Respiratory muscle training improves diaphragm citrate synthase activity and hemodynamic function in rats with heart failure

Abstract INTRODUCTION: Enhanced respiratory muscle strength in patients with heart failure positively alters the clinical trajectory of heart failure. In an experimental model, respiratory muscle training in rats with heart failure has been shown to improve cardiopulmonary function through mechanisms yet to be entirely elucidated. OBJECTIVE: The present report aimed to evaluate the respiratory muscle training effects in diaphragm citrate synthase activity and hemodynamic function in rats with heart failure. METHODS: Wistar rats were divided into four experimental groups: sedentary sham (Sed-Sham, n=8), trained sham (RMT-Sham, n=8), sedentary heart failure (Sed-HF, n=7) and trained heart failure (RMT-HF, n=7). The animals were submitted to a RMT protocol performed 30 minutes a day, 5 days/week, for 6 weeks. RESULTS: In rats with heart failure, respiratory muscle training decreased pulmonary congestion and right ventricular hypertrophy. Deleterious alterations in left ventricular pressures, as well as left ventricular contractility and relaxation, were assuaged by respiratory muscle training in heart failure rats. Citrate synthase activity, which was significantly reduced in heart failure rats, was preserved by respiratory muscle training. Additionally, a negative correlation was found between citrate synthase and left ventricular end diastolic pressure and positive correlation was found between citrate synthase and left ventricular systolic pressure. CONCLUSION: Respiratory muscle training produces beneficial adaptations in the diaphragmatic musculature, which is linked to improvements in left ventricular hemodynamics and blood pressure in heart failure rats. The RMT-induced improvements in cardiac architecture and the oxidative capacity of the diaphragm may improve the clinical trajectory of patients with heart failure.

Effect of hydrogen peroxide on rabbit urinary bladder citrate synthase activity in the presence and absence of a grape suspension

PURPOSE: The etiology of obstructive bladder dysfunction includes free radical damage to mitochondria. Feeding rabbits a standardized grape suspension protects the ability of the bladder to contract and empty in part by preventing mitochondrial damage, thus maintaining smooth muscle and mucosal metabolism. The objective of the current study is to determine the direct effect of this grape suspension on the response of mitochondria to the oxidative effects of hydrogen peroxide. MATERIALS AND METHODS: Six male rabbits were anesthetized with sodium pentobarbital and the bladders excised. Four full thickness strips were obtained for contractile studies and the balance separated into smooth muscle and mucosa compartments by blunt dissection. The effect of hydrogen peroxide on the contractile response to field stimulation was quantitated. Each tissue was homogenized and the effects of increasing concentrations of hydrogen peroxide in the presence and absence of grape suspension on citrate synthase activity was determined. RESULTS: Citrate synthase activity was significantly higher in the mucosa than in the muscle. The grape suspension had no effect on control citrate synthase activity. However, the grape suspension provided significant protection of both smooth muscle and mucosal citrate synthase activity. CONCLUSIONS: These studies support the conclusion that the grape suspension provides direct protection of mitochondrial function.

Swimming training increases cardiac vagal activity and induces cardiac hypertrophy in rats

The effect of swimming training (ST) on vagal and sympathetic cardiac effects was investigated in sedentary (S, N = 12) and trained (T, N = 12) male Wistar rats (200-220 g). ST consisted of 60-min swimming sessions 5 days/week for 8 weeks, with a 5 percent body weight load attached to the tail. The effect of the autonomic nervous system in generating training-induced resting bradycardia (RB) was examined indirectly after cardiac muscarinic and adrenergic receptor blockade. Cardiac hypertrophy was evaluated by cardiac weight and myocyte morphometry. Plasma catecholamine concentrations and citrate synthase activity in soleus muscle were also determined in both groups. Resting heart rate was significantly reduced in T rats (355 ± 16 vs 330 ± 20 bpm). RB was associated with a significantly increased cardiac vagal effect in T rats (103 ± 25 vs 158 ± 40 bpm), since the sympathetic cardiac effect and intrinsic heart rate were similar for the two groups. Likewise, no significant difference was observed for plasma catecholamine concentrations between S and T rats. In T rats, left ventricle weight (13 percent) and myocyte dimension (21 percent) were significantly increased, suggesting cardiac hypertrophy. Skeletal muscle citrate synthase activity was significantly increased by 52 percent in T rats, indicating endurance conditioning. These data suggest that RB induced by ST is mainly mediated parasympathetically and differs from other training modes, like running, that seems to mainly decrease intrinsic heart rate in rats. The increased cardiac vagal activity associated with ST is of clinical relevance, since both are related to increased life expectancy and prevention of cardiac events.

