A morphological/biochemical study on the actions of corticosteroids on rat skeletal muscle

Rice Germ Attenuates Chronic Unpredictable Mild Stress-Induced Muscle Atrophy

Chronic stress leads to hypothalamic-pituitary-adrenal axis dysfunction, increasing cortisol levels. Glucocorticoids (GCs) promote muscle degradation and inhibit muscle synthesis, eventually causing muscle atrophy. In this study, we aimed to evaluate whether rice germ supplemented with 30% γ-aminobutyric acid (RG) attenuates muscle atrophy in an animal model of chronic unpredictable mild stress (CUMS). We observed that CUMS raised the adrenal gland weight and serum adrenocorticotropic hormone (ACTH) and cortisol levels, and these effects were reversed by RG. CUMS also enhanced the expression of the GC receptor (GR) and GC-GR binding in the gastrocnemius muscle, which were attenuated by RG. The expression levels of muscle degradation-related signaling pathways, such as the Klf15, Redd-1, FoxO3a, Atrogin-1, and MuRF1 pathways, were enhanced by CUMS and attenuated by RG. Muscle synthesis-related signaling pathways, such as the IGF-1/AKT/mTOR/s6k/4E-BP1 pathway, were reduced by CUMS and enhanced by RG. Moreover, CUMS raised oxidative stress by enhancing the levels of iNOS and acetylated p53, which are involved in cell cycle arrest, whereas RG attenuated both iNOS and acetylated p53 levels. Cell proliferation in the gastrocnemius muscle was reduced by CUMS and enhanced by RG. The muscle weight, muscle fiber cross-sectional area, and grip strength were reduced by CUMS and enhanced by RG. Therefore, RG attenuated ACTH levels and cortisol-related muscle atrophy in CUMS animals.

Magnesium supplementation alleviates corticosteroid-associated muscle atrophy in rats

PURPOSE

Corticosteroid (CS) therapy for infectious and rheumatological diseases showed to decrease serum magnesium (Mg++) level and induce muscle atrophy in patients. The present study investigated the effects of Mg++ supplementation on preventing CS-induced muscle atrophy in an animal model, which provided experimental data for potential clinical translation.

METHODS

Twelve 24-week-old male Sprague-Dawley rats were treated with lipopolysaccharide (LPS) and CS methylprednisolone (MPS) to induce muscle atrophy, with half of the rats also given daily 50 mg/kg Mg++ oral supplementation. Additional six rats without LPS + CS treatments were used as normal controls. After treatment for 6 weeks, serum was collected for Mg++ quantification, animal dual-energy X-ray absorptiometry (DXA) was performed for tissue composition, and the extensor digitorum longus (EDL) was collected for muscle functional test and histology including muscle fiber size, intramuscular fat infiltration and fiber typing. In vitro myotube atrophy model was used to study the in vitro effect associated with in vivo muscle atrophy.

RESULTS

LPS + CS treatments induced hypomagnesemia while the serum Mg++ level was in normal range after Mg++ supplementation. DXA showed 53.0% lower fat percent and 29.7% higher lean mass in LPS + CS + Mg group when compared to LPS + CS group. Muscle functional test showed 22.2% higher specific twitch force and 40.3% higher specific tetanic force in LPS + CS + Mg group when compared to LPS + CS group. Histological analysis showed 4.1% higher proportion of muscle fibers area to total area and 63.6% lower intramuscular fat infiltration in EDL sections in LPS + CS + Mg group when compared to LPS + CS group. LPS + CS + Mg group had 33.0% higher area proportion and 29.4% higher cross-sectional area (CSA) of type IIb muscle fiber. Myoblast culture results showed that Mg++ supplementation group had larger myotube diameter. The mRNA expressions of the muscle atrophy marker genes MuRF1 and MAFbx were lower in Mg++ supplementation group both in vitro and in vivo.

CONCLUSION

The current study demonstrated that Mg++ supplementation successfully alleviated CS-associated muscle atrophy in rats at both functional and morphology levels, indicating a translational potential for patients undergoing CS therapy. This study provided the evidence for the first time that Mg++ supplementation could prevent muscle atrophy-an adverse effect of CS therapy, currently also adopted for treating coronavirus disease 2019 (COVID-19).

Corticotropin releasing factor-overexpressing mouse is a model of chronic stress-induced muscle atrophy

Chronic stress and continually high glucocorticoid levels can induce muscle atrophy. Unfortunately, there is a lack of appropriate animal models for stress-induced muscle atrophy research. Corticotropin releasing factor-overexpressing (CRF-OE) mice are a transgenic model of chronic stress that exhibit increased plasma corticosterone levels and Cushing’s syndrome; however, the skeletal muscle pathology of the CRF-OE mouse has not been well studied. We observed that male, 19-week-old CRF-OE mice had significantly lower skeletal muscle mass, average cross-sectional myofiber area, and total muscle protein content than their wild type (WT) littermates. Muscle function determined by grip strength, wire-hang, and open field tests showed that 19-week-old male CRF-OE mice had impaired physical ability. Additionally, the skeletal muscles of CRF-mice exhibited decreased expression of factors involved in the IGF-1/AKT/mTOR protein synthesis pathway and increased ubiquitin proteasome pathway activity compared to the WT control mice. In conclusion, 19-week-old CRF-OE mice display numerous features of muscle atrophy and thus serve as a model for investigating stress-induced muscle atrophy and interventions to target the deleterious effects of stress on skeletal muscle.

Quantitative ultrasound of muscle can detect corticosteroid effects

OBJECTIVES

In this study, we sought to determine whether quantitative ultrasound (QUS) could detect the impact of corticosteroids on muscle in the absence of frank weakness.

METHODS

QUS was performed on selected limb muscles of 20 brain tumor patients treated with dexamethasone and 30 healthy controls. Echointensity was quantified using gray scale level (GSL) analysis and compared between groups; correlation to corticosteroid exposure was also performed.

RESULTS

Average 4-muscle GSL (±standard deviation) was greater in patients compared to controls (35.5 ± 5.61 arbitrary units (AU) versus 30.4 ± 4.17 AU, p = 0.001), with the greatest differences in tibialis anterior. Average muscle GSL also correlated to length of corticosteroid therapy (rho = 0.52, p = 0.01).

CONCLUSIONS

These findings suggest that QUS may be able to quantify skeletal muscle alterations associated with chronic corticosteroid use. Further study of this approach is warranted.

SIGNIFICANCE

The findings of this study may provide a tool to evaluate corticosteroid myopathy.

