Evidence for reproductive death of dividing cells in thymus and spleen following whole-body gamma-irradiation of mice.

Mice were given whole-body gamma-irradiation with 300 and 800 rad 1 hour or 1 day after the administration of 3H-thymidine. The time-course of the specific activity of DNA in thymus and spleen and the release of radioactivity into the fraction of DNA soluble in 0-14 N NaCl were determined for 28 hours after exposure. The results indicate that on average the loss of mitotically-active cells was delayed compared with the loss of a representative fraction of non-dividing cells. This suggested that different mechanisms might be implicated in the dying process of the dividing and non-dividing lymphoid cells. Using a dose-fractionation method, the total activity of DNA was determined in thymus and spleen at 24 hours after the first exposure and 25 hours after the in vivo labelling of DNA. A parallelism has been found between the results of this experiment and the recovery effect of the Elkind-Sutton type. It may be concluded that the dying process responsible for the loss of the dividing cells from thymus and spleen after irradiation probably involves reproductive death.