Progesterone synthesis by human amnion, chorion, and decidua at term.

We investigated the ability of human fetal membranes to produce progesterone from a variety of substrates. Chorion is more active than decidua, and amnion produces little progesterone. Cholesterol or low-density lipoprotein cholesterol was not used as a substrate. Chorion used pregnenolone, pregnenolone sulfate, and 20 alpha-dihydroprogesterone for progesterone synthesis. Decidua also used these three substrates but produced significantly less progesterone than chorion. Amnion used only 20 alpha-dihydroprogesterone as a substrate. Exogenous human chorionic gonadotropin or gonadotropin-releasing hormone or its analogues did not influence progesterone production by any of the tissues. There were several significant changes in substrate usage for progesterone synthesis by the tissues around the time of the onset of labor. Tissue concentrations of progesterone are approximately 4 ng/mg protein, and it appears that local production rates could completely account for this. These data are compatible with the hypothesis that local regulatory mechanisms may determine progesterone concentrations in fetal membrane tissues and that important changes may occur around the time of the onset of parturition.