The administration of testosterone via Silastic capsules has been shown previously to maintain advanced spermatid number quantitatively in intact rats in which LH but not FSH was suppressed, but not in hypophysectomized rats, indicating that pituitary factors in addition to LH are required for the quantitative maintenance of spermatogenesis in the rat. The objective of the present study was to examine whether testosterone is capable of maintaining quantitatively normal spermatogenesis in rats in which both LH and FSH are suppressed. Intact adult male rats were actively immunized against GnRH by intradermal injection of GnRH conjugated to human serum globulin; control rats received intradermal injections of saline and adjuvant. Four weeks after the primary immunization, GnRH-immunized rats received the first booster injection and, at the same time, received testosterone-filled polydimethlysilox-ane (PDS) implants of 4, 8, 12, or 24 cm or empty implants. Booster injections were repeated every 2 weeks for 8 weeks. At that time, rats were killed, and serum levels of LH, FSH, and testosterone, testicular advanced spermatid number, and seminiferous tubule fluid testosterone concentrations were determined. Four weeks after the initial administration of GnRH immunogen, i.e. before the first booster injection, serum levels of testosterone, LH, and FSH and the number of advanced spermatids per testis were not different from those in controls. Eight weeks after the first booster injection, serum LH and FSH and advanced spermatids were undetectable in all GnRH-im-munized rats. The administration of testosterone-filled PDS implants of 4 and 8 cm to GnRH-immunized rats for 8 weeks resulted in the maintenance of 105 ± 6 and 161 ± 5 × 106 advanced spermatid/testis, respectively, significantly less than the control value (237 ± 19 × 106). In GnRH-immunized rats that received testosterone-filled PDS implants of 12 or 24 cm, the advanced spermatid numbers per testis (228 ± 4 and 229 ± 8 × 106, respectively) were not significantly different from those in controls. These results indicate that testosterone is capable of maintaining spermatogenesis quantitatively in the adult rats testis in the absence of both radioimmunoassayable LH and FSH.
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