Which receptor primarily mediates dobutamine's inotropic effect?

Which receptor primarily mediates dobutamine's inotropic effect?

• A. Beta-1 adrenergic receptor
• B. Alpha-1 adrenergic receptor
• C. Beta-2 adrenergic receptor
• D. Dopamine receptor D1

Answer: (A)

Dobutamine mainly strengthens heart muscle contraction through beta-1 adrenergic receptor activation on cardiac myocytes. When beta-1 is stimulated, it activates the Gs protein, increasing cyclic AMP, which boosts calcium entry and release inside the cells. The higher calcium availability enhances the strength of each contraction, raising stroke volume and cardiac output. While dobutamine has some beta-2 activity (which can modestly vasodilate) and little alpha-1 effect (which would raise afterload), these factors contribute less to the inotropic change than beta-1 activation. The dopamine D1 pathway isn’t responsible for increasing myocardial contractility. So, the receptor driving dobutamine’s inotropic effect is the beta-1 adrenergic receptor.

Dobutamine mainly strengthens heart muscle contraction through beta-1 adrenergic receptor activation on cardiac myocytes. When beta-1 is stimulated, it activates the Gs protein, increasing cyclic AMP, which boosts calcium entry and release inside the cells. The higher calcium availability enhances the strength of each contraction, raising stroke volume and cardiac output. While dobutamine has some beta-2 activity (which can modestly vasodilate) and little alpha-1 effect (which would raise afterload), these factors contribute less to the inotropic change than beta-1 activation. The dopamine D1 pathway isn’t responsible for increasing myocardial contractility. So, the receptor driving dobutamine’s inotropic effect is the beta-1 adrenergic receptor.