Dissociation in the control of cervical eosinophilic infiltration and collagenolysis at the end of pregnancy or after pseudopregnancy in ovariectomized steroid-treated rats.

Previous studies have demonstrated that during parturition the physiological ripening that permits dilation of the cervical canal is due to a widespread collagenolysis that follows a heavy polymorphonuclear leukocyte invasion of the uterine cervix. The aim of this study was to investigate whether there is any association between the ovarian steroid hormones involved in rat parturition and this phenomenon. Pregnant or pseudopregnant rats were ovariectomized (OVX) at Day 9 and then given a hormonal treatment (sufficient to maintain fetal viability) until Day 23. Cervical biopsies, taken from animals killed intrapartum or 1 h before expected parturition, were studied for eosinophilic infiltration and collagen birefringence. Intrapartum or sham-OVX pregnant rats showed a massive eosinophilic infiltration and a widespread collagenolysis as indicated by a loss of collagen birefringence. Ovariectomized pregnant rats treated with estrogen plus progesterone or with progesterone alone showed neither infiltration nor collagenolysis. In rats OVX during pseudopregnancy, estrogen given alone induced a significant infiltration of eosinophils in the cervical stroma; however, treatment with the combination of estrogen and progesterone was not able to promote eosinophilic infiltration. Collagenolysis was absent in all pseudopregnant animals. These results show that estrogen induced a cervical eosinophilic infiltration in rats but that when progesterone was added to the estrogen treatment the infiltration was not present; in addition, none of the steroid hormones assessed were responsible for the collagenolysis found in the cervical tissue at term.