Synergistic Effect of Radiation on N‐2‐Fluorenylacetamide‐induced Hepatocarcinogenesis in Male ACI/N Rats

The effect of radiation on chemical hepatocarcinogenesis was examined in 3 groups of male ACI/N rats. In Group I, 21 rats received dietary administration of N‐2‐fluorenylacetamide (FAA) (0.02%) for 16 weeks. Six of the rats were killed at the cessation of FAA exposure. The remaining rats were then given the basal diet until termination (32 weeks). In Group II, 16 rats were given FAA for 16 weeks. The animals were then given radiation (whole body; 3 Gy) and kept on the diet for the subsequent 16 weeks. Thirteen rats of Group III were kept on the basal diet throughout the experiment. They received radiation for 16 weeks after the start of the experiment. Liver tumors were obtained in Groups I and II. The multiplicity of the neoplastic nodules or hepatocellular carcinomas of Group II (6.5 ± 2.5 or 1.4 ± 0.9) was significantly greater than that of Group I (2.9 ± 1.7 or 0.3 ± 0.4, respectively) (P< 0.001). Furthermore, the incidence of hepatocellular carcinoma of Group II (13/16) was also significantly higher than that of Group I (4/15) (P< 0.003). The results clearly indicate a synergistic effect of radiation with FAA on the hepatocarcinogenesis. The effect of radiation in this rat model appeared to be on the early progression of the carcinogenesis.