Effect of Acclimation to Intermittent Hypobaric Hypoxia on NO Homeostasis

Abstract

Hypoxia is one of the major stimuli to produce nitric oxide (NO). Recent studies have shown that conversion of nitrogen dioxide (NO2) to NO is independent of nitric oxide synthase (NOS) activity, and exercise is responsible for NO production by its reduction of metabolic products NOx, nitrite (NO2−)/nitrate (NO3−). This study was to examine the effects of training on NO homeostasis after high altitude exposure.Aerobic capacity (i.e., VO2max) and NO related molecules, cyclic guanosine monophosphate (cGMP), NOx or NO2, were measured by use of an fluorometric and enzyme immunoassay (EIA) analysis (Cayman Inc., USA) from bloods: Fourteen healthy exercisers comparatively corresponding to mountaineers during high‐intensity aerobic exercise who has climbed up 5,000 meters above the sea level, and volunteers who had 7 days before and after aerobic training on treadmill and bicycle ergometer based on 75% HR max and sleeping in hypobaric hypoxic conditions (3000m~5000m) for 4 days.VO2/75%HRmax of acclimation at an altitude of 5,000 meters was significantly increased by 21.45% (p = 0.0016). In addition, cGMP concentration in post‐training group (3.35 ± 1.082 pmol/ml) was also increased compared to pre‐training one (1.54 ± 0.751 pmol/ml) (p < 0.001), whereas NOx or NO2 concentration was decreased significantly (i.e., NOx, 16.49 ± 6.357 vs. 11.32 ± 2.805 μM, p = 0.0027; NO2, 12.62 ± 8.321 vs. 7.39 ± 2.273 nM, p = 0.0395) These findings suggest that increase of cGMP via an NO production may ameliorate physical activity at high altitudes, which is associated with the changes of systemic concentration of NOx and NO2.