Arginine Vasopressin (AVP), also called antidiuretic hormone, and oxytocin are peptide hormones of the neurohypophysis, and are also called neurohypophysial peptide hormones, as they are formed in supraoptical and paraventricular nuclei of hypothalamus, where the neurosecretory neurons are located. The axons of these neurons form the supraoptical hypophysial tract that brings the secretory material of these neurons to the posterior lobe of hypophysis. Under the microscope this part of the hypophysis consists of pituicytes, capillaries, and amyelinic fibers that contain neurosecretory granules. Besides vasopressin and oxytocin, such hormones as somatostatin, thyroliberine, and substance P have been extracted from neurohypophysis. It was demonstrated by immunocytochemical and radioimmune methods that oxytocin and vasopressin are synthesized in the neurons of supraoptical and paraventricular nuclei. The hormones that have been synthesized in the hypothalamic nuclei are transported together with the corresponding neurophysines along the axons of neurohypophysial tract into the posterior lobe of the hypophysis, where they are reserved “in case of emergency”. The hormones are transferred along the axons as granules that also contain specific proteins called neurophysines (mol. weight approx 10000). The speed of transport of the hormones along the axons is around 2-3mm/hour. The liberation of vasopressin from the granules is done by means of exocytosis. Vasopressin can be liberated not only in blood, but also in the spinal fluid, where its concentration is lower than in blood plasma. It is suspected that the secretion of hormones into the spinal fluid and the neurohypophysis is done by various neurons of the hypothalamus, as the patients with neurogenic diabetes insipidus, the total amount of vasopressin in the spinal fluid is normal. However besides the main way of transport into the posterior hypophysial lobe, there is a second neurosecretory pathway through the portal system of the hypophysis to the cells of the anterior hypophysial lobe, where these hormones play a vital role in regulating the secretion of adrenocorticotropin. The level of vasopressin in the portal system is higher that in the plasma of the peripheral blood. This indicates the importance of vasopressin in the regulation of hypotonia, hypovolemia, and other conditions that accompany a stressful situation. As was mentioned earlier, the membrane vesicles containing AVP and oxytocin are transported along the axons of hypothalamus’ neurons as a part of hypothalamo-hypophysial tract into the posterior part of the hypophysis, and through axo-vasal synapses are being secreted into the bloodstream. The secretion of oxytocin and AVP is regulated by impulsive axon activity of neurosecretory neurons. At this moment, oxytocin just as AVP detaches from neurophysines and proceeds into the bloodstream. The targets of oxytocin are smooth muscle cells (SMC) of myometrium and myoepithelial cells of the mammary gland. In the uterus, oxytocin stimulates the contraction of myometrium’s SMC during the act of child delivery, orgasm, and menstruation. In the mammary gland oxytocin stimulates the contraction of myoepithe