Anabolic agents for improving muscle regeneration and function after injury

Discussing Conflicting Explanatory Approaches in Flexibility Training Under Consideration of Physiology: A Narrative Review

The mechanisms underlying range of motion enhancements via flexibility training discussed in the literature show high heterogeneity in research methodology and study findings. In addition, scientific conclusions are mostly based on functional observations while studies considering the underlying physiology are less common. However, understanding the underlying mechanisms that contribute to an improved range of motion through stretching is crucial for conducting comparable studies with sound designs, optimising training routines and accurately interpreting resulting outcomes. While there seems to be no evidence to attribute acute range of motion increases as well as changes in muscle and tendon stiffness and pain perception specifically to stretching or foam rolling, the role of general warm-up effects is discussed in this paper. Additionally, the role of mechanical tension applied to greater muscle lengths for range of motion improvement will be discussed. Thus, it is suggested that physical training stressors can be seen as external stimuli that control gene expression via the targeted stimulation of transcription factors, leading to structural adaptations due to enhanced protein synthesis. Hence, the possible role of serial sarcomerogenesis in altering pain perception, reducing muscle stiffness and passive torque, or changes in the optimal joint angle for force development is considered as well as alternative interventions with a potential impact on anabolic pathways. As there are limited possibilities to directly measure serial sarcomere number, longitudinal muscle hypertrophy remains without direct evidence. The available literature does not demonstrate the necessity of only using specific flexibility training routines such as stretching to enhance acute or chronic range of motion.

Physiology of Stretch-Mediated Hypertrophy and Strength Increases: A Narrative Review

Increasing muscle strength and cross-sectional area is of crucial importance to improve or maintain physical function in musculoskeletal rehabilitation and sports performance. Decreases in muscular performance are experienced in phases of reduced physical activity or immobilization. These decrements highlight the need for alternative, easily accessible training regimens for a sedentary population to improve rehabilitation and injury prevention routines. Commonly, muscle hypertrophy and strength increases are associated with resistance training, typically performed in a training facility. Mechanical tension, which is usually induced with resistance machines and devices, is known to be an important factor that stimulates the underlying signaling pathways to enhance protein synthesis. Findings from animal studies suggest an alternative means to induce mechanical tension to enhance protein synthesis, and therefore muscle hypertrophy by inducing high-volume stretching. Thus, this narrative review discusses mechanical tension-induced physiological adaptations and their impact on muscle hypertrophy and strength gains. Furthermore, research addressing stretch-induced hypertrophy is critically analyzed. Derived from animal research, the stretching literature exploring the impact of static stretching on morphological and functional adaptations was reviewed and critically discussed. No studies have investigated the underlying physiological mechanisms in humans yet, and thus the underlying mechanisms remain speculative and must be discussed in the light of animal research. However, studies that reported functional and morphological increases in humans commonly used stretching durations of > 30 min per session of the plantar flexors, indicating the importance of high stretching volume, if the aim is to increase muscle mass and maximum strength. Therefore, the practical applicability seems limited to settings without access to resistance training (e.g., in an immobilized state at the start of rehabilitation), as resistance training seems to be more time efficient. Nevertheless, further research is needed to generate evidence in different human populations (athletes, sedentary individuals, and rehabilitation patients) and to quantify stretching intensity.

Doping in Racing Pigeons (Columba livia domestica): A Review and Actual Situation in Belgium, a Leading Country in This Field

Pigeon racing is a sport in which trained homing pigeons (Columba livia domestica) are released between 60 and 1200 km from their loft and then have to return home as quickly as possible. The first race was held in 1818 in Belgium and since then, Belgium has led the world in pigeon breeding. Unfortunately, as in other sports, doping has become a major issue and doping controls have been implemented. This review provides information about pigeon racing, rules from the Royal Federation Colombophile of Belgium, and laws applicable in Belgium as doping control issues cannot be understood without including them as part of pigeon racing. The main pharmacological data concerning corticoids, non-steroidal anti-inflammatory drugs, anabolic steroids, pain relievers and narcotic analgesics, bronchodilators and β-agonists, drugs acting on the central nervous system and other performance-enhancing drugs, in addition to methods relevant to doping in pigeons are presented. Moreover, the chosen matrix and analytical methods are described.

