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Unaltered aerobic power and endurance following glucocorticoid-induced muscle atrophy.

The present study was undertaken to evaluate whether the muscle atrophy associated with glucocorticoid excess results in a reduction in maximal oxygen uptake (VO2max) and endurance during exercise. Female rats were administered single subcutaneous injections of cortisone acetate (CA) (100 mg X kg-1 b.w.) or the vehicle (1% carboxymethyl cellulose) for 14 consecutive days. The weights of plantaris muscles (which were used as a marker of the atrophy) of CA-treated rats were 27% less than those of plantaris muscles in the vehicle-treated rats. This condition also produced a 12-fold increase in free serum glucocorticoid concentrations (cortisol) but did not alter serum androgen (testosterone) levels. Peak VO2 (ml X kg-1 X min-1) and endurance were greater in CA-treated vs vehicle-treated animals; however, these effects were shown to be a function of body weight loss. Homogenate oxygen uptakes in the presence of pyruvate or palmitate were also similar in slow-twitch soleus, fast-twitch red vastus, and fast-twitch white vastus lateralis muscles between CA- and vehicle-treated groups. These data provide no evidence to demonstrate that the catabolic actions of glucocorticoids in skeletal muscle result in a decrement in work capacity through at least 14 d of treatment.

Animals↗

Interleukin-15 responses to aging and unloading-induced skeletal muscle atrophy.

Interleukin-15 (IL-15) mRNA is constitutively expressed in skeletal muscle. Although IL-15 has proposed hypertrophic and anti-apoptotic roles in vitro, its role in skeletal muscle cells in vivo is less clear. The purpose of this study was to determine if skeletal muscle aging and unloading, two conditions known to promote muscle atrophy, would alter basal IL-15 expression in skeletal muscle. We hypothesized that IL-15 mRNA expression would increase as a result of both aging and muscle unloading and that muscle would express the mRNA for a functional trimeric IL-15 receptor (IL-15R). Two models of unloading were used in this study: hindlimb suspension (HS) in rats and wing unloading in quail. The absolute muscle wet weight of plantaris and soleus muscles from aged rats was significantly less when compared with muscles from young adult rats. Although 14 days of HS resulted in reduced muscle mass of plantaris and soleus muscles from young adult animals, this effect was not observed in muscles from aged animals. A significant aging times unloading interaction was observed for IL-15 mRNA in both rat soleus and plantaris muscles. Patagialis (PAT) muscles from aged quail retained a significant 12 and 6% of stretch-induced hypertrophy after 7 and 14 days of unloading, respectively. PAT muscles from young quail retained 15% hypertrophy at 7 days of unloading but regressed to control levels following 14 days of unloading. A main effect of age was observed on IL-15 mRNA expression in PAT muscles at 14 days of overload, 7 days of unloading, and 14 days of unloading. Skeletal muscle also expressed the mRNAs for a functional IL-15R composed of IL-15Ralpha, IL-2/15R-beta, and -gammac. Based on these data, we speculate that increases in IL-15 mRNA in response to atrophic stimuli may be an attempt to counteract muscle mass loss in skeletal muscles of old animals. Additional research is warranted to determine the importance of the IL-15/IL-15R system to counter muscle wasting.

Aging↗

Juvenile neurogenic muscle atrophy with lysosomal enzyme deficiencies: new disease or variant of mucopolysaccharidosis?

An 18-year-old boy showed childhood onset of mental retardation, neurogenic muscle atrophy with hyperreflexia, Marfan-like features, multiple epiphyseal dysplasia, increased urinary excretion of dermatan sulfate, and decreased lysosomal enzyme activities in beta-galactosidase, beta-glucuronidase, and N-acetyl-beta-D-glucosaminidase. This case may be a new syndrome, the combination of neurogenic muscle atrophy with lysosomal enzyme deficiencies.

Adolescent↗

Isometric resistance exercise fails to counteract skeletal muscle atrophy processes during the initial stages of unloading.

