Subsensitivity to epinephrine following the administration of epinephrine and ephedrine to normal individuals Harold S. Nelson, M.D., J. Waylon Black, M.D., 1. Bernard Branch, M.D., Bruce Pfuetre, M.D., Harry Spaulding, M.D., Richard Summers, M.D.,

and Dale Wood, M.D. Dewuer, Cola.

Cardiovascular and metabolic responses to exercise and conseozltive epinephrine infusions 94 hours apart were measzurea in 7 normal indtiidnals before and fol- lowing a week’s administration of ephedrine sulfate. There was evidence of less beta adrenergk response to the second control epinephrine infusion compared to the first control infusion, and the depression of the rise in blood lactate was significantly different. A week of ephedrine produced more profound depression of the beta adTeneTgiG responses to epinephrine with significant differences in the rise in blood glucose and lactate, and th,e pulse and blood pressure responses. Fwrthermore, these same responses remained signi$colttly altered when a second epinephrine infusion was performed 36 hours following the last dose of ephedrine. The alterations in the response to epinephrine indnoed by ephedrine are consistent with the concept of effector cell “subsensitivity,” an adaptive response to prolonged excessive stimulation.

A number of investigators have reported abnormal responses to beta adrenergic stimulation in patients with bronchial asthma. When patients with bronchial asthma have been challenged with epinephrine or isoproterenol, they have often had less than the expected rise in blood glucose,1-5 blood lactate,59 6 blood-free fatty acidq7 and urinary and ,plasma cyclic adenosine monophos- phate.8p Q With beta adrenergic stimulation patients with bronchial asthma have been reported to have less fall in circulating eosinophils,ll higher diastolic blood pressures,l and slower pu1ses5, 7 than normal control subjects. In addition, the rise in plasma-free fatty acids that follows exercise has been reported to be absent in patients with bronchial asthma who developed post-exercise broncho- constriction.1°

The existence of depressed responses to beta adrenergic stimulation in many patients with bronchial asthma lends support to the theory that impaired beta adrenergic responsiveness underlies bronchial asthma.‘* It is often difficult to determine, however, whether the impaired beta adrenergic responsiveness pre- cedes or follows the development of bronchial asthma and particularly to what

From The Allergy-Immunology Service, Fitzsimons Army Medical Center. The opinions or assertions contained herein are the private views of the authors and are not

to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense.

Received for publication March 20, 1974. Reprint requests to: Harold S. Nelson, M.D., Chief, Allergy-Immunology Service, Fitzsimons

Army Medical Center, Denver, Colo. 80240.

Vol. 55, No. 5, pp. 699309

300 Nelson et al. J. ALLERGY CLIN. IMMUNOL. MAY 1975

TABLE I. Plan of study*

Day Exercise

1

Epinephfine infusion

(4tlr.l Xanthine-

free diat

x

-

Ephedrine (26-3;7:6 mg. q.i.d.)

“The exercise test and epinephrine infusions were performed fasting, beginning at 8:OO A.M. on consecutive days as indicated. Ephedrine sulfate administration began immediately following the second epine brine infusIon and ended at 1O:OO P.M. on day IO. The morning dose of ephedrine was with R eld on day 10 until completion of the exereise test.

extent medication given as treatment for asthma may contribute to the decreased responses.

In a previous study we reported that the administration of ephedrine, a drug commonly used in the treatment of bronehial asthma, induced altered metabolic and cardiovascular responses to epinephrine in normal men similar to those reported in patients with severe bronchial asthma.‘” Others, employing somewhat different methods, were unable to confirm these results.‘” The present study WEIS

undertaken to reexamine the effect of ephedrine on metabolic and cardiovascular responses to epinephrine, to measure the duration of any effects observed, to

determine whether ephedrine altered the response of circulating eosinophils and the urinary excretion of cyclic adenosine monophosphate to epinephrine, and finally, to study the influence of ephedrine on the bronchial and metabolic responses to exercise.

MAWkiAU A@& MST#4iBW*

Seven normal male volunteer subjects with no evidence or history of asthma participated

in the study. Subjects ate a normal diet, but avoided xanthines on the day before and on the

day of the exercise tests and epinephrine infusions.

The plan of the study is outlined in Table I. The exereise test employed the mult~istage exercise capacity test of Bruce15 which is designed to maintain the subject for 30 seconds at

85 per cent of his predicted maximum heart rate. Continuous telemetry EKG monitoring was

used throughout the period of exercise. A one-second forced expiratory volume and blood for free fatty acids and lactate were obtained prior to and immediately following exercise and ~lt 5-minute intervals for the following 20 minutes. For the second exercise test the workload of

the first test was repeated rather than employing the pulse rate criterion for duration of exercise.

