American Board of Surgery Qualifying Exam (ABS QE) Practice Test

Phenylephrine is recognized as a selective alpha-1 adrenergic agonist, which primarily causes vasoconstriction through its action on alpha-1 adrenergic receptors. When phenylephrine binds to these receptors, it leads to an increase in peripheral vascular resistance and therefore an increase in blood pressure.

This selectivity makes phenylephrine particularly useful in clinical settings where vasodilation is undesirable, such as in treating hypotension or during surgical procedures to maintain blood pressure. In contrast, while norepinephrine, dopamine, and epinephrine can also exert vasoconstrictive effects, they are not selective for the alpha-1 receptor. Norepinephrine and epinephrine activate both alpha and beta receptors, leading to varying cardiovascular effects, including increased heart rate and cardiac output alongside vasoconstriction. Dopamine has variable effects that depend on the dose, acting on dopaminergic, beta, and alpha receptors, further demonstrating its lack of selectivity as a vasoconstrictor.