Post-Exercise Skeletal Muscle Glycogen Related to Plasma Cytokines and Muscle IL-6 Protein Content, but not Muscle Cytokine mRNA Expression

David C. Nieman, Kevin A. Zwetsloot, Mary Pat Meaney, Dominic D. Lomiwes, Suzanne M. Hurst, Roger D. Hurst

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.