CHANGES IN THE ABUNDANCE OF MESSENGER-RNA FOR TYPE-I3-BETA-HYDROXY-STEROID DEHYDROGENASE DELTA-5-]DELTA-4 ISOMERASE IN THE HUMAN PLACENTA AND FETAL MEMBRANES DURING PREGNANCY AND LABOR

A local decrease in progesterone synthesis in the placenta and fetal m embranes has long been proposed as a possible mechanism in the control of human labor. We have examined whether changes occur in the abundan ce of mRNA for 3beta-hydroxysteroid dehydrogenase/DELTA5-->DELTA4 isom erase (3beta-HSD), the enzyme which catalyzes the conversion of pregne nolone to progesterone in human placenta and fetal membranes, by North ern blot analysis using a cDNA probe to human placental type-I 3beta-H SD, the predominant isoenzyme in the placenta. The abundance of 3beta- HSD mRNA (1.7-kb transcript) was about 10-fold greater in term placent a than in chorio-decidua, but undetectable in total RNA from amnion. T here was no change in the abundance of 3beta-HSD mRNA in either placen ta or chorio-decidua obtained after elective cesarean section at term, after preterm labor, or after term or postterm vaginal delivery. We c onclude that the abundance of 3beta-HSD mRNA does not change in the pl acenta or fetal membranes with labor, consistent with the view that ch anges in 3beta-HSD gene expression and decreased progesterone producti on are unlikely to effect intrauterine paracrine/autocrine regulatory mechanisms leading to term or preterm labor in women.