Significance of germ cells for the expression of testicular endocrine function in rats

Germ-cell depletion was induced in rats by busulphan administration during the fetal period (Group B). Although a sigmoidal increase of serum testosterone concentration was observed 1 h after the administration of graded doses of hCG (0.3-15.0 i.u./100 g body weight) in intact rats and those in Group B, a shift in the dose-response curve to the right was observed in the latter, suggesting that the sensitivity of testicular response to gonadotrophin was lower in germ cell-depleted rats. However, since the sensitivity was almost identical for both groups of rats for isolated Leydig cells incubated in vitro for 3 h with hCG (0.5-312.5 i.u./ml), the intrinsic nature of the cells was not affected in Group B rats. When the responses of testicular tissue blocks were examined in the in-vitro incubation system, reduced sensitivity reappeared for those from Group B rats, and the presence of testicular tissue components including seminiferous tubules was considered to be responsible for the difference in Leydig cell sensitivity between intact rats and those exposed to busulphan. By the combination of in-vivo and in-vitro experiments, we have demonstrated that germ cells are involved in the endocrine function of the testis.