Adrenergic Drugs

Adrenergic Drugs

1. Definition, scope & terminology

• Adrenergic (sympathomimetic) drugs have actions similar to adrenaline or to sympathetic stimulation; antiadrenergic / adrenergic antagonist drugs antagonise the receptor action of adrenaline and related agonists at α, β, or both receptor classes (KDT 8e Ch.9, pp.141; Ch.10, p.153).
• Agents acting on the adrenergic system either mimic endogenous catecholamines, block their synthesis/release/reuptake, or antagonise them at adrenoceptors on the cell membrane (G&G 14e Ch.14, p.251).
• Three endogenous catecholamines (CAs) act as signal molecules — noradrenaline (NA / norepinephrine), adrenaline (Adr / epinephrine), dopamine (DA) (KDT 8e Ch.9, p.136).
  • NA — transmitter at postganglionic sympathetic sites (except sweat glands and some vasodilator fibres) and in certain brain areas; only small quantities secreted by adrenal medulla; acts locally in innervated tissue (KDT 8e Ch.9, p.136; G&G 14e Ch.14, p.251).
  • Adr — major adrenal-medullary hormone, secreted into the circulation and acting on target tissues by its circulating concentration; possible transmitter role in brain but not at peripheral sympathetic terminals (KDT 8e Ch.9, p.136; G&G 14e Ch.14, p.251).
  • DA — major transmitter in basal ganglia, limbic system, CTZ, anterior pituitary; limited peripheral role (renal vessels) (KDT 8e Ch.9, p.136).
• Isoprenaline (isoproterenol, INE) — synthetic NA derivative; a pure β agonist used as a pharmacological tool to activate all cellular β receptors (R&D Ch.15, p.2; G&G 14e Ch.14, p.261).
• Both NA and Adr underpin the "fight or flight" response of sympathetic activation (Katzung Ch.9, p.142).