cately maintained that an otherwise undetectable alteration in renal funct ion would per

m i t the formation of such amines to exceed their destruction or excretion, r esultin g in an

elevation of bloo d pr essure. T h er e is evidence to the contrar y that must beconsidered.

T h e k i d n ey is neither the only n or even the major source of amin e oxidase. B h agv at,

B l a s c h k o , andR i c h t e r (80) and other investigators (109, 189) have found the enzyme to

be widely distributed in thebody . R ich ter , L ee, an d H i l l (184) determined that theh u

man body was capable of deaminat ing phenethylamine at a rate of 26 mg. per kg. of bodyweight per ho ur . T h e fact that /8-phenyi -n-pr opyl amin e, wh ich was deaminated by amine

oxidase, was not excreted assuch wh en admini stered oral ly unless the l iver was inju red by

an hepatoxic agent, suggests that organ as a p r i n c i p a l source of amine oxidase (25). I n

th e rat, w h i c h is so widely used for studies in hypertension, decreased deamination of

pressor amines in damaged kidneys does not contr ibute to theelevation of blood pressure,

for there is no amine oxidase in thek id ne y of that animal (122). B r o w n an d M a eg r a i t h

(45) found no reduct ion in the amine oxidase content of other organs of hypertensive rats.

F o r that matter, there isgood reason to believe that deamination probably does not p lay a

domin ant ro le i n the inact ivat i on ofphenolic pressor amines (105,186).

Elimination and Inactivation of Pressor AminesT h e e l iminat ion ofph enolic pressor amines combines in acti vati on an d excretion. T h i s

field has been reviewed in recent years by B e r n h e i m (14), DeM e i o (59), H a r t u n g (89), an d

Beyer (23, 26).

T r ansme t hy la t i o n as a step in the1 'deacti vati on " (from a cardiovascular standpoint)

of noradr enaline i n the body is suggested by the recent report by Goldenberg, Pines, B a l d

w i n , Greene, and Roh 82). A l t ho ug h t he y g iv e no enzymologic studies to substantiate

their hypothesis they suggest that essential hypertension might beconsidered to be a met-



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 3




abolie disease of def ic ient t ransmethylat ion—that is, of norepinephr ine to epinephr ine.

T h e i r concept arose fr om experim ents w her ein they i njected -̂epineph ri ne and if-norepi-

nephr ine into nor motensive patients an d others wi th essential hy pertension . D i r ect meas

urements were made simultaneously of card iac ou tpu t, systemic ar teri al pr essure, and

pulmon ary a r ter ia l p ressure. E p in ephr ine , in doses sufficient to cause significant hy

pertension, was found to act as an over -all vasodilator aswell as a powerful cardiac st imulant . Theresponse of hypertensive patients to adrenaline was increased but was qua l i ta

t ively the sameasi n nor mal subjects. T h e pr im ar y act ion ofnoradrenaline was an intense

generalized vasoconstr ict ion without signif icant cardiac effects in the dose range studied

and this response was greater in hypertensive than in normotensive individuals . The

vasoconstr ictor action of Z-arterenol was blocked completely by the synchronous adminis

t ra t ion of equal doses of epineph ri ne. T h ey conclude that their findings are compat ible

w i t h the concept that norepinephr ine is a sympathetic mediator of over-a l l vasoconstr ic

t ion andsuggest that a distur bed balance between both symp athetic transmi tters coul d

be concerned in the production of hypertension.

R egardless of theuntested merits of theabove work , methy i a t ion as a first step in the

deact ivat ion of noradrenal ine in the body is just as plausible as is the evidence that

methy ia t ion is the final step in the synthesis of adrenaline. The evidence for and against

this route of synthesis has been discussed previously in th is review. T a in ter et a l . (155)

reported that in dogs under phénobarbital anesthesia -̂ar terenoi h ad a pressor activity 1.7

times that of l -epinephrine. I n th is sense then, methyiat ion might beconsidered a process

of in acti vati on . H ow ever, they found i n contrast that theacute toxicity of ^-epinephrine

(LDso) wasabout four times that of ^-norepinephrine {114,155).

OA T * 2 . 4 5 KOfut!

I

L E F T K I D N E YU N C L A M P E D

I O M G . DOPS IN 3 C C . SOLN . AT l i : 4 5

J . .1 i

2 0 25 30

MIN MIN MI N

1 1

4 5 6 0

MIN MIN

i . . . . . . . . -

I 4 ! 2 4 T I M E : 3 0 S E C .

