Cholinomimetic Agent

any of several chemical compounds whose action largely coincides with the effects of the excitation of cholinergic nerve fibers or of the mediator acetylcholine.

A distinction is made between m- and n-cholinomimetic agents according to the particular choline receptors they affect. M-cholinomimetic agents are similar in action to muscarine, an alkaloid obtained from certain species of the fungus Amanita. These agents excite the m-choline receptors of effector organs situated at the endings of postganglionic cholinergic fibers, causing contraction of the bronchial muscles, dilation of the vessels, slowing of the pulse, contraction of the pupils, and intensified secretion of the salivary, sweat, lacrimal, and digestive glands. Pilocarpine and Benzamon are m-cholinomimetic agents.

N-cholinomimetic agents are similar in action to nicotine, that is, they excite the n-choline receptors of the sympathetic and parasympathetic ganglia, adrenal medulla, carotid glomeruli, hypophysis, and skeletal musculature. In small doses, n-cholinomi-metics have an excitatory effect, and in large doses, an inhibitory effect. The compounds lobeline, cytisine, sparteine, and anabasine exert n-cholinomimetic action.

When crossing the blood-brain barrier, certain cholinomimetic agents facilitate the transmission of nerve impulses in the central nervous system. This is true of central m- and n-choline receptors and of central m- and n-cholinomimetic agents. A number of acetylcholinesterase inhibitors exert cholinomimetic action, for example, physostigmine, phosphacol, galanthamine, neostigmine methyl sulfate, phosphorus-containing insecticides, and such phosphorus-containing war gases as tabun, sarin, and soman.

M-cholinomimetic agents are used to prevent and treat atonia of the intestine and urinary bladder, stimulate labor contractions, and treat paroxysmal tachycardia and glaucoma. N-cholinomimetic agents such as lobeline are used as reflex stimulants of respiration. Anticholinesterases are used to treat myasthenia, peripheral paralysis, and glaucoma. Cholinomimetic agents are also used as antidotes in cases of poisoning by cholinolytics.