Atropine-acetylcholine antagonism

Ipratropium Atrovent HFA, Atrovent Nasal) [Bronchodilotor/ Anticholinergic] Uses Bronchospasm w/ COPD, rhinitis, rhinorrhea Action Synthetic anticholinergic similar to atropine antagonizes acetylcholine receptors, inhibits mucous gland secretions Dose Adults Feds >12 y. Nebuliza-tion 500 meg in 2.5-3.0 mL NS Feds. Nebulization 125-250 meg in 2.5-3.0 mL NS Caution [B, +/-] w/ inhal insulin Contra Allergy to soya lecithin/related foods Disp HFAmet-dose inhal 18 meg/dose inhal soln 0.02% nasal spray 0.03,... 

The alkaloids namely atropine, hyoscyamine and scopolamine are obtained from Atropa belladonna. Atropine is dl-hyoscyamine, and, 1-isomer is more potent than d-form both peripherally and centrally. Atropine blocks the muscarinic effects of acetylcholine, the antagonism between acetylcholine and atropine is of competitive... 

The miotic effects of carbachol and bethanechol are greater than those of acetylcholine. Atropine is able to antagonize all cholinergic (muscarinic) effects produced by acetylcholine, methacholine, carbachol, and bethanechol. However, this antagonism is least evident with carbachol. 

Atropine antagonizes OP poisoning by blocking acetylcholine receptor sites... 

FIGURE 1.17 Schild plot for the action of atropine in antagonizing the action of acetylcholine on guinea-pig ileum. Each point gives the mean the standard error of the mean of the number of observations shown. 

Hopf2 concludes that although insect nerve tissues produce substances that simulate acetylcholine and a cholinesterase which is inhibited by organo-phosphorus insecticides, these substances (in locusts at any rate) are not antagonized by atropine. Furthermore, tubocurarine does not poison insects, although it is active in warm-blooded animals and affects the neuromuscular junctions (see pp. 36, 37). In short, different physiological mechanisms appear to be at work in insects. In particular, it seems that acetylcholine, when injected into a variety of insects, has no marked toxic action. It seems then that, in some... 

About scaritoxin, the following results were reported. This toxin was found to depress the oxidative metabolic process in the rat brain (20) and to have a depolarizing action on excitable membranes (38). In the guinea-pig atria, scaritoxin caused a marked potentiation of the acetylcholine negative inotropic and chronotropic effects (39). In rat atria, we observed biphasic inotropic and chronotropic effects similar to those of ciguatoxin. Negative inotropic and chronotropic effects were antagonized by atropine. 

Atropine, a tertiary amine, competitively antagonizes acetylcholine activity. Full therapeutic doses of atropine produce definite and prolonged inhibitory effects on the motor activity of the stomach, duodenum, jejunum, ileum, and colon, characterized by a decrease in tone and in amplitude and frequency of peristaltic contractions. 

The action of administered acetylcholine on effector systems innervated by parasympathetic postganglionic neurons (smooth muscle cells, cardiac muscle cells, and exocrine gland cells) resembled the actions produced by the naturally occurring plant alkaloid muscarine. The actions of both acetylcholine and muscarine on the visceral effectors are similar to those produced by parasympathetic nerve stimulation. Furthermore, the effects of acetylcholine, muscarine, and parasympathetic nerve stimulation on visceral effectors are antagonized by atropine, another plant alkaloid. 

Muscarinic Receptor Interactions. Excitatory muscarinic effects, such as temporary stimulation of salivation and stimulation of intestinal peristalsis, were seen with 2-PAM. Atropine-like actions were seen at high concentrations (15-20 mg/kg or more), and, when injected rapidly, 2-PAM caused temporary diplopia (nicotinic block) and loss of accommodation in the eye.Both TMB-4 and 2-PAM blocked bradycardia induced by vagal stimulation. At low concentrations, neither compound affected normal intestinal peristalsis, but they did block peristalsis caused by increased vagal stimulation. TMB-4, 2-PAM, and toxogonin antagonized the effect of acetylcholine, acetyl- -methyl-choline, and other agonists on Isolated guinea pig ileum.62... 

The physiological effects of the accumulation of acetylcholine can be antagonized by the administration of atropine, and the symptoms alleviated. 

FIGURE 19-2 Structures of acetylcholine and atropine. Atropine and similar agents antagonize the effects of acetylcholine by blocking muscarinic cholinergic receptors. 

Homatropine is a synthetic parasympatholytic representing the ester of tropine and mandelic add (Fig. 1). This drug antagonizes acetylcholine on MR and is thus used as mydriatic with less detrimental paralytic effects on ciliary eye muscle than atropine but showing faster and shorter action [1,33], Therefore, it belongs to the WHO list of essential medicines as mydriatic eye drops representing an alternative to atropine [41],... 

In the case of acute poisoning resulting from excessive exposure there are two antidotes that can be used. The first is atropine (which is found in deadly nightshade berries and is also known as belladonna), which antagonizes the effects of the acetylcholine that accumulates in the body... 

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