. . . . . . • , · . , . . .

Figure 9. Blood Pressure Response to Unclampîng of Opposite Kidney in Same Cat

Used for Figure 8

Ten mg. of dihydroxyphenylserine had been injected into kidney at time renal pedicle was clamped, 2 hours

preceding this record

T h e r o le of amine oxidase in the inact ivat ion of sympathomimetic amines rests on a

much firmer basis. The enzymatic oxidative deamination of t y r a mi n e wasdescribed first

b y H a r e (87). K o h n (105) par t ia l ly pur i f ied it but the enzyme is widely distr ibuted in

mammalian t issues (30, 109), is cyanide insensit ive (15), and has resisted isolation. The

name monamine oxidase hasbeen suggested for theenzyme (154) referred to in the l i te ra

ture as tyramine oxidase, adrenaline oxidase (40), andaliphatic amine oxidase (128).

T h i s enzyme r api dly deaminates cer tain pr im ar y an d secondary u nsubstituted p-hy-

d r o x y - and 3,4-dihydroxyphenylethylamines wherein the amino group is on the termina l

carbon atom of the side chain (4,18,22,40,128).



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 3




I t seems establish ed th at the presence ofami ne oxidase i n the body , an d especially t h at

i n the l iver, determines the oral efficacy of £-phenylethylamines. I n general those c o m

pounds of this nature having an alp ha carbon atom adjacent to that bear ing the a m i n e —

that is, /3-phenyl isopropylamine—are not deaminated by amine oxidase (134), are act ive

on oral administ rat ion, and areexcreted in the u r i n e as such fo l lowing oral or parenteral

admin is t ra t ion (28, 102, 132, 151).

Figure 10. Pressor Response to Intravenous Injection of 10

Mg . of 3,4-Dihydroxyphenylserine into Cat following Record

Obtained in Figure 9

P r i n c i p a l l y because amine oxidase was so abun dant ly present in thebody and could be

shown to deaminate certai n pressor amines in vit r o, it hasbeen though t by some to p l a y a

ro le i n the i n v iv o i nac t iv a tio n of adrenal ine an d i n theetiology of hyp ertens ion. T h e ad

min is t ra t ion of cru de amin e oxidase has been reported to have decreased the blood pressure of n o r m a l and hypertensive rats (142), but th is has not pr ovoked substant iat ion.

Cr o x at t o andC r o x a t t o (53, 54) have shown th at renal hy pertensinase and amine oxidase

were different enzy mes. A lso , B i n g , Zucker , and Perk ins 34) found angiotonin and ami ne

oxidase to be fundamental ly d ifferent. T h u s the hypertens in and the phenylethyl (pres

sor) amin e appr oaches to hy per tension seem quite dissim ilar on these grounds.

Ho we v e r , it seemsun li kely th at ami ne oxidase pl ays a fundamental ro le i n the in act i va

t ion of the phenolic pressor amines even though it is of great importance in determining

th e fate of the /3-phenylethylamines.

T h e ph enol oxidases pr obably p l ay no impor tant ro le in the e l iminat ion of pheno l ic

pressor amines, in spite of the impor tance that has been attach ed to the ox idat ion of the

catechol nucleus in the past. The names phenolase and cresolase, polyphenol oxidase,

an d catechol oxidase serve to ident ify the enzyme with its mo no - or diphenolic substrate,

but they usually occur together and are diff icultly separated. The enzymes have been

purif ied and their characteristics have been described (56, 104, 106, 156). Beyer (21),

Allés (3), andR a n d a l l a n d H i t c h i n g s (129) have described the re lat ionship of st ructure of

the ph enolic pressor ami nes to therate of ox idat ion of the ir nucleus i n thepresence of these

enzymes.

T h e functi onal signif icance an d even the normal presence of other than a D O P A o x i -



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 3




dase i n the mamm ali an bod y hav e not been well establish ed ( 3 1 . B loch ( 4 3 ) described the

" D O P A r eact i on" of sk in , i n w h i c h case melanin was formed when D O P A was incubated

with sk in, an d thi s has been confir med by P u gh ( 1 2 7 ) and Char les ( 5 0 ) . C ad d e n and D i l l

( 4 7 ) repor ted a polyphenolase to be present i n ki dney , but th is di d not oxidi ze phenolic

pressor amines. H ogeboom and A da ms ( 9 4 ) have reported the presence of a phenolase in

a mouse melanoma that oxidized tyramine, and this is probably the most authentic representation of a phenol oxidase that could oxidize the phenolic nucleus of pressor amines in

the body.

