Midrange doses of dopamine cause vasoconstriction primarily through stimulation of which receptor?

• A. Beta-1 adrenergic receptor
• B. Dopamine D1 receptor
• C. Alpha-1 adrenergic receptor
• D. D2 receptor

Answer: (A)

Dopamine works in a dose-dependent way by activating different receptors. At low doses it primarily stimulates D1 receptors, which dilate renal and some mesenteric vessels and raise renal blood flow. At moderately low to midrange doses it mainly stimulates beta-1 adrenergic receptors in the heart, increasing heart rate and contractility, which boosts cardiac output and can raise blood pressure. Only at higher doses does dopamine start to activate alpha-1 adrenergic receptors, leading to vasoconstriction and increased systemic vascular resistance.

So midrange dopamine’s main cardiovascular effect is via beta-1 receptors increasing cardiac output, not vasoconstriction. Vasoconstriction would be expected with higher doses through alpha-1 receptor stimulation. If a question asks about dopamine-induced vasoconstriction specifically, the receptor involved would be alpha-1 and this occurs at higher, not midrange, doses.