COLLAGENASE, ITS INHIBITORS, AND DECORIN IN THE LOWER UTERINE SEGMENTIN PREGNANT-WOMEN

OBJECTIVE: It is postulated that collagenase activity in the cervix an d lower uterine segment is important for dilatation at the time of lab or. if so, the enzyme must partially escape from control by inhibitors . A second hypothesis is that an elevated ratio of decorin (dermatan s ulfate proteoglycan) to collagen may also contribute to the dilatation process. STUDY DESIGN: The activity of collagenase, its natural inhib itors (tissue inhibitor of metalloproteinase-1 and alpha2-macroglobuli n), elastase, hydroxyproline (collagen), and decorin were quantified i n biopsies of the lower uterine segment at term (not dilated) and duri ng active labor. RESULTS: Collagenase concentration is 23 times higher in the cervix of patients in labor than at term. The sum of alpha2-ma croglobulin plus tissue inhibitor of metalloproteinase-1 increased onl y twofold in labor, as did elastase. The ratio of decorin to collagen doubled. CONCLUSION: The imbalance caused by collagenase increasing mu ch more than its inhibitors may contribute to collagen breakdown and d ilatation. Neutrophils may be responsible for much of this increase of collagenase. The increased ratio of decorin to collagen supports the hypothesis that the interaction of these two components is important i n dilatation.