Decreased type I collagen expression in human uterine cervix during pregnancy.

To provide some insight into the mechanism of cervical ripening, the expression of type I collagen was investigated in human uterine cervical tissues obtained from the first (n = 4) and third (n = 3) trimesters of normal pregnancy. Indirect immunofluorescent staining was performed for type I collagen, and Northern blot analysis was done to assess expression of mRNA for the alpha1(I) chain. Collagens were also extracted from the human cervical tissues in the first and third trimesters of pregnancy. Immunohistochemical analysis revealed loose distribution of type I collagen in the uterine cervix of the first trimester compared with the third trimester of pregnancy. The relative levels of various collagens were evaluated by SDS-PAGE. The ratios of the intensity of the band of alpha1(I) to that of total collagen alpha1 chain in cervical tissues of the third trimester were significantly lower than those in cervical tissues of the first trimester of pregnancy (P < 0.05). In contrast, the ratios of the intensity of the band of alpha1(III) to that of total collagen alpha1 chain in cervical tissues of the third trimester were significantly higher than those in cervical tissues of the first trimester of pregnancy (P < 0.05). Northern blot analysis revealed that the cervical expression of mRNA for the alpha1(I) chain was significantly reduced in the third trimester compared with the first trimester of pregnancy (P < 0.01). These results suggest that type I collagen might play an important role in the maintenance of pregnancy and that decreased expression of this collagen could be associated with the process of uterine cervical ripening.