Vagally mediated low pressure baroreflex evokes biphasic changes in sympathetic nerve activity and resets the arterial baroreflex (1169.12)

Abstract

Background: Although volume loading activates the low pressure baroreflex (LBR), its quantitative impact on sympathetic nerve activity (SNA) and arterial baroreflex (ABR) remains unknown. The aim of this study is to clarify how the LBR affects SNA and ABR.Methods/Results: In 10 anesthetized rats, we isolated carotid sinuses and controlled carotid sinus pressure (CSP). We infused dextran to activate LBR. We measured central venous pressure (CVP) and SNA. We fixed CSP at 90mmHg to abolish ABR. We infused dextran of 5% blood volume stepwise with or without vagotomy. In the low CVP range (2.6±0.8 to 4.5±0.7mmHg), volume loading increased SNA as much as 64.8±19.5% from the baseline, while further volume loading in the high CVP range (4.5±0.7 to 7.0±0.8 mmHg) returned SNA to the baseline level. Bilateral vagotomy totally abolished those changes in SNA. To assess the impact of LBR on the ABR central system, we changed CSP stepwise from 60 to 160 mmHg at the normal volume, mild volume loading and high volume loading while recording SNA responses. Mild volume loading (CVP: 3.8±0.6 mmHg) increased SNA by resetting the CSP‐SNA relation upward (+45.2%), while, high volume loading (CVP: 6.0±0.3 mmHg) decreased SNA by resetting the CSP‐SNA relation to the baseline level.Conclusions: Volume loading evokes biphasic changes in SNA through the resetting of CSP‐SNA relation in ABR. LBR is a powerful modulator of sympathetic nervous system.