This study tested the hypothesis that an isometric resistance training paradigm targeting the medial gastrocnemius of adult rodents is effective in preventing muscle atrophy during the early stages of hindlimb unloading by maintaining normal activation of the insulin receptor substrate-1 (IRS-1)/phosphoinositide-3 kinase (PI3K)/Akt signaling pathway. This pathway has been shown to simultaneously create an anabolic response while inhibiting processes upregulating catabolic processes involving expression of key enzymes in the ubiquitination of proteins for degradation. The findings show that during the 5 days of unloading 1) absolute medial gastrocnemius muscle weight reduction occurred by approximately 20%, but muscle weight corrected to body weight was not different from normal weight-bearing controls (P < 0.05); 2) normalized myofibril fraction concentration and content were decreased; and 3) a robust isometric training program, known to induce a hypertrophy response, failed to maintain the myofibril protein content. This response occurred despite fully blunting the increases in the mRNA for of atrogin-1, MURF-1, and myostatin, e.g., sensitive gene markers of an activated catabolic state. Analyses of the IRS-1/PI3K/Akt markers indicated that abundance of IRS-1 and phosphorylation state of Akt and p70S6 kinase were decreased relative to normal control rats, and the resistance training failed to maintain these signaling markers at normal regulatory level. Our findings suggest that to fully prevent muscle atrophy responses affecting the myofibril system during unloading, the volume of mechanical stress must be augmented sufficiently to maintain optimal activity of the IRS-1/PI3K/Akt pathway to provide an effective anabolic stimulus on the muscle.

Animals↗

[Skeletal muscle atrophy and fall-related fractures in elderly people].

Skeletal muscle atrophy was developed in elderly people, and it was related to falls and fractures. Muscle weakness decreased physical function and daily activity. Many study demonstrated exercise program prevented fall in elderly. To prevent falls and fractures in elderly, improvement of muscle strength is important.

Accidental Falls↗

Role of afferent input in muscle atrophy.

It is well known that soleus muscle of rat atrophies following spaceflight or hindlimb suspension (Ohira et al., 1992). It is, further, reported that the electromyogram (EMG) of soleus muscle disappears immediately in response to unloading by exposure to actual micro-g environment (Kawano et al., 2002; Leterme and Falempin, 1998) and by hindlimb suspension of rats (Alford et al., 1987; Ohira et al., 2000). However, the EMG level is increased gradually to the control level following 7-10 days of continuous hindlimb suspension (Alford et al., 1987; Ohira, 2000), while muscle atrophy is progressing (Winiarski et al., 1987). We previously reported that reduction of the EMG level of rat soleus in response to actual micro-g environment, created by a parabolic flight of a jet airplane, was closely associated with a decrease of the afferent input recorded at the L5 segmental level of spinal cord (Kawano et al., 2002). However, it is still unclear how the EMG level of soleus muscle adapts to unloading condition. The current study was performed to investigate the responses of soleus EMG and both afferent and efferent neurogram at the L5 segmental level of spinal cord to acute (20 seconds) and chronic (14 days) unloading.

Animals↗

Masseter muscle atrophy after ostectomy of the mandibular angle in rabbits.

In order to get information about changes in the masseter muscle when operations are performed on the mandibular angle area, we classified 70 New Zealand White rabbits into group O (ostectomy) and group D (dissection). In group O we performed unilateral ostectomy of the mandibular angle, while in group D we performed unilateral dissection of the masseter muscle limited to the mandibular angle area. Then we compared morphologic, histologic, and histochemical changes in experimental masseter muscles with those in normal control masseter muscles. We examined 5 rabbits in each group at the following intervals: 1, 2, 4, 6, 8, 12, and 24 weeks. In group D (dissection), there were no remarkable changes at all examinations. In group O (ostectomy), there was a 30 percent decrease in experimental muscle mass compared with control muscle. On examination of muscle fiber types, a decrease in type I fibers and an increase in type IIA and IIB fibers were noticed (p < 0.05). Each experimental muscle fiber became more irregularly and angularly shaped, and mean fiber area also was reduced. Sarcomere lengths of experimental muscle fibers were significantly reduced to 80 percent of control values (p < 0.05) during the first 4 weeks, but after 6 weeks they were lengthened to control values. Collagen and fibrin did not show much difference between experimental and control muscles. All these findings imply that masseter muscle atrophy after ostectomy of the mandibular angle is not due to connective-tissue changes but to individual muscle fiber atrophy accompanied by functional adaptation of sarcomeres and changes in muscle fiber types.

