Autonomic receptor subtypes !

Where each adrenergic, muscarinic and nicotinic receptor is found, what it does and which drugs target it: the map behind autonomic pharmacology.

Updated 2026-11-01

Adrenergic receptors (alpha-1, alpha-2, beta-1, beta-2, beta-3) and muscarinic receptors (M1 to M5) are G protein-coupled; nicotinic receptors are ion channels with a muscle type and a neuronal type. Knowing where each subtype sits and which signal it uses explains both the uses and the side effects of most autonomic drugs.

Adrenergic receptors

Alpha-1 · Gq · vessels, radial muscle of the iris, prostate and bladder neck · agonist phenylephrine; blockers prazosin, tamsulosin
Alpha-2 · Gi · presynaptic terminals, brainstem, pancreatic beta cells · agonists clonidine, methyldopa (via its metabolite), dexmedetomidine
Beta-1 · Gs · heart, juxtaglomerular cells · agonist dobutamine; selective blockers metoprolol, bisoprolol, atenolol
Beta-2 · Gs · bronchi, skeletal muscle vessels, uterus, liver · agonists salbutamol, formoterol; propranolol blocks beta-1 and beta-2
Beta-3 · Gs · fat tissue, detrusor · agonist mirabegron for overactive bladder
Mixed blockers: carvedilol and labetalol block beta and alpha-1

Muscarinic receptors

M1 · Gq · brain, autonomic ganglia, gastric glands
M2 · Gi · heart (sinoatrial and atrioventricular nodes): slows rate and conduction · atropine blocks it in bradycardia
M3 · Gq · exocrine glands, bronchial and gut smooth muscle, detrusor, iris sphincter, ciliary muscle, endothelium (nitric oxide-mediated vasodilation) · agonist pilocarpine; blockers tiotropium, oxybutynin
M4 and M5 · mainly in the brain

Nicotinic receptors

NM (muscle type) · skeletal muscle end plate · blocked by rocuronium (competitive) and depolarised by suxamethonium
NN (neuronal type) · autonomic ganglia, adrenal medulla, brain · stimulated by nicotine; partial agonist varenicline (brain subtype) for smoking cessation; blocked by ganglionic blockers

Reading side effects from the map

Non-selective beta blockade can tighten the airways (beta-2) and blunt warning signs of hypoglycaemia; alpha-1 blockade causes orthostatic hypotension; antimuscarinics cause dry mouth, constipation, urinary retention, blurred near vision and confusion in older adults. Selectivity is dose-dependent and never absolute.

Test yourself

Think of the answer, then tap the question to see it.

Which adrenergic receptor mediates renin release, and what does blocking it do?

Beta-1 on juxtaglomerular cells; beta blockers reduce renin release, part of how they lower blood pressure.

Why can a non-selective beta blocker worsen asthma?

It blocks beta-2 receptors in bronchial smooth muscle, removing adrenergic bronchodilation.

Which receptor does mirabegron act on, and where?

Beta-3 receptors on the bladder detrusor, which relax the muscle in overactive bladder.

Which muscarinic subtype slows the heart, and through which G protein?

M2, through Gi, on the sinoatrial and atrioventricular nodes.

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Example drugs

← All of pharmacology

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: 15.1 Divisions of the Autonomic Nervous System (OpenStax (Rice University), 2022); 15.4 Drugs that Affect the Autonomic System (OpenStax (Rice University), 2022); DailyMed - ROCURONIUM BROMIDE injection, solution (DailyMed (U.S. National Library of Medicine), 2026).

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Representative model, for educational purposes only.