Atrial natriuretic peptide lowers blood pressure by binding to a receptor on vascular smooth muscle and renal tubular cells. The second messenger generated directly by this receptor is:

• A cAMP formed by a Gs-coupled adenylyl cyclase
• B IP3 formed by phospholipase C activation
• C cGMP formed by an intrinsic guanylyl cyclase domain ✓
• D PIP3 formed by phosphoinositide 3-kinase

Explanation

The ANP receptor (GC-A, natriuretic peptide receptor A) has an extracellular ligand-binding domain, a single transmembrane segment, and an intracellular guanylyl cyclase catalytic domain. Ligand binding directly stimulates cGMP production without any G-protein intermediate. cGMP then activates protein kinase G, causing vasodilation and natriuresis. Option A is wrong because ANP signalling is entirely independent of heterotrimeric G proteins; this distinguishes it from most peptide hormone receptors.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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