Suppression of growth hormone does not affect ongoing spermatogenesis in rats

Recent evidence suggests that growth hormone (GH) may enhance physiologic p rocesses, such as spermatogenesis, in addition to causing classical anaboli c effects. We have previously shown that testosterone restores spermatogene sis in rats that were made azoospermic by immunization against gonadotropin -releasing hormone (GnRH). In this study, we investigated whether suppressi on of GH affects spermatogenesis and the ability of testosterone to restore spermatogenesis following immunization against GnRH and/or growth hormone- releasing hormone (GHRH). Twelve rats were actively immunized against GnRH (anti-GnRH), twelve rats were actively immunized against GHRH (anti-GHRH), six rats were immunized against both GnRH and GHRH (anti-GnRH/GHRH), and si x rats served as controls. Two weeks after the second booster, six rats eac h from the anti-GnRH and anti-GHRH groups as well as the six anti-GnRH/GHRH rats received 24-cm testosterone-filled Silastic implants (T), and the rem aining six rats from each of these groups received empty Silastic implants. All rats were euthanized 2 months later. Weights of testes and testicular sperm counts were determined. Serum testosterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH), growth hormone (GH), and insulin-like growth factor-1 (IGF-1) concentrations were determined by radioimmunoassays . Serum GH and IGF-1 were suppressed in anti-GHRH rats. IGF-1 was partially restored by testosterone in anti-GHRH and in anti-GnRH/GHRH rats. but GH w as restored to control value in anti-GnRH/GHRH rats. Serum LH and FSH were suppressed in anti-GnRH and anti-GnRH/GHRH rats, but only FSH was partially restored by testosterone. Suppression of GH did not affect maintenance of spermatogenesis. However, because T partially restored GH and IGF-1 levels in anti-GnRH/GHRH rats and because spermatogenesis was found to be restored in these rats, we conclude that GH does not play a role in the maintenance of spermatogenesis in adult rats, but it may be required for the replenish ment of germ cells in experimentally induced regressed rat testes.