Comparison of Wistar vs. Fischer rat in the incidence of 1,2-dimethylhydrazine induced intestinal tumors

Background. Many investigators have observed differences in the susceptibility to induce intestinal tumors by 1,2-dimethylhydrazine (DMH) between various strains of rodents. The results are difficult to compare because of the different regimes used for induction. The purpose of our study was to evaluate the influence of strain on DMH-induced intestinal tumors between Wistar and Fischer rats. Materials and methods. We used 29 Fischer and 30 Wistar male rats that were injected subcutaneously DMH, weekly, at a dosage of 25 mg/kg-body weight for 20 weeks. After 25 weeks from the beginning of the experiment, the animals were sacrificed and autopsied. The complete length of colorectum and all macroscopic changes were examined histologically. Results. The induction of intestinal tumors was 97% in Fischer rats and 100% in Wistar rats. In Wistar rats 184 tumors were found: 133 adenomas, 50 tubular adenocarcinomas and 1 signet-cell carcinoma. 77% of carcinomas were found in colorectum and 23% in the small intestine. In Fischer rats, 126 tumors were found: 94 adenomas, 26 tubular adenocarcinomas, 5 signet-cell carcinomas and 1 mucinous carcinoma; 42% of carcinomas were found in the colorectum and 58% in the small intestine. The strain difference in the incidence of all induced tumors was statistically significant (P=0.001). The differences in the occurrence of the malignant and benign tumors was also significant (P<0.001; P=0.011). Extra intestinal tumors were not found. Conclusions. Wistar rats showed greater percentage of colorectal tumors, and also the distribution of tumors in colorectum resembled more the distribution found in human pathology. That is why we recommend Wistar rat rather than Fischer rat for the research work on the colorectal tumors. (author)