Subcellular localization of gonadotropins and testosterone in the developing fetal rat testis

Gonadotropins and testosterone were immunocytochemically localized in the fetal rat testes 16-18 days of gestation with the unlabeled antibody-peroxidase anti-peroxidase complex technique. Maximum staining for gonadotropins with antiserum to the beta chain of human chorionic gonadotropin (anti-hCGbeta) occurred at 16 days gestation in the seminferous tubule and 17 days gestation in interstitial (Leydig) cells. Anti hCGbeta sites were on the plasma membranes at the luminal aspects of Sertoli cells at 16 days gestation. In addition, intracellular hCGbeta sites were evident including the nucleus, nucleolus, ribosomes, some vesicles, lysosomes and centrioles. The stain for hCGbeta disappeared rapidly and by 17 days was limited to patches in the cytoplasm and nuclei. In the fetal testes, staining for anti-testosterone binding sites was most intense at 18 days of gestation either in lipid droplets or on nuclei of Leydig and Sertoli cells. Very little testosterone stain was observed before 18 days of gestation. These findings agree with physiologic data that suggest that gonadotropins bind to receptors and stimulate testicular development and the capacity for testosterone production.