Restoration of spermatogenesis by high levels of testosterone in hypophysectomized rats after long-term regression

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Abstract
In order to correlate the levels of intratesticular testosterone and the status of spermatogenesis, the present study examined the spermatogenic responses of mature chronically hypophysectomized (HPX) rats to different regimens of testosterone (T) replacement, i.e. implantation of a 2 × 5 or 6 × 5 cm long testosterone capsule (TC), or injection of 25 mg or 100 mg of testosterone enanthate (TE) every 4 days for 90 days. These regimens restored the testicular testosterone of the HPX rats to 25–96% of that measured in normal control rats. The testis weight of untreated HPX rats was below 30% of the normal control values. It was restored to 60–80% of control values in the TC implanted rats and to 50% in those receiving TE injection. Complete spermatogenesis of HPX rats was restored in those receiving TC implants and 100 mg TE injections. It was incomplete in those given 25 mg TE injections. Quantitative evaluation of germ cells revealed that spermatogonial populations of HPX rats were restored to 70 and 50% of the normal levels in rats receiving TC implants and TE injection, respectively. Differentiation of these cells resulted in the population of preleptotene spermatocytes to the same extent as those observed in spermatogonia. The yield of spermatids in both TC- and TE-treated HPX rats was below 50% of normal controls. Ratios between two successive generations of germ cells in stage VII epithelium revealed both dosage and regimen effects upon the yield of meiotic cells and spermatids. These results suggest that both T concentration and the mode of T availability to the testis may be important for specific steps of germ cell development in different stages of the cycle of the seminiferous epithelium. The results of the present study demonstrate that as little as 25% of normal testicular T concentration is sufficient to support all stages of spermatogenesis. Failure to restore a normal germ cell number even in the presence of a normal testicular T concentration suggests the need of other factors for quantitative spermatogenesis. Furthermore, despite a higher testicular T concentration achieved by TE injections, the restoration of spermatogenesis was less pronounced by this regimen. This finding suggests that the consistency of testicular T may also be important for normal spermatogenesis.