Ultrastructural changes in the architecture of collagen in the human cervix treated with urea

Injection of a solution of 30% urea in acetate buffer at pH 4.0 into the stroma of the uterine cervix results in a marked change in the mechanical properties of the tissue with subsequent easy dilatation. This study analyzes the changes in the collagenous matrix of the cervix by ultrastructural and biochemical methods. Collagen fibrils in urea-treated sections of the cervix are swollen and unravelled, showing spiral configuration of subunits in both cross-sections and longitudinal sections. The regular localization of ruthenium-red-positive material is absent in urea-treated tissues. Chemical analysis of incubated cervical tissues shows a reduction of the total glycosaminoglycans and of dermatan sulfate with release of the latter into the medium. It is suggested that urea dissociates intercollagen linkages by solubilizing a certain glycosaminoglycan, possibly dermatan sulfate. After this solubilization the collagen fibril is prompted to unwind, resolving the collagen microfibrils, which appear to be organized in a spiral fashion.