In an isolated artery preparation, acetylcholine relaxes the vessel only when the endothelium is intact; it has no effect after the endothelium is removed. The second messenger responsible for this relaxation is:

• A cGMP generated by soluble guanylate cyclase ✓
• B cAMP generated by adenylate cyclase
• C IP3-mediated calcium release
• D Direct opening of potassium channels

Explanation

Acetylcholine acts on endothelial M3 receptors, stimulating nitric oxide synthase to produce NO, which diffuses to smooth muscle and activates soluble guanylate cyclase, raising cGMP and causing relaxation. This explains the endothelium dependence. IP3 and calcium would cause contraction, not relaxation, and cAMP is the pathway used by beta-2 agonists such as isoproterenol, not by acetylcholine.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.