Anabolic Androgenic Steroids in Orthopaedic Surgery: Current Concepts and Clinical Applications

Despite the well-documented effects of testosterone and its synthetic derivatives—collectively termed anabolic androgenic steroids (AASs)—on the musculoskeletal system, the therapeutic use of these agents has received limited investigation within the field of orthopaedic surgery. In the last 2 decades, preclinical and clinical research has started to identify promising applications of the short-term use of AASs in the perioperative period. There is evidence to suggest that AASs may improve postoperative recovery after anterior cruciate ligament reconstruction and total joint arthroplasty. In addition, AASs may augment the biological healing environment in specific clinical scenarios including muscle injury, fracture repair, and rotator cuff repair. Current literature fails to present strong evidence for or against the use of AASs in orthopaedics, but there is continuous research on this topic. The purpose of this study was to provide a comprehensive overview of the current status of AAS applications in orthopaedic surgery, with an emphasis on preclinical data, clinical studies, and future directions.

Needling on trigger point promotes muscle regeneration after bupivacaine injection induced injury

Dry needling treatment has a promising relieving effect on Myofascial Pain Syndrome (MPS). In China, acupuncture practitioners use acupuncture needle instead to insert the "A-Shi" acupoint to treat MPS which is defined as the same as the trigger point of dry needling. This method has been applied for thousands of years in China. In this study, bupivacaine injection induced gastrocnemius muscle injury in mice. We applied the clinical improved needling method on animal model by making the angle between the skin and needle less than 30 degree. Animals got needling treatment 24 h later at the point where the bupivacaine was injected. Results of muscle H.E. staining showed that, compared to bupivacaine injection group without needling, acupuncture treatment group showed more intact muscle fibers, less inflammatory cell infiltration and fractured muscle fibers. By RNA sequencing analysis, our work firstly demonstrated that the physical stimulation of needling changed the gene expression of muscle tissue to accelerate the muscular regeneration process. Therefore, our study proved that simple needling at "A-Shi" acupoint promoted muscle regeneration and revealed underlying mechanisms of the beneficial effects of acupuncture and dry needle treatments.

Exploring nanofibrous self-assembling peptide hydrogels using mouse myoblast cells for three-dimensional bioprinting and tissue engineering applications

Injured skeletal muscles which lose more than 20% of their volume, known as volumetric muscle loss, can no longer regenerate cells through self-healing. The traditional solution for recovery is through regenerative therapy. As the technology of three-dimensional (3D) bioprinting continues to advance, a new approach for tissue transplantation is using biocompatible materials arranged in 3D scaffolds for muscle repair. Ultrashort self-assembling peptide hydrogels compete as a potential biomaterial for muscle tissue formation due to their biocompatibility. In this study, two sequences of ultrashort peptides were analyzed with muscle myoblast cells (C2C12) for cell viability, cell proliferation, and differentiation in 3D cell culture. The peptides were then extruded through a custom-designed robotic 3D bioprinter to create cell-laden 3D structures. These constructs were also analyzed for cell viability through live/dead assay. Results showed that 3D bioprinted structures of peptide hydrogels could be used as tissue platforms for myotube formation - a process necessary for muscle repair.

A novel decellularized skeletal muscle-derived ECM scaffolding system for in situ muscle regeneration

The cell-based tissue engineering strategies have gained attention in restoring normal tissue function after skeletal muscle injuries; however, these approaches require a donor tissue biopsy and extensive cell expansion process prior to implantation. In order to avoid this limitation, we developed a novel cell-free muscle-specific scaffolding system that consisted of a skeletal muscle-derived decellularized extracellular matrix (dECM) and a myogenic factor, insulin growth factor-1 (IGF-1). Rheological, morphological, and biological properties of this muscle-specific scaffold (IGF-1/dECM) as well as collagen and dECM scaffolds were examined. The cell viability in all scaffolds had over 90% at 1, 3, and 7 days in culture. The cell proliferation in the IGF-1/dECM was significantly increased when compared with other groups. More importantly, the IGF-1/dECM strongly supported the myogenic differentiation in the scaffold as confirmed by myosin heavy chain (MHC) immunofluorescence. We also investigated the feasibility in a rabbit tibialis anterior (TA) muscle defect model. The IGF-1/dECM had a significantly greater number of myofibers when compared to both collagen and dECM groups at 1 and 2 months after implantation. We demonstrated that this novel muscle-specific scaffolding system could effectively promote the muscle tissue regeneration in situ.

