The APR has been associated with many infectious and heritable disease processes in dogs and humans. The acute-phase components most often evaluated in dogs are haptoglobin, CRP, and serum amyloid A, with CRP being the most widely evaluated for a variety of acute and chronic inflammatory processes. Changes in CRP concentrations can be subtle, as is the case in inflammatory bowel disease (40 to 100 μg/mL), or extremely robust, as is the case for infectious agents (> 300 μg/mL).1-8 The increase in serum concentrations of CRP can be highly variable, which may reflect a systemic response to the degree of inflammatory stimuli.
Rigorous exercise in humans results in an APR, particularly in individuals who participate in events associated with endurance-related exercise. Ultramarathon and triathlon participants have the most consistent APR, including severe hypoferritinemia, hypoalbuminemia, and increases in concentrations of CRP and other acute-phase proteins.9–11 In many instances, a strong increase in CRP concentrations can be measured well into recovery and can provide a marker for the APR of exercise.9–15 There has been much debate regarding the kind of exercise that induces this response. It has been observed that concentric exercise (eg, weight lifting or typical training for a sporting activity) does not induce an APR, whereas prolonged eccentric exercise (triathlons and marathons) induces a robust APR with increases in CRP concentrations preceding an increase in IL-6 concentrations, which is thought to help drive this APR.9–17 This increase in CRP concentrations often precedes a progressive decrease in serum concentrations of iron and albumin, which suggests that dramatic increases in concentrations of CRP may be a potential marker for chronic fatigue or overtraining syndrome.11 However, depending on the study evaluated, the increase in IL-6 or CRP concentrations can be 4 to 50 times as high as the baseline concentration and may be brief or extended14; therefore, the role of IL-6 in the induction of exercise-induced APR and the potential use of IL-6 or CRP concentrations as markers of exercise stress have been contested.14,18,19
The most pronounced increases in CRP concentrations and decreases in serum concentrations of iron and albumin are evident in ultramarathon participants because of the rigorous nature of the exercise.11 However, an athlete that often surpasses the exertion of a human ultramarathon participant is an endurance sled dog. Endurance sled dogs participate in races that require running 128 to 160 km each day. To our knowledge, there has been no evaluation of the APR in these elite canine athletes. Because of the rigorous nature of the exercise these dogs perform, evaluation of these dogs may provide a better understanding of the APR during exercise through investigation of the relationship among IL-6, CRP, albumin, and iron concentrations. We hypothesized that sled dogs participating in a 557-km endurance race would have increases in serum concentrations of CRP and IL-6 and marked decreases in serum concentrations of serum iron and albumin as well as serum biochemical changes similar to those detected in other studies20–23 of endurance sled dogs that raced in Alaska.
Tumor necrosis factor-α
Antech Laboratory, Portland, Ore.
Bayer Advia 120, Siemens Corp, New York, NY.
Hitachi 917, Roche Diagnostics, Indianapolis, Ind.
Canine CRP ELISA, Tridelta PLC, Morris Plains, NJ.
Lincoplex canine cytokine multiplex, LINCO Research, St Charles, Mo.
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