Influence of dietary selenium on the distribution of tritium-labeled vitamin E in the rate Public Deposited

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  • A series of four trials were conducted to determine the influence of selenium supplementation of a selenium- and vitamin E-deficient basal diet on the absorption, excretion, tissue distribution and placental transfer of a single dose of tritium-labeled α-tocopherol in the rat. In the first trial, the effect of supplementation of the basal diet with 1.0 ppm selenium, 500 IU vitamin E per kg diet, or 1.0 ppm selenium and 500 IU vitamin E per kg diet, on the placental transfer of a dose of labeled tocopherol was examined. Twenty-four hours after dosing, the fetuses of the basal group contained a significantly higher (P < 0.005) percentage of the dose than did those of any of the other groups. Approximately equal fetal uptake of the dose occurred in those groups receiving supplementation with either vitamin E or selenium, while the lowest uptake was observed in the group receiving both vitamin E and selenium supplementation. These data indicate that the provision of selenium reduced the fetal tocopherol requirement. The second trial was concerned with the effect of supplementation of the basal diet with 0.5, 1.0, and 2.0 ppm selenium on the absorption and excretion of a dose of tritium-labeled α-tocopherol. Neither the urinary nor fecal excretion over a 72 hour period after dosing was affected by the addition of selenium. A significant inverse correlation was found between urinary excretion of the radioactivity and body weight. About 1.5% of the dose was excreted in the urine over the 72 hour experimental period, while 45-50% was excreted in the feces. No effect of level of selenium supplementation on the absorption of the radioactive tocopherol was found. The effect of supplementation of the basal diet with either 2.0 ppm selenium or 500 IU vitamin E per kg diet on the absorption, excretion and distribution of a dose of labeled tocopherol was examined in the third trial. As in the second trial, no effect of supplementary selenium on the absorption or excretion of the radioactive material was observed. Supplementation with vitamin E resulted in a slight increase in fecal excretion of the dose, probably because of reduced absorption. The urinary excretion of radioactivity was markedly affected by vitamin E supplementation; with almost twice as much activity excreted by this group as by the basal and selenium-supplemented animals. The plasma level of radioactivity was significantly higher (P < 0.01) in the basal group than in the selenium-supplemented rats, while the plasma radioactivity was significantly lower (P < 0.01) in the vitamin E-supplemented group than in the basal or selenium-supplemented groups. The level of protein-bound plasma radioactivity was also significantly higher (P < 0.01) in the basal group than in those receiving selenium, and significantly lower (P < 0.01) in the vitamin E supplemented group than in the others. The percentage of the plasma radioactivity that was protein-bound was not affected by treatment. The results indicate that selenium may have a role in promoting the withdrawal of vitamin E from the blood. The radioactivity content of the heart and liver tended to be higher in the selenium-supplemented groups than in the basal animals but the difference was not statistically significant. The fourth experiment compared the distribution of labeled vitamin E at intervals of 12, 24, 48 and 72 hours after dosing in rats on the basal diet and a group receiving supplementation with 2.0 ppm selenium. The plasma level of radioactivity was higher at all time intervals in the basal group, substantiating the results of the third trial which suggested that selenium may promote the withdrawal of vitamin E from the plasma. The levels of radioactivity in the heart and liver were not significantly different between the two groups. The rate of uptake and depletion of the labeled tocopherol varied among the tissues examined; the liver and plasma reached the peak level prior to 12 hours after dosing, and declined to less than half the 12 hour level by 24 hours. The radioactivity in the heart did not show appreciable variation over the experimental period. These experiments indicate that in the rat, selenium does not influence the absorption or excretion of α-tocopherol. Selenium does appear to modify tissue distribution of vitamin E; it was found that the plasma level of vitamin E was reduced when the basal diet was supplemented with selenium. The placental transfer of labeled vitamin E was reduced when the basal diet was supplemented with selenium, suggesting that the fetal requirement for α-tocopherol may be reduced in the presence of selenium.
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