[Biosynthesis and secretion of vasopressin]

Oxytocin and vasopressin (AVP), which are octapeptides with a molecular mass of approximately 1.1 kd, are posterior pituitary hormones. AVP produced by magnocellular neurons in the supraoptic and paraventricular nuclei of the hypothalamus is in a form bound to the specific peptide neurophysin II, in the neurosecretory granula (NSG). Cleavage of this prohormone occurs within the NSGs during its transport via the axons to the neurohypophysis. Neurohypophyseal secretion of these peptides is believed to occur by exocytosis, which might be regulated by intracellular Ca++. The biosynthesis and secretion of AVP are mainly regulated by plasma osmolality (osmotic regulation) and blood pressure or blood volume (nonosmotic regulation). Some drugs, neurotransmitters, and other chemical agents modulate the regulation of AVP release.