Mild hyperbaric oxygen inhibits the growth-related decline in skeletal muscle oxidative capacity and prevents hyperglycemia in rats with type 2 diabetes mellitus

Background: Humans and animals with type 2 diabetes mellitus (T2DM) exhibit low skeletal muscle oxidative capacity and impaired glucose metabolism. The aim of the present study was to investigate the effects of exposure to mild hyperbaric oxygen on these changes in obese rats with T2DM. Methods: Five-week-old non-diabetic Long-Evans Tokushima Otsuka (LETO) and diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats were divided into normobaric (LETO-NB and OLETF-NB) and mild hyperbaric oxygen (LETO-MHO and OLETF-MHO) groups. The LETO-MHO and OLETF-MHO groups received 1266 hPa with 36% oxygen for 3 h daily for 22 weeks. Results: Fasting and non-fasting blood glucose, HbA1c, and triglyceride levels were lower in the OLETF-MHO group than in the OLETF-NB group (P < 0.05). In the soleus muscle, peroxisome proliferator-activated receptor δ/β (Pparδ/β), Pparγ, and PPARγ coactivator-1α (Pgc-1α) mRNA levels were lower in the OLETF-NB group than in all other groups (P < 0.05), whereas myogenin (Myog) and myogenic factor 5 (Myf5) mRNA levels were higher in the OLETF-MHO group than in the LETO-NB and OLETF-NB groups (P < 0.05). The soleus muscles in the OLETF-NB group contained only low-oxidative Type I fibers, whereas those in all other groups contained high-oxidative Type IIA and Type IIC fibers in addition to Type I fibers. Conclusions: Exposure to mild hyperbaric oxygen inhibits the decline in skeletal muscle oxidative capacity and prevents the hyperglycemia associated with T2DM. Pgc-1α, Myog, and Myf5 mRNA levels appear to be closely associated with skeletal muscle oxidative capacity in rats with T2DM.