The effect of creatine supplementation on mass and performance of rat skeletal muscle

This study investigated the effect of dietary creatine supplementation on hypertrophy and performance of rat skeletal muscle. Male Sprague-Dawley rats underwent either tibialis anterior ablation or partial ablation of the plantaris/gastrocnemius to induce compensatory hypertrophy of the extensor digitorum longus (EDL) or soleus respectively, or sham surgery. Creatine (300 mg/kg) was administered to one half of each group for 5 weeks, after which force production was measured. With the leg fixed at the knee and ankle, the distal tendon of the EDL or soleus was attached to a force transducer and the muscle was electrically stimulated via the sciatic nerve. Synergist ablation resulted in a significant increase in EDL mass and in soleus mass relative to control muscles. However, no effect of creatine supplementation on muscle mass or performance was found between control and either group of creatine-treated rats. Despite an apparent increase in muscle creatine content, creatine supplementation did not augment muscle hypertrophy or force production in rat EDL or soleus muscle, providing evidence that the potential benefits of creatine supplementation are not due to a direct effect on muscle but rather to an enhanced ability to train.     

Muscle atrophy and hypoplasia with aging: impact of training and food restriction

The purpose of this work is to study the influence of aging, training, and food restriction on skeletal muscle mass and fiber number. Male Fischer 344 rats (n = 49) at 3 mo postpartum were assigned to three groups: 1) sedentary control (confined to cage), 2) exercise trained (18 m/min, 8 degrees grade, 20 min/day, 5 days/wk), or 3) food restricted (alternate days of free access and no access to food). At 12 and 27 mo postpartum the soleus and extensor digitorum longus (EDL) muscles were excised, weighed, and fiber number was quantified after HNO3 digestion. At 27 mo the masses of soleus and EDL muscles of sedentary control rats were 83 and 70%, respectively, of 12-mo values (138 +/- 5 and 151 +/- 4 mg). At 27 mo, soleus muscle mass of trained rats was 113% of sedentary control values, whereas EDL muscle mass was unaffected by training. At 27 mo, food restriction had no effect on the mass of both muscles compared with 27-mo sedentary control values. Fiber number was not affected by training or food restriction in both muscles. Fiber number for soleus and EDL muscles of combined groups declined with age by 5.6 and 4.2%, respectively. With aging, the small loss of muscle fibers can account at most for approximately 25% of the observed skeletal muscle atrophy.     

Skeletal muscle glucose uptake following overload-induced hypertrophy.

While endurance exercise training has been shown to enhance insulin action in skeletal muscle, the effects of high resistance strength training are less clear. The purpose of this study was to determine the rate of glucose uptake in skeletal muscle in which compensatory hypertrophy was induced by synergist muscle ablation. Basal and insulin mediated [3H] 2-deoxyglucose uptake were measured in soleus and EDL muscles using the perfused rat hindquarter preparation. Neither basal nor insulin mediated glucose uptake, when expressed per gram muscle, were enhanced in hypertrophied soleus muscles compared with control muscles, despite a twofold increase in mass (P less than 0.01). In the EDL, muscle mass increased 60% with synergist ablation (P less than 0.01), however insulin mediated glucose uptake was not different from that of control muscles. The basal rate of glucose uptake in hypertrophied EDL muscles was increased twofold over that of control muscles (P less than 0.05), possibly due to changes in neural input and/or loading. These results suggest that the stimulus for development of increased muscle mass is different from that for metabolic adaptations.     

Effect of resistance exercise training on expression of Hsp70 and inflammatory cytokines in skeletal muscle and adipose tissue of STZ-induced diabetic rats

