STEM-CELL KINETICS IN RAT TESTIS AFTER IRREVERSIBLE INJURY-INDUCED BY2,5-HEXANEDIONE

Stem cells provide a continuous supply of committed progenitor cells f or the process of spermatogenesis. In rodents, stem cells have been id entified as single, undifferentiated type A spermatogonia. The rate of stem cell division has not been definitively determined because of di fficulty in locating stem cells among a normal compliment of germ cell s. The testicular toxicant 2,5-hexanedione (2,5-HD) induces irreversib le testicular atrophy with only Sertoli cells and spermatogonia remain ing after injury. Stem cell kinetics could be assessed in this toxican t model because of the absence of most mature germ cells, It is also n ot known if 2,5-HD-exposed rats possess an active stem spermatogonia p opulation. Charles River CD rats were exposed to 1% 2,5-HD in drinking water for 5 wk. At 7 or 35 wk following toxicant exposure, rats were exposed to bromodeoxycytidine continuously via Alzet mini-pumps for 1- 28 days. Serial cross sections of testis were used to identify single stem spermatogonia and to determine whether the cells were positive or negative for bromodeoxyuridine incorporation. We obtained a continuou s labeling index for stem cells from rats 7 and 35 wk after 2,5-HD exp osure and found that stem cells had a cell cycle time of approximately 8-14 days at both time points after toxicant exposure. In conclusion, we have developed a method for the assessment of stem cell kinetics a nd verified the presence of an actively dividing stem cell population in irreversibly injured testes.