Which statement about norepinephrine and the pulmonary vasculature is true?

Which statement about norepinephrine and the pulmonary vasculature is true?

• A. It has no effect on pulmonary vessels
• B. It reduces PVR
• C. It causes pulmonary vasodilation
• D. It causes pulmonary vasoconstriction and increases PVR

Answer: (D)

Norepinephrine mainly acts on alpha-1 receptors on vascular smooth muscle, causing constriction. In the pulmonary circulation, this alpha-1–mediated smooth muscle contraction leads to narrowing of the pulmonary arteries, which increases pulmonary vascular resistance and raises pulmonary artery pressures. While there is some beta-receptor activity, it does not produce enough pulmonary vasodilation to outweigh the alpha-1 effect, so the net result is vasoconstriction. That makes the statement true: it causes pulmonary vasoconstriction and increases PVR. This also helps explain why providing norepinephrine can raise right ventricular afterload in patients with existing pulmonary hypertension or right-heart strain.

Norepinephrine mainly acts on alpha-1 receptors on vascular smooth muscle, causing constriction. In the pulmonary circulation, this alpha-1–mediated smooth muscle contraction leads to narrowing of the pulmonary arteries, which increases pulmonary vascular resistance and raises pulmonary artery pressures. While there is some beta-receptor activity, it does not produce enough pulmonary vasodilation to outweigh the alpha-1 effect, so the net result is vasoconstriction. That makes the statement true: it causes pulmonary vasoconstriction and increases PVR. This also helps explain why providing norepinephrine can raise right ventricular afterload in patients with existing pulmonary hypertension or right-heart strain.