Impairment of adipose tissue and skeletal muscles accrued following type 1 diabetes is associated with protein misfolding and loss of adipose mass and skeletal muscle atrophy. Resistance training can maintain muscle mass by changing both inflammatory cytokines and stress factors in adipose tissue and skeletal muscle. The purpose of this study was to determine the effects of a 5-week ladder climbing resistance training program on the expression of Hsp70 and inflammatory cytokines in adipose tissue and fast-twitch flexor hallucis longus (FHL) and slow-twitch soleus muscles in healthy and streptozotocin-induced diabetic rats. Induction of diabetes reduced body mass, while resistance training preserved FHL muscle weight in diabetic rats without any changes in body mass. Diabetes increased Hsp70 protein content in skeletal muscles, adipose tissue, and serum. Hsp70 protein levels were decreased in normal and diabetic rats by resistance training in the FHL, but not soleus muscle. Furthermore, resistance training decreased inflammatory cytokines in FHL skeletal muscle. On the other hand, Hsp70 and inflammatory cytokine protein levels were increased by training in adipose tissue. Also, significant positive correlations between inflammatory cytokines in adipose tissue and skeletal muscles with Hsp70 protein levels were observed. In conclusion, we found that in diabetic rats, resistance training decreased inflammatory cytokines and Hsp70 protein levels in fast skeletal muscle, increased adipose tissue inflammatory cytokines and Hsp70, and preserved FHL muscle mass. These results suggest that resistance training can maintain skeletal muscle mass in diabetes by changing inflammatory cytokines and stress factors such as Hsp70 in skeletal muscle and adipose tissue.     

Time course in calpain activity and autolysis in slow and fast skeletal muscle during clenbuterol treatment

Calpains are Ca2+ cysteine proteases that have been proposed to be involved in the cytoskeletal remodeling and wasting of skeletal muscle. Cumulative evidence also suggests that β2-agonists can lead to skeletal muscle hypertrophy through a mechanism probably related to calcium-dependent proteolytic enzyme. The aim of our study was to monitor calpain activity as a function of clenbuterol treatment in both slow and fast phenotype rat muscles. For this purpose, for 21?days we followed the time course of the calpain activity and of the ubiquitous calpain 1 and 2 autolysis, as well as muscle remodeling in the extensor digitorum longus (EDL) and soleus muscles of male Wistar rats treated daily with clenbuterol (4?mg·kg-1). A slow to fast fiber shift was observed in both the EDL and soleus muscles after 9?days of treatment, while hypertrophy was observed only in EDL after 9?days of treatment. Soleus muscle but not EDL muscle underwent an early apoptonecrosis phase characterized by hematoxylin and eosin staining. Total calpain activity was increased in both the EDL and soleus muscles of rats treated with clenbuterol. Moreover, calpain 1 autolysis increased significantly after 14?days in the EDL, but not in the soleus. Calpain 2 autolysis increased significantly in both muscles 6 hours after the first clenbuterol injection, indicating that clenbuterol-induced calpain 2 autolysis occurred earlier than calpain 1 autolysis. Together, these data suggest a preferential involvement of calpain 2 autolysis compared with calpain 1 autolysis in the mechanisms underlying the clenbuterol-induced skeletal muscle remodeling.     

Differential adaptations during growth spurt and in young adult rat muscles

During the post-weaning growth and maturation period (25/90 days after birth), rat limb muscles are submitted to specific adaptations. Our aim was to characterize the mechanical properties of two muscles that are opposite in terms of fibre-type distribution, the soleus and the extensor digitorum longus (EDL) muscles of male Wistar rats. Results showed a fast-to-slow fibre-type transition in soleus while no modification in fibre-type distribution was observed in EDL. A growth-induced increase in muscle force was observed. Soleus underwent an increase in twitch kinetics, but EDL showed no modification. Resistance to fatigue was higher in 90-day-old soleus but not modified in the EDL. Surprisingly, analysis of maximal shortening velocity showed a decrease in both soleus and EDL. Finally, tension/extension curves indicated a growth-induced increase in series elastic stiffness in the two muscles. These results suggest that during this growth period, skeletal muscles are submitted to differential adaptations. Moreover, whereas adaptation of biomechanical properties observed can be explained partly by an adaptation of fibre profile in soleus, this is not the case for EDL. It is suggested that changes in muscle architecture, which are often disregarded, could explain some variations in mechanical properties, especially when muscles undergo an increase in both mass and length.     

