The major objective of the studies presented herein was to compare the extent to which exogenously administered testosterone is able to restore spermatogenesis in adult rats made azoospermic by withdrawal of all pituitary hormones (hypophysectomy for 4 weeks) vs. withdrawal of LH alone [tes-tosterone- and estradiol-filled (TE) polydimethylsiloxane im-plants of 2.5 and 0.1 cm, respectively, for 8 weeks]. In hypophy- sectornized (Hypox) rats, serum LH and FSH were both unde-tectable; in the rats that received TE implants, serum LH was undetectable, but FSH was unaffected compared to control values. Seminiferous tubule fluid testosterone concentrations were reduced significantly from their control values of 60-65 to 1.4-1.7 ng/ml in the azoospermic Hypox and TE rats. These rats then received testosterone-filled implants of 4, 12, 18, or 24 cm and were killed 2 months later. In both the Hypox and TE rats, seminiferous tubule fluid testosterone concentrations rose linearly with increasing capsule sizes, and with each of the implant sizes, these concentrations did not differ significantly between the Hypox and TE rats. This made it possible for the first time to examine the effects of comparable intratesticular testosterone concentrations on the numbers of advanced sper-matids per testis that could be restored in the azoospermic testes of rats lacking all pituitary factors vs. those lacking only LH. The results that we present demonstrate that the numbers of restored advanced spermatids were consistently and signifi-cantly lower in Hypox than in TE rats despite equivalent semi-niferous tubule fluid testosterone concentrations. These results provide quantitative conclusive evidence to support the conten-tion that pituitary factors in addition to LH are required for the quantitative restoration of spermatogenesis in the adult rat testis.
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