Unloading-induced atrophy and decreased oxidative capacity of the soleus muscle in rats are reversed by pre- and postconditioning with mild hyperbaric oxygen

Ai Takemura,Roland R Roy,Ikumi Yoshihara,Akihiko Ishihara

doi:10.14814/phy2.13353

Ai Takemura, Roland R Roy + Show 2 more

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https://doi.org/10.14814/phy2.13353

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Abstract

Our aim was to determine the effects of pre‐ and/or postconditioning with mild hyperbaric oxygen (1.25 atmospheric pressure, 36% oxygen for 3 h/day) on the properties of the soleus muscle that was atrophied by hindlimb suspension‐induced unloading. Twelve groups of 8‐week‐old rats were housed under normobaric conditions (1 atmospheric pressure, 20.9% oxygen) or exposed to mild hyperbaric oxygen for 2 weeks. Ten groups then were housed under normobaric conditions for 2 weeks with their hindlimbs either unloaded via suspension or not unloaded. Six groups subsequently were either housed under normobaric conditions or exposed to mild hyperbaric oxygen for 2 weeks: the suspended groups were allowed to recover under reloaded conditions (unrestricted normal cage activity). Muscle weights, cross‐sectional areas of all fiber types, oxidative capacity (muscle succinate dehydrogenase activity and fiber succinate dehydrogenase staining intensity) decreased, and a shift of fibers from type I to type IIA and type IIC was observed after hindlimb unloading. In addition, mRNA levels of peroxisome proliferator‐activated receptor γ coactivator‐1α decreased, whereas those of forkhead box‐containing protein O1 increased after hindlimb unloading. Muscle atrophy and decreased oxidative capacity were unaffected by either pre‐ or postconditioning with mild hyperbaric oxygen. In contrast, these changes were followed by a return to nearly normal levels after 2 weeks of reloading when pre‐ and postconditioning were combined. Therefore, a combination of pre‐ and postconditioning with mild hyperbaric oxygen can be effective against the atrophy and decreased oxidative capacity of skeletal muscles associated with hindlimb unloading.

Highlights

Hindlimb unloading in rodents results in atrophy of all fiber types, a shift of fibers from type I to type II, de novo synthesis of type IIx myosin heavy chain, reduced oxidative capacity, decreased mRNA levels of heat shock proteins and peroxisome proliferator-activated receptor c coactivator-1a (Pgc-1a), and increased mRNA levels of forkhead box-containing protein O1 (FoxO1) in hindlimb skeletal muscles (Ishihara et al 1997, 2004, 2008; Nagatomo et al 2011a)
Effects of hindlimb unloading on the soleus muscle
Mild hyperbaric oxygen reduces blood pressure and oxidative stress levels in spontaneously hypertensive rats (Nagatomo et al 2010a), suggesting that mild hyperbaric oxygen decreases sympathetic activation in hypertensive rats. These results suggest that mild hyperbaric oxygen does not increase oxidative stress and instead inhibits elevated oxidative stress

Summary

Introduction

Hindlimb unloading in rodents results in atrophy of all fiber types, a shift of fibers from type I to type II, de novo synthesis of type IIx myosin heavy chain, reduced oxidative capacity, decreased mRNA levels of heat shock proteins and peroxisome proliferator-activated receptor c coactivator-1a (Pgc-1a), and increased mRNA levels of forkhead box-containing protein O1 (FoxO1) in hindlimb skeletal muscles (Ishihara et al 1997, 2004, 2008; Nagatomo et al 2011a) These changes, are muscleand fiber type specific, that is, predominantly slow antigravity muscles and high oxidative slow fibers are affected the greatest by hindlimb unloading.

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