17β-hydroxysteroid dehydrogenase type 1 and 2 expression in the human fetus

The present study investigates the expression patterns of 17βhydroxysteroid dehydrogenase (17βHSD) isozymes in human fetal tissues to understand how estrogenic activity is regulated in the human fetus. Using enzyme assay, high 17βHSD activity was detected in the placenta and liver, and low levels of 17βHSD activity were also present in the gastrointestinal tract and kidney. After Northern blot analysis, we detected the messenger ribonucleic acid for 17βHSD type 1 (17βHSD1) only in the placenta, whereas that for 17βHSD type 2 (17βHSD2) was detected in the placenta, liver, gastrointestinal tract, and urinary tract at 20 gestational weeks. In RT-PCR analysis of the messenger ribonucleic acid transcripts, 17βHSD 1 was predominantly expressed in the placenta, brain, heart, lung, and adrenal, whereas 17βHSD2 expression was predominantly detected in the liver, gastrointestinal tract, and kidney. In addition, we detected 17βHSD2 immunoreactive protein in surface epithelial cells of the stomach, absorptive epithelial cells of the small intestine and colon, hepatocytes of the liver, and interstitial cells surrounding the urinary tubules of the renal medulla. 17βHSD2 in these tissues may be functioning in the prevention of in utero exposure of the fetus to excessive estradiol from the maternal circulation and amniotic fluids.