Increased matrix metalloproteinase activity and reduced tissue inhibitor of metalloproteinases-1 levels in amniotic fluids from pregnancies complicated by premature rupture of membranes

OBJECTIVES: It has been suggested that increased matrix metalloproteinases activity promotes the weakening of the amniochorion during normal and premature rupture of membranes. This study was designed to determine whether levels of matrix metalloproteinases and the tissue inhibitor of metalloproteinases-1 in amniotic fluid change in a pattern consistent with this hypothesis. STUDY DESIGN: Gelatinolytic activity, measured by a soluble substrate assay and zymography, and the concentrations of tissue inhibitor of metalloproteinases-1 were estimated in amniotic fluid obtained from (1) normal early gestations, (2) normal term pregnancies with labor, (3) normal term pregnancies without labor, and (4) pregnancies complicated by premature rupture of membranes. The 92 kd type IV collagenase (matrix metalloproteinase-9) was also detected in amniotic fluid by Western blotting. RESULTS: Matrix metalloproteinase activities were higher in amniotic fluid from normal term pregnancies with labor and pregnancies complicated by premature rupture of membranes than from early pregnancies and term gestations without labor. The amniotic fluid from term pregnancies with labor or pregnancies with premature rupture of membranes contained several gelatinases, as revealed by zymography. The major amniotic fluid gelatinolytic activity in premature rupture of membranes and term pregnancies with labor corresponded to matrix metalloproteinase-9. Tissue inhibitor of metalloproteinases-1 concentrations were highest in early-pregnancy amniotic fluid, followed by term gestation with labor, term gestation without labor, and premature rupture of membranes. CONCLUSIONS: Normal labor and premature rupture of membranes are associated with increased levels of matrix metalloproteinases, particularly matrix metalloproteinase-9 in amniotic fluid. Premature rupture of membranes is associated with reduced levels of tissue inhibitor of metalloproteinases-1. The imbalance between matrix metalloproteinases and tissue inhibitor of metalloproteinases-1 in amniotic fluid may reflect a disorder that promotes premature rupture of membranes. (AM J OBSTET GYNECOL 1996;174:1371-6.)