Hemodynamics during pregnancy and sex steroid administration in guinea pigs

We investigated the time course and possible mechanisms by which the maternal cardiovascular system adapts to the demands of pregnancy. Control, 20-, 40-, and 60-day gestation guinea pigs (total 68 days) and nonpregnant virgin female guinea pigs chronically dosed with cholesterol (control), estrogen (17beta-estradiol), progesterone, and estrogen plus progesterone were studied. In vivo heart rates, pressures, cardiac outputs, blood volumes, and in vitro left ventricular pressure-volume relations were measured. There was no difference in heart rate, mean arterial, right atrial, or left ventricular end-diastolic pressures, or left ventricular weights between the various pregnant animals or hormone-dosed animals and their respective controls. By 20 days gestation blood volume (24%, P less than 0.005), cardiac output (22%, P less than 0.005), and stroke volume (22%, P less than 0.05) were increased, whereas uterine blood flow was unchanged. Chronic estrogen administration resulted in similar increases in cardiac output (24%, P less than 0.05), stroke volume (31%, P less than 0.05), and blood volume (13%, P less than 0.05). In vitro left ventricular pressure-volume relations were shifted to the right in all pregnant and hormone-dosed groups. Increases in left ventricular size and output occur before changes in uterine blood flow in guinea pig pregnancy, and these adaptations can be elicited by chronic sex steroid administration.