What is the effect of norepinephrine on peripheral vascular resistance (PVR)?

What is the effect of norepinephrine on peripheral vascular resistance (PVR)?

• A. Decreases
• B. Increases
• C. No change
• D. Fluctuates

Answer: (B)

Norepinephrine mainly acts on alpha-1 receptors on vascular smooth muscle, especially in arterioles, causing vasoconstriction. This constricts the peripheral vessels, narrows the lumen, and raises systemic vascular resistance—i.e., peripheral vascular resistance increases. The underlying mechanism involves alpha-1 activation triggering the Gq pathway, increasing intracellular calcium and promoting smooth muscle contraction. While norepinephrine also has beta-1 effects that can boost cardiac output, these do not counteract the dominant vasoconstrictive action on resistance vessels, so the net effect is an increase in PVR. It does not cause vasodilation or no change, and while dose can influence balance with other receptor effects, the typical pharmacodynamic outcome is an increase in peripheral vascular resistance.

Norepinephrine mainly acts on alpha-1 receptors on vascular smooth muscle, especially in arterioles, causing vasoconstriction. This constricts the peripheral vessels, narrows the lumen, and raises systemic vascular resistance—i.e., peripheral vascular resistance increases. The underlying mechanism involves alpha-1 activation triggering the Gq pathway, increasing intracellular calcium and promoting smooth muscle contraction. While norepinephrine also has beta-1 effects that can boost cardiac output, these do not counteract the dominant vasoconstrictive action on resistance vessels, so the net effect is an increase in PVR. It does not cause vasodilation or no change, and while dose can influence balance with other receptor effects, the typical pharmacodynamic outcome is an increase in peripheral vascular resistance.