Metabolism of Selenate Administered into Rats

Abstract

The metabolic fate of selenium (Se) administered intravenously in the form of selenate (natural abundance) to rats (0.3 mg Se/kg body weight) was studied by HPLC-mass spectrometry with ionization by inductively coupled argon plasma (ICP MS) in comparison with that of selenite. Selenate was either excreted directly into the urine within 6 hrs (14% of the dose) or was taken up by the liver without being metabolized in the bloodstream in both cases. The Se of selenate origin taken up by the liver was utilized for the synthesis of selenoprotein P (Sel P) and an increase in the Sel P peak started to be observed within 1 hr after the injection. Selenate taken up by the liver was also methylated for excretion into the urine. However, the production of methylated products was not significant in the urine before 6 hrs after the injection in the selenate group. Although reduction of selenite to selenide was readily observed in vitro in the presence of glutathione (GSH) or on incubation in a liver supernatant fraction, selenate was not reduced in vitro in the presence of GSH or dithiothreitol (DTT). However, selenate was reduced slowly on incubation in a liver homogenate or supernatant fraction, suggesting that the reduction of selenate to selenite takes place during the uptake or immediately after the uptake. The chemical forms of Se in the blood plasma, liver supernatant and urine were determined by the HPLC-ICP MS method, which demonstrated the importance of speciation of each Se metabolite.