Irreversible morphological changes in leg bone following chronic gravitational unloading of growing rats

Ohira, Yoshinobu; Kawano, Fuminori; Wang, X.D.; Sudoh, Masamichi; Iwashita, Youichirou; Majima, Hideyuki J.; Nonaka, Ikuya

doi:10.1016/j.lfs.2006.02.022

Cited by 19 publications

(25 citation statements)

References 27 publications

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“…However, no tension was detected and the electromyogram activity was reduced ϳ88% when the ankle joints were stretched during hindlimb unloading because of the passive shortening of muscle fibers and sarcomeres. The electromyogram activity was also inhibited in soleus muscle during unloading in the present study (29). Thus, it is clear that both electrical and mechanical activities of soleus were inhibited during the longterm unloading.…”

Section: Discussionsupporting

confidence: 71%

“…Thus, it is suggested that mechanical and/or neuronal activities may not play an essential role in muscle fiber formation during postnatal development. The data obtained in the current study also suggest that muscle fiber formation or fiber number in soleus muscle may be genetically programmed or influenced by passive stretch due to the longitudinal growth of bone (29), as is also stated below. Stretching of muscle fibers generally causes hypertrophy and/or increase in protein content (13,38).…”

Section: Fiber Numbersupporting

confidence: 78%

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Essential role of satellite cells in the growth of rat soleus muscle fibers

Kawano¹,

Takeno²,

Nakai³

et al. 2008

American Journal of Physiology-Cell Physiology

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Effects of gravitational loading or unloading on the growth-associated increase in the cross-sectional area and length of fibers, as well as the total fiber number, in soleus muscle were studied in rats. Furthermore, the roles of satellite cells and myonuclei in growth of these properties were also investigated. The hindlimb unloading by tail suspension was performed in newborn rats from postnatal day 4 to month 3 with or without 3-mo reloading. The morphological properties were measured in whole muscle and/or single fibers sampled from tendon to tendon. Growth-associated increases of soleus weight and fiber cross-sectional area in the unloaded group were ∼68% and 69% less than the age-matched controls. However, the increases of number and length of fibers were not influenced by unloading. Growth-related increases of the number of quiescent satellite cells and myonuclei were inhibited by unloading. And the growth-related decrease of mitotically active satellite cells, seen even in controls (20%, P > 0.05), was also stimulated (80%). The increase of myonuclei during 3-mo unloading was only 40 times vs. 92 times in controls. Inhibited increase of myonuclear number was not related to apoptosis. The size of myonuclear domain in the unloaded group was less and that of single nuclei, which was decreased by growth, was larger than controls. However, all of these parameters, inhibited by unloading, were increased toward the control levels generally by reloading. It is suggested that the satellite cell-related stimulation in response to gravitational loading plays an essential role in the cross-sectional growth of soleus muscle fibers.

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Section: Discussionsupporting

confidence: 71%

Section: Fiber Numbersupporting

confidence: 78%

Essential role of satellite cells in the growth of rat soleus muscle fibers

Kawano¹,

Takeno²,

Nakai³

et al. 2008

American Journal of Physiology-Cell Physiology

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“…3). The EMG activities in both the soleus (~86%) and plantaris (90%) muscles were decreased in response to hindlimb suspension, relative to those during rest on the f loor [5,19]. However, the magnitude of hindlimb suspension induced by reduction in the absolute EMG activity in the plantaris muscle (~90 mV/h) was minor relative to that in the soleus muscle (~473 mV/h).…”

Section: Discussionmentioning

confidence: 99%

“…It is suggested that the decreased mRNA expression levels of these HSPs in the slow-twitch day in a slow-twitch soleus neuromuscular unit, but only 3,000 impulses are generated per day in a fast-twitch tibialis anterior neuromuscular unit [18]. Similarly, EMG activities (~550 mV/h) of the soleus muscle in rats at rest are approximately 5 times greater than those (~100 mV/h) of the plantaris muscle [5,19].…”

Section: Spacefl Ightmentioning

confidence: 99%

Gene Expression Levels of Heat Shock Proteins in the Soleus and Plantaris Muscles of Rats after Hindlimb Suspension or Spaceflight

et al. 2008

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Gene expression levels of heat shock proteins (HSPs) in the slow-twitch soleus and fast-twitch plantaris muscles of rats were determined after hindlimb suspension or spaceflight. Male rats were hindlimb-suspended for 14 d or exposed to microgravity for 9 d. The mRNA expression levels of HSP27, HSP70, and HSP84 in the hindlimb-suspended and microgravity-exposed groups were compared with those in the controls. The mRNA expression levels of the 3 HSPs in the soleus muscle under normal conditions were higher compared with those in the plantaris muscle. The mRNA expression levels of the 3 HSPs in the soleus muscle were inhibited by hindlimb suspension and spaceflight. The mRNA expression levels of the 3 HSPs in the plantaris muscle did not change after hindlimb suspension. It is suggested that the mRNA expression levels of the 3 HSPs are regulated by the mechanical and neural activity levels, and therefore the decreased mRNA expression levels of HSPs in the slow-twitch muscle following hindlimb suspension and spaceflight are related to a reduction in the mechanical and neural activity levels.

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“…With disuse, the skeleton seems to recognize that not all of its bone mass is needed to maintain structural integrity; bone mass decreases as a result of mineral density reduction (11), the bone architectural structure deteriorates, and osteopenia results. Weakening of the bone may lead to fractures or other musculoskeletal damage when physical activities are resumed (12,13).…”

Section: Introductionmentioning

confidence: 99%

Biomechanics and structural adaptations of the rat femur after hindlimb suspension and treadmill running

Shimano¹,

Volpon²

2009

Braz J Med Biol Res

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We microscopically and mechanically evaluated the femurs of rats subjected to hindlimb unloading (tail suspension) followed by treadmill training. Female Wistar rats were randomly divided into five groups containing 12-14 rats: control I (118 days old), control II (139 days old), suspended (tail suspension for 28 days), suspended-released (released for 21 days after 28 days of suspension), and suspended-trained (trained for 21 days after 28 days of suspension). We measured bone resistance by bending-compression mechanical tests of the entire proximal half of the femur and three-point bending tests of diaphyseal cortical bone. We determined bone microstructure by tetracycline labeling of trabecular and cortical bone. We found that tail suspension weakened bone (ultimate load = 86.3 ± 13.5 N, tenacity modulus = 0.027 ± 0.011 MPa·m vs ultimate load = 101.5 ± 10.5 N, tenacity modulus = 0.019 ± 0.006 MPa·m in control I animals). The tenacity modulus for suspended and released animals was 0.023 ± 0.010 MPa·m vs 0.046 ± 0.018 MPa·m for trained animals and 0.035 ± 0.010 MPa·m for control animals. These data indicate that normal activity and training resulted in recovered bone resistance, but suspended-released rats presented femoral head flattening and earlier closure of the growth plate. Microscopically, we found that suspension inhibited new bone subperiosteal and endosteal formation. The bone disuse atrophy secondary to hypoactivity in rats can be reversed by an early regime of exercising, which is more advantageous than ordinary cage activities alone.

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Irreversible morphological changes in leg bone following chronic gravitational unloading of growing rats

Cited by 19 publications

References 27 publications

Essential role of satellite cells in the growth of rat soleus muscle fibers

Essential role of satellite cells in the growth of rat soleus muscle fibers

Gene Expression Levels of Heat Shock Proteins in the Soleus and Plantaris Muscles of Rats after Hindlimb Suspension or Spaceflight

Biomechanics and structural adaptations of the rat femur after hindlimb suspension and treadmill running

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