Muscle contraction accelerates IL-6 mRNA expression in the rat masseter muscle

Objective: : This study was conducted to determine if interleukin-6 (IL-6) and interleukin-1β (IL-1β) mRNA expression increase in response to muscle contraction caused by repetitive electrical stimulation of the rat masseter muscle. Methods: : Male Wistar rats weighing 140-160 g were divided randomly into the following three groups: electrical stimulation (ES) group (n = 21), carrageenan injection (CI) group (n = 24), and ES under dantrolene sodium (muscle relaxant) injection (ESDI) group (n = 7). ES or CI was done to the left masseter; and mock ES or mock CI to the right. Muscle tissues on both sides were sampled for total RNA isolation. Real-time RT-PCR was performed, with the cyclophilin A (CypA) mRNA level in each sample as an internal control. Mean relative IL-6 (il-6/cypA) and IL-1β (il-1β/cypA) mRNA levels were compared between the experimental and mock-treated sides within each group. Results: : Mean IL-6/CypA levels in the ES- or CI-treated muscle significantly increased, without any significant incremental change observed in either mock-treated muscle. Interestingly, the increase in the il-6/cypA level caused by the ES was suppressed by the injection of dantrolene sodium in the ESDI group. Furthermore, the mean il-1β/cypA level in the CI-treated masseter also significantly increased without any significant incremental change observed in the mock-treated muscle. However, there was no significant difference in the mean il-1β/cypA levels in the masseter between the ES- and the mock-treated sides. Conclusions: : These results show that IL-6 mRNA expression in the rat masseter muscle was accelerated by the CI or by repetitive muscle contraction induced by ES. Since the mRNA level of IL-1β, a well-known proinflammatory cytokine, was not altered by the contraction, the accelerated IL-6 mRNA expression elicited by the muscle contraction does not seem to be related to local inflammation.