Adrenergic Receptor

Adrenergic receptors are a class of G protein-coupled receptors that are targets of the catecholamines, especially norepinephrine and epinephrine. Many cells possess these receptors, and the binding of a catecholamine to the receptor will generally stimulate the sympathetic nervous system. The sympathetic nervous system is responsible for the fight-or-flight response, which includes widening the pupils of the eye, mobilizing energy, and diverting blood flow from non-essential organs to skeletal muscle. There are two main groups of adrenergic receptors, α and β, with several subtypes. α receptors have the subtypes α1 and α2. β receptors have the subtypes β1, β2 and β3. All three are linked to Gs proteins, which in turn are linked to adenylate cyclase. Agonist binding thus causes a rise in the intracellular concentration of the second messenger cAMP. Downstream effectors of cAMP include cAMP-dependent protein kinase (PKA), which mediates some of the intracellular events following hormone binding.