Skeletal Muscle Response to Deflazacort, Dexamethasone and Methylprednisolone

Glucocorticoids represent some of the most prescribed drugs that are widely used in the treatment of neuromuscular diseases, but their usage leads to side effects such as muscle atrophy. However, different synthetic glucocorticoids can lead to different muscle effects, depending upon its chemical formulation. Here, we intended to demonstrate the muscle histologic and molecular effects of administering different glucocorticoids in equivalency and different dosages. Methods: Seventy male Wistar rats distributed into seven groups received different glucocorticoids in equivalency for ten days or saline solution. The study groups were: Control group (CT) saline solution; dexamethasone (DX) 1.25 or 2.5 mg/kg/day; methylprednisolone (MP) 6.7 or 13.3mg/kg/day; and deflazacort (DC) 10 or 20 mg/kg/day. At the end of the study, the animals were euthanized, and the tibialis anterior and gastrocnemius muscles were collected for metachromatic ATPase (Cross-sectional area (CSA) measurement), Western blotting (protein expression of IGF-1 and Ras/Raf/MEK/ERK pathways) and RT-PCR (MYOSTATIN, MuRF-1, Atrogin-1, REDD-1, REDD-2, MYOD, MYOG and IRS1/2 genes expression) experiments. Results: Muscle atrophy occurred preferentially in type 2B fibers in all glucocorticoid treated groups. DC on 10 mg/kg/day was less harmful to type 2B fibers CSA than other doses and types of synthetic glucocorticoids. In type 1 fibers CSA, lower doses of DC and DX were more harmful than high doses. DX had a greater effect on the IGF-1 pathway than other glucocorticoids. MP more significantly affected P-ERK1/2 expression, muscle fiber switching (fast-to-slow), and expression of REDD1 and MyoD genes than other glucocorticoids. Compared to DX and MP, DC had less of an effect on the expression of atrogenes (MURF-1 and Atrogin-1) despite increased MYOSTATIN and decreased IRS-2 genes expression. Conclusions: Different glucocorticoids appears to cause muscle atrophy affecting secondarily different signaling mechanisms. MP is more likely to affect body/muscles mass, MEK/ERK pathway and fiber type transition, DX the IGF-1 pathway and IRS1/2 expression. DC had the smallest effect on muscle atrophic response possibly due a delayed timing on atrogenes response.

Role of Myofibrillar Protein Catabolism in Development of Glucocorticoid Myopathy: Aging and Functional Activity Aspects

Muscle weakness in corticosteroid myopathy is mainly the result of the destruction and atrophy of the myofibrillar compartment of fast-twitch muscle fibers. Decrease of titin and myosin, and the ratio of nebulin and MyHC in myopathic muscle, shows that these changes of contractile and elastic proteins are the result of increased catabolism of the abovementioned proteins in skeletal muscle. Slow regeneration of skeletal muscle is in good correlation with a decreased number of satellite cells under the basal lamina of muscle fibers. Aging causes a reduction of AMP-activated protein kinase (AMPK) activity as the result of the reduced function of the mitochondrial compartment. AMPK activity increases as a result of increased functional activity. Resistance exercise causes anabolic and anticatabolic effects in skeletal muscle: muscle fibers experience hypertrophy while higher myofibrillar proteins turn over. These changes are leading to the qualitative remodeling of muscle fibers. As a result of these changes, possible maximal muscle strength is increasing. Endurance exercise improves capillary blood supply, increases mitochondrial biogenesis and muscle oxidative capacity, and causes a faster turnover rate of sarcoplasmic proteins as well as qualitative remodeling of type I and IIA muscle fibers. The combination of resistance and endurance exercise may be the fastest way to prevent or decelerate muscle atrophy due to the anabolic and anticatabolic effects of exercise combined with an increase in oxidative capacity. The aim of the present short review is to assess the role of myofibrillar protein catabolism in the development of glucocorticoid-caused myopathy from aging and physical activity aspects.

Proximal myopathy: diagnostic approach and initial management

Proximal myopathy presents as symmetrical weakness of proximal upper and/or lower limbs. There is a broad range of underlying causes including drugs, alcohol, thyroid disease, osteomalacia, idiopathic inflammatory myopathies (IIM), hereditary myopathies, malignancy, infections and sarcoidosis. Clinical assessment should aim to distinguish proximal myopathy from other conditions that can present similarly, identify patients who need prompt attention, like those with cardiac, respiratory or pharyngeal muscle involvement, and determine underlying cause of myopathy. Initial evaluation should include simple tests, like creatine kinase, thyroid function and (25)OH vitamin D levels, but further evaluation including neurophysiological studies, muscle imaging and muscle biopsy should be considered for patients in whom no toxic, metabolic or endocrine cause is found, and in those with clinical features suggestive of inflammatory or hereditary myopathy. Additionally, screening for malignancy and testing for anti-Jo1 antibody is indicated for selected patients with IIM. Management depends on underlying cause, and includes measures, such as removal of offending agent, correction of endocrine or metabolic problem, corticosteroids and immunosuppressive therapy for IIM, and physical therapy, rehabilitation and genetic counselling for muscular dystrophies.

Corticosteroids in brain cancer patients: benefits and pitfalls

Glucocorticoids have been used for decades in the treatment of brain tumor patients and belong to the most powerful class of agents in reducing tumor-associated edema and minimizing side effects and the risk of encephalopathy in patients undergoing radiation therapy. Unfortunately, corticosteroids are associated with numerous and well-characterized adverse effects, constituting a major challenge in patients requiring long-term application of corticosteroids. Novel antiangiogenic agents, such as bevacizumab (Avastin®), which have been increasingly used in cancer patients, are associated with significant steroid-sparing effects, allowing neuro-oncologists to reduce the overall use of corticosteroids in patients with progressive malignant brain tumors. Recent experimental studies have revealed novel insights into the mechanisms and effects of corticosteroids in cancer patients, including modulation of tumor biology, angiogenesis and steroid-associated neurotoxicity. This article summarizes current concepts of using corticosteroids in brain cancer patients and highlights potential pitfalls in their effects on both tumor and neural progenitor cells.

Time course expression of Foxo transcription factors in skeletal muscle following corticosteroid administration

Increased expression of forkhead box O (Foxo) transcription factors were reported in cultured myotubes and mouse limb muscle with corticosteroid (CS) treatment. We previously reported that administration of CS to rats resulted in muscle fiber atrophy only by day 7. The aim of this study, therefore, was to evaluate the time-course changes in the expression of Foxo transcription factors and muscle-specific ubiquitin E3 ligases in rat limb muscle following CS administration. Triamcinolone (TRI; 1 mg x kg(-1) x day(-1) im) was administered for 1, 3, or 7 days. Control (CTL) rats were given saline. Muscle mRNA was analyzed by real-time RT-PCR. Compared with CTL, body weights of TRI-treated animals decreased by 3, 12, and 21% at days 1, 3, and 7, respectively. Muscle IGF-1 mRNA levels decreased by 33, 65, and 58% at days 1, 3, and 7 in TRI-treated rats compared with CTL. Levels of phosphorylated Akt were 28, 50, and 36% lower in TRI animals at these time points. Foxo1 mRNA increased progressively by 1.2-, 1.4-, and 2.5-fold at days 1, 3, and 7 in TRI animals. Similar changes were noted in the expression of Foxo3a mRNA (1.3-, 1.4-, and 2.6-fold increments). By contrast, Foxo4 mRNA was not significantly changed in TRI animals. With TRI, muscle atrophy F box/Atrogin-1 increased by 1.8-, 4.1-, and 7.5-fold at days 1, 3, and 7 compared with CTL rats. By contrast, muscle RING finger 1 increased only from day 7 (2.7-fold). Gradual reduction in IGF-I expression with TRI over the time series paralleled that of Akt. These findings are consistent with a progressive stimulus to muscle protein degradation and the need to process/remove disassembled muscle proteins via the ubiquitin-proteasome system. Elucidating the dynamic catabolic responses to CS challenge is important in understanding the mechanisms underlying muscle atrophy and therapeutic measures to offset this.

The effect of high glucocorticoid administration and food restriction on rodent skeletal muscle mitochondrial function and protein metabolism

Background

Glucocorticoids levels are high in catabolic conditions but it is unclear how much of the catabolic effects are due to negative energy balance versus glucocorticoids and whether there are distinct effects on metabolism and functions of specific muscle proteins.

