Which receptor subtype is primarily associated with increased heart rate?

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

Answer: (B)

Beta-1 adrenergic receptors in the heart are the ones that drive a faster heart rate. When stimulated by catecholamines like adrenaline, these receptors increase the rate of spontaneous firing in the SA node, speed up conduction through the AV node, and boost the strength of each beat. The net effect is tachycardia.

Other receptor types have different primary roles: alpha-1 receptors cause vasoconstriction and raise blood pressure but don’t set the heart rate directly; beta-2 receptors mainly cause vasodilation in certain vessels and bronchodilation, with only indirect effects on heart rate; alpha-2 receptors inhibit norepinephrine release, dampening sympathetic output. So the receptor subtype most closely linked to increasing heart rate is beta-1.