I n spite of the fact that ph enol oxidase pr obably pl ays no im po r tant role i n the in ac-

t ivat ion of pressor amines i n the body , it has been r epor ted th at the inj ectio n of the enzy me

into h ypertensive r ats led to a reducti on i n their blood pr essure ( 1 4 U 1 4 ® ) - It is diff icult

to assess the value of these experiments because of the nonspecific depressor effects of

crude pr otein pr eparations on blood pressure. F or example, P r in zmetal e t a l . ( 1 2 6 )

found that their tyrosinase preparations inactivated by boiling decreased the blood pres

sure of hy pertensive patients as well as di d their enzymi cali y active pr eparati ons.

T h ere are other modes of in acti vati on of pressor amines that pr obably are not h ig h ly

signif icant factors from our present standpo in t. T h ese in clude the effect of the cyto

chr ome C -cyto ch r om e oxidase oxidatio n of catechol derivatives to the correspondin g or th o-

quinone ( 4 1 , 1 0 3 ) , the oxidation of the phenolic nucleus by the ascorbic-dehydroascorbic

acid system ( 1 8 ) , and the deamination of pressor amines in the presence of aldehydes ( 1 2 0 ,

1 2 1 , 1 5 2 ) . O ne may refer to the reviews by H ar tu ng ( 8 9 ) and by Beyer ( 2 3 ) for discus

sions of these systems.

Figure 11 . Effect o f Intravenously Injected Phenylserine, p-Hydroxyphenylserine, a n d

/-Epinephrine on Blood Pressure o f Anesthetized D o g

C onj ugati on appears to be the pr inc ipa l mode of inac tiv ati on of phenolic pressor

amines in the bod y. I n the auth or 's experi ence the adm in istr ati on of ph enolic pressor amin es

conjugated w ith organic or inorgani c acid radicals on either the h yd r ox yl group of the r i n g

or the alip hati c amin o group reduces or abolishes acti vi ty. T h i s is also tr ue for th e acety -lat ion of p-aminoph enylethyl amines. B arger and D ale ( 1 3 ) found acetoxyphenylethyl-

amin e in active on intr avenous in jection. L oeper ( 1 1 2 ) reported the synthesis of the sul

furic ester of tyramine and found it inactive as a pressor agent unless it was hydroiyzed to

tyramine (111).

T h e i n vi vo conjugation of symp athom im etic amines h avi ng a catechol nucleus seems

well established. T h e id enti ty of the conjugate seems clear but is not certai n. R ic h ter

( 1 3 3 ) and R i ch t e r and M ac i n t o sh ( 1 3 5 ) reported the excretion of conjugated epinephrine



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 3




after the parent compound was administered oral ly . No free compound was excreted.

After aci d hydr olysis theepinephrine was recovered in theur ine by the iodoadrenochrome

reaction. Also, thepressor effect ofthe hydro lyzed compound was demonstrated. T h ey

believed the conjugation to be with sulfuric acid, and proposed that it was mediated

through a sulfosynthase. H ow ever , they di d notdefinitely id entify theconjugate as be

i ng with sulfuric acid. Beyer and Shapiro (27) quantitated the iodoadrenochrome react ion and reported that the 3,4-dih ydr oxyph enylethylam in e derivatives, cobefrin and epi -

nine, were excreted to the extent of about 65 and 85%, respectively, as a hydro lyzable

conjugate in urine following their oral administration to man. Both compounds and

epineph ri ne were excreted asconjugates by dogs andthis quali tative observation was not

affected by the route of administrat ion of thedr ugs. T h e pressor effect of thehydro lyzed

ur ine containing epinephrin e was conf irmed. Holtz andCredner (98) reported that when

h u m a n subjects were given D O P A orally they excreted both free and conjugated 3,4-dihy

droxyp henylethylamin e. T h ey presumed theconjugation to bewi th sulfuric ac id .

DOG ? 8.8 Kg.BARBITURATE ANESTHESIA

ο MM.Hq.

I

EPINEPHRINE

BASE LINE

lOV 20 r

3,4 0IHY0ROXYPHENYLSERINE EPI. DOPA DOPA EPI.

