Dietary nitrate restores compensatory vasodilation and exercise capacity in response to a compromise in oxygen delivery in the non-compensator phenotype

Recently dietary nitrate supplementation has been shown to improve exercise capacity in healthy individuals through a potential nitrate-nitrite-nitric oxide pathway. Nitric oxide has been shown to play an important role in compensatory vasodilation during exercise under hypoperfusion. Previously we established that certain individuals lack a vasodilation response when perfusion pressure reductions compromise exercising muscle blood flow. Whether this lack of compensatory vasodilation in healthy young individuals can be restored with dietary nitrate supplementation is unknown. 6 healthy (21±2 yrs) recreationally active males completed rhythmic forearm exercise. During steady state exercise, the exercising arm was rapidly transitioned from an uncompromised (below heart) to a compromised (above heart) position resulting in a reduction in local pressure of -31±1 mmHg. Exercise was completed following 5 days of nitrate rich (70 ml, 0.4 g nitrate) and nitrate depleted (70 ml, ~0 g nitrate) beetroot juice consumption. Forearm blood flow (FBF (ml/min); brachial artery Doppler and Echo ultrasound), mean arterial blood pressure (MAP (mmHg); finger photoplethysmography), exercising forearm venous effluent (ante-cubital vein catheter), and plasma nitrite concentrations (chemiluminescence) revealed two distinct vasodilatory responses. Nitrate supplementation increased [plasma nitrite] compared to placebo (245±60 vs. 39±9 nmol/L; P<0.001). Compensatory vasodilation was present following nitrate supplementation (568±117 vs. 714±139 ml/min/100mmHg; P=0.005), but not in placebo (687±166 vs. 697±171 ml/min/100mmHg; P=0.42). As such, peak exercise capacity was reduced to a lesser degree (-4±39 vs. -39±27 N; P=0.01). In conclusion, dietary nitrate supplementation during a perfusion pressure challenge is an effective means of restoring exercise capacity and enabling compensatory vasodilation.

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