RESUMO
Protocols that mimic resistance exercise training (RET) in rodents present several limitations, one of them being the electrical stimulus, which is beyond the physiological context observed in humans. Recently, our group developed a conditioning system device that does not use electric shock to stimulate rats, but includes fasting periods before each RET session. The current study was designed to test whether cumulative fasting periods have some influence on skeletal muscle mass and function. Three sets of male Wistar rats were used in the current study. The first set of rats was submitted to a RET protocol without food restriction. However, rats were not able to perform exercise properly. The second and third sets were then randomly assigned into three experimental groups: 1) untrained control rats, 2) untrained rats submitted to fasting periods, and 3) rats submitted to RET including fasting periods before each RET session. While the second set of rats performed a short RET protocol (i.e., an adaptation protocol for 3 weeks), the third set of rats performed a longer RET protocol including overload (i.e., 8 weeks). After the short-term protocol, cumulative fasting periods promoted loss of weight (P<0.001). After the longer RET protocol, no difference was observed for body mass, extensor digitorum longus (EDL) morphology or skeletal muscle function (P>0.05 for all). Despite no effects on EDL mass, soleus muscle displayed significant atrophy in the fasting experimental groups (P<0.01). Altogether, these data indicate that fasting is a major limitation for RET in rats.
Assuntos
Jejum/fisiologia , Músculo Esquelético/fisiologia , Condicionamento Físico Animal/fisiologia , Treinamento Resistido/métodos , Adaptação Fisiológica , Animais , Peso Corporal/fisiologia , Ingestão de Alimentos/fisiologia , Masculino , Distribuição Aleatória , Ratos Wistar , Valores de Referência , Fatores de TempoRESUMO
Two experiments were performed, in which male Wistar Walker 256 tumor-bearing rats were inoculated with 4 × 10(7) tumor cells subcutaneously and received either creatine (300 mg/kg body weight/day; CR) or placebo (water; PL) supplementation via intragastric gavage. In experiment 1, 50 rats were given PL (n = 22) or CR (n = 22) and a non-supplemented, non-inoculated group served as control CT (n = 6), for 40 days, and the survival rate and tumor mass were assessed. In experiment 2, 25 rats were given CR or PL for 15 days and sacrificed for biochemical analysis. Again, a non-supplemented, non-inoculated group served as control (CT; n = 6). Tumor and muscle creatine kinase (CK) activity and total creatine content, acidosis, inflammatory cytokines, and antioxidant capacity were assessed. Tumor growth was significantly reduced by approximately 30 % in CR when compared with PL (p = 0.03), although the survival rate was not significantly different between CR and PL (p = 0.65). Tumor creatine content tended to be higher in CR than PL (p = 0.096). Tumor CK activity in the cytosolic fraction was higher in CR than PL (p < 0.0001). Blood pCO2 was higher in CT and CR than PL (p = 0.0007 and p = 0.004, respectively). HCO3 was augmented in CT compared to PL (p = 0.03) and CR (p = 0.001). Plasma IL-6 was lower and IL-10 level was higher in CR than PL (p = 0.03 and p = 0.0007, respectively) and TNF-alpha featured a tendency of decrease in CR compared to PL (p = 0.08). Additionally, total antioxidant capacity tended to be lower in CT than PL (p = 0.07). Creatine supplementation was able to slow tumor growth without affecting the overall survival rate, probably due to the re-establishment of the CK-creatine system in cancer cells, leading to attenuation in acidosis, inflammation, and oxidative stress. These findings support the role of creatine as a putative anti-cancer agent as well as help in expanding our knowledge on its potential mechanisms of action in malignancies.
Assuntos
Antineoplásicos/farmacologia , Creatina Quinase Forma MM/metabolismo , Creatina/farmacologia , Proteínas de Neoplasias/metabolismo , Neoplasias Experimentais/tratamento farmacológico , Animais , Antineoplásicos/farmacocinética , Creatina/farmacocinética , Masculino , Neoplasias Experimentais/enzimologia , Neoplasias Experimentais/patologia , Ratos , Ratos WistarRESUMO
Skeletal muscle is the major deposit of protein molecules. As for any cell or tissue, total muscle protein reflects a dynamic turnover between net protein synthesis and degradation. Noninvasive and invasive techniques have been applied to determine amino acid catabolism and muscle protein building at rest, during exercise and during the recovery period after a single experiment or training sessions. Stable isotopic tracers ((13)C-lysine, (15)N-glycine, ²H5-phenylalanine) and arteriovenous differences have been used in studies of skeletal muscle and collagen tissues under resting and exercise conditions. There are different fractional synthesis rates in skeletal muscle and tendon tissues, but there is no major difference between collagen and myofibrillar protein synthesis. Strenuous exercise provokes increased proteolysis and decreased protein synthesis, the opposite occurring during the recovery period. Individuals who exercise respond differently when resistance and endurance types of contractions are compared. Endurance exercise induces a greater oxidative capacity (enzymes) compared to resistance exercise, which induces fiber hypertrophy (myofibrils). Nitrogen balance (difference between protein intake and protein degradation) for athletes is usually balanced when the intake of protein reaches 1.2 g · kg(-1) · day(-1) compared to 0.8 g · kg(-1) · day(-1) in resting individuals. Muscular activities promote a cascade of signals leading to the stimulation of eukaryotic initiation of myofibrillar protein synthesis. As suggested in several publications, a bolus of 15-20 g protein (from skimmed milk or whey proteins) and carbohydrate (± 30 g maltodextrine) drinks is needed immediately after stopping exercise to stimulate muscle protein and tendon collagen turnover within 1 h.
