The effects of epinephrine on the myocardium are generally negative and are influenced by which receptors?

The effects of epinephrine on the myocardium are generally negative and are influenced by which receptors?

• A. a-1
• B. a-2
• C. B-1
• D. B-2

Answer: (C)

The key idea is that the heart’s response to epinephrine is mediated mainly by beta-1 adrenergic receptors on cardiac muscle. When epinephrine binds these receptors, it activates a Gs protein, increases cyclic AMP, and activates protein kinase A. This boosts calcium influx and calcium release from the sarcoplasmic reticulum, which strengthens each beat (positive inotropy) and speeds up heart rate (positive chronotropy). Beta-2 receptors on the heart can contribute a smaller effect, but beta-1 is the dominant receptor governing the myocardium’s direct response. Alpha receptors drive vascular actions such as vasoconstriction, which can raise afterload and influence overall cardiac performance, but the direct myocardial effect is governed by beta-1.

The key idea is that the heart’s response to epinephrine is mediated mainly by beta-1 adrenergic receptors on cardiac muscle. When epinephrine binds these receptors, it activates a Gs protein, increases cyclic AMP, and activates protein kinase A. This boosts calcium influx and calcium release from the sarcoplasmic reticulum, which strengthens each beat (positive inotropy) and speeds up heart rate (positive chronotropy). Beta-2 receptors on the heart can contribute a smaller effect, but beta-1 is the dominant receptor governing the myocardium’s direct response. Alpha receptors drive vascular actions such as vasoconstriction, which can raise afterload and influence overall cardiac performance, but the direct myocardial effect is governed by beta-1.