Which receptor mediates vasodilation in the pulmonary vasculature at low epinephrine concentrations?

Which receptor mediates vasodilation in the pulmonary vasculature at low epinephrine concentrations?

• A. Beta2
• B. Alpha1
• C. Beta1
• D. Alpha2

Answer: (A)

Vasodilation in the pulmonary circulation at low epinephrine concentrations is driven by β2-adrenergic receptors on pulmonary arterial smooth muscle. When epinephrine activates these receptors, it stimulates Gs proteins to raise cAMP, causing smooth muscle relaxation and thus vessel dilation, which lowers pulmonary vascular resistance. β1 receptors mainly affect heart rate and contractility, not pulmonary vessel tone, while α1 receptors cause vasoconstriction and require higher epinephrine levels to become influential. Therefore, the β2 receptor mediates the observed vasodilation at low epinephrine concentrations.

Vasodilation in the pulmonary circulation at low epinephrine concentrations is driven by β2-adrenergic receptors on pulmonary arterial smooth muscle. When epinephrine activates these receptors, it stimulates Gs proteins to raise cAMP, causing smooth muscle relaxation and thus vessel dilation, which lowers pulmonary vascular resistance. β1 receptors mainly affect heart rate and contractility, not pulmonary vessel tone, while α1 receptors cause vasoconstriction and require higher epinephrine levels to become influential. Therefore, the β2 receptor mediates the observed vasodilation at low epinephrine concentrations.