Muscarine

MUSCARINE, Muscarinum, an extremely poisonous alkaloid discovered by Schmiedeberg in 1868 in the fly agaric mushroom Agaricus muscarius L., or Amanita muscaria Pers., which belongs to the subfamily of agaric mushrooms (Agaricaceae, fam. Hymenomycetes). The fly agaric mushroom is found in pine and birch forests across most of Europe and Siberia; it consists of a stipe and a cap; the latter is bright red with white scales; the stipe, gills, and membranous ring of the mushroom are white. Fly agarics are among very poisonous mushrooms. It is remarkable that in a fresh state the fly agaric is very toxic to flies, whereas when dried it becomes completely harmless to them, from which it must be concluded that the substance poisonous to flies is easily destroyed or disappears when the mushroom dries. Up to now, this poisonous substance remains completely unknown. Peoples living in northern Siberia—the Kamchadals, Tungus, Yakuts, Samoyeds, and some others—prepare an intoxicating drink from fly agarics, the effect of which on the central nervous system is explained by the action of a special fungal toxin (Harmsen). The chemical composition of this toxin is unknown. In addition to muscarine, Harmsen's toxin, and the substance that kills flies, the fly agaric has also been found to contain muscaridine, choline, and potassium salts. Muscarine was also found by Boehm in the mushrooms Amanita pantherina and Boletus luridus Schaeff., and by Fahrig in the mushroom Inocybe lateraria Rick. Muscarine extracted from mushrooms is called natural or fungal muscarine; the empirical formula of natural muscarine is C₅H₁₅NO₃, while its structural formula has not been determined. Natural muscarine is a colorless, odorless, and tasteless, strongly alkaline, thick syrupy liquid that gradually turns into a crystalline state upon drying over sulfuric acid; in air, muscarine crystals rapidly deliquesce, and muscarine again becomes a syrupy liquid. Muscarine is readily soluble in water and alcohol, very sparingly in chloroform, and completely insoluble in ether. When heated above 100°, muscarine decomposes, emitting a faint tobacco odor; upon treatment with caustic alkalis or lead oxide while heated, it forms trimethylamine; with hydrochloric and sulfuric acids, it forms crystalline salts. It was believed that muscarine is close in structure to choline C₅H₁₅NO₂: H₃C\ /CH₂CH₂OH H₃C/ \NCH₂CH₂OH H₃C^N/

H₃C/ ^xOH muscarine

choline or, according to some authors, an anhydride of muscarine with an aldehyde group. However, artificial muscarine obtained synthetically from choline by Schmiedeberg and Harnack showed a difference in action upon experiments on animals compared to natural muscarine, which gives the right to deny the identity of artificial and natural muscarine. The above formula of muscarine refers only to artificial muscarine, while the structure of natural muscarine remains unknown. In addition to choline-muscarine, i. e., artificial muscarine obtained from choline, several other artificial muscarines were produced: in 1884 Berlinerblau synthesized anhydro-muscarine, which is oxidized by silver oxide to betaine, but is not reduced to choline; in 1889 Bode obtained isomuscarine or oxycholine from neurine; in 1885 Brieger obtained cadaveric muscarine or ptomato-muscarine from decomposing meat of navaga; in 1903 Harmsen from cat urine; in 1909 Fühner from rabbit urine; the latter author, calling such muscarine urinary muscarine (Uromuskarin), expresses the assumption of the identity of uromuscarine with ptomatomuscarine. In 1905 Kutscher obtained from Liebig's meat extract meat muscarine - Carnomuscarin. Each of the named artificial muscarines in its composition (C₅H₁₅NO₃) is an isomer of fungal, i. e., natural muscarine, thus forming with it one group of muscarines. Under the name of muscarine, a coloring matter of composition C₁₈H₁₅N₂O₂Cl is also known, which has nothing in common with the above-mentioned substances of the muscarine group, except for the name. The medical significance of fungal muscarine, as well as synthetically obtained ones, is considerable, despite the fact that muscarine is not used at all for therapeutic purposes. Attempts to use muscarine internally in epilepsy and in the treatment of glandular tumors, externally in eye practice, and also in the treatment of ulcers, were soon completely abandoned due to the toxicity of muscarine. The theoretical, toxicological, and physiological-pharmacological significance of muscarine is very great. This alkaloid belongs to typical parasympathicotropic poisons acting excitingly on the peripheral parts of the parasympathetic nerves, and the action on the indicated nervous system manifests itself strictly selectively, which makes muscarine a particularly valuable pharmacological agent, making it possible to use this substance in experiments similarly and instead of electrical stimulation. Natural muscarine, introduced in small doses into the animal organism, slows down cardiac activity (negative chronotropic and negative inotropic action), and in a correspondingly larger dose causes, after slowing and weakening of systolic contractions, a complete stop of the heart in the diastolic phase. The stopped heart of a frog is heavily filled with blood, stretched. In a frog, the cardiac arrest from muscarine can last for hours, and yet with every mechanical or electrical stimulation of the ventricles, the heart each time responds with a single full contraction, which indicates first of all that cardiac arrest does not depend on heart paralysis. Since the slowing and stopping of the heart from muscarine resembles the same phenomena observed upon stimulation of the cervical trunk of the vagus nerve in a frog by an induction current, and since upon atropinization of the frog's heart neither vagus nerve stimulation nor the effect of muscarine on the heart causes either slowing or stopping of the heart, Schmiedeberg, and after him other researchers, came to the conclusion that muscarine acts in an excitatory manner on the inhibitory apparatus of the heart - on the peripheral endings