Pharmacokinetics of selenium after sodium selenite administration to rats

Selenium (Se) concentrations in plasma, urine, and feces were determined by PIXE analysis before and after intravenous (iv) / oral (po) administration of sodium selenite (a dose equivalent to 2 mg/kg of selenium) to rats. The concentration-time profiles of Se were analyzed by a pharmacokinetic approach. The plasma Se profile after iv injection was biphasic and well-fit to a 2-compartment open model, showing two half lives (tl/2). The first tl/2 was about 0.3 hr and the second tl/2 was 6.9 hrs. The plasma concentration reached almost basal level after about 80 hrs of injection. On the other hand, plasma profiles after po administration showed absorption rate-limiting elimination. The bioavailability of oral sodium selenite (about 49%) and significantly higher amount of fecal Se excretion indicated relatively poor intestinal absorption of sodium selenite, compared to the previously published data. Urinary Se excretion was almost comparable between iv and po groups. The total recovery of the dose excreted in urine and feces was 30 ± 10% in iv and 56 ± 15% in po group. The renal excretion was considered to be a major route of Se excretion after absorption. Significant amount of Se that was not fully excreted was noted, suggesting Se distribution or accumulation in organs, together with volatile excretion. (author)