Vasopressin System
The hormonal system centred on vasopressin (antidiuretic hormone), a 9 amino acid peptide that regulates water balance and blood pressure through V1 and V2 receptors. Vasopressin is used in vasodilatory shock, while desmopressin is a V2-selective analogue for diabetes insipidus and nocturnal enuresis.
Technical Context
Vasopressin (ADH, argipressin) is a 9 amino acid cyclic peptide (Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly-NH2, with a 1-6 disulphide bridge) with three receptor subtypes: V1a (vascular smooth muscle, liver — vasoconstriction, glycogenolysis), V1b/V3 (anterior pituitary — ACTH co-regulation), and V2 (renal collecting duct — water reabsorption via aquaporin-2 insertion). Synthetic vasopressin is used in vasodilatory shock (V1a-mediated vasoconstriction) and cardiac arrest. Desmopressin (1-deamino-8-D-arginine vasopressin) has enhanced V2 selectivity (antidiuretic:pressor ratio approximately 3000:1 vs 1:1 for vasopressin) and longer half-life (~3 hours vs 6-20 minutes), making it suitable for diabetes insipidus, nocturnal enuresis, and von Willebrand disease (V2-mediated release of stored vWF).