Heart Period Variability During Estrogen Exposure and Withdrawal in Female Rats
Heart period, heart period variability, and an estimate of vagal tone were evaluated during estrogen exposure and withdrawal in ovariectomized, freely moving female rats. Spectral analysis was used to quantify the respiratory component of heart period variability (V?), which has been found to be sensitive to alterations of vagal tone to the heart. During estrogen withdrawal, V? decreased significantly and was accompanied by a decrease in heart period. There were no significant differences in heart period or V? between the experimental (estrogen) group and the control (no estrogen) group during estrogen exposure. Total heart period variability did not differ significantly from controls during estrogen withdrawal but it did exhibit an increase during estrogen exposure. In this experiment V? appeared to be more sensitive to changes in estrogen levels than total heart period variability. These data suggest that decreases in cardiac vagal tone and heart rate occur during estrogen withdrawal.