Monitoring the histogenesis of colonic tumors in the Sprague-Dawley rat.

A total of 306 male Sprague-Dawley rats, injected with dimethylhydrazine (DMH), dose 21 mg/kg body weight s.c., were investigated. Of the 109 rats receiving the dose once only, seven colonic adenocarcinomas developed; all seven (100%) were seen to originate in discrete lymphoid patches. Of the 97 rats treated with one dose/week for 3 months, only 6% of the 50 adenocarcinomas developed in discrete lymphoid patches, while 46% were seen to originate in a pre-existing adenoma. Of the remaining 100 rats, receiving one dose/week for 6 months, only 3.5% of the 57 adenocarcinomas arose from discrete lymphoid patches; 43.9% arose from a pre-existing adenoma. Thus, the histogenesis of adenocarcinomas at our laboratory appears to be dose-dependent. Experiments are therefore being designed to monitor in detail the events of these two histogenetically different adenocarcinomas in the colonic mucosa in our animal model.