In the absence of ADH, collecting ducts(CD)of the nephron are impermeable to water.ADH increases the permeability of CD by its action on V2 receptors.

Stimulation of these receptors elevates cAMP levels that increase aquaporins on the apical membrane of CD(by decreasing endocytosis and increasing exocytosis).

V2 receptor activation also increases the permeability of CD to urea by stimulating the urea transporter.Vasopressin(ADH)as the name suggests is a potent pressor of blood vessels.

vasoconstrictor action is mediated by the activation of V1(also called V1a)receptors. This action requires a much higher concentration than V2 receptor activation.V2 receptor-mediated vasodilatory action( due to the release of NO) has also been demonstrated.

ADH is also involved in the release of vWF and factor Vlll from the endothelium. This action is also mediated by V2 receptors.V3 receptors(previously known as V1b receptor)are involved in the release of ACTH.

1. A) Loop of Henle
2. B) Proximal tubule
3. C) Distal tubule
4. D) Cortical collecting duct

Ans: D