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A muscarinic receptor antagonist is an agent that reduces the activity of the muscarinic acetylcholine receptor. Most of them are synthetic, but scopolamine and atropine are belladonna alkaloids, and are naturally extracted.

Effects

Effect on CNS

It is stimulate CNS as a result of stimulation of medulla and higher cerebral centers. At low doses of atropine, causes slight restlessness; and at high or toxic doses it causes restlessness, agitation, hallucination. In atropine poisoning marked excitation and agitation leads to hyper activity and increased in body temperature by lose of sweating. Scopolamine in therapeutic doses causes CNS depression characterized by amnesia, fatigue and reduction in REM (Rapid Eye Movement) sleep. Hyoscine has anti-emetic activity, so used in motion sickness. Also used as anti-parkinsonian drug. In Parkinsonism, there is imbalance between Ach & dopamine occurs. In it there is increase level of Ach or degeneration of dopaminergic pathway (nigro-straital pathway). Thus, in Parkinsonism there is decrease level of dopamine. For, balancing the neurotransmitters, one treatment is considered that decrease level of Ach or decrease activity of Ach by MRA.

Effect on heart

Atropine acts on the M2-receptors of the heart and antagonized the activity of Ach. It causes tachycardia by blocking vagal effects on the SA node. Ach hyperpolarize the SA node which is over come by MRA and increase the heart rate. If atropine is given by intra muscular or sub cutaneous, it causes initial bradycardia. This is because; by i.m/s.c it acts on presynaptic M1-raceptors (auto receptors). So. The intake of Ach in axoplasm is prevented. Due to it, presynaptic nerve releases more Ach in to synapse which causes bradycardia, initially. At AV node, RP is abbreviated which facilitates conduction and also due to shortened PR-interval of ECG. It have alternative effect on BP. Due to tachycardia and stimulation of vasomotor centre causes increase in BP. But due to feed back regulation of VMC there is fall in BP due to vasodilation.

Important^[1] muscarinic antagonists include atropine, hyoscine, ipratropium, tropicamide, cyclopentolate and pirenzepine.

Comparison table

Substance	Trade names	Mechanism^[2]	Clinical use^[2]	Adverse effects^[2]
Atropine (D/L-Hyoscyamine)		non-selective antagonism, CNS stimulation	in anaesthesia anticholinesterase poisoning bradycardia antispasmodic in gastrointestinal hypermotility	urinary retention xerostomia blurred vision
Scopolamine (L-Hyoscine)		non-selective antagonism, CNS depression	as atropine motion sickness	as atropine sedation
Ipratropium		non-selective antagonism, without any mucociliary excretion inhibition.	in asthma and bronchitis
Tropicamide		short acting non-selective antagonism, CNS depression	produce mydriasis and cycloplegia in diagnostics	may cause ocular hypertension
Pirenzepine		M1 receptor-selective antagonist inhibits gastric secretion	in peptic ulcer (not much anymore)	(fewer than non-selective ones)
Diphenhydramine	Benadryl		for extrapyramidal symptoms from typical antipsychotic medications
Dimenhydrinate	Dramamine		motion sickness
dicyclomine
flavoxate
oxybutynin
tiotropium	Spiriva
cyclopentolate		short acting non-selective antagonism, CNS depression	produce mydriasis and cycloplegia in diagnostics	may cause ocular hypertension
atropine methonitrate		non-selective antagonism, blocks transmission in ganglia	antispasmodic in gastrointestinal hypermotility
trihexyphenidyl	Artane
tolterodine	Detrusitol
solifenacin	Vesicare
darifenacin	Enablex
benztropine	Cogentin
Mebeverine	Bought U.K	^[3]

References

^ Rang, H. P. (2003). Pharmacology. Edinburgh: Churchill Livingstone. ISBN 0-443-07145-4. Page 147
^ ^a ^b ^c Unless else specified in table boxes, then ref is: Rang, H. P. (2003). Pharmacology. Edinburgh: Churchill Livingstone. ISBN 0-443-07145-4. Page 147
^ ...

External links

Effects of Muscarinic Antagonist
http://cvpharmacology.com/antiarrhy/atropine.htm
Muscarinic+antagonists at the U.S. National Library of Medicine Medical Subject Headings (MeSH)

This pharmacology-related article is a stub. You can help Wikipedia by expanding it.

