Maintenance of spermiogenesis by exogenous testosterone in rats treated with a GnRH antagonist: relationship with androgen-binding protein status.

The relationship of the testicular distribution and [3H]dihydrotestosterone-binding capacity of androgen-binding protein (ABP) to the completion of spermiogenesis was examined in mature rats given daily injections of 25 or 250 micrograms kg-1 body weight of GnRH antagonist (GnRH-A; Ac-D(2), Nal1, 4Cl-D, Phe2, D-Trp3, D-Arg6, D-Ala10) for two weeks with or without subcutaneous implantation of 10 cm testosterone capsules. GnRH-A administration resulted in a dose-dependent suppression of serum FSH, which was partially prevented in the 250 micrograms GnRH-A kg-1 group by exogenous testosterone. The total testicular testosterone content and concentration of testosterone in seminiferous tubular fluid were equally suppressed in both groups of rats treated with GnRH-A and receiving the testosterone supplement. ABP concentrations in interstitial and seminiferous tubular fluid were normal in rats given the 25 micrograms GnRH-A kg-1 dose, and were increased (P < 0.05) by concomitant testosterone treatment. In contrast, ABP concentrations in interstitial and seminiferous tubular fluid were increased in rats given the 250 micrograms GnRH-A kg-1 dose. This effect was attenuated when exogenous testosterone was given. Although binding of [3H]dihydrotestosterone by ABP in seminiferous tubular fluid was not affected by GnRH-A treatment, with or without exogenous testosterone, it was reduced in interstitial fluid by GnRH-A in a dose-dependent manner, and partially restored by testosterone administration. While complete spermatogenesis was maintained in rats given 25 micrograms GnRH-A kg-1, the number of step 7 and step 19 spermatids were both reduced by 35%, and were not affected by testosterone implants.(ABSTRACT TRUNCATED AT 250 WORDS)