Adaptation, Physiological↗

Temporal alterations in protein signaling cascades during recovery from muscle atrophy.

Currently, the repertoire of cellular and molecular pathways that control skeletal muscle atrophy and hypertrophy are not well defined. It is possible that intracellular regulatory signaling pathways are active at different times during the muscle hypertrophy process. The hypothesis of the given experiments was that cellular signals related to protein translation would be active at early time points of skeletal muscle regrowth, whereas transcriptional signals would be active at later time points of skeletal muscle regrowth. The phosphorylation status of p38 MAPK and JNK increased at the end of limb immobilization but returned to control values at recovery day 3. Transient increases in phosphorylation and in protein concentration occurred during recovery of soleus muscle mass. Phosphorylation of Akt, p70S6k, and signal transducer and activator of transcription 3 (STAT3) peaked on recovery day 3 compared with day 0. Glycogen synthase kinase (GSK)-3beta phosphorylation was increased on the sixth and fifteenth recovery day. In addition, transient peaks in seven protein concentrations occurred at different times of recovery: STAT3, calcineurin A (CaNA), CaNB, and beta4E-BP1 protein concentrations peaked on the third recovery day; p70S6k, STAT3, Akt, and GSK3-beta peaked on the sixth recovery day; and GSK3-beta peaked on the fifteenth recovery day. The apexes of STAT3 and GSK3-beta protein concentrations remained elevated for two recovery time points. Thus the time course of increase in molecules of signaling pathways differed as the young rat soleus muscle regrew from an atrophied state.

Adaptation, Physiological↗

Clinico-electrophysiological correlation of extensor digitorum brevis muscle atrophy in children with charcot-marie-tooth disease 1A duplication.

The purpose of the study is to describe the electrophysiologic abnormalities accounting for the appearance and progression of extensor digitorum brevis (EDB) muscle atrophy in Charcot-Marie-Tooth-disease type 1A (CMT-1A) children. Twelve children with CMT-1A duplication were serially evaluated. Initial ages of clinico-electrophysiological exams ranged from 1 month to 4 years (mean: 2 years) and final ages from 6 to 23 years (mean: 13). All subjects had two or more electrophysiological studies of the peroneal nerve. EDB atrophy was observed in two out of 12 (17%) patients by the age of 5, in eight out of ten (80%) examined between 5 and 9 years, and in all eight (100%) patients who had reached the second decade at the end. Nerve conduction maturation was systematically abnormal, but by age of 5 the mean values of nerve conduction parameters of peroneal nerve did not significantly differ from those in older patients. Compound muscle action potential (CMAP) amplitudes of EDB were reduced in 42% of cases initially and 100% upon last exam. Furthermore, a constant finding throughout the study was progressive attenuation of CMAPs, these becoming unobtainable in four cases. EDB muscle atrophy in CMT-1A children is an age-dependent sign which is accounted for by gradual reduction of the distal peroneal nerve CMAP amplitudes.

Action Potentials↗

The effects of therapeutic electric stimulation on acute muscle atrophy in rats after spinal cord injury.

OBJECTIVE: To evaluate the effects of electric stimulation in preventing acute muscle atrophy after spinal cord transection in rats. DESIGN: A randomized experimental design. SETTING: Animal facilities for experimental medicine. ANIMALS: Fifty-six adult male Wistar rats assigned to control, low-frequency, and high-frequency groups. INTERVENTIONS: The rats were implanted with a percutaneous intramuscular electrode in the vicinity of the peroneal nerve; then the spinal cord was transected in a T9 level. The stimulation frequency was low (20Hz) or high (100Hz). The stimulation cycle was 4 seconds of stimulation every 8 seconds. MAIN OUTCOME MEASUREMENTS: The lesser fiber diameters from type 1, 2A, and 2B muscle fibers were measured. In another assessment, maximal contraction force was measured. The muscle force produced at 20 and 100Hz was expressed as increasing values in tetanic force. RESULTS: Comparison between nonstimulated and stimulated tibialis anterior muscles found that atrophy of type 1 fibers (p < .01) and type 2B fibers (p < .05) at both stimulated levels and of type 2A fibers at 100-Hz level (p < .05) was prevented by therapeutic electric stimulation (TES). There were significant differences in the size of muscle fiber diameter between nonstimulated and stimulated muscles at 100Hz in type 2A and, markedly, in type 2B. The increasing value of muscle force was significantly greater at 100Hz than at 20Hz (p < .05). No significant histologic differences were observed between high- and low-frequency stimulated fibers of any of the 3 muscle types. CONCLUSIONS: Acute atrophy of muscle fibers was more effectively prevented by high-frequency stimulation (100Hz) than by no stimulation or low-frequency stimulation (20Hz). The increasing value of muscle force was significantly greater at high-frequency than low-frequency stimulation, suggesting that the clinical application of high-frequency stimulation in acute spinal cord injury should be studied.

