The mechanism of cocarcinogenic action of ethanol in rat liver.

The effects of chronic alcohol consumption on nitrosamine metabolism in vivo, DNA synthesis and repair, and carcinogen-induced preneoplasia were studied in rat liver. Following a single injection of different doses of 14C-N-nitrosodimethylamine, there was no significant difference between controls and ethanol-pretreated rats in the alkylation pattern of cellular protein nor in the levels of the alkylation products 7-methylguanine and O6-methylguanine isolated from liver DNA. O6-Methylguanine-specific DNA repair was also unchanged. An increase in the number and size of foci staining negative for adenosine triphosphatase and/or positive for gamma-glutamyltranspeptidase was observed in rats treated intermittently with ethanol and N-nitrosomorpholine. The numbers of clear-cell and mixed-cell foci were also increased. An ethanol-mediated enhancement of DNA synthesis, which was ascertained by different methods, may be related to this cocarcinogenic action of the alcohol. Ethanol, however, failed to demonstrate promoting activity. Long-term treatment of carcinogen pretreated rats with ethanol, according to the classical initiation-promotion protocol, had no effect on the incidence of preneoplastic foci in liver.