Which receptor type mediates the myocardial effects of epinephrine?

Which receptor type mediates the myocardial effects of epinephrine?

• A. a-1
• B. a-2
• C. B-1
• D. B-2

Answer: (C)

Epinephrine’s effects on the heart are mediated mainly by beta-1 adrenergic receptors on cardiac muscle. When beta-1 is stimulated, it activates Gs proteins, increases adenylyl cyclase activity, and raises cAMP levels. This activates protein kinase A, which enhances calcium entry through L-type channels and boosts calcium release from the sarcoplasmic reticulum. The result is increased contractility, faster heart rate, and quicker conduction through the AV node. Beta-1 receptors are the dominant mediators of these myocardial responses, while alpha receptors largely drive vascular effects, and beta-2 plays a smaller role in the heart. Therefore, the myocardial effects of epinephrine are mediated by beta-1 receptors.

Epinephrine’s effects on the heart are mediated mainly by beta-1 adrenergic receptors on cardiac muscle. When beta-1 is stimulated, it activates Gs proteins, increases adenylyl cyclase activity, and raises cAMP levels. This activates protein kinase A, which enhances calcium entry through L-type channels and boosts calcium release from the sarcoplasmic reticulum. The result is increased contractility, faster heart rate, and quicker conduction through the AV node. Beta-1 receptors are the dominant mediators of these myocardial responses, while alpha receptors largely drive vascular effects, and beta-2 plays a smaller role in the heart. Therefore, the myocardial effects of epinephrine are mediated by beta-1 receptors.