Expression of diazepam binding inhibitor-like immunoreactivity in rat testis is dependent on pituitary hormones

Diazepam binding inhibitor-like immunoreactivity (DBI-LI) in normal and hypophysectomized (HPX) rat testis was studied by light and electron microscopic immunohistochemistry. In normal testis DBI-LI was observed in interstitial Leydig cells and Sertoli cells of most seminiferous tubules. At the electron microscopic level, DBI-LI was distributed throughout the cytoplasm of labeled cells; a concentration of the labeling product was observed in the smooth endoplasmic reticulum, Golgi apparati, and the outer membrane of the mitochondria. In the seminiferous epithelium, labeled processes of Sertoli cells could be traced among developing germ cells. After HPX a gradual disappearance of DBI-LI was observed in all Leydig cells. The number of labeled Sertoli cells was reduced in the majority of tubules after HPX, whereas in some tubules the staining was only slightly reduced. Replacement therapy of the HPX animals with human CG prevented the disappearance of DBI-LI from Leydig cells, whereas replacement with FSH did not prevent the disappearance of DBI-LI in Leydig cells. In Sertoli cells replacement therapies were not effective in restoring DBI-LI. In rat testis DBI and mitochondrial benzodiazepine binding sites are highly concentrated in the Leydig cells. Mitochondrial benzodiazepine binding sites and DBI are involved in the regulation of steroid production. As the expression of DBI-LI is under the control of pituitary hormones, DBI may play a role as an endogenous regulator of intracellular metabolic functions, such as steroidogenesis, in rat testis.