Which hormone secreted by the adrenal medulla increases blood pressure by vasoconstriction without affecting cardiac output?

• A. Norepinephrine
• B. Epinephrine
• C. Dopamine
• D. Vasopressin

Answer: (A)

Norepinephrine is the hormone released by the adrenal medulla that primarily increases blood pressure through vasoconstriction. It acts mainly on alpha-1 receptors in vascular smooth muscle, causing constriction of blood vessels, which raises systemic vascular resistance and therefore raises blood pressure. Its effect on beta receptors, which would boost heart rate and cardiac output, is relatively limited compared to epinephrine. That means cardiac output does not rise significantly with its action; BP goes up mainly from the constricted vessels rather than from the heart pumping harder or faster.

Epinephrine, while it can raise blood pressure, also strongly stimulates beta-1 receptors in the heart and beta-2 receptors in some vessels, increasing heart rate, contractility, and sometimes causing vasodilation in skeletal muscle. That combination typically increases cardiac output, so it doesn’t fit the description of increasing BP by vasoconstriction without affecting cardiac output.

Dopamine isn’t the principal adrenal medulla hormone responsible for this specific pattern, and vasopressin, though a potent vasoconstrictor, is released from the pituitary, not the adrenal medulla.