Blood pressure responses to skeletal muscle contraction relative to salt sensitivity in humans and rats (1165.11)

Salt sensitivity of blood pressure (BP) is linked to increased mortality. Salt sensitive (SS) rats display exaggerated BP responses to muscle afferent stimulation, a finding not yet studied in humans. We hypothesized that SS adults would have greater BP responses to muscle contraction than salt resistant (SR) adults. To define salt sensitivity status, a median split of 24hr mean BP (MAP) responses (%∆) to dietary sodium (20 mmol/d x 7 d to 300 mmol/d x 7 d sodium) was used in 12 adults and resulted in 6 SS (6.4±1.5 %∆) and 6 SR (‐0.1±1.6 %∆ p<0.05). Static handgrip (HG; 2 min 40% maximal voluntary contraction) was performed during normal sodium intake. MAP responses to HG tended to be greater in SS than SR (30.2±5.1 vs. 16.7±4.0 %∆, p=0.06). Salt induced %∆MAP was correlated to HG %∆MAP (r=0.658 p<0.05). Parallel experiments in Dahl SS (DSS, n=4) & Dahl SR (DSR, n=4) rats fed 0.1% NaCl confirms that stimulation of sciatic afferent nerves (500uA, 5Hz, 1ms pulse) produce greater increases in MAP (SS 26±4; SR 15±2 mmHg, p<0.05). Additionally we found greater renal sympathetic nerve activity (SS 175±12; SR 147±8 %, p<0.05). These preliminary data suggest greater BP responses to muscle contraction in SS humans & rats due to greater sympathetic activity; this may be a factor in the poorer CV outcomes in SS adults. Grant Funding Source : Supported by NIH R01 HL104106, NIH R01HL113270 and AHA EIA, & ACSM Foundation Research Grant.