Experimental chronic low‐frequency resistance training produces skeletal muscle hypertrophy in the absence of muscle damage and metabolic stress markers

Volitional animal resistance training constitutes an important approach to modeling human resistance training. However, the lack of standardization protocol poses a frequent impediment to the production of skeletal muscle hypertrophy and the study of related physiological variables (i.e., cellular damage/inflammation or metabolic stress). Therefore, the purposes of the present study were: (1) to test whether a long‐term and low frequency experimental resistance training program is capable of producing absolute increases in muscle mass; (2) to examine whether cellular damage/inflammation or metabolic stress is involved in the process of hypertrophy. In order to test this hypothesis, animals were assigned to a sedentary control (C, n = 8) or a resistance trained group (RT, n = 7). Trained rats performed 2 exercise sessions per week (16 repetitions per day) during 12 weeks. Our results demonstrated that the resistance training strategy employed was capable of producing absolute mass gain in both soleus and plantaris muscles (12%, p < 0.05). Furthermore, muscle tumor necrosis factor (TNF‐α) protein expression (soleus muscle) was reduced by 24% (p < 0.01) in trained group when compared to sedentary one. Finally, serum creatine kinase (CK) activity and serum lactate concentrations were not affected in either group. Such information may have practical applications if reproduced in situations where skeletal muscle hypertrophy is desired but high mechanical stimuli of skeletal muscle and inflammation are not. Copyright © 2010 John Wiley & Sons, Ltd.     

Beta2-adrenoceptor agonist fenoterol enhances functional repair of regenerating rat skeletal muscle after injury.

Beta(2)-adrenoceptor agonists such as fenoterol are anabolic in skeletal muscle, and because they promote hypertrophy and improve force-producing capacity, they have potential application for enhancing muscle repair after injury. No previous studies have measured the beta(2)-adrenoceptor population in regenerating skeletal muscle or determined whether fenoterol can improve functional recovery in regenerating muscle after myotoxic injury. In the present study, the extensor digitorum longus (EDL) muscle of the right hindlimb of deeply anesthetized rats was injected with bupivacaine hydrochloride, which caused complete degeneration of all muscle fibers. The EDL muscle of the left hindlimb served as the uninjured control. Rats received either fenoterol (1.4 mg x kg(-1) x day(-1)) or an equal volume of saline for 2, 7, 14, or 21 days. Radioligand binding assays identified a approximately 3.5-fold increase in beta(2)-adrenoceptor density in regenerating muscle at 2 days postinjury. Isometric contractile properties of rat EDL muscles were measured in vitro. At 14 and 21 days postinjury, maximum force production (P(o)) of injured muscles from fenoterol-treated rats was 19 and 18% greater than from saline-treated rats, respectively, indicating more rapid restoration of function after injury. The increase in P(o) in fenoterol-treated rats was due to increases in muscle mass, fiber cross-sectional area, and protein content. These findings suggest a physiological role for beta(2)-adrenoceptor-mediated mechanisms in muscle regeneration and show clearly that fenoterol hastens recovery after injury, indicating its potential therapeutic application.     

Metabolic and physiologic characteristics of skeletal muscle determine its response to clenbuterol treatment

beta-Adrenoceptor agonists are reported to induce skeletal muscle hypertrophy and hence serve as valuable adjunct to the treatment of wasting disorders. In the present study, we attempted to find out whether metabolic and physiologic characteristics of fibres are important in determining skeletal muscle response to clenbuterol (an adrenergic receptor agonist) therapy, as proposed in the treatment of wasting disorders. The treatment of mice with clenbuterol (2 mg/kg body wt for 30 days) resulted in skeletal muscle hypertrophy, more common amongst fast-twitch glycolytic fibres/muscle, with increase in body mass and a parallel rise in muscle mass to body mass ratio. Measurement of fibre diameters in soleus (rich in slow-twitch oxidative fibres), ALD or anterior latissimus dorsi (with a predominance of fast-twitch glycolytic fibres) and gastrocnemius (a mixed-type of muscle) from clenbuterol-treated mice for 30 days revealed noticeable increase in the per cent population of narrow slow-twitch fibre and a corresponding decline in white-type or fast-twitch glycolytic fibres in gastrocnemius and ALD. As revealed by counting of muscle cells in soleus, narrow red fibres declined with corresponding increase in white-type glycolytic fibres population. A significant decline in the succinic dehydrogenase activity was observed, thereby suggesting abnormality in oxidative activity of skeletal muscles in response to clenbuterol therapy.     