Assuntos
Aminoácidos Essenciais/administração & dosagem , Atletas , Proteínas Alimentares/administração & dosagem , Exercício Físico/fisiologia , Proteínas Musculares/metabolismo , Músculo Esquelético/metabolismo , Recomendações Nutricionais , Aminoácidos Essenciais/farmacocinética , Metabolismo Energético/fisiologia , Humanos , Proteínas do Leite/administração & dosagem , Proteínas Musculares/fisiologia , Músculo Esquelético/fisiologia , Resistência Física/fisiologia , Biossíntese de Proteínas/fisiologia , Proteínas do Soro do LeiteRESUMO
Abstract quality of life. Since there is no currently effective and safe treatment available for skeletal muscle atrophy, the search for new alternatives is necessary. Resistance exercise (RE) seems to be an important tool in the treatment of disuse-induced skeletal muscle atrophy by promoting positive functional (strength and power) and structural (hypertrophy and phenotypic changes) adaptive responses. Human and animal studies using different types of resistance exercise (flywheel, vascular occlusion, dynamic, isometric, and eccentric) have obtained results of great importance. However, since RE is a complex phenomenon, lack of strict control of its variables (volume, frequency, intensity, muscle action, rest intervals) limits the interpretation of the impact of the manipulation on skeletal muscle remodeling and function under disuse. The aim of this review is to critically describe the functional and morphological role of resistance exercise in disuse-induced skeletal muscle atrophy with emphasis on the principles of training.
Assuntos
Força Muscular/fisiologia , Músculo Esquelético/fisiopatologia , Atrofia Muscular/terapia , Treinamento Resistido/efeitos adversos , Humanos , Hipertrofia/terapiaRESUMO
Heart failure (HF) is associated with changes in the skeletal muscle (SM) which might be a consequence of the unbalanced local expression of pro- (TNF-alpha) and anti- (IL-10) inflammatory cytokines, leading to inflammation-induced myopathy, and SM wasting. This local effect of HF on SM may, on the other hand, contribute to systemic inflammation, as this tissue actively secretes cytokines. Since increasing evidence points out to an anti-inflammatory effect of exercise training, the goal of the present study was to investigate its effect in rats with HF after post-myocardial infarction (MI), with special regard to the expression of TNF-alpha and IL-10 in the soleus and extensor digitorum longus (EDL), muscles with different fiber composition. Wistar rats underwent left thoracotomy with ligation of the left coronary artery, and were randomly assigned to either a sedentary (Sham-operated and MI sedentary) or trained (Sham-operated and MI trained) group. Animals in the trained groups ran on a treadmill (0% grade at 13-20 m/min) for 60 min/day, 5 days/week, for 8-10 weeks. The training protocol was able to reverse the changes induced by MI, decreasing TNF-alpha protein (26%, P<0.05) and mRNA (58%, P<0.05) levels in the soleus, when compared with the sedentary MI group. Training also increased soleus IL-10 expression (2.6-fold, P<0.001) in post-MI HF rats. As a consequence, the IL-10/TNF-alpha ratio was increased. This "anti-inflammatory effect" was more pronounced in the soleus than in the EDL, suggesting a fiber composition dependent response.
