[Effect of thyroxine on the mitotic cycle of cell cultures]

Thyroxin taken in concentration of 10 mug/ml exert a different influence on the mitotic cycle periods of the HeLe-cells in the log and stationary growth phases of the culture. During the log phase of growth thyroxine reduces the tG 2min period (for 2 hours), without influencing the other periods of mitotic cycle. In the stationary growth phase thyroxine reduces the mitotic cycle duration by 3--7 hours, chiefly on account of the accelerated G1 plus 1/2 M (by 4--8 hours) and partially of the G2min periods (by 1 hour). A conclusion on the hormonal stimulation of the cell entry into the mitotic cycle from the Go periods in the stationary culture was drawn.