Exchange of endogenous selenium for dietary selenium as 82Se-enriched selenite in brain, liver, kidneys and testes

Male Wistar rats were fed a diet containing selenium (Se) in the form of 82Se-enriched selenite at the adequate concentration of 0.2 microg Se/g diet, i.e. a Se-deficient diet (<0.03 microg Se/g) fortified with 82Se-enriched selenite, from 5 weeks of age for 20 days, and the systemic disposition of the labelled Se and exchange of endogenous naturally occurring Se for the labelled Se were monitored in four organs. Features characteristic of each organ in terms of Se metabolism were revealed by plotting the disposition of 82Se and exchange of endogenous Se for 82Se against the number of days of feeding 82Se-selenite. Labelled Se amounted to 83.7, 80.8, 73.2 and 41.9% of the total Se in the liver, kidneys, testes and brain, respectively, after feeding 82Se-selenite for 20 days, suggesting that the disposition and exchange were most efficient in the liver but least efficient in the brain. However, when the weight gain of the four organs during the feeding period was taken into consideration, the apparent higher exchange was concluded to be caused by weight gain, i.e., more efficient uptake of the labelled Se by proliferating cells than non-proliferating cells in the liver, kidneys and testes. On the other hand, the uptake and exchange in non-proliferating cells were greater in the brain than in the other organs, especially in the late observation period. The relative metabolic turnover rates of selenoproteins were shown to be easy to determine from the relative exchange rates of endogenous Se for exogenous Se in the distribution profiles of Se obtained by the HPLC-ICP MS method.