Adrenergic receptor subtypes and physiological effects
Core concept
| Receptor | G protein | Second messenger | Main effects |
|---|---|---|---|
| Alpha-1 | Gq | inc IP3/DAG -> inc Ca | Vascular smooth muscle contraction (inc SVR), mydriasis, bladder neck and prostate contraction, GI/bladder sphincter contraction, pilomotor, hepatic glycogenolysis |
| Alpha-2 | Gi | dec cAMP | Presynaptic autoreceptor -> dec noradrenaline release; central sympatholysis (dec BP), dec insulin secretion, platelet aggregation, dec aqueous humour |
| Beta-1 | Gs | inc cAMP | inc HR (chronotropy), inc contractility (inotropy), inc AV conduction (dromotropy), renin release from JG cells |
| Beta-2 | Gs | inc cAMP | Bronchodilation, vasodilation (skeletal muscle, coronary), uterine and detrusor relaxation, hepatic and skeletal muscle glycogenolysis, K+ shift INTO cells (Na/K-ATPase), tremor, insulin release |
| Beta-3 | Gs | inc cAMP | Lipolysis in adipose; detrusor relaxation (mirabegron) |
| D1 | Gs | inc cAMP | Renal, mesenteric, coronary vasodilation |
- Alpha-1 = squeeze. Beta-1 = pump. Beta-2 = relax and mobilise fuel. Alpha-2 = brake.
- *Beta-2 effects explain the salbutamol side-effect profile in one line - tremor, tachycardia (partly reflex, partly beta-1 cross-reactivity), hypokalaemia*, hyperglycaemia, lactic acidosis
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