The endurance sled dog is the ultimate endurance athlete in which to examine the exercise-associated acute phase and myokine responses that might be related to changes in muscle metabolism and damage. An inciting cause for increased C-reactive protein has yet to be elucidated, which might involve interleukin-6 and other myokines.
To examine concentrations of interleukin-6 (IL-6), interleukin-15 (IL-15), interleukin-8 (IL-8), and tumor necrosis factor-α (TNF-α), and markers of the inflammatory response of exercise; monocyte chemoattractant protein-1(MCP-1) and C-reactive protein (CRP) before, during, and after an endurance racing event.
26 sled dogs completing a 1650-km race.
In a prospective study, cephalic venipuncture was performed before racing, at the midpoint, and after racing. Body weight and serum CRP, MCP-1, IL-15, IL-8, IL-6, and TNF-α concentrations were evaluated using enzyme-linked immunoabsorbance-based assays or a luminex multiplex assay.
There were no significant differences in concentrations of IL-6, IL-15, IL-8, or TNF-α at the 3 time points, whereas there were significant increases in MCP-1 (median and range—start: 86 pg/mL [30–1845]; midpoint: 179 pg/mL [53–730]; finish: 180 pg/mL [21–1294]; P < .01) and CRP (median and range—start: 18 μg/mL [11–58]; midpoint: 76 μg/mL [12–198]; finish: 60 μg/mL [12–170]; P < .01) at the midpoint and race finish. There was a significant linear relationship between MCP-1 and IL-6 (R = 0.68; P < .01).
Conclusions and Clinical Significance
The inflammatory response to exercise increases as measured by MCP-1 during and after endurance exercise in sled dogs. IL-6 appears to be associated with MCP-1; however, the reasons for increases in the acute phase response (CRP) cannot be attributed to IL-6 or other myokines. IL-6 and MCP-1 concentrations might be useful in future investigations of exertional rhabdomyolysis.