Methodology/Principal Findings

We determined whether 14 days of high dose methylprednisolone (MPred, 4 mg/kg/d) Vs food restriction (FR, food intake matched to MPred) in rats had different effects on muscle mitochondrial function and protein fractional synthesis rates (FSR). Lower weight loss (15%) occurred in FR than in MPred (30%) rats, while a 15% increase occurred saline-treated Controls. The per cent muscle loss was significantly greater for MPred than FR. Mitochondrial protein FSR in MPred rats was lower in soleus (51 and 43%, respectively) and plantaris (25 and 55%) than in FR, while similar decline in protein FSR of the mixed, sarcoplasmic, and myosin heavy chain occurred. Mitochondrial enzymatic activity and ATP production were unchanged in soleus while in plantaris cytochrome c oxidase activity was lower in FR than Control, and ATP production rate with pyruvate + malate in MPred plantaris was 28% lower in MPred. Branched-chain amino acid catabolic enzyme activities were higher in both FR and MPred rats indicating enhanced amino acid oxidation capacity.

Conclusion/Significance

MPred and FR had little impact on mitochondrial function but reduction in muscle protein synthesis occurred in MPred that could be explained on the basis of reduced food intake. A greater decline in proteolysis may explain lesser muscle loss in FR than in MPred rats.

Strength and endurance of the respiratory and handgrip muscles after the use of flunisolide in normal subjects

OBJECTIVE

To evaluate the effects of the inhaled flunisolide upon the strength and endurance of the respiratory and peripheral muscles of normal subjects.

DESIGN

A randomized, double blind and placebo-controlled study.

SETTING

A university-affiliated teaching hospital.

PARTICIPANTS

Thirteen normal volunteers selected from a graduation course.

INTERVENTION

Subjects were randomly allocated to receive a placebo or corticosteroid (flunisolide) to be inhaled twice a day for 4 weeks. After 2 weeks of a washout period, subjects who were receiving the placebo, received flunisolide and vise versa for another 4-week period.

MEASUREMENTS AND RESULTS

Spirometry was used to define the volunteers as being normal in terms of pulmonary function. During the study, subjects performed tests of respiratory muscle function (strength and endurance), measurements of handgrip strength and endurance and anthropometric measurements. Muscle strength was measured each week while muscle endurance was measured every 2 weeks. There was no significant difference in the maximal inspiratory and expiratory pressure and handgrip strength during weeks 1-4 when the subjects used either flunisolide or placebo. However, we observed an increase in the endurance time of the respiratory and handgrip muscles in the 4th week of both flunisolide and placebo use, what may be considered due to a learning effect.

CONCLUSION

Inhalation of flunisolide by normal subjects for 1 month does not cause any acute or clinically perceived effect in the peripheral or respiratory muscles.

ICU-Acquired Weakness

Observational studies of patients receiving prolonged mechanical ventilation and other forms of critical care support have determined acquired neuromuscular disorders to be extremely common. Early studies used electrophysiologic investigations to diagnose critical illness polyneuropathy (CIP) and muscle biopsy to confirm critical illness myopathy (CIM). More recent approaches seek to obviate these invasive techniques and build on a standardized bedside neuromuscular examination to identify patients with acquired weakness syndromes. Serial examination in the alert patient may serve as a reasonable prognosticator for most patients. The importance of ICU-acquired weakness syndromes is supported by the observation that muscle wasting and weakness are among the most prominent long-term complications of survivors of ARDS. In addition, a strong association appears to exist between acquired weakness and protracted ventilator dependence, an important determinant of ICU length of stay. Multivariate analysis has identified several risk factors associated with increased incidence for ICU-acquired weakness, including severe systemic inflammation, medications (specifically, corticosteroids and neuromuscular blocking agents), glycemic control, and immobility. We advocate an approach to this common syndrome that identifies risk factors early in the hope of minimizing their impact.

Corticosterone, locomotor performance, and metabolism in side-blotched lizards (Uta stansburiana)

Elevated levels of circulating corticosterone commonly occur in response to stressors in wild vertebrates. A rise in corticosterone, usually in animals of subordinate rank, results in a variety of effects on behavior and physiology. Behavioral and physiological responses to short-term increases in corticosterone are well studied. In contrast, the effects of chronic elevated levels of corticosterone are poorly understood, particularly in lizards. Here, we examined the long-term effects of exogenous corticosterone on locomotor performance, resting and active metabolic rate, and hematocrit in male side-blotched lizards Uta stansburiana. Corticosterone implantation resulted in higher levels of stamina relative to sham-surgery controls. In addition, lizards with elevated corticosterone exhibited lower resting metabolic rates relative to controls. Corticosterone had no effect on peak activity metabolism but did result in faster recovery times following exhaustive exercise. We suggest that elevated levels of corticosterone in response to dominance interactions promote enhanced locomotor abilities, perhaps as a flight response to avoid agonistic interactions. Furthermore, stressed lizards are characterized by lower resting metabolic rates, which may serve as strategy to conserve energy stores and enhance survival.

Molecular and cellular defects of skeletal muscle in an animal model of acute quadriplegic myopathy

Muscle denervation and concomitant high-dose dexamethasone treatment in rodents produces characteristic pathologic features of severe muscle atrophy and selective myosin heavy filament (MyHC) depletion, identical to those seen in acute quadriplegic myopathy (AQM), also known as critical illness myopathy. We tested the hypothesis that defective pre-translational processes contribute to the atrophy and selective MyHC depletion in this model. We examined the effects of combined glucocorticoid-denervation treatment on MyHC and actin mRNA populations; we also studied mRNA expression of the myogenic regulatory factors (MRFs), primary transcription factors for MyHC. Adult female rats were subjected to proximal sciatic denervation followed by high-dose dexamethasone (DD) treatment (5 mg/kg body weight daily) for 7 days. Disease controls included rats treated with denervation alone (DN) or dexamethasone alone (DX). At 1 week the plantaris atrophied by approximately 42% in DD muscles. DD treatment resulted in selective MyHC protein depletion; actin protein concentration was not significantly changed. Despite an increase in total RNA concentration in DN and DD muscles, MyHC and actin mRNA concentrations were significantly decreased in these muscles. MyHC mRNA showed a significantly more extensive depletion relative to actin mRNA in DD muscles. Glucocorticoid treatment did not influence a denervation-induced increase in the mRNA expression of the MRFs. We conclude that a deleterious interaction between glucocorticoid and denervation treatments in skeletal muscle is responsible for pre-translational defects that reduce actin and MyHC mRNA substrates in a disproportionate fashion. The resultant selective MyHC depletion contributes to the severe muscle atrophy.

Apoptosis of skeletal muscle on steroid-induced myopathy in rats

Apoptotic cell death of differentiated skeletal muscle has been reported in an experimental steroid-induced myopathy of rats. To investigate the underlying molecular changes in the apoptosis of skeletal muscle, in situ end labeling (ISEL), Fas expression, and Western blot analysis for apoptosis-related proteins in the soleus muscle of triamcinolone acetonide (TA)-induced myopathy of rats were studied. Proteins for Western blot analysis included Fas-associated death domain (FADD) and caspase 8 for extrinsic pathway, as well as Bcl-2, Bcl-XL, Bax, Bad, Bid, Akt, p-Akt, and caspase 9 for intrinsic pathway. ISEL-positive myonuclei in TA-treated rats were 1.8 +/- 1.2%, whereas Fas-positive muscle fibers were 4.5 +/- 2.0%. One-fourth of Fas-positive muscle fibers had ISEL-positive myonuclei. Levels of FADD, Bax, Bad, and Bid were substantially increased in the TA-induced myopathy group, whereas Bcl-2, Bcl-XL, Akt, p-Akt, and caspase 9 did not change between control and myopathy groups. Caspase 8 activity increased in the myopathy group. These findings indicate that apoptosis of skeletal muscle in TA-induced myopathy may be triggered by Fas-Fas ligand signals and promoted mainly by overexpression of the pro-apoptotic molecules of FADD and caspase 8 involving the extrinsic pathway. The apoptotic process presented in this study supports a direct, nongenomic effect of a glucocorticoid on cellular membranes leading to cellular apoptosis rather than genomic effector mechanism of steroid hormone mediated by cytosolic steroid receptors.

