A low molecular weight substance bound to methylmercury in the human, rabbit, mouse, and rat erythrocytes was identified, and the relationship between the distribution pattern of methylmercury in erythrocytes and the behavior of methylmercury in the blood were studied using different species of animals. Results of gel filtration using Sephadex G-15 and thin-layer chromatography suggest that the low molecular weight substance which is bound to methylmercury in erythrocytes is glutathione (GSH). The in vitro releasing rate of methylmercury taken up in erythrocytes into bovine serum albumin solution was investigated, and a remarkably low value was obtained in the case of rat erythrocytes which have an extremely smaller percentage of methylmercury bound to the low molecular weight substance compared to the other animals used. Because the considerable amount of methylmercury are bound to the low molecular weight substance in men, rabbits, and mice, it is conceivable that methylmercury bound to the low molecular weight substance is more easily released out of erythrocytes. When time-dependent changes in the methylmercury concentration in the blood taken from rats, rabbits, and mice injected sc or iv with methylmercury were evaluated, the concentration in rat blood was maintained at a very high level compared to that in rabbit or mouse blood. This seems to reflect the results of the in vitro release experiment described above.
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