Epinephrine was administered intravenously for 4 hours at 7.3 pg per minute (5 indi-

*The protocol under which this study was performed was reviewed and approved by the A&y Investigational Drug Review Board and the United States Army Surgeon Germral’s (Sfihi&l Invest‘ ation and Human Use Committees, as well as the Fitzsimo~s Army Medical Confer Clinica Research and Human Use Review Boards. P

VOLUME 55 NUMBER 5

Am

30

20

10

0

-10

-20

-30

n I

Subsensitivity to epinephrine 301

'Pas [ 1 "Pal

FIG. 1. Change in mean blood pressures during epinephrine infusions. Preinfusion blood

pressures showed no significant difference. Indicated on the graph is the rise or fall in

mean blood pressure during the infusion. Each point is a mean of 4 determinations each

on 7 subiects. Significance of differences shown below the graph was determined by

Analysis of Variance.

viduals) or 8.8 sg per minute (2 individuals), using a high-capacity infusion/withdrawal

pump (Harvard Apparatus Co., Millis, Mass.). Continuous EKG monitoring was employed.

Blood for glucose, free fatty acids, and lactate was obtained prior to the infusion and after 30, 60, 120, 180, and 240 minutes of the infusion. Glucose was determined by the Technicon

Method, N-2b modification of the method of Hoffman (Technicon Instrument Corporation, Tarrytown, New York). Free fatty acids were determined by the method of Antonis.

Lactate was determined by an automated adaptation of the method of &l~olz and Associates.17 Total eosinophil counts were performed prior to and at the end of the 4-hour infusion. Urine

was collected overnight and during the course of the infusion for cyclic adenosine mono- phosphate determination by the method of GilmanJs Pulse and blood pressure by auscultation

302 Nelson et al. J. AtLERGY CLIN. IMMCINOL. MAY 1975

FIG. 2. Change in pulse rate during epinephrine infusions. Preinfusion puke rates dii

not differ significantly. Indicated on the graph is the rise or fall in mean pulse rate during the infusions. Each point is a mean of 4 determinations each on 7 sub@& Si$niGcanr;e

of differences shown below the graph was determined by Analysis of Variasice.

were measured until stable prior to the infusion and again at 15-minute intervals during the infusion.

Ephedrine sulfate, 25 mg. (5 subjects) or 37.5 mg. (2 subjects) was administered 4 times daily beginning immediately following the second epineph+ne infusion. On day 10 the @at morning dose of ephedrine was withheld until after completion of the exercise test. StatisticrtI signiikance was determined by Analysis of Variance.

One week of oral ephedrine administered 4 timas daily si@&ieantly a@ectrs%l the response of the blood glucose, blood lactate, mean blood ppesaure, and px&%e rate to subsequent epinephrine infusions.

VOLUME 55 NUMBER 5

Subsensitivity to epinephrine 303

amgiW ml glucose

I

4 POST-EPHEDRINE 1

[

'P

l *P

<I C.01 I

FIG. 3. Rise in blood glucose during epinephrine infusions. Preinfusion glucose levels did not differ significantly. Indicated on the graph is the rise in glucose during the in-

fusions. Significance of differences shown below the graph was determined by Analysis of Variance.

The mean blood pressures prior to the epinephrine infusions were: first control, 97.6 + 5.9 mm. Hg, second control, 94.4 f 7.2 mm. Hg, first postephedrine, 94.3 t 7.3 mm. Hg, and second postephedrine, 91.6 + 8.6 mm. Hg. These values are not significantly different. The changes in the mean blood pressure during the epinephrine infusions are shown in Fig. 1. During the first control epi- nephrine infusion, the mean blood pressure fell. During the second control epinephrine infusion 24 hours later there was little change in mean blood pres- sure, but the difference from the first control infusion was not statistically significant. After a week of ephedrine the mean blood pressure rose during the epinephrine infusion. The values were significantly higher than those of the first infusion for all 4 hours (p < 0.01 for first, second, and fourth hours and p < 0.05 for the third hour). They were significantly higher than the values for the second control infusion for the first and second hours (p < 0.01) and the fourth hour (p < 0.05), but were significantly higher than the second post- ephedrine infusion only for the first hour (p < 0.05). After a further 24 hours following the last dose of ephedrine, the mean blood pressure, although lower, still rose during the infusion. The levels were significantly higher than those

304 Nelson et al. J. ALLERGY CLiN. IMMUNOL MAY 1975

FfG. 4. Rise in brood lactate during epinephrine infusions. Preinfusion lactate Ieveh showed

no significant differences. The graph indicaates the rise in blood lactate levels during the

infusions. The significance of differences shown below the graph was determined, by Analysis of Variance.

during the first control infusion for the first, second, and third hours (p < 0.05 ) .