Effect of short-term prednisone use on blood flow, muscle protein metabolism, and function

Glucocorticoids can cause muscle atrophy, but the effect on muscle protein metabolism in humans has not been adequately studied to know whether protein synthesis, breakdown, or both are altered. We tested the effect of 6 d of oral prednisone (Pred, 0.5 mg/kg.d) on muscle protein metabolism and function. Six healthy subjects (three men/three women, 22-41 yr) completed two trials (randomized, double-blind, cross-over) with Pred and placebo. Fasting glucose, insulin, IGF-I, and glucagon were higher on Pred vs. placebo, whereas IGF-II and IGF binding protein-1 and -2 were lower. Whole-body amino acid fluxes, blood urea nitrogen, and urinary nitrogen loss were not statistically different between trials. Leg blood flow was 25% lower on Pred leading to 15-30% lower amino acid flux among the artery, vein, and muscle. However, amino acid net balance and rates of protein synthesis and breakdown were unchanged, as were synthesis rates of total mixed, mitochondrial, sarcoplasmic, and myosin heavy chain muscle proteins. Muscle mitochondrial function, muscle strength, and resting energy expenditure were also unchanged. These results demonstrate that a short-term moderate dose of prednisone affects glucose metabolism but has no effect on whole-body or leg muscle protein metabolism or muscle function.

Influence of corticosteroids on myonuclear domain size in the rat diaphragm muscle

Skeletal muscle fibers are multinucleated. Each myonucleus regulates gene products and protein expression in only a restricted portion of the muscle fiber, the myonuclear domain (MND). In the rat diaphragm muscle (DIAm), corticosteroid (CoS) treatment causes atrophy of fibers containing myosin heavy chain (MHC): MHC2X and/or MHC2B. We hypothesized that DIAm fiber MND size is maintained during CoS-induced atrophy. Adult male rats received methylprednisolone for 11 days at 1 (CoS-Low, n = 8) or 8 mg·kg−1·day−1 (CoS-High, n = 8). Age-matched (CTL-AgeM, n = 8), sham-operated (SHAM-AgeM, n = 8), and weight-matched (CTL-WtM, n = 8) animals served as controls. In single DIAm fibers, cross-sectional area (CSA), MND size, and MHC expression were determined. Fiber CSA and MND size were similar in CTL-AgeM and SHAM-AgeM groups. Only fibers containing MHCslow or MHC2A displayed smaller CSA in CTL-WtM than in CTL-AgeM and SHAM-AgeM groups, and MND size was reduced in all fibers. Thus fibers containing MHCslow and MHC2A maintain the number of myonuclei, whereas MHC2X or MHC2B fibers show loss of myonuclei during normal muscle growth. Both CoS groups displayed smaller CSA and MND size than CTL-AgeM and SHAM-AgeM groups. However, compared with CTL-WtM DIAm fibers, only fibers containing MHC2X or MHC2B displayed reduced CSA and MND size after CoS treatment. Thus little, if any, loss of myonuclei was associated with CoS-induced atrophy of MHC2X or MHC2B DIAm fibers. In summary, MND size does not appear to be regulated during CoS-induced DIAm atrophy.

Myosin heavy chain composition of different skeletal muscles in Large White and Meishan pigs1

Four major sarcomeric myosin heavy chains (MyHC) (i.e., I, IIa, IIx, and IIb) are expressed in pig skeletal muscle during postnatal development. The objective of the current study was to compare MyHC composition at mRNA and protein levels in LM, a fast-twitch glycolytic muscle, and rhomboideus (RM), a mixed slow- and fast-twitch oxido-glycolytic muscle, between two pig breeds exhibiting dramatic differences in postnatal muscle growth and meat quality. Eight Large White (LW) and eight Meishan (MS) females were fed under the same standard conditions, and slaughtered at an average BW of 62 kg (131 and 142 d in LW and MS pigs, respectively). In addition to conventional fiber typing by histoenzymology, MyHC composition was analyzed by combining immunocytochemistry, in situ hybridization, and a newly developed real-time PCR assay. Enzyme activities of lactate dehydrogenase, citrate synthase, and beta-hydroxy-acyl-CoA-dehydrogenase were used as markers of glycolytic, oxidative and beta-oxidation capacities, respectively. Results showed that conventional fiber typing in three classes by histoenzymology was insufficient in LM. For the first time, four monoclonal antibodies specific of each MyHC isoform, working in immunocytochemistry, were used. Our results are consistent with the sequential I<-->IIa<-->IIx<-->IIb MyHC transition rule. Breed effect on MyHC composition differed between muscle types. In LM of MS pigs, a shift from IIb to IIx, and to a lesser extent, to IIa, occurred without affecting type I MyHC. In RM, where IIb is absent, a shift from IIx to type I occurred, with a slight decrease in the IIa isoform. Effects were very similar at the mRNA and protein levels, suggesting a transcriptional regulation. In both muscles, MS pigs exhibited a decrease in the relative fiber type specific expression of the fastest isoform (i.e., IIb in LM and IIx in RM). The shift toward a slower phenotype in MS pigs was consistent with a less glycolytic and more oxidative metabolism, potentially using more lipids as fuel. A dramatic increase in cross-sectional area of type I fibers in RM (+27%) and a decrease in that of the fastest IIb fibers in LM (-25%) were observed in MS pigs. Overall, interpretation of earlier data regarding muscle fiber type has been flawed by inaccurate fiber typing in most pig skeletal muscles.

Insulin-like growth factor I prevents corticosteroid-induced diaphragm muscle atrophy in emphysematous hamsters

The aim of this study was to evaluate whether recombinant human insulin-like growth factor I (rhIGF-I) could attenuate or prevent diaphragm (DIA) fiber atrophy with corticosteroid (CS) administration to emphysematous (EMP) hamsters. DIA muscle IGF-I responses to CS administration with and without exogenous rhIGF-I administration were evaluated. Three groups were studied: 1) EMP; 2) EMP + triamcinolone (T; 0.4 mg.kg-1.day-1 im); and 3) EMP + T + IGF-I (600 microg/day by constant infusion). After 4 wk, the DIA was analyzed histochemically and biochemically (IGF-I mRNA levels by RT-PCR and endogenous and exogenous IGF-I peptide levels immunochemically). Body weights of EMP-T progressively decreased, while those of EMP and EMP-T-IGF-I remained stable despite similarly reduced food intake in both T groups. DIA weight was reduced with T but preserved with rhIGF-I infusion. DIA fiber proportions were similar among the groups. The cross-sectional areas of types I, IIa, and IIx fibers were reduced (17 to 31%) with T administration but unchanged with rhIGF-I infusion. DIA IGF-I mRNA levels were similar across all groups. By contrast, the endogenous DIA IGF-I levels were reduced (41%) in the EMP-T-IGF-I animals. Total DIA IGF-I levels (endogenous + exogenous) were still significantly reduced. IGF-I immunoreactivity confirmed this reduction in all DIA fibers. We conclude that DIA fiber atrophy with T was completely prevented by exogenous rhIGF-I administration. This effect was likely mediated by the pharmacological influences of exogenously administered rhIGF-I. We speculate that this results from increased bioavailability of free IGF-I to react with muscle receptors. Reduced endogenous IGF-I levels in the DIA likely reflect a negative-feedback influence. These results may have important clinical implications for treatment options to offset the adverse effects of CS on the respiratory muscles in patients with chronic lung disorders.

