Posterior Pituitary gland_2

8/7/2019 Posterior Pituitary gland_2

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Endocrine PhysiologyEndocrine PhysiologyPosterior pituitary hormonesPosterior pituitary hormones


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The posterior pituitary glandThe posterior pituitary gland

y Composed mainly of cellscalled Pituicytes, which

act as packing & supportingcells.

y Stores & releases hormonesinto the close capillaries.

y These hormones areproduced in hypothalamus.


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The posterior pituitary gland hormonesThe posterior pituitary gland hormones

Posterior pituitary gland releases 2 hormones:

1. Antidiuretic hormone (ADH), or arginine vasopressin(AVP).

2. Oxytocin

Both hormones are produced in hypothalamic nuclei:

- Supraoptic nucleus p (ADH + 1/6 oxytocin)- Paraventricular nucleus p (Oxytocin + 1/6 ADH)


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The posterior pituitary gland hormones cont.The posterior pituitary gland hormones cont.

y Both hormones are polypeptides, each contains 9amino acids.

Both are transported slowly along thehypothalamo-hypophyseal tract in combinationwith carrier protein called neurophysin, to the

nerve endings in the posterior pituitary gland wherethey are stored.


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The posterior pituitary hormonesThe posterior pituitary hormones

11. ADH (vasopressin):. ADH (vasopressin):

Antidiuretic hormone (ADH), or arginine vasopressin(AVP), is produced mainly in SON of hypothalamus.

ADH activates (2) second messenger systems:1. cAMP2. IP3/Ca

2+


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Action of ADHAction of ADH

ADH has 2 main effects:

1. o water re-absorption (retention) by distal tubules& collecting ducts of the kidneys p decreaseosmotic pressure of the blood.

* This effect is regulated by V2 receptors, through theaction of cAMP.

2. Contraction of vascular smooth muscles pgeneralized vasoconstriction.

* This effect is regulated by V1 receptors, through the actionof IP3/Ca

2+.


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Control of ADH releaseControl of ADH release

1. o in osmotic pressure of the ECF (o in plasmaosmolality), as in dehydration which will stimulateosmoreceptors in the hypothalamus p oADH.

Hyperosmolarity of ECF

Receptors inhypothalamus

More ADH release Thirst

Collecting ducts of kidneys

Reabsorption of water

o Water intake

Dilution of ECF

-ve feedback


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Control of ADH release cont.Control of ADH release cont.

Loss of ECF volume

Less pressure in Rt.atrium & great vessels

Less nerve impulse to

the hypothalamus

Thirst

More ADH release

More water reabsorption by kidneys

o Water intake

Maintains ECF volume

2. q blood volume (u 10%) p stimulate mechanoreceptors inthe great arteries (aorta & carotids) & right atrium p oADH.


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Control of ADH release cont.Control of ADH release cont.

3. q arterial blood pressure, due to q blood volume p oADH.

4. Age: p oADH secretion p water retention & hyponatremia.

5. Pain, emotional stress & physical trauma p oADH secretion.

6. Drugs, e.g. morphine, barbiturates, & nicotine p oADH

secretion.

7. Alcohol p qADH secretion.


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Abnormalities of ADH releaseAbnormalities of ADH release

HyposecretionHyposecretion::

Lack of ADH p Diabetes insipidus.

2 types of DI: a. Neurogenic (central, or cranial)Problem in Hypothalamus or Post pituitarygland; could be 1ry or 2ry.R/: ADH.

b. Nephrogenicresistance of V2 receptorsin collecting ducts of the kidneys.

- No ADH is needed as treatment.

Symptoms: Polyurea } 20L/day (N } 1.5 L/d), Polydepsia,q specific gravity of urine (diluted urine),o plasma osmolality.


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Abnormalities of ADH releaseAbnormalities of ADH release

HypersecretionHypersecretion::

oADH, Schwartz-Bartter Syndrome:

p - occurs after surgery.- adenoma, ectopic kidney.- Bronchial carcinoma.

Signs & Symptoms:

- Hyponatremia, i.e. [Na+] q extracellularly to 110 mM.(N = 140 mM); resulting in:- Mental confusion.- Coma.- Death, due to ventricular fibrillation.


