Muscle Adaptation to Varying Oxygen Concentrations During Weaning in Rats.

INTRODUCTION: This study examined the effects of different oxygen concentrations on muscle tissue and oxidative stress dynamics in rats during the weaning period and aimed to reveal the specificity of development during the growth stage. METHODS: Thirty three-week-old male Wistar rats were randomly divided into five groups: control (group III), 10% oxygen (group I), 15% oxygen (group II), 40% oxygen (group IV), and 80% oxygen (group V). After the experiment, the soleus and plantaris muscles were stained with an adenosine triphosphatase stain. The percentage of muscle fiber types and cross-sectional area (CSA) was calculated, and oxidative stress was measured using blood serum. Scheffé's test was used for analysis. Statistical significance was set at p<0.05. RESULTS: The percentage of type Ⅰ fibers in the soleus muscle was significantly higher in groups I, II, and IV compared to group III. CSA in the soleus muscle were significantly smaller in groups I, II, IV, and V than in group III. Conversely, CSA in the plantaris muscle were significantly lower in groups I and II compared to group III, whereas groups IV and V exhibited significantly greater CSA than group III. No significant differences in oxidative stress levels were observed among the groups. CONCLUSION: Exposure to different oxygen concentrations induced muscle fiber type-specific adaptive responses during development, without promoting excessive reactive oxygen species production. Therefore, our results suggest that varying oxygen concentrations require consideration for applications in developmental physiology, pediatric rehabilitation, and preventive medicine.