Failure of spermatogenesis to recover despite the presence of a spermatogonia in the irradiated LBNF1 rat.

The dose and time response of LBNF1, rat testis to gamma irradiation was studied with use of single doses from 2.5 Gy to 6.0 Gy. Germ cells were initially depleted as a result of killing the radiosensitive differentiating spermatogonia. Some recovery of spermatogenesis was observed at 4 and 6 wk after irradiation as indicated by the repopulation of tubules with germ cells derived from surviving stem spermatogonia. Although spermatogenesis showed additional recovery and was maintained throughout the 60-wk follow-up period after 2.5 Gy, at doses from 3.5 Gy to 6.0 Gy, repopulation indices declined after 6 wk to less than 2%. The numbers of Sertoli cells per nonrepopulating tubule were constant, independent of radiation dose or time. In addition, the nonrepopulating tubules contained an average of one A spermatogonium per 100 Sertoli cells. The size and shape of these cells corresponded to undifferentiated A spermatogonia in nonirradiated control tests. Despite high labeling (40%) and mitotic (20%) indices, the numbers of A spermatogonia changed very little with time, and no differentiated cells were produced in these tubules. The failure of spermatogenesis to recover was not due to hormone deficiency: serum gonadotropin levels increased after irradiation, and serum testosterone remained at control levels. The irradiated LBNF1 rat model may be useful for studying the regulation of differentiation of A spermatogonia.