Phenylephrine-induced vasoconstriction mainly occurs in which vascular beds?

Phenylephrine-induced vasoconstriction mainly occurs in which vascular beds?

• A. Arterioles only
• B. Veins only
• C. Capillaries
• D. Arterioles and veins

Answer: (D)

Phenylephrine is a selective alpha-1 adrenergic agonist, so it constricts vascular smooth muscle by activating alpha-1 receptors. Smooth muscle is present in both arterioles and veins, making them the primary sites of action. Constriction of arterioles raises systemic vascular resistance, increasing arterial pressure, while constriction of veins reduces venous capacitance and boosts venous return to the heart. Capillaries, on the other hand, lack smooth muscle, so they don’t constrict in response to alpha-1 stimulation. That’s why the main vasoconstrictive effect occurs in arterioles and veins.

Phenylephrine is a selective alpha-1 adrenergic agonist, so it constricts vascular smooth muscle by activating alpha-1 receptors. Smooth muscle is present in both arterioles and veins, making them the primary sites of action. Constriction of arterioles raises systemic vascular resistance, increasing arterial pressure, while constriction of veins reduces venous capacitance and boosts venous return to the heart. Capillaries, on the other hand, lack smooth muscle, so they don’t constrict in response to alpha-1 stimulation. That’s why the main vasoconstrictive effect occurs in arterioles and veins.