The effect of estrogen and progesterone on the volume-pressure curve of the uterine ampulla in late pregnant rats

Volume-pressure curves of the uterine ampullae, taken on day 17 of pregnancy from intact pregnant and ovariectomized, vehicle- or estradiol and/or progesterone-treated pregnant rats, during infusion of Ca-free Tyrode's solution containing EGTA at a constant rate were determined, and the effects of the steroids on the Vz value, which was obtained by extrapolating the linear part of the curve to zero pressure, and compliance were evaluated. Both the parameters examined were decreased by ovariectomy. Treatments with estradiol or progesterone alone did not but the steroids combined restored Vz to the level of intact pregnant rats, and partially restored compliance. The significance of the development of Vz by estrogen and progesterone for the maintenance of pregnancy is discussed.