KINETICS OF PRENEOPLASTIC EPITHELIA OF THE INTESTINAL MUCOSA INDUCED IN BUFFALO RATS BY ORAL ADMINISTRATION OF N, N'-2, 7-FLUORENYLENEBISACETAMIDE

A diet containing 0.025% of N, N'-2, 7-fluorenylenebisacetamide (2, 7-FAA) was administered orally to 18 Buffalo rats for 3 months and to 21 rats for 5 months which corresponded to non-neoplastic stage and preneoplastic stage of carcinogenesis of the intestinal mucosa, respectively. The mitotic index, labeling index, and generation time of the epithelia of the intestinal mucosa of these stages were examined by autoradiography. 1) The mitotic index and labeling index decreased in the rats fed 2, 7-FAA for 3 months than those of the non-treated controls. 2) Decrease of both indices was also observed in the rats fed 2, 7-FAA for 5 months, except for the proximal part of the colon. 3) Around 1-hr prolongation of the generation time was observed in the epithelia of rats fed 2, 7-FAA for 3 months compared with the non-treated control rats, and this was mainly due to the prolongation of the duration of the G1 phase. 4) Two- or three-hour prolongation of the generation time was observed in the epithelia of rats fed 2, 7-FAA for 5 months compared with the non-treated control rats, and this was mainly due to the prolongation of the duration of the S phase.