32P-postlabeling analysis of liver DNA adducts in rats chronically fed a choline-devoid diet

Liver DNA, obtained at various time intervals from rats chronically fed a choline-devoid diet, was analysed for the presence of aromatic or alkyl adducts by the 32P-postlabeling assay. Alkyl adducts were not detected. Aromatic DNA adduct lesions were revealed, but only at levels (1 adduct per 0.5-3 X 10(9) nucleotides) which are at the limits of the extremely high sensitivity of the method used, levels which remained constant throughout the period of feeding. Thus, contamination of the total environment of the animals with chemical carcinogens does not appear to be responsible for the genesis of the hepatocellular carcinomas that develop in rats chronically fed a choline-devoid diet. The diet, therefore, either acts as a complete carcinogen, or promotes the evolution to cancer of endogenous, 'spontaneously' initiated liver cells.