This MedLibrary.org supplementary page on Muscarinic antagonist is provided directly from the open source Wikipedia as a service to our readers. Please see the note below on authorship of this content, as well as the Wikipedia usage guidelines. To search for other content from our encyclopedia supplement, please use the form below:
Related Sponsors
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.
Contents |
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 |
|
||
| Scopolamine (L-Hyoscine) | non-selective antagonism, CNS depression |
|
|
|
| Ipratropium | non-selective antagonism, without any mucociliary excretion inhibition. |
|
||
| Tropicamide | short acting non-selective antagonism, CNS depression |
|
|
|
| Pirenzepine | M1 receptor-selective antagonist
|
|
(fewer than non-selective ones) | |
| Diphenhydramine | Benadryl |
|
||
| Dimenhydrinate | Dramamine | |||
| Dicyclomine | ||||
| Flavoxate | ||||
| Oxybutynin | ||||
| Tiotropium | Spiriva | |||
| Cyclopentolate | short acting non-selective antagonism, CNS depression |
|
|
|
| Atropine methonitrate | non-selective antagonism, blocks transmission in ganglia |
|
||
| Trihexyphenidyl | Artane | |||
| Tolterodine | Detrusitol | |||
| Solifenacin | Vesicare | |||
| Darifenacin | Enablex | |||
| Benzatropine | Cogentin | |||
| Mebeverine | Colofac |
See also
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
- MeSH Muscarinic+antagonists
 |
This pharmacology-related article is a stub. You can help Wikipedia by expanding it. |
|
|||||||||||
|
|||||||||||||||||
|
||||||||
|
|||||||||||||||||||||||||||||
Wikipedia content modification information:
- This page was last modified on 25 June 2008, at 13:49.
Wikipedia Authorship and Review
Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.
Wikipedia Usage Guidelines
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Muscarinic antagonist".
The URL for this specific entry is:
All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.