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Vasopressin

Antidiuretic hormone (ADH), or arginine vasopressin (AVP), is a peptide hormone produced by the hypothalamus, and stored in the posterior part of the pituitary gland. ADH acts on the kidneys, concentrating the urine by promoting the reabsorption of water from the cortical collecting duct.

Contents

1 Physiology 1.1 Control 1.2 Actions 2 Pharmacology 3 Role in disease

Physiology

Control

ADH is activated by "water receptors" in both the extracellular fluid volume and the intracellular fluid volume. Ethanol and caffeine block the release of ADH from the posterior pituitary gland. This decrease in water reabsorption leads to a higher volume of urine output.

In the extracellular fluid the activators are mainly baroreceptors in the veins, atria, and arterioles. In the intracellular fluid the activators are mainly osmoreceptors in the hypothalamus.

Actions

ADH acts on three different receptors, termed V1a, V1b and V2. The receptors are differently expressed in different tissues, and exert different actions:

• V1a - vasoconstriction, gluconeogenesis in the liver, platelet aggregation and release of factor VIII and von Willebrand factor.
• V1b - corticotropin secretion from the pituitary gland.
• V2 - control of free water clearance in the renal medulla (through adenylate cyclase).

Pharmacology

ADH is used therapeutically in various conditions, and its long-acting synthetic analogue desmopressin is used in conditions featuring low ADH, as well as for control of bleeding (in some forms of von Willebrand disease) and in extreme cases of bedwetting by children. Terlipressin and related analogues are used as vasocontrictors in certain conditions.

A new class of medication (conivaptan, tolvaptan, relcovaptan, lixivaptan) acts by inhibiting the action of ADH on its receptors (V1 and V2), with tolvaptan acting on V1a and V2 and the remainder mainly on V1a. The main use of these agents is expected to be the treatment of hyponatremia (low blood sodium levels), which may be due to increased secretion of ADH.

Role in disease

Decreased ADH release leads to diabetes insipidus, a condition featuring hypernatremia (increased blood sodium content), polyuria (excess urine production) and thirst.

Raised ADH (syndrome of inappropriate antidiuretic hormone) occurs in brain diseases and conditions of the lungs. It features hyponatremia.

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