[Proliferative activity of the epithelium of the rat large intestine during carcinogenesis].

Labelling index and mitotic regimen in the epithelium of the rat descending colon and the ileum was studied during the tumour induction with 1,2-dimethylhydrazine. One month after the beginning of the experiments there was a marked increase of abnormal mitoses (up to 51%) and a change in the proportion of the mitotic phases with the metaphase prevalence (up to 73%). Later, these parameters were unchanged. Beginning from the 3rd month of the experiment there was found an increase in the labelling index (especially, in the carcinoma in situ) and of the mitotic index. In the mucosa of the ileum (where the tumours never developed) no changes of the proliferative activity and of mitotic regimen were found.