ACETYLCHOLINE

From Big Medical Encyclopedia

ACETYLCHOLINE — mediator of nervous excitement. It is synthesized in an organism from amino alcohol of sincaline and acetic to - you. Biologically very active agent.

And. has multilateral effect on an organism. The main function — mediation of nervous impulses. The nerve fibrils and the neurons corresponding to them which are carrying out transfer of nervous impulses by means of And., are called cholinergic. Motor-neurons, the innervating skeletal muscles concern to them; preganglionic neurons of parasympathetic and sympathetic nerves; postganglionic neurons of all parasympathetic and some sympathetic nerves (uterus, sweat glands) and some neurons of c. N of page. All cholinergic fibers contain cholineacetyltransferase — specific enzyme by means of which there is a synthesis of acetylcholine. And. is in nerve terminations in bubbles from which it streams in a synaptic gap at the time of arrival of nervous impulse. Release And. nerve terminations has quantum character. Apparently, contents of a bubble also make that smallest portion And. (quantum), edges can be allocated. In normal conditions each nervous impulse causes allocation of several hundred quanta of A. Vzaimodeystvuya with a specific macromolecule on a postsynaptic membrane — a holinoretseptor, And. increases permeability of a membrane for ions: there is a postsynaptic potential which changes excitability of an effector cell, and in case of a neuromuscular synapse is a proximate cause of generation of action potential. Effect And. stops under the influence of enzyme of acetylcholinesterase (see. Cholinesterases ), which hydrolyzes And. on low-active sincaline and acetic to - that, and also owing to simple diffusion And. from a synaptic gap. In a molecule A. there are two active groups providing interaction with a holinoretseptor: the loaded trimetilammoniyevy group (cationic «head»), edges reacts with anion group in a holinoretseptor, and strongly polarized ester group reacting with the so-called esterofilny site of a holinoretseptor.

Distinguish two types of action And.: muskarinopodobny and nicotinosimilar. Muskarinopodobny action it is shown by the effects similar to that which arise at irritation of parasympathetic nerves of unstriated muscles, hearts, glands, and acts atropine; nicotinosimilar it is expressed by excitement vegetative gangliyev and marrow of adrenal glands, and also skeletal muscles and acts high doses of nicotine, Hexonium, tubocurarine. According to it holinoreaktivny systems of different bodies designate as m-holinoreaktivnye (muskarinochuvstvitelny) and N-holinoreaktivnye (nicotinosensitive).

In usual conditions muskarinopodobny action prevails And. At instillation And. in an eye there is a narrowing of a pupil and a spasm of accommodation, intraocular pressure decreases. At hit in the general blood stream the lowering of blood pressure caused by vasodilatation is observed (coronary vessels of the person A. narrows) and to a lesser extent delay of cordial activity, strengthening of a physical activity went. - kish. a path, reduction of muscles of bronchial tubes, bilious and a bladder, a uterus, strengthening of secretion of glands with a cholinergic innervation, especially salivary and stalemate.

Nicotinosimilar action And. on vegetative a ganglion and adrenal glands it is shown after atropinization and during the use of higher doses. It is expressed in pressor effect. And. also stimulates nicotinosensitive systems of carotid balls and reflex excites breath.

All effects of acetylcholine can be strengthened by preliminary administration of antikholinesterazny substances (Eserinum, prozerin, etc.). At usual ways of introduction And. does not get through a blood-brain barrier and does not exert impact on c. N of page. Variety of effects And., among which can appear undesirable, weakening each other, and also short duration of action extremely limit its use in medical practice. And. widely use at pilot study of functions of cholinergic structures in the form of well soluble salt — acetylcholine of chloride (Acetylcholini chloridum, Acetylcholinum chloratum; joint venture. Б). Form of release: ampoules on 5 ml containing 0,2 g of drug.

See also Mediators , Cholinomimetic substances .

Acetylcholine as mediator of allergic reactions

Similarity of a picture of poisoning And. at dogs with a picture of development in them acute anaphylaxis (see) allowed to assume direct participation of the cholinergic processes taking place in activity of some bodies in the mechanism of allergic reactions of these bodies. Such body is, e.g., the language of a dog having a parasympathetic innervation. It was supposed that as a point of application of antigen in sensibilized body serve the terminations of parasympathetic nerves. It was confirmed experimentally. Administration of antigen in vessels of language to a sensibilized dog causes overt vasodilating effect. Normal these phenomena are not observed. At switching off of a parasympathetic innervation of a half of language by preliminary (a month before experience) enucleation submaxillary and hypoglossal sialadens and together with them submaxillary and hypoglossal peripheral nodes of the parasympathetic innervatsionny device of vessels of language of a dog the reaction of vessels of this half of language to antigen described above completely is removed. At the same time at section of a lingual nerve the nature of vascular reaction to antigen does not change that testifies to lack of reaction to antigen of the sensitive terminations of somatic nerves. Participation And. in processes of spread of poisoning in an organism it is improbable. The role of anaphylactic poison in this sense is carried out, obviously, more resistant decomposition products of fabric, to the Crimea belong active kinina, serotonin, a histamine, etc. Thus, an atsetilkholinovy hypothesis of a pathogeny of an allergy in any degree does not contradict idea of participation of a histamine as one of important links in the mechanism of allergic alteration of fabric. Participation And. and cholinergic processes in the mechanism of a «organ» allergy, i.e. in the conditions of its action in loco nascendi in the corresponding cholinergic synapses, matters essential, and in a number of structures and a fundamental unit in definition of functional expressions of an allergy. Synoptic bonds in vegetative and the central nervous system, a parasympathetic vasomotor innervation, an innervation of heart etc. belong to such structures. Possibly, in them activity of cholinesterase changes, the speed of release increases And. at excitement by their specific antigen and that the most important, in them appears excitability to a specific antigen which absolutely or almost absolutely was absent in a normality.

See also Mediators of allergic reactions .


Bibliography: Anichkov S. V. and Grebenkina M. A. The pharmacological characteristic of holinoretseptor of the central nervous system, Bulletin ekspery. biol, and medical, t. 22, No. 3, page 28, 1946; Kibyakov A. V. Chemical transfer of nervous excitement, M. — L., 1964, bibliogr.; Michelson M. Ja. and Zeymal E. V. Atsetilkholin, about the molecular mechanism of action, L., 1970, bibliogr.; The guide to pharmacology, under the editorship of N. V. Lazarev, t. 1, page 137, L., 1961; T. M tourist's shares. Mediator function of acetylcholine and nature of a holino-receptor, M., 1962; E to l with D. Fiziologiya of synapses, the lane with English, M., 1966, bibliogr.; Central cholinergic transmission and its behavioral aspects, Fed. Proc., v. 28, p. 89, 1969, bibliogr.; Dale H.H. The action of certain esters and ethers of choline, and their relation to muscarine, J. Pharmacol., v. 6, p. 147, 1914; Goodman L. S. a. G i 1 m a n A. Pharmacological basis of therapeutics, N. Y., 1970; Katz B. The release of neural transmitter substances, Springfield, 1969, bibliogr.; Michelson M. J. a. Danilov A. F. Cholinergic transmissions, in book: Fundament. biochem. Pharmacol., ed. by Z. M. Bacq, p. 221, Oxford a. o., 1971.

H. Ya. Lukomskaya, M. Ja. Michelson; A. D. Ado (ave).

Яндекс.Метрика