Adrenergic

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Receptors

There are three major types of adrenergic receptors, β, α1 and α2, each of which also has three subtypes.

Alpha receptors are those that have the comparative potencies epinephrinenorepinephrine >> isoproterenol. α1 receptors are distributed in smooth muscle, and cause vasoconstriction. α2 receptors are mostly presynaptic, and act to inhibit norepinepherine release from nerve terminals as part of a negative feedback loop.

Beta receptors have the comparative potencies isoproterenol > epinephrinenorepinephrine. β1 receptors are found in the heart, and increase heart rate and contractility. β2 receptors are found in smooth muscle, and cause dilatation and relaxation. β3 receptors are found in adipocytes, and cause lipolysis.