Ginseng administration protects skeletal muscle from oxidative stress induced by acute exercise in rats

Enzymatic activity was analyzed in the soleus, gastrocnemius (red and white) and plantaris muscles of acutely exercised rats after long-term administration of Panax ginseng extract in order to evaluate the protective role of ginseng against skeletal muscle oxidation. Ginseng extract (3, 10, 100, or 500 mg/kg) was administered orally for three months to male Wistar rats weighing 200 ± 50 g before exercise and to non-exercised rats (N = 8/group). The results showed a membrane stabilizing capacity of the extract since mitochondrial function measured on the basis of citrate synthase and 3-hydroxyacyl-CoA dehydrogenase activities was reduced, on average, by 20 percent (P < 0.05) after exercise but the activities remained unchanged in animals treated with a ginseng dose of 100 mg/kg. Glutathione status did not show significant changes after exercise or treatment. Lipid peroxidation, measured on the basis of malondialdehyde levels, was significantly higher in all muscles after exercise, and again was reduced by about 74 percent (P < 0.05) by the use of ginseng extract. The administration of ginseng extract was able to protect muscle from exercise-induced oxidative stress irrespective of fiber type.

Physiological constraints in the aerobic performance of hummingbirds

Hovering flight has been described as the most energetically expensive form of locomotion. Among the vertebrates, hummingbirds weighing only 1.5-20 g are the elite practitioners of this aerial art. Their flight muscles are, therefore, the most oxygen demanding locomotor muscles per unit tissue mass of all vertebrates. Tissue level functional and structural adaptations for oxygen transport are compared between hummingbirds and mammals in this paper. Hummingbirds present extreme structural adaptations in their flight muscles. Mitochondrial densities greater than 30 per cent are observed in their pectoral muscles, and the surface area of the inner membrane of their mitochondria is tvace that of mammals. This doubling of their mitochondrial oxidative capacity is accompanied by a proportional increase in the specific activity (per g tissue) of the mitochondrial manganese superoxide dismutase (SOD-Mn) in their flight muscles, thus indicating that oxygen toxicity is not a constraint in the aerobic performance of hummingbirds during hovering flight. Finally, the liver appears to play a major role in providing the necessary substrates for their high aerobic performance, and also in eliminating the oxygen free radicals formed during oxidative phosphorylation.

Esforço contínuo vs esforço intermitente: adaptaçäo bioquímica / Continous exercise vs intermittent exercise: biochemical adaptation

Foi estudo o efeito crônico de dois tipos de exercício (intermitente e contínuo) sobre a atividade de algumas enzimas do músculo do ratinho. O programa de treinos teve a duraçäo de 6 meses, 5 dias por semana, e foi executado num tapete rolante adaptado para animais. O grupo sujeito a corrida intermitente realizou o exercício a uma velocidade de 975m/h com fases de esforço de 30 segundos e com períodos de recuperaçäo de igual duraçäo. O grupo sujetio a exercício contínuo realizou o protocolo com igual velocidade sem fases de recuperaçäo. Os dois protocolos tiveram a duraçäo de 2 x 30 minutos com intervalo de 10 minutos. Foi analisada a atividade enzimática da creatina-quinase (CK), da lactato-desidrogenase (LDH) e da citrato-sintetase (CS). Näo foi encontrada qualquer variaçiao signficativa entre os grupos exercitados, apesar de se ter verificado näo só uma descida da atividade da LDH e uma subida da atividade da CK nos grupos exercitados, mas também uma descida ligeiro da atividade da CS no grupo intermitente e um aumento da atividade da CS no grupo sujeito a esforço contínuo. Os resultados sugerem diferentes mecanismos da adaptaçäo enzimática aos diferentes programas de treino

Citrate Synthase ande lactate dehydrogenase activities in rat cerebral cortex following the administration of the convulsants bicuculline and 3-mercaptopropionic acid

La administración intraperitoneal de bicuculina (Bic) y ácido 3-mercaptopropiónico (MP) produce convulsiones generalizadas en animales de laboratorio. En este trabajo se estudió el efecto de estos convulsivantes sobre la actividad de la lactato deshidrogenasa y de citrato sintasa de corteza cerebral de rata. La Bic se administró en dosis de1.0 mg/Kg (subconvulsiva) y 7.5 mg/Kg (convulsiva) y el MP en dosis de 150 mg/Kg (convulsiva). La actividad de lactato deshidrogenasa en fracciones solubre y particulada de corteza cerebral no se modificó por la administración de Bic o MP. La actividad de citrato sintasa en homogeneizados de corteza cerebral aumentó alrededor del 40% por la administración de Bic en dosis subconvulsiva y convulsiva; un aumento semejante se encontró por la administración de MP. No se encontró modificación en la actividad de la enzima hepática, sugiriendo especificidad de tejido. La mayor actividad de citrato sintasa en homogeneizados de corteza cerebral encontrada luego de la administración de los convulsivantes se correlaciona con el aumento en los niveles de citrato cerebral descriptos en estados convulsivos