The relationship between sympathetic activity and specific spectral components of blood pressure (BP) variability has been investigated in conscious Wistar Kyoto (WKY) rats and in spontaneously hypertensive rats (SHR), the latter being characterized by sympathetic overactivity.

The study was based on the evaluation of BP spectral powers in SHR and WKY rats with intact sympathetic nervous system and after abolition of efferent sympathetic activity obtained by chemical sympathectomy. In each spontaneously behaving rat, systolic blood pressure, diastolic blood pressure and pulse interval (the reciprocal of heart rate) were monitored beat-to-beat for 90 min. The spectral powers of these parameters were calculated by FFT technique and integrated over three frequency bands (HF 0.8-3 Hz, MF 0.1-0.6 Hz and LF 0.025-0.1 Hz). The obtained data showed a non-univocal relationship between sympathetic activity and the MF and LF components of BP variability. Furthermore, to estimate the residual components of BP variability in sympathectomized SHR and WKY rats also beyond the LF band, a wideband analysis from 0.0007 to 3 Hz was computed. Our results indicated that the abolition of sympathetic efferent activity did not cancel the differences of BP spectral profiles between SHR and WKY rats, thus suggesting that these differences are due, at least in part, to structural and/or humoral factors.