Reduction of skeletal muscle atrophy by a proteasome inhibitor in a rat model of denervation

The ubiquitin-proteasome system is the primary proteolytic pathway implicated in skeletal muscle atrophy under catabolic conditions. Although several studies showed that proteasome inhibitors reduced proteolysis under catabolic conditions, few studies have demonstrated the ability of these inhibitors to preserve skeletal muscle mass and architecture in vivo. To explore this, we studied the effect of the proteasome inhibitor Velcade (also known as PS-341 and bortezomib) in denervated skeletal muscle in rats. Rats were given vehicle or Velcade (3 mg/kg po) daily for 7 days beginning immediately after induction of muscle atrophy by crushing the sciatic nerve. At the end of the study, the rats were euthanized and the soleus and extensor digitorum longus (EDL) muscles were harvested. In vehicle-treated rats, denervation caused a 33.5 +/- 2.8% and 16.2 +/- 2.7% decrease in the soleus and EDL muscle wet weights (% atrophy), respectively, compared to muscles from the contralateral (innervated) limb. Velcade significantly reduced denervation-induced atrophy to 17.1 +/- 3.3% in the soleus (P < 0.01), a 51.6% reduction in atrophy associated with denervation, with little effect on the EDL (9.8 +/- 3.2% atrophy). Histology showed a preservation of muscle mass and preservation of normal cellular architecture after Velcade treatment. Ubiquitin mRNA levels in denervated soleus muscle at the end of the study were significantly elevated 120 +/- 25% above sham control levels and were reduced to control levels by Velcade. In contrast, testosterone proprionate (3 mg/kg sc) did not alleviate denervation-induced skeletal muscle atrophy but did prevent castration-induced levator ani atrophy, while Velcade was without effect. These results show that proteasome inhibition attenuates denervation-induced muscle atrophy in vivo in soleus muscles. However, this mechanism may not be operative in all types of atrophy.     

Effect of exercise on muscle fibre composition and enzyme activities of skeletal muscles in young rats

Young Wistar rats underwent dynamic (D) or static (S) exercise from the 5th to 35th day after birth. Histochemical and biochemical analysis were performed in the extensor digitorum longus (EDL) and the soleus muscle (SOL). Lactate dehydrogenase (LDH) (regulating anaerobic metabolism) and citrate synthase (CS) and hydroxyacyl-CoA dehydrogenase (HAD) (both regulating aerobic metabolism) activities were determined spectrophotometrically. An increase of the fast oxidative-glycolytic (FOG) muscle fibres was found in the slow SOL muscle in both trained groups, i.e. by 10% in group D and by 7% in group S in comparison with the C group. The EDL muscle fibre distribution did not differ from those of control animals in respect to the slow oxidative (SO) fibre type. A higher percentage of FOG fibres by 19% was found in group D contrary to a decreased number of the fast glycolytic (FG) muscle fibres in this trained group. The greatest increase of CS (EDL 185%, SOL 176%) and HAD (EDL 83%, SOL 178%) activities were found in group D as compared with control group (C). Only small differences were observed in LDH activity. The values of characteristic enzyme activity ratios show that dynamic training resulted in an elevation of oxidative capacity of skeletal muscle, while the static load led preferentially along the glycolytic pathway. It may be concluded that an adaptive response to the training load during early postnatal development is different due to the type of exercise (dynamic or static) and/or the type of skeletal muscle (fast or slow).     

