Hemodynamic changes in early-pregnant and pseudopregnant rats are comparable, indicating that the trophoblast does not contribute to these changes. It is unclear whether the presence of the uterus is needed for the normal early-pregnancy hemodynamic adaptation. In this study we tested the hypothesis that uterine factors do not contribute to the systemic hemodynamic changes in early pseudopregnancy. To this end, we studied systemic hemodynamics in conscious pseudopregnant rats subjected to a hysterectomy, and compared these results with those obtained in a control group of pseudopregnant rats. The animals were studied on days 4, 8, 12 and 19 postmating. On day 8 of pseudopregnancy, cardiac output has increased by 23+/-7% in the hysterectomized group and 15+/-5% in the control group. In both groups this rise in cardiac output was entirely accomplished by a rise in stroke volume, by 28+/-8% and 19+/-5%, respectively. Mean arterial pressure did not change appreciably. Therefore, total peripheral resistance also decreased in both groups (17+/-6%) by day 8. After day 12 the hemodynamic parameters returned to baseline. We conclude that systemic hemodynamic changes in hysterectomized pseudopregnant rats closely resemble those in intact pseudopregnant rats. Therefore, the uterus does not seem to play a role in these changes. This supports the hypothesis that only hormones from ovarian origin trigger the initial hemodynamic adaptation to early pregnancy.