[Rang147-1] Rang, H. P. (2003). Pharmacology. Edinburgh: Churchill Livingstone. ISBN 0-443-07145-4. Page 147

[Rang147Unless-2] Unless else specified in table boxes, then ref is: Rang, H. P. (2003). Pharmacology. Edinburgh: Churchill Livingstone. ISBN 0-443-07145-4. Page 147

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@@ Line 1: / Line 1: @@
 A '''muscarinic receptor antagonist''' is an agent that reduces the activity of the [[muscarinic acetylcholine receptor]]. Most of them are synthetic, but [[scopolamine]] and [[atropine]] are belladonna alkaloids, and are naturally extracted.
+==Effects==
+===Effect on CNS===
+It is stimulate CNS as a result of stimulation of medulla and higher cerebral centers.
+At low doses of atropine, causes slight restlessness; and at high or toxic doses it causes restlessness, agitation, hallucination.
+In atropine poisoning marked excitation and agitation leads to hyper activity and increased in body temperature by lose of sweating.
+Scopolamine in therapeutic doses causes CNS depression characterized by amnesia, fatigue and reduction in REM (Rapid Eye Movement) sleep.
+Hyoscine has anti-emetic activity, so used in motion sickness.
+Also used as anti-parkinsonian drug. In Parkinsonism, there is imbalance between Ach & dopamine occurs. In it there is increase level of Ach or degeneration of dopaminergic pathway (nigro-straital pathway). Thus, in Parkinsonism there is decrease level of dopamine. For, balancing the neurotransmitters, one treatment is considered that decrease level of Ach or decrease activity of Ach by MRA.
+===Effect on heart===
+Atropine acts on the M2-receptors of the heart and antagonized the activity of Ach. It causes tachycardia by blocking vagal effects on the SA node. Ach hyperpolarize the SA node which is over come by MRA and increase the heart rate.
+If atropine is given by intra muscular or sub cutaneous, it causes initial bradycardia. This is because; by i.m/s.c it acts on presynaptic M1-raceptors (auto receptors). So. The intake of Ach in axoplasm is prevented. Due to it, presynaptic nerve releases more Ach in to synapse which causes bradycardia, initially.
+At AV node, RP is abbreviated which facilitates conduction and also due to shortened PR-interval of ECG.
+It have alternative effect on BP. Due to tachycardia and stimulation of vasomotor centre causes increase in BP. But due to feed back regulation of VMC there is fall in BP due to vasodilation.
 Important<ref name=Rang147> {{cite book |author=Rang, H. P. |title=Pharmacology |publisher=Churchill Livingstone |location=Edinburgh |year=2003 |pages= |isbn=0-443-07145-4 |oclc= |doi=}} Page 147 </ref> muscarinic antagonists include [[atropine]], [[hyoscine]], [[ipratropium]], [[tropicamide]], [[cyclopentolate]] and [[pirenzepine]].
@@ Line 159: / Line 177: @@
 ==External links==
+* [http://www.pharmacology.googlepages.com/effect-of-mra.html Effects of Muscarinic Antagonist]
 * http://cvpharmacology.com/antiarrhy/atropine.htm
 * {{MeshName|Muscarinic+antagonists}}

v t e Urologicals, including antispasmodics (G04B)
Acidifiers	Ammonium chloride Calcium chloride
Urinary antispasmodics (primarily antimuscarinics)	Darifenacin Desfesoterodine Emepronium Fesoterodine Flavoxate Imidafenacin Meladrazine Mirabegron Oxybutynin Propiverine Solifenacin Terodiline Tolterodine Trospium chloride Vibegron
Other urologicals	Urea analogues: Acetohydroxamic acid Salicylhydroxamic acid Other: Collagen Dapoxetine Dimethyl sulfoxide Magnesium hydroxide Pentosan polysulfate Phenazopyridine Phenyl salicylate Succinimide Tiopronin

v t e Ophthalmologicals: mydriasis and cycloplegia (S01F)
Anticholinergics/antimuscarinics	Atropine Scopolamine Methylscopolamine Cyclopentolate Homatropine Tropicamide (+phenylephrine)
Sympathomimetics	Phenylephrine (+ketorolac) Ephedrine Ibopamine