Muscarinic cholinoceptors

Christopoulos A, Lanzafame A, Michelson E. Allosteric interactions at muscarinic cholinoceptors. Clin Exp Pharmacol Physiol 1998 25 185-194. 

Schroder H, Zilles K, Luiten PG, Strosberg AD. 1990. Immu-nocytochemical visualization of muscarinic cholinoceptors in the human cerebral cortex. Brain Res 514 249-258. 

Ga-GDP has no affinity for the effector protein and reassociates with the p and Y subunits (A). G-proteins can undergo lateral diffusion in the membrane they are not assigned to individual receptor proteins. However, a relation exists between receptor types and G-protein types (B). Furthermore, the a-subunits of individual G-proteins are distinct in terms of their affinity for different effector proteins, as well as the kind of influence exerted on the effector protein. G -GTP of the Gs-protein stimulates adenylate cyclase, whereas G -GTP of the Gr protein is inhibitory. The G-protein-coupled receptor family includes muscarinic cholinoceptors, adrenoceptors for norepinephrine and epinephrine, receptors for dopamine, histamine, serotonin, glutamate, GABA, morphine, prostaglandins, leukotrienes, and many other mediators and hormones. 

Anticholinergics. Antagonists at muscarinic cholinoceptors, such as betuatropine and biperiden (p. 106), suppress striatal cholinergic overactivity and thereby relieve rigidity and tremor however, akinesia is not reversed or is even exacerbated. Atropinelike peripheral side effects and impairment of cognitive function limit the tolerable dosage. 

The side effects of tricyclic antidepressants are largely attributable to the ability of these compounds to bind to and block receptors for endogenous transmitter substances. These effects develop acutely. Antagonism at muscarinic cholinoceptors leads to atropine-like effects such as tachycardia, inhibition of exocrine glands, constipation, impaired micturition, and blurred vision. 

Hi-receptor but also at muscarinic cholinoceptors, serotonin receptors, and adrenoceptors. This explains the atropine-like side effects of those drugs. The cationic amphophilic structure of these substances resemble that of antiarrhythmic agents which might explain the arrhythmogenic properties seen with some of these Hi-antagonists. 

Most of the direct organ system effects of muscarinic cholinoceptor stimulants are readily predicted from a knowledge of the effects of parasympathetic nerve stimulation (see Table 6-3) and the distribution of muscarinic receptors. Effects of a typical agent such as acetylcholine are listed in Table 7-3. The effects of nicotinic agonists are similarly predictable from a knowledge of the physiology of the autonomic ganglia and skeletal muscle motor end plate. 

The pupillary constrictor muscle (see Figure 6-9) depends on muscarinic cholinoceptor activation. This activation is blocked by topical atropine and other tertiary antimuscarinic drugs and results in unopposed sympathetic dilator activity and mydriasis (Figure 8-3). Dilated pupils were considered cosmetically desirable during the Renaissance and account for the name belladonna (Italian, "beautiful lady") applied to the plant and its active extract because of the use of the extract as eye drops during that time. 

The first-generation H receptor antagonists have many actions in addition to blockade of the actions of histamine. The large number of these actions probably results from the similarity of the general structure (Figure 16-1) to the structure of drugs that have effects at muscarinic cholinoceptor, a adrenoceptor, serotonin, and local anesthetic receptor sites. Some of these actions are of therapeutic value and some are undesirable. 

Autonomic nervous system Loss of accommodation, dry mouth, difficulty urinating, constipation Muscarinic cholinoceptor blockade... 

Parasympathetic stimulation increases bronchoconstriction via muscarinic cholinoceptors. A muscarinic agonist will increase bronchoconstriction, so this drug is definitely not recommended. 

Alupenf" ordprenaUne. alverine [inn] (alverine citrate [usan]) is a diphenyldipropylamine compound, a MUSCARINIC CHOLINOCEPTOR ANTAGONIST, which can be used as an ANTISPASMODIC AGENT to treat irritable bowel syndrome, alverine citrate alverine. amacid brilliant blue indigotin disulfonate sodium. 

A number of types of parasympathomimetics are used. Muscarinic agonists used include carbachol and pilocarpine (see MUSCARINIC CHOLINOCEPTOR agonists) ANTICHOLINESTERASES include demecarium bromide, dyflos, ecothiopate iodide, pl sostigmine sulphate and pyridostigmine bromide. 

Anticholinergic drugs are only really suitable in the case of agents that show some gastric-selectivity, e.g. pirenzepine and telenzepine (see MUSCARINIC CHOLINOCEPTOR antagonists). They work by reducing the secretion of peptic acid by the stomach mucosa. 

Arduan pipecuronium bromide, arecoline is an alkaloid from Areca catechu (Palmae). It is a MUSCARINIC CHOLINOCEPTOR AGONIST (experimental use), and is hypotensive. It has purgative actions and can be used as a vermifuge and taenifuge in veterinary medicine. Aredia pamidronic acid. 

Benadryl diphenhydramine, benaprizine benapryzine. benapryzine [ban] (benaprizine [inn] benapryzine hydrochloride [usan]) is a benzilate, a muscarinic CHOLINOCEPTOR ANTAGONIST which has been used as an ANTIPARKINSONIAN AGENT. 

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