Assuntos
Interleucina-10/metabolismo , Músculo Esquelético/metabolismo , Infarto do Miocárdio/metabolismo , Condicionamento Físico Animal , Fator de Necrose Tumoral alfa/metabolismo , Animais , Peso Corporal , Ecocardiografia , Insuficiência Cardíaca/metabolismo , Masculino , Músculo Esquelético/anatomia & histologia , Tamanho do Órgão , Distribuição Aleatória , Ratos , Ratos WistarRESUMO
OBJECTIVE: Since visceral adipose tissue (VAT) may account for impaired peripheral and hepatic insulin sensitivity (IS), it has been hypothesized that the partial removal of VAT could result in improved insulin action, while the re-growth of the excised tissue and/or compensatory growth of non-excised depots seems to occur. Thus, it was aimed to investigate whether or not VAT removal and exercise affect IS. METHODS: Male Wistar rats were fed a high-fat diet and subsequently assigned randomly to one of four groups: 1. exercised plus lipectomized (EL), 2. exercised plus sham-lipectomized (ES), 3. sedentary plus lipectomized (CL), 4. sedentary plus sham-lipectomized (CS). After lipectomy, EL and ES animals underwent a 7-consecutive-day training period. Body weight, food intake, basal metabolic rate, fasting glucose, and glucose tolerance were assessed before and after the interventions. Fasting insulin and the HOMA index, body fat mass, and the expression of pro-inflammatory genes were assessed after the interventions. RESULTS: EL group showed greater insulin sensitivity compared to all other groups. EL and ES groups showed lower fasting insulin levels when compared to CL and CS groups, respectively. The EL group showed improved IS when compared to the remaining groups. The CL group showed impaired glucose tolerance and increased TNF-alpha gene expression. Body weight and fat mass did not differ among the groups. PPAR gamma gene expression was increased in the EL and ES groups. CONCLUSIONS: These results showed that short-term swimming training improved insulin sensitivity, but failed to prevent fat regain in lipectomized animals. Lipectomy induced impaired glucose tolerance, which is probably related to increased TNF-alpha gene expression. It is possible that a high-fat diet might be implicated in faster regain of adipose tissue after lipectomy. Our results also show that short-term exercise associated with lipectomy could improve insulin sensitivity.
Assuntos
Gorduras na Dieta/administração & dosagem , Intolerância à Glucose/prevenção & controle , Lipectomia/efeitos adversos , Condicionamento Físico Animal/fisiologia , Aumento de Peso/fisiologia , Gordura Abdominal/metabolismo , Tecido Adiposo/química , Adiposidade , Animais , Metabolismo Basal , Biomarcadores/metabolismo , Glicemia/análise , Peso Corporal , Dieta , Ingestão de Energia , Epididimo , Jejum/sangue , Intolerância à Glucose/etiologia , Teste de Tolerância a Glucose , Inflamação/metabolismo , Insulina/sangue , Masculino , Músculo Esquelético/metabolismo , PPAR alfa/genética , PPAR alfa/metabolismo , RNA Mensageiro/metabolismo , Distribuição Aleatória , Ratos , Ratos Wistar , Natação , Fator de Necrose Tumoral alfa/genética , Fator de Necrose Tumoral alfa/metabolismoRESUMO
BACKGROUND/OBJECTIVES: We applied three dietary assessment methods and aimed at obtaining a set of physical, social and psychological variables that can discriminate those individuals who did not underreport ('never under-reporters'), those who underreported in one dietary assessment method ('occasional under-reporters') and those who underreported in two or three dietary assessment methods ('frequent under-reporters'). PARTICIPANTS/METHODS: Sixty-five women aged 18-57 years were recruited for this study. Total energy expenditure was determined by doubly labelled water, and energy intake was estimated by three 24-h diet recalls, 3-day food records and a food frequency questionnaire. A multiple discriminant analysis was used to identify which of those variables better discriminated the three groups: body mass index (BMI), income, education, social desirability, nutritional knowledge, dietary restraint, physical activity practice, body dissatisfaction and binge-eating symptoms. RESULTS: Twenty-three participants were 'never under-reporters'. Twenty-four participants were 'occasional under-reporters' and 18 were 'frequent under-reporters'. Four variables entered the discriminant model: income, BMI, social desirability and body dissatisfaction. According to potency indices, income contributed the most to the total discriminant power, followed in decreasing order by social desirability score, BMI and body dissatisfaction. Income, social desirability and BMI were the characteristics that mainly separated the 'never under-reporters' from the under-reporters (occasional or frequent). Body dissatisfaction better discriminated the 'occasional under-reporters' from the 'frequent under-reporters'. CONCLUSIONS: 'Frequent under-reporters' have a greater BMI, social desirability score, body dissatisfaction score and lower income. These four variables seemed to be able to discriminate individuals who are more prone to systematic under reporting.