of the vagus nerves in the frog's heart. The same phenomena - slowing and stopping of the heart from muscarine - were obtained on isolated hearts of frogs and rabbits, which proved that in the just-indicated action of muscarine on the heart, the excitation of the vagus nerve centers plays no role. The excitation of the peripheral inhibitory elements of the vagus nerves by muscarine is indirectly confirmed by the fact that a frog's heart stopped by muscarine can be induced to contract again if the excitation of the heart muscles or cardiac motor ganglia is caused by such poisons as physostigmine, veratrine, digitalin, guanidine, camphor, and some others. The circumstance that muscarine does not cause cardiac arrest in the spring in frogs, in which cardiac arrest is not obtained even upon stimulation of the vagus nerves by an induction current, also serves as proof that the action of muscarine concentrates on the endings of the vagus nerves. However, Straub holds different views on the site and mechanism of action of muscarine as a poison causing slowing and stopping of the heart. According to Straub, muscarine acts on the muscle tissue of the heart, exerting an effect only at the moment of penetration into the muscle cells; once inside the cell, muscarine does not cause further action; for this reason, the heart with the gradual introduction of small doses of muscarine into it continues to contract, despite the fact that a significant amount of muscarine accumulates in the heart itself; this amount of muscarine is quite sufficient to surely cause complete cardiac arrest in another frog if muscarine is used in a concentrated form. The antagonism of atropine's action in relation to muscarine is explained by Straub by the fact that atropine delays the penetration of muscarine into the cell. Straub's theory of the action of muscarine is supported by some authors, but is not generally accepted. Experimental data that muscarine has no effect on the hearts of invertebrate animals, e. g., crabs, snails, insects, as well as on the hearts of chicken embryos, in which differentiation of muscle tissue from nerve tissue has not yet occurred, also speak in favor of the action of muscarine on the inhibitory nerve elements in the heart, and not on the muscle elements. Nikolaev's work on the hearts of frogs with degenerated vagus nerves showed that the site of action of muscarine in the heart is not the pericellular networks by which the vagus nerves end on ganglionic cardiac cells, but the automatic nervous apparatus located in the heart of the frog. The latter can fully determine the effect of muscarine. The latest works of Razenkov and Lavrentiev and their students give reason to conclude that the point of application of muscarine in the hearts of higher animals is located in a similar automatic nervous apparatus of the heart. In warm-blooded animals, muscarine, just like in frogs, slows down and stops the heartbeat; blood pressure drops rapidly and significantly. Schmiedeberg pointed out that fungal muscarine dilates the vessels of the rabbit's ear. Mainly by vessel dilation and blood pressure drop is explained the large drop in temperature (by 9–10°) observed in animals during their slow poisoning by muscarine. Respiration from small doses becomes more frequent, and from large doses, after a short acceleration, slows down, weakens, and completely stops. After muscarine, during inspiration, all chest muscles work intensively; expiration occurs in jerks and is of a convulsive character. In the opinion of Schmiedeberg, death from muscarine occurs as a result of paralysis of the respiratory center. Some researchers prove that muscarine also has a paralyzing effect on the peripheral respiratory nerves. The stomach and intestines under the influence of muscarine contract intensively; the movement of the intestines can be noticed through the abdominal wall. Peristaltic contractions upon introduction of large doses of muscarine are disorderly, often replaced by antiperistaltic ones; diarrhea and vomiting occur. Spastic contractions of the entire stomach or its parts with subsequent relaxation represent a usual phenomenon in muscarine poisoning. Schmiedeberg believes that the strong influence of muscarine on the stomach and intestines depends on the action of muscarine not only on the endings of the vagus nerves embedded in the indicated organs, but also on the action on the ganglionic cells of Auerbach's plexus. Spasmodic contractions from muscarine also occur in other organs having smooth musculature: in the urinary bladder, spleen, and uterus. The cause of contractions is the irritating action of muscarine on the peripheral endings of the parasympathetic nerves embedded in the organs, or the action on automatic nerve ganglionic devices, similar to how this happens in relation to the heart (Nikolaev). From the action of muscarine on the eye, the pupil is strongly constricted, accommodation spasm occurs. Both of these phenomena depend on the action of muscarine on the endings of the parasympathetic fibers of the oculomotor nerve in the circular muscles of the iris and in the ciliary muscle. Fungal muscarine does not affect motor nerves, which was long ago established by Schmiedeberg and confirmed by Hans Meyer, and later by Honda, whereas artificial muscarine has a paralyzing effect on motor nerve endings. Therefore, one can speak about curare-like properties of muscarine only in relation to artificial muscarines, in particular muscarine obtained from choline. Fungal muscarine enhances the secretion of the glands of the stomach, intestines, bile secretion, and pancreatic juice; perspiration, salivation, and lacrimation also increase. The action of muscarine on saliva secretion depends on the stimulation by muscarine of the peripheral nerve endings of the chordae tympani, as Schmiedeberg showed. The increased secretion of secrets by all other glands occurs from the irritating action of muscarine on the secretory nerves of the glands; the point of application of muscarine's action in these cases is the peripheral nerve endings.

