Selective beta blockers act on which receptor?

• A. Beta-2
• B. Beta-1
• C. Alpha-1
• D. Dopamine

Answer: (B)

Selective beta blockers block beta-1 receptors most strongly. These receptors are mainly in the heart (where their activation increases heart rate, contractility, and AV nodal conduction) and in the kidney (where they promote renin release). Blocking beta-1 reduces heart rate, lowers contractility, slows AV conduction, and decreases renin release, which helps lower blood pressure and reduce cardiac workload. Because they prefer beta-1 over beta-2 receptors, they have less effect on beta-2–mediated actions in the lungs and vasculature, making them safer for patients with asthma or COPD than nonselective beta blockers. At high doses, selectivity can diminish and beta-2 effects may appear. The other choices involve receptors not primarily targeted by selective beta blockers.