· . . . « . · • . · • ·

0.2 MG. 1.0 MG 0.5 M G 3 O X 10 MG 10. MG 20 >

10:36 1050 11.01 l i :08 Ii:i8

TIME = 30 SEC.

Il;28 11:38 11:41 Ι Γ 4 3

Figure 12. Effect of Intravenously Injected /-Epinephrine, Dihydroxyphenylserine,

and Dihydroxyphenylalanine (DOPA) on Blood Pressure of Anesthetized Dog

A l tho ugh no free epinephrine is excreted under the condit ions ofthose experiments

just described, it is permissible toquestion whether they are representative ofthefate of

epinephrine as it is secreted in thebody, or whether conjugation is a mode of inact ivat ion

of catechol pressor amines administered as drugs. The relatively minute amounts of

adrenal ine or noradrenaline secreted normally and the l imitations of present analytical

methods definitely handicap a direct approach to the problem. However, it has been

possible to study thefate of adr enalin e secreted by thebody in amore or less physiological

type of experiment.

T h e r e is a tumor of the adrenal medul la th at has been described as physiologically

mal ignant buthistologically benign (119). T h a t is to say, thesymptoms of hypertension

are rapidly progressive although the tumor cells are benign, within the meaning of thatterm tothepath ologi st. T hese cells secrete adr enal in e in large amounts that areat first

released only intermittently but later thehypertension may be sustained. The paragan

gl ioma is a similar type of tumor of the sympathetic chain ganglia that gives rise to c l in i

cal l y identical symptoms. M u n tz (119) an d hi s associates rep orted the r emov al of a pheo-

chromocytoma that, on the basis of Chen's assay, was estimated tocontain 2.3496grams of

adrenali ne. T h ey estimated that it would take a herd of 31 cattle to y ie ld the same

amo unt of adrenalin e. O thers have reported theisolation of adrenaline from such tum ors,



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 3




although B u l b r i n g andB u r n (46) andH o l t o n (95) have reported recently that both nor

mal adrenal g land and the ph eochrom ocytoma contain noradrenal ine in ad d i t i o n to

adrenaline.

T h e autho r (24) has had an o p p o r t un i t y to study the pheochromocytomas re

mo ved from three patients, an d their uri ne specimens obtain ed between an d dur ing h y p e r

tensive attacks (116). I n general, only free adrenal ine andnoradrenal ine were found inthe tumor and only conjugated drug in theur ine at the t ime of thehypertensive attacks.

A c t u a l l y the differentiation between epinephr ine and ar terenoi wasmade only in two of

the cases for the iodoadrenochrome method (27) does not differentiate between the two

compounds. Auerbach and A ng e l l (9) developed a method to estimate arterenoi in

the presence of epinephr ine. U sin g this method they found arterenoi to be present in

U . S . P . samples of epinephrine from biological source to theextent of 10.5 to 17.5%, in

conf irmation of the wo r k of Goldenberg et a l . (81). Indeed, T u l l a r (159) wasable to iso

late Z-arterenol from natural U . S . P . ep inephr ine . T h us it seems incontrovert ib le that

noradrenal ine aswell asadrenaline is a nor mal constituent of the adrenal medul la . T h i s

wo u ld seem tobeconsistent w it h the view p r eviously expressed h erein th at norepin ephr ine

is apr ecursor that can beconverted into ep inephr i ne by t ransmethy lat ion.

T h e conjugat ion ofepinephr ine i n thebody iswi th both sulfur ic an d glucur onic acids,

although there seems to besome difference of o p in io n as to w h i c h is themore important

route . A r no l t and DeM e i o (5,60), B e r n h e i m (17) , an d L i p s c h i t z and Be ud in g (110) have

reported that theconjugat ion of phenols in the intestine, l iver , an d spleen isan enzymatic

process. Apparently it is a coupled oxidative system. I n sulfate conjugation, inorganic

sulfate serves as the precursor (108). D e i c h m a n n (58) fed ep inephr ine to rabbits and

found a mar ked increase in theexcretion of organic sulfates wit ho ut an increase in the ex

cret ion ofglucuronates. He concluded that ep inephr ine conjugation waspr inc ipa l ly w i t h

sulfuric ac id . C onverse ly , Dodgson, G ar ton, and Wi l l i ams (61) conducted a similar i n

vestigation wherein d-epinephrine wasadrninistered or al ly . No free d r u g wasexcreted,

bu t in th is case the conjugat ion was with g lucuronic ac id . Onewo uld be led to believe

that p robably both sulfur ic an d g lucuronic acids p l ay a ro le in the conjugat ion of catechol

pressor amines.

