Effect of chronic selenite supplementation on selenium excretion and organ accumulation in rats

We examined the effect of chronic selenite supplementation on whole body and selected organ selenium (Se) accumulation, urine excretion of total Se and trimethylselenonium ion, and Se balance in adult male rats. Animals were housed in metabolic cages and given either deionized water or water containing 4 μg of Se/mL as selenite for 30 d. Absorption of selenite was nearly complete, with only ~10% of ingested Se appearing in feces. There was a rapid rise in urinary Se that reached a plateau within a few days and accounted for 54 ± 2% of the intake. Excretion of trimethylselenonium ion (TMSe) in urine increased rapidly, representing 35-40% of urinary Se in the supplemented animals compared with only 2% for the control group. In one experiment, rats were killed at 30 d and total carcass Se was measured using isotope dilution analysis. Supplemented rats had only a modest increase in whole body Se (94 ± 4 μg Se vs. 66 ±3 in controls). Calculation of Se balance in the supplemented rats showed that ~35% of ingested Se could not be accounted for by urine plus fecal losses combined with the portion retained in the carcass. The results from this study demonstrate that under the condition of supplementation at 4 μg of Se/mL of drinking water, pathways other than urinary and fecal excretion may account for a substantial portion of Se loss.