Influence of hindlimb unweighting and intermittent weight bearing on dynamics of nuclei in rat soleus muscle

Treadmill Exercise Suppresses Histological Progression of Disuse Atrophy in Articular Cartilage in Rat Knee Joints during Hindlimb Suspension

OBJECTIVE

The purpose of this study was to determine the preventive effects of treadmill exercise or physiological loading on disuse atrophy in the rat knee joint cartilage and bone during hindlimb suspension.

DESIGN

Twenty male rats were divided into 4 experimental groups, including the control, hindlimb suspension, physiological loading, and treadmill walking groups. Histological changes in the articular cartilage and bone of the tibia were histomorphometrically and immunohistochemically evaluated 4 weeks after the intervention.

RESULTS

Compared with the control group, the hindlimb suspension group showed thinning of cartilage thickness, decreased matrix staining, and decreased proportion of noncalcified layers. Cartilage thinning, decreased matrix staining, and decreased noncalcified layers were suppressed in the treadmill walking group. The physiological loading group exhibited no significant suppression of cartilage thinning or decreased noncalcified layers, but the decreased matrix staining was significantly suppressed. No significant prevention of bone mass loss or changes in subchondral bone thickness were detected after physiological loading or treadmill walking.

CONCLUSION

Disuse atrophy of the articular cartilage caused by unloading conditions could be prevented by treadmill walking in rat knee joints.

Physiological Reloading Recovers Histologically Disuse Atrophy of the Articular Cartilage and Bone by Hindlimb Suspension in Rat Knee Joint

OBJECTIVE

This study aimed to clarify physiological reloading on disuse atrophy of the articular cartilage and bone in the rat knee using the hindlimb suspension model.

DESIGN

Thirty male rats were divided into 3 experimental groups: control group, hindlimb suspension group, and reloading after hindlimb suspension group. Histological changes in the articular cartilage and bone of the tibia were evaluated by histomorphometrical and immunohistochemical analyses at 2 and 4 weeks after reloading.

RESULTS

The thinning and loss of matrix staining in the articular cartilage and the decrease in bone volume induced by hindlimb suspension recovered to the same level as the control group after 2 weeks of reloading. The proportion of the noncalcified and calcified layers of the articular cartilage and the thinning of subchondral bone recovered to the same level as the control group after 4 weeks of reloading.

CONCLUSIONS

Disuse atrophy of the articular cartilage and bone induced by hindlimb suspension in the tibia of rats was improved by physiological reloading.

The Effect of Reloading on Disuse Muscle Atrophy: Time Course of Hypertrophy and Regeneration Focusing on the Myofiber Cross-sectional Area and Myonuclear Change

The purpose of this study was to investigate the effect of reloading on atrophied muscle and the time course of hypertrophy and regeneration. Forty-nine male Wistar rats were randomly assigned to groups for hindlimb suspension (HS), hindlimb suspension and reloading (R), or control (C0). Rats in the HS group were suspended for 14 days. Rats in the R group were randomly divided into five subgroups for different post-hindlimb-suspension recovery times. Briefly, each subgroup was suspended for 14 days and given 1 day of reloading (R1), 3 days of reloading (R3), 7 days of reloading (R7), 10 days of reloading (R10), or 14 days of reloading (R14). Myonuclear numbers were significantly decreased in the groups with hindlimb suspension and 1 day and 3 days of reloading compared with that in the control group. We focused on the processes of change of mean myofiber cross-sectional area and myonuclear domain size; the degrees of increase of both indexes were limited until 3 days of reloading, and significantly increased after 7 days of reloading. An important finding of the current study was that the processes of muscle hypertrophy and regeneration did not show uniform change. In addition, there were differences in the ratio of increase among the stages of hypertrophy and regeneration. Therefore, consideration of the duration and method of physiotherapeutic intervention for atrophied muscle on the basis of the process of hypertrophy and regeneration is needed to provide more effective physiotherapy.

Effects of intermittent weight-bearing and clenbuterol on disuse atrophy of rat hindlimb muscles

The present study was undertaken to evaluate the effects of intermittent weight-bearing (IWB) combined with β 2-agonist clenbuterol (Cb) medication for suppressing muscle atrophy during progressive disuse atrophy. Male Wistar rats (age: 8weeks, body weight: 232 ± 14 g) were divided into a control group (CON) and an experimental group. The experimental group was further subdivided into a Cb medication group under normal conditions and a hindlimb unweighting (HU) treatment group. The HU treatment group was composed of four groups: HU treatment-only, HU treatment + IWB, HU treatment + Cb medication and HU treatment + IWB + Cb medication. IWB was performed by temporarily removing the suspension device for one hour daily. On Day 14, bilateral soleus muscle (SOL) and extensor digitorum longus muscle (EDL) were extracted. Muscles from the right side were used for the measurement of contractile properties (physiological functional evaluations). Muscles from the left side were used for histochemical and biochemical analysis. During HU, IWB combined with Cb medication worked to preserve the wet weight and relative weight of SOL as compared to CON. Its contractile properties were affected by weight-bearing, while the cross-sectional area of type I fiber and protein concentration were affected by Cb. This combined therapy had marked effects on the morphology of EDL, particularly on the cross-sectional area of type II fiber. The protein concentration and contractile properties of EDL were unaffected by this combined therapy. The effect of a combination of IWB and Cb medication was specific to fiber-type and region. The data suggested that 1) IWB was effective on functional aspects such as contractile properties and useful for physical therapy, 2) Cb medication exerted the atrophy-suppressive effect in morphological parameters and manifested less effect on functional aspects. The results in this study indicated the possibility of elevating the efficacy of IWB by Cb medication in SOL.

Effects of combined stretching and clenbuterol on disuse atrophy in rat soleus muscle

BACKGROUND AND PURPOSE

Clinically, disuse muscle atrophy is often seen among patients who are severely debilited and are on prolonged bed rest. Common physical therapy interventions are not successful in preventing disuse muscle atrophy early in the medical treatment of critically ill patients. In situations such as this, the use of a β 2-adrenergic agonist such as clenbuterol (Cb) may be of benefit in preventing atrophy. Also, recent studies have suggested that stretching is possible in preventing disuse muscle atrophy and the decline in muscle strength. The objective of this study was to evaluate the effects of Cb medication combined with stretching (ST) on rat soleus muscle (SOL) during the progression of disuse muscle atrophy.

SUBJECTS

Thirty-five male Wistar rats were used in this study.

METHODS

The rats were divided into five groups: control (CON), hindlimb-unweighting (HU) only, HU+ST, HU+Cb medication, and HU+ST+Cb groups. The right SOL in stretching groups was maintained a stretched position for one hour daily by passively dorsiflexing the ankle joint under non-anesthesia. The experimental period was 2 weeks.

RESULTS

In the ST group, peak twitch tension per cross-sectional area in soleus muscle was significantly larger than in the Cb group, while there was no significant difference between the CON and ST groups. The conversion of type I to type II fibers that was observed in the Cb group was not recognized in the combined ST and Cb group.

DISCUSSION AND CONCLUSION

Distinct effect of combined stretching and Cb medication was not recognized statistically. The results indicate that Cb affects muscle morphological characteristics while stretching affects contractile properties. These data suggest that a combined ST and Cb intervention considered the type-specificity of muscle fiber may be need more consideration for preventing disuse muscle atrophy and the decline in muscle strength.