The ability of a cell to withstand oxidative stress has been hypothesized to be related to its ploidy status. We used the intragastric feeding rat model for alcoholic liver disease to evaluate the relationship between severity of liver injury, antioxidant mRNA levels, and DNA ploidy of liver cells. Rats were fed ethanol with different dietary fats (saturated fat, corn oil, and fish oil); pair-fed control animals received isocaloric amounts of dextrose. All animals were euthanized at 1 month and had evaluation of pathologic changes in the liver, DNA content by flow cytometry, and mRNA levels for catalase and glutathione peroxidase. The fish oil-ethanol group exhibited the most severe pathology, the corn oil-ethanol group had intermediate pathologic changes, and no pathologic changes were seen in the saturated fat-ethanol and dextrose-fed controls. Flow cytometric analysis of propidium iodide-stained nuclei revealed that saturated fat-dextrose and corn oil-dextrose groups had about 65% of cells with (diploid) G1 DNA content and about 30% of cells with tetraploid (4C) nuclei. The fish oil-dextrose had a significantly higher (p < 0.001) number of 4C cells (67.4 +/- 2.1%) compared to the other two dextrose-fed groups. In the animals showing pathologic liver injury, there was a higher percentage of cells with hypertetraploid nuclei. The highest percentage of these hypertetraploid cells was seen in the fish oil-ethanol group. Catalase and glutathione peroxidase mRNA levels correlated significantly with polyploidy. A significant correlation was seen between the number of cells in the greater than G2 + M phase and glutathione peroxidase mRNA levels (r = 0.91, p < 0.01) and catalase mRNA. The different slopes of correlation analysis between catalase mRNA and dietary fats show that the degree of saturation of fatty acids may influence catalase mRNA expression in cells with different ploidy states. We propose that polyploidization of liver cell nuclei may serve as a defense mechanism against ethanol-induced hepatotoxicity. This defense mechanism may also, in part, account for the antiregenerative effect of ethanol on hepatocytes.