Effects of X-Irradiation on the Mitotic Cycle of Ehrlich Ascites Tumor Cells

The effects of x irradiation (300, 500, and 1000 r) on mitosis and DNA synthesis in Ehrlich ascites tumor cells were studied. Dose-effect relations and time sequence of effects on the two processes were compared. The technique of H/ sup 3/-thymidine labeling of DNA with autoradiography was utilized, in conjunction with the mitotic index, to study alterations in the mitotic cycle. It was concluded that x irradiation affected cells in the G/sub 2/ and S periods so that the rate of exit from G/sub 2/ was reduced. Evidence, based on mean grain count per labeled cell and percentage of cells labeled, was found for a slight reduction in rate of DNA synthesis after irradiation. The delay in rate exit from G/sub 2/, however, was apparently a block at the end of the period. (auth)