adrenolytic

Adrenolytic refers to substances that counteract the actions of adrenaline (epinephrine) and noradrenaline (norepinephrine). They achieve this either by blocking adrenergic receptors on target tissues or by decreasing the production, storage, or release of catecholamines from sympathetic nerve terminals and the adrenal medulla. The term is largely historical; in contemporary pharmacology the preferred terms are adrenergic antagonists or sympatholytics.

Adrenolytics comprise receptor antagonists and indirect agents. Receptor antagonists include alpha-adrenergic blockers, which inhibit alpha-1 or alpha-2 receptors, and beta-adrenergic blockers, which inhibit beta-1 and/or beta-2 receptors. Examples include phentolamine and phenoxybenzamine (alpha blockers); propranolol and metoprolol (beta blockers). Indirect adrenolytics reduce sympathetic signaling through mechanisms such as inhibiting catecholamine synthesis, storage, or release. Classic agents include reserpine, guanethidine, and metirosine, which decrease catecholamine availability, as well as drugs that impair release from sympathetic nerve endings. The net effect of these actions is reduced vascular tone, decreased heart rate and contractility, and lowered blood pressure.

Clinical use of adrenolytics centers on conditions with excessive or unwanted sympathetic activity. They are employed in the management of hypertension, certain tachyarrhythmias, and pheochromocytoma to prevent perioperative catecholamine surges. They are also used in migraine prophylaxis for some beta-blockers. Safety considerations include the potential for orthostatic hypotension, bradycardia, fatigue, and, with non-selective beta-blockers, bronchospasm or metabolic effects. The choice of an adrenolytic agent depends on receptor selectivity, the clinical indication, and patient comorbidity.