Immunochemical and immunohistochemical evidence of estrogen-mediated collagenolysis as a mechanism of cervical dilatation in the guinea pig at parturition.

The mechanism of dilatation of the uterine cervix at birth is poorly understood. Several indirect lines of evidence have suggested that cervical ripening is accompanied by collagen degradation. In this study, immunochemical methods have been developed to identify and analyze type I collage degradation in the cervix of the pregnant guinea pig. Using cyanogen bromide-derived peptides of purified guinea pig type I collagen as an immunogen, a polyclonal rabbit antiserum was prepared that recognizes epitopes on the denatured and degraded alpha 2 chain of type I collagen as demonstrated by enzyme-linked immunosorbant assay and immunoblotting. This antibody was used to demonstrate degradation of type I collagen in the extracellular matrix of the dilated cervix at parturition. Moreover, physiological concentrations of 17 beta-estradiol stimulated degradation of type I collagen in the nonpregnant cervix in organ culture. Collagenase degradation products were detected in the extracellular matrix and in the culture media. The effect of 17 beta-estradiol (10(-6) M) was completely blocked by progesterone (10(-4) M). These studies suggest that dilatation of the guinea pig cervix at parturition may be associated with estrogen-mediated degradation of type I collagen.