INDUCTION OF S-PHASE ENTRY BY A GONADOTROPIN-RELEASING-HORMONE AGONIST (BUSERELIN) IN THE FROG, RANA-ESCULENTA, PRIMARY SPERMATOGONIA

In the testis of the frog, Rana esculenta, mitotic activity of primary spermatogonia is regulated by gonadotropins and synergistically by te stosterone. In addition GnRH-like material directly stimulates gonadal activity. Intact animals were treated with a GnRH agonist (GnRHa, bus erelin, Hoechst) and/or a GnRH antagonist giving injections intraperit oneally on alternate days for 15 days. Moreover, testes were treated i n vitro for 24 hr with GnRHa. H-3-thymidine and colchicine were used t o assess the labelling and the mitotic index (LI and MI) of primary sp ermatogonia. Both LI and MI were increased by the treatment with GnRHa but the rate of cells measured by LI was significantly higher than th at of cells measured by MI. Therefore, our results confirm the role of GnRH-like material as local regulator of the testicular activity in v ertebrates and show its involvement in promoting the G1-S transition o f spermatogonial cell cycle in the frog, Rana esculenta.