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

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Abstract
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-sulfate (DHA-sulfate) 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-sulfate stimulates phospholipase A2 activity. The same amounts of pregnenolone-sulfate and estrone-sulfate also enhanced the enzymatic activity, while cholesterol-sulfate, free steroids such as DHA, progesterone, cortisol and estrogens revealed no effect. Steroid sulfates may be involved in the regulatory mechanism for PG synthesis in amniotic membrane.