Exercise in hypobaric hypoxia increases markers of intestinal injury and symptoms of gastrointestinal distress.

Abstract

What is the central question of this study? What is the effect of hypobaric hypoxia on markers of exercise-induced intestinal injury and symptoms of gastrointestinal (GI) distress? What is the main finding and its importance? Exercise performed at 4300m of simulated altitude increased intestinal fatty acid binding protein (I-FABP), claudin-3 (CLDN-3) and lipopolysaccharide binding protein (LBP), which together suggest that exercise-induced intestinal injury may be aggravated by concurrent hypoxic exposure. Increases in I-FABP, LBP and CLDN-3 were correlated to exercise-induced GI symptoms, providing some evidence of a link between intestinal barrier injury and symptoms of GI distress. We sought to determine the effect of exercise in hypobaric hypoxia on markers of intestinal injury and gastrointestinal (GI) symptoms. Using a randomized and counterbalanced design, nine males completed two experimental trials: one at local altitude of 1585m (NORM) and one at 4300m of simulated hypobaric hypoxia (HYP). Participants performed 60min of cycling at a workload that elicited 65% of their NORM . GI symptoms were assessed before and every 15min during exercise. Pre- and post-exercise blood samples were assessed for intestinal fatty acid binding protein (I-FABP), claudin-3 (CLDN-3) and lipopolysaccharide binding protein (LBP). All participants reported at least one GI symptom in HYP compared to just one participant in NORM. I-FABP significantly increased from pre- to post-exercise in HYP (708±191 to 1215±518pgml-1 ; P=0.011, d=1.10) but not NORM (759±224 to 828±288pgml-1 ; P>0.99, d=0.27). CLDN-3 significantly increased from pre- to post-exercise in HYP (13.8±0.9 to 15.3±1.2ngml-1 ; P=0.003, d=1.19) but not NORM (13.7±1.8 to 14.2±1.6ngml-1 ; P=0.435, d=0.45). LBP significantly increased from pre- to post-exercise in HYP (10.8±1.2 to 13.9±2.8μgml-1 ; P=0.006, d=1.12) but not NORM (11.3±1.1 to 11.7±0.9μgml-1 ; P>0.99, d=0.32). I-FABP (d=0.85), CLDN-3 (d=0.95) and LBP (d=0.69) were all significantly higher post-exercise in HYP compared to NORM (P≤0.05). Overall GI discomfort was significantly correlated to ΔI-FABP (r=0.71), ΔCLDN-3 (r=0.70) and ΔLBP (r=0.86). These data indicate that cycling exercise performed in hypobaric hypoxia can cause intestinal injury, which might cause some commonly reported GI symptoms.