Among the agents that have the property of eliminating the action of muscarine, atropine can be pointed out, which, by paralyzing the endings of the parasympathetic nerves, is a direct antagonist of muscarine in all those cases where the mechanism of action depends on the irritating effect of muscarine on the peripheral endings of one or another parasympathetic nerve. Therefore, the diastolic cardiac arrest, as well as the slowing of heart contractions resulting from muscarine, are rapidly eliminated by atropine. Atropine also stops the increased peristaltic, antiperistaltic, and spasmodic movements of the stomach and intestines, pupil contraction and accommodation spasm, contractions of the bladder, as well as the increased secretory activity of the salivary, sweat, and other glands. The required amount of atropine sulfate for an antagonistic action against muscarine is usually very small: from 0.001 to 0.1 mg. On the other hand, there are indications that the action of atropine on the eye, on the frog heart, on the sweat glands, and on the submandibular gland was stopped by muscarine. Therefore, it is believed that the antagonism between atropine and muscarine is mutual. To eliminate the action of atropine, relatively large amounts of muscarine are required (up to 7 g), as a result of which one can hardly speak in these cases of the specific action of muscarine, and the question of the antagonism of muscarine with respect to atropine, i.e., bilateral antagonism, is left open by many pharmacologists. Hyoscyamine and scopolamine are also antagonists of muscarine, as well as veratrine, aconitine, delphinine, physostigmine, camphor, digitaline, helleborin, adrenaline, and chloral hydrate. Of interest is the antagonistic effect of calcium chloride with respect to muscarine, pointed out by Zondek (S. G. Zondek). -- The toxicity of muscarine with respect to various animals varies greatly. Cats are especially sensitive to muscarine, in which death occurs a few hours after 3-4 mg of muscarine administered subcutaneously, and at doses of 8-12 mg for an average weight of a cat (3 kg), death occurs in 10-15 minutes. Dogs tolerate large doses of muscarine. Humans are very sensitive to muscarine; 1-3 mg of muscarine injected subcutaneously by Schmiedeberg and Koppe (Koppe) caused symptoms of poisoning: severe salivation, rush of blood to the head, redness of the facial skin, weakness, dizziness, nausea, rumbling and cutting pain in the abdomen, accelerated pulse, visual disturbance, accommodation spasm, heavy sweating on the face and to a somewhat lesser extent on other parts of the body. The picture of poisoning by fly agaric mushrooms is sometimes similar to that described for muscarine poisoning, but for the most part differs sharply, obviously due to the presence in fly agarics of various atropine-like poisonous substances, then muscarine, etc., which, having an effect on the central nervous system, on the other hand can counteract the action of muscarine as such. Therefore, poisoning can manifest itself either with symptoms from the gastrointestinal tract (abdominal pain, nausea, vomiting, severe diarrhea) or completely differently: dizziness, a state of intoxication with severe agitation and delirium, with a frantic urge for movement and an irrepressible need to break and destroy everything; after this, tremors of the whole body begin, tetanic and epileptiform convulsions, pupil dilation; the pulse, which had previously become frequent, becomes small; respiration is initially dyspneic, later stertorous. A soporose state develops, deep collapse with a sharp drop in temperature, and death occurs on the second or third day. Upon recovery, the poisoned person heals slowly. Regarding the blood in muscarine poisonings, a certain hyperleukocytosis and lower blood coagulability were noted; however, the question of blood changes cannot yet be considered resolved; nor are there data on pathological anatomical changes in the body during muscarine poisoning. -- Assistance to those poisoned by mushrooms consists predominantly in removing the contents of the stomach and intestines: emetics are given, the stomach is washed out through a tube, and the intestines via enemas; castor oil is administered internally in large doses. In cases where symptoms of muscarine poisoning appear, atropine is used subcutaneously, which is contraindicated when mushroom poisoning develops, apparently mainly due to the action of atropine-like substances. Regarding the action of artificial muscarine obtained from choline, see Choline. Regarding other artificial muscarines, literary information is very scant. Anhydromuscarine has no effect on the heart and eye, but causes increased secretion of saliva and sweat. Death ensues from respiratory paralysis. -- Isomuscarine does not cause cardiac arrest, but only slows the heartbeat; such slowing is eliminated by atropine. Only in birds does it cause pupil contraction. In mammals, it causes increased gland secretion and a curare-like effect on motor nerves, increases blood pressure, but has no effect on the eye or intestine. -- Ptomatomuscarine is similar in its action to cholinemuscarine, and therefore the question of its identity with the latter in chemical relations is raised. -- Uromuscarines are classified as ptomatomuscarines; nothing definite can yet be said about the pharmacological action of uromuscarines. Carnomuscarine also remains unstudied in pharmacological respects.