Multiple polyps and colonic neoplasia induced in the rat
The symmetrical dialkylhydrazine, 1,2-dimethylhydrazine dihydrochloride (DMH) was administered subcutaneously to male Sprague-Dawley rats in a dose of 15 mg/kg each week for 16 wk. This model is a reliable and reproducible method for inducing early dysplastic changes selectively in the colon. Once the carcinogen has been stopped, these focal areas in the colon progress to a carcinomatous change and allow greater specificity for tumor induction with less chemical toxicity. The earliest changes were seen histologically at 4 wk with macroscopic polypoidal tumors being found from the 16th wk after the 1st injection. These benign tumors progressed from adenomatous polyps to adenocarcinoma, which were both histologically and morphologically similar to colorectal cancer developing in patients with polyposis coli.