RESPONSE OF THE TESTIS TO GONADOTROPIN REPLACEMENT IN YOUNG HYPOPHYSECTOMIZED VS GONADOTROPIN-RELEASING-HORMONE ANTAGONIST-TREATED RATS

We have studied the response of atrophic Leydig cells to gonadotrophin replacement in young hypophysectomized (HX) and GnRH antagonist (GnRH -ANT)-treated rats. Hypophysectomy was performed at 28 days of age. Ag e-matched rats were treated with GnRH-ANT from 28 to 51 days of age. F rom 45 to 51 days of age, animals were injected with 5 IU recFSH, 10 I U hCG or vehicle. Body and testicular weights, as well as the diameter of the seminiferous tubules were significantly higher in GnRH-ANT-tre ated than in HX rats. Both recombinant FSH and hCG treatments induced a similar increase in testicular weight and tubule diameter in HX and GnRH-ANT-treated rats. However, hCG treatment induced a significantly higher increase in Leydig cell size in HX (3.2-fold) than in GnRH-ANT- treated (1.4-fold) rats. These results suggest that the response of at rophic Leydig cells to gonadotrophin supplementation was partially inh ibited in the presence of GnRH antagonist, whereas Sertoli cell-mediat ed responses seem not to be affected.