Lactate up-regulates the expression of lactate oxidation complex-related genes in left ventricular cardiac tissue of rats.

BACKGROUND: Besides its role as a fuel source in intermediary metabolism, lactate has been considered a signaling molecule modulating lactate-sensitive genes involved in the regulation of skeletal muscle metabolism. Even though the flux of lactate is significantly high in the heart, its role on regulation of cardiac genes regulating lactate oxidation has not been clarified yet. We tested the hypothesis that lactate would increase cardiac levels of reactive oxygen species and up-regulate the expression of genes related to lactate oxidation complex. METHODS/PRINCIPAL FINDINGS: Isolated hearts from male adult Wistar rats were perfused with control, lactate or acetate (20mM) added Krebs-Henseleit solution during 120 min in modified Langendorff apparatus. Reactive oxygen species (O2●-/H2O2) levels, and NADH and NADPH oxidase activities (in enriched microsomal or plasmatic membranes, respectively) were evaluated by fluorimetry while SOD and catalase activities were evaluated by spectrophotometry. mRNA levels of lactate oxidation complex and energetic enzymes MCT1, MCT4, HK, LDH, PDH, CS, PGC1α and COXIV were quantified by real time RT-PCR. Mitochondrial DNA levels were also evaluated. Hemodynamic parameters were acquired during the experiment. The key findings of this work were that lactate elevated cardiac NADH oxidase activity but not NADPH activity. This response was associated with increased cardiac O2●-/H2O2 levels and up-regulation of MCT1, MCT4, LDH and PGC1α with no changes in HK, PDH, CS, COXIV mRNA levels and mitochondrial DNA levels. Lactate increased NRF-2 nuclear expression and SOD activity probably as counter-regulatory responses to increased O2●-/H2O2. CONCLUSIONS: Our results provide evidence for lactate-induced up-regulation of lactate oxidation complex associated with increased NADH oxidase activity and cardiac O2●-/H2O2 driving to an anti-oxidant response. These results unveil lactate as an important signaling molecule regulating components of the lactate oxidation complex in cardiac muscle.

Impact of leucine supplementation on exercise training induced anti-cardiac remodeling effect in heart failure mice.

Leucine supplementation potentiates the effects of aerobic exercise training (AET) on skeletal muscle; however, its potential effects associated with AET on cardiac muscle have not been clarified yet. We tested whether leucine supplementation would potentiate the anti-cardiac remodeling effect of AET in a genetic model of sympathetic hyperactivity-induced heart failure in mice (α2A/α2CARKO). Mice were assigned to five groups: wild type mice treated with placebo and sedentary (WT, n = 11), α2A/α2CARKO treated with placebo and sedentary (KO, n = 9), α2A/α2CARKO treated with leucine and sedentary (KOL, n = 11), α2A/α2CARKO treated with placebo and AET (KOT, n = 12) or α2A/α2CARKO treated with leucine and AET (KOLT, n = 12). AET consisted of four weeks on a treadmill with 60 min sessions (six days/week, 60% of maximal speed) and administration by gavage of leucine (1.35 g/kg/day) or placebo (distilled water). The AET significantly improved exercise capacity, fractional shortening and re-established cardiomyocytes' diameter and collagen fraction in KOT. Additionally, AET significantly prevented the proteasome hyperactivity, increased misfolded proteins and HSP27 expression. Isolated leucine supplementation displayed no effect on cardiac function and structure (KOL), however, when associated with AET (KOLT), it increased exercise tolerance to a higher degree than isolated AET (KOT) despite no additional effects on AET induced anti-cardiac remodeling. Our results provide evidence for the modest impact of leucine supplementation on cardiac structure and function in exercised heart failure mice. Leucine supplementation potentiated AET effects on exercise tolerance, which might be related to its recognized impact on skeletal muscle.

Resistance training regulates cardiac function through modulation of miRNA-214.

