Increased Dietary Salt Augments the Exercise Pressor Reflex
Authors: Babcock Matthew C , Robinson Austin T , Watso Joseph C , Migdal Kamila U , Wenner Megan M , Stocker Sean D , Farquhar William B 
Published: June 2021

Purpose

More than 90% of American's overconsume dietary sodium (Na+) – a contributor to increased cardiovascular disease risk. Published animal data indicate that high dietary Na+ intake is linked to augmented increases in sympathetic nerve activity (SNA) and blood pressure (BP) during exercise pressor reflex activation, however this has not been studied in normotensive humans. Therefore, we tested the hypothesis that high dietary Na+ would augment SNA and BP responses to isometric handgrip exercise in healthy young adults.

Methods

Twenty‐two participants (age 25±5 years, BMI 25.3±3.5 kg/m2, 12 females) completed this controlled feeding study. Participants consumed three isocaloric diets containing either low (LS; 1,000 mg/d), recommended (RS; 2,300 mg/d), or high (HS; 7,000 mg/d) Na+ in random order separated by 3four weeks. Participants collected their urine for the final 24 hours of each diet. On day 10, SNA (microneurography) and beat‐to‐beat BP (photoplethysmography) were recorded during a 10‐minute resting baseline and during a handgrip (HG) exercise trial. The HG trial included two minutes of isometric handgrip at 40% maximum voluntary contraction and three minutes of postexercise ischemia (PEI). Triplicate nerve recordings were obtained in 10 participants. SNA is reported as burst frequency and burst incidence. Differences in urinary and blood measures were assessed via one‐way repeated measures ANOVA. The effects of dietary Na+ on SNA and BP during isometric handgrip exercise and PEI were tested using a two‐way repeated measures ANOVA (diet x time: minutes one and two of HG and PEI). Data are mean±SD.

Results

There was a stepwise increase in urinary Na+ excretion (LS = 38±26, RS = 90±47, HS = 250±74 mmol/24 hours; p<0.001). Serum Na+ (LS = 139.8±1.6, RS = 140.7±2.6, HS = 141.6±2.2 mEq/L p=0.002), but not plasma osmolality (LS = 287.7±3.5, RS = 288.2±3.6, HS = 288.3±3.0 mOsm/kg H2O p=0.678), was significantly increased following increased Na+ intake. There was an effect of diet on resting MSNA burst frequency (LS = 12.8±4.2, RS = 12.8±3.9, HS = 9.2±4.2 bursts·min−1; p=0.028), which appeared to be driven by modestly lowered values during HS. Mean BP (LS = 97±16, RS = 97±14, HS = 100±21 mmHg; p=0.412) was not different between diets. Increases in SNA during isometric HG exercise and PEI were augmented with increased Na+ intake when expressed as burst frequency (Δ values during minute two of HG: LS = 8.4±13.2, RS = 10.2±12.3, HS = 14.1±10.0 bursts·min−1, main effect of diet: p=0.032) and burst incidence (main effect of diet: p=0.040). Similarly, systolic BP (Δ values during minute two of HG: LS = 17.8.4±9.0, RS = 20.9±11.5, HS = 21.7±8.2 mmHg, main effect of diet: p=0.031), diastolic BP (Δ values during minute two of handgrip exercise: LS = 14.7±7.2, RS = 16.7±6.5, HS = 17.4±5.7 mmHg, main effect of diet: p=0.010), and mean BP (main effect of diet: p=0.014) responses were all augmented with increased Na+ intake.

Conclusions

These preliminary data indicate that high dietary Na+ augments sympathetic and blood pressure responses to exercise pressor reflex activation.

Support or Funding Information

Supported by NIH Grant 1R01HL128388 and NIGMS P20GM113125

This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.