T h e fate ofmonophenolic pressor amines is notsocer ta in. E wi ns and L a id law found

that w hen large amounts of t y r amine were fedtodogs, up to 25%was excreted in the urine

as p-hydr oxyph enylaeet ie ac id . T h ey found that this occurr ed wh en tyr amin e wasp e r

fused through liver and uterus, but when the d r u g wasperfused through theheart it was

destroyed (78) . Simi la r ly , B e r n h e i m and B e r n h e i m (16) found that the heart was ca

pable ofopening thephenol ic r i n g i n t y r amine .

Present evidence indicates that monophenolic pressor amines, such as ty ramine , may

be excreted partially assuch and ina conjugated form w ith and withou t deamin at ion andoxidat ion to the corresponding ac id . Beyer and Stutzman (29) administered tyramine

an d /3-(p-hydroxyphenyl) isopropylamine to both man and dog . A l th ough a physio log ical

effect of the agent was not demonstrable, theur ine was found to conta in a compound that

appeared to be ident ical with the dru g that was administe red . T h i s was judged by the

fact that it wasoxidized by phenol oxidase, deaminated by amine oxidase in the case of ty

ramine, andpossessed pressor pr operties. Theamount of the mater ial excreted was not

determined, but since then the results have been repeated and conf irmed qual itat ive ly.

U nd o ub t ed ly t h i s does not account foral l thedrug that wasgiven, and it isquite possible

that the d r u g was conjugated loosely d u r i n g itspassage through the body. Har t les and

W i l l i ams (88) studied the detoxication of p -hydroxybenzy iamine and p - hy d r o x y b e nz y l -

methylamin e administered to rabbits. T h ey found i n both instances that the compoundswere excreted asthesulfates, thesulfate conjugation being greater for thep r i mar y amine.

B o t h compounds also were deaminated andexcreted as p -hydroxypheny lacet ic ac id and

the corresponding glucuronide.

Comment

A l t h o u g h ithas been beyon d the pr ovin ce of thi s review to discuss theseveral theories

of the etiology of essential h yp ertension, it is theo p in io n of this author that the var ious



0 2 1 / b a - 1 9 5 0 - 0 0

0 2 . c

h 0 0 3




concepts are not mutually exclusive and that to ho ld one or another theory wholly ac

countable for thecl inical picture ofessential hypertension is misleading and un warr anted

at present. T h e pr obabil ity that inm a n y or even most instances hypertension is neuro

genic in origin seems most attractive. Since theautonomic impulses that initiate vaso

constri ction are adrenergic, Sym path in Ε (noradrenaline), and to a lessor extent adrenaline,

undoubtedly play amaj or role i n the earlier phases of the disease.V asoconstricti on brought about i n this manner th rough psychic stimu lation has been

shown to decrease rena l bl ood flow. It isattractive to hypothesize that this may initiate

a more severe renal cortical ischemia than is apparent from over-all blood flow measure

ments, if the cortical vasoconstriction should beaccompanied by the openin g of subcortical

arteriovenous shunts such as have been described by T r u e t a (157). Such a circumstance

would set up the conditions requisite for the elaboration of renin, or the decarboxylated

precursors of adrenaline or noradrenaline that require adequate oxygenation for thei r in

activation, or theestablishment of theendocrine kidney of Selye (146). Over the course

of time it is possible that these nephrogenic agents mayperpetuate thehypertension and

the conditi ons for their conti nu ed fun cti on. T h e pathogenesis of the degenerative arterio-

l i t ic lesions would be in it iated, on thi s basis, as reparative and compensatory responses tothe traumatic effect of theearly wide fluctuations inpressure and thelater continued in

sult from that source. In the case of the pheochromocytoma, that mimics so closely

th e cl inical picture of essential hypertension of other origin, the initiation and progress

of the disease are attributable to an exaggeration of the normal functions of the adrenal

medulla.

Acknowledgment

T h e records of rates of decarboxylation and blood pressure studies on theamino acidprecursors of pressor amines were obtained with thecooperation of W. M. Gov ier and A.

R . La tv en .

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ALLES—DISCUSSION OF PAPER ON PHENYLETHYL (PRESSOR) AMINES 57

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Discussion of Paper on Biosynthesis andMetabolism

of Phenylethyl (Pressor) Amines

GORDON A. ALLES

Universit y of California Medical School , San Francisco, Calif .