AIMS: To determine the effects of resistance training (RT) on the expression of microRNA (miRNA)-214 and its target in sarcoplasmic reticulum Ca2+-ATPase (SERCA2a), and on the morphological and mechanical properties of isolated left ventricular myocytes. MAIN METHODS: Male Wistar rats were divided into two groups (n = 7/group): Control (CO) or trained (TR). The exercise-training protocol consisted of: 4 × 12 bouts, 5×/week during 8 weeks, with 80% of one repetition maximum. KEY FINDINGS: RT increased the left ventricular myocyte width by 15% and volume by 12%, compared with control animals (p < 0.05). The time to half relaxation and time to peak were 8.4% and 4.4% lower, respectively, in cells from TR group as compared to CO group (p < 0.05). RT decreased miRNA-214 level by 18.5% while its target SERCA2a expression were 18.5% higher (p < 0.05). SIGNIFICANCE: Our findings showed that RT increases single left ventricular myocyte dimensions and also leads to faster cell contraction and relaxation. These mechanical adaptations may be related to the augmented expression of SERCA2a which, in turn, may be associated with the epigenetic modification of decreased miRNA-214 expression.

Exercise training prior to myocardial infarction attenuates cardiac deterioration and cardiomyocyte dysfunction in rats.

OBJECTIVES: The present study was performed to investigate 1) whether aerobic exercise training prior to myocardial infarction would prevent cardiac dysfunction and structural deterioration and 2) whether the potential cardiac benefits of aerobic exercise training would be associated with preserved morphological and contractile properties of cardiomyocytes in post-infarct remodeled myocardium. METHODS: Male Wistar rats underwent an aerobic exercise training protocol for eight weeks. The rats were then assigned to sham surgery (SHAM), sedentary lifestyle and myocardial infarction or exercise training and myocardial infarction groups and were evaluated 15 days after the surgery. Left ventricular tissue was analyzed histologically, and the contractile function of isolated myocytes was measured. Student's t-test was used to analyze infarct size and ventricular wall thickness, and the other parameters were analyzed by the Kruskal-Wallis test followed by Dunn's test or a one-way analysis of variance followed by Tukey's test (p<0.05). RESULTS: Myocardial infarctions in exercise-trained animals resulted in a smaller myocardial infarction extension, a thicker infarcted wall and less collagen accumulation as compared to myocardial infarctions in sedentary animals. Myocardial infarction-induced left ventricular dilation and cardiac dysfunction, as evaluated by +dP/dt and -dP/dt, were both prevented by previous aerobic exercise training. Moreover, aerobic exercise training preserved cardiac myocyte shortening, improved the maximum shortening and relengthening velocities in infarcted hearts and enhanced responsiveness to calcium. CONCLUSION: Previous aerobic exercise training attenuated the cardiac dysfunction and structural deterioration promoted by myocardial infarction, and such benefits were associated with preserved cardiomyocyte morphological and contractile properties.

Exercise training prior to myocardial infarction attenuates cardiac deterioration and cardiomyocyte dysfunction in rats

OBJECTIVES: The present study was performed to investigate 1) whether aerobic exercise training prior to myocardial infarction would prevent cardiac dysfunction and structural deterioration and 2) whether the potential cardiac benefits of aerobic exercise training would be associated with preserved morphological and contractile properties of cardiomyocytes in post-infarct remodeled myocardium. METHODS: Male Wistar rats underwent an aerobic exercise training protocol for eight weeks. The rats were then assigned to sham surgery (SHAM), sedentary lifestyle and myocardial infarction or exercise training and myocardial infarction groups and were evaluated 15 days after the surgery. Left ventricular tissue was analyzed histologically, and the contractile function of isolated myocytes was measured. Student's t-test was used to analyze infarct size and ventricular wall thickness, and the other parameters were analyzed by the Kruskal-Wallis test followed by Dunn's test or a one-way analysis of variance followed by Tukey's test (p<0.05). RESULTS: Myocardial infarctions in exercise-trained animals resulted in a smaller myocardial infarction extension, a thicker infarcted wall and less collagen accumulation as compared to myocardial infarctions in sedentary animals. Myocardial infarction-induced left ventricular dilation and cardiac dysfunction, as evaluated by +dP/dt and -dP/dt, were both prevented by previous aerobic exercise training. Moreover, aerobic exercise training preserved cardiac myocyte shortening, improved the maximum shortening and relengthening velocities in infarcted hearts and enhanced responsiveness to calcium. CONCLUSION: Previous aerobic exercise training attenuated the cardiac dysfunction and structural deterioration promoted by myocardial infarction, and such benefits were associated with preserved cardiomyocyte morphological and contractile properties. .

