The change in solubility of type I collagen in human uterine cervix in pregnancy at term

Abstract

Collagen changes in the human uterine cervix in pregnancy at term were investigated. Collagen concentration per dry tissue significantly decreased to about 50% of the control and more than 90% of cervical collagen was insoluble. The insoluble collagen was extracted by pepsin digestion, and about 52% of insoluble collagen in the control and 94% in pregnancy at term were solubilized. In pepsin-soluble fractions, genetically distinct types I and III collagens were isolated by different salt precipitation and identified by ion-exchange chromatography, SDS disc gel electrophoresis, and amino acid composition analysis. Although the rates of pepsin-soluble collagen fraction in control and in pregnancy at term were different, types I III ratios in the fraction were about 2 and 4.7, respectively. The BrCN collagen peptide analyses of pepsin-insoluble residues of control which was about 50% of whole collagen indicated that most of residual collagen was type I. Therefore the ratio of types I III collagen in control of whole collagen approaches the value of 4.7 in pregnancy at term, indicating that the solubility of type I collagen was significantly increased by pregnancy. Both decrease in collagen concentration and increased in type I collagen solubility are important factors to induce the cervical dilatation and effacement in pregnancy at term.