Adverse and beneficial functions of proteolytic enzymes in skeletal muscle. An overview

Proteolytic enzymes (proteases) comprise a family of enzymes which hydrolyse protein or peptide substrates in the generalised process of intracellular protein degradation, a process essential for the normal functioning of all cells. Proteases may also have a wide range of additional functions, including metabolic control of physiologically active oligopeptides or precursor protein forms, antigen presentation/recognition by the major histocompatibility complex in the cellular immune response, as well as in digestion, blood clotting, complement activation, etc. In this article, the nomenclature and classification of proteolytic enzymes in skeletal muscle, and their role in normal muscle physiological processes have been reviewed, including exercise, muscle development and ageing. Although proteases play an important role in normal muscle functioning, in pathological situations the enzymes may themselves be regarded as 'toxic agents' in terms of their damaging effects on muscle tissue. Muscle damage resulting from inappropriate activity of proteolytic enzymes in muscle wasting associated with muscular dystrophies, denervation atrophy, inflammatory myopathies, cancer, sepsis, diabetes and alcoholism have been reviewed. In addition, evidence that the adverse effects of drugs known to induce muscle wasting, such as corticosteroids, (or beneficial effects of growth promoting drugs) may be mediated via proteolytic enzymes is also reviewed.

Performance and physiologic adaptations to resistance training

Weight lifting, or resistance training, is a potent stimulus to the neuromuscular system. Depending on the specific program design, resistance training can enhance strength, power, or local muscular endurance. These improvements in performance are directly related to the physiologic adaptations elicited through prolonged resistance training. Optimal resistance training programs are individualized to meet specific training goals. When trained properly (i.e., similar intensity and volume), these functional and physiologic adaptations are similarly impressive among women and the aged as they are among young men. Yet, in contrast to relative measurements, sex and age differences exist in the absolute magnitude of adaptation. Of equal importance, perhaps most notably among the elderly, are the important health benefits that may also be derived from resistance training. For example, bone density, insulin sensitivity, and co-morbidities associated with obesity can be effectively managed with resistance exercise when it is conducted on a regular basis. The extent of the functional and health benefits to be accrued from resistance training depend on factors such as initial performance and health status, along with the specification of program design variables such as frequency, duration, intensity, volume, and rest intervals.

Fas mediates apoptosis in steroid-induced myopathy of rats

Recently, apoptotic cell death has been reported in differentiated skeletal muscle, where apoptosis was generally assumed not to occur. To investigate whether apoptosis may contribute to the steroid-induced myopathy, rats treated with triamcinolone acetonide (TA) for 9 days were sacrificed for detecting apoptosis by in situ end-labelling (ISEL) and DNA electrophoresis in soleus muscles. Immunohistochemical stainings of Fas antigen and p53 protein were performed to examine whether apoptosis-related proteins were present in the myopathy. Muscle fibre necrosis and apoptotic myonuclei appeared in soleus muscles following administration of TA, while control muscles showed no evidences for apoptosis. Fas antigen was not detected in control muscles, but expressed in soleus muscles of steroid-induced myopathy. Some of the Fas antigen-expressing muscle fibres were positive for ISEL. p53 Protein was not detected in any muscle fibres. These findings indicate that TA can induce apoptosis in differentiated skeletal muscles, and Fas antigen might be partly related to apoptotic muscle death in steroid-induced myopathy.

Induction of a catabolic state in rats by dexamethasone: dose or time dependency?

BACKGROUND

Daily injections of dexamethasone (DEX) given to adult rats are a recognized but nonstandardized model of stress. The aim of this work was to establish a reproducible and accurate model of stress in adult rats by chronic injection of DEX in order to standardize it. For this purpose, the effect of the duration of treatment and the effect of DEX dose were tested. To help understand the mechanisms of the catabolic effect of DEX, the study was extended to the metabolism of glutamine (GLN). In experiment 1, 60 male Sprague-Dawley rats (3 months old) were divided into 8 groups of 6 rats: groups G3, G5, G7, and G9 received 1.50 mg/kg/d of DEX by intraperitoneal (i.p.) injection for 3, 5, 7, or 9 days, respectively. Groups G3PF, G5PF, G7PF, or G9PF were pair-fed to groups G3, G5, G7, or G9, respectively. Group AL (n = 12) was healthy rats fed ad libitum.

RESULTS

In treated rats, nitrogen balance reached its lowest value at day 5. After 9 days treatment by DEX, the catabolic state was reduced. An increase in GLN-synthetase activity and a decrease in muscle GLN content were related to DEX per se not to DEX-induced anorexia. In experiment 2, 25 rats were divided into 5 groups of 5 animals. Groups G0.75, G1.50, and G2.50 received 0.75, 1.50, and 2.50 mg/kg/d, respectively, of DEX by i.p. injection for 5 days. Group PF was pair-fed to group G2.50 and group AL was control rats.

RESULTS

DEX induced a decrease in nitrogen balance that was dose-independent. GLN-synthetase activity was increased maximally in gastrocnemius by 0.75 mg/kg.

CONCLUSIONS

Five days of treatment by DEX and a dose of 0.75 mg/kg/d induced a marked catabolic state.

Growth hormone and insulin-like growth factor-I therapy promote protein deposition and growth in dexamethasone-treated piglets

BACKGROUND

Dexamethasone treatment facilitates the weaning of premature infants from mechanical ventilation but impairs protein homeostasis, lean tissue deposition, and growth. The current study was conducted to investigate whether dexamethasone mediates these effects by reducing protein synthesis or elevating protein breakdown, and whether adjuvant growth hormone+/-insulin-like growth factor-I therapy can attenuate such effects.

METHODS

Piglets (n = 24) were randomized to placebo, a tapered course of dexamethasone (0.5, 0.3, 0.2 mg/kg per day for 5, 5 and 4 days each, respectively), dexamethasone + growth hormone 0.1 mg/kg per day, or dexamethasone + growth hormone + insulin-like growth factor-I 0.1 mg/kg per day for 14 days. On day 13, 15N-glycine was administered as a single oral dose, and urine was collected at timed intervals during the subsequent 48 hours.

RESULTS

Total urinary N and cumulative 15N excretion were higher in all dexamethasone groups than in control subjects. Protein synthesis was suppressed, whereas protein breakdown was unaltered by dexamethasone. Adjunctive growth hormone+/-insulin-like growth factor-I therapy enhanced protein synthesis, but only combined therapy improved net protein gain compared with dexamethasone alone. Higher circulating insulin-like growth factor-I may have mediated the greater net protein gain. Blood urea nitrogen was elevated in all dexamethasone-treated groups at days 6 and 11 but was normalized by day 15 with adjunctive growth hormone+/-insulin-like growth factor-I. From a functional perspective, both adjunctive growth hormone and growth hormone+/-insulin-like growth factor-I partially attenuated the dexamethasone-induced reduction in weight and length gain but not in whole body lean and fat mass.

CONCLUSION

Adjunctive growth hormone+/-insulin-like growth factor-I therapy partially reverses the dexamethasone-induced reduction in protein synthesis, resulting in improved growth when given concurrently with a low tapering dose of dexamethasone.

