EARLY CHANGES IN CELL-CYCLE KINETICS AFTER IONIZING IRRADIATION BELOW1 GY

The present study describes a procedure for quantifying cell cycle alt erations within 15 h after radiation viith doses below 1 Gy. For detec tion and assessment of the relevant changes, 5-bromo-2'-deoxyuridine ( BrdUrd)-labelling and flow cytometry were used. Using this approach, a s early as 6 h after exposure of radiosensitive leukemic HL-60 cells, radiation-induced changes in cell cycle progression could be measured even with radiation doses as low as 0.25 Gy. As a result, a method to define transition rates for a single cell cycle phase or from one phas e to another is described. Even minor changes can be described. Moreov er, the BrdUrd assay allows for discrimination of cells irradiated in different phases of the cell cycle. Thus, it is possible to follow die progression in the cell cycle of cells either irradiated in G(1), S, or G(2) + M phase, respectively. Radiation effects on single cell cycl e phases can be analysed separately. A detailed evaluation of the cell ular response to irradiation regarding dose, time, and effect is descr ibed. The value of cell cycle parameters for assessment of various bio logical indicators of radiation effect is discussed.