Studies regarding the long-term effects of irradiation on the testis have also been carried out in rodents. In the mouse, an ongoing outgrowth of spermatogenic colonies, formed by surviving stem cells, during the first 4-6 mo after irradiation was found, which leveled off thereafter. These colonies generally showed full spermatogenesis, although after higher doses, cell production in some colonies was poor. In contrast, in LBNF1 rats, spermatogenesis at first starts to recover but then deteriorates again, and no recovery was seen within 60 wk. Administration of gonadotropin-releasing hormone antagonist to these rats initiated recovery, and it was later shown that the high testosterone levels in the testes of these rats inhibited differentiation of spermatogonia.
We now have studied testicular histology, the epididymides, and hormone levels in adult rhesus monkeys (Ma-caca mulatta) that received high doses of total-body x-ir-radiation before adulthood. The results indicate extensive killing of spermatogonial stem cells and of Sertoli cells, leading to permanent damage to the seminiferous epithelium. To our knowledge, this is the first account of long-term intratesticular changes in the primate after TBI before adulthood.