Intrauterine hypoxia, an important marker of potentially abnormal outcome in the neonatal period, may lead to perinatal asphyxia (Supnet et al. 1994). In addition, intrapartum acidosis is a common cause of fetal cerebral damage in preterm deliveries (Low et al. 1994). Evidence suggests that production of reactive oxygen species (ROS) and reduced antioxidant capacity accompanies these dysfunctional pregnancies. The aim of this study was to investigate expression levels of key antioxidative enzymes (superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSHpx)) and the levels of lipid peroxidation as a marker of oxidative stress in human myometrium with term and preterm parturition.

The study was approved by the Southern Derbyshire Ethics Committee and written informed consent was obtained from all women taking part in the study. Myometrial biopsies were obtained from women undergoing either elective (not in labour) or emergency (in labour) sections at both term and preterm (< 36 weeks) gestations. The patients were divided as follows: term not in labour TNL (n = 11), preterm non-labour PTNL (n = 9), term in labour TL (n = 10) and preterm in labour PTL (n = 5). Tissues were homogenized and centrifuged to give cytosolic and membrane fractions with only the cytosolic component being used for Western blotting. Proteins were resolved by SDS-PAGE and blots probed with antisera to SOD, CAT and GSHpx followed by chemiluminescent detection of enzyme expression. Densitometric analysis was carried out and enzyme expression compared amongst the four groups. The membrane fraction was used to colorimetrically determine the level of lipid peroxidative damage. Malonialdehyde (MDA), a product of lipid peroxidation present in biological samples, reacts with thiobarbituric acid (TBA) under acidic conditions at 95°C with an absorbance maximum at 532 nm. Statistical analysis was carried out by one-way analysis of variance (ANOVA) with Scheffé correction to determine differences between groups. A probability level (P) of < 0.05 was considered statistically significant.

This study demonstrated that SOD and CAT enzyme levels in human myometrium of non-labouring or labouring women do not change with term or preterm gestations. However, GSHpx levels were found to be significantly (P < 0.05) lower in the TL and PTL compared with TNL and PTNL groups. This finding was also mirrored by a significant (P < 0.05) increase in lipid peroxidation levels in both the TL and PTL groups when compared with the TNL and PTNL groups.

Our results indicate that increased lipid peroxidation observed with the onset of labour may arise as a result of reduced antioxidative GSHpx expression. Further studies are necessary to investigate whether lipid peroxidation and/or altered antioxidative enzyme expression are consequences or causes of normal and dysfunctional labour.

This work was supported by NHS Trent R&D.