Rapid induction of colorectal tumors in rats initiated with 1,2-dimethylhydrazine followed by dextran sodium sulfate treatment.

To establish a rapid bioassay system with neoplastic end-points for detection of colorectal carcinogenesis modifiers, we evaluated the effects of dextran sodium sulfate (DSS) treatment on the different stages of carcinogenesis in rats initiated with 1,2-dimethylhydrazine (DMH). F344 male rats were given three subcutaneous injections of DMH (40 mg/kg body weight) in a week, and were administered drinking water containing 1.0% DSS ad libitum either during or after the initiation period for a week, or both during and after initiation periods for 2 weeks. At the 10th week of the experiment, although the numbers of aberrant crypt foci were significantly decreased in all groups treated with DSS and given DMH-initiation as compared with DMH alone, dysplastic foci/adenomas/adenocarcinomas were increased. The incidences and multiplicities of these lesions were highest in rats treated with DSS after DMH-initiation period. At the 26th week, the incidences of adenocarcinomas (100 vs. 20% in DMH alone) and their multiplicities (6.6 +/- 0.8/rat vs. 0.2 +/- 0.4/rat in DMH alone) were also highest in this group. These results indicate that short-term DSS-treatment in the post-initiation period significantly accelerates DMH-induced colorectal tumor development in rats, so that this protocol may effective for establishment of a rapid bioassay system with neoplastic end-points.