Acetylcholine, antagonists

In contrast to muscarine, atropine blocks these actions of acetylcholine and muscarine. Atropine is, therefore, an acetylcholine antagonist. It binds where acetylcholine binds and therefore prevents the binding of the latter but does not activate it. Two molecules cannot occupy the same binding site at the same time. Atropine is isolated from the plant Atropa belladonna. Extracts of this plant have been used for millennia for a variety of purposes. Although large doses are poisonous (Atropos is the name of the Fate who cuts the thread of life), small doses causes dilation of the pupils, a consequence of its action as an acetylcholine antagonist, and has been used for cosmetic purposes by women, hi Itahan, belladonna means beautiful woman. 

Mechanism of Action An acetylcholine antagonist that inhibits the action of acetylcholine by competing with acetylcholine for common binding sites on muscarinic receptors, which are located on exocrine glands, cardiac and smooth-muscle ganglia, and intramural neurons. This action blocks all muscarinic effects. Therapeutic Effect Decreases GI motility and secretory activity, and GU muscle tone (ureter, bladder) produces ophthalmiccycloplegia, and mydriasis. 

New applications of dioxolane-containing compounds include the use of 22 as a new perfume type <98MI21>, inhibition of tumour necrosis factor by 23 <99MIP16766> and compounds 24 as muscarinic acetylcholine antagonists <99M189>. 

Diphenhydramine is a histamine antagonist (antihistamine) as well as well as an acetylcholine antagonist and is a local... 

This type of response may be caused by several mechanisms. For instance, the muscle relaxation induced by succinylcholine, discussed in more detail in chapter 7, is due to blockade of neuromuscular transmission. Alternatively, acetylcholine antagonists such as tubocurarine may compete for the receptor site at the skeletal muscle end plate, leading to paralysis of the skeletal muscle. Botulinum toxin binds to nerve terminals and prevents the release of acetylcholine the muscle behaves as if denervated, and there is paralysis. This will be discussed in more detail in chapter 7. 

Acetylcholine antagonists (blockers) that block the nicotine-like effects (neuromuscular blockers and autonomic ganglion blockers) are described elsewhere (see Ch. 18). 

Acetylcholine antagonists that block the muscarine-like effects, e.g. atropine, are often imprecisely called anticholinergics.The more precise term antimuscarinic is preferred here. 

Kier, L.B. and Hall, L.H. (1978). A Molecular Connectivity Study of Muscarinic Receptor Affinity of Acetylcholine Antagonists. J.Pharm.ScL, 67,1408-1412. 

As substances that block the action of acetylcholine (antagonists)... 

A series of quaternary ammonium salts of pilocarpine (13) have been shown to possess acetylcholine antagonist properties. 

The time to death of animals given a mixture of spirolides was increased after pretreatment with physostigmine [46]. Conversely, the time to death was decreased when atropine or other acetylcholine antagonists were given before administration of spirolide [46]. 

New applications of compounds in this section include the use of simple 1,3-dioxolan-4-ones as electrolyte solvents for batteries <01MIP38319>, use of ketals of pyruvic acid 34 as "dietary supplements" <01USP6177576>, evaluation of the four diastereomers of 35 as muscarinic acetylcholine antagonists <01BMCL247> and use of dioxolanone-conlaining compounds such as 36, which act as squalene and cholesterol synthetase inhibitors, for treatment of hypercholesterolaemia <01JAP187789>. 

It is of interest to see if the inhibitory effect of acetylcholine could be blocked with acetylcholine antagonists. The experiments carried out so far have shown that muscarinic antagonists such as atropine do not block the inhibitory effect of acetyl-choUne. The effect of nicotinic antagonists was difficult to disentangle, as explained in Sect.D.IIL4. 

Espada, A., Jimenez, C Debitus, C and Riguera, R. (1993) Villagorgin A and B. New type of indole alkaloids with acetylcholine antagonist activity from the gorgonian Villagorgia rubra. Tetrahedron Lett., 34, 7773-7776. 

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