The enzyme complex 3-beta-hydroxy-5-ene-steroid dehydrogenase and steroid DELTA-5 --> 4-ene-isomerase (3-beta-HSD) is involved in the biosynthesis of all classes of active steroids, namely glucocorticoids, mineralocorticoids, progesterone, and sex steroids. To obtain more information about the age-specific expression of 3-beta-HSD in the human ovary, we have localized this enzyme by immunocytochemistry at the light microscopic level during fetal and postnatal periods of development in the human. Immunocytochemical localization was achieved using specific polyclonal antibodies developed against purified human placental 3-beta-HSD. In the fetal ovary of 28-34 weeks, specific immunostaining for 3-beta-HSD was exclusively detected in thecal cells surrounding primary follicles and in interstitial cells. From birth until puberty, no significant immunostaining for 3-beta-HSD could be observed, while from puberty to menopause, staining was detected in theca interna cells as well as granulosa cells of growing follicles. The intensity of staining in the theca interna cells was always much higher than that in granulosa cells. Immunostaining was also found in the cytoplasm of luteinized granulosa and theca interna cells of the corpus luteum. Interestingly, there was an absence of immunoreactivity for 3-beta-HSD in one to several layers of theca interna cells lying just beneath the basement membrane. These negative cells may correspond to fibroblast-like cells that are devoid of 3-beta-HSD activity. In postmenopausal ovaries, immunolabeling was only found in dispersed interstitial cells, thus suggesting that the ovaries of postmenopausal women might be involved in sex steroid hormone secretion.
