To what extent can spermatogenesis be maintained in the hypophysectomized adult rat testis with exogenously administered testosterone

In a previous study it was demonstrated that spermatogenesis can be maintained quantitatively with exoge-nously administered testosterone in adult intact rats that lack LH. The studies described herein were designed to examine the extent to which spermatogenesis can be maintained quantita-tively with exogenously administered testosterone in adult rats that lack all pituitary hormones. Adult male rats were hypophy-sectomized and testosterone was administered at the time of hypophysectomy via sustained release polydimethylsiloxane (PDS) capsules of increasing lengths. We used the PDS capsules to clamp testosterone at defined concentrations within the sem-iniferous tubule fluid over a 2- to 3-month treatment period. Mean testis weights and advanced spermatid numbers per testis stabilized by 8 weeks of testosterone treatment regardless of testosterone dose. Both testis weight and advanced spermatid number responded to testosterone dose, reaching plateaus of 1.2 g and 170 × 10⁶ per testis, respectively. These values were 60% of, and significantly less than, the respective control values. This result was in striking contrast to the results of our previous study of LH-suppressed intact rats, in which exogenously ad-ministered testosterone resulted in testis weights and advanced spermatid numbers that plateaued at values not significantly different from those in controls. These different effects of tes-tosterone in intact and hypophysectomized rats occurred despite the fact that the seminiferous tubule fluid testosterone concen-trations achieved in the hypophysectomized rats (up to 25 ng/ml) were greater than the minimal testosterone concentration found previously to be required to maintain spermatogenesis quantitatively in LH-suppressed intact rats (13 ng/ml). Taken together, these results demonstrate clearly that intratesticular testosterone doses that are as high as or higher than those that maintain spermatogenesis quantitatively in intact rats lacking LH fail to maintain spermatogenesis quantitatively in rats lack-ing all pituitary hormones.