Pathogenesis of Dimethylnitrosamine-Induced Hepatocellular Cancer in Hamster Liver and Lack of Enhancement by Phenobarbital

: The early stages of dimethylnitrosamine (CAS: 62-75-9)-induced liver cancer and the effect of administration of phenobarbital (CAS: 50-06-6) after dimethylnitrosamine were studied in Syrian golden hamsters. A single ip injection of 6 mg dimethylnitrosamine/kg (body wt) induced hepatocellular altered foci by 6 months. Most foci were composed mainly of large clear glycogen-containing cells, while smaller numbers were formed by cells with abnormally acidophilic or basophilic cytoplasms. Biliary cysts, but not biliary neoplasms, also occurred. A few neoplastic (hyperplastic) nodules and hepatocellular carcinomas developed by 12 months. gamma-Glutamyltranspeptidase activity was not present in any of the hepatocellular lesions, but foci of all types, neoplastic nodules, and carcinomas were characterized by a lack of iron accumulation. Phenobarbital at 0.05% in the diet for up to 12 months did not increase the number of lesions of any type, indicating a lack of promoting effect under these conditions.