For which receptor subtype is vasodilation a predominant effect?

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

Answer: (D)

Vasodilation in vascular smooth muscle is mainly produced when adrenergic receptors of the Beta-2 subtype are activated. These receptors couple to Gs proteins, increasing cyclic AMP inside the cell, which activates protein kinase A and lowers intracellular calcium. That sequence relaxes the smooth muscle and widens the vessel, particularly in skeletal muscle beds, promoting increased blood flow.

Other receptor types have opposing effects: Alpha-1 receptors trigger vasoconstriction by raising intracellular calcium through the Gq pathway; Alpha-2 receptors mainly regulate norepinephrine release and can contribute to constriction in some tissues; Beta-1 receptors mostly affect heart rate and contractility rather than directly controlling vascular tone.

So the receptor subtype whose activation leads to predominant vasodilation is Beta-2.