Modulation of exercise training related adaptation of body composition and regulatory pathways by anabolic steroids

Anabolic steroids have a long history of abuse in amateur and professional athletics. However, their interaction with training and the resulting effects on body composition and tissue adaptation, relying on a concert of factors and pathways, remain under investigation. This study aims at investigating the changes of body composition and the expression of selected genes and pathways essential for this adaptation process. Therefore, male wistar rats were treated with the anabolic steroid metandienone in two groups (n = 16; metandienone, metandienone + exercise) alongside with control groups (n = 16; control, exercise). Following a 6-week steep-angle treadmill training protocol, weight of organs, visceral fat and muscles was determined. M. gastrocnemius was histologically assessed by ATPase staining, mRNA and protein levels of factors of regeneration, hypertrophy and myogenesis and selected master regulators and markers were determined. Results show additive effects of anabolic steroids and exercise on body, tibia and reproductive organs weight. Mm. gastrocnemius and soleus weight was increased by training but not anabolic steroids. Muscle fiber diameter and composition remained unchanged. Visceral fat mass and fat cell size was affected by training and anabolic steroids but no additive effects could be observed. Exercise and anabolic steroids result in a complex regulation of the expression of genes in M. Gastrocnemius involved in skeletal muscle metabolism, hypertrophy, inflammation and regeneration. In summary, our data suggests distinct molecular mechanisms involved in the adaptation of the skeletal muscle to anabolic androgenic steroids and exercise. Metandienone treatment neither results in skeletal muscle hypertrophy nor liver-toxic effects but in an induction of skeletal muscle regeneration and an activation of endocrine negative feedback. Moreover our study demonstrates that visceral fat and bone responds with higher sensitivity to ASS and exercise than the skeletal muscle. This apparent plasticity of adipose and bone tissue rather than skeletal muscle could indicate a potentially superior future role of fat rather than muscle related parameters to detect and AAS abuse in a biologic passport strategy in professional athletes.

Injury Occurrence and Return to Dance in Professional Ballet: Prospective Analysis of Specific Correlates

Professional ballet is a highly challenging art, but studies have rarely examined factors associated with injury status in ballet professionals. This study aimed to prospectively examine gender-specific correlates of injury occurrence and time-off from injury in professional ballet dancers over a one-year period. The participants were 99 professional ballet dancers (41 males and 58 females). Variables included: (i) predictors: sociodemographic data (age, educational status), ballet-related factors (i.e., experience in ballet, ballet status), cigarette smoking, alcohol drinking, and consumption of illicit drugs; and (ii) outcomes: injury occurrence and time-off from injury. Participants were questioned on predictors at the beginning of the season, while data on outcomes were collected continuously once per month over the study period. Dancers reported total of 196 injuries (1.9 injuries (95% CI: 1.6–2.3) per dancer in average), corresponding to 1.4 injuries per 1000 dance-hours (95% CI: 1.1–1.7). In females, cigarette smoking was a predictor of injury occurrence in females (OR: 4.33, 95% CI: 1.05–17.85). Alcohol drinking was a risk factor for absence from dance in females (OR: 1.29, 95% CI: 1.01–4.21) and males (OR: 1.21, 95% CI: 1.05–3.41). Less experienced dancers were more absent from dance as a result of injury than their more experienced peers (Mann-Whitney Z: 2.02, p < 0.04). Ballet dancers and their managers should be aware of the findings of this study to make informed decisions on their behavior (dancers) or to initiate specific programs aimed at the prevention of substance use and misuse in this profession (managers).

