Decrease in annexin I messenger ribonucleic acid expression in human amnion with labor

OBJECTIVE: Annexins are a superfamily of proteins that are thought to inhibit phospholipase A₂ activity and hence inhibit prostaglandin production. The purpose of this study was to test the hypothesis that annexin I concentration in human amnion is reduced with labor and that this reduction is mediated by a decrease in annexin I messenger ribonucleic acid expression. STUDY DESIGN: Amnion and choriodecidua were collected from term singleton pregnancies, eight after spontaneous vaginal delivery and eight from elective cesarean section without labor. Annexin I protein was quantitated by Western blotting. Ribonucleic acid was isolated from amnion, and then annexin I messenger ribonucleic acid was identified by Northern hybridization and quantitated by slot blotting. RESULTS: Annexin I (35 kd) was identified in amnion tissue. The concentration in the group undergoing labor (320 ± 45 integrated optical density units, mean ± SE) was significantly reduced (p < 0.05) compared with that in the group not undergoing labor (635 ± 65 units). The size of the annexin I messenger ribonucleic acid was approximately 1.8 kb. The mean integrated optical density for the labor group (840 ± 139 units, mean ± SE) was significantly reduced (p < 0.05) compared with that of the nonlabor group (1912 ± 464 units). CONCLUSION: There is a significant decrease in annexin I messenger ribonucleic acid expression in human amnion with labor, corresponding to a significant decrease in annexin I protein concentration. This may contribute to the increased phospholipase A+₂ activity, arachidonic acid mobilization, and prostaglandin production at labor in humans.