[Synchronization of cellular proliferation in mice with sarcoma 37 by using hydroxyurea]

The synchronizing effect of hydroxyurea on the passage of sarcoma 37 cells through the stage of the S-phase and mitosis was investigated in albino mice. The study was performed with consideration to the circadian variations in the mitotic activity and the labelled nuclei indices. The degree of synchronization was assessed by the changes in the cell count and the rate of changes in synchronicity. The tumour consisted of at least two cell populations in which the variations in the number of cells both at the S-period, and, possibly, in mitosis were shifted in respect to one another by phase. The rate of artificial cell synchronization in the mitosis proved to be much greater than the natural one in the tumour undivided into individual populations. However, the number of cells subjected to artificial synchronization showed no significant difference not only from the cell count in the tumour undivided into individual populations, but also from the number of cells synchronized naturally in one of the populations. This could be explained by the fact that hydroxyurea acted on one group of cells only since variations in the number of DNA-synthesizing cells were shifted in individual populations in respect to one another by phase.