Concentrations of signal transduction proteins exercise and insulin responses in rat extensor digitorum longus and soleus muscles

Differences in the concentrations of signal transduction proteins often alter cellular function and phenotype, as is evident from numerous, heterozygous knockout mouse models for signal transduction proteins. Here, we measured signal transduction proteins involved in the adaptation to exercise and insulin signalling in fast rat extensor digitorum longus (EDL; 3% type I fibres) and the slow soleus muscles (84% type I fibres). The EDL and soleus were excised from four rats, the proteins extracted and subjected to Western blots for various signal transduction proteins. Our results show major differences in signal transduction protein concentrations between EDL and soleus. The EDL to soleus concentration ratios were: Calcineurin: 1.43 +/- 0.10; ERK1: 0.38 +/- 0.18; ERK2: 0.61 +/- 0.16; p38alpha, beta: 1.36 +/- 0.15; p38gamma/ERK6: 0.95 +/- 0.11; PKB/AKT: 1.44 +/- 0.08; p70S6k: 6.86 +/- 3.58; GSK3beta: 0.69 +/- 0.03; myostatin: 1.95 +/- 0.43; NF-kappaB: 0.32 +/- 0.10 (values >1 indicate higher expression in the EDL, and values < 1 indicate higher expression in the soleus). With the exception of p38gamma/ERK6, the concentration of each signal transduction protein was uniformly higher in one muscle than in the other in all four animals. These experiments show that signal transduction protein concentrations vary between fast and slow muscles, presumably reflecting a concentration difference on a fibre level. Proteins that promote particular functions such as growth or slow phenotype are not necessarily higher in muscles with that particular trait (e.g. higher in larger fibres or slow muscle). Interindividual differences in fibre composition might explain variable responses to training and insulin.     

Effects of high-intensity training on MCT1, MCT4, and NBC expressions in rat skeletal muscles: influence of chronic metabolic alkalosis

This study investigated the effects of high-intensity training, with or without induced metabolic alkalosis, on lactate transporter (MCT1 and MCT4) and sodium bicarbonate cotransporter (NBC) content in rat skeletal muscles. Male Wistar rats performed high-intensity training on a treadmill 5 times/wk for 5 wk, receiving either sodium bicarbonate (ALK-T) or a placebo (PLA-T) prior to each training session, and were compared with a group of control rats (CON). MCT1, MCT4, and NBC content was measured by Western blotting in soleus and extensor digitorum longus (EDL) skeletal muscles. Citrate synthase (CS) and phosphofructokinase (PFK) activities and muscle buffer capacity (betam) were also evaluated. Following training, CS and PFK activities were significantly higher in the soleus only (P < 0.05), whereas betam was significantly higher in both soleus and EDL (P < 0.05). MCT1 (PLA-T: 30%; ALK-T: 23%) and NBC contents (PLA-T: 85%; ALK-T: 60%) increased significantly only in the soleus following training (P < 0.01). MCT4 content in the soleus was significantly greater in ALK-T (115%) but not PLA-T compared with CON. There was no significant change in protein content in the EDL. Finally, NBC content was related only to MCT1 content in soleus (r = 0.50, P < 0.01). In conclusion, these results suggest that MCT1, MCT4, and NBC undergo fiber-specific adaptive changes in response to high-intensity training and that induced alkalosis has a positive effect on training-induced changes in MCT4 content. The correlation between MCT1 and NBC expression suggests that lactate transport may be facilitated by NBC in oxidative skeletal muscle, which may in turn favor better muscle pH regulation.     

Acute effect of fatty acids on metabolism and mitochondrial coupling in skeletal muscle

Acute effects of free fatty acids (FFA) were investigated on: (1) glucose oxidation, and UCP-2 and -3 mRNA and protein levels in 1 h incubated rat soleus and extensor digitorium longus (EDL) muscles, (2) mitochondrial membrane potential in cultured skeletal muscle cells, (3) respiratory activity and transmembrane electrical potential in mitochondria isolated from rat skeletal muscle, and (4) oxygen consumption by anesthetized rats. Long-chain FFA increased both basal and insulin-stimulated glucose oxidation in incubated rat soleus and EDL muscles and reduced mitochondrial membrane potential in C2C12 myotubes and rat skeletal muscle cells. Caprylic, palmitic, oleic, and linoleic acid increased O₂ consumption and decreased electrical membrane potential in isolated mitochondria from rat skeletal muscles. FFA did not alter UCP-2 and -3 mRNA and protein levels in rat soleus and EDL muscles. Palmitic acid increased oxygen consumption by anesthetized rats. These results suggest that long-chain FFA acutely lead to mitochondrial uncoupling in skeletal muscle.     

