TYPE-II PHOSPHOLIPASE-A(2) IN HUMAN GESTATIONAL TISSUES - EXTRACTABLEIMMUNO- AND ENZYMATIC-ACTIVITY IN FETAL MEMBRANES

In this study, we have established the presence of immunoreactive (ir) Type II PLA2 in human amnion and choriodecidua obtained from women at term prior to the onset of labour. The content of irType II PLA2 pres ent in 1 M NaCl extracts of choriodecidua and amnion averaged 3.5 +/- 3.1 and 10.6 +/- 5.2 ng/mg tissue protein (n = 3), respectively. PLA 2 enzymatic activity present in the same tissues averaged 1.3 +/- 0.2 a nd 1.9 +/- 0.7 nmol phosphatidylethanolamine (PE) hydrolysed/ mg tissu e protein per h (n = 3), respectively. To allow intra-patient comparis on of the relative distribution in gestational tissues, irType II PLA2 and PLA 2 enzymatic activity was also determined in placenta obtained from the same group of women, and averaged 26.0 +/- 7.0 ng/mg tissue protein and 3.5 +/- 1.0 nmol PE hydrolysed/mg protein per h (n = 3), r espectively. As has been previously reported for human placenta, the r ecovery of Type II PLA2 and PLA2 enzymatic activity from amnion and ch oriodecidua was increased between 16- and 25-fold when tissues were ho mogenized in high-ionic strength media (i.e., 10% (w/v) ammonium sulph ate or 1 M NaCl) compared with that recovered when tissues were homoge nized in low-ionic strength media (i.e., 0.32 M sucrose-20 mM Hepes). The data obtained represent the first quantitative estimates of immuno reactive Type II PLA2 in human amnion and choriodecidua, and support t he conclusion that previous analyses of the PLA2 enzymatic activity pr esent in gestational tissues have essentially excluded the contributio n made by this PLA2 isozyme to net enzymatic activity. We suggest that this isozyme represents a major component of the PLA2 enzymatic activ ity present in human gestational tissues at term and that it contribut es significantly to the phospholipid metabolism and arachidonic acid r elease which occurs during late pregnancy and at the time of labour.