Chronic clenbuterol treatment compromises force production without directly altering skeletal muscle contractile machinery.

Clenbuterol is a ß2 -adrenergic receptor agonist known to induce skeletal muscle hypertrophy and a slow-to-fast phenotypic shift. The aim of the present study was to test the effects of chronic clenbuterol treatment on contractile efficiency and explore the underlying mechanisms, i.e. the muscle contractile machinery and calcium-handling ability. Forty-three 6-week-old male Wistar rats were randomly allocated to one of six groups that were treated with either subcutaneous equimolar doses of clenbuterol (4 mg kg(-1) day(-1) ) or saline solution for 9, 14 or 21 days. In addition to the muscle hypertrophy, although an 89% increase in absolute maximal tetanic force (Po ) was noted, specific maximal tetanic force (sPo) was unchanged or even depressed in the slow twitch muscle of the clenbuterol-treated rats (P < 0.05). The fit of muscle contraction and relaxation force kinetics indicated that clenbuterol treatment significantly reduced the rate constant of force development and the slow and fast rate constants of relaxation in extensor digitorum longus muscle (P < 0.05), and only the fast rate constant of relaxation in soleus muscle (P < 0.05). Myofibrillar ATPase activity increased in both relaxed and activated conditions in soleus (P < 0.001), suggesting that the depressed specific tension was not due to the myosin head alteration itself. Moreover, action potential-elicited Ca(2+) transients in flexor digitorum brevis fibres (fast twitch fibres) from clenbuterol-treated animals demonstrated decreased amplitude after 14 days (-19%, P < 0.01) and 21 days (-25%, P < 0.01). In conclusion, we showed that chronic clenbuterol treatment reduces contractile efficiency, with altered contraction and relaxation kinetics, but without directly altering the contractile machinery. Lower Ca(2+) release during contraction could partially explain these deleterious effects.

Is the Disabilities of the Arm, Shoulder and Hand (DASH) Questionnaire Adequate to Assess Individuals With Subacromial Pain Syndrome? Rasch Model and International Classification of Functioning, Disability and Health.

OBJECTIVE: The Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire is widely used to assess patients with symptoms of subacromial pain syndrome (SPS). No study has analyzed the DASH by using the Rasch model in these patients and related the level of difficulty of the items with the International Classification of Functioning Disability and Health (ICF) domains. The purpose of this study was to evaluate the measurement properties of the DASH in individuals with SPS and to describe which ICF components are influenced by SPS based on the DASH. METHODS: The full version of the DASH was used to assess upper limb pain and function in individuals with SPS. Responses were assessed using the Rasch model. DASH items were grouped according to the level of difficulty and associated with the ICF domains to identify the most compromised aspect in these individuals. RESULTS: Reliability and internal consistency for the DASH were shown to be 0.93 and 0.95, respectively. Item 3 ("Turn a key") was the easiest and 25 ("Pain during specific activity") the most difficult. Only item 30 ("Less capable/confident/useful") was as an erratic item. Item 15 ("Put on a sweater") showed differential functioning by age and item 11 ("Carry a heavy object") by sex. Seven items showed differential functioning related to the angular onset of pain during arm elevation. Sixty percent of the most difficult items belonged to the "Body function" domain of the ICF. CONCLUSION: Although some psychometric properties of the DASH are adequate according to the Rasch model, adjustments to some items are necessary for individuals with SPS. Clinicians should be cautious when interpreting the DASH, especially in patients with angular onset of pain above 120 degrees of arm elevation. IMPACT: The information contained in this study should be used by clinicians to interpret the results of the DASH when assessing individuals with SPS. The DASH may not be adequate to assess those with shoulder pain above 120 degrees of arm elevation. These results are not generalizable to other shoulder pathologies.

Is entheses ultrasound reliable? A reading Latin American exercise.

