Effects Of Icing With Or Without Heat Stress On Skeletal Muscle Fibrosis Following Injury

Abstract

PURPOSE: The aims of the present study were to investigate 1) the effects of icing treatment as first aid following skeletal muscle injury on fibrosis in the regenerating muscle, and 2) whether the different start timing of heat treatment impacts fibrosis followed by the icing treatment after skeletal muscle injury. METHODS: Male Wistar rats (10 weeks of age) were randomly assigned to injured, injured with icing (ICE), and injured with icing and heat treatments (I + H) groups. The I + H group was further divided into two groups depending on the difference of timing to start the heat treatment (d1 and d2). Bupivacaine (BPVC) was injected into slow soleus muscles bilaterally in order to induce muscle injury in all rats. Application of icing treatment (ice pack, 0 °C for 20 min) was performed in the ICE and I + H groups only once immediately after the BPVC injection. Rats in the I + H group further received intermittent heat treatment (42 °C for 30 min on alternating days) started from 1- or 2-day after the injury until the day 14. At 1, 3, 7, 14, and 28 days after the injury, soleus muscles were dissected and analyzed. RESULTS: At 28 days after BPVC injection, the fibrotic area in regenerating soleus muscle was significantly higher in ICE than in injured groups (P < 0.05). In addition, mRNA microarray analysis showed that the expression level of genes involved in fibrosis, myogenesis, and muscle differentiation was upregulated when icing treatment was applied immediately following the injury at 3, 7, and 14 days after BPVC injection (P < 0.05). On the other hand, there was no significant difference in the fibrotic area in injured soleus between injured and both I + H groups at 28 days following the injury. The fibrotic area in the I + Hd1 group was also significantly lower than that in the ICE and I + Hd2 groups (P < 0.05). CONCLUSIONS: These results revealed that icing treatment applied immediately following skeletal muscle injury facilitated fibrosis in the regenerating muscle via, in part, inducing a change in gene expression dynamics of some specific gene groups. Our results also suggested that application of intermittent heat treatment, especially when started from 1-day after skeletal muscle injury, followed by icing treatment could be a potential strategy to attenuate the icing-related progression of fibrosis.