Kinetic impairment of nitrogen and muscle glutamine metabolisms in old glucocorticoid-treated rats

Aged rats are more sensitive to injury, possibly through an impairment of nitrogen and glutamine (Gln) metabolisms mediated by glucocorticoids. We studied the metabolic kinetic response of adult and old rats during glucocorticoid treatment. The male Sprague-Dawley rats were 24 or 3 mo old. Both adult and old rats were divided into 7 groups. Groups labeled G3, G5, and G7 received, by intraperitoneal injection, 1.50 mg/kg of dexamethasone (Dex) for 3, 5, and 7 days, respectively. Groups labeled G3PF, G5PF, and G7PF were pair fed to the G3, G5, or G7 groups and were injected with an isovolumic solution of NaCl. One control group comprised healthy rats fed ad libitum. The response to aggression induced specifically by Dex (i.e., allowing for variations in pair-fed controls) appeared later in the aged rats (decrease in nitrogen balance from day 1 in adults but only from day 4 in old rats). The adult rats rapidly adapted to Dex treatment, whereas the catabolic state worsened until the end of treatment in the old rats. Gln homeostasis was not maintained in the aged rats; despite an early increase in muscular Gln synthetase activity, the Gln pool was depleted. These results suggest a kinetic impairment of both nitrogen and muscle Gln metabolisms in response to Dex with aging.

Alpha and beta glucocorticoid receptor mRNA expression in skeletal muscle

The aim of the present study was to investigate the occurrence and autoregulation of both glucocorticoid receptor mRNAs in rat gastrocnemius muscle. The expression of both receptor forms was studied 1, 4 or 12 hours after intra-tracheal instillation of a high dose (100 micrograms) of budesonide; muscular expression was compared with glucocorticoid receptor expression in lung tissue. After Northern blot analysis, hybridization was performed with glucocorticoid receptor, glyceraldehyde-3-phosphate dehydrogenase and glutamine synthetase probes. In the gastrocnemius muscle, both the alpha and beta glucocorticoid receptor mRNA forms were detected and found to be downregulated four hours after the budesonide instillation. alpha/beta glucocorticoid receptor ratios were lower in the gastrocnemius (1.1 +/- 0.2) than in the lungs (2.6 +/- 0.6). In the lungs, at all time points, the average alpha glucocorticoid receptor mRNA levels did not differ from controls, although glutamine synthetase mRNA levels were upregulated. The beta glucocorticoid receptor mRNA was slightly reduced at 1 and 4 hours. In conclusion, after intra-tracheal instillation of budesonide, both alpha and beta glucocorticoid receptor forms were downregulated in muscle tissue. The difference in alpha/beta glucocorticoid receptor mRNA ratios and concentrations between lung and gastrocnemius muscle supports the hypothesis of differential gene regulation by glucocorticoids in different cell types.

Effect of glucocorticoid excess on skeletal muscle and heart protein synthesis in adult and old rats

This study was carried out to analyse glucocorticoid-induced muscle wasting and subsequent recovery in adult (6-8 months) and old (18-24 months) rats because the increased incidence of various disease states results in hypersecretion of glucocorticoids in ageing. Adult and old rats received dexamethasone in their drinking water for 5 or 6 d and were then allowed to recover for 3 or 7 d. As dexamethasone decreased food intake, all groups were pair-fed to dexamethasone-treated old rats (i.e. the group that had the lowest food intake). At the end of the treatment, adult and old rats showed significant increases in blood glucose and plasma insulin concentrations. This increase disappeared during the recovery period. Protein synthesis of different muscles was assessed in vivo by a flooding dose of [13C]valine injected subcutaneously 50 min before slaughter. Dexamethasone induced a significant decrease in protein synthesis in fast-twitch glycolytic and oxidative glycolytic muscles (gastrocnemius, tibialis anterior, extensor digitorum longus). The treatment affected mostly ribosomal efficiency. Adult dexamethasone-treated rats showed an increase in protein synthesis compared with their pair-fed controls during the recovery period whereas old rats did not. Dexamethasone also significantly decreased protein synthesis in the predominantly oxidative soleus muscle but only in old rats, and increased protein synthesis in the heart of adult but not of old rats. Thus, in skeletal muscle, the catabolic effect of dexamethasone is maintained or amplified during ageing whereas the anabolic effect in heart is depressed. These results are consistent with muscle atrophy occurring with ageing.

Toxic myopathies

Toxic myopathies may occur with a variety of prescribed medications, illicit drug abuse, or other toxins. The article discusses an overview of some of the compounds that may cause myopathy, the clinical and laboratory features, histology, mechanisms of action, and potential risk factors of myopathy. The ability to recognize these syndromes is essential to avoid unnecessary tests and to avoid delay in treatment, especially in critically ill patients or patients with other neuromuscular diseases.

Glucocorticoid-induced muscle atrophy. The role of exercise in treatment and prevention

Glucocorticoids have catabolic effects on skeletal muscle. These effects demonstrate fiber type specificity: Type IIB fibers are most susceptible and type I fibers least susceptible to the atrophy effects of glucocorticoids. Exercise training has been used frequently to counteract glucocorticoid-induced muscle atrophy. Studies have demonstrated that both resistance exercise and endurance exercise are effective in attenuating this atrophy. The cellular mechanisms mediating the attenuating effect of exercise on glucocorticoid-induced atrophy are not completely understood. More research is needed to further elucidate the details of these mechanisms and to determine the most efficacious exercise protocols for deterring glucocorticoid-induced muscle atrophy. Exercise evaluation of patients with glucocorticoid-induced myopathy and subsequent exercise prescription must be individualized and based on the patient's initial muscle function and medical status.

Effect of prednisone on protease activities and structural protein levels in rat muscles in vivo

To further elucidate the biochemical mechanism by which the corticosteroid prednisone induces differential changes in muscle mass (via altered protein synthesis/degradation rates) in normal or degenerating muscle tissues, we have determined the activity of a range of proteolytic enzyme types, together with levels of muscle structural proteins, in five innervated and denervated muscle types from control and drug treated rats. In both normal and wasting muscles, the activity of many protease types was substantially down-regulated following treatment with prednisone; however, accompanying net decreases in muscle mass were observed (although the structural protein composition of muscles was unaltered following drug treatment). We conclude that whilst overall rates of protein degradation in both normal and degenerating muscle may be reduced (via protease down-regulation) following prednisone treatment, the effect of the latter in reducing protein synthesis rates must be proportionately greater (even in actively degenerating tissue). Thus, the data do not support the hypothesis that the beneficial effect of prednisone in maintaining muscle mass in pathological tissues (e.g., Duchenne muscular dystrophy (DMD)) operates principally via down-regulation of protease action/protein catabolism.

