Epinephrine acts on which receptors to increase cardiac output and mean arterial pressure (MAP)?

• A. Alpha receptors only
• B. Beta-1 receptors only
• C. Alpha and Beta-1 receptors only
• D. Alpha, Beta-1, and Beta-2 receptors

Answer: (D)

Epinephrine raises cardiac output primarily through beta-1 receptor stimulation, which increases heart rate and contractility, boosting stroke volume. It raises mean arterial pressure mainly through alpha-1 receptor activation that causes vasoconstriction and increases systemic vascular resistance. Epinephrine also activates beta-2 receptors, which can cause vasodilation in certain beds (like skeletal muscle) and bronchodilation, adding a balancing effect in some tissues. Because epinephrine affects all three receptor types, the combined actions lead to an increase in both cardiac output and MAP. The choices that omit one or two receptor types fail to capture this full range of effects, making the all-three option the most accurate.