Effects of estradiol infusion in GnRH immunized boars on spermatogenesis

Active immunization of boars against gonadotropin-releasing hormone (GnRH) inhibits luteinizing hormone (LH) and testicular steroids, so that mitosis of spermatogonia is reduced and apoptosis increased. To clarify whether high amounts of estrogens which are synthesized in the boar testis support spermatogenesis, a group of 6 boars was immunized against GnRH and then infused for 7 weeks with estradiol (E2-17beta). For comparison, intact boars and immunized boars were infused with saline only. Testicular tissue was then analyzed by immunocytochemistry for apoptosis (TUNEL, EM), mitosis (Ki67), and estrogen receptor alpha (ER alpha). The specificity of ER alpha staining was confirmed by RT-PCR and Western blot. Immunization decreased LH and testosterone to minimal concentrations in immunized and E(2)17beta-infused immunized boars, whereas follicle-stimulating hormone (FSH) was not significantly altered. Estradiol decreased to base levels after immunization. Infusion increased E2-17beta in peripheral blood plasma of the immunized boars to physiological levels. Except for A-spermatogonia, all spermatogenic cells decreased after immunization by about 60%. After estradiol infusion, cell counts increased again and were intermediate between control and immunized boars. Mitosis of spermatogonia was reduced by nearly 50% due to immunization but was partly restored by E2-17beta infusion. Expression of ER alpha was localized in spermatogonia, suggesting stimulation of mitosis, which was further confirmed due to its predominant occurrence in stage I of the seminiferous epithelial cycle (main stage of cell division). Apoptosis was minimal in boars but elevated in the other 2 groups. Data showed that estrogens in physiological concentrations supported mitosis but were not sufficient to normalize sperm production because apoptosis was still high.