Assuntos
Água Corporal/metabolismo , Ingestão de Energia/fisiologia , Avaliação Nutricional , Autorrevelação , Mulheres/psicologia , Adolescente , Adulto , Índice de Massa Corporal , Deutério , Registros de Dieta , Análise Discriminante , Comportamento Alimentar/psicologia , Feminino , Humanos , Renda , Rememoração Mental , Pessoa de Meia-Idade , Obesidade/psicologia , Isótopos de Oxigênio , Desejabilidade Social , Inquéritos e Questionários , Magreza/psicologia , Adulto JovemRESUMO
Recent findings have indicated that creatine supplementation may affect glucose metabolism. This study aimed to examine the effects of creatine supplementation, combined with aerobic training, on glucose tolerance in sedentary healthy male. Subjects (n = 22) were randomly divided in two groups and were allocated to receive treatment with either creatine (CT) ( approximately 10 g . day over three months) or placebo (PT) (dextrose). Administration of treatments was double blind. Both groups underwent moderate aerobic training. An oral glucose tolerance test (OGTT) was performed and both fasting plasma insulin and the homeostasis model assessment (HOMA) index were assessed at the start, and after four, eight and twelve weeks. CT demonstrated significant decrease in OGTT area under the curve compared to PT (P = 0.034). There were no differences between groups or over time in fasting insulin or HOMA. The results suggest that creatine supplementation, combined with aerobic training, can improve glucose tolerance but does not affect insulin sensitivity, and may warrant further investigation with diabetic subjects.
Assuntos
Creatina/farmacologia , Exercício Físico/fisiologia , Glucose/metabolismo , Insulina/fisiologia , Adulto , Teste de Tolerância a Glucose , Humanos , Insulina/sangue , MasculinoRESUMO
During intense exercise there is an augmented production of ammonia and IMP in the exercised muscle that could be related to the establishment of peripheral fatigue. In order to prevent this accumulation, the urea cycle in the liver eliminates ammonia in the form of urea and the skeletal muscle buffers the increase of ammonia via transamination reactions. In the present study we evaluated the effect of arginine, citrulline and ornithine supplementation, intermediates of the urea cycle, on the performance of sedentary and swimming-trained rats submitted to a single bout of exhaustive exercise. We also measured the glycogen content of the soleus and gastrocnemius muscles and of the liver, as well as the plasma concentrations of ammonia, urea, glutamine, glucose and lactate. The results indicate that arginine, citrulline and ornithine supplementation increased the flux of substrate through the reaction catalysed by glutamine synthetase, leading to increased glutamine production after an exhaustive bout of exercise, and of the mechanism involved in ammonia buffering.
Assuntos
Arginina/administração & dosagem , Citrulina/administração & dosagem , Ornitina/administração & dosagem , Natação/fisiologia , Amônia/metabolismo , Animais , Suplementos Nutricionais , Glutamato-Amônia Ligase/metabolismo , Glutamina/metabolismo , Glicogênio/metabolismo , Fígado/metabolismo , Masculino , Músculo Esquelético/metabolismo , Ratos , Ratos Wistar , Ureia/metabolismoRESUMO
The present study examined the effect of diet supplementation of oxaloacetate precursors (aspartate and asparagine) and carnitine on muscle metabolism and exercise endurance. The results suggest that the diet supplementation increased the capacity of the muscle to utilize FFA and spare glycogen. Time to exhaustion was about 40% longer in the experimental group compared to the control, which received commercial diet only. These findings suggest that oxaloacetate may be important to determine the time to exhaustion during a prolonged and moderate exercise.
Assuntos
Asparagina/farmacologia , Ácido Aspártico/farmacologia , Carnitina/farmacologia , Músculo Esquelético/metabolismo , Esforço Físico/fisiologia , Animais , Asparagina/sangue , Ácido Aspártico/sangue , Glicemia/metabolismo , Carnitina/sangue , Citrato (si)-Sintase/metabolismo , Dieta , Ácidos Graxos/metabolismo , Glicogênio/metabolismo , Glicogênio Hepático/metabolismo , Masculino , Músculo Esquelético/efeitos dos fármacos , Músculo Esquelético/enzimologia , Oxaloacetatos/metabolismo , Oxirredução , Condicionamento Físico Animal , Ratos , Ratos Wistar , NataçãoRESUMO
The mitochondrial pyruvate carboxylase catalyses the ATP-dependent carboxylation of pyruvate to oxaloacetate. Since pyruvate carboxylase generates oxaloacetate for Krebs cycle function, it is proposed that the enzyme activity may be enhanced by exercise. To investigate this proposition, pyruvate carboxylase activity was determined in the heart, soleus and gastrocnemius (white portion) muscles of sedentary and swimming-trained adult rats (1 hour per day, 5 days a week, during 5 weeks) under the following conditions: rest, one hour of exercise and exhaustion. The results show that the pyruvate carboxylase activity is increased during exercise in both the sedentary and trained groups of rats. The stimulatory mechanism is unknown but it is possibly related to the generation of pyruvate from the breakdown of glycogen and acetyl CoA during fatty acid oxidation.