[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › Autonomic receptor subtypes [Pharmacology](https://durgical.com/en/pharmacology/) · Topic # 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. ## Key points - Alpha-1 (Gq): smooth muscle contraction: vasoconstriction, pupil dilation, bladder neck and prostate contraction. - Alpha-2 (Gi): presynaptic brake on noradrenaline release; central alpha-2 agonists lower sympathetic outflow. - Beta-1 (Gs): heart rate, contractility and conduction up; renin release from the kidney. - Beta-2 (Gs): bronchodilation, vasodilation in skeletal muscle, uterine relaxation, liver glycogen breakdown; beta-3 (Gs): lipolysis and detrusor relaxation. - M2 (Gi) slows the heart; M3 (Gq) drives glands, bronchial and gut smooth muscle, the detrusor and the pupil sphincter; M1 is mainly neural and in gastric glands. - Nicotinic: NM at the muscle end plate; NN in ganglia, the adrenal medulla and the brain. ## 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. ## Memory aid Every beta uses Gs; for alpha and muscarinic receptors, odd numbers use Gq and even numbers use Gi (alpha-1 q, alpha-2 i; M1 q, M2 i, M3 q). ## 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. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/topics/autonomic-receptor-subtypes/) ## Related classes - [Beta blockers](https://durgical.com/en/pharmacology/classes/beta-blockers/) - [Alpha blockers](https://durgical.com/en/pharmacology/classes/alpha-blockers/) - [Beta-2 adrenergic agonists](https://durgical.com/en/pharmacology/classes/beta-2-adrenergic-agonists/) - [Antimuscarinics (anticholinergics)](https://durgical.com/en/pharmacology/classes/antimuscarinics/) - [Vasopressors and inotropes](https://durgical.com/en/pharmacology/classes/vasopressors-and-inotropes/) - [Muscarinic (cholinergic) agonists](https://durgical.com/en/pharmacology/classes/muscarinic-agonists/) ## Example drugs - [Phenylephrine](https://durgical.com/en/pharmacology/phenylephrine/) - [Clonidine](https://durgical.com/en/pharmacology/clonidine/) - [Dobutamine](https://durgical.com/en/pharmacology/dobutamine/) - [Salbutamol](https://durgical.com/en/pharmacology/salbutamol/) - [Mirabegron](https://durgical.com/en/pharmacology/mirabegron/) - [Metoprolol](https://durgical.com/en/pharmacology/metoprolol/) - [Propranolol](https://durgical.com/en/pharmacology/propranolol/) - [Tamsulosin](https://durgical.com/en/pharmacology/tamsulosin/) - [Atropine](https://durgical.com/en/pharmacology/atropine/) - [Oxybutynin](https://durgical.com/en/pharmacology/oxybutynin/) - [Tiotropium bromide](https://durgical.com/en/pharmacology/tiotropium-bromide/) - [Pilocarpine](https://durgical.com/en/pharmacology/pilocarpine/) - [Carvedilol](https://durgical.com/en/pharmacology/carvedilol/) - [Labetalol](https://durgical.com/en/pharmacology/labetalol/) [← All of pharmacology](https://durgical.com/en/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](https://openstax.org/books/anatomy-and-physiology-2e/pages/15-1-divisions-of-the-autonomic-nervous-system) (OpenStax (Rice University), 2022); [15.4 Drugs that Affect the Autonomic System](https://openstax.org/books/anatomy-and-physiology-2e/pages/15-4-drugs-that-affect-the-autonomic-system) (OpenStax (Rice University), 2022); [DailyMed - ROCURONIUM BROMIDE injection, solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=a18fce42-0f3d-4354-845e-57c37ac3a147) (DailyMed (U.S. National Library of Medicine), 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/topics/autonomic-receptor-subtypes/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/topics/autonomic-receptor-subtypes/