Gastric Tumorigenicity of 1,2‐Dimethylhydrazine on the Background of Gastric Intestinal Metaplasia Induced by X‐Irradiation in CD (SD) Rats

Five‐week‐old male CD (SD) rats were X‐irradiated with a total of 20 Gy in 2 equal fractions with a 3‐day interval. After the second irradiation, rats were fed normal diet supplemented with 1% sodium chloride, which is known to increase intestinal metaplasia. 1,2‐Dimethylhydrazine (DMH) solution was injected i.m. into the back musculature at a dose of 20 mg/kg body weight weekly for 10 weeks, beginning 20 weeks after the final irradiation. Twelve months after the initial carcinogen treatment, gastric tumors in the glandular stomach were observed in 2 (3 lesions) of 30 animals in the X‐irradiated and DMH‐treated group fed diet supplemented with 1% sodium chloride. No gastric tumors were observed in the group which excluded X‐irradiation from the experimental protocol.