Antidiuretic hormone, also known as vasopressin is a hormone released by the posterior pituitary. It is important mainly for its actions on the kidneys where it increases the re-absorption of water. Vasopressin is also a powerful vasoconstrictor. Its effects are through two types of receptors, V1 and V2.
Water retention is mediated through V2 receptors, occurs at low plasma concentrations of vasopressin and is due to activation of adenylate cyclase and increased cAMP production in the collecting ducts of the nephrons. It increases the permeability of the membrane to water.
Vasopressin causes contraction of smooth muscle, mainly in the cardiovascular system. Vasocontriction occurs by mediation of V1 receptors and requires higher concentrations if vasopressin.
