Vasopressin (ADH): Definition

Detailed Explanation

Vasopressin (also called antidiuretic hormone, ADH, or arginine vasopressin/AVP) is a 9-amino-acid cyclic peptide hormone (Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly-NH₂) with a disulfide bridge between Cys1 and Cys6. Like oxytocin, it is synthesized in the hypothalamus and released from the posterior pituitary. Vasopressin differs from oxytocin at only two positions: Phe3 (vs. Ile in oxytocin) and Arg8 (vs. Leu in oxytocin).

Vasopressin's primary physiological role is water conservation. It acts on V2 receptors in the kidney collecting ducts to insert aquaporin-2 water channels, allowing water reabsorption from urine back into the bloodstream. This concentrates the urine and prevents dehydration. Deficiency causes diabetes insipidus — a condition of massive dilute urine output (up to 20 liters/day) unrelated to diabetes mellitus. Vasopressin also constricts blood vessels (via V1a receptors), stimulates ACTH release from the pituitary (via V1b receptors), and modulates social behavior, aggression, and pair-bonding in mammals.

Clinically, synthetic vasopressin (desmopressin/DDAVP) is used to treat diabetes insipidus, bedwetting (nocturnal enuresis), hemophilia A (it releases stored von Willebrand factor), and as a vasopressor in septic shock. Vasopressin receptor antagonists (tolvaptan, conivaptan) — called 'vaptans' — treat hyponatremia (low sodium) caused by excess vasopressin in conditions like heart failure and SIADH.

Key Facts

← Back to Full Dictionary