The mean pulse rates prior to the epinephrine infusions were ~2;. s~i~~t~y different; they were: first control, 65.7 ? 9.4 beats per minute (bpm); second control, 68.6 + 9.0 bpm; first postephedrine, 70.0 c 7.5 bpm; and seeand post- ephedrine, 65.7 + 7.9 bpm. The changes in pulse rate during the epinephrine infusions are shown in Fig. 2. There was a progressive rise in the mean p&e rate throughout the first control epinephrine infusion. During the seeand NEF&%& infusion 24 hours later, the rise in pulse rate was less marked, the difference was not statistically significant. The pulse rate declined during the

VOLUME 55 NUMBER 5

Subsensitivity to epinephrine 305

first infusion after ephedrine, and during the second postephedrine infusion 24 hours later there was still no appreciable rise in heart rate. Statistical analysis revealed that the pulse rates during the first postephedrine infusion were significantly lower than during the first control infusion (p < 0.01 for all 4 hours) and less than those during the second control infusion (p < 0.01 first and second hours and p < 0.05 third and fourth hours). During the first hour the pulse was significantly slower during the first compared to the second post- ephedrine infusion (p < 0.05). Pulse rates were significantly lower during the second postephedrine infusion compared to the first control infusion (p < 0.01 second and fourth hours and p < 0.05, third hour) and compared to the second control infusion during the second hour ( p < 0.05).

The mean preinfusion blood glucose levels for the 4 infusions were: first control, 88 -I 6 mg./lOO ml.; second control, 92 t 9 mg./lOO ml.; first post- ephedrine, 86 + 6 mg./lOO ml. and second postephedrine, 87 + 10 mg./lOO ml. These values are not significantly different. The change in blood glucose in response to the epinephrine infusions is shown in Fig. 3. There was no significant difference in the glucose response to the two control infusions. There also was no significant difference in the glucose response during the two postephedrine epinephrine infusions. There were, however, highly significant differences be- tween the two control infusions on the one hand and the two postephedrine infusions on the other, becoming evident after 1 hour and continuing throughout the d-hour infusions. The values during the first postephedrine infusion were lower than those of the first control infusion at 120 and 180 minutes (p < 0.01) and 240 minutes (p < 0.05)) and significantly lower than during the second control infusion at 120 minutes (p < 0.01) and 180 minutes (p < 0.05). The values during the second postephedrine infusion were significantly less than during the first control infusion at 60 minutes (p < 0.05) and 120 and 180 minutes (p < 0.01) ; they were significantly lower than values during the second control infusion at 60 minutes (p < 0.05 and 120 minutes (p < 0.01).

The mean preinfusion blood lactate values were: first control, 117 t 77 ng./ml., second control, 127 & 46 ng./ml., first postephedrine, 117 + 36 ng./ml., and second postephedrine, 112 ? 28 ng./ml. These values do not differ signifi- cantly from each other. The responses of the blood lactate to epinephrine infusion are shown in Fig. 4. There was a progressive rise in blood lactate during the first control infusion. The rise in lactate was significantly lower during the second control infusion 24 hours later (p < 0.05 at 180 minutes and p < 0.01 at 240 minutes). The lactate response after one week of ephedrine was con- sistently but not significantly lower than the first control infusion. The lactate values during the second postephedrine infusion, however, were the lowest beginning at 60 minutes and were significantly lower than those of the first control infusion (p < 0.05 at 60, 120, and 180 minutes and p < 0.01 at 240 minutes).

The mean preinfusion values for blood-free fatty acids were not significantly different. The rise in free fatty acids was least in the first infusion following ephedrine, but the differences between infusions were not marked and the values were not significantly different from each other.

306 Nelson et cd. J. ALLERGY CLIN. IMMUNOL. MAY 1975

The total eosinophil counts performed prior to the epinephrinc infusions and after 4 hours with the percentage fall were : first control infusion, 135 + 82/mm.“, 31 + 19/mm.” (-77%) ; second control infusion, 111 rt 54/mm.“, 35 + 22/mm.:’ (-69%) ; first postephedrine infusion, 112 * 56/mm.“, 50 ? 33/nun.:’ (-56%) ; and second postephedrine infusion, 144 k ll/mm.“, 52 t 46/mnl.3 (-64%). Whilr the percentage fall is less following ephedrine, the differences were not statisti- cally significant.

