Immunohistologic detection of non-pancreatic phospholipase A2 (type II) in human placenta and its possible involvement in normal parturition at term

Placenta is one of the richest sources of non-pancreatic phospholipase A2 (npPLA2) (type II) in the human body, and the enzyme is the key enzyme releasing unsaturated fatty acids from membrane phospholipids. Prostaglandins (PGs) play a critical role in the initiation and progression of parturition. Cytokines are presumed to play a central role in the initiation of normal labor at term, and cytokines are also found to regulate both synthesis and secretion of npPLA2 enzyme. In an attempt to resolve the physiologic function of the npPLA2 enzyme in placental tissue, immunohistologic localization and enzymatic activity measurements of npPLA2 enzyme were performed. NpPLA2 protein was detected in vascular smooth muscle, endothelial cells and connective tissue cells in placenta and umbilical cord, and the protein was weakly stained in trophoblast cells in placenta. Enzymatic activity was not increased in sera from mother nor child compared to sera from healthy individuals, but the activity in amniotic fluid was considerably higher. Our findings support the candidacy for npPLA2 in enzymatic arachidonic acid release from foetal membranes.