Influence of Neonatal Exposure to Hyperoxia on Skeletal Muscle in a Rat Model

<b>Background/Objectives</b>: Premature births below 32 weeks of gestation generally require respiratory oxygen support, leading to a relatively hyperoxic environment compared to in utero conditions. Transient hyperoxia exposure has been linked to an elevated risk of chronic lung disease and retinopathy of prematurity; however, its effects on skeletal muscles remain elusive. This study aimed to investigate the effects of hyperoxic exposure in rats as a model of premature infants receiving supplemental oxygen (30-60% O₂ for several weeks). We hypothesized that rats exposed to postnatal hyperoxia would exhibit muscle fiber atrophy and alterations in fiber type. <b>Methods</b>: We used a rat model in which newborns were exposed to 80% oxygen from birth until postnatal day 12. We assessed the gastrocnemius muscles of rat legs at 12 weeks. <b>Results</b>: Rats exposed to hyperoxia showed substantially increased protein expression of Atrogin-1, along with elevated levels of adipophilin, myogenic differentiation factor 1, and myogenin. No significant changes were observed in the expression of slow or fast myosin heavy chain proteins. However, myofiber size in the gastrocnemius muscle was reduced in the hyperoxia-exposed group compared to the control group. <b>Conclusions</b>: Thus, transient hyperoxia exposure during early life can impede skeletal muscle development, potentially extending into adulthood.