Hemodynamic changes in pseudopregnancy in chronically instrumented conscious rats

B. F. Slangen, I. C. Out, C. M. Verkeste, J. F. Smits and L. L. Peeters Department of Obstetrics and Gynecology, University of Limburg, Maastricht, The Netherlands. It is unclear whether the trophoblast is needed for the normal early-pregnancy hemodynamic adaptation. In this study we tested the hypothesis that the presence of trophoblast is not essential for the initial hemodynamic adaptation in pregnancy. To this end, we measured systemic hemodynamics in conscious pseudopregnant rats and compared the results with those obtained in a concomitantly studied control group of virgin rats as well as with a previously studied group of pregnant rats. The rats were studied daily from day 4 postmating until day 10 and on days 12, 14, 18, and 20. In pseudopregnant rats, cardiac output (CO) increased from day 5 onward, to 14 +/- 3% above the initial value by day 8. This rise in CO was entirely accomplished by a rise in stroke volume (21 +/- 4% by day 8). Mean arterial pressure did not change appreciably. Therefore, total peripheral resistance also decreased by 21 +/- 4% by day 8. Meanwhile, peak flow, aortic flow acceleration, and stroke work, indicators of myocardial performance, had increased, and the hematocrit had decreased (15 +/- 1% by day 8). Between day 10 and day 20 the hemodynamic parameters gradually returned to baseline. We conclude that systemic hemodynamic changes do take place in pseudopregnancy. They consist of a rise in CO by a rise in stroke volume, an increase in myocardial performance, and hemodilution. The observed changes closely resemble those in early normal pregnancy. Therefore, we accept our hypothesis that trophoblast is not essential for the initial hemodynamic changes in rat pregnancy.