adrenergic

Adrenergic refers to actions, receptors, or agents related to the catecholamines epinephrine (adrenaline) and norepinephrine (noradrenaline), which are central to the body’s sympathetic fight-or-flight response. The term covers physiological processes driven by sympathetic neurotransmission as well as pharmacological agents that mimic or oppose these signals.

Adrenergic receptors are a family of G protein–coupled receptors divided into alpha (α1, α2) and beta (β1, β2, β3) subtypes. α1 receptors couple to Gq proteins and promote vasoconstriction and smooth muscle contraction; α2 receptors couple to Gi proteins and inhibit norepinephrine release. β1, β2, and β3 receptors couple to Gs proteins and increase intracellular cyclic AMP, producing effects such as increased heart rate and contractility (β1), bronchodilation and vasodilation in some vascular beds (β2), and lipolysis (β3). Receptors mediate responses to circulating catecholamines and to neurotransmitters released by sympathetic neurons.

Physiologically, adrenergic signaling regulates cardiovascular, respiratory, metabolic, and systemic responses to stress. In addition to endogenous catecholamines, a class of drugs known as adrenergic agonists and antagonists broadly modulates these receptors, with clinical roles in treating cardiac arrest, anaphylaxis, asthma, nasal congestion, hypertension, and other conditions. Examples include epinephrine and norepinephrine as endogenous mediators; isoproterenol and albuterol as β-agonists; prazosin and phentolamine as α-blockers.