Collagenase, its inhibitors, and decorin in the lower uterine segment in pregnant women.

OBJECTIVE

It is postulated that collagenase activity in the cervix and lower uterine segment is important for dilatation at the time of labor. If so, the enzyme must partially escape from control by inhibitors. A second hypothesis is that an elevated ratio of decorin (dermatan sulfate proteoglycan) to collagen may also contribute to the dilatation process.

STUDY DESIGN

The activity of collagenase, its natural inhibitors (tissue inhibitor of metalloproteinase-1 and alpha 2-macroglobulin), elastase, hydroxyproline (collagen), and decorin were quantified in biopsies of the lower uterine segment at term (not dilated) and during active labor.

RESULTS

Collagenase concentration is 23 times higher in the cervix of patients in labor than at term. The sum of alpha 2-macroglobulin plus tissue inhibitor of metalloproteinase-1 increased only twofold in labor, as did elastase. The ratio of decorin to collagen doubled.

CONCLUSION

The imbalance caused by collagenase increasing much more than its inhibitors may contribute to collagen breakdown and dilatation. 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 in dilatation.