Enhancement of human amniotic phospholipase A2 activity by steroid-sulphate derived from the foeto-placental unit.

To study the control of production of prostaglandins (PG) during pregnancy and parturition, amniotic membranes obtained from normal vaginal delivery were incubated with the substrate of phosphatidylcholine containing [14C]arachidonic acid in the Sn-2 position. Phospholipase A2 activity was calculated as the rate of release of [14C]arachidonic acid from the substrate. Various steroids were added to the incubation medium to elucidate the effect of steroids on the enzymatic activity. The addition of dehydroepiandrosterone-sulphate (DHA-sulphate) to the medium increased by 7-fold the rate of [14C]arachidonic acid release from phosphatidylcholine at a concentration of 1.67 mM. The enhanced rate of arachidonic acid release suggests that DHA-sulphate stimulates phospholipase A2 activity. The same amounts of pregnenolone-sulphate and oestrone-sulphate also enhanced the enzymatic activity, while cholesterol-sulphate, free steroids such as DHA, progesterone, cortisol and oestrogens revealed no effect. These results suggest that steroid sulphates may be involved in the regulatory mechanism for PG synthesis in amniotic membrane.