High dietary sodium augments vascular tone and attenuates low-flow mediated constriction in salt-resistant adults

Introduction Low-flow mediated constriction (L-FMC) has emerged as a valuable and complementary measure of flow-mediated dilation (FMD) for assessing endothelial function non-invasively. High dietary sodium has been shown to impair FMD independent of changes in blood pressure (BP), but its effects on L-FMC are unknown. Purpose To test the hypothesis that high dietary sodium would attenuate brachial artery L-FMC in salt-resistant adults. Methods Fifteen healthy, normotensive adults (29 +/- 6 years) participated in a controlled feeding study. Following a run-in diet, participants completed a 7-day low sodium (LS; 20 mmol sodium/day) and 7-day high sodium (HS; 300 mmol sodium/day) diet in randomized order. On the last day of each diet, 24 h urine was collected and assessments of 24 h ambulatory BP and L-FMC were performed. Salt-resistance was defined as a change in 24 h ambulatory mean arterial pressure (MAP) between the LS and HS diets of <= 5 mmHg. Resting vascular tone and L-FMC were calculated from ultrasound-derived arterial diameters. Results High dietary sodium increased serum sodium and urinary sodium excretion (p < 0.001 for both), but 24 h MAP was unchanged (p = 0.16) by design. High dietary sodium augmented vascular tone (LS: 91 +/- 23%, HS: 125 +/- 56%, p = 0.01) and attenuated L-FMC (LS: - 0.58 +/- 0.99%, HS: 0.17 +/- 1.23%, p = 0.008). Conclusion These findings in salt-resistant adults provide additional evidence that dietary sodium has adverse vascular effects independent of changes in BP.