Treinamento em natação atenua a disfução contrátil de cardiomiócitos de ratos diabéticos / Swimming training attenuates contractile dysfunction in diabetic rat cardiomyocytes / Entrenamiento en natación atenúa la disfunción contráctil de cardiomiocitos de ratones diabéticos

FUNDAMENTO: O diabete experimental promove disfunção contrátil em cardiomiócitos, mas os efeitos do treinamento em natação nesta disfunção não são conhecidos. OBJETIVO: Testar os efeitos de um programa de treino em natação (PTN) sobre a disfunção contrátil de cardiomiócitos de ratos com diabete experimental. MÉTODOS: Ratos Wistar (idade: 30 dias; peso corporal médio: 84,19 g) com diabete induzida por estreptozotocina (60 mg/kg de peso corporal; glicemia > 300 mg/dl) foram alocados em diabéticos sedentários (DS, n = 10) e diabéticos exercitados (DE, n = 13). Animais da mesma idade e peso serviram de controles sedentários (CS, n = 10) e controles exercitados (CE, n = 06). Os animais DE e CE foram submetidos a um PTN (05 dias/semana, 90 min/dia), por 08 semanas. Os miócitos do ventrículo esquerdo (VE) foram isolados e estimulados eletricamente a 3,0 Hz em temperatura ambiente (∼ 25º C). RESULTADOS: O diabete reduziu a função contrátil nos cardiomiócitos dos animais em relação aos controles (i.e., menor amplitude de contração, maior tempo de contração e relaxamento). O PTN atenuou a redução na amplitude de contração (CS, 11 ± 0,2 por cento vs DE, 11,6 ± 0,2 por cento), o tempo para o pico de contração (CS, 319 ± 5,8 ms vs DE, 333 ± 4,8 ms) e o tempo para 50 por cento de relaxamento (CS, 619 ± 22,2 ms vs DE, 698 ± 18,6 ms) dos cardiomiócitos dos animais diabéticos. O diabete reduziu as dimensões dos cardiomiócitos, porém, o PTN minimizou a redução da largura e volume celular, sem alterar o comprimento. CONCLUSÃO: O programa de treino em natação atenuou a disfunção contrátil dos miócitos do VE de ratos com diabete experimental.

BACKGROUND: Experimental diabetes promotes contractile dysfunction in cardiomyocytes, but the effects of swimming in this disorder are not known. OBJECTIVE: To test the effects of a swimming training program (STP) on cardiomyocyte contractile dysfunction in rats with experimental diabetes. METHODS: Wistar rats (age: 30 days; mean body weight: 84.19 g) with diabetes induced by streptozotocin (60 mg/kg body weight; glucose > 300 mg/dl) were divided into sedentary diabetic rats (SD, n = 10) and exercised diabetic rats (ED, n = 13). Animals of same age and weight served as sedentary controls (SC, n = 10) and exercised controls (EC, n = 06). Animals and ED and EC underwent a STP (05 days/week, 90 min/day) for 08 weeks. Left ventricular (LV) myocytes were isolated and electrically stimulated at 3.0 Hz at room temperature (∼ 25º C). RESULTS: Diabetes reduced contractile function in cardiomyocytes of animals compared to controls (i.e., lower amplitude of contraction, longer duration of contraction and relaxation). The STP attenuated the reduced amplitude of contraction (SC, 11 ± 0.2 percent vs ED, 11.6 ± 0.2 percent), time to peak contraction (SC, 319 ± 5.8 ms vs ED, 333 ± 4.8 ms) and time to 50.0 percent of relaxation (SC, 619 ± 22.2 ms vs ED 698 ± 18.6 ms) of cardiomyocytes of diabetic rats. Diabetes reduced the size of cardiomyocytes, however, the STP minimized the reduction of cell volume and width, without changing length. CONCLUSION: The swimming training program attenuated the contractile dysfunction of the LV myocytes of rats with experimental diabetes.

