Methylmercury biliary excretion

The model simulations were in close agreement with the observed results from the distribution and metabolism studies. Physiological processes that were highlighted by the results and the discrepancies that did occur include the probable active transport into the brain (versus passive diffusion) of a methyl-mercury-cysteine complex, the bidirectional transport of methylmercury between the gut lumen and gut tissue as a more important determinant of methylmercury fecal excretion than biliary secretion, the importance for the determination of methylmercury half-life in rats of the recycling of mercury from ingested hair, and the need for better estimates of the rate constants for the demethylation of methylmercury in order to adapt the model to other species. 

Ballatori N, Clarkson T. 1982. Developmental changes in the biliary excretion of methylmercury and glutathione. Science 216(2) 61-63. 

The rate of biliary excretion of Hg is very low in comparison with methylmercury excretion (Ballatori and Clarkson 1984b). The form of Hg2+ excreted into the bile has been identified as a complex with GSH (GSHgSG) (Ballatori and Clarkson 1984b). Inhibition of biliary secretion of GSH by administration of sulfobromophthalein (BSP) resulted in a parallel inhibition of Hg secretion (Ballatori and Clarkson 1984a). Thus, the biliary secretion of Hg may be in large part dependent on the biliary transport of GSH. The mechanism of urinary excretion of Hg has not yet been clarified. As described above, Hg is incorporated into the kidneys by a y-GTP-dependent system, and inhibition of y-GTP significantly increases urinary excretion of Hg (Tanaka et al. 1990). Therefore, GSHgSG which has escaped from the action of y-GTP may be excreted into the urine. 

Urano T, Naganuma A, Imura N (1988b) Species differences in biliary excretion of methylmercury role of non-protein sulfhydryls in bile. Res Commun Chem Pathol Pharmacol 62 339-351... 

Organic Mercury. The fecal (biliary) pathway is the predominant excretory route for methylmercury, with less than one-third of the total mercury excretion occurring through the urine, following oral and inhalation exposure (Norseth and Clarkson 1970). In humans, nearly all of the total mercury in the feces after organic mercury administration is in the inorganic form. The conversion of methylmercury to inorganic mercury is a major step that is dependent on the duration of exposure and/or the duration after cessation of exposure. 

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