Gastrointestinal tract metabolism

PUSZTAI A, BARDOCZ s (1996) Biological effect of plant lectins on the gastrointestinal tract Metabolic conseqnences and applications. Trends Glycosci Glycotech. 8 149-65. 

Oral treatment of sheep and cattle (Bos spp.) with diflubenzuron is followed by absorption of the compound through the gastrointestinal tract, metabolism, and elimination of residues through the urine, feces, and, to a very limited extent, milk. Intact diflubenzuron is eliminated in the feces of orally dosed cattle and sheep (Ivie 1978). Major metabolites of diflubenzuron excreted by cattle and sheep result from hydroxylation on the difluorobenzoyl and chlorophenyl rings, and by cleavage between the carbonyl and amide groups to produce metabolites that are excreted free or as conjugates (Ivie 1978). Cattle dosed repeatedly with diflubenzuron had detectable residues only in liver... 

Pharmacokinetics Amphetamines are completely absorbed from the gastrointestinal tract, metabolized by the liver, and excreted in the urine. Amphetamine abusers often administer the drugs by intravenous injection and by smoking. The euphoria caused by amphetamine lasts 4 to 6 hours, or 4 to 8 times longer than the effects of cocaine. The amphetamines produce addiction—dependence, tolerance and drug-seeking behavior. 

Many metabolites produced by hepatic metabolism are eliminated into the intestinal tract via the bile. These metabolites may be excreted in feces but are often reabsorbed. Organic anions (i.e. glucuronides) and cations are actively transported into bile by carrier systems that are similar to those in the renal tubules. Similarly, charged ions can compete for transport by these systems because both are non-selective. Steroidal and related substances are transported by a third carrier mechanism. Glucuronide-conjugated metabolites undergo extensive enterohepatic recirculation— a cycle of absorption from the gastrointestinal tract, metabolism in the liver and excretion in bile—and this cycle delays elimination when the final step in elimination from the body is via the kidneys. 

Pyrethroids are poorly absorbed through the skin and are only moderately absorbed in the gastrointestinal tract. Metabolism of deltamethrin occurs rapidly through ester cleavage and hydroxylation. Deltamethrin is eliminated more slowly from adipose tissues than from other sites such as brain or blood. In one case of dermal exposure, absorption was estimated to be 3%. Urinary excretion is the primary route of elimination. 

In a study with rats, TBBPA was readily absorbed from the gastrointestinal tract, metabolized in the liver and excreted via the bile to the gut. Of the dose administered to the rats, 90% was excreted in the feces as parent TBBPA. Three glucoronide conjugates of TBBPA were identified in the feces but only accounted for a small amount of the administered dose. Urine was a minor route for excretion of TBBPA. The half-life of TBBPA in rats was estimated to be less than 3 days with the longest half-lives in fat and testes. The shortest half-lives were in liver and kidneys. In a study of occupationally exposed Swedish workers, the half-life for elimination from the serum was 2.2 days indicating a rapid elimination from the body. 

Keywords Tannins Miaobial ecology Gastrointestinal tract Metabolism Rumen fermentation Resistance mechanisms Ruminants... 

C2H5OH, ethanol is formed by bacteria in the gastrointestinal tract in low amounts. Most of the ethanol of bacterial source is metabolized during the first liver passage yielding acetaldehyde and subsequently acetic acid. 

The pentose phosphate pathway is an alternative route for the metabolism of glucose. It does not generate ATP but has two major functions (1) The formation of NADPH for synthesis of fatty acids and steroids and (2) the synthesis of ribose for nucleotide and nucleic acid formation. Glucose, fructose, and galactose are the main hexoses absorbed from the gastrointestinal tract, derived principally from dietary starch, sucrose, and lactose, respectively. Fructose and galactose are converted to glucose, mainly in the liver. 

These studies represent the first report of the metabolism of brevetoxins by mammalian systems. PbTx-3 was rapidly cleared from the bloodstream and distributed to the liver, muscle, and gastrointestinal tract. Studies with isolated perfused livers and isolated hepatocytes conflrmed the liver as a site of metabolism and biliary excretion as an important route of toxin elimination. [ H]PbTx-3 was metabolized to several compounds exhibiting increased polarity, one of which appeared to be an epoxide derivative. Whether this compound corresponds to PbTx-6 (the 27,28 epoxide of PbTx-2), to the corresponding epoxide of PbTx-3, or to another structure is unknown. The structures of these metabolites are currently under investigation. 

It has recently been shown (14) that nitrate from food can be detected in the feces of germfree animals but not in the feces of conventional animals. This result and the results of Witter et al. (18-20) suggest that nitrate is available in the lower gastrointestinal tract and is metabolized by the microbial flora. The intestine may thus be a site for the endogenous formation of N-nitroso compounds. 

The liver was the first organ in the gastrointestinal tract in which the role of ROMs in liver injury was established. Mitchell et al. (1973a, 1973b) demonstrated the roles of several drug-metabolizing enzymes in the formation of... 

Gout is caused by an abnormality in uric acid metabolism. Uric acid is a waste product of the breakdown of purines contained in the DNA of degraded body cells and dietary protein. Uric acid is water soluble and excreted primarily by the kidneys, although some is broken down by colonic bacteria and excreted via the gastrointestinal tract. 

Oral colchicine is absorbed rapidly from the gastrointestinal tract and metabolized extensively in the liver. 

Absorption of americium is greater in iron deficient animals than in iron replete adult animals (Sullivan and Ruemmler 1988 Sullivan et al. 1986) (see Section 3.4.1.2). Concurrent oral exposure to Fe3+ and americium also appears to increase the absorption of ingested americium the latter effect may result from redox reactions in the gastrointestinal tract catalyzed by Fe3+ (Sullivan et al. 1986). These differences are accounted for in the discussions and dosimetric/metabolic models of the ICRP (1989, 1993) and the NEA (1988). 

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