[Stages of carcinogenesis of experimental colonic tumors induced with 1-2 dimethylhydrazine]

The authors poisoned 500 female Wistar rats with a dialy dose of 15 mg/kg, The total dose ranged from 15 mg/kg to 420 mg/kg, according to the group. The animals were either killed when the dose defined for each group and been reached, or allowed to live. In a first series of 6 groups (120 animals), the following facts were noted: tumours deeveloped in all animals left alive, after 28 weeks (total dose of 1/2 D.M.H. = 420 MG/KG). Changes in the mucosa were seen from the 40th day on with, in the descending colon, a punctate abnormality involving two or three glandular tubes, in general at the summit of the folds. This abnormality consisted of basophilia of the upper part of the tubes, with a loss of mucus secretion. All transitional stages were seen between this lesion, hyperplasia of the apex of the tubes, the formation of "polyp seeds" and the appearance of polyps. Carcinomas most frequently developed in polyps but sometimes in flat mucosa. In the ascending colon, changes in mucosecretion were seen after a similar time delay at the base of the glandular crypts.