DIETARY PROTEIN AND THE TOXICITY OF SODIUM SELENITE IN THE WHITE RAT’

The present study, which is concerned with the relation of the protein content of the diet to the toxicity of inorganic selenium compounds in the young white rat, was begun under the direction of the senior author (L.) in 1935. At that time, the relation of dietary protein to selenium intoxication had not been the subject of investigation. In 1937, the results of a short series of earlier experiments with white rats from the Agricultural Experi.. ment Station of South Dakota indicated that a high protein diet afforded “more protection against selenium ” than a low protein diet (1). The protein, casein, was fed at levels of 55, 20, and 10 per cent. Schneider (2) had pre-viously observed that 0.2, 0.4, or 0.6 per bent of cystine as a supplement to a basal low protein diet, whose protein was supplied by whole milk powder and gelatin, neither mitigated the growth-arresting effects nor delayed the ulti-mate lethal action of dietary inorganic selenium (35 p.p.m.). This failure of cystine supplements to influence beneficially the toxicity of inorganic selenium was confirmed by the South Dakota investigators (1). More recently, Smith (3) has suggested that the toxicity of naturally occur-ring food selenium is influenced significantly by the protein-selenium ratio and has raised the question as to whether the quality as well as the quantity of dietary protein may play a role in determining the toxicity of selenium. In the experiments of Smith, 20 per cent of casein was added to a diet containing 50 per cent of whole wheat flour (approximate protein content, 13 to 15 per cent, calculated from the total nitrogen) in order to supply a high level of protein. The experiments here reported present studies of the effect of variations of dietary protein and of supplementary cystine and methionine on the toxic action of inorganic selenium (sodium selenite). High levels of casein (30 per cent) significantly decreased the toxicity of selenium in comparison wit