Dobutamine is used in cardiogenic shock for its positive inotropic effect. Its mechanism differs from dopamine. Dobutamine's primary haemodynamic action results from activation of which receptor?

• A Dopamine D1 receptors in the renal vasculature causing selective renal vasodilation
• B Alpha-1 adrenoceptors causing peripheral vasoconstriction and increased afterload
• C Beta-2 adrenoceptors causing bronchodilation as the primary therapeutic action
• D Beta-1 adrenoceptors predominantly, with minimal beta-2 and alpha-1 effects, increasing cardiac contractility ✓

Explanation

Dobutamine is a synthetic catecholamine that acts predominantly on beta-1 adrenoceptors in the myocardium, producing a strong positive inotropic effect (increased contractility) with relatively modest chronotropy and less peripheral vasoconstriction than noradrenaline. This makes it preferred in cardiogenic shock where increased cardiac output without excessive tachycardia or vasoconstriction is desired. At low doses, dopamine preferentially activates D1 receptors causing renal vasodilation; at moderate doses, dopamine activates beta-1 receptors; at high doses, alpha-1 receptors. Dobutamine does not act through D1 receptors.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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