Dietary nitrate supplementation: effects on plasma nitrite and pulmonary O 2 uptake dynamics during exercise in hypoxia and normoxia

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology integrative and comparative physiology, 2014-10, Vol.307 (7), p.R920-R930
• Main Authors: Kelly, James, Vanhatalo, Anni, Bailey, Stephen J., Wylie, Lee J., Tucker, Christopher, List, Stephen, Winyard, Paul G., Jones, Andrew M.
• Format: Article
• Language: English
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00068.2014

We investigated the effects of dietary nitrate (NO 3 − ) supplementation on the concentration of plasma nitrite ([NO 2 − ]), oxygen uptake (V̇o 2 ) kinetics, and exercise tolerance in normoxia (N) and hypoxia (H). In a double-blind, crossover study, 12 healthy subjects completed cycle exercise tests, twice in N (20.9% O 2 ) and twice in H (13.1% O 2 ). Subjects ingested either 140 ml/day of NO 3 − -rich beetroot juice (8.4 mmol NO 3 ; BR) or NO 3 − -depleted beetroot juice (PL) for 3 days prior to moderate-intensity and severe-intensity exercise tests in H and N. Preexercise plasma [NO 2 − ] was significantly elevated in H-BR and N-BR compared with H-PL ( P < 0.01) and N-PL ( P < 0.01). The rate of decline in plasma [NO 2 − ] was greater during severe-intensity exercise in H-BR [−30 ± 22 nM/min, 95% confidence interval (CI); −44, −16] compared with H-PL (−7 ± 10 nM/min, 95% CI; −13, −1; P < 0.01) and in N-BR (−26 ± 19 nM/min, 95% CI; −38, −14) compared with N-PL (−1 ± 6 nM/min, 95% CI; −5, 2; P < 0.01). During moderate-intensity exercise, steady-state pulmonary V̇o 2 was lower in H-BR (1.91 ± 0.28 l/min, 95% CI; 1.77, 2.13) compared with H-PL (2.05 ± 0.25 l/min, 95% CI; 1.93, 2.26; P = 0.02), and V̇o 2 kinetics was faster in H-BR (τ: 24 ± 13 s, 95% CI; 15, 32) compared with H-PL (31 ± 11 s, 95% CI; 23, 38; P = 0.04). NO 3 − supplementation had no significant effect on V̇o 2 kinetics during severe-intensity exercise in hypoxia, or during moderate-intensity or severe-intensity exercise in normoxia. Tolerance to severe-intensity exercise was improved by NO 3 − in hypoxia (H-PL: 197 ± 28; 95% CI; 173, 220 vs. H-BR: 214 ± 43 s, 95% CI; 177, 249; P = 0.04) but not normoxia. The metabolism of NO 2 − during exercise is altered by NO 3 − supplementation, exercise, and to a lesser extent, hypoxia. In hypoxia, NO 3 − supplementation enhances V̇o 2 kinetics during moderate-intensity exercise and improves severe-intensity exercise tolerance. These findings may have important implications for individuals exercising at altitude.