Metabolism of selenite labelled with enriched stable isotope in the bloodstream

The metabolism of selenium (Se) in the bloodstream of rats was studied using HPLC-ICP-MS with an enriched Se stable isotope, and the results were used as Se-specific indicators for Se nutritional status. Concentration of endogenous Se in plasma depended on dietary Se, while changes in concentrations and distributions of exogenous Se revealed its metabolic pathway. Namely, selenite was taken up by red blood cells and reduced to selenide, and then reappeared in plasma in a form bound selectively to albumin within 10 min, disappeared from plasma again within 30 min after injection. Then, the concentration of labelled Se started to increase slowly as selenoprotein P and extracellular glutathione peroxidase, and attained a maximum level at about 6 h after injection. The isotope ratio of endogenous to exogenous Se concentrations in plasma after 48 h post-injection was proposed to represent the Se-specific indicator in plasma reflecting the nutritional status of Se.