ROLE OF RELAXIN AND ESTROGEN IN THE CONTROL OF EOSINOPHILIC INVASION AND COLLAGEN REMODELING IN RAT CERVICAL TISSUE AT TERM

Ripening and dilation of the rat cervix at term involves a widespread reduction in the density and organization of collagen fibers following a polymorphonuclear eosinophilic invasion. These are hormonally regul ated events; however, the correlation between hormonal milieu and thes e morphological changes is not well understood. To investigate the rol e of preparturient relaxin and estradiol-17 beta (E-2) in cervical col lagen remodeling and eosinophilic infiltration, pregnant rats were eit her sham-ovariectomized (group C) or ovariectomized in the morning of Day 22. Ovariectomized rats were treated with E-2 (group OE), relaxin (group OR), E-2 plus relaxin (group OER), or hormone vehicles (group O ). There were 4 or 5 animals per group. Cervices were taken from anima ls killed approximately 1 h before expected parturition. Five-micromet er serial sections of paraffin-embedded cervices were stained with eit her Sirius Red in alkaline solution to measure eosinophil infiltration or in Picrosirius to measure collagen birefringence. Ovariectomized r ats treated with E-2 (group OE or OER) showed high levels of eosinophi lic infiltration that did not differ from those in group C intact cont rols. However, the values of eosinophilic infiltration in ovariectomiz ed rats treated with relaxin or hormone vehicles (groups OR and O) wer e low and far below (p < 0.01) those of groups OE and C. In ovariectom ized rats treated with E-2 alone (group OE), the widespread reduction in collagen organization that occurred in group C controls was not obs erved. It was only in ovariectomized rats treated with relaxin or E-2 + relaxin (groups OR and OER) that the values of birefringence were lo w, and they were as low as in control group C. In conclusion, this stu dy indicates that eosinophilic infiltration and collagen remodeling in the rat cervix at term are under the control of different hormones: E -2 stimulates eosinophilic invasion, and relaxin promotes a widespread reorganization of collagen fibers.