INDUCTION OF COLON ADENOCARCINOMAS IN RATS FED TRYPSIN AND TAMOXIFEN DIETS BY PARENTERAL AND INTRAGASTRIC 1,2-DIMETHYLHYDRAZINE

Male Sprague-Dawley rats, 25 days of age, were placed on a control rat ion and diets containing trypsin (2429 u/g) and tamoxifen (initial lev el: 4 PPM) at which time, 1,2-dimethylhydrazine was injected s.c. at 2 0 mg base/kg and continued once/week for 20 weeks. Most of the animals were killed 65 days after injection 20. In view of weight losses, the tamoxifen supplement was decreased to a final level of 0.50 PPM witho ut intervening control diet feeding. The total number of colon adenoca rcinomas and the distribution in the proximal and distal portions did not differ significantly from the respective controls and the tumor fr equencies in the small intestine were not remarkable. However, the gen eral animal conditions, weight changes and the presence of other tumor types were more extreme as compared to a similar trypsin supplement r eported for rats administered carcinogen by gavage once weekly for 15 consecutive weeks. With the latter series, colon adenocarcinoma freque ncies were markedly decreased.