Acute interruption of treatment with nandrolone decanoate is not sufficient to reverse cardiac autonomic dysfunction and ventricular repolarization disturbances in rats

Anabolic androgenic steroids are a class of synthetic compounds derived from testosterone, eventually used by athletes, to improve physical performance. However, anabolic steroids can also modify normal cardiovascular function. Thus, we investigated cardiac electrophysiological and autonomic abnormalities in rats, through a electrocardiographic variability protocol during and after interruption of administration of nandrolone decanoate (DECA) anabolic steroid. Twenty male Wistar rats (60-70 days old) received DECA (10 mg. kg^-1i.m) once a week or vehicle, during eight weeks. Electrocardiogram was recorded in conscious rats by a noninvasive method, and time and domain analysis of heart rate variability as well as electrocardiogram intervals (QTc / QTd) were performed. Body mass was lower in treated rats compared to control after 4th and 8th weeks, but not at the end of 14th week. QTc and QTd were longer in DECA group compared to control on 4th, 8th, 11th, but equal on 14th week. Cardiac autonomic dysfunction (vagal attenuation) was present on DECA group after 4th week and did not normalize after interruption of treatment. The animals of DECA group showed a correlation between attenuated parasympathetic modulation and increased correct QT interval. Our data allow us to conclude that long-term treatment with DECA impairs autonomic cardiac physiology, predisposing to cardiovascular risk and sudden death, and interruption of administration does not recovery the normality immediately.

Biomimetic scaffolds for regeneration of volumetric muscle loss in skeletal muscle injuries

Skeletal muscle injuries typically result from traumatic incidents such as combat injuries where soft-tissue extremity injuries are present in one of four cases. Further, about 4.5 million reconstructive surgical procedures are performed annually as a result of car accidents, cancer ablation, or cosmetic procedures. These combat- and trauma-induced skeletal muscle injuries are characterized by volumetric muscle loss (VML), which significantly reduces the functionality of the injured muscle. While skeletal muscle has an innate repair mechanism, it is unable to compensate for VML injuries because large amounts of tissue including connective tissue and basement membrane are removed or destroyed. This results in a significant need to develop off-the-shelf biomimetic scaffolds to direct skeletal muscle regeneration. Here, the structure and organization of native skeletal muscle tissue is described in order to reveal clear design parameters that are necessary for scaffolds to mimic in order to successfully regenerate muscular tissue. We review the literature with respect to the materials and methodologies used to develop scaffolds for skeletal muscle tissue regeneration as well as the limitations of these materials. We further discuss the variety of cell sources and different injury models to provide some context for the multiple approaches used to evaluate these scaffold materials. Recent findings are highlighted to address the state of the field and directions are outlined for future strategies, both in scaffold design and in the use of different injury models to evaluate these materials, for regenerating functional skeletal muscle.

STATEMENT OF SIGNIFICANCE

Volumetric muscle loss (VML) injuries result from traumatic incidents such as those presented from combat missions, where soft-tissue extremity injuries are represented in one of four cases. These injuries remove or destroy large amounts of skeletal muscle including the basement membrane and connective tissue, removing the structural, mechanical, and biochemical cues that usually direct its repair. This results in a significant need to develop off-the-shelf biomimetic scaffolds to direct skeletal muscle regeneration. In this review, we examine current strategies for the development of scaffold materials designed for skeletal muscle regeneration, highlighting advances and limitations associated with these methodologies. Finally, we identify future approaches to enhance skeletal muscle regeneration.

TNF-α and IGF1 modify the microRNA signature in skeletal muscle cell differentiation

Background

Elevated levels of the inflammatory cytokine TNF-α are common in chronic diseases or inherited or degenerative muscle disorders and can lead to muscle wasting. By contrast, IGF1 has a growth promoting effect on skeletal muscle. The molecular mechanisms mediating the effect of TNF-α and IGF1 on muscle cell differentiation are not completely understood. Muscle cell proliferation and differentiation are regulated by microRNAs (miRNAs) which play a dominant role in this process. This study aims at elucidating how TNF-α or IGF1 regulate microRNA expression to affect myoblast differentiation and myotube formation.

Results

In this study, we analyzed the impact of TNF-α or IGF1 treatment on miRNA expression in myogenic cells. Results reveal that i) TNF-α and IGF1 regulate miRNA expression during skeletal muscle cell differentiation in vitro, ii) microRNA targets can mediate the negative effect of TNF-α on fusion capacity of skeletal myoblasts by targeting genes associated with axon guidance, MAPK signalling, focal adhesion, and neurotrophin signalling pathway, iii) inhibition of miR-155 in combination with overexpression of miR-503 partially abrogates the inhibitory effect of TNF-α on myotube formation, and iv) MAPK/ERK inhibition might participate in modulating the effect of TNF-α and IGF1 on miRNA abundance.

