Stimulation of which receptor mediates vasoconstriction of arterioles and arteries?

• A. Beta One Adrenergic Receptors
• B. Beta Two Adrenergic Receptors
• C. Muscarinic Receptors
• D. Alpha One Adrenergic Receptors

Answer: (D)

Alpha-1 adrenergic receptors on vascular smooth muscle drive constriction. When these receptors are stimulated by sympathetic neurotransmitters like norepinephrine, they activate a Gq protein pathway that leads to phospholipase C activation, IP3 and DAG production, a rise in intracellular calcium, and contraction of the smooth muscle in arterioles and arteries. This vasoconstriction increases systemic vascular resistance and raises blood pressure.

Beta-1 receptors mainly affect the heart (increasing rate and contractility) and don’t cause arteriolar constriction. Beta-2 receptors promote vasodilation in some vascular beds (like skeletal muscle) and bronchodilation, not constriction. Muscarinic receptors are part of parasympathetic signaling and can cause vasodilation via endothelial NO release in many vessels, rather than constriction.