Enhancing effects of carbon tetrachloride in mouse hepatocarcinogenesis

The enhancing effects of 4 or 8 necrogenic doses of carbon tetrachloride (CCl₄) on hepatocarcinogenesis were studied in female B6C3F1 mice previously treated with a single dose of N-nitroso-N-diethylamine (NDEA) at 7 days of age. The CCl₄ treatments were given every other week and started either after weaning or at 18-26 weeks of age, and the animals were observed until 36 weeks of age. The number and size of hepatocellular nodules were then scored and analysed. Hepatocellular nodules were not observed in mice receiving either 4 or 8 CCl₄ treatments without NDEA initiation. Both 4 and 8 CCl₄ treatments promoted NDEA-initiated hepatocarcinogenesis, increasing nodule size but not nodule frequency. Eight CCl₄ doses were more effective than 4 and gave the greatest increase in nodule size when administered from 18 to 32 weeks of age. In an additional experiment, 3 mice bearing hepatocellular nodules induced by a single infantile NDEA treatment were administered CCl₄ once and killed 52 h later. Nine neoplastic nodules were examined and found to be resistant to the CCl₄ induced necrosis, although cells in the nodules were actively dividing at the same rate as in the regenerating surrounding normal liver parenchyma. The ability of a few necrogenic CCl₄ doses to enhance hepatocarcinogenesis may be related to a differential cytotoxicity on neoplastic and normal hepatocytes and to a similar mitogenic stimulus on both cell types.