Evidence That Endogenous Relaxin Promotes Growth of the Vagina and Uterus during Pregnancy in Gilts

Recently, it was demonstrated that endogenous relaxin promotes growth of the vagina during the second half of pregnancy in rats and that administration of porcine relaxin promotes growth of the uterus in nonpregnant or early pregnant gilts. This study examined the effects of circulating relaxin on growth of both the vagina and uterus during the last two thirds of the 114-day gestation period in gilts. Furthermore, this study employed an in vitro immunohistochemical localization technique to determine whether the vagina and uterus in pigs have specific relaxin-binding sites. Three groups of pregnant gilts were used: sham-ovariectomized controls (group C; n = 8), ovariectomized progesterone-treated (group OP; n = 6), and ovariectomized progesterone- plus relaxin-treated (group OPR; n = 7). Gilts were either sham ovariectomized or ovariectomized on day 40 of gestation. Hormone replacement therapy with progesterone (group OP), progesterone plus relaxin (group OPR), or hormone vehicles (group C) began on day 3...