Human placental phospholipase A2 activity in term and preterm labour

Phospholipase A2 activity (EC 3.1.1.4) was estimated in low-speed supernatants of human placenta by measuring the release of arachidonic acid from phosphatidylcholine, 1-stearoyl-2-[3H]arachidonyl and other phospholipids under alkaline conditions (pH 8). Activity was calcium dependent and followed Michaelis-Menten kinetics with an apparent Km of 0.19 (SD 0.04) mM and a Vmax of 486 (SD 52) pmol/mg protein per h. Placental phospholipase A2 activity was relatively high in early pregnancy (8-11 weeks gestation) and following spontaneous preterm labour (31-34 weeks), but decreased significantly towards term with no changes in relation to parturition. By contrast, activity in the fetal membranes (amnion and chorio-decidua) was low after preterm labour and increased significantly towards term. The placenta and fetal membranes have the capacity to contribute to the increased intra-uterine release of arachidonic acid and eicosanoids that occurs during term and preterm labour, but at present there is no evidence that this increase involves direct changes in phospholipase A2 activity.