Acute effect of fatty acids on metabolism and mitochondrial coupling in skeletal muscle

Acute effects of free fatty acids (FFA) were investigated on: (1) glucose oxidation, and UCP-2 and -3 mRNA and protein levels in 1 h incubated rat soleus and extensor digitorium longus (EDL) muscles, (2) mitochondrial membrane potential in cultured skeletal muscle cells, (3) respiratory activity and transmembrane electrical potential in mitochondria isolated from rat skeletal muscle, and (4) oxygen consumption by anesthetized rats. Long-chain FFA increased both basal and insulin-stimulated glucose oxidation in incubated rat soleus and EDL muscles and reduced mitochondrial membrane potential in C2C12 myotubes and rat skeletal muscle cells. Caprylic, palmitic, oleic, and linoleic acid increased O(2) consumption and decreased electrical membrane potential in isolated mitochondria from rat skeletal muscles. FFA did not alter UCP-2 and -3 mRNA and protein levels in rat soleus and EDL muscles. Palmitic acid increased oxygen consumption by anesthetized rats. These results suggest that long-chain FFA acutely lead to mitochondrial uncoupling in skeletal muscle.     

Effects of exogenous growth hormone on skeletal muscle of young female rats

We examined the effects of exogenous growth hormone (GH) treatment on the soleus and rectus femoris muscles of young female rats. Rat GH (1.8 IU/mg) was administered for 3 weeks by subcutaneous injection, twice a day, at doses of 0.5, 0.6, and 0.8 mg/day during the 1st, 2nd, and 3rd week, respectively. Final body weight, as well as wet and dry weight, of the soleus and rectus femoris muscles were significantly greater in the GH-treated group, compared to controls. Muscle weight to body weight ratios did not differ between the two groups. The fiber type composition of the soleus muscle was determined by histochemical staining for myosin ATPase activity. No statistically significant difference was found between the GH-treated and the control groups in the percentages of fiber types. However, GH treatment significantly increased the cross-sectional area of type II fibers of the soleus muscle. These results suggest that, in young female rats, acceleration of body weight gain by homologous GH administration is accompanied by a proportional hypertrophy of skeletal muscle mass. Increased muscle mass is due to hypertrophy of muscle fibers. Type II muscle fibers appear to be more sensitive to GH stimulation.     

Regulation of skeletal muscle dihydropyridine receptor gene expression by biomechanical unloading.

Biomechanical unloading of the rat soleus by hindlimb unweighting is known to induce atrophy and a slow- to fast-twitch transition of skeletal muscle contractile properties, particularly in slow-twitch muscles such as the soleus. The purpose of this study was to determine whether the expression of the dihydropyridine (DHP) receptor gene is upregulated in unloaded slow-twitch soleus muscles. A rat DHP receptor cDNA was isolated by screening a random-primed cDNA lambda gt10 library from denervated rat skeletal muscle with oligonucleotide probes complementary to the coding region of the rabbit DHP receptor cDNA. Muscle mass and DHP receptor mRNA expression were assessed 1, 4, 7, 14, and 28 days after hindlimb unweighting in rats by tail suspension. Isometric twitch contraction times of soleus muscles were measured at 28 days of unweighting. Northern blot analysis showed that tissue distribution of DHP receptor mRNA was specific for skeletal muscle and expression was 200% greater in control fast-twitch extensor digitorum longus (EDL) than in control soleus muscles. A significant stimulation (80%) in receptor message of the soleus was induced as early as 24 h of unloading without changes in muscle mass. Unloading for 28 days induced marked atrophy (control = 133 +/- 3 vs. unweighted = 62.4 +/- 1.8 mg), and expression of the DHP receptor mRNA in the soleus was indistinguishable from levels normally expressed in EDL muscles. These changes in mRNA expression are in the same direction as the 37% reduction in time to peak tension and 28% decrease in half-relaxation time 28 days after unweighting. Our results suggest that muscle loading necessary for weight support modulates the expression of the DHP receptor gene in the soleus muscle.     

