M. H. Wong

Type II phospholipase A2 in human gestational tissues: Subcellular distribution of placental immuno and catalytic activity

The aims of this study were to determine the subcellular distribution of Type II phospholipase A2 immunoactivity (irPLA2) and in vitro net PLA2 catalytic activity in human term placenta and to establish the efficacy of previously utilised homogenisation procedures with respect to the quantitative recovery of Type II PLA2 immunoreactive and in vitro net PLA2 catalytic activity. Type II PLA2 immunoactivity and PLA2 catalytic activity recovered in 900 x g supernates prepared from placental tissue (n = 3) homogenised in low ionic strength media (sucrose 0.32 M Hepes 20 mM; phosphate-buffered saline or phosphate-buffered saline containing 3 mM EGTA) was less than 10% of that recovered following homogenisation in high ionic strength medium (ammonium sulphate 10%, w/v). The subcellular distribution of Type II PLA2 immunoactivity and PLA2 catalytic activity was established by the differential centrifugation (10,000, 20,000 and 100,000 x g) of placental homogenates (n = 3). Although Type II PLA2 immunoactivity was equally distributed throughout the particulate subcellular fractions examined, PLA2 catalytic activity increased by comparison in 100,000 x g particulate material. This apparent dissociation between irType II PLA2 and catalytic activity may indicate the presence of other types of PLA2 in this fraction. The data obtained in this study indicate that previous studies which have utilised low ionic strength extractions of human gestational tissue to characterise PLA2 catalytic activity and subcellular distribution have largely excluded the contribution made by Type II PLA2. Consequently, much of the available published data on the role of PLA2 in human parturition is inadequate. A reappraisal of this enzymes contribution to the biochemical events associated with human pregnancy and labour is required.

Immunoreactive prostaglandin G/H synthase content increases in ovine cotyledons during late gestation

In this study, using gel electrophoresis and Western blotting, we have demonstrated that the content of irPGHS in ovine placenta increases during late gestation prior to the onset of labour. This increase in PGHS tissue content may contribute to the corresponding increased production of prostaglandins by the ovine placenta during this period of pregnancy. Although the mechanism by which PGHS tissue content is elevated at this time remains to be established, one possibility which is currently being investigated in our laboratory is that increased PGHS content reflects an increased level of PGHS gene expression.

Immunolocalisation of Interleukin-4 and Interleukin-4 Receptor in Placenta and Fetal Membranes in Association with Pre-Term Labour and Pre-Eclampsia

The aim of this study was to characterise the localisation and staining intensity of immunoreactive (ir) interleukin-4 (IL-4) and IL-4 receptor (IL-4R) in human placenta and fetal membranes in association with pre-term and term labour, and pre-eclampsia. The data obtained in this study establish the presence of irIL-4 and IL-4R in human placenta and fetal membranes obtained from women at 25–41 completed weeks of gestation. IL-4 and IL-4R immunohistochemical staining was principally localised in villous and chorionic trophoblast, and to amnion epithelial cells. The intensity of IL-4 and IL-4R immunohistochemical staining was not significantly affected by labour status at term or pre-term (p > 0.05), with the exception of IL-4R in the amnion (p < 0.05). In term amnion, IL-4R was only detectable following labour onset. When data were stratified with respect to the presence or absence of pre-eclampsia, no statistical difference in immunohistochemical localisation or staining intensity for either IL-4 or IL-4R could be identified for any of the tissues studied. Co-localisation of IL-4 and IL-4R within gestational tissues may indicate auto- and/or paracrine mechanisms of action for this cytokine. Tissue-specific, labour-associated induction of IL-4R may contribute to the regulation of biological effects of IL-4 within the uteroplacental unit.

Gestational profile of the stimulatory effects of porcine amniotic and allantoic fluids on prostaglandin G/H synthase activity

The effects of porcine fetal fluids (amniotic and allantoic) on microsomal prostaglandin G/H synthase (PGHS) activity were assessed. Both amniotic and allantoic fluids obtained from late-gestation sows stimulated PGHS activity (as indicated by increased formation of radiolabelled prostaglandin) in a dose-dependent manner. At the maximum dose tested, amniotic and allantoic fluids stimulated prostaglandin (PG) formation by 55.5 +/- 1.5 and 58.5 +/- 4.7%, respectively (n = 3, P less than 0.01). Based upon ED50 values, amniotic fluid was approximately threefold more effective than allantoic fluid in stimulating PG formation. The stimulatory effect of amniotic but not allantoic fluid increased significantly (P less than 0.01) during gestation (Days 47-112). The observed changes in the stimulatory effect of amniotic fluid on microsomal PG formation parallels the in vivo changes that occur in intra-uterine PG synthesis. Amniotic fluid stimulatory activity may contribute to this gestational increase in PG synthesis.