2005 Volume 51 Issue 2 Pages 265-272
20α-Hydroxysteroid dehydrogenase (20α-HSD) catalyzes the conversion of progesterone to its inactive form 20α-dihydroprogesterone (20α-OHP). 20α-HSD is expressed in the murine placenta, suggesting a role, yet unidentified, played by this enzyme during the course of pregnancy. To elucidate the possible roles of 20α-HSD during pregnancy, 20α-HSD gene expression in the placenta was examined by Northern blot analysis, and progestin (progesterone and 20α-OHP) concentrations in the maternal and fetal sera and the amniotic fluid were measured by radioimmunoassay in pregnant Shiba goats. The expression of 20α-HSD mRNA was observed in the placenta and the intercaruncular part of the uterus during mid to late pregnancy. Analysis by in situ hybridization revealed that 20α-HSD mRNA was mainly localized in the endometrial epithelium of the caruncle side of the placenta. Considerable enzyme activity of 20α-HSD was also detected in the cytosolic fraction of the placenta and intercaruncular part of the uterus. Although concentrations of progesterone and 20α-OHP in the maternal serum showed similar profiles, progesterone levels in the fetal serum stayed extremely low throughout the pregnancy. The 20α-OHP concentration in the fetal serum was always higher than that in the maternal serum. In the amniotic fluid, the concentrations of both progesterone and 20α-OHP remained at very low levels throughout the pregnancy. These results support the notion that 20α-HSD protects the fetus from the cytotoxic effects of progesterone, and thereby maintains the normal development of the fetus.