Uptake and Excretion

One of the clinical signs associated with MeHg intoxication is a myasthenia gravis-like muscle weakness in adults (Rustam et al. 1975), a syndrome which responded well to therapy with neostigmine, a reversible acetylcholinesterase inhibitor. In this syndrome, two effects of MeHg on synaptic transmission at the neuromuscular junction were demonstrated using intracellular microelectrode recording techniques (Atchison and Narahashi 1982 Atchison et al. 1984). First, nerve-evoked, synchronous quantal release of acetylcholine (ACh) is inhibited, as indicated by a decrease in end-plate potential (EPP) amplitude. Second, spontaneous quantal release 

Early postnatal exposure to MeHg seems to inhibit the development and maturation of the brain. Choi et al. (1981) observed incomplete arborization of the dendritic tree of Purkinje cells in mice exposed to MeHg in the early postnatal period. 

Yoshino et al. (1966) reported that protein synthesis in nervous tissues from rat injected with MeHg thioacetamide was inhibited before the first clinical signs of intoxication. The effects of MeHg on protein synthesis have since been studied repeatedly (Carmichael et al. 1975 Omata et al. 1980, 1982 Syversen 1982 Fair et al. 1987), indicating that MeHg directly interacts with some parts of the protein synthetic machinery. 

Since the first report by Ganther et al. (1972), selenium has been shown to interfere with the metabolism and the toxic effect of MeHg (Who 1976, 1990). Administration of equivalent amounts or lower doses of selenium to rodents decreased toxicity of MeHg. Selenium deficiency enhanced the fetal toxicity of MeHg (Nishikido et al. 1987). The mechanisms of these protective effects of selenium are still unknown. It has been shown that bismethyl- 

Chang et al. (1978) and Welsh (1979) reported that vitamin E protects MeHg toxicity in rodents. According to Ganther (1978), vitamin E modifies MeHg metabolism by acting as a radical scavenger. 

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Nomiyama K, Nomiyama H. 1974b. Respiratory retention, uptake, and excretion of organic solvents in man. Int Arch Arbeitsmed 32 75-83. 

In the overall metabolism of the living organism distinguished are exogenous metabolism, which comprises extracellular transformations of materials on the way to their uptake and excretion by the cells, and intermediary metabolism, which occurs in the cells. The intermediary metabolism is conceived as the sum total of chemical reactions that occur in the living cell. 

M. F., Wilkinson, G. R., Kim, R. B., OATP and P-glycoprotein transporters mediate the cellular uptake and excretion of fexofenadine, Drug Metab. Dispos. 1999, 27, 866-871. 

Waiwood, B.A., V. Zitko, K. Haya, L.E. Burridge, and D.W. McLeese. 1987. Uptake and excretion of zinc by several tissues of the lobster (Homarus americanus). Environ. Toxicol. Chem. 6 27-32. 

Zitko, V. 1980. The uptake and excretion of mirex and dechloranes by juvenile Atlantic salmon. Chemosphere 9 73-78. 

ABC transporters are involved in both uptake and excretion of a variety of substrates from ions to macromolecules. Whereas export systems of this type are present in all kingdoms of life, import systems are exclusively found in prokaryotes. ABC transporters are minimally composed of two hydrophobic membrane embedded components and two ATPase units. 

Further information on endrin uptake and excretion is in Chapter 2. 

In a similar static condition where approximately 1 ppm of malathion, diazinon or fenitrothion was added, Kanazawa (12) examined uptake and excretion of the compounds in minnows (Psedorasbora parva Temminck et Schlegel) at 23 2°C. The concentration of the compounds decreased with the lapse of time, after 4 weeks to 0.27 ppm for diazinon and 0.02 ppm for fenitrothion. Malathion disappeared much more promptly, to less than 0.01 ppm... 

Cvetkovic M, Leake B, Fromm MF, Wilkinson GR and Kim RB (1999) OATP and P-Glycoprotein Transporters Mediate the Cellular Uptake and Excretion of Fexofenadine. Drug Metab Dispos 27 pp 866-871. 

Medinsky MA, Dutcher JS, Bond JA, et al. 1985. Uptake and excretion of [ "Cjmethyl bromide as influenced by exposure concentration. Toxicol AppI Pharmacol 78 215-225. 

Differential effects on uptake and excretion. If the tissue in which the lethal process occurs is separated from the source of the toxicant and from an excretory or detoxifying... 

As the human body is able to store many minerals, deviations from the daily ration are balanced out over a given period of time. Minerals stored in the body include water, which is distributed throughout the whole body calcium, stored in the form of apatite in the bones (see p. 340) iodine, stored as thyroglobulin in the thyroid and iron, stored in the form of ferritin and hemosiderin in the bone marrow, spleen, and liver (see p. 286). The storage site for many trace elements is the liver. In many cases, the metabolism of minerals is regulated by hormones—for example, the uptake and excretion of H2O, Na, ... 

B29. Brown, W. R., Grodsky, G. M., and Carbone, J. V., Intracellular distribution of tritiated bilirubin during hepatic uptake and excretion. Amer, J. Physiol. 267, 1237-1241 (1964). 

DiVincenzo GD, Hamilton ML, Kaplan CJ, et al. 1978. Studies on the respiratory uptake and excretion and the skin absorption of methyl n-butyl ketone in humans and dogs. Toxicol AppI Pharmacol 44 593-604. 

An adult human ingests 2-5 mg of copper per day, about 30% of which is absorbed. The total body content of copper is 100 mg ( 2 x 10 4 mol/kg), and both uptake and excretion (via the bile) are regulated. Since an excess of copper is toxic, regulation is important. 

Kawanaka, M., Hayashi, S. and Carter, C.E. (1986) Uptake and excretion of amino acids and utilization of glucose by Schistosoma japonicum eggs. Japanese Journal of Medical Sciences and Biology 39, 199-206. 

Drablos PA, Hetland S, Schmidt F et al. 1992. Uptake and Excretion of Aluminum in Workers Exposed to Aluminum Fluoride and Aluminum Oxide. Aluminum Assoc/et al. Aluminum Health 2nd Int Conf, Tampa, FL 157(4) Feb 2-6, 92. 

A study of the uptake and excretion of (-l-)-tubocurarine (154) and its trimethyl derivative in the rat reported no evidence for biotransformation of either substrate in vivo or in vitro with isolated perfused livers (117). A similar study with (+ )-2,3-dehydroemetine (158) showed that although metabolism occurred in vivo to give unidentified product(s) no in vitro biotransformation was carried out by rat liver microsomes (118). 

Kanazawa, J. (1975) Uptake and excretion of organophosphorus and carbamate insecticides by fresh water, Motsugo (Pseudorasbora parva). Bull. Environ. Contam. Toxicol. 14, 346-352. 

Kim RB, Cvetkovic M, Fromm MF, et al. OATP and P-glycoprotein mediate the uptake and excretion of fexofenadine. Clin Pharmacol Ther 1999 65 111. 

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