OBJECTIVETo elucidate the relationship between collagen degradation and cervical ripening by detecting dynamic expressions of matrix metalloproteinases 2 (MMP-2) and 8 (MMP-8) in rat cervix.

METHODSPF rats were divided into 5 groups (n=6), namely non-pregnancy estrus interval group, gestational days 10, 16, and 19 groups, and immediately postpartum group. The wet weight of the cervix was measured and HE staining was used to display the general structure of the cervix. VG staining was applied to visualize the collagen fibers and muscular fibers. Immunohistochemistry was performed to observe the expressions of MMP-2 and MMP-8 in the cervix.

RESULTSHE staining showed that the rat uterine cervix consisted mainly of fibroblasts and fibrous connective tissues. A small quantity of neutrophils could be seen in the cervix stroma of the rats immediately after immediately parturition, but not at the other time points. The wet weight of the antepartum cervix had increased, and a more obvious increase was seen in the wet weight of the cervix immediately after parturition. The collagen fibers of the cervix consisted of collagen fibers and smooth muscle fibers, and their proportions showed no significant variation at the time points around the parturition. Immediately after parturition, the collagen fibers and muscular fibers in the cervix became loosened as compared with that before parturition. MMP-2 expression was found in the cervical stroma but not in the squamous epithelium in nonpregnancy, term pregnancy, and immediately after parturition; the smooth muscle cells, vascular wall, and stromal fibroblasts showed positive expression of MMP-2. Enhanced intensity of MMP-2 staining was seen in term pregnancy and postpartum group in comparison with that in the other groups. MMP-8 expression was observed in the cervix of rats immediately after parturition, with scattered neutrophils positive for MMP-8 spotted in the stroma of the ripened cervix. MMP-8 expression was not detected in the other groups.

CONCLUSIONRipened cervical fibrous tissue becomes loose and broken, and cervical ripening is accompanied by infiltration of neutrophils from exogenous vessels. These changes are particularly evident after parturition. MMP-2 and MMP-8 cooperate to degrade the cervical fibers, leading to cervical softening and expansion.