Parasympathomimetic agents

Q57 Pilocarpine is a tertiary amine parasympathomimetic agent that is mainly used in the treatment of glaucoma. Pilocarpine is commonly administered with timolol eye drops. 

Whether a toxin is naturally reactive to biological macromolecules or receptors, or requires metabolic activation to produce such a species, e.g. the enzyme-mediated transformation of tremorine (9) to the active parasympathomimetic agent oxotremorine (10), it will usually be subject to chemical or enzymic inactivation in vivo. Interruption of the latter process via appropriate substitution may thus lead to an increase in biological activity or toxicity over that of the parent compound. Perhaps the most striking example of this is provided by the extreme metabolic stability and toxicity of TCDD and the nontoxicity of its de- chloro analogue dibenzodioxin (Table 3). 

Q12 Bethanechol is a parasympathomimetic agent which mimics the actions of acetylcholine. It is capable of stimulating the muscarinic receptors on the detrusor muscle and can contract the bladder, leading to more effective emptying of urine. 

Parasympathomimetic agents increase cyclic GMP in many tissues, providing extracellular Ca is present [37]. This suggests that the increase in cyclic GMP is a secondary event brought about by an increased cytoplasmic Ca concentration. In frog heart, cyclic AMP levels rise and cyclic GMP levels fall during early systole but return to normal during early diastole [68]. 

There are few, if any, indications for the therapeutic use of miotics in the horse. However, a 2% solution of the parasympathomimetic agent pilocarpine can induce miosis in normal eyes after repeated topical application (van der Woerdt et al 1998). The cholinesterase irihibitor topical miotics, including demecarium bromide and echothiophate iodide, appear to be potentially uveitogenic in the horse and should not be used. 

Pilocarpine nitrate is a parasympathomimetic agent possessing muscarinic effects of acetylcholine. It is mostly used as a solution (1 to 5%) to exert an action on the eye to cause miosis and retard intraocular tension in the treatment of open-angle glaucoma. Pilocarpine nitrate being less hygroscopic than its corresponding hydrochloride and hence it is more easy to handle. 

Main toxic constit. of the fly fungus Amanita muscaria and various Inocybe spp. V. powerful parasympathomimetic agent causing hypotension and broncho-constriction. Stereoisomers show only a fraction of the activity. V hygroscopic. 

Second, uric acid retention was not observed after administration of several parasympathomimetic agents. 

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