Vasopressin (arginine vasopressin, AVP; antidiuretic hormone,ADH) plays an important role in the long-term control of bloodpressure through its action on the kidney to increase water reab-sorption.
AVP also plays an important role in the short-term regula-tion of arterial pressure by its vasoconstrictor action. It increases total peripheral resistance when infused in doses less than those required to produce maximum urine concentration. Such doses do not normally increase arterial pressure because the vasopressor activity of the peptide is buffered by a reflex decrease in cardiac output. When the influence of this reflex is removed, eg, in shock, pressor sensitivity to AVP is greatly increased. Pressor sensitivity to AVP is also enhanced in patients with idiopathic orthostatic hypotension. Higher doses of AVP increase blood pressure even when baroreceptor reflexes are intact.