Ultracytochemistry of 3β-hydroxysteroid dehydrogenase in Leydig cell precursors and vascular endothelial cells of the postnatal rat testis

In the biosynthesis of steroid hormones 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) is a key enzyme. The present report describes the subcellular localization of the enzyme in the fetal-type Leydig cells, the fibroblast-like precursors of adult-type Leydig cells and in endothelial cells of interstitial capillaries. Histochemical methods for light microscopy and ultracytochemical methods for electron microscopy were used on rat testes of postnatal day 15. 3 beta-HSD reactivity was located at subcellular levels by means of the ferricyanide method. A specific, distinct localization of reaction product in the form of copper ferrocyanide precipitates was observed on the membranes of the smooth endoplasmic reticulum not only in the fetal-type Leydig cells and the fibroblastlike precursors of adult-type Leydig cells, but also focally in the endothelial cells of interstitial blood capillaries. Topographically, the 3 beta-HSD-positive precursors were most often found in the outer layer of the boundary tissue and surrounding interstitial blood vessels. The capillaries with 3 beta-HSD-positive endothelial cells were usually located in the vicinity of 3 beta-HSD-positive Leydig cells. For the first time, 3 beta-HSD has been located at the subcellular level in precursors of adult-type Leydig cells and focally in capillary endothelial cells associated with them. Due to the close association between 3 beta-HSD-positive vascular endothelial cells and Leydig cells a paracrine relationship between the two cell types may be involved in the acute regulation of steroidogenesis by blood-borne luteinizing hormone.