Free oxygen radicals are generated during muscle contraction, and are known to induce the expression of heat shock proteins (HSP). HSP are ubiquitous proteins known to regulate the expression of other genes. Of note, it has been shown that HSP72 (the inducible form of the 70 kDa family of HSP) can induce the expression of the cytokine interleukin (IL)-6 in cultured monocytes (Asea et al. 2000). Recent work from our group has demonstrated that both HSP72 (Febbraio & Koukoulas, 2000) and IL-6 (Steensberg et al. 2001) gene expression are increased in contracting skeletal muscle. Hence, it has been suggested that the increase in IL-6 in contracting skeletal muscle may be mediated via the induction of HSP72. Of note, the increase in HSP72-mediated IL-6 in monocytes only occurred via a CD-14-dependent pathway (Asea et al. 2000), suggesting that IL-6 can only be mediated by extracellular HSP72. We hypothesized, therefore, that the production of muscle-derived IL-6 during concentric exercise occurs through an HSP72-independent pathway and that anti-oxidant treatment would inhibit the exercise-induced increase in HSP72 mRNA, but not the exercise-induced increase in IL-6 mRNA.

To test these hypotheses, eleven healthy, young males ingested either 400 IU of vitamin E and 500 mg of vitamin C (Anti-Ox) or a placebo (Control) daily for 4 weeks before completing 3 h of two-legged knee-extensor exercise at 50 % of maximal power output. Muscle biopsies were obtained before, immediately after, and 3 h following exercise. Ethical permission was granted. The muscle samples were analysed for HSP72 and IL-6 mRNA using real-time PCR and the data were statistically analysed using a two-way (group X time) ANOVA.

There were no differences in either IL-6 or HSP72 gene expression at rest. However, 3 h of exercise markedly increased (P < 0.05) IL-6 mRNA in both Anti-Ox and Control and while these values decreased (P < 0.05) 3 h following exercise, IL-6 mRNA was still elevated (P < 0.05) compared with Rest. No differences, however, were observed in IL-6 mRNA when comparing Anti-Ox with Control. Importantly, HSP72 increased (P < 0.05) ~4-fold in Control when comparing Post-exercise with Rest, but no such increase was observed in Anti-Ox (see Fig. 1). These data demonstrate that 3 h of non-damaging exercise was sufficient to induce both an IL-6 and HSP72 response. However, since anti-oxidant treatment blunted the exercise-induced HSP72, but not IL-6 response, our data suggest that in contracting muscle, IL-6 is not mediated via an HSP72-dependent pathway.