HUMAN 17-BETA-HYDROXYSTEROID DEHYDROGENASE TYPE-2 MESSENGER-RIBONUCLEIC-ACID EXPRESSION AND LOCALIZATION IN TERM PLACENTA AND IN ENDOMETRIUM DURING THE MENSTRUAL-CYCLE

According to the current hypothesis, 17 beta-hydroxysteroid dehydrogen ases (17HSDs) regulate the extent of estrogen influence in the endomet rium by converting estradiol (E-2) locally into a biologically less ac tive sex steroid, estrone (E-1), and vice versa. Recently, we have sho wn that both 17HSD type 1 and type 2 are expressed in the human endome trium, and in the present work, using in situ hybridization, we show t hat 17HSD type 2 is localized in the glandular epithelial cells as pre viously shown for the type 1 enzyme, but in contrast to type 1, the ex pression of type 2 is highest at the end of the cycle. Hence, we hypot hesize that the differential expression of the two 17HSD enzymes, with opposite activities in same cell types, could modulate intracellular E-2 concentrations during the end of the luteal phase of the menstrual cycle. We further analyzed the expression of 17HSD type 1 and type 2 mRNAs in term human placenta. Expression of 17HSD type 1 mRNA was dete cted in the syncytiotrophoblasts, and signals for type 2 mRNA were fou nd inside the villi, corresponding to cytotrophoblasts. The expression of 17HSD type 2 in the placenta may serve to maintain the presence of inactive sex steroids and attenuate the formation of biologically pot ent androgens and estrogens.