Type II phospholipase A₂ in human gestational tissues: extractable immuno- 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 present 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. PLA₂, enzymatic activity present in the same tissues averaged 1.3 ± 0.2 and 1.9 ± 0.7 nmol phosphatidylethanolamine (PE) hydrolysed/mg tissue protein per h (n = 3), respectively. To allow intra-patient comparison of the relative distribution in gestational tissues, irType II PLA₂ and PLA₂ 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), respectively. As has been previously reported for human placenta, the recovery of Type II PLA₂ and PLA₂ enzymatic activity from amnion and choriodecidua was increased between 16- and 25-fold when tissues were homogenized in high-ionic strength media (i.e., 10% (w/v) ammonium sulphate or 1 M NaCl) compared with that recovered when tissues were homogenized in low-ionic strength media (i.e., 0.32 M sucrose-20 mM Hepes). The data obtained represent the first quantitative estimates of immunoreactive Type II PLA₂ in human amnion and choriodecidua, and support the conclusion that previous analyses of the PLA₂ enzymatic activity present in gestational tissues have essentially excluded the contribution made by this PLA₂ isozyme to net enzymatic activity. We suggest that this isozyme represents a major component of the PLA₂ enzymatic activity present in human gestational tissues at term and that it contributes significantly to the phospholipid metabolism and arachidonic acid release which occurs during late pregnancy and at the time of labour.