1. Posterior Pituitary Hormones
Arginine vasopressin
Oxytocin
May 14, 2019
posterior pituitary

2. Posterior Pituitary Called neurohypophysis
Composed glial cells (pituicytes)
They are the supporting cells for
Nerve terminals that originate in the supraoptic & paraventricular nuclei
Nerve endings lie on the capillaries
Release vasopressin & oxytocin
May 14, 2019
posterior pituitary

3. Hormones of Posterior Pituitary
The hormones of the posterior pituitary
Arginine vasopressin (ADH, vasopressin)
Oxytocin
May 14, 2019
posterior pituitary

4. Structure Arginine Vasopressin S S NH2 Tyr Phe Gln Asn Cys Pro Arg Gly3 4 5 6 7 9 1 2 8 S S
Oxytocin
NH2
Cys
Tyr
Ile
Gln
Asn
Cys
Pro
Leu
Gly 2 3 4 5 7 1 6 8 9
May 14, 2019
posterior pituitary

5. Structure Vasopressin & oxytocin Small peptide hormones
Have nine AA residues
Have similar structure except
They differ by 2 amino acids
May 14, 2019
posterior pituitary

6. Synthesis They are synthesized by the magnocellular neurons of
Para ventricular nucleus
They are synthesized by the magnocellular neurons of
Supraoptic nucleus
Paraventricular nucleus
Supra- optic nucleus
Posterior pituitary
Axon transport
May 14, 2019
posterior pituitary

7. Synthesis ADH is formed primarily in
Para ventricular nucleus
ADH is formed primarily in
Supraoptic nucleus
Oxytocin is formed mainly in the paraventricular nucleus
Supra- optic nucleus
Posterior pituitary
Axon transport
May 14, 2019
posterior pituitary

8. Synthesis Both hormones can be synthesized in either nuclei
Para ventricular nucleus
Both hormones can be synthesized in either nuclei
Vasopressin neurons & oxytocin neurons are found in both nuclei
Supra- optic nucleus
Posterior pituitary
Axon transport
May 14, 2019
posterior pituitary

9. Synthesis They are synthesized in hypothalamic nuclei
Para ventricular nucleus
They are synthesized in hypothalamic nuclei
Transported to posterior pituitary
Down the axons by
Axon-transport system
They are secreted from the axon terminal
In response of action potentials in axon terminal
Supra- optic nucleus
Posterior pituitary
Axon transport
May 14, 2019
posterior pituitary

10. Synthesis Like other peptide hormones Post. Pit hormones
Synthesized as part of
Larger precursor molecule
May 14, 2019
posterior pituitary

11. Synthesis Pre-propressophysin Pre-pro-oxyphysin Vasopressin 9AA
Glycopeptide 39AA
Neurophysin II 95 AA
Signal peptide 19AA
Pre-propressophysin
Signal peptide 19AA
Neurophysin I 95 AA
Oxytocin 9AA
Pre-pro-oxyphysin
May 14, 2019
posterior pituitary

12. Synthesis The precursor for vasopressin is Pre-propressophysin
Contain 19 AA residue leader sequence
Followed by vasopressin
Followed by neurophysin II and
A gylcopeptide
May 14, 2019
posterior pituitary

13. Synthesis The precursor for oxytocin Prepro-oxyphysin
Similar to prepropressophysin but
Lacks the glycopeptide
May 14, 2019
posterior pituitary

14. Synthesis Precursor molecule Transported down axon to terminal
Synthesized in ribosomes of cell bodies of neurons
Leader sequence is removed in endoplasmic reticulum
Packaged in Golgi apparatus
Transported down axon to terminal
Axoplasmic transport system
May 14, 2019
posterior pituitary

15. Synthesis Cleavage of precursor molecule occur
As they are being transported
Stored in granules (Herring bodies) which contain
Free vasopressin + neurophysin-II
Free oxytocin + neurophysin-I
May 14, 2019
posterior pituitary

16. Effects of Vasopressin
Cause retention of water by the kidneys
Hence called “antidiuretic hormone”
 permeability of collecting duct
Water enters the hyper-tonic interstitium of renal pyramids
Urine becomes concentrated & its volume 
May 14, 2019
posterior pituitary