A s stated by Beyer , it nowdoes appear that both noradrenaline and adrenaline are im

plicated in thehumoral mediation of adrenergic nerve impulses. The hypothesis that

adrenoxine asproduced by any action of a catechol oxidase in the body acts under appro

priate conditions asthevasodilator substance presently appears to be very doubtful , al

though some of theevidence along this line presented by B a c q (1) an d by H e i r m a n and

B a c q (7) appeared to be reliable. Sh ortl y after their reports appeared Carro l l H a n d l e y

an d the author inthepharmacology laboratory of theUn iv ers i ty of Cal i fornia M e d i c a lSchool tried toconfirm the apparent reversal of netvasomotor effects of catechol oxidase

oxidation ofadrenaline solutions but failed toobserve any effects beyond those that could

be ascri bed tothe destru ction ofapart ofthe adrenaline activi ty.

I n some recent comparisons of thepressor responses of adrenaline and noradrenaline,

the appreciably longer duration of pressor action of the nor compound was noticed, and

this isevidenced in the figures shown by L ud uena and co-workers (10) i n their recent care

fu l quantitative studies onthe relative activities of the two compounds asestimated by

various methods on different animals and organs of the body. T h i s longer du rati on of act ion of noradrenaline indicates that theover-ail inactivation rate in the body is indeed

slower. This is inagreement with the indications from the work of West (15) on j ugu

l ar /por ta l and splenic artery/vein equipressor ratios that the two compounds are apparently inactivated differently by the liver and spleen.

It may indeed be, asB acq and F isher (2) and G oldenberg and co-workers (6) suggest,

that thesynthesis of adrenaline is through the transmethylation of noradrenaline as a

final step and that thedeactivation of noradrenaline is through the transmethylation of

noradrenaline asan init ial step. I n this connection it is of interest that Shaw (13) found

i n his studies on the oxidation of adrenaline and noradrenaline by an arsenomolybic

reagent that the former catechol amine wasabout twelve times more r api dl y oxidi zed and

that an increase ofabout five times was from some phenomenon associated with the add i

t ion of alkal i . J ust what thephenomena noted by Shaw are due to isnotclear but they

do demonstrate that an order of five to twelve times difference in oxidation rates between

noradrenaline and adrenaline may be on some simple chemical reaction basis.T h e thought that tran smethylation of noradrenaline maybean init ial step in its de

activation i n thebody makes onewonder whether further transmethylation of adrenaline

is also nota common biological process. As a result of studies of the various alkaloids of

plants of th e E p h e d r a species, itwas noted that not only ^-ephedrine and its stereoisomer d -

pseudoephedrine are present but also that ^-norephedrine, d-norpseudoephedrine, l -

methylephedrine, and d-methylpseudoephedrine (8) are present. The quaternary tri-

methylammonium compounds corresponding to these were not reported but very



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probably were not looked for and would be difficult of isolation in pure form because of

their high base strength.

T h e question as to wh ether al l of the possible ΛΓ-methylation compounds of noradren

aline are indeed commonly present in storage places in the body such as the adrenal me

dul la, or the caroti d bod y, or other gangli a or per ip her al synapses wil l pr obably not be an

swered soon, for the intensity of the pharmacological activity of iV '-dimethylnoradrenalinean d noradrenaline tri methy lam mon iu m i on is not great as reported by Stehle, M elvi l l e,

and O ldham ( 1 4 ) who unfortunately do not give any of the chemical details regarding the

id enti ty or pur it y of the prepar ations they used.

However, the question as to whether the first methyiation step, the conversion from

norad renali ne to adrenali ne, is an activ e process over-ail in the body should be susceptible

of fairly easy study by repeating the experiments of R ich ter and M ac i n tosh ( 1 2 ) and of

Beyer and Shapiro ( 4 ) but administering noradrenaline instead of adrenaline. T h e ur in e-

excreted compounds could be bioassayed after suitable hydrolysis and the relative amounts

of noradrenaline and adrenaline in the hydrolyzate determined by using the differential

activities of the two compounds on rabbit intestine and rat uterus as first reported by

West ( 1 6 ) . T h e differences between n or ma l persons an d those i n successive stages of essential hypertension with regard to their abilities to conjugate noradrenaline and adrena

line and with regard to their abilities to transform the former into the latter surely should

be a subject of precise ch emic al stud y i n the near futu r e.

