Adrenergic receptor. Computer illustration of an adrenergic receptor molecule (yellow) in a cell membrane (horizontal). Adrenergic receptors (or adrenoceptors) are a class of G protein-coupled receptor that are the target of catecholamines, especially norepinephrine (noradrenaline) and epinephrine (adrenaline). Many cells possess these receptors, and the binding of a catecholamine to the receptor will generally stimulate the sympathetic nervous system.