adrenerg

Adrenergic refers to the components of the nervous system and pharmacology that respond to or imitate the actions of the catecholamines adrenaline (epinephrine) and noradrenaline (norepinephrine). The term is rooted in the connection to the adrenal glands and the sympathetic nervous system, where these transmitters regulate a wide range of physiological responses.

Endogenous catecholamines are synthesized from tyrosine in sympathetic neurons and the adrenal medulla, stored in vesicles, and released in response to stress or stimulation. Epinephrine and norepinephrine act on a family of adrenergic receptors, which are G protein–coupled receptors. The main receptor subtypes are alpha-1, alpha-2, beta-1, beta-2, and beta-3, each with distinct tissue distributions and effects. Alpha-1 activation typically causes vasoconstriction and increased peripheral resistance; alpha-2 can inhibit further transmitter release. Beta-1 receptors increase heart rate and contractility; beta-2 receptors promote bronchodilation and certain vasodilatory effects; beta-3 is involved in lipolysis. Receptor signaling mostly uses G proteins to regulate second messengers such as cAMP or calcium.

Pharmacologically, adrenergic agents include agonists that mimic sympathetic stimulation and antagonists that block it. Examples of agonists are epinephrine, norepinephrine, isoproterenol, phenylephrine, and salbutamol. Antagonists include nonselective blockers like phentolamine and propranolol, as well as selective blockers such as prazosin (alpha-1) and metoprolol (beta-1). Clinically, adrenergic drugs are used to treat hypotension, cardiac arrest, anaphylaxis, asthma, and nasal congestion, among other conditions. Metabolic and cardiovascular effects, including changes in heart rate, blood pressure, and airway tone, reflect the integrated role of the adrenergic system. Catecholamines are terminated by reuptake and enzymatic metabolism via monoamine oxidase and catechol-O-methyltransferase.