Vasopressin

Vasopressin, also called antidiuretic hormone (A D H) or arginine vasopressin (AVP), is another hormone key to water homeostasis and blood pressure regulation. A rginine vasopressin is produced in the neurones of the hypothalamus and stored in vesicles within the posterior pituitary. Vasopressin is released in response to increased blood osmolality detected by hypothalamic osmoreceptors; systemic hypotension or hypovolaemia detected by cardiopulmonary baroreceptors of the great veins and atria; or angiotensin I I acting on the hypothalamus.

Vasopressin is a peptide hormone secreted by the hypothalamus via the posterior pituitary. Its primary role is the regulation of body fluid balance. It is secreted in response to hypotension and promotes retention of water by action on specific cAMP-coupled V2 receptors. It causes vasoconstriction by stimulating V1 receptors in VSM and is particularly potent in hypotensive patients. It is increasingly used in the treatment of refractory vasodilatory shock which is resistant to catecholamines. The vasopressin analogue desmopressin is used to treat diabetes insipidus and in the management of von Willebrand's disease. Terlipressin (another analogue) is used to limit bleeding from oesophageal varices in patients with portal hypertension. When used for the management of low SVR states, vasopressin is administered as an i.v. infusion at a rate of 0.01–0.1 units min–1.

Human vasopressin, or Arg-vasopressin, is chemically very similar to oxytocin and therefore sometimes is referred to as [Phe3, Arg8]oxytocin. The physiological role of vasopressin is the regulation of water reabsorption in the renal tubules (an antidiuretic action, thus often referred to as the antidiuretic hormone). In high doses, vasopressin promotes the contraction of arterioles and capillaries, resulting in an increase in blood pressure, thus the name vasopressin. An inadequate output of pituitary antidiuretic hormone can cause diabetes insipidus, which is characterized by the chronic excretion of large amounts of pale urine and results in dehydration and extreme thirst.

The nonapeptide vasopressin is well known for its role on fluid metabolism, but it also is a key regulator of the HPA axis. Stress stimulates the release of vasopressin in the pituitary gland, where it strongly potentiates the effects of CRF on adrenocorticotropic hormone release. These findings suggest that HPA axis dysregulation in depression might be associated with the development of centrally acting vasopressin receptor antagonists for the treatment of depression.