The effects of mifepristone (RU486) on prostaglandin dehydrogenase in decidual and chorionic tissue in early pregnancy.

Prostaglandin dehydrogenase is the main inactivating enzyme for prostaglandins and therefore controls local levels of prostaglandins. Since there is some evidence that the expression of this enzyme is under progesterone control it is reasonable that one of the effects of antiprogestin is to reduce the concentration of this enzyme and thus increase the effective concentration of prostaglandin within tissue. We have investigated the amount of enzyme activity within decidua and chorionic villi from women receiving the antigestagen mifepristone (RU486) 12, 24 and 36 h prior to surgical abortion, and examined the effect on tissue concentrations of prostaglandin dehydrogenase. Women receiving mifepristone in all groups had a significant reduction in concentration of prostaglandin dehydrogenase enzyme in decidual tissue. There was also a marked reduction in prostaglandin dehydrogenase in decidual cells following RU486, as demonstrated by immunochemical methods. At this stage of pregnancy, prostaglandin dehydrogenase was present in abundance in cytotrophoblast cells of chorionic villi but virtually absent from syncytiotrophoblast. In chorionic villi after RU486 administration in vivo, there were no obvious differences in prostaglandin dehydrogenase distribution or reactivity in the majority of cases.