ACUTE-PHASE RESPONSE IN EXERCISE .3. NEUTROPHIL AND IL-1-BETA ACCUMULATION IN SKELETAL-MUSCLE

Nine untrained men (22-29 yr) performed 45 min of downhill running (16 % incline, 70% of maximum heart rate). Needle biopsies of the vastus l ateralis were performed before, 45 min after, and 5 days after exercis e. Immunohistochemical staining of muscle cross sections revealed a 13 5% increase in muscle interleukin-1beta (IL-1beta) immediately after a nd a 250% increase (P < 0.03) 5 days after exercise. Using a rating sc ale (0-3) for the presence of neutrophils, light microscopic examinati on showed a significant accumulation of neutrophils in muscle biopsies taken 45 min after and 5 days after exercise [before: 0.5 +/- 0.2, 45 min after: 1.5 +/- 0.3 (P < 0.01), and 5 days after: 1.2 +/- 0.2 (P < 0.04)]. In addition, electron microscopic analysis showed an increase in the percentage of damaged Z-bands relative to total Z-bands [befor e: 4.8 +/- 3.5%, 45 min after: 32.5 +/- 8.6% (P < 0.05), and 5 days af ter: 14.1 +/- 3.2%]. Neutrophil accumulation was positively correlated to intracellular Z-band damage (rho = 0.66, P < 0.001). Immunohistoch emical staining for IL-1beta was related to neutrophil accumulation in muscle (rho = 0.38, P < 0.06) and to plasma creatine kinase levels (r ho = 0.416, P < 0.04). These data indicate that after eccentric exerci se ultrastructural damage to skeletal muscle is associated with neutro phil infiltration and muscle IL-1beta accumulation.