Growth hormone in the male reproductive tract of the chicken: heterogeneity and changes during ontogeny and maturation.

Growth hormone (GH) gene expression is not confined to pituitary somatotrophs and occurs in many extrapituitary tissues. In this study, we describe the presence of GH moieties in the chicken testis. GH-immunoreactivity (GH-IR), determined by ELISA, was found in the testis of immature and mature chickens, but at concentrations <1% of those in the pituitary gland. The immunoassayable GH concentration in the testis was unchanged between 4 and 66 weeks of age, and approximately 10-fold higher than that at 1-week of age and 25-fold higher than that in 1-day-old chicks and perinatal (embryonic day 18) embryos. This immunoreactivity was associated with several proteins of different molecular size, as in the pituitary gland, when analyzed by SDS-PAGE under reducing conditions. However, while most of the GH-IR in the pituitary ( approximately 40 and 15%, respectively) is associated with monomer (26 kDa) or dimer (52 kDa) GH moieties GH-IR in the testis is primarily (30-50%) associated with a 17 kDa moiety. GH bands between 32 and 45 kDa are also relatively more abundant in the testis than in the pituitary. During ontogeny the relative abundance of a 14 kDa GH and 40 kDa GH moieties in the testis significantly declined, whereas the relative abundance of the 17 and 45 kDa moieties increased with advancing age. In adult birds, GH-IR was widespread and intense in the seminiferous tubules. Although the GH-IR was not present in the basal compartment of Sertoli cells, nor in spermatogonia and primary spermatocytes, it was abundantly present in secondary spermatocytes and spermatids in the luminal compartments of the tubules as well as in some surrounding myocytes and interstitial cells. In summary, immunoreactive GH moieties are present in the chicken testis but at concentrations far less than in the pituitary. Age-related changes in the relative abundance of testicular GH variants may be related to local (autocrine/paracrine) actions of testicular GH. The localization of GH in spermatocytes and spermatids suggests hitherto unsuspected roles in gamete development.