How does dopamine act at various doses as an inotrope/vasopressor?

• A. Low doses increase systemic vasodilation via beta-2 receptors.
• B. Moderate doses decrease heart rate via beta-1 receptors.
• C. At all doses dopamine has no effect on blood pressure.
• D. Low to moderate doses increase heart rate and contractility (beta-1); higher doses cause vasoconstriction (alpha-1).

Answer: (D)

Dopamine works in a dose-dependent way on different receptors to produce inotropic and vasopressor effects. At low to moderate doses, dopamine primarily stimulates beta-1 receptors in the heart, which increases both heart rate and contractility, boosting cardiac output. As the dose rises, alpha-1 receptor stimulation becomes more prominent, leading to vasoconstriction and an increase in systemic vascular resistance and blood pressure. There is also a dopaminergic (D1) effect at very low doses that can dilate renal vessels, but in the context of inotropy and vasopressor action the key progression is from beta-1–mediated enhancement of cardiac performance to alpha-1–mediated vasoconstriction with higher doses. This matches the described pattern: low to moderate doses raise heart rate and contractility, and higher doses cause vasoconstriction.