A2-adrenergic receptor

The alpha-2 (α₂) adrenergic receptor (or adrenoceptor) is a G protein-coupled receptor (GPCR) associated with the G_i heterotrimeric G-protein. It consists of three highly homologous subtypes, including α_2A-, α_2B-, and α_2C-adrenergic. Some species other than humans express a fourth α_2D-adrenergic receptor as well.Catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) signal through the α₂-adrenergic receptor in the central and peripheral nervous systems.

The α_2A adrenergic receptor is localised in the following central nervous system (CNS) structures:

Whereas the α_2B adrenergic receptor is localised in the following CNS structures:

and the α_2C adrenergic receptor is localised in the CNS structures:

The α₂-adrenergic receptor is classically located on vascular prejunctional terminals where it inhibits the release of norepinephrine (noradrenaline) in a form of negative feedback. It is also located on the vascular smooth muscle cells of certain blood vessels, such as those found in skin arterioles or on veins, where it sits alongside the more plentiful α₁-adrenergic receptor. The α₂-adrenergic receptor binds both norepinephrine released by sympathetic postganglionic fibers and epinephrine (adrenaline) released by the adrenal medulla, binding norepinephrine (noradrenaline) with slightly higher affinity. It has several general functions in common with the α₁-adrenergic receptor, but also has specific effects of its own. Agonists (activators) of the α₂-adrenergic receptor are frequently used in veterinary anaesthesia where they affect sedation, muscle relaxation and analgesia through effects on the central nervous system (CNS).

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