Acute Disease↗

Centrifugal intensity and duration as countermeasures to soleus muscle atrophy.

Mechanical acceleration is a countermeasure that may be employed to prevent atrophy of slow-twitch muscle during non-weight bearing. In the present study, daily centrifugation of rats for different durations (1 or 2 h) and at different gravitational intensities (1.5 or 2.6 G) was used to test whether mechanical acceleration could ameliorate the atrophy of the soleus muscle induced by non-weight bearing (tail-traction model). The soleus muscle atrophied 32% during 7 days of non-weight bearing without countermeasures. Centrifugation treatment did not completely prevent atrophy relative to precontrol wet weight of the soleus muscle. Non-weight-bearing groups receiving 2-h daily treatments of 1, 1.5, or 2.6 G had 48, 56, and 65%, respectively, of the atrophy observed in the non-weight-bearing-only group compared with the precontrol group. No evidence was obtained that centrifugation at 2.6 G was more effective than exposure to 1 or 1.5 G as a countermeasure to non-weight-bearing-induced atrophy of the soleus muscle.

Animals↗

The COX-2 pathway regulates growth of atrophied muscle via multiple mechanisms.

Loss of muscle mass occurs with disease, injury, aging, and inactivity. Restoration of normal muscle mass depends on myofiber growth, the regulation of which is incompletely understood. Cyclooxygenase (COX)-2 is one of two isoforms of COX that catalyzes the synthesis of prostaglandins, paracrine hormones that regulate diverse physiological and pathophysiological processes. Previously, we demonstrated that the COX-2 pathway regulates early stages of myofiber growth during muscle regeneration. However, whether the COX-2 pathway plays a common role in adult myofiber growth or functions specifically during muscle regeneration is unknown. Therefore, we examined the role of COX-2 during myofiber growth following atrophy in mice. Muscle atrophy was induced by hindlimb suspension (HS) for 2 wk, followed by a reloading period, during which mice were treated with either the COX-2-selective inhibitor SC-236 (6 mg x kg(-1) x day(-1)) or vehicle. COX-2 protein was expressed and SC-236 attenuated myofiber growth during reloading in both soleus and plantaris muscles. Attenuated myofiber growth in the soleus was associated with both decreased myonuclear addition and decreased inflammation, whereas neither of these processes mediated the effects of SC-236 on plantaris growth. In addition, COX-2(-/-) satellite cells exhibited impaired activation/proliferation in vitro, suggesting direct regulation of muscle cell activity by COX-2. Together, these data suggest that the COX-2 pathway plays a common regulatory role during various types of muscle growth via multiple mechanisms.

Animals↗

Protective effect of glutamine from glucocorticoid-induced muscle atrophy occurs without alterations in circulating insulin-like growth factor (IGF)-I and IGF-binding protein levels.

