Nicotine acetylcholine resembling

Of the 25 animal phyla, almost half are worms. Thus, it is not at all surprising that some worms contain toxins. The nemertines are a phylum of over 800 known species which resemble flatworms but are active predators on crustaceans and other worms. This phylum is exceptionally toxic among the various worm phyla. The Heteronemertine side possesses peptide toxins which appear to be only defensive, as these animals have no means of injecting a venom. The peptides include neurotoxins, which enhance excitability of nerve membranes, and cytolysins, which permeabilize and destroy cell membranes. Members of the Hoplonemertine class inject a venom into their prey using a mineralized stylet located in their proboscis, which is also used to immobilize the prey. Their toxins are alkaloids similar to nicotine which in minute amounts paralyze crustaceans and annelid worms and primarily activate nicotinic acetylcholine receptors. Another well-known worm toxin is nereistoxin, a disulfide-containing alkaloid which also binds to nicotinic... 

Burn, J. H., Leach, E. H., Rand, M. J., and Thompson, J. W., 1959, Peripheral effects of nicotine and acetylcholine resembling those of sympathetic stimulators, J. Physiol. (London) 148 332. 

Before proceeding further we may note that many pharmacologists have found it convenient to describe the action at a synapse or neuromuscular junction as nicotine-like or muscarinelike as the case may be (see figs. 3 and 6). Thus the effect of nicotine resembles the action of acetylcholine at the junction... 

The action of acetylcholine at the skeletal muscle motor end plate resembles that produced by nicotine. Thus, the choUnoreceptor on skeletal muscle is a nicotinic receptor. Based on antagonist selectivity, however, the autonomic and somatic nicotinic receptors are not pharmacologically identical (see Chapter 14). 

In humans, the symptoms of acetylcholine poisoning resemble on the one hand the syndrome of nicotine poisoning (muscle twitch, excitability, followed by muscular paralysis) and, on the other hand, the syndrome of muscarine poisoning (nausea, pain, exudation, increased diuresis, dyspnoea, pulmonary oedema). Owing to the effect on the central nervous system, the loss of sense of orientation, ataxy, tremor, derangement of consciousness and fainting occur simultaneously. 

Acetylcholine—the acetic ester of choline—has very strong and multiple biological actions. It excites or inhibits many organs and tissues in concentrations as low as 10" -10 ° even much higher sensitivity to ACh has been described. Dale divided the diverse effects of ACh into two large groups muscarinic and nicotinic effects. The muscarinic effects of ACh include its action on smooth muscle, for example its capacity to stimulate intestinal muscles or to cause a fall in blood pressure its inhibitory action on the cardiac pace-maker and muscles its action on the glands, the ability to induce salivary secretion, for instance. The muscarinic action of ACh resembles the effects of parasympathetic nerves it is reproduced by muscarine and blocked by atropine. 

When the microelectrode is inserted into more remote regions of the muscle fibres, the e.p.p. quickly diminishes and disappears at a distance of about 4 mm from the end-plate (Fig. 2A). E.p.p. is diminished by tubocurarine and increased and greatly prolonged by anticholinesterases (Fig. 2B). The microapplication of ACh to the end-plate induces an acetylcholine-potential depolarization resembling the e.p.p. which also is potentiated by anticholinesterases and blocked by tubocurarine (Fig. 2C). The same effect as with ACh can be reproduced by several cholinomimetics carbocholine, nicotine, decamethonium and others. 

The methyl ester of P-trimethylammoniopropionate (13.62) may be regarded as acetylcholine in which the order of the ethereal and carbonyl oxygen atoms has been reversed. It is a very poor substrate for acetylcholinesterase, and does not inhibit this enzyme. However, it has strong muscarinic and moderate nicotinic properties, as well as some small measure of individuality in the pharmacological properties (Bass et al., 1950)-The resemblance between this structure and that of arecoline (13.57) is noteworthy. 

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