Human placenta and fetal membranes contain two types of 11beta-hydroxysteroid dehydrogenase (11beta-HSD). 11Beta-HSD1 interconverts cortisol and cortisone and is the predominant isoform found in the fetal membranes. 11Beta-HSD2, which predominates in the placenta syncytiotrophoblast, converts cortisol to cortisone. It has been proposed that placental 11beta-HSD protects the fetus from high levels of maternal glucocorticoids. In this study, cultured term human placental and chorionic trophoblasts were used to examine the regulation of 11beta-HSD1 and 11beta-HSD2 activities and mRNA expression by progesterone, estrogen, and activators of adenylate cyclase (forskolin) and protein kinase C (phorbol 12-myristate 13-acetate, PMA). Placental trophoblast displayed mainly type 2 oxidase activities. 11Beta-HSD in the chorionic trophoblast was exclusively an 11beta-HSD1 reductase. Progesterone (0.001-1 microM) inhibited 11beta-HSD2 activity in a dose-dependent fashion. Inhibition of endogenous progesterone production with trilostane enhanced 11beta-HSD2 activity. The inhibitory effect of progesterone on 11beta-HSD2 activity was not reversed by the progesterone receptor antagonists RU-486 or onapristone. Progesterone (1 microM) also reduced levels of 11beta-HSD2 mRNA, an effect that was attenuated by both RU-486 and onapristone. Estradiol (1 microM) inhibited type 2 oxidase activity as well. Activation of adenylate cyclase by forskolin (100 microM) up-regulated both 11beta-HSD2 activity and mRNA expression; there was no effect of PMA (1 microM) on 11beta-HSD2. 11Beta-HSD1 reductase activity was unaffected by progesterone, estrogen, forskolin, or PMA in either the placental or chorionic trophoblasts. We conclude that both progesterone and estrogen are inhibitors of 11beta-HSD2 activity in term human placenta in vitro. Levels of 11beta-HSD2 activity and mRNA are increased by activation of the cAMP pathway. Progesterone also suppresses levels of 11beta-HSD2 mRNA.