antidiuretic hormone (ADH), a hormone that decreases the production of urine by increasing the reabsorption of water by the renal tubules. It is secreted by cells of the hypothalamus and stored in the neurohypophysis. ADH is released in response to a decrease in blood volume, an increased concentration of sodium or other substances in plasma, pain, stress, or the action of certain drugs. ADH causes contraction of smooth muscle in the digestive tract and blood vessels, especially capillaries, arterioles, and venules. Acetylcholine, methacholine, nicotine, large doses of barbiturates, anesthetics, epinephrine, and norepinephrine stimulate ADH release; ethanol and phenytoin inhibit production of the hormone. Increased intracranial pressure promotes inappropriate increases and decreases in ADH. Synthetic ADH is used in the treatment of diabetes insipidus. Normal values are 1 to 5 pg/mL or less than 1.5 ng/L. Also called vasopressin.