The objective of this study is to evaluate inter-reader entheses ultrasound (US) reliability and the influence of the type of image or degree of sonographer experience on US reliability in patients with spondyloarthritis (SpA). Eighteen Latin American ultrasonographers with different experience took part in an US reading exercise evaluating 60 entheseal images (50 % static images and 50 % videos) from healthy controls and SpA patients. The following sonographic lesions were assessed: structure, thickness, bone proliferation/tendon calcification, erosions, bursitis, and Doppler signal. Another group of three experts with significant experience in entheses US read all images too. Inter-reader reliability among participants and experts was calculated by the Cohen's kappa coefficient. Thresholds for kappa values were <0.2 poor, 0.21-0.4 fair, 0.41-0.6 moderate, 0.61-0.8 good, and 0.81-1 excellent. Furthermore, the results for the expert group were stratified based on the type of image. Kappa correlation coefficients among participants, showed variability depending on the type of lesion, being fair for structure and thickness, moderate for calcifications, erosions, and bursitis, and excellent for Doppler signal. Inter-reader reliability among experts was higher, being moderate for structure and thickness, good for calcifications and bursitis, and excellent for erosions and Doppler. Inter-reader reliability for assessing calcification and structure using static images was significantly higher than for videos. Overall inter-reader reliability for assessing entheses by US in SpA is moderate to excellent for most of the lesions. However, special training seems fundamental to achieve better inter-reader reliability. Moreover, the type of image influenced these results, where evaluation of entheses by videos was more difficult than by static images.

Antioxidants and mitochondrial respiration in lung, diaphragm, and locomotor muscles: effect of exercise.

Previous studies have shown that exhaustive exercise may increase reactive oxygen species (ROS) generation in oxidative muscles that may in turn impair mitochondrial respiration. Locomotor muscles have been extensively examined, but there is few report about diaphragm or lung. The later is a privileged site for oxygen transit. To compare the antioxidant defense system and mitochondrial function in lung, diaphragm and locomotor muscles after exercise, 24 young adult male rats were randomly assigned to a control (C) or exercise (E) group. E group rats performed an exhaustive running test on a motorized treadmill at 80-85% VO2max Mean exercise duration was 66+/-2.7 min. Lung, costal diaphragm, mixed gastrocnemius, and oxidative muscles (red gastrocnemius and soleus: RG/SOL homogenate) were sampled. Mitochondrial respiration was assessed in tissue homogenates by respiratory control index (RCI: rate of uncoupled respiration/rate of basal respiration) measurement. Lipid peroxidation was evaluated by malondialdehyde concentration (MDA) and we determined the activity of two antioxidant enzymes: superoxide dismutase (SOD) and glutathione peroxidase (GPX). We found elevated basal (C group data) SOD and GPX activities in both lung and diaphragm compared to locomotor muscles (p<.001). Exercise led to a rise in GPX activity in red locomotor muscles homogenate (GR/SOL; C = 10.3+/-0.29 and E = 14.4+/-1.51 micromol x min(-1) x gww(-1); p<.05), whereas there was no significant change in lung and diaphragm. MDA concentration and mitochondrial RCI values were not significantly changed after exercise. We conclude that lung and diaphragm had higher antioxidant protection than locomotor muscles. The exercise test did not lead to significant oxidative stress or alteration in mitochondrial respiration, suggesting that antioxidant function was adequate in both lung and diaphragm in the experimental condition.

Streptozotocin-induced diabetes decreases rat sarcolemmal lactate transport.

