Controversy still exists regarding the involvement of relaxin (RLX) in cervical reorganization throughout parturition in the human, despite its well-known role in facilitating extensive extracellular matrix (ECM) remodeling in diverse organs. Therefore, the aim of the present study was to examine the influence of RLX and estrogen (E2) on the cervical tissue of the common marmoset monkey. Two experimental designs were used: 1) in vivo analysis of the intracervical diameter under locally applied RLX and 2) ovariectomized (ov) marmosets were treated systemically with either recombinant human (rh) RLX, E2 or rhRLXCE2 to examine their action on the cervix. In vivo-locally applied rhRLX induced a distinct and significant widening of the cervix (before: 4.8G1.1 mm versus after: 5.7G0.9 mm in diameter; P!0.030, MVGS.E.M.). This widening effect was most pronounced in animals without previous pregnancies. In vitro investigation of cervical tissue showed significantly increased wet weights after all three hormone treatments (E2: 0.27G0.07 g, RLX: 0.25G0.04 g, E2C RLX: 0.30G0.11 g; all P!0.05; MVGS.E.M.) versus controls (0.10G0.04 g). Furthermore, morphological changes such as loosening of the connective tissue structure and decline in collagen content, an increase in the number of eosinophils, increased the expression of matrix metalloproteinases (MMP1) and MMP2, as well as gene and protein expression of the RLX receptor RXFP1 could be detected in the cervical tissue after all hormone treatments, compared with controls. In summary, RLX has a potent widening effect on the cervix of the common marmoset monkey. Although E2 is not required for this RLX effect, a combined application of E2 and RLX induced the most prominent cervical ripening.

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