At what infusion rate does dopamine begin to primarily stimulate beta-receptors?

Dopamine is a catecholamine that has dose-dependent effects on various adrenergic receptors in the body. At lower infusion rates, specifically below 3 micrograms per kilogram per minute, dopamine primarily stimulates dopaminergic receptors, leading to renal and mesenteric vasodilation. As the infusion rate increases to between 5 and 10 micrograms per kilogram per minute, dopamine starts to exert a significant effect on beta-1 adrenergic receptors, which are responsible for increasing heart rate and cardiac contractility.

This range is considered optimal for stimulating cardiac function while still maintaining renal perfusion. At higher doses, particularly over 10 micrograms per kilogram per minute, there's an increased stimulation of beta-1 receptors and also more prominent activation of alpha-adrenergic receptors, leading to vasoconstriction and increased systemic vascular resistance. Therefore, the infusion rate of 5-10 micrograms per kilogram per minute is the critical range where the primary action shifts toward beta-receptor stimulation, making it the correct answer.