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Action of oxytocinAction of oxytocin

1. Contraction of smooth muscles of the uterus penhance labor.

2. Contraction of mammary gland myoepithelial cells ofthe alveoli & the ducts p Ejection of milk as a reflex inlactating women.

3. In men p o ejaculation.

Remember: Oxytocin is concerned with releasing orejection of milk, while prolactin is concerned with

synthesis & production of milk.


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BIOASSAY OF POSTERIOR PITUITARY INJECTION

PRINCIPLE

Potency of the test and the std. sample iscompared with reference to their respective

oxytocic, pressor and anti-diuretic activity

by a biological method.

Standard preparation and unit: 1 unit = 0.5

mg.


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It is the quantity of dried acetone-extractedsubstance obtained from the posterior lobes offresh pituitary glands of oxen. This unit is

specified by the Ministry of Govt. of India and isthe same as the International Unit.


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PREPARATION

Pituitary glands of oxen are obtained from theslaughter house. They are made free from othertissues and extracted repeatedly with acetone toremove the attached tissues. The gland is cut intosmall pieces and again extracted with acetone.

Then, it is dried over cacl2 in an evacuateddesiccators (for five hours). It is powdered andagain dried over phosphorous pentoxide. Then it

Exactly 20 units of the powder is weighed and

extracted with dilute solution of glacial acetic acid.It is diluted to represent finally 2 units/ml. and isstored at0oC.


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OXYTOCIC ACTIVITY

As soon as the female guinea pigswean, they should be separted fromthe males and used for the test whenthey weigh between 170-350 g. theanimal is isolated and one horn issuspended in a bath containing asfollowing


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DALESSOLUTION

Sodium Chloride 9.0 g.

Potassium chloride 0.42 g.

Calcium Chloride 0.24 g.

Glucose 0.50 g.

Magnesium Chloride 0.25 g.Distilled Water add upto 1000 ml.


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The bath is maintained at a temperature of37o

C and is oxygenated. The contractions of the

uterine horn are recorded by a frontal lever on thesurface of a smoked paper fixed on a slowlyrevolving drum.

Standard pituitary extract in a dose of0.55-0 .1unit is added into the inner bath. This causes theuterus to contract, and when contraction iscomplete; the solution of the bath is drained outand fresh solution is run in and the muscle isallowed to relax. Repeated additions of pituitary

extract may be made at regular intervals. Thepotency of the test sample is calculated comparingthe height of contraction with that produced by thestd. sample.

(Refer graphical method of bioassay)


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The carotid artery is cannulated by means of anarterial cannula and then joined to the manometerfor recording B.P on the kymograph. Initially,

normal B.P is recorded .Repeated injections ofpituitary extract are made at regular intervals oftime. A dose of0.05-1 unit at intervals of thirtymen. Will give suitable rise in B.P. a fixed volume ofnormal saline I passed to push the extract towardsthe heart & to maintain blood volume. The doses ofthe standard extract & the test sample are adjusteduntil they produce an equal rise in B.P alternatelywith varying doses of the test sample; till both

produce the same rise in B.P. the activity isexpressed in units/mL.


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ANTI DIURETIC ACTIVITY

The experiment is conducted on sixteen male albinorats. They should not weigh less than 120gm & notmore than 240gm. The animal must be fasted overnight. Warm sterile distilled water is given to themin the doses of 5mL/100gm of body weight,intraperitoneally. Then they are divided in to twogroups & posterior pituitary extract is injected sc.

As follows:


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The rats are put in metabolic cages so that the urine is collected ina graduated measuring cylinder. Following timings are noted:

When each group receives water & an injection of posteriorpituitary.

When urine is first collected in a cylinder for each group and thereafter volume is

After this period, the urine flow stops & observations arediscontinued. Time in minutes for excretion of half the volume ofurine is calculated for each group. Crossover test is carried out after24hours. Those rats which received the std.sample previously arenow given the test sample and vice versa. The experiment is run onsimilar lines, is carried out to minimize errors due to animalvariation. From the results of two parts of the test, mean values areobtained. These mean values should be between 95 and 135 min. If

they are the same for the std. and the test sample, then bothshould contain the same units. If the times are different then therelative potency can be calculated by comparing with the standard.


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Posterior Pituitary gland_2

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