Expression of superoxide dismutase and xanthine oxidase in myometrium, fetal membranes and placenta during normal human pregnancy and parturition

Superoxide, an agent which attenuates the half-life of nitric oxide, ismetabolized and synthesized by superoxide dismutase (SOD) and xanthineoxidase, respectively. Over the last few years much work has focused on therole of nitric oxide in human parturition. The aim of this study was todetermine whether the onset of human parturition is associated with achange in the expression of copper/zinc superoxide dismutase (Cu/Zn SOD),manganese superoxide dismutase (Mn SOD) or xanthine oxidase within theuterus. Samples of myometrium, placenta, decidua and fetal membranes wereobtained from women before and after the onset of labour at term.Immunocytochemistry was used to localize Cu/Zn SOD, Mn SOD and xanthineoxidase and measure SOD enzyme activity. Cu/Zn and Mn SOD-likeimmunoreactivity was detected in syncytiotrophoblast cells, villous stromalcells and endothelial cells of blood vessels in the placenta. In themyometrium Cu/Zn and Mn SOD were localized to myocytes and endothelialcells and to some vascular smooth muscle cells. In the fetal membranes weobserved staining for Cu/Zn SOD and Mn SOD in the amnion, chorion,extravillous trophoblast and decidua. There was no difference in SOD enzymeactivity or staining intensity for SOD between different cell types beforeand during labour. Xanthine oxidase immunoreactivity was identified in eachof the tissues examined and again there was no difference in immunostainingin tissues obtained from women delivered before or after the onset oflabour. These results show that the pregnant uterus is capable of bothsynthesizing and degrading superoxide and suggest that superoxide dismutaseand xanthine oxidase may play a role in the maintenance of uterinequiescence during pregnancy, but not in the initiation of parturition.