[Experiments and theoretical cell kinetic calculations on the problem of in vivo synchronization with vincristine in L 1210 ascites tumor cells and crypt cells of the mouse (author's transl)].

Experiments are described on synchronizing L 1210 ascites tumor cells and jejunal crypt cells of the mouse with vincristine. In both cases the percentage of mitoses increases to a peak value 4 hrs after application of vincristine and decreases during the following 8 hrs ("releasing time") to the level of the normal mitotic index. Following this first mitotic peak no futher peak of neither the mitotic nor the labeling index was observed during 48 hrs in L 1210 ascites tumor cells and during 38 hrs in crypt epithelia. Thus, in both cell types it was not possible to obtain a synchronizing effect by applying vincristine. Based on cell kinetic considerations it was examined whether peaks of the mitotic as well as the labeling index can be expected at all under the given circumstances. The results show that the theoretical course of the mitotic index coincides with the measured values. This means that no peak of the mitotic index can be expected from the theoretical point of view. In calculating the time course of the labeling index the theoretical curve proved to depend to a high degree on the variations of the cycle time which are not known in detail, especially not after application of vincristine. However, the theoretical conditions show that also in the case of the labeling index no peak can be expected. This agrees with the experimental results. The general significance of a long "releasing time" of 8 hrs or more for the lack of a synchronizing effect is discussed.