Oxytocin is a cyclic nonapeptide hormone secreted by the hypothalamus &stored in the posterior lobe of pituitary gland. It causes the uterus to contract. The response is greater during the late stage of pregnancy. Oxytocin also stimulates the smooth muscle associated with secretory epithelium of the lactating breast causing the ejection of milk, but having no direct effect on the milk secretion. It has relatively little pressor or antidiuertic action.