Beetroot juice enhances functional sympatholysis in hypertensive humans

Functional sympatholysis (FS) is attenuated in patients diagnosed with hypertension (HTN) and hypertensive animal models alike. There is conflicting evidence, however, between human and animal models on the role of nitric oxide (NO) in determining the degree of FS. Therefore, we sought to determine if an oral dose of dietary nitrate [beetroot juice (BRJ)], which increases NO bioavailability, would increase the ability to blunt vasoconstriction in the face of increased neural outflow during hang-grip exercise (HGE) in HTN patients. We tested the hypothesis that the decrease in vascular conductance experienced by hypertensive individuals would be attenuated when ingesting BRJ two hours prior to performing 20% maximal voluntary contraction (MVC) HGE, compared to the placebo (PL) condition. To date, five of the planned fifteen patients (1 male, 4 females) diagnosed with HTN have completed the study. Using a randomized, double-blind, crossover design, forearm blood flow and conductance responses to reflex increases in sympathetic nerve activity evoked by a cold pressor test (CPT) at rest and during dynamic handgrip exercise were evaluated following consumption of BRJ and PL. Following familiarization, a five-minute resting baseline was used to obtain resting forearm blood-flow (FBF) and conductance (FVC) followed by a two-minute CPT. To evaluate FS, HGE was performed at 20% MVC for seven minutes with CPT for the final two minutes. At the time of testing patients were taking various types of medication to treat HTN (e.g., angiotensin converting enzyme inhibitor + diuretic, β-blocker, angiotensin II receptor blocker + diuretic). In resting conditions, mean arterial pressure (MAP) increased and FBF and FVC decreased during the CPT, but there was no difference between BJR and PL. During HGE at 20% MVC, MAP increased with the addition of CPT by ∼ 20 mmHg, with no difference between BJR and PL. However, changes in FVC were blunted following dietary nitrate supplementation compared to placebo. Baseline MAP (

BRJ:

104.7±4.4 mmHg) (PL: 104.3±4.5 mmHg) effect size (ES)= 0.04. Baseline FBF (

BRJ:

55.6±3.8 ml/min-1) (PL: 88.0±17.4 ml/min-1) ES=0.92. Steady state (SS) MAP (

BRJ:

121.8±3.4 mmHg) (PL: 121.0±4.1 mmHg) ES=0.09. MAP during CPT (

BRJ:

126.7±2.3 mmHg) (PL: 126.7±5.3 mmHg) ES=0.09. SS HGE vascular conductance (

BRJ:

229.0±24.9 ml/mmHg-1) (PL: 235.2±28.4 ml/mmHg1) ES=0.04. SS vascular conductance during HGE+CPT (

BRJ:

228.9±21.1 ml/mmHg-1) (PL: 222.0±28.0 ml/mmHg1) ES=0.10. δFVC (

BRJ:

-2.5±5.51%) (PL: -15.1±3.8 %) ES=1.0. The data from this study provide preliminary evidence that indicates dietary nitrates via BRJ may enhance FS in hypertensive humans during small muscle mass exercise in the face of increased neural outflow via CPT.