Prednisone can protect against exercise-induced muscle damage

In an experimental animal exercise model we tested whether daily administration of prednisone prevents the development of mechanically induced muscle fibre damage. Six-week-old rats were treated with different doses of prednisone ranging from 1 to 50 mg/kg body weight per day or with placebo, for 8 days. On day 6 of treatment the rats were forced to run for 2 h on a level treadmill. Two days after exercise morphological damage in the soleus muscles was quantified using light microscopy and a semi-automatic image analysis system. Creatine kinase (CK) activity was measured before exercise (day 5) and directly after exercise (day 6). The expression of dystrophin in a placebo group and in a group that received 5 mg prednisone/kg body weight per day with and without performing exercise was studied with Western blotting. The effect of prednisone on fibre type distribution was determined with an antibody against fast myosin and the effect of prednisone on the proliferative activity of muscle satellite cells was studied using bromodeoxyuridine (BrdU) immunohistochemistry. Exercise-induced muscle fibre damage varied in a dose-dependent way. In the placebo group the mean (SEM) damaged muscle fibre area was 4% (1%). The groups that received low doses of prednisone, 1 or 2.5 mg/kg per day, showed a similar level of muscle damage. However, with 5 mg prednisone/kg per day the amount of muscle fibre damage [mean (SEM)] was significantly reduced to 1.4% (0.5%) (P <or= 0.05, Student's t-test). High doses of prednisone had no protective effect. Directly after exercise the CK activity was increased two-fold, except in the group that received 50 mg prednisone/kg body weight per day. No changes in the amount of dystrophin were found after densitometric analysis of the Western blots. Prednisone did not affect the fibre distribution or the labelling index of satellite cells. We conclude that prednisone, given in an appropriate dose, protects muscle fibres against the development of mechanically induced damage, possibly by stabilizing the muscle fibre membranes. This action may explain the beneficial effect of prednisone observed in Duchenne muscular dystrophy patients.

Inspiratory muscle training during treatment with corticosteroids in humans

In a previous study performed by us, functional alterations in the inspiratory muscles were evaluated in patients receiving corticosteroids for diseases other than respiratory. We have shown that patients who received high-dose steroids for several weeks developed inspiratory muscle weakness that was reversible following withdrawal of the drug treatment. The present study was designed to evaluate the ability of specific inspiratory muscle training (SIMT) to prevent the effects of a therapeutic dosage of corticosteroids on inspiratory muscle function in patients receiving the drug for diseases other than pulmonary, with no underlying respiratory or muscular disease. Twelve patients, 5 men and 7 women, with ages ranging from 19 to 41 years, who received corticosteroids for diseases other than respiratory were recruited into two groups: 6 patients were assigned to the control group and got sham training and 6 patients received SIMT while receiving corticosteroids in a single-blind group-comparative trial. In both groups, there was no difference between the post-treatment and pretreatment values as regard to the FEV1/FVC relationship. However, in the control group but not in the training group, there was a small but significant decrease, from 99.2 +/- 3.0 to 94.3 +/- 2.8 (mean +/- SEM, p < 0.01) in FEV1 (percent of predicted normal values) and from 103.5 +/- 4.0 to 88.7 +/- 3.1 (p < 0.001) in the FVC, following treatment. All subjects had normal inspiratory muscle strength, as expressed by the maximal inspiratory mouth pressure (PImax) at residual volume, and inspiratory muscle endurance as expressed by the relationship between peak pressure and the PImax before treatment. Following administration of corticosteroids, there was a gradual decrease in both inspiratory muscle strength (from 117.5 +/- 9.4 to 80.5 +/- 3.3 cm H2O, p < 0.005) and endurance (from 82.7 +/- 2.6 to 40.2 +/- 1.7%, p < 0.001) in the control group. On the contrary, despite corticosteroid therapy, there were no significant changes in the inspiratory muscle function in the patients whose inspiratory muscles were specifically trained. We conclude that corticosteroids have a significant deteriorating effect on respiratory muscle function in humans. This weakness is preventable by using SIMT during corticosteroid treatment.

Interaction of glucocorticoids and activity patterns affect muscle function

The purpose of this study was to determine the effects of glucocorticoids on muscle mass and contractile properties of muscles of similar fiber composition but differing in activity patterns. Rats were divided into two groups and administered prednisolone (5 mg/kg per day) (P; N = 9) or served as controls (C; N = 10) for 10 days. Contractile properties were then determined in the left gastrocnemius-plantaris-soleus (GPS) muscle complex and a strip of costal diaphragm (D). An index of fatigue was also determined in both muscle preparations. Whole-body, GPS, and D weights decreased (P < 0.05) in the P animals (22%, 17%, and 15%, respectively) when compared to C. Specific tension (PO) increased (P < 0.05) in the GPS complex (21%) and decreased in the D (26%). Maximal shortening velocity (Vmax) was not different (P > 0.05) between groups in either the GPS or the D. While the index of fatigue was not different (P > 0.05) between groups in the D, there was a 30% increase (P < 0.05) in the rate of fatigue in the GPS. These data indicate that, although glucocorticoids cause decreased muscle mass in both D and GPS, a change in muscle architecture may prevent a decrease in force-generating ability in some limb muscles. However, glucocorticoids do not increase D fatigability as seen in the GPS.

Thyroid-induced changes in the growth of the liver, kidney, and diaphragm of neonatal rats

Eu-, hypo- and hyper-thyroid rats were studied 12 days postpartum. Hypothyroidism was induced by administering propylthiouracil (PTU) via the mother's drinking water between late gestation and throughout lactation. This procedure effectively blocked the normal early postnatal surge of T3 and T4. In contrast, hyperthyroidism was induced in the young pups by daily injections of T4 from day 3 postpartum. The effects of these experimental manipulations of thyroid status on the rates of protein turnover and growth of the liver, kidney, and diaphragm were studied and compared with measurements made on appropriate euthyroid control tissues. Tissue rates of protein synthesis were decreased in response to hypothyroidism with consequent growth retardation of all three tissues and the whole animal. In contrast, the three body tissues responded very differently to the induction of hyperthyroidism. Hepatic rates of protein synthesis and growth were completely unaffected by thyroid excess. The response of the diaphragm was essentially the reverse of that seen with hypothyroidism, i.e., the enhanced rates of protein synthesis and protein degradation leading to muscle hypertrophy. The rates of protein turnover in the kidney were also increased, but unlike the diaphragm the net result was renal atrophy. Clearly, thyroid hormones influence the normal rapid growth of the neonate and its individual tissues. However, beyond a certain concentration the threshold of responsiveness to these hormones seems to vary between individual tissues.

Turnover of skeletal muscle contractile proteins in glucocorticoid myopathy

Muscle weakness in glucocorticoid myopathy results mainly from muscle atrophy, the reason for which is the accelerated catabolism of muscle proteins. As the content of lysosomes in skeletal muscle, particularly in fast-twitch glycolytic fibers, is relatively low the non-lysosomal pathway makes a particularly significant contribution and has special importance in the initial rate-limiting steps in the catabolism of contractile proteins and in the regulation of their turnover rate. The turnover rate of actin and the myosin heavy chain is decreased in all types of muscle fibers, and more rapid turnover of the myosin light chain is registered in the fast-twitch glycolytic and oxidative-glycolytic fibers. Exercise and simultaneous glucocorticoid treatment is an effective measure in retarding skeletal muscle atrophy and provides protection against muscle wasting.

Effect of fasting and thyroidectomy on cysteine proteinase activities in liver and muscle

Prolonged starvation mimics chronic negative nitrogen balance observed in many physiopathological situations. During starvation, an initial decrease in protein utilization (phase I) is followed by a long period of protein sparing (phase II) that ends with a marked rise in nitrogen excretion (phase III). Variations in protein metabolism during starvation are determined by changes in protein synthesis and degradation rates (Cherel, Y., Attaix, D. Rosolowska-Huszcz, D., Belkhou, R., Robin, J.P., Arnal, M. and Le Maho, Y. (1991) Clin. Sci. 81, 611-619), but little information is available on expression of proteolytic systems. In this study, cathepsin B, H and L activities were compared in hindlimb muscles and liver at various phases of starvation in thyroidectomized and sham-operated rats. In muscle, cathepsin activities fell from the fed state to phase II, which suggests that cathepsins may play a role in the curtailment of muscle proteolysis during protein sparing phase. This decrease of muscle cathepsin activities was reproduced by thyroidectomy alone. In contrast, liver cathepsin B and H activities fell during starvation, but were not affected by thyroidectomy alone. Liver cathepsin L decreased only during starvation in thyroidectomized animals. These observations emphasize that different mechanisms modulate cathepsin expression in skeletal muscle and liver.

