Heart rate and arterial pressure variability and baroreflex sensitivity in ovariectomized spontaneously hypertensive rats.

AIMS

The present study evaluated the effects of ovariectomy on heart rate and arterial pressure variability and cardiac baroreflex sensitivity (BRS) in female spontaneously hypertensive (SHR) and Wistar-Kyoto rats (WKY).

MAIN METHODS

Sham-surgery animals were used as control. Sixteen weeks after ovariectomy or sham-surgery, animals were recorded. Time series of pulse interval (PI) and systolic AP (SAP) were analyzed by means of autoregressive spectral analysis, which quantifies the power of very low (VLF=0.01-0.25 Hz), low (LF=0.25-0.75 Hz) and high frequency (HF=0.75-2.5 Hz) bands. BRS was assessed by means of linear regression between changes of PI and SAP induced by vasoactive drugs or calculation of alpha-index, a spontaneous BRS index.

KEY FINDINGS

There was no difference in baseline PI or SAP between ovariectomized and sham SHR. Spectral analysis of heart rate variability suggested a shift of sympatho-vagal balance toward sympathetic predominance in ovariectomized SHR (LF/HF=1.8+/-0.2 versus 0.7+/-0.2 in sham SHR, p<0.05). Ovariectomy increased total variance and VLF power of SAP in SHR (29.1+/-9.6 mmHg2 and 18.6+/-6.3 mmHg2 versus 9.1+/-2.1 mmHg2 and 4.3+/-1.4 mmHg2, respectively, in sham SHR, p<0.05). In addition, ovariectomy reduced reflex bradycardia in SHR (0.18+/-0.03 ms/mmHg versus 0.34+/-0.06 ms/mmHg in sham SHR, p<0.05). Ovariectomy did not affect heart rate and SAP variability or BRS in WKY.

SIGNIFICANCE

These data showed that ovarian hormones deprivation induced marked changes on cardiovascular control, increasing SAP variability and cardiac sympatho-vagal balance and blunting BRS in female hypertensive animals, which reinforce the possible protective role of ovarian hormones on the cardiovascular system.