FAILURE OF SPERMATOGENESIS TO RECOVER DESPITE THE PRESENCE OF A SPERMATOGONIA IN THE IRRADIATED LBNF(1), RAT

The dose and lime response of LBNF(1) 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 dif ferentiating spermatogonia. Some recovery of spermatogenesis was obser ved at 4 and 6 wk after irradiation as indicated by the repopulation o f tubules with germ cells derived from surviving stem spermatogonia. A lthough 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 constan t, independent of radiation dose or rime, In addition, the nonrepopula ting tubules contained an average of one A spermatogonium per 100 Sert oli cells. The size and shape of these cells corresponded to undiffere ntiated A spermatogonia in nonirradiated control testis. Despite high labeling (40%) and mitotic (20%) indices, the numbers of A spermatogon ia changed very little with time, and no differentiated cells were pro duced in these tubules. The failure of spermatogenesis to recover was not due to hormone deficiency: serum gonadotropin levels increased aft er irradiation, and serum testosterone remained at control levels. The irradiated LBNF(1) rat model may he useful for studying the regulatio n of differentiation of A spermatogonia.