Dose Rate-Effect of Adaptive Response of Thymocyte Apoptosis and Cell Cycle Progression Induced by Low Dose X-ray Radiation in Mice

Objective:To observe the dose rate effect of adaptive response of thymocyte apoptosis and cell cycle progression induced by low dose X ray radiation. Methods:Kunming male mice were irradiated with the inductive dose(D 1: 75 mGy; dose rate: 6.25, 12.5, 25, 50, 100 and 200 mGy·min -1 ,respectively)and the challenging dose (D 2: 1.5 Gy; dose rate: 287 mGy·min -1 ). The time interval between D 1 and D 2 were 6 h. The changes of thymocyte apoptosis and cell cycle progression were measured with flow cytometry. Results:When the dose rates were 6.25, 12.5 and 25 mGy·min -1 ,respectively, the percentages of apoptotic cells in D 1+D 2 groups were significantly lower than those in D 2 group( P 0.05 or P 0.01), and the percentages of G 0/G 1 and G 2+M phase cells decreased remarkably, while the percentages of S phase cells increased significantly ( P 0.05 or P 0.01). Conclusion:When the mice were irradiated by X ray with 75 mGy (dose rates of D 1: 6.25, 12.5 and 25 mGy·min -1 ) 6 h before 1.5 Gy (dose rate of D 2: 287 mGy·min -1 ) exposure, the adaptive response of thymocyte apoptosis and cell cycle progression could be induced under the condition of whole body irradiation.