Vasopresin

Vasopresin, more commonly spelled vasopressin, is a peptide hormone of the neurohypophysis that regulates body water balance and vascular tone. It is also known as arginine vasopressin (AVP) or antidiuretic hormone (ADH). Vasopressin is a nonapeptide with a disulfide bond between two cysteine residues and is produced as part of a larger precursor in hypothalamic magnocellular neurons before being released from the posterior pituitary into the bloodstream.

Vasopressin acts through three receptor subtypes: V1a, V1b, and V2. V1a receptors, located on vascular smooth muscle, mediate vasoconstriction and some social and behavioral effects. V1b receptors, found mainly in the pituitary, stimulate adrenocorticotropic hormone (ACTH) release in response to stress. V2 receptors, expressed in the kidney’s collecting ducts, promote water reabsorption by increasing the insertion of aquaporin-2 water channels into the apical membrane, concentrating the urine.

Regulation of vasopressin release is driven primarily by plasma osmolality and, to a lesser extent, by blood volume. Osmoreceptors in the hypothalamus detect increased osmolality or dehydration, triggering hormone release. Baroreceptors respond to falls in blood pressure or volume, modulating release accordingly.

Clinically, vasopressin deficiency underlies central diabetes insipidus, characterized by polyuria and polydipsia, whereas nephrogenic diabetes insipidus arises from renal insensitivity to vasopressin. Pharmacologically, desmopressin is a selective V2 agonist used to treat central diabetes insipidus and certain bleeding disorders, while vasopressin itself serves as a vasopressor in critical care. Careful management is required to avoid hyponatremia and fluid imbalance.