Radiosensitivity of testicular cells in the fetal mouse

The effects of prenatal X irradiation on postnatal development of the CBA/P mouse testis was studied. At days 14, 15 and 18 post coitus pregnant female mice were exposed to single doses of X rays ranging from 0.25-1.5 Gy. Higher doses resulted in extensive loss of fetal mice. In the male offspring, at days 3 and 31 post partum, the numbers of gonocytes, type A spermatogonia and Sertoli cells per testis were determined using the disector method. Furthermore, after irradiation at day 15 post coitus, the numbers of Leydig cells, mesenchymal cells, macrophages, myoid cells, lymphatic endothelial cells, endothelial cells and perivascular cells per testis were also determined at days 3 and 31 post partum. At day 3 post partum, the number of germ cells was decreased after irradiation at days 14 and 15 post coitus. A D0 value of 0.7 Gy was determined for the radiosensitivity of the gonocytes at day 14 post coitus. A D0 value of 0.8 Gy was determined for the gonocytes at day 15 post coitus which, however, seems to be less accurate. No accurate D0 value could be determined for the gonocytes at day 18 post coitus. At day 31 post partum, the repopulation of the seminiferous epithelium as well as testis weights and tubular diameters were more affected by irradiation with increasing age of the mice at the time of irradiation. The percentage of tubular cross sections showing spermatids decreased with increasing dose after irradiation at days 15 and 18 post coitus, but not after irradiation at day 14 post coitus. Furthermore, in tubular cross sections showing spermatids, exposure of testes to 1.25 and 1.5 Gy at day 18 post coitus resulted in significantly lower numbers of spermatids per cross section when compared to those testes exposed to the same doses at day 15 post coitus. This indicates that the radiosensitivity of the gonocytes increases with fetal age. Prenatal irradiation did not cause significant changes in the numbers per testis of the Sertoli cells or the interstitial cell types. The present results indicate that, in the fetal mouse testis, the spermatogonial stem cells are more sensitive to X irradiation than in the adult testis, while Sertoli cells and interstitial cells are relatively resistant.