Fetal X-Irradiation and Fertility. ∗

Abstract

Summary and Conclusions

1. Mice x-irradiated in utero to 300 r accumulated in 6 exposures of 50 r each on 6 consecutive days beginning on the 14th day of gestation, reveal various degrees of sterility at 6 months, the period of peak reproductive activity in the mouse. The 10 pregnant females, producing these litters, were all made sterile by this x-irradiation. 2. Within any single litter, there were variations in response of fetuses indicating, possibly, a slight spread in the developmental stage of the gonad primordia at the instant of x-irradiation. Certainly one can hardly visualize a dosimetry sufficiently different within a fetal litter to account for the variations in response. 3. Testes sterility was correlated with the relative number of seminiferous tubules in which maturation stages occur. In those testes where 40% or more of the tubules contain maturation figures, the male was fertile. The completely sterile testes contained 10% or less of tubules having maturation stages. 4. The precursors of the Sertoli cells, interstitial tissue and ovarian stroma are radioresistant. The primordia of the maturation stages and ovarian germinal nests are definitely radiosensitive. It must be emphasized again that at the time of x-irradiation these stages were not yet differentiated so that the sensitivity is related to the primordia of these various cell types, and not to the fully formed cell types. 5. The testes are reduced in size to a degree correlated with the failure of the seminiferous tubules to develop maturation stages. Consequently there is sterility. This failure to develop is accompanied by an apparent relative increase in the interstitial tissue within the testis from some 15% in the controls to 44% in the completely sterile testes. 6. A sub-lethal exposure of the mouse fetus to 300 r will produce sterility in roughly 2/3 of all offspring, with the slightly greater sterility among the males but a greater number of first generation teratologies among the females, mated to control animals. The genetic sequelae of such x-irradiation exposure, while undoubtedly of serious moment, are not considered in this study.