Cell population kinetics of 1,2-dimethylhydrazine-induced colonic neoplasms and their adjacent colonic mucosa in the mouse

The parameters of cell population kinetics of symmetrical 1,2-dimethylhydrazine-induced colonic neoplasms and their adjacent colonic mucosa in the mouse were analyzed using the fraction labeled-mitoses curve method and compared with those of three groups of epithelial cells in the crypt of the descending colon of normal mouse. The analysis of three groups of epithelial cells in the crypt of normal mouse indicates that differentiation of epithelial cells was associated not only with a smaller proliferative pool of cells but also with a shortening of the duration of G2 phase and a prolongation of mitotic time. Other parameters of cell cycle did not change significantly. The mean cell cycle time of neoplastic cells in chemically induced colonic neoplasms was similar to that of epithelial cells in normal colon, but the variance was much greater in neoplastic cells. In neoplastic cells, the proliferative pool was greater, the G1 phase prlonged, and the S phase and the mitotic time became shorter as compared to epithelial cells in normal colon. The duration of G2 phase of neoplastic cells fell between the values of presumptive stem cells and differentiating cells in normal colon, compatible with the hypothesis that neoplastic cells are transformed stem cells defective in cellular differentiation. In the colonic mucosa immediately adjacent to neoplasms, the fraction-labeled-mitoses curve showed a flat second wave, indicating that the group of cells initially labeled by the pulse became a mixture of cells, some continuing the proliferative cycle normally, some going out of cycle, some slowing down in their passage from S through G2 to M, and some being arrested in mitotic phase. Such heterogeneous behavior of cells may be closely related to expansion of neoplasms. With some assumptions, however, cell cycle parameters of those normally cycling cells were estimated: the cell cycle time and the duration of G1 phase and mitotic phase were prolonged as compared to neoplastic cells and epithelial cells of normal colon.

Cell proliferation in the descending colon of dimethylhydrazine treated rats and in dimethylhydrazine induced adenocarcinomata

A stathmokinetic technique which has estimable precision has been used to estimate mitotic rates in the crypts of Lieberkühn in the descending colon of normal, and of dimethylhydrazine (DMH)-treated rats, as well as in DMH-induced adenocarcinomata. Estimates of the mean number of proliferating and of non-proliferating cells per crypt of Lieberkühn were also made in normal and in DMH-treated rats. In normal rats, epithelial cell proliferation was found to be relatively slow in the basal one-fifth of the crypts of Lieberkühn and to be most rapid in the second one-fifth of the crypt. In DMH-treated rats the number of cells around the circumference of transversely sectioned crypts was significantly increased, as was the number of proliferating cells present in longitudinally sectioned crypts. The region of relatively slow cell proliferation in the base of the crypts was expanded to occupy the lower two-fifths of the crypt in DMH-treated rats whilst the region of most rapid cell proliferation was displaced upwards to occupy the third one-fifth of the crypt. In DMH-induced adenocarcinomata cell proliferation occurred at a rate similar to that in the relatively quiescent zone at the bases of the colinic crypts in normal animals. However, tumour cell proliferation was substantially slower than that in the second one-fifth of the crypt in normal animals.