Adaptation of Rats to Selenium Intake

Changes of liver selenium after intake of organic selenium at different levels and for various lengths of time were studied in 236 young rats. In litters born to mothers fed a diet containing 4.5 ppm selenium (in seleniferous sesame press cake) and kept on this diet after weaning, the liver levels decreased steadily; these levels increased in stock rats fed the same diet. The graphical presentation of these changes resulted in two straight lines, crossing each other. When the selenium diet was fed to dams 5 to 7 days prior to parturition and thereafter, the liver levels of the litters rose rapidly; liver levels increased at a slower rate in rats bom to females fed the diet 15 to 19 days prior to birth and decreased in litters from mothers kept on the diet prior to mating. When litters from stock females were nursed by dams fed the seleniferous diet during pregnancy and changed to the stock ration after the birth of their litters, the liver selenium levels rose rapidly for about 3 weeks after weaning and then decreased. On a diet containing 10 ppm selenium, liver values in rats from the stock culony rose for 2 to 3 weeks to high levels and then decreased. Animals bred on the diet containing 4.5 ppm selenium exhibited a slower, more continuous rise of liver selenium when the high selenium diet was fed. The results suggest the exis­ tence of an adaptation mechanism which allows rats exposed to chronic selenium in­ gestion to store less of this element than previously unexposed controls. In previous experiments on the effect of selenium in growing rats, it was observed that a dietary level of this element which resulted in a small but significant growth depression in young animals from the stock colony was without notable effect in litters born to dams which had been kept on an experimental seleniferous diet prior to mating (1). This was quite unexpected because higher selenium body levels at the start of the experiment would have made the opposite result more likely, and also because young animals are often more severely affected by dietary injury when exposed to it during embryonic life. In an­ other study from this laboratory, it was found that the characteristic drop in hem­ atocrit and hemoglobin levels in rats fed high selenium diets was significantly de­ layed when the experimental animals had been bred on a seleniferous ration as com­ pared with controls bred on stock rations, (2). These observations pointed to the possible existence of some adaptation to chronic selenium intake in rats. The pres­ ent experiments were undertaken to inves­ tigate whether such a mechanism could be detected through the accumulation of selenium in the liver.