Cyclo-oxygenase distribution in human placenta and decidua does not change with labour after term or preterm delivery

Our objective was to determine, in an immunohistochemical study, the distribution of cyclo-oxygenase in placental and decidual tissues before and after labour at varying gestations. Subjects were pregnant women undergoing singleton delivery after idiopathic preterm labour at less than 34 weeks' gestation (n = 13); spontaneous term labour at 37-42 weeks' gestation (n = 11); preterm caesarean section at less than 34 weeks' gestation for pre-eclampsia or intrauterine growth retardation (n = 8); elective term caesarean section at 37-42 weeks' gestation for cephalopelvic disproportion (n = 7). Within the placental basal plate cyclo-oxygenase was localised in decidual stromal cells, extravillous trophoblast, and the apical border of villous syncytiotrophoblast, both before and after labour, regardless of gestational age. Within the placental membranes, decidual stromal cells showed intense cytoplasmic cyclo-oxygenase labelling and the chorion laeve strong membrane-associated cyclo-oxygenase reactivity before and after labour, regardless of gestational age. The amnion showed a heterogeneous staining pattern. After labour at term there was either positive cytoplasmic (5/10) or apical staining (5/10). Cyclo-oxygenase was demonstrated in an apical distribution in only 50% of the other subject groups. Cyclo-oxygenase is present in both decidua and placental tissues prior to the onset of labour at term. Demonstration of decidual and trophoblastic cyclo-oxygenase in both preterm and term subjects suggests that differential availability of cyclo-oxygenase is unlikely to be important in preterm delivery. Research into the withdrawal of inhibition or increased substrate availability is most likely to shed light on the signal pathways involved in the onset of labour, regardless of gestation.