Presynaptic alpha-2 receptors have what primary action?

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Multiple Choice

Presynaptic alpha-2 receptors have what primary action?

Explanation:
Presynaptic alpha-2 receptors act as autoinhibitory brakes on sympathetic nerves. When activated, they couple to Gi proteins and reduce calcium influx, which lowers norepinephrine release into the synapse. That dampens sympathetic signaling and tends to decrease vascular tone and heart rate. The listed postoperative or tissue-specific effect of vasoconstriction on the postsynaptic side can occur in certain vascular beds, but the defining action of the presynaptic receptor is to inhibit norepinephrine release.

Presynaptic alpha-2 receptors act as autoinhibitory brakes on sympathetic nerves. When activated, they couple to Gi proteins and reduce calcium influx, which lowers norepinephrine release into the synapse. That dampens sympathetic signaling and tends to decrease vascular tone and heart rate. The listed postoperative or tissue-specific effect of vasoconstriction on the postsynaptic side can occur in certain vascular beds, but the defining action of the presynaptic receptor is to inhibit norepinephrine release.

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