Norepinephrine does not significantly activate which receptor subtype?

Norepinephrine does not significantly activate which receptor subtype?

• A. Beta-2 receptors
• B. Alpha-1 receptors
• C. Alpha-2 receptors
• D. Beta-1 receptors

Answer: (A)

Norepinephrine has a receptor activity profile that favors alpha-adrenergic and beta-1 receptors, with little effect on beta-2 receptors. This means it acts mainly through alpha-1 to cause vasoconstriction (raising systemic vascular resistance and blood pressure) and through beta-1 to increase heart rate and contractility. Beta-2 activation, which would produce skeletal muscle vasodilation and bronchodilation, is not significantly triggered by norepinephrine because its affinity for beta-2 receptors is low. Epinephrine, by contrast, stimulates beta-2 receptors more strongly, producing those beta-2–mediated effects. So norepinephrine does not significantly activate beta-2 receptors.

Norepinephrine has a receptor activity profile that favors alpha-adrenergic and beta-1 receptors, with little effect on beta-2 receptors. This means it acts mainly through alpha-1 to cause vasoconstriction (raising systemic vascular resistance and blood pressure) and through beta-1 to increase heart rate and contractility. Beta-2 activation, which would produce skeletal muscle vasodilation and bronchodilation, is not significantly triggered by norepinephrine because its affinity for beta-2 receptors is low. Epinephrine, by contrast, stimulates beta-2 receptors more strongly, producing those beta-2–mediated effects. So norepinephrine does not significantly activate beta-2 receptors.