Abstract
Seventy male rats aged four to eight days were exposed to 0–430 r x-irradiation. Counts were made at 12, 24 and 72 hours after irradiation of normal and degenerating germ cells at different developmental stages and of ‘supporting’ cells. The decrease in the number of gonocytes which normally occurs with advancing age was partially inhibited by irradiation. The number of gonocytes undergoing lysis increased after treatment. No reduction in the number of type-A spermatogonia was detected until 72 hours after irradiation. In contrast, intermediate-type and type-B spermatogonia, as well as primary spermatocytes, became markedly depleted at 72 hours. The numbers of normal ‘supporting’ cells decreased sharply after irradiation. Cells undergoing degeneration were consistently more numerous in irradiated than in control animals. While the radio-sensitivity of intermediate-type and type-B spermatogonia is of the same order in neonatal and adult rats, type-A spermatogonia are slightly more radio-sensitive in the adult. Irradiation of the testis of the neonatal rat appears to cause inhibition of mitosis as well as cell-death.

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