The effect of corticosteroids on inspiratory muscle performance in humans

Functional alterations in the inspiratory muscles were evaluated in patients receiving corticosteroids for diseases other than respiratory. Inspiratory muscle strength, as expressed by the maximal inspiratory mouth pressure (PImax), and inspiratory muscle endurance (PmPeak/PImax), using a pressure threshold breathing device, were evaluated in eight patients with normal pulmonary and inspiratory muscle functions (two patients with rapidly progressive glomerulonephritis, two with glomerulonephritis with minimal changes, two with idiopathic thrombocytopenic purpura, and two with subacute thyroiditis). There was a gradual decrease in both inspiratory muscle strength and endurance following corticosteroid administration. After 8 weeks of treatment PmPeak/PImax decreased from 84.4 +/- 2.4 to 67.9 +/- 3.1 percent (p < 0.001), while inspiratory muscle strength dropped from 126.9 +/- 9.6 to 86.5 +/- 7.4 cm H2O (p < 0.005). Gradual steroid dosage tapering resulted in marked improvement in both strength and endurance; the inspiratory muscle strength rose significantly to 112.2 +/- 8.1 cm H2O (p < 0.0005) when steroid treatment was stopped, and even more significantly 6 months later (to 123.1 +/- 8.1 cm H2O [p < 0.0001]), and the PmPeak/PImax rose to 60.6 +/- 3.4 percent (p < 0.001) and to 74.7 +/- 3.2 percent (p < 0.0001), respectively. We conclude that corticosteroids have a significant deteriorating effect on respiratory muscle function in humans. This weakness is reversible while tapering steroid dosage. Steroid therapy should be reconsidered in patients with underlying lung disease.

Exercise training fails to prevent glucocorticoid-induced muscle alterations in young growing rats

The aim of this study was to determine the impact of chronic treatment for 8 weeks with hydrocortisone acetate (5 mg kg-1 day-1) on skeletal muscles, and to evaluate whether sprint training can prevent glucocorticoid-induced muscle atrophy better than endurance training. Biochemical, histological and contractile properties were employed to determine the influence of this steroid on skeletal musculature, and the results were compared to pair-weight animals to take into account the influence of corticoids on growth rate. It was found that hydrocortisone acetate treatment results in a stunted growth, adrenal atrophy and depressed plasma corticosterone levels. Mild corticoid-induced losses of muscle mass and protein content (9%-13%) were observed in fast-twitch skeletal muscles. It appeared that the impact of corticoids is strictly directed toward type IIb fibres, which displayed a 12%-18% reduction in cross-sectional areas. No alterations occurred in plantaris contractile speed or tensions properties. Neither endurance training (30 m/min; 90 min/day; 5 days/week) nor sprint training (60 m/min; 15 min/day; 5 days/week) for 8 weeks was able to counteract the effects of corticoids. These data suggest that increased contractile activity, as induced by treadmill running, is not sufficient to counteract the muscular effects of glucocorticoids when administered at a dose of 5 mg kg-1 day-1.

Loss and renewal of thick myofilaments in glucocorticoid-treated rat soleus after denervation and reinnervation

Denervation of rat soleus muscle and simultaneous administration of high doses of corticosteroids for 7 days caused marked muscle fiber atrophy and selective loss of thick myofilaments from many muscle fibers by light and electron microscopy. Myosin heavy chain/actin ratios were greatly reduced on polyacrylamide gel electrophoresis. Nerve crush instead of cut permitted reinnervation after 2 weeks and demonstrated the reversibility of the muscle changes within a week after reinnervation. There was formation of new thick filaments and their reintegration into myofibrils without further breakdown, although large areas of Z-disc streaming appeared. The mechanism of A-band breakdown remains obscure, but it presumably starts with limited proteolysis and continues with disaggregation of myosin molecules. This is consistent with our observation that the muscle fibers retain a relatively good reactivity to antibodies against myosin heavy chain 1 week after denervation and corticosteroid administration. A syndrome recalling these experiments is seen in severely asthmatic patients receiving corticosteroids and pharmacologically paralyzed for mechanical respiration.

Effect of clenbuterol on skeletal muscle atrophy in mice induced by the glucocorticoid dexamethasone

1. The ability of clenbuterol to antagonize the catabolic effect of the glucocorticoid dexamethasone on the skeletal muscles, soleus, gastrocnemius and extensor digitorum longus was studied in mice. 2. Daily injections of 5 mg dexamethasone/kg body weight over 10 days caused a significant (20%) loss of muscle weight and protein content in fast twitch but not in slow twitch muscles. 3. Inclusion of clenbuterol (4 mg/kg) in the diet for the period of dexamethasone treatment partly prevented glucocorticoid-induced muscle atrophy, and increasing the concentration of clenbuterol to 8 mg/kg diet totally prevented glucocorticoid-induced protein loss in all muscles.

Specific effect of corticoids on acetylcholine receptor expression in rat skeletal muscle cell cultures

The potential effect of different classes of steroids on the expression of acetylcholine receptors (AChR) was studied in different primary cultures of newborn-rat skeletal muscle cells. Comparison among three techniques for preparing newborn skeletal muscle cells showed that these systems were equivalent to study AChR expression. Only corticoids stimulated myogenesis as a twofold increase in AChR expression indicated. Among the corticoids, the glucocorticoids were the more potent, whereas the mineralocorticoid aldosterone had less marked effect. The sex hormones progesterone and testosterone partially blocked these effects, without inducing any significant effect when given alone. The steroids tested differed in efficacy in correlation with their different chemical structures. Among the glucocorticoids a clear structure-activity relationship could be established. These results emphasize the specificity of corticoid action on muscle cells and suggest an explanation for the effects induced by glucocorticoids used in treating human muscular or neuromuscular diseases.

Dexamethasone increases plasma amino acid concentrations in bronchopulmonary dysplasia

Nine ventilated low birthweight babies were treated with dexamethasone (0.6 mg/kg/day). Appreciable suppression of weight gain was accompanied by uraemia and significant increases in the concentration of all amino acids except phenylalanine, tyrosine, threonine, and glutamate. Ornithine, citrulline, alanine, glutamine, and cystine concentrations increased threefold or more. The findings could not be explained by changes in dietary intake and presumably reflect pronounced catabolism, though the effects of dexamethasone on intermediary metabolism and membrane transport could also play a part.

Corticosteroid therapy and respiratory muscle function in humans

We examined the effects of prednisone administration on respiratory muscle function in humans using a double-blind study with a placebo control group. A total of 16 normal subjects were randomized to receive 20 mg prednisone daily (n = 8) or placebo daily (n = 8) for 2 wk. Inspiratory muscle strength (Pimax), expiratory muscle strength (PEmax), diaphragmatic strength (Pdimax), and inspiratory muscle endurance were measured at the beginning and end of the study. There was no significant change with treatment for Pimax (-145 +/- 7 to -138 +/- 6 cm H2O), PEmax (171 +/- 17 to 169 +/- 14 cm H2O), Pdimax (194 +/- 11 to 196 +/- 12 cm H2O), or endurance (76 +/- 3 to 77 +/- 4%) for the prednisone group and no significant difference between the two groups. We conclude that prednisone in moderate dosage has no significant effect on respiratory muscle function in humans, at least in the short term.