Which vasopressor has no beta-adrenergic activity and increases systemic vascular resistance without vasodilation?

Which vasopressor has no beta-adrenergic activity and increases systemic vascular resistance without vasodilation?

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

Answer: (A)

Phenylephrine is a pure alpha-1 adrenergic agonist, so it causes vasoconstriction of the arterioles, which increases systemic vascular resistance and raises arterial pressure. Because it has no beta-adrenergic activity, it does not stimulate beta-1 receptors on the heart or beta-2–mediated vasodilation, so it typically avoids increasing heart rate or causing vasodilation. The result is a rise in blood pressure due to constricted peripheral vessels without beta-mediated cardiac stimulation. In contrast, agents with beta activity can boost heart rate and contractility (norepinephrine and epinephrine via beta-1) or cause vasodilation via beta-2 at certain doses, and vasopressin works through nonadrenergic receptors (V1) to raise SVR but isn’t a pure alpha-adrenergic vasopressor.

Phenylephrine is a pure alpha-1 adrenergic agonist, so it causes vasoconstriction of the arterioles, which increases systemic vascular resistance and raises arterial pressure. Because it has no beta-adrenergic activity, it does not stimulate beta-1 receptors on the heart or beta-2–mediated vasodilation, so it typically avoids increasing heart rate or causing vasodilation. The result is a rise in blood pressure due to constricted peripheral vessels without beta-mediated cardiac stimulation.

In contrast, agents with beta activity can boost heart rate and contractility (norepinephrine and epinephrine via beta-1) or cause vasodilation via beta-2 at certain doses, and vasopressin works through nonadrenergic receptors (V1) to raise SVR but isn’t a pure alpha-adrenergic vasopressor.