Abstract
This study was conducted to examine the effect of estrogen and/or pro-gesterone on intrauterine pressure during late stages of pregnancy in rats. On day 14 of pregnancy, rats were sham-ovariectomized or ovariectomized, and one of the con-ceptuses in an individual rat was replaced by a balloon. The volume of the balloon was adjusted daily to that of the conceptus in intact pregnant rats. Each ovariectomized pregnant rat with an intrauterine balloon was injected daily with either vehicle (oil), estradiol, progesterone or combined estradiol and progesterone from day 14. The intra-uterine pressure put on the balloon and the intraamniotic pressure in the conceptus with an alive fetus were measured on days 17 and 20. In some ovariectomized rats treated with either vehicle, estradiol or progesterone, the pressures could not be measured since these rats had the ruptured uterine wall over the balloon and/or no alive fetuses. Treatments with either estradiol or progesterone alone failed to lower the high intra-uterine and intraamniotic pressures induced by ovariectomy. Administrations of com-bined estradiol and progesterone, however, reduced the pressures to levels in sham-ovariectomized animals. These results suggested that estrogen and progesterone act synergistically to maintain a low intrauterine pressure during late pregnancy.