Impaired lactate metabolism is a metabolic disorder, which is not fully understood in the diabetic state including streptozotocin (STZ)-induced diabetes. We investigated whether STZ-induced diabetes results in altered lactate exchanges using the rat muscle sarcolemmal vesicles (SV) model. Fifteen days after diabetes onset (1 STZ-injection, 65 mg/kg, intraperitoneal [IP]), rats had higher blood and muscle lactate concentrations compared with normal rats (1.50 +/- 0.09 v 1.95 +/- 0.21 mmol/L (not significant [NS]) and 21.02 +/- 1.26 v 25.53 +/- 0.98 mmol/kg wet weight (ww); P < .05). The initial rate of lactate uptake was measured at various external lactate concentrations using SV of both group in zero-trans conditions. STZ-induced diabetes decreased the initial rate of total lactate influx at external lactate concentrations from 1 to 100 mmol/L (P < .05). This decrease in lactate transport was found in addition to an increased free radical production, as indicated by a significant increase in malonedialdehyde (MDA) concentration (64.3 +/- 8.7 v 100.3 +/- 13.5 nmol. g(-1) ww, P < .05), coupled with a higher glutathione peroxidase (Gpx) activity (48.03 +/- 3.13 v 84.7 +/- 15.01 micromol. min(-1). mg(-1) protein, P < .05) in red gastrocnemius. We concluded that STZ-induced diabetes decreases total lactate transport activity in rat SV and is associated with increased muscular oxidative stress.

Effect of food restriction on lactate sarcolemmal transport.

The objective of this study was to investigate the effects of 6 weeks of food restriction (FR) on sarcolemmal lactate transport in rats. The daily food consumption of rats was monitored for 10 days, after which they were assigned to either a control group (CTL, n = 7) that consumed food ad libitum or an FR group (n = 7) that received a daily ration equal to 60% of their predetermined baseline food intake. After the 6-week period, we observed in red gastrocnemius (RG) a fall of 48% in glycogen content (P <.01) and a reduction in glutathione peroxidase activity (P <.05), confirming that the FR program was well executed. FR resulted in a reduction in muscle lactate (P <.05) and liver glycogen contents (P <.01). Moreover, hyperlactatemia was noted in the FR group: 1.77 +/- 0.24 versus 2.67 +/- 0.29 mmol/L (P <.05). Lactate transport capacity was significantly increased (P <.05) in FR rats, although monocarboxylate transporter isoforms (MCT1 and MCT4) did not change significantly. We conclude that FR alters sarcolemmal lactate transport activity without affecting MCT1 and MCT4 expression.

Combined effects of hypoxia and endurance training on lipid metabolism in rat skeletal muscle.

AIM: To determine whether endurance training can counterbalance the negative effects of hypoxia on mitochondrial phosphorylation and expression of the long chain mitochondrial fatty acid transporter muscle carnitine palmitoyl transferase 1 (mCPT-1). METHODS: Male Wistar rats were exposed either to hypobaric hypoxia (at a simulated altitude of approximately 4000 m, PIO(2) approximately 90 mmHg) or to normoxia (sea level) for 5 weeks. In each environment, rats were randomly assigned to two groups. The trained group went through a 5-week endurance training programme. The control group remained sedentary for the same time period. Muscle fatty acid oxidation capacity was evaluated after the 5-week period on isolated mitochondria prepared from quadriceps muscles with the use of palmitoylcarnitine or pamitoylCoA + carnitine. RESULTS: Chronic hypoxia decreased basal (V(0), -31% with pamitoylCoA + carnitine and -21% with palmitoylcarnitine, P < 0.05) and maximal (V(max), -31% with pamitoylCoA + carnitine, P < 0.05) respiration rates, hydroxyacylCoA dehydrogenase activity (-48%, P < 0.05), mCPT-1 activity index (-34%, P < 0.05) and mCPT-1 protein content (-34%, P < 0.05). Five weeks of endurance training in hypoxia brought V(0), mCPT-1 activity index and mCPT-1 protein content values back to sedentary normoxic levels. Moreover, in the group trained in hypoxia, V(max) reached a higher level than in the group that maintained a sedentary lifestyle in normoxia (24.2 nmol O(2). min(-1) . mg(-1) for hypoxic training vs. 19.9 nmol O(2) . min(-1) . mg(-1) for normoxic sedentarity, P < 0.05). CONCLUSION: Endurance training can attenuate chronic hypoxia-induced impairments in mitochondrial fatty acid oxidation. This training effect seems mostly mediated by mCPT-1 activity rather than by mCPT-1 content.

