Cervical ripening after treatment with prostaglandin E2 or antiprogestin (RU486). Possible mechanisms in relation to gonadal steroids.

Objective: To compare the mechanisms for cervical ripening after treatment with prostaglandin E2 or antiprogestin (RU486) to spontaneous cervical ripening, with focus on gonadal steroid receptors.

Study Design: Cervical biopsies were obtained from postpartal women after treatment with prostaglandin E2 (n=10), or antiprogestin (n=5). Postpartal women after spontaneous cervical ripening (n=10) served as controls. Levels of estrogen and progesterone receptors, their mRNAs, insulin-like growth factor I mRNA and serum estradiol and progesterone were quantitated. The collagen concentration and solubility by pepsin were determined. Statistical tests used were Kruskal-Wallis and Mann-Whitney U test.

Results: After prostaglandin E2 treatment the collagen concentration was higher (P<0.05) as compared to spontaneous ripening. After antiprogestin treatment the estrogen receptor concentration was higher (P<0.05) in comparison to spontaneous ripening.

Conclusion: The elevated estrogen receptor concentration after antiprogestin treatment, in contrast to spontaneous ripening, and prostaglandin E2 treatment, indicates a that a receptor-mediated progesterone withdrawal does not explain the events behind spontaneous cervical ripening at parturition.