We investigated whether the prevention of glucocorticoid-induced muscle atrophy by glutamine infusion is associated with alterations in serum levels of insulin-like growth factor (IGF)-I and its binding proteins (IGFBPs). Hormone (cortisol acetate [CA], 100 mg/kg body wt/day) and vehicle (carboxymethyl cellulose [CMC])-treated female rats were infused with either saline or glutamine (240 mM, 0.75 ml/hr) for a 7-day period. Glutamine infusion prevented over 70% of the skeletal muscle mass loss due to the glucocorticoid injections. Serum IGF-I concentrations, which were measured by radioimmunoassay (RIA) after acid solid-phase extraction of IGFBPs, were not significantly different among groups (range of means: 373-395 ng/ml). Saline/CA treatment resulted in a 2-fold increase in circulating levels of IGFBP-3 (38- to 50-kDa bands from ligand blotting measurements) versus the saline/CMC group. Levels of 30- to 32-kDa bands were increased by approximately 3-fold in the CA-treated rats. Immunoprecipitation studies suggested that the increase in the 30- to 32-kDa binding proteins were not due to elevated levels of IGFBP-1, -2, or -5. None of the treatments significantly modified circulating levels of IGFBP-4 (24 kDa). Glutamine infusion did not reverse the effects of glucocorticoids on circulating levels of 38- to 50- and 30- to 32-kDa IGFBPs. We conclude that the attenuation of glucocorticoid-induced muscle atrophy by glutamine infusion is not associated with changes in circulating levels of IGF-I or IGFBPs.

Animals↗

Skeletal muscle myosin heavy chain expression in rats with monocrotaline-induced cardiac hypertrophy and failure. Relation to blood flow and degree of muscle atrophy.

BACKGROUND: In congestive heart failure (CHF) the skeletal muscle of the lower limbs develops a myopathy characterised by atrophy and shift from the slow to the fast type fibres. The mechanisms responsible for these changes are not clear yet. OBJECTIVES: We investigated the influence of blood flow and degree of muscle atrophy on the myosin heavy chains (MHC) composition of the soleus and extensor digitorum longus (EDL) of rats with right ventricle hypertrophy and failure. METHODS: CHF was induced in 16 rats by injecting 30 mg/kg monocrotaline. Eight animals had the same dose of monocrotaline but resulting in compensated right ventricle hypertrophy. Two age- and diet-matched groups of control animals (nine and five respectively) were also studied. The relative percentage of MHC1 (slow isoform), MHC2a (fast oxidative) and MHC2b (fast glycolytic) was determined by densitometric scan after electrophoretic separation. The relative weights of soleus and EDL (muscle weight/body weight) were taken as an index of muscle atrophy. Skeletal muscle blood flow was measured by injecting fluorescent micropheres. RESULTS: CHF and Control (Con) rats showed similar degree of atrophy both in soleus (0.40 +/- 0.06 vs. 0.44 +/- 0.06 p = NS), and EDL (0.47 +/- 0.04 vs. 0.45 +/- 0.02, p = 0.09). In CHF rats these two muscles showed a statistically significant MHCs redistribution toward the fast type isozymes. In fact in EDL of CHF rats MHC2a was 30.5 +/- 6.1% vs. 35.8 +/- 8.6% of the Con (p < 0.05). MHC2b was however higher (68.5 +/- 6.6% vs. 61.0 +/- 9.6%, p = 0.017). In the soleus of CHF rats MHC1 was decreased (87.6 +/- 3.4% vs. 91.9 +/- 5.2%, p = 0.02), while MHC2a was increased (12.04 +/- 3.5% vs. 7.9 +/- 5.2%; p = 0.028). Similar changes were not found in the muscles of the compensated hypertrophy animals. No correlation was found between MHC pattern and the relative muscle weight in the CHF animals. Soleus blood flow in CHF rats was significantly lower than that of Con (0.11 +/- 0.03 ml/min/g vs. 0.22 +/- 0.03 p < 0.05), while no differences were found in EDL (0.06 +/- 0.02 ml/min/g vs. 0.08 +/- 0.02, p = NS). CONCLUSIONS: In rats with CHF a skeletal muscle myopathy characterised by a shift of the MHCs toward the fast type isoforms occurs. The magnitude of the shift correlates neither with the degree of atrophy, nor with the skeletal muscle blood flow, suggesting that these two factors do not play a pivotal role in the pathogenesis of the myopathy.

Animals↗

Muscle atrophy and histopathology of the soleus in 6-mercaptopurine-treated rats.