17. Vasopressin Effects The overall effect In the absence of ADH
Retention of water in excess of solute
 effective osmotic pressure of body fluids
In the absence of ADH
Urine is hypotonic
 urine volume
There is net water loss
 osmolarity of body fluids
May 14, 2019
posterior pituitary

18. Mechanism of Action of ADH
The antidiuretic effects
Mediated by activation of V2 receptors
Facilitate the insertion of water channels (aquaporin) in the luminal membrane of collecting ducts
May 14, 2019
posterior pituitary

19. Mechanism of Action of ADH
Under normal conditions
Aquaporins are stored in endosomes inside the cells
Binding of ADH to receptor
Activate Gs protein
Receptor
Adenyl cyclase
Gs protein
ATP
cAMP
Prot. Kinase-A
Phosphorylated Prot. Of vesicles
Insertion of vesicles in membrane
May 14, 2019
posterior pituitary

20. Mechanism of Action of ADH
Which in turn activates
Adenyl cyclase enzyme
ATP is converted to cAMP
This leads to phosphorylation of the vesicles which leads to
There translocation into membrane
 Permeability
Receptor
Adenyl cyclase
Gs protein
ATP
cAMP
Prot. Kinase-A
Phosphorylated Prot. Of vesicles
Insertion of vesicles in membrane
May 14, 2019
posterior pituitary

21. Vasopressin
Stimuli that cause increase in secretion of vasopressin include
 in effective osmotic pressure of plasma
 in ECF volume
Pain , emotion
Stress – surgical operation
Nausea, vomiting
Angiotensin II
May 14, 2019
posterior pituitary

22. Vasopressin Stimuli that inhibit ADH secretion
 effective osmotic pressure of blood
 in ECF volume
Alcohol
May 14, 2019
posterior pituitary

23. Effects of Oxytocin Oxytocin acts primarily on Oxytocin receptors
Breasts & uterus
Oxytocin receptors
G protein coupled receptors
Found in human uterine muscles & mammary glands
It triggers  levels of intra-cellular ca++
May 14, 2019
posterior pituitary

24. Effects of Oxytocin In mammals oxytocin causes
Contraction of myoepithelial cells
Smooth muscle-like cells that line the duct of breasts
Squeeze milk out of alveolar of lactating breast into sinuses
Cause milk ejection
May 14, 2019
posterior pituitary

25. Milk Ejection Reflex Touch receptors around breast nipple
Supraoptic paraventricular
Touch receptors around breast nipple
Generate impulses
Relayed to hypothalamus
Cause oxytocin release
Post pit.
Oxytocin
Milk ejection
Touch receptor on breast
May 14, 2019
posterior pituitary

26. Milk Ejection Reflex Infant suckling at breast
Supraoptic paraventricular
Infant suckling at breast
Stimulate touch receptors
Hypothalamic nuclei stimulated
Oxytocin released
Milk is expressed into sinuses
Ready to flow into the mouth
Post pit.
Oxytocin
Milk ejection
Touch receptor on breast
May 14, 2019
posterior pituitary

27. Milk Ejection Reflex In lactating women
Supraoptic paraventricular
In lactating women
Genital stimulation & emotional stimuli
Produce oxytocin secretion
Post pit.
Oxytocin
Milk ejection
Touch receptor on breast
May 14, 2019
posterior pituitary

28. Other Actions of Oxytocin
Cause contraction of uterine muscles
Sensitivity of uterine muscle
Enhanced by oestrogen
Inhibited by progesterone
May 14, 2019
posterior pituitary

29. Other Actions of Oxytocin
In late pregnancy
Uterus becomes very sensitive to oxytocin
Due to  number of receptors
May 14, 2019
posterior pituitary

30. Other Actions of Oxytocin
Hypothalamus
Descent of fetus
Stimulate cervix
Impulses relayed to hypothalamus
Oxytocin secreted by post pituitary
Oxytocin causes
 contraction of uterine muscles
Post pit
Oxytocin
Pressure of fetal head on cervix
May 14, 2019
posterior pituitary