Selenate and
selenite injected intravenously into rats were speciated by the HPLC-ICP MS method with use of an enriched stable
isotope as the tracer. In dose-relation experiments, 82Se-enriched
selenate or
selenite was injected intravenously into male Wistar rats of 8 weeks of age (three rats/group) at single doses of 10, 25, 50, 100 and 200 microg/kg
body weight for the
selenate group, and 2, 5, 10, 25 and 50 microg/kg
body weight for the
selenite group. The animals were sacrificed 1 or 24 h later, and the concentrations and distributions of 82Se in the liver, kidneys, serum, and urine remaining in the bladder or 24-h urine were determined. In time-course experiments, 82Se-enriched
selenate and
selenite were injected at doses of 50 and 10 microg/kg
body weight, respectively, and the animals were sacrificed 5, 15, 30, 60 and 180 min later. It was suggested that
selenate is directly taken up by the liver with an efficiency of approximately 1/2 compared with
selenite, the latter being taken up by the liver after being metabolized to selenide in red blood cells. Although
selenate and
selenite were metabolized differently in the bloodstream, and also a part of only
selenate was excreted directly into the urine, the 82Se taken up by the liver was shown to be metabolized in a manner indistinguishable between
selenate and
selenite. 82Se of
selenite origin but not of
selenate origin was suggested to undergo redox reaction in the bloodstream. These results suggest that although parenteral
selenate is utilized less efficiently by the body, it is utilized in the liver in a similar manner to
selenite much more safely.