Conclusions

The inhibitory effects of TNF-α or the growth promoting effects of IGF1 on skeletal muscle differentiation include the deregulation of known muscle-regulatory miRNAs as well as miRNAs which have not yet been associated with skeletal muscle differentiation or response to TNF-α or IGF1. This study indicates that miRNAs are mediators of the inhibitory effect of TNF-α on myoblast differentiation. We show that intervention at the miRNA level can ameliorate the negative effect of TNF-α by promoting myoblast differentiation. Moreover, we cautiously suggest that TNF-α or IGF1 modulate the miRNA biogenesis of some miRNAs via MAPK/ERK signalling. Finally, this study identifies indicative biomarkers of myoblast differentiation and cytokine influence and points to novel RNA targets.

Electronic supplementary material

The online version of this article (doi:10.1186/s12964-015-0083-0) contains supplementary material, which is available to authorized users.

Temporal changes in ERK phosphorylation are harmonious with 4E-BP1, but not p70S6K, during clenbuterol-induced hypertrophy in the rat gastrocnemius

Extracellular signal-regulated kinase (ERK) is required for clenbuterol (CB)-dependent fast-type myofibril enlargement; however, its contribution to translation control is unclear. ERK mediates translational regulation through mammalian target of rapamycin complex 1 (mTORC1) activation and (or) mTORC1-independent pathways. In this study, we aimed to investigate the role of ERK in translational control during CB-induced muscular hypertrophy by measuring time-dependent changes in the phosphorylation statuses of ERK, p70 ribosomal S6 kinase (p70S6K; an indicator of mTORC1 activity), 4E-binding protein 1 (4E-BP1), eukaryotic elongation factor 2 (eEF2), and other related signaling molecules in rat gastrocnemius muscles. Five-day administration of CB induced phenotypes associated with muscular hypertrophy (significant increases in wet weight and isometric ankle flexion torque in the gastrocnemius muscle), but was not accompanied by elevated ERK or p70S6K phosphorylation. One-day administration of CB caused significant increases in the phosphorylation of ERK, p70S6K, and 4E-BP1. In contrast, 3-day administration of CB caused significant increases in the phosphorylation of ERK and 4E-BP1, but not p70S6K. In addition, positive correlations were observed between ERK and 4E-BP1 on days 1 and 3, whereas a correlation between ERK and p70S6K was only observed on day 1. eEF2 phosphorylation was unchanged on both days 1 and 3. These findings suggest that ERK accelerates the initiation of translation, but does not support the involvement of ERK in translational elongation. Furthermore, ERK may play a major role in promoting translational initiation by mediating the phosphorylation of 4E-BP1, and may contribute to the initial activation of mTORC1 during CB administration.

Sirtuin 1 in skeletal muscle of cachectic tumour-bearing rats: a role in impaired regeneration?

BACKGROUND: In advanced malignant disease, cachexia and muscle wasting appear to be among the most common manifestations. This phenomenon is partially related with a decreased muscle regeneration capacity, as previously described in our laboratory. METHODS AND RESULTS: Rats bearing the Yoshida AH-130 ascites hepatoma were used in the experiments. The animals experienced a marked weight loss with decreases in skeletal muscle weights (13% gastrocnemius, 18% extensor digitorum longus, and 12% tibialis muscles). Muscle gene expression was measured using real-time polymerase chain reaction. Skeletal muscle from cachectic tumour-bearing rats is associated with a decreased expression of genes involved in regeneration such as Pax-7 (39%), myogenin (24%), and MyoD (17%). mRNA levels of Sirt1 increased (91%) in cachectic skeletal muscle. The Sirt1 gene has been shown to be associated with changes in muscle myoblast differentiation. Treatment of the tumour-bearing animals with formoterol-a beta2-agonist-normalizes the expression of genes involved in regeneration (i.e., increase of Pax7 (139%)), at the same time as it does with that of Sirt1 (42% decrease). CONCLUSIONS: It is suggested that the lack of muscle regeneration observed during muscle wasting in tumour-bearing animals is linked to the action of Sirt-1, possibly via PGC-1α. These factors may constitute possible targets of pharmacological treatment against muscle loss, thus potentially contributing to the understanding and mitigation of muscle atrophy associated with disease.

