Salt loading increases the muscle sympathetic nerve activity response to upright tilt: a pilot study (1170.3)

Increased sodium intake reduces resting muscle sympathetic nerve activity (MSNA). We hypothesized that the increase in MSNA during upright tilt would be greater following a high sodium (HS) diet compared to a low sodium (LS) diet. Six healthy women (40±6[SD]yrs) were tested following a 7 day HS (5750mgNa+/day) and 7 day LS diet (1150mgNa+/day) in randomized order during the mid-luteal phase. Blood pressures (BP, SunTech), heart rate (HR, ECG), cardiac output (Qc, C2H2 rebreathing) and MSNA (microneurography) were measured at rest, 30o and 60o head-up tilt. Stroke volume (SV) and total peripheral resistance (TPR) were calculated. BP was similar at supine and 30o but higher at 60o following the HS when compared to LS diet. HR, Qc, SV and TPR were similar following each diet. Supine MSNA burst frequency and burst incidence (BI) respectively were lower following the HS (13±8 bursts.min-1, 22±13 bursts.100beats-1) than the LS diet (22±10 bursts.min-1, 36±18 bursts.100beats-1). The increase in BI from baseline ...