Effect of normobaric hyperoxia exposure on skeletal muscle capillary density and mitochondrial activity in type 1 diabetic rats

Abstract Background Hyperbaric hyperoxia exposure improves skeletal muscle capillary rarefaction and mitochondrial activity in diabetes mellitus (DM). However, the hyperbaric environment is limited, and normobaric hyperoxia exposure effects on skeletal muscle capillaries and mitochondrial activity in DM are unknown. We determined normobaric hyperoxia exposure effects on skeletal muscle capillary density and mitochondrial activity in type 1 DM rats. Methods Seven-week-old male Wistar rats were randomly divided into control, DM, DM with 40% oxygen exposure (DM40), and DM with 50% oxygen exposure (DM50) groups. A single intraperitoneal injection of streptozotocin was administered to induce type 1 DM. DM40 and DM50 exposures were conducted daily for 60 min for 4 weeks. The soleus muscle, extensor digitorum longus muscle, and plantaris muscle samples were sectioned. The capillary-to-fiber ratio was measured using alkaline phosphatase staining. Succinate dehydrogenase (SDH) activity was measured by SDH staining. Scheffe’s test was performed for multiple comparisons, and Pearson’s correlation coefficients between the ratio and SDH activity were calculated. Statistical significance was set at < 5%. Results The ratio in the soleus and extensor digitorum longus muscles was significantly higher in DM40 and DM50 rats than in DM rats (all p < 0.01). Moreover, SDH activity in the soleus muscle was significantly higher in DM40 rats than in DM rats; the same was found for the plantaris muscle (all p < 0.01). A significant positive correlation was observed between the ratio and SDH activity in the soleus and plantaris muscles (all p < 0.05). Conclusions Normobaric hyperoxia affected all skeletal muscles, reflecting their fiber characteristics. Skeletal muscle capillary density was associated with mitochondrial activity, suggesting improved DM metabolism.