Abstract

1,2-dimethylhydrazine induced colonic carcinogenesis was performed to examine colsely the preneoplastic changes and progress of colonic carcinoma in rats. Rats were grouped into 5 by differences of chow in their properties of cellulose-composition. For the purpose of reducing the artificial errors, the metabvlic and energy balances among groups were homogenized by the control of metabolic energy and fixation of several nutrients of chow significantly affecting colonic carcinogenesis. At the same time, low-dose and high-frequency injection of DMH was applied for the approximation of natural carcinogenesis. The results were analysed by autoradiography using tritiated thymidine on 18 weeks after start of l)K1H-injection. As compared to the controi, 2 to 27 fold-increase of crypt height, labeled cells, and labeling index were identified in the l)MH-injected. The loss of body weight as well as these findings of significant increase in hyperplastic celis should reveal the preneoplastic changes during that period. Among the cloinic segments, the labeling results showed the highest in the ascending colon and it coincided with thc highest incidence of adenocarcinomn in the same segment. The distributing pattern of labeled cells showed that the lower 1/3 predominated over the middle and upper 1/3 with significant difference, in other words. downward migratory pattern was found. De novo formation rif colonic carcinoma in DMH-induced culonic carcinogenesis in rats was highly suspected clue tv clownward migratory pattern of labeled cells and no adenoma-carcinoma sequence in uur histopathologic results. Incidcnce of colonic adenocarcinoma reduced significantly in the group fed on 20%-cellulose containing group compared to the non-fiber group and the lowest labeling in the 5%-cellulose group might be due to the protective effects of cellulose.

• Keywords: 1,2-Dimethylhydrazine, Colon carcinogenesis, Autoradiography, Sequence