Spinal cord injury level and the circulating cytokine response to strenuous exercise

PURPOSE: A complete spinal cord injury (SCI) above the 6th thoracic vertebra (T6) results in the loss of sympathetic innervation of the adrenal medulla. This study examined the effect of a complete SCI above and below T6 on plasma concentrations of epinephrine, circulating interleukin (IL)-6 and other inflammatory cytokines in response to acute strenuous exercise. METHODS: Twenty-six elite male wheelchair athletes (8=C6-C7 tetraplegic (TETRA); 10=T6- L1 paraplegic (PARA); 8=non-spinal cord injured controls (NON-SCI)) performed a submaximal exercise test followed by a graded exercise to exhaustion on a motorised treadmill. Blood samples were taken pre-exercise, post-exercise and 30 min post-exercise (post30) and analysed for concentrations of IL-6, IL-10, IL-1 receptor-antagonist (IL-1ra), tumor necrosis factor-alpha (TNF-α), epinephrine and cortisol. RESULTS: Circulating IL-6 concentration was significantly elevated at post-exercise and post30 (~5-fold) in NON-SCI and PARA (P=0.003) whereas concentrations in TETRA did not change significantly from pre-exercise values. IL-10, IL-1ra and TNF-α were unaffected by exercise in all groups, however both SCI groups presented elevated concentrations of IL-10 compared with NONSCI (P=0.001). At post-exercise, epinephrine concentrations were significantly higher than pre-exercise and post30 concentrations in NON-SCI (~3-fold) and PARA (~2-fold) (P=0.02). Plasma epinephrine concentrations were unchanged in TETRA throughout exercise; concentrations were significantly lower than NON-SCI and PARA at all-time points. Plasma cortisol concentrations were significantly elevated in all groups at post-exercise and post30 compared with pre-exercise (P<0.001). Total exercise time was similar between groups (NON-SCI= 38±6; PARA= 35±5; TETRA= 36±5 min). CONCLUSION: These findings suggest the sympathetic nervous system plays an important regulatory role in the circulating IL-6 response to exercise and has implications for the metabolic and inflammatory responses to exercise in individuals with injuries above T6.