What is the mechanism of action of ACE inhibitors?

• A. Block beta-adrenergic receptors to reduce heart rate.
• B. Inhibit conversion of angiotensin I to angiotensin II, reducing vasoconstriction and aldosterone-mediated volume retention.
• C. Inhibit HMG-CoA reductase.
• D. Inhibit Na+/K+/2Cl- cotransporter in the thick ascending limb.

Answer: (B)

ACE inhibitors work by blocking the angiotensin-converting enzyme, so angiotensin I cannot be turned into angiotensin II. With less angiotensin II, there’s reduced vasoconstriction and less aldosterone release from the adrenal glands, which decreases sodium and water retention. The result is lower blood pressure and reduced fluid volume. The buildup of bradykinin from ACE inhibition can enhance vasodilation, which explains some side effects like cough or, rarely, angioedema. They do not affect beta receptors, they do not inhibit cholesterol synthesis, and they do not block the Na+/K+/2Cl− transporter in the thick ascending limb.