Influence of aerobic fitness on gastrointestinal barrier integrity and microbial translocation following a fixed-intensity military exertional heat stress test.
PURPOSE
Exertional-heat stress adversely disrupts gastrointestinal (GI) barrier integrity, whereby subsequent microbial translocation (MT) can result in potentially serious health consequences. To date, the influence of aerobic fitness on GI barrier integrity and MT following exertional-heat stress is poorly characterised.


METHOD
Ten untrained (UT; VO2max = 45 ± 3 ml·kg-1·min-1) and ten highly trained (HT; VO2max = 64 ± 4 ml·kg-1·min-1) males completed an ecologically valid (military) 80-min fixed-intensity exertional-heat stress test (EHST). Venous blood was drawn immediately pre- and post-EHST. GI barrier integrity was assessed using the serum dual-sugar absorption test (DSAT) and plasma Intestinal Fatty-Acid Binding Protein (I-FABP). MT was assessed using plasma Bacteroides/total 16S DNA.


RESULTS
UT experienced greater thermoregulatory, cardiovascular and perceptual strain (p < 0.05) than HT during the EHST. Serum DSAT responses were similar between the two groups (p = 0.59), although Δ I-FABP was greater (p = 0.04) in the UT (1.14 ± 1.36 ng·ml-1) versus HT (0.20 ± 0.29 ng·ml-1) group. Bacteroides/Total 16S DNA ratio was unchanged (Δ; -0.04 ± 0.18) following the EHST in the HT group, but increased (Δ; 0.19 ± 0.25) in the UT group (p = 0.05). Weekly aerobic training hours had a weak, negative correlation with Δ I-FABP and Bacteroides/total 16S DNA responses.


CONCLUSION
When exercising at the same absolute workload, UT individuals are more susceptible to small intestinal epithelial injury and MT than HT individuals. These responses appear partially attributable to greater thermoregulatory, cardiovascular, and perceptual strain.
['Ogden|Henry B|HB|http://orcid.org/0000-0001-7827-0922', 'Fallowfield|Joanne L|JL|', 'Child|Robert B|RB|', 'Davison|Glen|G|', 'Fleming|Simon C|SC|', 'Delves|Simon K|SK|', 'Millyard|Alison|A|', 'Westwood|Caroline S|CS|', 'Layden|Joseph D|JD|']
D000328:Adult D001439:Bacteroides D000072599:Cardiorespiratory Fitness D005227:Fatty Acids D000069196:Gastrointestinal Microbiome D018882:Heat Stress Disorders D006801:Humans D007408:Intestinal Absorption D007413:Intestinal Mucosa D008297:Male D005082:Physical Exertion D000073893:Sugars
I-FABP Exercise Endotoxemia Exertional heat stroke Gut health