Immunohistochemical localization of phospholipase A₂ isoforms in human myometrium during pregnancy and parturition

OBJECTIVE: The purpose of this study was to localize secretory/phospholipase A₂ and cytosolic phospholipase A₂ isoforms in pregnant human myometrium and to determine changes in expression with gestational age or parturition. STUDY DESIGN: Myometrium was collected at cesarean section at term (>37 weeks) or preterm (<37 weeks) from patients who were or were not in labor (n = 5 each group). Frozen sections were incubated with specific monoclonal antibodies against secretory phospholipase A₂ or cytosolic phospholipase A₂ and immunostaining visualized with the Vectastain ABC method. The intensity of immunostaining in different cellular localizations was scored by an investigator blinded to tissue identity and compared among tissues with use of the Mantel-Haenszel χ² test. RESULTS: Secretory phospholipase A₂ immunostaining was dispersed in the perinuclear region throughout the myometrial smooth muscle fibers and in vascular smooth muscle. Cytosolic phospholipase A₂ immunostaining was predominantly localized to endothelial cells of myometrial blood vessels and weakly throughout myometrial fibers. There was no apparent change in intensity of immunostaining for either isoform with gestational age or with the absence or presence of labor. CONCLUSION: The differential localization of the two phospholipase A₂ isoforms suggests different functions. The apparent lack of change in expression during late gestation or with labor possibly suggests changes in myometrial phospholipase A₂ activity and hence local myometrial arachidonic acid mobilization and presumably prostaglandin synthesis may not be associated with the onset of or maintenance of parturition.