The morphologic characteristics of cervical ripening induced by the hormones relaxin and prostaglandin F2α in a rabbit model

In previous studies, both purified porcine relaxin and prostaglandin F2 alpha, have been applied vaginally in the human to promote cervical ripening near term. In this study, the histologic changes in the cervix induced by these locally applied hormones are described in a rabbit model. Similar histologic changes occurred following treatment with relaxin or prostaglandin F2 alpha and these changes were comparable with those seen in the cervix following the spontaneous onset of labor in control rabbits. The main histologic features were a dissolution of the collagen bundles and an apparent increase in the ground substance. However, a unique giant cell infiltrate was seen in the relaxin-treated rabbits and the control rabbits in spontaneous labor. The nature and possible function of these giant cells are discussed. The similarity of the general morphologic changes in the cervix induced by relaxin and prostaglandin F2 alpha supports the concept that these hormones may act (either in sequence or separately) to activate the same collagenolytic system to produce the same effect in cervical connective tissue rather than act in parallel to produce separate or complementary structural changes.