Adrenergic receptor

β₂ adrenoceptor (PDB: 2rh1) shown binding carazolol (yellow) on its extracellular site. β₂ stimulates cells to increase energy production and utilization. The membrane the receptor is bound to in cells is shown with a gray stripe.

The adrenergic receptors or adrenoceptors are a class of G protein-coupled receptors that are targets of many catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) produced by the body, but also many medications like beta blockers, beta-2 (β₂) agonists and alpha-2 (α₂) agonists, which are used to treat high blood pressure and asthma, for example.

Many cells have these receptors, and the binding of a catecholamine to the receptor will generally stimulate the sympathetic nervous system (SNS). The SNS is responsible for the fight-or-flight response, which is triggered by experiences such as exercise or fear-causing situations. This response dilates pupils, increases heart rate, mobilizes energy, and diverts blood flow from non-essential organs to skeletal muscle. These effects together tend to increase physical performance momentarily.