"The findings suggest that prolonged physical activity reduces the essential fatty acid status of canine endurance athletes highlighting the significance of these nutrients in the diets of performance animals."

Final Report: IFSS Supported Sled Dog Project - Burned Membrane Syndrome

Dr. Stephen Phinney, Dr. Doug Bibus and Dr. Mike Davis
12/30/05

This $5,000 grant (From IFSS World Cup dedicated revenue) was awarded to evaluate the hypothesis that a prolonged period of intense exercise has a negative impact on the essential fatty acid content of cell membranes due to excessive oxidative stress. The funds were used to partially defray travel costs and shipping necessary to collect samples from 3 dog teams, 2 teams running the 2005 Iditarod (teams #1 and #2), and one participating in the Yukon Quest (team #3). Red blood cell samples were obtained from teams #1 and #3 and cheek mucosal swabs were obtained from all three. The remainder of the funds were used to defray the costs of fatty acid extraction and gas chromatographic analysis performed by Lipid Technologies, Inc (Dr. Doug Bibus, Austin, MN).

Red blood cells from 6 dogs per team from teams #1 and #3 obtained before and after the race have been analyzed. Cheek cells from 3-5 animals per team from all 3 teams were also analyzed. The red blood cell data demonstrates highly variable responses between the two teams, but consistent data within the teams. Whereas team #3 showed no significant reductions in either essential fatty acids or metabolically labile fats across the race, red blood cells from team #1 showed marked reductions in membrane omega-3 fatty acids, and variable reductions in arachidonic acid.

Cheek cell analysis from all three teams revealed at least modest - and in some cases quite prominent - reductions in arachidonic acid at the end of the race compared to the pre-race samples. Again, there was considerable variability in the individual fatty acid values between teams, whereas there was relative consistency in these values within any one team. This between team variability indicates that membrane fatty acids are significantly influenced by the diet fed both before and during the race, and that dietary manipulation has the potential to prevent or reduce the potential for membrane damage that can occur during a prolonged period of intense exercise.

Red blood cells were selected as the reference standard for analysis in this study because they are readily obtainable, physiologically important, and are less subject to day-to-day dietary variation than serum lipids. The cheek cell assay was included to assess a novel method to obtain a non-invasive sample of mucosal cells from the GI tract. In addition, given the more rapid turnover of cheek cells and their anatomical location in the GI tract, they have the potential to better reflect the effects of a 10-day period of oxidative stress on membrane fatty acids than do red blood cells.

Although firm conclusions are necessarily limited by the relatively small number of animals sampled and our inability to obtain end-of-race red cell samples from one of the three participating teams, the data confirm that: 1) cheek cell membranes are more responsive to a 10-day period of intense exercise stress than red blood cells, 2) the changes seen in the cheek cell membranes in the three teams provides support for our proposed mechanism for the causation of exercise-induced mucosal damage and GI bleeding, and 3) the consistency in membrane composition within teams and the variability between teams indicates that membrane damage due to prolonged intense exercise can be moderated by the fatty acid composition of both the pre-race and during-race diet.

This study represents an important first step in establishing a mechanism for exercise-induced GI bleeding. However, although our hypothesized exercise-induced membrane changes were confirmed, these results were obtained from a relatively small number of dogs, and they do not absolutely link membrane essential fatty acid depletion to GI bleeding. To firmly establish this mechanistic connection, we would need to perform a study during a race such as the Iditarod demonstrating that a dietary intervention designed to prevent these membrane changes also prevented the occurrence of gastric erosions and/or gastro-intestinal blood loss.