Hormonal control of the cervix in pregnant gilts. II. Relaxin promotes changes in the physical properties of the cervix in ovariectomized hormone-treated pregnant gilts.

The effects of relaxin on the physical properties of both the uterine and vaginal portions of the cervix were studied between days 80 and 110 of pregnancy in ovariectomized gilts given progesterone to maintain pregnancy. In controls gilts the extensibility, lumen diameter, and wet weight of the uterine portion of the cervix were less than those of the vaginal portion of the cervix on day 80, but increased thereafter, and by day 110 did not differ (extensibility and wet weight) or approached (lumen diameter) those values of the vaginal portion of the cervix. When gilts were ovariectomized on either days 80 or 100 and given progesterone only (groups OP-100 and OP-110) extensibility, lumen diameter, and wet weight failed to increase in both the uterine and vaginal portions of the cervix. After replacement therapy with progesterone plus relaxin (groups OPR-100 and OPR-110), extensibility, lumen diameter, and wet weight increased to values as least as large as those in control groups in both portions of the cervix. In all groups the uterine portion of the cervix changed more dramatically than the vaginal portion. After hormone replacement therapy, blood levels of relaxin were moderately higher, and blood levels of progesterone were somewhat lower than those in control gilts. There was little or no difference in estrogen levels between ovariectomized and control gilts. We conclude that relaxin plays an important role in promoting increased growth and extensibility in both the uterine and vaginal portions of the cervix after day 80 of gestation in the gilt.