Dobutamine primarily increases cardiac output by stimulating which receptor type?

• A. Alpha 1 receptors
• B. Dopaminergic receptors
• C. Beta 2 receptors
• D. Beta 1 receptors

Answer: (D)

Dobutamine raises cardiac output primarily through stimulation of beta-1 adrenergic receptors on the heart. When these receptors are activated, they increase the production of cAMP inside heart muscle cells, which enhances calcium availability during the heartbeat. That boost in intracellular calcium strengthens myocardial contraction (positive inotropy), leading to a higher stroke volume. Since cardiac output is the product of heart rate and stroke volume, the rise in stroke volume drives the increase in output. There can be some mild beta-2–mediated vasodilation, which may lower afterload a bit, but the dominant effect is the beta-1–driven increase in contractility. This is why dobutamine is used to improve cardiac output in situations like acute heart failure or cardiogenic shock.