Serum and tissue cytokines and chemokines increase with repetitive upper extremity tasks

We investigated inflammation in rats performing a low repetition, negligible force (LRNF) or high repetition, negligible force (HRNF) task of reaching and retrieving food pellets at target rates of two or four reaches/min for 2 h/day, for 6–8 weeks. Serum was assayed for 11 cytokines and chemokines; forelimb tissues for four cytokines. Macrophages were counted in forelimb tissues of LRNF rats to add to results from our previous studies of HRNF rats. In HRNF rats, serum IL‐1α, IL‐1β, TNFα, MIP2, MIP3a, and RANTES were elevated in weeks 6 and 8. In contrast, only MIP2 and MIP3a increased in serum of LRNF rats. In 8 week HRNF reach limb tissues, IL‐1α, IL‐1β, TNFα, and IL‐10 increased in distal bones, IL‐1α and ‐β in muscles, and TNFα in tendons. Only IL‐10 increased in LRNF reach limb muscles in week 8. Serum IL‐1α and MIP2 correlated with macrophages in LRNF loose connective tissues, serum MIP3a and MIP2 correlated negatively with grip strength, while serum TNFα, MIP3a, and MIP2 correlated positively with total number of reaches. Thus, several tissue and circulating cytokines/chemokines increase in an exposure dependent manner following short‐term performance of repetitive reaching tasks and correlate with macrophage infiltration and decreasing grip strength. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1320–1326, 2008