High plasmatic angiotensin-converting enzyme (ACE) activity is not correlated with training-induced left ventricular growth in ACE congenic rats.

AIM: The aim of this study was to determine the influence of angiotensin-converting enzyme (ACE) genotype on left ventricular growth after endurance training, in ACE congenic rats with plasma ACE activity twice as high as the donor strain (LOU), thus mimicking the ACE I/D polymorphism observed in humans. METHODS: LOU and congenic rats (n = 12) were submitted to an endurance training on a treadmill for 7 weeks, while similar LOU and congenic rats (n = 10) constituted the control groups. Blood pressure, skeletal muscle citrate synthase activity, plasma and left ventricular ACE activity were assessed, and echocardiography was performed before and after the training. RESULTS: Angiotensin-converting enzyme plasmatic activity of congenic rats (188.2 +/- 26.6 in controls and 187.1 +/- 22.6 IU in trained rats respectively) was twofold that of the LOU strain (91.9 +/- 23.3 in controls, and 88.3 +/- 18.1 IU in trained rats respectively). After training, congenic and LOU rats showed a similar significant increase in citrate synthase activity (P < 0.05), and in the left ventricular mass/body mass ratio x 10(3): 3.7 +/- 0.3 and 3.6 +/- 0.6 in the trained congenic and LOU groups, respectively, vs. 3.0 +/- 0.1 and 2.9 +/- 0.2 in the control congenic and LOU groups respectively (P < 0.05). There was no significant correlation between ACE plasma activity and left ventricular mass in trained or untrained congenic rats. CONCLUSION: We conclude that training-induced left ventricular growth is not associated with plasma ACE activity in congenic rats.

Does high-sucrose diet alter skeletal muscle and liver mitochondrial respiration?

A diet high in sucrose or fructose progressively impairs glucose and lipid metabolism, which leads to insulin resistance. As mitochondria are the sites of the oxidation and utilization of these substrates, we hypothesized that a high sucrose diet would alter mitochondrial respiration. Male Wistar rats were fed high-sucrose (SU) or control (CTL) diet for one week; mitochondrial respiration was investigated in mitochondria isolated from liver and both glycolytic and oxidative muscles, with pyruvate and palmitate as substrates. To test for metabolic disturbances, we measured not only glycogen content in muscles and liver, but also lactate, glucose and triglyceride blood concentrations. After one week of high-sucrose intake, we found no change in blood concentration of these variables, but glycogen content was significantly increased in liver (17.28 +/- 2.98 mg/g tissue SU vs 6.47 +/- 1.67 mg/g tissue CTL), oxidative muscle (1.59 +/- 0.21 mg/g tissue SU vs 0.70 +/- 0.24 mg/g tissue CTL) though not in glycolytic muscle (1.72 +/- 0.44 mg/g tissue SU vs 1.52 +/- 0.20 mg/g tissue CTL). State 3 mitochondrial respiration was significantly decreased in SU rats compared with CTL (p < 0.05) with pyruvate, while no change was observed with palmitate. This study shows that 1-week of high-sucrose diet altered mitochondrial pyruvate oxidation in rats and suggests that, in the context of a high-sucrose diet, impaired mitochondrial respiration could contributed to the development of insulin resistance.

Impaired sarcolemmal vesicle lactate uptake and skeletal muscle MCT1 and MCT4 expression in obese Zucker rats.

