Abstract
The purpose of this study was to correlate post-exercise muscle glycogen levels with changes in plasma cytokine, and muscle mRNA cytokine expression and protein content. Twenty-four male runners (age 36.5 ± 1.8 years, VO2max 60.0 ± 1.5 mL⋅kg(-1) ⋅ min(-1)) ran twice (separated by 4 weeks) on treadmills to exhaustion at 70% VO2max (average time and distance of 2.24 ± 0.09 h and 24.9 ± 1.1 km). Muscle biopsies from the vastus lateralis and blood samples were collected before and after each run, with IL-6, IL-8, and MCP-1 measured in muscle (mRNA and protein) and plasma. Data from the two runs were averaged. Participants experienced a 35.3 ± 4.2% decrease (P < 0.001) in skeletal muscle glycogen content (67.5 ± 2.8 to 44.3 ± 3.7 mmol⋅kg(-1) wet weight). Muscle mRNA expression for IL-6, IL-8, and MCP-1 increased 7.34 ± 0.90-, 13.9 ± 2.3-, and 4.10 ± 0.60-fold, respectively (all, P < 0.001). Skeletal muscle IL-6, IL-8, and MCP-1 protein content increased 35.8 ± 10.6, 80.6 ± 12.1, and 105 ± 17.9%, respectively (all, P ≤ 0.005). Plasma IL-6, IL-8, and MCP-1 increased 47.1 ± 10.0-, 2.6 ± 0.3-, and 1.6 ± 0.1-fold, respectively (all, P < 0.001). Post-exercise muscle glycogen concentrations were negatively correlated with run time to exhaustion (r = -0.70, P < 0.001), and changes in muscle IL-6 protein content (r = -0.44, P = 0.049), plasma IL-6 (r = -0.72, P < 0.001), IL-8 (r = -0.60, P = 0.002), and MCP-1 (r = -0.589, P = 0.002), but not with changes in muscle IL-8 and MCP-1 protein content, or muscle mRNA expression for IL-6, IL-8, and MCP-1. Prolonged and intensive running increased muscle mRNA expression, muscle protein content, and plasma levels for IL-6, IL-8, and MCP-1, and post-run muscle glycogen levels were most strongly related to plasma cytokine levels.
Highlights
Cytokines are a broad category of small proteins that are important in cell signaling, act through receptors, and affect the behavior of other cells
Changes in serum cortisol and plasma epinephrine were not significantly related to changes in muscle IL-6, IL-8, or monocyte chemoattract protein-1 (MCP-1) messenger RNA (mRNA) or protein levels. These data from 24 male endurance athletes who ran twice on treadmills to exhaustion at ~70% VO2max showed increases in muscle IL-6, IL-8, and MCP-1 mRNA and protein content, and corresponding increases in plasma levels for these three cytokines
This study focused on the linkage between muscle glycogen availability and cytokine mRNA expression and production, and showed that post-run muscle glycogen content was negatively related to plasma but not muscle mRNA levels for IL-6, IL-8, and MCP-1
Summary
Cytokines are a broad category of small proteins that are important in cell signaling, act through receptors, and affect the behavior of other cells. The six cytokines with the greatest fold increase in plasma during prolonged and intensive exercise include IL-6, IL-10, granulocyte colony stimulating factor (G-CSF), IL-8, interleukin-1 receptor antagonist (IL-1ra), and monocyte chemoattract protein-1 (MCP-1) [4,5,6]. These cytokines exert anti-inflammatory and chemotactic influences, and are produced by multiple cell types both within and outside the immune system and skeletal muscle tissue [1, 3, 7]. The acute, large exercise-induced increases in IL-6 and other cytokines orchestrate anti-inflammatory influences, augment lipolysis, stimulate chemotaxis, improve insulin sensitivity, serve as signaling agents for training adaptations and tissue repair, and function in many other roles related to health [1,2,3, 8]
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