Gamma-Ray Sensitivity of Oocytes of Immature Mice

Abstract

Summary

Sensitivity of oocytes of 10-day-old mice to radiation-induced cell death has been estimated by counting surviving cells 72 hr after Co⁶⁰ gamma-ray exposures of 0, 1, 3, 5, 7, 10, 15, and 25 r. An LD₅₀ of 8.4 r, with 95% confidence limits of 7.2 and 9.7 r has been estimated for stage 1, and an LD₅₀ of 9.4 r, 95% confidence limits of 6.7 and 14.9 r, was obtained for stage 2 oocytes. Acute irradiation was more effective than chronic exposure in both young and adult females. After chronic exposure, survival is higher in the adult than for equivalent oocyte stages of young mice. This could result either from higher radiation sensitivity of oocytes of 7-14-day-old females, or from more efficient repair mechanisms in adult females. Oocytes in later stages of follicular development appeared to be more resistant in both immature and adult females. This result is in agreement with the fertility pattern of irradiated female mice and indicates highest resistance for more mature follicle stages. These data are discussed in relation to changes in fertility response of the mouse at different fetal and early postnatal oocyte stages. The possibility that radiation might have extremely severe effects on the ovary at particularly sensitive periods of development in other species is emphasized.