A series of inhibitors of azo dye hepatocarcinogenesis partially reverse the azo dye-induced decrease in liver RNA/DNA ratio.

The DNA and RNA content and the mitotic index were determined in the livers of rats pair-fed for 10 days on a control diet, and diets containing 0.06% 3'-methyl-4-dimethylaminoazobenzene (3'MeDAB), either alone or in combination with the inhibitors of azo dye carcinogenesis acetanilide (0.08%), p-hydroxypropiophenone (PHP, 1%), urea (5%), dehydroacetic acid (DHAA, 0.25%), butylated hydroxytoluene (BHT, 0.3%) and 3-methylcholanthrene (3MC, 0.067%). The liver RNA/DNA ratio was increased in rats fed the 3'MeDAB diet following ingestion of each of the inhibitor plus carcinogen-containing diets. The increases were significant except in the instance of urea. The increase was mainly due to increased RNA content in rats fed 3'MeDAB plus acetanilide, DHAA, BHT and 3MC when compared with rats fed 3'MeDAB alone. In rats fed PHP and 3'MeDAB, an increase in total liver DNA that was noted in rats fed 3'MeDAB alone did not take place, while total liver RNA content was similar in both groups; the RNA/DNA ratio was therefore greater in rats protected from 3'MeDAB carcinogenesis by PHP. The results are discussed in relationship to the effects of carcinogens on RNA forming genes and the role of the nucleolus in cell differentiation.