Spleen desoxyribonucleic acid content as an index of recovery in x-radiated mice treated with spleen homogenate.

1. The time course of total DNA/spleen and spleen DNA concentration in LAF1 mice following whole-body exposure to 740 r x-rays (an LD100 dose) and the effect of spleen homogenate treatment on this end-point have been studied. At 24 hours postirradiation, the DNA content/spleen decreased from a normal value of 1,963 ± 70 µg. After 3 days the DNA level had declined further to 229 µg., and this low level persisted in the control, irradiated mice until death (9th day). DNA concentration was likewise depressed from normal values of 19.7 ± 0.35 µg/mg to levels of 8 µg/mg until death. 2. A single postirradiation injection of spleen homogenate into the irradiated mice elicited a profound regeneration of the spleen in terms of DNA content, concomitant with survival of these animals. The recovery phenomenon is characterized by reversal of the depression in total DNA content/spleen, which is, however, not manifest until the 6th day; by the 9th day the total DNA values exceed those of normal mice. Further evidence for the relationship between spleen DNA content and recovery was provided by DNA analyses on splenectomized mice which had received spleen homogenate treatment. 3. The magnitude of the response in DNA content/spleen, both during involution and in the recovery phase, was greater by factors of 2 and 3, respectively, than the spleen weight response. Recovery of the spleen DNA in x-radiated mice receiving spleen homogenate precedes that of peripheral leucocyte count and body weight loss. The results indicate that the DNA level of the spleen provides a sensitive biochemical index of recovery following x-radiation exposure. It is suggested that this end-point be employed as a biochemical assay for the spleen radiation protection factor.