Histopathological Studies on Rat Colo-rectal Carcinoma Induced by N-methyl-N'-nitro-N-nitrosoguanidine

Abstract

Donryu rats received an infusion of various amounts of N-methyl-N'-nitro-N-nitrosoguanidine from the anus were kept under the observation for a maximum period of 61 weeks and sacrificed at certain intervals for the histopathological studies. A total of 133 tumors was found in 59 out of 138 effective animals. These tumors were histologically 19 adenocarcinomas, 73 adenomatous lesions, 20 hyperplastic lesions, and 21 hyperplastic lymph nodes. All these lesions were found to locate only in the segment of colon where the carcinogen contacted directly. These were all macroscopically elevated types, which included thickened folds. Tumor occurrence in the animals given 0.5ml of 0.25% N-methyi-N'-nitro-N-nitrosoguanidine solution daily for 32 days (total dose of the carcinogen 40mg), was 76 per cent at the end of 40 weeks after anal infusion. Adenomatous lesions were found at the end of 17 weeks or later after infusion, while adenocarcinomas occurred at 35 weeks. Histologically, all the lesions of adenocarcinoma were located immediately adjacent to the adenomatous lesions, and the histological feature of the experimental tumors was similar to that of human colo-rectal tumors. The similarity of adenocarcinomas and adenomatous lesions strongly suggested that the former might, have originated from the latter.