. "The alpha-2 (\u03B12) adrenergic receptor (or adrenoceptor) is a G protein-coupled receptor (GPCR) associated with the Gi heterotrimeric G-protein. It consists of three highly homologous subtypes, including \u03B12A-, \u03B12B-, and \u03B12C-adrenergic. Some species other than humans express a fourth \u03B12D-adrenergic receptor as well. Catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) signal through the \u03B12-adrenergic receptor in the central and peripheral nervous systems."@en .