Abstract P120: Acute Dietary Nitrate Supplementation Does Not Attenuate Oxidative Stress or the Hemodynamic Response During Submaximal Exercise in Hypobaric Hypoxia

Abstract

Introduction: Oxidative stress is exacerbated during hypoxic conditions (i.e. high altitude exposure, congestive heart failure, or peripheral artery disease). Dietary nitrate supplementation increases plasma nitrite (denotes nitric oxide bioavailability), reduces resting/submaximal blood pressure (BP) and may enhance exercise performance in certain healthy and diseased populations. Hypothesis: We hypothesized dietary nitrate would improve arterial oxygen saturation (SaO 2 ) and reduce: oxidative stress while reducing submaximal oxygen consumption, BP, and perceived exertion (RPE) during exercise in hypobaric hypoxia (3500m). Methods: Nine well-trained (60.0±7.0 ml/kg/min) males (29±7 yr) completed a maximal aerobic capacity test (VO 2max ) and five 5-min cycling bouts of increasing intensity at their normobaric elevation (1600m). Intensities at 25, 40, 50, 60, 70% VO 2max were used during trial 2 (T2) and trial 3 (T3) cycling bouts. Participants minimized nitrate-rich food consumption during a 4-day dietary washout prior to T2 and T3. Participants consumed a nitrate-depleted placebo (PL) or nitrate-rich (12.8 mmol; NR) beverage 2.5 hours prior to T2 and T3 in a double-blind, placebo-controlled, crossover study. Exercise during hypobaric hypoxia (3500m; T2 and T3) consisted of a 5-min warm-up (25% of normobaric VO 2max ) and four (40, 50, 60, 70% of normobaric VO 2max ) additional 5-min cycling bouts each separated by a 4-min passive rest. Results: Pre-exercise plasma nitrite was elevated following NR consumption compared to PL (p<0.05). Beverage-specific oxygen consumption, SaO 2 , BP and RPE were similar at all submaximal intensities. In both conditions (PL and NR), following exercise at 3500m, markers of oxidative stress (catalase and 8-isoprostane) were elevated compared to baseline resting values (p<0.05). However, post-exercise oxidative stress markers were similar between groups (placebo vs nitrate rich) for both catalase and 8-isoprostane (p=.94 and p=.16; respectively). Conclusions: Our findings do not support the efficacy of dietary nitrate supplementation prior to exercise at altitude in a healthy population.