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.