Sedimentation of nucleoids from thymus and spleen cells of rats after X-irradiation in vitro and in vivo

The reaction to irradiation of thymocytes was tested immediately and 6 hours after whole body X-irradiation of rats with doses from 190 cGy up to 1520 cGy by nucleoid sedimentation. For comparison, examinations of thymus and spleen cells after X-irradiation in vitro were done. Preliminary analyses should find a possible coergism between X-rays on one side and hyperthermia and inhibitors of DNA-synthesis or DNA-repair (cytosinearabinoside, dideoxythymidine, 3-amino-benzamide, ethidiumbromide, and novobiocine) on the other side. From the results the following conclusions may be drawn: 1) With respect to the detection of in vivo effects of X-irradiation, the nucleoid sedimentation is less sensitive than biochemical methods. 2) Some hours after sublethal X-irradiation in vivo, free DNA and/or polydesoxyribonucleotides appear. At the same time cross-links can be detected in the chromatin fraction. 3) The reduction of the nucleoid sedimentation immediately after high doses of whole-body irradiation is the result of primary DNA lesions. The changes detectable some hours after are due to the secondary enzymatic changes, that are connected with the interphase death of thymocytes, and coincide with the present opinions about the irradiation induced apoptosis of cells. (orig./ECB)