What is the mechanism of action of angiotensin converting enzyme (ACE) inhibitors?

• A. They block the renin-angiotensin-aldosterone system (RAAS).
• B. They increase aldosterone secretion.
• C. They dilate coronary arteries by acting on beta receptors.
• D. They directly inhibit platelet aggregation.

Answer: (A)

ACE inhibitors work by blocking the conversion of angiotensin I to angiotensin II, which reduces angiotensin II–mediated vasoconstriction and decreases aldosterone release from the adrenal glands. With less angiotensin II, you get vasodilation and reduced sodium and water retention, lowering both afterload and preload and improving cardiac performance in hypertension or heart failure. In addition, ACE inhibition increases bradykinin levels by preventing its breakdown, contributing to further vasodilation (though it can cause cough or angioedema in some patients). This mechanism reflects blocking the RAAS rather than increasing aldosterone, acting via beta receptors, or directly inhibiting platelets.