antidiuretisch

Antidiuretisch, or antidiuretic, refers to processes and substances that reduce urine output by promoting water reabsorption in the kidneys. The main endogenous antidiuretic hormone is vasopressin (antidiuretic hormone, ADH), produced in the hypothalamus and released from the posterior pituitary in response to signals such as increased plasma osmolality or decreased blood volume.

Mechanism: ADH binds to V2 receptors on principal cells of the kidney’s collecting ducts, activating a cAMP signaling pathway that triggers insertion of aquaporin-2 water channels into the apical membrane. This increases water permeability, enhances water reabsorption, concentrates the urine, and stabilizes plasma osmolality and volume.

Regulation: Release is driven primarily by increased plasma osmolality detected by hypothalamic osmoreceptors. Decreased blood volume or pressure, detected by baroreceptors, and other stress-related factors can also stimulate release. Alcohol inhibits ADH secretion, tending to increase urine production; caffeine has milder inhibitory effects.

Clinical relevance: Disturbances of ADH secretion or action disrupt water balance. Central diabetes insipidus results from insufficient ADH production, causing polyuria and polydipsia. Nephrogenic diabetes insipidus involves renal insensitivity to ADH. Syndrome of inappropriate antidiuretic hormone secretion (SIADH) causes excessive ADH activity, leading to hyponatremia and concentrated urine. Treatments include desmopressin for central diabetes insipidus; fluid restriction and, in some cases, vasopressin receptor antagonists for SIADH, with careful monitoring to avoid rapid shifts in serum sodium.