Differential effects of beta-naphthoflavone and pregnenolone-16alpha-carbonitrile on dimethylnitrosamine-induced hepatocarcinogenesis.

The effect of administration of beta-naphthoflavone (beta-NF) or pregnenolone-16alpha-carbonitrile (PCN) on the hepatocarcinogenicity of dimethylnitrosamine (DMN) in male SD rats was explored. Both beta-NF and PCN are potent repressors of the low Michaelis constant enzymatic form of DMN-demethylase, a mixed-function oxidase that catalyzes DMN demethylation. DMN-induced hepatocarcinogenesis was inhibited by PCN and was enhanced by beta-NF. Seven liver tumors were found in 45 rats fed DMN plus PCN compared to 14 liver tumors in 43 rats fed DMN alone; 32 liver tumors were found in 43 rats fed DMN plus beta-NF. No liver tumors were detected in rats that received only PCN, beta-NF, or the administration vehicles. Of the 53 liver tumors observed, 53% were angiosarcomas; this type of tumor was found in all 3 groups of rats that received DMN.