The rate of urinary excretion of cyclic adenosine monophosphate was mea- sured overnight prior to each infusion and during each of the 4-hour epinephrinc infusions. The mean rate of cyclic AMP excretion prior to the infusion, during the infusion, and the percentage increase were: first control, 326 + 70 nmoles per hour, 472 * 146 nmoles per hour (+49%) ; second control infusion, 345 + 55 nmoles per hour, 538 + 104 nmoles per hour (+550/o) ; first postephedrine in- fusion, 347 + 116 nmoles per hour, 569 + 169 nmoles per hour (+720/F) ; and second postephedrine infusion, 295 2 55 nmoles per hour, 513 f 78 nmoles per hour (+81%). Neither the differences in baseline excretion rate nor in the response to epinephrine infusion are statistically significant.

The post-exercise rise in blood-free fatty acids and lactate was consistently lower following a week of ephedrine administration, however the differences were not statistically significant. The pre-exercise serum lactate level was not, significantly altered by ephedrine administration. Five minutes following the control exercise the lactate peaked at 51.6 ?I 211 ng. per milliliter above the pre- exercise level. Following ephedrine the peak was 368 + 168 ng. per milliliter above the pre-exercise level (KS). The prc-exercise levels of serum-free fatty acids were also not significantly different in the two studies. Again, prior to ephedrine the post-exercise rise in free fatty acids was maximal 5 minutes fol- lowing exercise with a rise of 0.79 t 1.20 mEq. per liter while following ephedrine the 5-minute rise was only 0.29 2 0.72 mEq. per liter (WS) .

There was no evidence of exercise-induced hronchoconstriction following either exercise test. The mean pre-exercise FEV, was 3,480 ? 570 cc. before the exercise test and rose 200 cc. at 10 minutes following exercise. The mean FEVl prior to the second study was 3,535 + 498 and rose 205 cc. at 10 minutes fol- lowing exercise.

DISCUSSION

The present study confirms our previous finding that the administration of ephedrine sulfate for 1 week to normal adults results in subsensitivity of many beta adrenergic effector cells to the subsequent administration of epinephrine.‘” Following ephedrine the epinephrine-induced rise in blood glucose and blood lactate was less; there was a rise rather than a fall in the mean blood pressure and slowing of the pulse rate rather than tachycardia. Another aspect of the ephedrine-induced subsensitivity to beta adrenergic stimulation which this study provides some insight into is its duration. Although the total duration of altered responses has not been established, it is evident from the data that there were still significant abnormalities of lactate, glucose, mean blood pressure, and p&e

VOLUME 55 NUMBER 5

Subsensitivity to epinephrine 307

responses to epinephrine at the end of the second infusion 38 hours following the last dose of ephedrine.

It is also evident that the administration of epinephrine under the conditions of this study alters the beta adrenergic responses to a second administration of epinephrine 24 hours later. This altered response to the second control infusion was evident in many of the studies performed, but was statistically significant only in the rise in blood lactate.

The pattern of altered responsiveness to beta adrenergic stimulation fol- lowing ephedrine that was observed in this study is the same as has been induced ip normal individuals by experimental beta adrenergic blockade with pro- pranolol. Of the parameters measured that did not show significant changes following ephedrine, there was a trend in some instances for the response to be altered in the direction that would be induced by beta adrenergic blockade, but the degree of change was not statistically significant. Thus the rise in free fatty acids and lactate following exercise and the rise in free fatty acids during epinephrine infusion were lower following ephedrine than in the respective control studies. Also the epinephrine-induced fall in the total eosinophil count was least following ephedrine, but the differences from the control period were not significant.

In two instances the data did not change in a direction that would suggest occurrence of partial beta adrenergic blockade. There was no fall in the FEV, following exercise either before or after ephedrine. Zaid, Beall, and Heimlich,‘” however, have reported that the administration of propranolol to normal indi- viduals in doses sufficient to block the ionotropic response to epinephrine did not induce a post-exercise bronchoconstriction. The other response that did not show a trend that would suggest the occurrence of partial beta adrenergic blockade was the change in the urinary excretion of cyclic AMP. While the changes in excretion rate during the 4 epinephrine infusions were not significantly dif- ferent, the trend was toward a greater increase in cyclic AMP excretion fol- lowing ephedrine than before. The urinary excretion of cyclic AMP may not be a suitable measure of beta adrenergic responsiveness. Ball and coworkerszo have shown that only a portion of the urinary cyclic AMP is derived from the plasma, the remainder being of renal origin. With experimental beta adrenergic blockade in normal individuals, the plasma cyclic AMP response to beta stimulation is decreased, but the nephrogenous cyclic AMP response increases, and urinary excretion of cyclic AMP may rise.

