Bioavailability of Selenite, Selenomethionine and Selenocystine in Rats with Silver Loading

Abstract

Growing rats with silver loading (250μg/g diet as silver acetate) were examined for silver and selenium contents and glutathione peroxidase activities in various tissues. Silver was found at a much higher level in the livers than in the kidneys. Silver loading for 4 weeks caused a decrease in the selenium contents and glutathione peroxidase activities in the tissues without affecting rat growth. Since addition of silver to the diet led to a few-fold increase in fecal selenium excretion, the decreased selenium availability in silver-loaded rats was considered to arise from obstruction of selenium uptake in the intestine. In another experiment, selenite, selenomethionine and selenocystine were administered via intraperitoneal injection (50μg/kg once a day for 7 days) to rats previously given silver for 3 weeks. The glutathione peroxidase activities in the livers and kidneys were markedly elevated by the selenium administration, although they were inferior to those in rats not receiving silver. The selenium availability in silver-loaded rats varied with the chemical form of selenium and was to a lesser extent in the case of selenite administration. On the other hand, a significant difference was observed between the rats with and without silver loading regarding the selenium contents in the 105, 000×g pellets of liver and kidney homogenates. The accumulation of selenium there was accompanied by that of silver of about ten or a hundred times as much as selenium in concentration (μg/g tissue). Such excess silver accumulation may be explained with the assumption that silver ions undergo reduction by selenite or selenocysteine, but not by selenomethionine, to accumulate as non-charged silver metal within the cells.