FUNDAMENTO: La diabetes experimental promueve el trastorno contráctil de los cardiomiocitos, pero los efectos del entrenamiento en natación en este trastorno no se conocen. OBJETIVO: Probar los efectos de un programa de capacitación en natación (PTN) sobre el trastorno contráctil de cardiomiocitos de ratas con diabetes experimental. MÉTODOS: Ratas Wistar (edad: 30 días, peso corporal medio: 84,19 g) con diabetes inducida por estreptozotocina (60 mg/kg de peso corporal, glucosa > 300 mg/dl) fueron divididos en diabéticos sedentarios (DS, n = 10) y diabéticos ejercitados (DE, n = 13). Animales de la misma edad y peso sirvieron de controles sedentarios (CS, n = 10) y controles ejercitados (CE, n = 06). Los animales DE y CE se sometieron a un PTN (05 días/semana, 90 min/día), por 08 semanas. Los miocitos del ventrículo izquierdo (VI) fueron aislados y estimulados eléctricamente a 3,0 Hz en temperatura ambiente (~ 25º C). RESULTADOS: La diabetes disminuyó la función contráctil de los cardiomiocitos de los animales en comparación con los controles (es decir, menor amplitud de la contracción, la duración de la contracción y relajación). El PTN atenuó la reducción de la amplitud de la contracción (CS, 11 ± 0,2 por ciento frente a la DE, 11,6 ± 0,2 por ciento), el tiempo para la contracción máxima (CS, 319 ± 5,8 ms vs DE, 333 ± 4,8 ms) y el tiempo para el 50 por ciento de relajación (CS, 619 ± 22,2 ms vs DE, 698 ± 18,6 ms) de los cardiomiocitos de los animales diabéticos. La diabetes redujo las dimensiones de los cardiomiocitos, sin embargo, el PTN minimizó la reducción de la anchura y volumen celular, sin cambiar la longitud. CONCLUSIÓN: El programa de entrenamiento de natación atenuó la disfunción contráctil de los miocitos del VI de las ratas con diabetes experimental.

Treinamento em natação com baixa intensidade não protege músculo esquelético contra lesões induzidas por exercício exaustivo em ratos / Low-intensity swimming training does not protect the skeletal muscle

Enquanto o exercício aeróbico regular promove adaptações benéficas ao músculo esquelético, o exercício físico exaustivo induz lesões musculares. O objetivo deste estudo foi verificar se um programa de natação com baixa intensidade é capaz de proteger músculos esqueléticos contra lesões induzidas por exercício exaustivo. Ratos Wistar (peso: 376,50 ± 4,36g; idade: 90 dias) foram divididos aleatoriamente em quatro grupos: controle sedentário (CS); sedentário submetido a teste de exaustão (SE); treinado em natação (TN); treinado em natação submetido a teste de exaustão (TNE). Animais dos grupos TN e TNE foram submetidos a um programa de natação sem sobrecarga por 90 minutos/dia, cinco dias/semana, durante 17 semanas. Após este período, os grupos SE e TNE foram submetidos a um teste de exaustão em natação. Após eutanásia, fragmentos dos músculos sóleo e reto femoral foram coletados e submetidos à análise histológica e de proteínas de choque térmico (HSP70). Os resultados mostraram que o tempo até a exaustão foi maior no grupo TNE que no SE (125,0 ± 6,0 vs. 90,0 ± 8,5min, respectivamente, P < 0,05). Os níveis de lactato sanguíneo durante o teste e exaustão foram menores no grupo TNE que no SE (5,31 ± 0,22 vs. 8,76 ± 0,59mmol/L, respectivamente, P < 0,05). A frequência de fibras lesadas nos músculos foi maior nos grupos SE (sóleo: 34,86 ± 0,04; reto femoral: 37,57 ± 0,07) e TNE (sóleo: 41,57 ± 0,08; reto femoral: 39,57 ± 0,05), comparada aos grupos CS (sóleo: 13,88 ± 0,81; reto femoral: 16,75 ± 0,79) e TN (sóleo: 24,14 ± 0,06; reto femoral: 24,0 ± 0,05), respectivamente (P < 0,05). Não houve diferença significativa nos níveis de HSP70 dos músculos analisados entre os quatro grupos. Concluimos que apesar do treinamento em natação melhorar o desempenho dos animais no teste de exaustão, não promoveu proteção aos seus músculos esqueléticos contra as lesões induzidas pelo exercício exaustivo.