Clenbuterol and formoterol decrease force production in isolated intact mouse skeletal muscle fiber bundles through a beta2-adrenoceptor-independent mechanism

Although the acute actions of short-acting β(2)-adrenoceptor agonists on force production in isolated mammalian skeletal muscle fibers have been the subject of a number of previous studies, those of long-acting β(2)-adrenoceptor agonists have never been investigated. Also, little is known about the cellular signal transduction events mediating their actions. Therefore, the primary aim of this study was to investigate the acute effects of treatment of mouse fast- and slow-twitch muscle fiber bundles with clenbuterol, formoterol, and salbutamol. Both clenbuterol and salbutamol increased the levels of cAMP in both fiber types, and this effect was reversed by ICI-118551. On the other hand, clenbuterol and formoterol decreased force production in both fiber types. They also increased the phosphorylation of phospholamban and β(2)-adrenoceptors in slow-twitch fiber bundles, and their effects were insensitive to propranolol, ICI-118551, and 14-22 amide. In contrast, salbutamol increased force production in both fiber types. It also increased the phosphorylation of β(2)-adrenoceptors in slow-twitch fibers only, but it had no effect on the phosphorylation of phospholamban in either fiber type. These effects were reversed by propranolol and ICI-118551 but not by 14-22 amide. Instead, 14-22 amide further potentiated the effects of salbutamol on force. In summary, long- and short-acting β(2)-adrenoceptor agonists have opposite effects on force production in isolated intact mouse skeletal muscle fiber bundles. From these results, we suggest that the acute actions of short-acting β(2)-adrenoceptor agonists on force production in mammalian skeletal muscles are mediated through the β(2)-adrenoceptor, whereas those of long-acting β(2)-adrenoceptor agonists are not.

Beta2-adrenergic agonist-induced hypertrophy of the quadriceps skeletal muscle does not modulate disease severity in the rodent meniscectomy model of osteoarthritis

OBJECTIVE

To examine whether beta2-adrenergic agonist-induced hypertrophy of the quadriceps skeletal muscle can modulate the severity of osteoarthritis (OA) in the rodent meniscectomy (MNX) model.

METHODS

Male Lewis rats were subcutaneously administered with 1.5 mg/kg/day clenbuterol hydrochloride (n=15) or saline vehicle (n=20) for 14 days. Following pre-treatment, five animals from each group were sacrificed to assess the immediate effects of clenbuterol. The remaining animals underwent either invasive knee surgery (clenbuterol pre-treated n=10; saline pre-treated n=10) or a sham control surgical procedure (saline pre-treated n=5). During disease initiation and progression, weight bearing was assessed by hindlimb loading. Myosin heavy chain (MHC) protein isoforms were quantified by silver stained SDS PAGE. OA severity was graded by assessment of toluidine blue stained step coronal sections of the total knee joint.

RESULTS

Clenbuterol treatment resulted in an increase in total bodyweight, growth rate and in quadriceps skeletal muscle mass. Meniscal surgery resulted in the development of OA-like lesions, changes to weight bearing, and changes in MHC protein expression in the quadriceps. Clenbuterol-induced skeletal muscle hypertrophy had no effect on either weight bearing or articular pathology following MNX surgery.

CONCLUSIONS

Our data reveal that clenbuterol-induced skeletal muscle hypertrophy is unable to mimic the beneficial clinical effects of increased musculature derived through targeted strength training in humans, in a rodent model of MNX-induced OA. In addition we observed fibre-type switching to "slow twitch" in the quadriceps muscle during the induction of OA that warrants further investigation as to its relationship to joint stability.

