V1 receptors cause which vascular effect?

• A. Increased water resorption in the nephrons
• B. Vasoconstriction of vascular smooth muscle
• C. Bronchodilation
• D. Renal and mesenteric vasodilation

Answer: (B)

V1 receptors on vascular smooth muscle mediate vasoconstriction. When vasopressin binds to these receptors, it activates Gq proteins, which stimulate phospholipase C. This leads to the production of IP3 and DAG, increasing intracellular calcium and triggering smooth muscle contraction. That constricts the vessels and raises vascular tone.

The water-resorption effect comes from V2 receptors in the kidney’s collecting ducts, not from V1 in vessels. Bronchodilation is driven by β2-adrenergic receptors in the airways, not vasopressin receptors. While vasopressin can influence different beds under certain conditions, the typical vascular effect of V1 activation is constriction, not dilation.