The physiological role of relaxin in the pregnant gilt: The effects of relaxin on the physical and biochemical properties of the cervix and on mammary development in ovariectomized hormone-treated pregnant gilts

The purpose of this research was to determine the physiological roles of relaxin in pregnant gilts by ovariectomizing gilts during the last third of gestation followed by hormone replacement therapy. Nara and coworkers demonstrated that in pigs ovariectomized in late pregnancy a prolonged delivery and a low incidence of live births occurred in the absence of relaxin replacement. Eldridge-White and coworkers demonstrated that in intact pregnant pigs beginning about day 80 of pregnancy and continuing until term, cervical extensibility and size increased coinciding with rising relaxin and estrogen levels.In the first study I explored the hypothesis that the deleterious effects on birth seen in the absence of relaxin were, at least partially, attributable to a failure of the cervix to grow and soften. This study demonstrated that in ovariectomized pregnant pigs increases in extensibility and growth of the cervix occurred only in the presence of relaxin. The second study demonstrated that the growth and softening of the cervix promoted by relaxin in ovariectomized pregnant pigs is accompanied by a decrease in collagen concentration and increases in water content, dry weight, and the glycosaminoglycan:collagen ratio. These results support the hypothesis that relaxin-induced changes in cervical connective tissue components may account, in part, for relaxin's effects on cervical extensibility, cervical growth and normal birth in pigs.The third study examined relaxin's influence on mammary gland development. In ovariectomized pregnant pigs, growth of the mammary parenchymal tissue during the last third of gestation occurred only with relaxin administration. These results suggest that relaxin' s stimulation of mammogenesis may be important for normal lactation in pigs.In conclusion, this research demonstrates two important physiological roles for relaxin during pregnancy in pigs. Relaxin promotes increased cervical extensibility and growth, as well as, mammary gland development.U of I OnlyETDs are only available to UIUC Users without author permissio