Effects of administering testosterone undecanoate in rats subjected to physical exercise: effects on the estrous cycle, motor behavior and morphology of the liver and kidney

The aim of the work was evaluate the effects of testosterone undecanoate (TU) treatment combined with moderate physical training on: the estrous cycle, body weight (BW), motor behavior (MB), and the morphohistology of the reproductive system, the liver and kidney in rats. Female Wistar rats (180 g - 250 g) were divided as follows: sedentary + TU (S + TU), trained + TU (T + TU), sedentary + vehicle (S + V), trained + vehicle (T + V). The rats swam 50 min/Day, strapped with a 5% BW load, for 4 weeks. During this training, (BW) was monitored daily as well as the estrous cycle (EC) by vaginal smear. The TU (15 mg/kg s.c) was administered 3 times/week for 4 weeks. At the end of the study, data on MB, BW and morphohistopathological changes in viscera were compiled. The (T + TU) group had on average, a higher (BW) in the fourth week compared to the first week, and (BW) higher than (S + V) and (S + TU) groups. We noted an interruption in the EC and a decrease in weight of ovaries in animals treated with TU. In addition, there was an increase in the relative weight of the heart in groups (T + V) and (T+ TU), and kidneys in group (T + TU). Histopathological analysis showed periportal congestion and isolated foci of hepatic necrosis in rats with TU. Thus, TU combined with training abolished the EC, promoted ovarian atrophy, liver necrosis, cardiac hypertrophy and a decrease in motor activity.

The role of beta-adrenoceptor signaling in skeletal muscle: therapeutic implications for muscle wasting disorders

PURPOSE OF REVIEW

The beta-adrenergic signaling pathway represents a novel therapeutic target for skeletal muscle wasting disorders due to its roles in regulating protein synthesis and degradation. beta-Adrenoceptor agonists (beta-agonists) have therapeutic potential for attenuating muscle wasting associated with sarcopenia (age-related muscle wasting), cancer cachexia, sepsis, disuse, burns, HIV-AIDS, chronic kidney or heart failure, and neuromuscular diseases such as the muscular dystrophies. This review describes the role of beta-adrenergic signaling in the mechanisms controlling muscle wasting due to its effects on protein synthesis, protein degradation, and muscle fiber phenotype.

RECENT FINDINGS

Stimulation of the beta-adrenergic signaling pathway with beta-agonists has therapeutic potential for muscle wasting since administration can elicit an anabolic response in skeletal muscle. As a consequence of their potent muscle anabolic actions, the effects of beta-agonist administration have been examined in several animal models and human conditions of muscle wasting in the hope of discovering a new therapeutic. The repartitioning characteristics of beta-agonists (increasing muscle mass and decreasing fat mass) have also made them attractive anabolic agents for use in livestock and by some athletes. However, potentially deleterious cardiovascular side-effects of beta-agonists have been identified and these will need to be obviated in order for the therapeutic potential of beta-agonists to be realized.

SUMMARY

Multiple studies have identified anticachectic effects of beta-agonists and their therapeutic potential for pathologic states when muscle protein hypercatabolism is indicated. Future studies examining beta-agonist administration for muscle wasting conditions need to separate beneficial effects on skeletal muscle from potentially deleterious effects on the heart and cardiovascular system.

The inhibitory role of sympathetic nervous system in the Ca2+-dependent proteolysis of skeletal muscle

Mammalian cells contain several proteolytic systems to carry out the degradative processes and complex regulatory mechanisms to prevent excessive protein breakdown. Among these systems, the Ca2+-activated proteolytic system involves the cysteine proteases denoted calpains, and their inhibitor, calpastatin. Despite the rapid progress in molecular research on calpains and calpastatin, the physiological role and regulatory mechanisms of these proteins remain obscure. Interest in the adrenergic effect on Ca2+-dependent proteolysis has been stimulated by the finding that the administration of beta2-agonists induces muscle hypertrophy and prevents the loss of muscle mass in a variety of pathologic conditions in which calpains are activated. This review summarizes evidence indicating that the sympathetic nervous system produces anabolic, protein-sparing effects on skeletal muscle protein metabolism. Studies are reviewed, which indicate that epinephrine secreted by the adrenal medulla and norepinephrine released from adrenergic terminals have inhibitory effects on Ca2+-dependent protein degradation, mainly in oxidative muscles, by increasing calpastatin levels. Evidence is also presented that this antiproteolytic effect, which occurs under both basal conditions and in stress situations, seems to be mediated by beta2- and beta3-adrenoceptors and cAMP-dependent pathways. The understanding of the precise mechanisms by which catecholamines promote muscle anabolic effects may have therapeutic value for the treatment of muscle-wasting conditions and may enhance muscle growth in farm species for economic and nutritional purposes.