Microsomal 20α-Hydroxysteroid Dehydrogenase Activity for Progesterone in Human Placenta

抄録

Placental 20α-hydroxysteroid dehydrogenase (20α-HSD) activity was studied order to evaluate the mechanism of continuation of pregnancy and initiation labor. The placentas obtained at various gestational weeks were homogenized and fractionated into “nuclear”, “mitochondrial”, “microsomal” and “supernatant” fractions. Each fraction was incubated with ¹⁴C-progesterone a hydrogen donor. Enzymatic activity was measured by the conversion progesterone to 20α-dihydroprogesterone. The highest activity of 20α-HSD progesterone was found to be localized in “microsomal” fraction. The Km, constant of 20α-HSD was 4.5×10^-6M for progesterone in “microsomal” fraction. It was found that placental microsomal 20α-HSD required NADPH as well as NADH. 20α-HSD activity for progesterone increased as gestational weeks advanced. The addition of DHA-sulfate and DHA inhibited 20α-HSD activity for progesterone significantly, suggesting that the steroid produced by feto-placental unit may be involved in the metabolism of progesterone in human placenta.