The influence of diet on the riboflavin content and the ability of rat liver slices to destroy the carcinogen N,N-dimethyl-p-amino azobenzene.

The production of liver tumors in the rat by the oral administration of N,N-dimethyl-p-aminoazobenzene (DMB) is markedly influenced by diet. Our early work (1,2) showed that the maintenance of normal hepatic riboflavin levels was of importance in protecting rats against tumor formation. The work of Griffin and Baumann (3) and Miller, Miller, Kline, and Rusch (4) has emphasized the relationship between hepatic riboflavin levels and the carcinogenic action of DMB and related compounds. Riboflavin supplements are not effective in maintaining hepatic riboflavin levels or preventing tumor formation in the absence of adequate protein intake (2). In a study (5) from this laboratory of the effect of diet on the ability of rat liver slices to destroy DMB it was found that the maintenance of rats on a brown rice-carrot diet, which favors tumor production by DMB (6, 7), decreased this activity of rat liver. It was also observed that the addition of protective supplements such as dried brewers’ yeast or riboflavin and casein prevented this decrease. Measurement of the riboflavin content of the livers of rats on these diets indicated that, as the riboflavin level fell, the ability to destroy DMB also decreased. The use of brown rice diets in the preceding study (5), while suggesting that the changes observed were due to inadequate riboflavin and protein intake, made it necessary to rule out the presence of a “toxic” factor in the rice as the responsible agent. For this reason, and for the purpose of controlling the intake of other dietary constituents, the experiments have been repeated with diets which did not contain rice or carrot. As the Wisconsin group (8, 9) have published extensively on the effect of caseindextrose diets on the carcinogenic act,ion of DMB, the diets selected were modeled on the ones investigated by that group.