A lt ho ugh interest an d knowledge today is r api dl y incr easing wi th respect to no r ad

renalin e an d adrenalin e as hu mor al mediators i n the functi onin g of the symp athetic ner v

ous system, the possibilities should not be overlooked that less intensely active compoun ds

ma y be im pli cated i n the nor mal or pathological fu ncti oni ng of thi s nervous system i n man .

Along this line the vasoconstrictor material recently isolated from beef serum by Rapport,Green, and Page ( 1 1 ) is of consider able in terest. T h i s substance in its pur est state as re

ported has a vasoconstrictor activity of about that of tyramine though its various color

reactions in relation to its activity indicate it to be considerably different from this com

pound.

T yr am in e has appeared to be ordin ari ly quite rapi dly in activated in the body, pos

sibly by the amine oxidase mechanism that is active on aliphatic and phenylaliphatic

amin es. H owever , this should perhaps be reinvestigated i n relati on to hyp ertension i n

man, for B a i n ( 8 ) apparently found some isoamylamine i n the ur ine i n man , and although

Lo cket t ( 9 ) was not able to find th is com pou nd i n her studi es, there are in di cati ons of some

un kn own variables being in volv ed. L ock ett di d find pressor bases in ur ine that were more

active than isoamylamine and on further study a close correspondence between one of the

bases an d nicotin e was established. H owever , her prepar ations of male ur in e wh ic h i n

cluded some tobacco smokers corresponded to but 50 to 70 micrograms of nicotine per literi n physiological pressor activity and those of female nonsmokers' urine, to but 17 micro

grams of nicotine per liter.

T h e rein vestigation of vo n E u l e r ( S ) of ur in e of nonsmok ers i nd ic ated u p to about 10

mg. per liter of ether-soluble bases and a pressor act iv ity corr espondi ng to about 500 mi cr o

grams per liter . P ip eri di ne was isolated an d found to be the principal base present in the

ether-soluble bases and comparison between the pressor assay and colorimetric piperidine

determ in ation s showed a close corr espondence. I t was fur ther repor ted th at pi per id in e

was pr esent in the ur in es of the horse, pi g, cat, an d r abb it as well as th at of m an . T h e

meaning of its presence or its possible relation to the metabolism of other amines or the

functioning of the sympathetic nervous system in normal or hypertensive man has not

yet been developed.In closing, the excellent presentation of Beyer is recommended for close study by bio

logical, medi cal, an d organic chemists. I t is ver y well balan ced, up -to-date, an d the result

of mu ch th in k in g and wor ki ng along the lines he has talked about.

Literature Cited

(1) B acq, J . Ph ysi ol . (L ondon), 92, 28 (1938).

(2) B acq and Fisher, A r c h . i n t er n . physiol . , 55, 73 (1947).



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ALLES—DISCUSSION OF PAPER ON PHENYLETHYL (PRESSOR) AMINES

(3) Bain, Q u a r t . J . E x p t l . Physio l . , 8, 229 (1915).(4) Beyer and Shapiro, Am . J . Physio l . , 144, 321 (1945).(5) E uler, von, Acta Ph ysi ol . S c a n d . , 8, 380(1944).(6) Goldenberg, P ines, Bal dwi n, Gr eene, and R oh , Am . J . Med. ,5, 792(1948).(7) Heirman and Bacq, A r c h . i n t er n . physiol . , 57, 82 (1940).(8) H enry , "P lan t Alk aloi ds," 3rd ed., Ph iladelphia, P.Blakiston's Son & Co., 1939.

(9) L ockett, J . Ph ysi ol . (L ond on), 103,68-165 (1944).(10) L uduena, Ananenko, Siegmund, and M il ler , J . P h a r m a c o l . , 95, 155(1949).(11) Rapport, Green, and Page, J . B i o l . Chem., 174, 735(1948).(12) Richter and M ac Intosh, Am . J . Physio l . , 135, 1(1941).(13) Shaw, B i o c h e m . J ., 32, 19(1938).(14) Stehle, Melville, and Oldham, J . P h a r m a c o l . E x p t l . T h e r a p . , 56, 473 (1936).(15) West, B r i t . J . P h a r m a c o l . , 3, 189(1948).(16) West, J . Ph ysi ol . (L ond on), 106, 418(1947).



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002. Chemical Factors in Hypertension (1950)

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