Androgen action on the restoration of spermatogenesis in adult rats: effects of human chorionic gonadotrophin, testosterone and flutamide administration on germ cell number

Abstract

Spermatogonial proliferation is a critical but poorly understood determinant of the spermatogenic process. In rats, exogenous testosterone plus oestradiol (TE) markedly suppresses serum LH and testicular testosterone levels. In the TE-treated rat, spermatogonial number declines to approximately 65% of control levels while round to elongated spermatid maturation is interrupted. The partial restoration of testicular testosterone levels by exogenous testosterone administration restores spermatid maturation but neither testicular weight nor spermatogonial number are normalized. This study aimed to determine the role of testosterone and/or non-androgenic Leydig cell factors in the restoration of spermatogonial number in the testosterone-treated rat. Germ cell numbers were assessed using stereological methods and expressed as germ cell number per testis. Adult Sprague Dawley rats initially received 3 cm testosterone plus 0.4 cm oestradiol Silastic implants for 9 weeks to suppress spermatogenesis, followed by 10 days of either (i) exogenous testosterone using implants (T24 cm) or testosterone esters (5 or 25 mg sc every third day), or (ii) human chorionic gonadotrophin (hCG; 0.5, 1.25, 2.5 or 10 IU/kg sc daily) as an LH substitute to restore Leydig cell function. Following TE treatment, testicular weights and testicular testosterone levels were reduced to 31% and 1.3% of control levels, respectively. In response to exogenous testosterone administration, testicular weight was restored to 52-58% of controls while testicular testosterone levels increased to only 3.5-17.3% of controls despite serum testosterone levels 4.5-24-fold above control. In response to hCG treatment, a graded increase in testicular testosterone levels was achieved (2.6-20.5% of control) and testicular weights increased to 38-56% of control. TE suppression reduced (p < 0.05) type A spermatogonia and type B spermatogonia/preleptotene spermatocyte numbers per testis to 61% and 77% of control, respectively; however, neither subsequent testosterone nor hCG treatments significantly increased either germ cell number. In a second study, hCG (1.25 IU/kg) was administered alone or in combination with the androgen receptor antagonist, flutamide (100 mg/kg sc daily), to withdraw androgenic effects at all stages of spermatogenesis. The TE-induced suppression of type A spermatogonia (59% control) and type B spermatogonia/preleptotene spermatocytes (68% control) was not affected by hCG +/- flutamide. On the other hand, as expected, hCG increased the number of elongated spermatids (p < 0.05). The co-administration of flutamide reduced (p < 0.05) the numbers of all pachytene spermatocyte forms, round and elongated spermatids below those of TE-treated animals. We conclude that neither exogenous testosterone nor hCG is capable of restoring spermatogonial number in the TE-treated rat within 10 days despite the partial or full restoration of testicular testosterone levels. No evidence was found for the involvement of non-androgenic Leydig factors in the control of spermatogonial numbers. The data from flutamide-treated animals demonstrates that residual androgen effects are present in the TE model as, even in the presence of testicular testosterone levels below that needed for spermatid maturation, further inhibition of spermatocyte development and meiosis is apparent.