In this study, male and female Sprague-Dawley rats were treated neonatally with 6-MP-treatment (2 mg/kg s/c, between 2 and 22 days after birth) and evaluated at six months of age. Compared to the normal controls, the 6-MP-treated male and female rats showed similar sciatic nerve conduction to the soleus. However, there was a significant muscle atrophy (57-60%, P less than 0.01) and a decrease in areas of the type I (42-54%, P less than 0.05) and type II (41-71%, P less than 0.01) muscle fibers. The number of type II fibers declined significantly (7.4-14.8%, P less than 0.05). It is proposed that the soleus muscle atrophy and histopathology in 6-MP-treated rats is unrelated to nerve conduction defects and may be related to growth inhibition caused by an interference of the drug during normal differentiation of muscle fibers.

Animals↗

Dissociated small hand muscle atrophy in aging: the 'senile hand' is a split hand.

The term 'split hand' refers to a pattern of dissociated atrophy of hand muscles and was first described in ALS. We hypothesize that this phenomenon also occurs in 'normal' aging. We investigated healthy subjects of different ages and found a progressive dissociation in atrophy of the hand muscles, as measured with compound muscle action potential amplitudes, with increasing age. Different possible causes of this progressive dissociation are discussed. It might be related to preferential use of thenar muscles in humans, which render these muscles and their motor neurons more susceptible to oxidative stress. In addition, a difference in intrinsic susceptibility to oxidative stress might be involved. The relation between normal age-related muscle loss (sarcopenia) and the pathologic loss in motor neuron disease is discussed.

Adolescent↗

The physiology and biochemistry of skeletal muscle atrophy as a function of age.

The skeletal muscles are an important entity in the proper function of aging animals and humans. Studies have shown that until humans are 60-70 years old, age-related changes in muscle function and structure are relatively small, while after 70 years, these alterations are accelerated considerably. Factors responsible for the "aging" of skeletal muscles are complex and include intrinsic biochemical changes in muscle metabolism, changes in the distribution and size of muscle fibers, and a general loss of muscle mass. In addition, other factors like the control of muscle contraction by the motor neural system and the influence of external conditions such as exercise, immobility, nutrition and others may also contribute to the age-related decrease in muscle functions. Studies have shown that with age there is some loss of peripheral motor neurons, reduction in the number of motor units, alterations in the neuromuscular junctions, and selective denervation of Type II muscle fibers. These findings led to the concept of denervation atrophy of skeletal muscles as one of the major mechanisms for muscle degeneration in old age. However, it should be emphasized that the extent of age-related changes varies from muscle to muscle, and some do not seem to be affected by age. For example, it has been shown recently, in animal studies, that weight-bearing muscles are much more susceptible to senescent processes than non-weight-bearing muscles. More work is needed to clarify the contributions of the various factors, especially the role of muscle training in alleviating the symptoms of age-related muscle atrophy.

Aging↗

Muscle kinematics during isometric contraction: development of phase contrast and spin tag techniques to study healthy and atrophied muscles.

PURPOSE: To develop and compare phase-contrast (PC) and spin-tag (ST) MR imaging techniques for accurate quantification of velocity and displacement distribution in the muscle tendon complex of the lower leg during isometric contractions under in vivo conditions, in healthy subjects and subjects with atrophy. MATERIALS AND METHODS: Techniques were developed to acquire PC and ST dynamic images, gated to the force exerted by a subject during isometric contraction. Algorithms were optimized for correction of phase shading errors. Flow velocity quantification was validated in phantoms and ex vivo rabbit muscles. Trajectories of pixels calculated from PC images were compared with those in ST images. Velocity distributions were determined in healthy muscles, those atrophied by four weeks of suspension, and during physiotherapy-induced recovery. RESULTS: The technique developed allowed acquisition of images retrospectively gated to the isometric contraction performed with the subject in the scanner. Significant phase shading errors in PC images (approximately 3 cm/second over the field of view) were reduced to the background noise level by the correction algorithm. Tissue trajectories calculated from PC images agreed very well with those from ST images both in human and excised animal tissues. Peak velocities in atrophied muscles were significantly lower compared to the preatrophy state but recovered to baseline values after six weeks of therapy. CONCLUSION: We show the feasibility of monitoring muscle velocity and tissue displacement during voluntary contractions in humans under in vivo conditions using MR tissue motion mapping methods. The clinical feasibility of this technique in monitoring atrophied muscle is also demonstrated.

Adult↗