What is the mechanism of action of beta-blockers and one common adverse effect to watch for?

• A. Block beta-adrenergic receptors, reducing heart rate and contractility.
• B. Increase heart rate and contractility.
• C. Inhibit angiotensin-converting enzyme.
• D. Promote release of catecholamines from the adrenal gland.

Answer: (A)

Beta-blockers block beta-adrenergic receptors in the heart, dampening sympathetic stimulation. By preventing norepinephrine and epinephrine from binding these receptors, they slow the heart rate (negative chronotropy) and reduce the force of contraction (negative inotropy), which lowers cardiac output and blood pressure. A common adverse effect to watch for is bradycardia, since the heart may become too slow. The other statements describe actions that beta-blockers do not perform—opposing their effect by increasing heart rate and contractility, inhibiting ACE, or promoting catecholamine release.