Exercise & oxidative stress effects on the gastrointestinal barrier & the contribution of dietary pro- & anti-oxidants in Alaskan sled dogs

Scope and method of study. Exercise can lead to untoward effects when the intensity of exercise approaches extremes of performance. Gastrointestinal (GI) dysfunction occurs due to exercise and the mechanisms are unknown. Oxidative stress is encountered with exercise and a free radical mechanism has been implicated in causes of exercise-induced GI dysfunction. Little is known about the contribution of dietary pro-oxidants to GI mucosal barrier dysfunction in athletes. Alaskan sled dogs experience oxidative stress and GI dysfunction due to exercise. Sled dogs were chosen to test the hypothesis that dietary pro-oxidants and exercise-induced oxidative stress causes GI dysfunction. During multiple days of exercise, measurement of oxidative stress parameters (blood glutathione oxidation and exhaled ethane and pentane) was coupled with post-exercise gastroscopy and analysis of mucosal biopsies and GI permeability markers. Markers were reassessed while administering a flavonoid antioxidant before and during exercise. Also, lipid hydroperoxides were measured in foodstuffs used to sustain sled dogs.Findings and conclusions. Gastric dysfunction was similar to previous studies, but increased intestinal permeability and oxidative stress did not occur with exercise. Gastric mucosal defects appeared after 100 miles of exercise and did not progress. Also, oxidative stress occurred post-exercise, but only after six hours of rest with food following the first 100 miles. There was no correlation of oxidative stress to GI dysfunction. Histologically, gastric mucosal biopsies revealed persistence of lymphoplasmacytic and sometimes neutrophilic influx persisting for at least nine days of rest. Administration of a flavonoid antioxidant had no effect on oxidative stress or GI dysfunction. The flavonoid supplement reduced the protein carbonyl content of gastric mucosal biopsies (local antioxidant effect), but did not change the histologic appearance of the gastric mucosa. The lipid hydroperoxide load in sled dog foodstuffs was similar to levels in control diets used in studies of hydroperoxide modulation of mucosa. Our data indicate there is not a direct effect of oxidative stress on exercise induced GI dysfunction. However, local free radical modification (protein carbonyls) occurs and the persistent mucosal leukocytes may modulate exercise induced oxidative damage.