NUTRIENT DILUTION BEFORE AND AFTER X-IRRADIATION INCREASES THE RADIORESISTANCE OF LOG-PHASE AND PLATEAU-PHASE CHINESE-HAMSTER V79 CELLS

Previous observations have shown that cells cultured in standard growt h medium (100%) demonstrated similarly enhanced survival when incubate d postirradiation either in non-growth-promoting conditioned medium or in growth-promoting 40% growth medium (Reddy and Lange, Radial. Res. 119, 338-347, 1989). From these results, it was suggested that nutrien t dilution altered radiosensitivity by a mechanism independent of prog ression of cells through the cell cycle. In this study, we have examin ed the effects on radiosensitivity of incubation in 40% growth medium prior to irradiation on both log- and plateau-phase Chinese hamster V7 9 cells and the effects on the distribution of cells in the cell cycle of incubation in 40% or 100% growth medium before and after irradiati on. Radioresistance increased by a factor of 1.5-1.6 compared to 100% growth medium for both log-phase and plateau-phase cells cultured in 4 0% growth medium prior to X irradiation and incubated in either 40% gr owth medium or conditioned medium after X irradiation. The cell cycle distributions of log-phase cells in 100% and 40% growth medium before irradiation were identical. The change in cell cycle distribution indu ced by 10 Gy did not differ among log-phase cells incubated for 3 h po stirradiation in 100% growth medium, 40% growth medium or conditioned medium. These results, in addition to supporting our previous conclusi ons, demonstrate that culturing prior to irradiation in 40% growth med ium alone increases cell survival and that incubation in 40% growth me dium before and after irradiation maximizes the survival of V79 cells. (C) 1997 by Radiation Research Society