[DNA-protein cross-links in nuclei and mitochondria of tissue cells from rats of various age exposed to gamma-radiation].

The formation and repair of DNA-protein cross-links (DPC) in the mitochondria and nuclei from the brain and spleen of 2- and 29-month rats after their exposure to ionizing radiation were studied. The background level of DPC in brain and spleen mitochondria of old rats was shown to be about two times as high as in young rats. In the nuclei from the brain of old rats the background amount of DPC was also increased, unlike the nuclei of spleen of the same rats. At the doses 5 and 10 Gy (137Cs), the amount of DPC produced in the mitochondria and nuclei of brain and spleen of 29-month rats was 1.8-2.5 times greater than in the nuclei of the same tissues of young animals. At the same time, in the mitochondria of brain and spleen from irradiated rats the amount of DPC was by 30-80% higher than in the nuclei of the same tissues. Analysis of changes in DPC content during the post-radiation period showed that 5 h after irradiation of rats with a dose of 10 Gy, the level of these lesions in the nuclei of brain and spleen of young rats decreased by 40 and 65%, respectively, whereas the amount of these lesions in the mitochondria did not decrease. In this post-radiation period in nuclei of brain and spleen of old rats the amount of DPC decreased by 20-40%, respectively. However, the data on DPC obtained for the mitochondria of brain and spleen from both young and old rats showed that the amount of these lesions did not decrease during the 5 h post-radiation period. These results enable the suggestion that mitochondria do not possess a system of DPC repair. To summarize, ionizing radiation initiates in the nuclei of brain and spleen of old rats more DPC and their repair proceeds slower than in the nuclei of the same tissues of young animals. In the mitochondria of gamma-radiation exposed old rats more DPC are also produced than in young rats but no repair of DPC is observed in both old and young animals within the 5 h post-radiation period.