Sympathetic activation is known to promote wide blood pressure variations but the relationship between sympathetic influences and blood pressure variability under spontaneous behavioral conditions is less clear. To address this point we studied in conscious unrestrained rats the effects of chemical sympathectomy on the spontaneous variability of systolic blood pressure. Both overall blood pressure variability and its spectral components were examined in sympathectomized as well as in intact control rats. The spectral profiles were extracted by the FFT tecnique and the powers were computed in the high (HF, 3.0-0.8 Hz), mid (MF, 0.6-0.1 Hz) and low (LF, 0.1-0.025 Hz) frequency band.

The results showed that 1) overall blood pressure variability is greater in sympathectomized compared to control rats, 2) the spectral components of blood pressure variability present diversified sympathectomy-related alterations. In fact, only the LF component shows the same trend of overall variability (i.e. it is greater in sympathectomized rats) while the MF component is decreased and the HF component does not change. Thus under spontaneous behavioral conditions, sympathetic activity limits overall blood pressure variability, fails to affect HF, contributes to generate MF and opposes LF component of variability. These findings document the complex contribution of sympathetic influences on the blood pressure spectral profile.