Chronic effects of ethanol on muscle metabolism in the rat

Chronic ethanol feeding in the rat is associated with a skeletal myopathy involving primarily type-II muscle fibers, which is recognised to be mediated via a specific impairment in protein turnover. This paper investigates whether the cause of this myopathy may be related to abnormalities in carbohydrate and lipid metabolism in different muscles. [U-¹⁴C]Glucose metabolism was examined in two muscles with different fibre compsitions, the extensor digitorum longus (EDL) muscle, which contains predominantly type-II muscle fibres, and the soleus muscle, which is composed primarily of type-I muscle fibres. Feeding on the ethanol-supplemented Lieber-DeCarli liquid diet for 2 or 6 weeks was associated with profound distubances in glucose metabolism in both EDL and soleus muscles, particularly in relation to rates of glycogen and alanine formation. We discuss the importance of these metabolic changes in relation to the genesis of chronic alcoholic skeletal myopathy.     

Deficiency of alpha-sarcoglycan differently affects fast- and slow-twitch skeletal muscles

Alpha-sarcoglycan (Sgca) is a transmembrane glycoprotein of the dystrophin complex located at skeletal and cardiac muscle sarcolemma. Defects in the alpha-sarcoglycan gene (Sgca) cause the severe human-type 2D limb girdle muscular dystrophy. Because Sgca-null mice develop progressive muscular dystrophy similar to human disorder they are a valuable animal model for investigating the physiopathology of the disorder. In this study, biochemical and functional properties of fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus muscles of the Sgca-null mice were analyzed. EDL muscle of Sgca-null mice showed twitch and tetanic kinetics comparable with those of wild-type controls. In contrast, soleus muscle showed reduction of twitch half-relaxation time, prolongation of tetanic half-relaxation time, and increase of maximal rate of rise of tetanus. EDL muscle of Sgca-null mice demonstrated a marked reduction of specific twitch and tetanic tensions and a higher resistance to fatigue compared with controls, changes that were not evident in dystrophic soleus. Contrary to EDL fibers, soleus muscle fibers of Sgca-null mice distinctively showed right shift of the pCa-tension (pCa is the negative log of Ca2+ concentration) relationships and reduced sensitivity to caffeine of sarcoplasmic reticulum. Both EDL and soleus muscles showed striking changes in myosin heavy-chain (MHC) isoform composition, whereas EDL showed a larger number of hybrid fibers than soleus. In contrast to the EDL, soleus muscle of Sgca-null mice contained a higher number of regenerating fibers and thus higher levels of embryonic MHC. In conclusion, this study revealed profound distinctive biochemical and physiological modifications in fast- and slow-twitch muscles resulting from alpha-sarcoglycan deficiency.     

Prolonged treatment with the anabolic–androgenic steroid stanozolol increases antioxidant defences in rat skeletal muscle

Testosterone and its synthetic derivatives anabolic–androgenic steroids have been shown to increase skeletal muscle work capacity and fatigue resistance, but the molecular basis for these effects remains uncertain. Since muscle performance has been related to redox status of exercising muscles, this investigation was aimed at testing whether a treatment with suprapharmacological doses of the anabolic–androgenic steroid stanozolol, (2 mg/kg body weight, 5 days/week, for 8 weeks), either alone or in conjunction with treadmill training (12 weeks), enhanced antioxidant defences in rat muscles. Stanozolol treatment did not modify thiobarbituric acid reactive substances and glutathione content in soleus and extensor digitorum longus (EDL) homogenates. In soleus from sedentary rats, superoxide dismutase and glutathione reductase activities were increased by 25% (P < 0.05) and by 40% (P < 0.01) after stanozolol administration, whereas catalase and glutathione peroxidase activities were not modified. This response was similar to that induced by training alone. In EDL from sedentary rats, stanozolol increased only superoxide dismutase activity (20%, P < 0.05). In no case, the effects of steroid administration and training were additive. HSP72 levels were up-regulated in soleus (1.5-fold, P < 0.01) and EDL (threefold, P < 0.001) following training but remained unchanged after stanozolol treatment. Endurance capacity, assessed in a treadmill endurance test, was similar for treated and control rats. We conclude that stanozolol treatment increases antioxidant capacity in selected skeletal muscles from sedentary rats. However, the steroid was not effective in improving endurance capacity or enhancing the training effects on muscle antioxidant defence systems.