Synchronization of cell proliferation in sarcoma 37 of mice by hydroxyurea

Abstract

The synchronizing action of hydroxyurea on the passage of sarcoma 37 cells through the S phase and mitosis was investigated in mice, allowing for diurnal fluctuations in mitotic activity and the index of labeled nuclei. The degree of synchronization was estimated from changes in the number of proliferating or labeled cells and the rate of change of synchronization. The tumor consisted of at least two cell populations in which variations in the number of cells both in the S period and also, probably, in mitosis were out of phase. The degree of artificial synchronization of the cells in mitosis based on the rate of change of synchronization was much higher than the natural level in the tumor not divided into separate populations. However, the number of cells undergoing artificial synchronization was not significantly different not only from the number of cells in the tumor undivided into separate populations, but also from the number of cells naturally synchronized in one of the populations. A possible explanation of this fact is that hydroxyurea acted on only one group of cells, for fluctuations in the number of DNA-synthesizing cells in the separate populations also were out of phase.