Veterinary Physiology-III

OXYTOCIN

• It is a peptide hormone containing 8 amino acids.
• Seven amino acids are common between oxytocin and ADH.
• Oxytocin has a half life of 2 min.
• Oxytocin has specific effects on the smooth muscle of the uterus and the myoepithelial cells of the mammary gland.
• It also functions in the release of prostaglandins from the endometri­um.
• Along with estrogen and PGF₂ alpha , it causes powerful contractions in the pregnant uterus and helps in parturition.
• It helps sperm transport in estrogen-primed uterus during follicular phase of estrous cycle.
• In male it is released during mating to cause movement of sperm through the male duct system for ejaculation.
• On the udder it causes contraction of myoepithelial cells which results in milk letdown by a neuroendorcine reflex.
• Suckling stimulates hypothalamus, causes oxytocin release from neurohypophy­sis.
• In birds it has the ability to lower BP.
• Oxytocin is also secreted by corpus luteum which acts with estrogen and PGF to cause lysis of CL.
• CL also produces oxytocin .
• Gonadotropins, PGF and progesterone stimulate oxytocin from CL. At the end of luteal phase, when progesterone effect on CL is reduced, oxytocin induces luteolysis by initiating release of PGF2 alpha from endometrium.