Variation in the Radiosensitivity of the Cell Population in Developing Rat Retina

Abstract

Anauto-radiographic study was made of the effects of a single dose of 160 R X rays on the neural retina of 2-day-old rats. In rats killed at intervals until 72 hr. after exposure, accumulation of degenerate cells was maximal from 15-25 hr. Cells labelled with tritiated thymidine half an hour before irradiation accounted for only about 10% of the necrotic population 6 hours after exposure. Their incidence increased to around 25% by 30 hr. Retinal cells in the phases S, Gl and G2+M of the generation cycle, the durations of which had been previously determined, were labelled with tritiated thymidine before irradiation in each of 3 groups of rats which were killed 6 hours after exposure. Comparison of the yield of labelled degenerate cells from each Group of animals revealed that the DNA-synthetic phase was least and G2+M most sensitive to 160 R X rays, the latter having 5 times the sensitivity of the S phase. Over 50% of the radiosensitive cells came from the non-proliferative part of the retinal population.