Stimulation of alpha-adrenergic receptor sites during sympathetic discharge causes what response?

• A. Vasodilation
• B. Vasoconstriction
• C. Bronchodilation
• D. Cardiac acceleration

Answer: (B)

Alpha-adrenergic receptors on vascular smooth muscle, especially the alpha-1 type, trigger contraction when stimulated by sympathetic catecholamines. This causes vasoconstriction—the narrowing of small arteries and arterioles—which raises peripheral resistance and blood pressure during sympathetic arousal. Bronchodilation and cardiac acceleration come from other receptor types (beta-2 in the airways and beta-1 in the heart, respectively), so those responses aren’t produced by alpha-adrenergic activation. Vasodilation isn’t the typical result of stimulating these receptors in most vessels.