Pharmacology · single question
During a dental appointment, a patient with hyperlipidemia begins having crushing chest pain. Emergency medical services are activated and the patient is given a nitroglycerin tablet sublingually. What is the mechanism of action of nitroglycerin?
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Correct answer: B. Activates guanylyl cyclase
Nitroglycerin (an organic nitrate) is converted to nitric oxide (NO) in vascular smooth muscle. NO activates guanylyl cyclase, which converts GTP to cGMP. Elevated cGMP activates protein kinase G, which phosphorylates myosin light chains, causing smooth muscle relaxation and vasodilation. This reduces preload and myocardial oxygen demand, relieving angina.
- A. INCORRECT. cAMP is the second messenger for beta-adrenergic receptors and phosphodiesterase inhibitors — not nitroglycerin. Nitroglycerin works through the cGMP pathway.
- B. CORRECT. Nitroglycerin → Nitric oxide (NO) → activates guanylyl cyclase → ↑cGMP → smooth muscle relaxation → vasodilation (primarily venous dilation reduces preload, coronary vasodilation improves myocardial oxygen supply).
- C. INCORRECT. Calcium channel blockers (amlodipine, verapamil) prevent calcium influx into smooth muscle — a different mechanism from nitroglycerin.
- D. INCORRECT. COX enzyme inhibition is the mechanism of NSAIDs (aspirin, ibuprofen) — not nitroglycerin.