Pregnancy restores altered sympathetic vasomotor modulation and parasympathetic cardiac modulation in hypertensive rats.

Hypertension is associated to impaired baroreflex sensitivity (BRS). In spontaneously hypertensive rats (SHR), pregnancy reduces blood pressure, and this effect has been associated to increase nitric oxide (NO) bioavailability. Increased NO bioavailability has been linked to improve BRS in hypertensive animals. Therefore, we hypothesize that pregnancy improves the BRS in SHR. We performed experiments to evaluate the vasomotor and cardiac autonomic modulation, also to evaluate the BRS at baseline conditions (spontaneous) and after phenylephrine (PE) and sodium nitroprusside (SNP) administrations in non-pregnant (NP) and pregnant (P) Wistar rats and SHR. Beat-to-beat time series with systolic arterial pressure values were generated and processed by Fast Fourier Transform (spectral analysis). Next, spectra were integrated into low-frequency (LF) band and had their power taken as an index of sympathetic modulation on arterial pressure. Reduced mean arterial pressure was observed in P-groups when compared to NP matched rats, although we did not observe alterations in heart rate (HR). In SHR-NP, spectral analysis revealed altered cardiovascular autonomic modulation when compared to the other groups. However, in SHR-P the autonomic parameters were similar to those observed in Wistar-NP, suggesting that pregnancy changed autonomic modulation. BRS assessed by means of the sequence method was found similar in P-groups. Pregnancy reduced the BRS during hypotension in Wistar. BRS assessed with PE and SNP administration was found lower in SHR-NP as compared to Wistar-NP, and it was not altered by pregnancy. In conclusion, pregnancy did not improve the BRS in SHR, but normalized altered sympathetic vasomotor modulation in SHR.