A patient with refractory vasodilatory shock is unresponsive to norepinephrine. The intensivist adds vasopressin. Which receptor subtype mediates vasopressin-induced vasoconstriction in peripheral vascular smooth muscle?

• A V2 receptor coupled to Gs protein
• B V1b receptor coupled to Gi protein
• C OT receptor coupled to Gq protein
• D V1a receptor coupled to Gq protein ✓

Explanation

Vasopressin-induced peripheral vasoconstriction is mediated by V1a (also called V1) receptors coupled to Gq protein, which activates phospholipase C, increases IP3 and DAG, raises intracellular calcium, and contracts vascular smooth muscle. V2 receptors in renal collecting ducts are Gs-coupled and mediate antidiuretic effects via cAMP and aquaporin-2 insertion. V1b receptors are found in the anterior pituitary mediating ACTH release. OT (oxytocin) receptors share structural homology but are not the primary target for vasopressor effects.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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