The present studies do not permit final conclusions regarding the mechanism by which ephedrine and epinephrine alter the subsequent responses to beta adrenergic stimulation. It seems unlikely that accelerated destruction of epi- nephrine is responsible in view of the variability with which ephedrine and epinephrine induce altered responses and the varying duration that these altered responses persist. The first control epinephrine infusion, for example, profoundly altered the response of the blood lactate to the second control infusion, but had little effect on the response of the blood glucose to the second control infusion. The effect of ephedrine on the mean blood pressure and pulse rate responses to

308 Nelson et 01. J. ALLERGY ClIN. IMMUNOL. MAY 1975

epinephrine appeared to he definitely subsiding by the second postephcdrine infusion, while a return toward normal responsiveness was not apparent in the glucose and lactate responses to the second post-ephedrine infusion. It is also unlikely that the altered responsiveness is related to the known effect of ephcd- rinc in mobilizing norepinephrine from nerve endings. Sot only should norcpi- ncphrine depletion not produce a pieturc of depressed beta adrrncrgic respon- siveness, but also the induction of similar changes b.v epinephrine administration would argue against norepinephrinc depletion as the responsible mechanism. There remain several possible mechanisms for the obscrvcd changes. Thcrc could be binding of receptor sites on the cx~lls, substrate depletion, or induction of altered intracellular enzyme activity such as decreased activity of adenyl eyclasc or increased activity of phosphodiesterasc. Any of these possibilities would be compatible with the observations.

Diminished responsiveness induced by chronic administration of an adrencrgic agonist has been reported previously with isoproterenoP’ and epinephrine.2z Fleming, NcPhillips, and Westfall 25 have reviewed the altered sensitivity to acetylcholinc that can be induced by chronically increasing or decreasing the levels of the transmitter bathing the effeetor cell~.~:’ When acetyleholine levels are increased by inhibiting cholinesterase activity, there is a gradual decrease in response of the effector cells to acetylcholine that requires 2 to 3 days to develop and persists several days after acetylcholine levels return to normal. They termed this adaptation of the effcctor cells t.o increased levels of acetyleholine “sub- sensitivity” and suggested that it was a widespread physiologic phenomenon. The altered response to epincphrine that results from chronic ephedrine adminis- tration would appear to have many of the same characteristics as “subsen- sitivity,” particularly its persistence for significant periods following the last administration of ephedrine. It remains to be detcrmincd whether the altered responsiveness that followed cpinephrine in these studies reflects the sarnc adaptive mechanism.

The altered reactivity to beta adrenergie stimulation inducetl by cphedrint does not have any known deleterious effect on normal individuals or patients with bronchial asthma. Especially there arc no data t,hat specifically establish any altered reactivity of the bronchial tree resulting from ephedrine administra- tion. On the other hand, it has been reported 24 that the bronchodilator effect of ephedrine is diminished with chronic administration, and this may reflect the induction of similar changes in the bronchi to those reported in other organs in this study. There is, at present, no evidence of any airway hyperrtactivitp OI depressed response to the bronchodilating properties of agents such as iso- proterenol and epinephrine resulting from chronic ephetfrinc administration. However, this possibility should bc investigated.

Another implication of the results of these studies is on investigations into the presence of an adrenergic defect underlying bronchial asthma. The induction of altered beta adrenergic responses by epinephrinc and ephedrine underlines the necessity, when studying patients with asthma, of considering the et&et that chronic administration of drugs may have had on the patients’ autonomic responses.

VOLUME 55 Subsensitivity to epinephrine 309 NUMBER 5

We gratefully acknowledge the assistance and advice given us by Robert H. Herman,

M.D., Colonel, MC., Chief, Metabolic Division, USAMRNL, and the nursing assistance rendered by Janis Mullinnix, Captain, Army Nurse Corps, and Susie Sherrod, Captain, Army

Nurse Corps.

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22 Izard, S. R., Henson, E. C., Collins, A. D., and Brunson, J. G.: Increased sensitivity to anaphylactic shock in guinea pigs induced by prolonged treatment with epinephrine prior to challenge,J. ALLERGY 47: 309, 1971.

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24 Herxheimer, H.: Dosage of ephedrine in bronchial asthma and emphysema, Br. Med. J. 1: 350, 1946.