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

Abstract

Objectives: 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. Methods: 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. Results: 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. Conclusion: 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.