A local decrease in progesterone synthesis in the placenta and fetal membranes has long been proposed as a possible mechanism in the control of human labor. We have examined whether changes occur in the abundance of mRNA for 3fi-hydroxysteroid dehydrogenase/A5-»A4 isomerase (3fi-HSD), the enzyme which catalyzes the conversion of pregnenolone to progesterone in human placenta and fetal membranes, by Northern blot analysis using a cDNA probe to human placental type-I 3(J-HSD, the predominant isoenzyme in the placenta. The abundance of 3P-HSD mRNA (1.7-kb transcript) was about 10-fold greater in term placenta than in chorio-decidua, but undetectable in total RNA from amnion. There was no change in the abundance of 3fi-HSD mRNA in either placenta or chorio-decidua obtained after elective cesarean section at term, after preterm labor, or after term or postterm vaginal delivery. We conclude that the abundance of 3fJ-HSD mRNA does not change in the placenta or fetal membranes with labor, consistent with the view that changes in 3fi-HSD gene expression and decreased progesterone production are unlikely to effect intrauterine paracrine/autocrine regulatory mechanisms leading to term or preterm labor in women.
- 3β-hydroxysteroid dehydrogenase
- Fetal membranes