Alpha-2 receptor activation primarily results in which effect?

Alpha-2 receptor activation primarily results in which effect?

• A. Inhibits norepinephrine release
• B. Increases norepinephrine release
• C. Bronchodilation
• D. Vasoconstriction

Answer: (D)

Activation of alpha-2 receptors triggers signals that can reduce sympathetic activity, but there is an important distinction between where these receptors are located. On vascular smooth muscle, postsynaptic alpha-2 receptors produce vasoconstriction via Gi proteins that inhibit adenylyl cyclase, lowering cAMP and promoting smooth muscle contraction. This direct effect on the vessels is what the option points to: the they cause vasoconstriction, increasing vascular tone. It’s true that presynaptic alpha-2 receptors on sympathetic nerve endings inhibit norepinephrine release, a negative feedback mechanism, but the lasting, direct vascular response when alpha-2 receptors are activated in the vasculature is vasoconstriction.

Activation of alpha-2 receptors triggers signals that can reduce sympathetic activity, but there is an important distinction between where these receptors are located. On vascular smooth muscle, postsynaptic alpha-2 receptors produce vasoconstriction via Gi proteins that inhibit adenylyl cyclase, lowering cAMP and promoting smooth muscle contraction. This direct effect on the vessels is what the option points to: the they cause vasoconstriction, increasing vascular tone. It’s true that presynaptic alpha-2 receptors on sympathetic nerve endings inhibit norepinephrine release, a negative feedback mechanism, but the lasting, direct vascular response when alpha-2 receptors are activated in the vasculature is vasoconstriction.