Oxytocin causes ail EXCEPT:
ANSWER: (D) Milk productionREF: Ganongs 22nd ed p- 243, www.ncbi.nlm.nih.gov/pubmed/7922507OXYTOCIN:Oxytocin is a peptide of nine amino acids (a nonapeptide)released by the human posterior pituitary glandActions:Oxytocin has peripheral (hormonal) actions, and also has actions in the brain. Its actions are mediated by specific, high-affinity oxytocin receptors. The oxytocin receptor is a G-protein-coupled receptorActs on myoepithelial cells of the ducts in the breast to squeeze the milk out of areola of iactating breast causing galactokinesis or milk ejection or letting down reflex. Remember milk production is not a function of oxytocinInitiation of labour: it acts on uterine musculature to cause its contraction and initiates labour via positive feed back mechanism. However it's important to note that oxytocin acts on an endometrium primed by estrogen, and progesterone antagonises this function of oxytocin.It also acts on non pregnant uterus to cause sperm transportIt has been found that since the structure of oxytocin is similar to vasopressin it can act on VI receptors in the brain , although the effect is 10 times lesser , hence large doses of oxytocin can cause a state similar to vasopressin excessGiven as syntocinon for induction of labour in intravenous or nasal spray forms. Atosiban a tocolytic is its antagonistThere are three vasopressin receptors. They are ah G protein linked.VIAV1BV2* Acts by phosphatidyl hydrolysis* Located in area postrema, liver, spinal cord* Mediates vasoconstrictor action* Acts by phosphatidyl hydrolysis* Located in anterior pituitary to cause ACTH release* Also called V3 receptors* Neural action* Stimulates adenyl cyclase* Expressed in anterior pituitary and DCT of kidney and liver.* Antidiuretic action* Loss of this causes diabetes insipidus* Now called aquaporins and 5 types have been found aquaporin 1,2,3 found in kidney , aquaporin 4 in brain, and aquaporin 5 in lacrimal and salivary gland
Milk ejection
Induction of labour
Attaches to VI receptors
Milk production
Pituitary