ULTRACYTOCHEMISTRY OF 3-BETA-HYDROXYSTEROID DEHYDROGENASE IN LEYDIG-CELL PRECURSORS AND VASCULAR ENDOTHELIAL-CELLS OF THE POSTNATAL RAT TESTIS

In the biosynthesis of steroid hormones 3 beta-hydroxysteroid dehydrog enase (3 beta-HSD) is a key enzyme. The present report describes the s ubcellular localization of the enzyme in the fetal-type Leydig cells, the fibroblast-like precursors of adult-type Leydig cells and in endot helial cells of interstitial capillaries. Histochemical methods for li ght microscopy and ultracytochemical methods for electron microscopy w ere used on rat testes of postnatal day 15. 3 beta-HSD reactivity was located at subcellular levels by means of the ferricyanide method. A s pecific, distinct localization of reaction product in the form of copp er ferrocyanide precipitates was observed on the membranes of the smoo th endoplasmic reticulum not only in the fetal-type Leydig cells and t he fibroblastlike precursors of adult-type Leydig cells, but also foca lly in the endothelial cells of interstitial blood capillaries. Topogr aphically, the 3 beta-HSD-positive precursors were most often found in the outer layer of the boundary tissue and surrounding interstitial b lood vessels. The capillaries with 3 beta-HSD-positive endothelial cel ls 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 subcellu lar level in precursors of adult-type Leydig cells and focally in capi llary endothelial cells associated with them. Due to the close associa tion between 3 beta-HSD-positive vascular endothelial cells and Leydig cells a paracrine relationship between the two cell types may be invo lved in the acute regulation of steroidogenesis by blood-borne luteini zing hormone.