Low-Frequency Components of Renal Sympathetic Nerve Activity Are More Tightly Coupled with Blood Pressure and Renal Blood Flow in Conscious Hypertensive Rats
We examined how various frequency components of renal sympathetic nerve activity (RSNA) regulate blood pressure (BP) and renal blood flow (RBF) in conscious Wistar-Kyoto rats (WKY, n=7) and spontaneously hypertensive rats (SHR, n=7) of 15 wk old. BP, heart rate, RSNA, and ipsilateral RBF were simultaneously recorded. Signals were sampled at 2 kHz to A/D converter for 6.50 min and the data were assessed by power spectral analysis. RSNA was augmented in SHR compared with WKY despite higher BP. Peaks of RSNA obtained by power spectral analysis were found at frequencies of 0.05, 0.80, 1-2, 6-8 Hz. RSNA power at 0.8 Hz were much larger in SHR than in WKY. Peaks of coherence of cross-spectra between BP (input) and RSNA (output), and between RSNA (input) and RBF (output) were found at frequencies of 0.05 and 0.8 Hz both in WKY and SHR. The coherence of cross-spectrum between BP and RSNA at 0-1.0 Hz was significantly higher in SHR than that in WKY, and the transfer gain of BP to RSNA was significantly larger in SHR. Similarly, the coherence between RSNA and RBF at 0-1.0 Hz in SHR was significantly higher, whereas the transfer gain of RSNA to RBF was significantly smaller in SHR. Intravenous infusion of L-arginine (50 μmol/kg/min for 60min) decreased the coherence between BP and RSNA or between RSNA and RBF to less than 0.5 in SHR. Finally, we found that low-frequency components of RSNA < 0.1 Hz were inversely related to BP and RBF, suggesting that the baroreflex system exists in the low frequency band. These results suggest that low-frequency components of RSNA are important in regulating BP and RBF. The higher coherence shown in SHR may imply that RSNA is more tightly coupled with BP and RBF. The results using L-arginine infusion suggest that endogenous NO system is important for attenuating the tight coupling (higher coherence) between the sympathetic nervous system and BP or RBF.