Effect of whole-body irradiation with X-rays on apoptosis of thymocytes in mice

Radiation-induced apoptosis of thymocytes in mice was quantified by measuring the percentage of DNA fragmentation by fluorescence spectrophotometry, and qualitatively analysed by agarose electrophoresis. The results showed that DNA fragmentation of thymocytes began to increase 2 hours after exposure to 4Gy, reaching its peak value at 14 hours. After that the percentage of DNA fragmentation came down to about 50 % of the peak value at 24 hours. It was found that the apoptosis could be induced by high dose irradiation. A typical ladder appeared on agarose gel electrophoresis after 1-4Gy irradiation. The pattern of fragmentation represents oligonucleosomes with approximately 180bp and its multiples. The dose-effect relationship of DNA fragmentation as measured by fluorescence spectrophotometry after whole-body irradiation with 0. 025-4. 0Gy showed a J-shape curve with significantly reduced apoptosis at low doses.