A combination of RU 486 (mifepristone) and relaxin successfully hastened labor and promoted healthy delivery of pups in rats altered so that their reproductive systems mimicked the human reproductive system, researchers at the University of Illinois at Urbana-Champaign report in the January issue of the American Journal of Obstetrics and Gynecology.
Relaxin, a naturally occurring reproductive hormone, was the key to the natural delivery, said O. David Sherwood, a professor of molecular and integrative physiology. "Although the study was done with rats, it was designed with the idea that RU 486 and relaxin could be used at delivery in the human being. The results are compelling."
Shuangping Zhao, a postdoctoral researcher in Sherwood's laboratory, said that RU 486, an antiprogresterone, given alone induced labor in the rats but the cervix did not grow, leading to prolonged delivery and pup deaths. When relaxin was given subcutaneously, the cervix grew and softened (ripened), reducing delivery time and promoting healthy pups.
"If relaxin works in the human," she said, "it will likely not only shorten the duration of painful labor, but also reduce the incidence of Caesarean sections. This would be very beneficial for women and reduce health-care costs."
Genentech experimented without success administering relaxin in the vagina as a topical treatment in the 1990s, hoping it would penetrate the epithelial cells, enter the bloodstream and reach target cells in the cervix. The investigators in the trials, done in Australia and Great Britain, noted that relaxin failed to enter the bloodstream and suggested that the lack of absorption was the reason the treatments failed.