Recovery and Overrecovery from Acute Radiation Injury as a Function of Age in Drosophila

Recovery from radiation injury contributing to acute lethality was studied in imagoes of wild-type Drosophila melanogaster of various ages by giving a sublethal dose of x-rays followed after a variable interval by a second dose adjusted to permit determination of acute lethal dose, <tex-math>${\rm LD}_{50(1)}$</tex-math>. At all ages there is probably a latent period of about 6 hours before recovery begins, and thereafter it is probably exponential. Although it is clear that the half-time for recovery increases from about 5 hours at 1 day of age to 16 hours at 30 days of age, a satisfactory relation of recovery rate to age cannot be determined because, especially in young flies, complete recovery is succeeded by marked overrecovery, and the kinetics of the two processes are not separable. As measured by increase of lethal dose above its normal value, overrecovery may be as great or greater than the original injury, and it persists for the remainder of life, which, however, is shortened by the initial dose. We have assumed that life shortening is determined basically by injury to the cell nucleus and that acute lethality is determined by extranuclear injury. Nuclear injury appears not to recover.