What is the mechanism of action of ACE inhibitors?

• A. They inhibit angiotensin-converting enzyme, lowering angiotensin II and aldosterone, causing vasodilation and reduced blood pressure.
• B. They block aldosterone receptors.
• C. They directly dilate veins via nitrates mechanism.
• D. They increase angiotensin II levels.

Answer: (A)

ACE inhibitors work by blocking the angiotensin-converting enzyme, which normally converts angiotensin I into angiotensin II. With less angiotensin II, there’s reduced vasoconstriction and less aldosterone release from the adrenal gland, so sodium and water retention decrease. The overall effect is vasodilation and lower blood pressure. ACE inhibitors also raise bradykinin levels (since ACE helps break it down), which can add to the vasodilatory effect but explains why some patients develop a cough or angioedema. They do not block aldosterone receptors, they do not act by directly dilating veins via a nitrate mechanism, and they do not increase angiotensin II levels.