Document Type


Publication Date

Spring 2-18-1964


The cyclic behavior toward a second exposure of ionizing radiation during the early stages of recovery from radiation damage is an established response for mammalian systems. A lack of information, however, has prevented a correlation between the state of cell populations in the animal at the time of the second irradiation and the acute mortality response of the animal. In the present study, deoxyribonucleic acid behavior in the spleens of irradiated mice was investigated, and the results compared with the acute mortality response for animals of the same strain. Following a whole-body exposure of 400 r cobalt-60 gamma radiation, there was an early and pronounced inhibition of DNA synthesis in the spleen. This inhibition persisted until 12-13 hours postirradiation, at which time recovery of DNA snythesis began. An examination of the literature and results presented in the current study showed 12 hours post-irradiation to be a time of maximal sensitivity to a second irradiation for the mice employed. The finding of resumption of DNA synthesis in the spleen at the time of maximal sensitivity of the animal population supports the notion that late G1 - early S is a period of high radiosensitivity for cells, an effect which has been previously proposed for in vitro cellular systems. Investigation of prelabeled DNA in the spleen following irradiation revealed a rapid loss of label as compared to a gradual decrease for unirradiated control spleens, but the specific activity of the DNA for the irradiated spleens remained unchanged from the unirradiated control specific activity. The findings of the present study show a close correlation between the potential for survival of the DNA synthesizing cells in the spleens of mice and the survival of the animals.