Intestine cholinesterase

FIGURE 14.11 The pH activity profiles of four different enzymes. Trypsin, an intestinal protease, has a slightly alkaline pH optimnm, whereas pepsin, a gastric protease, acts in the acidic confines of the stomach and has a pH optimmn near 2. Papain, a protease found in papaya, is relatively insensitive to pHs between 4 and 8. Cholinesterase activity is pH-sensitive below pH 7 but not between pH 7 and 10. The cholinesterase pH activity profile suggests that an ionizable group with a pK near 6 is essential to its activity. Might it be a histidine residue within the active site ... 

The inhibition of two cholinesterase activities in blood can also be used to confirm exposure to certain organophosphate ester compounds. Red blood cell acetylcholinesterase is the same cholinesterase found in the gray matter of the central nervous system and motor endplates of sympathetic ganglia. Synonyms for this enzyme include specific cholinesterase, true cholinesterase, and E-type cholinesterase. Plasma cholinesterase is a distinct enzyme found in intestinal mucosa, liver, plasma, and white matter of the central nervous system. Synonyms for this enzyme include nonspecific cholinesterase, pseudocholinesterase, butyrylcholinesterase, and S-type cholinesterase (Evans 1986). Nonspecific cholinesterase is thought to be a very poor indicator of neurotoxic effects. 

The answer is c. (Hardman, p 1022.) Pyrantel pamoate is an antihelminthic that acts primarily as a depolarizing neuromuscular blocker. In certain worms, a spastic neuromuscular paralysis occurs, resulting in the expulsion of the worms from the intestinal tract of the host. Pyrantel also exerts its effect against parasites via release of acetylcholine and inhibition of cholinesterase. 

To test this possibility, they first examined the effect of phosphorofluoridates on isolated rabbit s intestine. On such a preparation the action of drugs, like acetylcholine, which act directly on the muscle differs characteristically from the action of those, like eserine, which act by inhibition of cholinesterase activity. The directly acting drugs produce an immediate contraction which proceeds rapidly to a maximum, and after the drug has been washed out the muscle again quickly relaxes. The contraction produced by cholinesterase-inhibiting drugs, such as... 

Carboxylesterases (EC 3.1.1.1) can be detected in most mammalian tissues. Besides organs with high carboxylesterase activity such as liver, kidney, and small intestine, esterase activity is present, e.g., in the brain, nasal mucosa, lung, testicle, and saliva. Compared to rat plasma, human plasma contains little carboxylesterase, its esterase activity being essentially due to cholinesterase [61][73][79][89-91],... 

Anticholinesterase agents can be employed in the treatment of adynamic ileus and atony of the urinary bladder, both of which may result from surgery. Neostigmine is most commonly used, and it can be administered subcutaneously or intramuscularly in these conditions. Cholinesterase inhibitors are, of course, contraindicated if mechanical obstruction of the intestine or urinary tract is known to be present. 

Mechanism of Action A depolarizing neuromuscular blocking agent that causes the release of acetylcholine and inhibits cholinesterase. Therapeutic Effect Results in a spastic paralysis of the worm and consequent expulsion from the host s intestinal tract. 

There are two types of esterases found in animal tissues. True cholinesterase which is found in neural structures, RBC and placenta and is concerned with destruction of acetylcholine released at the nerve endings. The second type is pseudocholinesterase (non-specific cholinesterase) is found in blood serum, intestines, liver and skin and is responsible for the hydrolysis of benzoylcholine and does not hydrolyse methacholine. Cholinesterase hydrolyses acetylcholine into choline and acetic acid. 

Metoclopramide is structurally related to orthoclopramide, a procaine derivative, and it can prolong the action of suxamethonium because of competition for cholinesterase. However, its common side effects are similar to those seen with phenothiazine derivatives. In high doses, a range of extrapyramidal symptoms may develop. The anti-emetic effects of metoclopramide are due to two main actions. Centrally, it blocks dopamine in the CTZ and peripherally, it hastens gastric emptying, abolishes irregular intestinal contractions, and increases... 

The cholinomimetics act on the neuromuscular junction (muscarinic), either by directly stimulating the acetylcholine receptors on the smooth muscle ceUs or by increasing the levels of acetylcholine in the neuromuscular junction by blocking cholinesterase activity. Some cholinomimetics, such as bethanechol, can act both at the level of the myenteric plexus (nicotinic) and directly on the intestinal smooth cells. 

Chole- Relating to the biliary system, cholestasis The failure of the normal bile flow to the intestine, causing cholestatic jaundice, cholinergic Nerve fibres that release ACETYLCHOLINE, cholinesterases Enzymes that hydrolyse choline esters, especially ACETYLCHOLINE of which there are two main forms acetylcholinesterase ( true cholinesterase ) is specific for acetylcholine, rapid in this action, and has a discrete distribution being especially located near cholinergic nerve terminals (and in erythrocytes) butyrylcholinesterase ( pseudo cholinesterase) is less selective and is able to hydrolyse some drugs (e.g. SUCCINYLCHOLINE CHLORIDE). Many drugs are known that inhibit the action of these enzymes. See anticholinesterases. chromatin A protein found in the nucleus which stains with basic dyes. It is used in the study of the behaviour of... 

The changes associated with OPC effects on the M-cholinoreactive system are of no small importance in the development of poisoning. OPC induce contraction of the orbicular muscle of eye, which results in pupil narrowing (miosis) and accommodation spasm, bronchial musculature (bronchospasm), musculature of the gastro-intestinal tract, bladder, uterine as well as amplify secretory function of the stomach and intestine. All these effects are determined by the anti-cholinesterase action of OPC on the peripheral M-cholinoreactive systems. 

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