At which dose range does dopamine increase cardiac contractility, cardiac output, and blood pressure without decreasing renal blood flow?

• A. 0-1 mcg/kg/min
• B. 1-5 mcg/kg/min
• C. 5-10 mcg/kg/min
• D. >15 mcg/kg/min

Answer: (C)

Dopamine’s effects change with dose because different receptors are activated at different ranges. At moderate doses, it mainly stimulates beta-1 receptors in the heart, boosting contractility and heart rate, which increases cardiac output and tends to raise blood pressure. This occurs without strong alpha-adrenergic vasoconstriction, so renal blood flow is preserved rather than reduced. At very low doses, renal dopaminergic receptors promote renal vasodilation and perfusion, but this doesn’t significantly raise blood pressure. At very high doses, alpha-adrenergic effects dominate, increasing systemic vascular resistance and BP but potentially decreasing renal blood flow due to renal vasoconstriction. Therefore, the mid-dose range—where beta-1 effects predominate and renal flow remains intact—best achieves increased contractility, cardiac output, and blood pressure without reducing renal perfusion.