Muscle contractions induce interleukin-6 mRNA production in rat skeletal muscles

1. The present study explored the hypothesis that interleukin-6 (IL-6) migh t be locally produced in response to skeletal muscle contractions and wheth er the production might reflect the type of muscle contraction performed. R ats were anaesthetized and the calf muscles of one limb were stimulated ele ctrically for concentric or eccentric contractions (4 x 10 contractions wit h 1 min of rest between the 4 series, 100 Hz). The contralateral muscles se rved as unstimulated controls. The mRNA levels for IL-6, tilt: glucose tran sport protein GLUT-4 and beta -actin in the rat muscles (white and red gast rocnemius and soleus) were quantified by quantitative competitive RT-PCR. 2. The IL-G mRNA level, measured 30 min after the stimulation, increased af ter both eccentric and concentric contractions and there were no significan t differences in IL-6 mRNA levels between the different muscle filtre types . No significant increase in IL-6 mRNA level was seen in the unstimulated c ontralateral muscle fit,res. 3. No increase in GLUT-4 mRNA level was detected, indicating that the incre ase in IL-B mRNA level was not due to general changes in transcription. 4. We conclude that IL-6 is locally produced after muscle contraction, with no significant differences between different muscle fibre types. This loca l production of IL-6 is not due to general changes in transcription, since no changes in the level of GLUT-4 mRNA were found. The fact that increased IL-6 mRNA levels were seen after both concentric and eccentric contractions : indicates that the production of IL-6 is not solely due to muscle damage, seen primarily after eccentric exercise.