Which statement best describes how adrenergic receptor subtypes influence vascular tone across the circulation?

Which statement best describes how adrenergic receptor subtypes influence vascular tone across the circulation?

• A. Alpha-1 receptors cause dilation in all vascular beds
• B. Beta-2 receptors cause dilation in some beds, while alpha-1 receptors cause constriction in many beds
• C. All adrenergic receptors cause vasoconstriction
• D. The net effect is independent of receptor distribution

Answer: (B)

Vascular tone across the circulation is governed by the different adrenergic receptor subtypes present in each vascular bed. Alpha-1 receptors on vascular smooth muscle signal through a Gq pathway to raise intracellular calcium, causing smooth muscle contraction and vasoconstriction in many beds. In contrast, beta-2 receptors couple to a Gs pathway that increases cAMP, relaxing smooth muscle and producing vasodilation in some beds, notably skeletal muscle and, in certain contexts, coronary vessels. Because the distribution of these receptor subtypes isn’t the same everywhere, the overall effect of sympathetic stimulation varies by location. Some vascular beds dilate due to beta-2 activation, while many others constrict due to alpha-1 activation, so the net vascular response across the circulation is a mix rather than uniform vasoconstriction or dilation. The other statements don’t fit because alpha-1 receptors do not cause dilation in all beds, not all adrenergic receptors promote vasoconstriction, and the overall effect is not the same everywhere but depends on where different receptor subtypes are expressed.

Vascular tone across the circulation is governed by the different adrenergic receptor subtypes present in each vascular bed. Alpha-1 receptors on vascular smooth muscle signal through a Gq pathway to raise intracellular calcium, causing smooth muscle contraction and vasoconstriction in many beds. In contrast, beta-2 receptors couple to a Gs pathway that increases cAMP, relaxing smooth muscle and producing vasodilation in some beds, notably skeletal muscle and, in certain contexts, coronary vessels. Because the distribution of these receptor subtypes isn’t the same everywhere, the overall effect of sympathetic stimulation varies by location. Some vascular beds dilate due to beta-2 activation, while many others constrict due to alpha-1 activation, so the net vascular response across the circulation is a mix rather than uniform vasoconstriction or dilation.

The other statements don’t fit because alpha-1 receptors do not cause dilation in all beds, not all adrenergic receptors promote vasoconstriction, and the overall effect is not the same everywhere but depends on where different receptor subtypes are expressed.