The present experiments were undertaken to characterize 1) the hindlimb muscle mass lactate uptake and 2) the expression of monocarboxylate transporter isoforms MCT1 and MCT4, as well as lactate dehydrogenase (LDH) isozyme distribution, in various skeletal muscles of Zucker fa/fa rats taken as a model of insulin resistance-related obesity. Initial lactate uptake at six different concentrations was measured in sarcolemmal vesicles (SV) by use of L-[U-(14)C]lactate. Compared with controls, the maximal rate of lactate uptake and affinity were decreased in SV of Zucker rats (approximately 30%) in which MCT4 content was significantly decreased (P < 0.05). MCT4 expression was decreased in soleus, extensor digitorum longus, and red tibialis anterior (RTA; P < 0.05), but not in white tibialis anterior, whereas MCT1 expression was decreased only in RTA of Zucker rats (P < 0.05). Obesity led to a shift toward type M-LDH isozyme in mixed muscles. We conclude that obesity leads to changes in muscular MCT1 and MCT4 expression, which, when associated with LDH isozyme redistribution, may contribute to the hyperlactatemia noted in insulin resistance.

Training does not protect against exhaustive exercise-induced lactate transport capacity alterations.

The effects of endurance training on lactate transport capacity remain controversial. This study examined whether endurance training 1) alters lactate transport capacity, 2) can protect against exhaustive exercise-induced lactate transport alteration, and 3) can modify heart and oxidative muscle monocarboxylate transporter 1 (MCT1) content. Forty male Wistar rats were divided into control (C), trained (T), exhaustively exercised (E), and trained and exercised (TE) groups. Rats in the T and TE groups ran on a treadmill (1 h/day, 5 days/wk at 25 m/min, 10% incline) for 5 wk; C and E were familiarized with the exercise task for 5 min/day. Before being killed, E and TE rats underwent exhaustive exercise (25 m/min, 10% grade), which lasted 80 and 204 min, respectively (P < 0.05). Although lactate transport measurements (zero-trans) did not differ between groups C and T, both E and TE groups presented an apparent loss of protein saturation properties. In the trained groups, MCT1 content increased in soleus (+28% for T and +26% for TE; P < 0.05) and heart muscle (+36% for T and +33% for TE; P < 0.05). Moreover, despite the metabolic adaptations typically observed after endurance training, we also noted increased lipid peroxidation byproducts after exhaustive exercise. We concluded that 1) endurance training does not alter lactate transport capacity, 2) exhaustive exercise-induced lactate transport alteration is not prevented by training despite increased MCT1 content, and 3) exercise-induced oxidative stress may enhance the passive diffusion responsible for the apparent loss of saturation properties, possibly masking lactate transport regulation.

Lactate transport in rat sarcolemmal vesicles after a single bout of submaximal exercise.

We investigated the effects of a single bout of non-exhaustive exercise (25 m x min(-1), 10% grade, for 30 min) on the initial rates of lactate uptake in rat skeletal muscle sarcolemmal vesicles and the monocarboxylate transporter 1 (MCT1) content in isolated hindlimb muscles in relation to the exercise-induced oxidative stress. The exercise led to a decrease in red gastrocnemius and red vastus lateralis muscle glycogen content by 74% and 83%, respectively, and an increase in blood lactate concentration from 1.67 +/- 0.15 to 3.44 +/- 0.47 mM (p < 0.05). Initial rates of lactate uptake were measured in zero-trans conditions, at pH 7.4, for 1, 10, 30 and 100 mM external lactate concentrations. Lactate transport capacity was significantly decreased at 1 mM in the exercised group (p < 0.05), while a non-significant trend towards an increase was observed at 10, 30 and 100 mM. We failed to obtain any change in soleus, red tibialis anterior and white gastrocnemius muscle MCT1 content (p>0.05), and no evidence of exercise-induced oxidative stress in terms of muscle malondialdehyde content and glutathione peroxidase and superoxide dismutase activities was observed after the 30 min exercise bout. These results indicate that a single bout of submaximal exercise, which did not induce an increase in muscle MCT1 content and apparent oxidative stress, decreased lactate transport capacity at low physiological concentration. Although the changes are small and independent of a MCT1-facilitated lactate transport regulation, we suggest that another MCT isoform with different kinetic properties from MCT1 could be present in the sarcolemma and responsible for lactate exchange alterations.