While regular aerobic exercise promotes beneficial adaptations to the skeletal muscle, acute exhaustive exercise causes structural damage to the skeletal muscle cells. The aim of this study was to verify whether a low-intensity swimming program protects the skeletal muscles against damage induced by exhaustive exercise. Male Wistar rats (weight: 376.50 4.36g; age: 90 days) were randomly divided into four groups: sedentary control (SC, N=8); sedentary submitted to exhaustive test (SE, N=7); swimming trained (TN, N=7); swimming trained submitted to exhaustive test (TNE, N=7). Animals of TN and TNE groups were submitted to a swimming regimen without overload for 90 min/day, 5 days/wk, during 17 weeks. Forty-eight hours after the last training session, animals from SE and TNE groups were submitted to an exhaustive exercise protocol. At sacrifice, fragments of soleus and rectus femoris muscles were collected and submitted to histological analysis and heat shock protein (HSP70) expression measurement. The results showed that the time until exhaustion was greater in the STE than in SE group (125.0 6.00 vs. 90.0 8.48 min, respectively, P<0.05). The levels of blood lactate during exhaustive exercise were lower in animals from TNE than SE (5.31 ± 0.22 vs. 876 ± 0.59 mmol/L, respectively, P<0.05)The frequency of damaged fibers in the muscles was greater in SE (soleus: 34.86±0.04; rectus femoris: 37.57 ± 0.07) and STE (soleus: 41.57±0.08; rectus femoris: 39.57 ± 0.05), compared to groups SC (soleus: 13.88±0.81; rectus femoris: 16.75 ± 0.79) and ST (soleus: 24.14±0.06; rectus femoris: 24.0 ± 0.05), respectively (P<0.05). There was no significant difference at the HSP70 levels of the analyzed muscles among the four groups (P>0.05). In conclusion, although a low-intensity swimming training increased the animals' performance in the exhaustive exercise test, it did not protect their skeletal muscles against damage induced by exhaustive exercise.

Swimming training attenuates contractile dysfunction in diabetic rat cardiomyocytes.

BACKGROUND: Experimental diabetes promotes contractile dysfunction in cardiomyocytes, but the effects of swimming in this disorder are not known. OBJECTIVE: To test the effects of a swimming training program (STP) on cardiomyocyte contractile dysfunction in rats with experimental diabetes. METHODS: Wistar rats (age: 30 days; mean body weight: 84.19 g) with diabetes induced by streptozotocin (60 mg/kg body weight; glucose > 300 mg/dl) were divided into sedentary diabetic rats (SD, n = 10) and exercised diabetic rats (ED, n = 13). Animals of same age and weight served as sedentary controls (SC, n = 10) and exercised controls (EC, n = 06). Animals and ED and EC underwent a STP (05 days/week, 90 min/day) for 08 weeks. Left ventricular (LV) myocytes were isolated and electrically stimulated at 3.0 Hz at room temperature (∼ 25º C). RESULTS: Diabetes reduced contractile function in cardiomyocytes of animals compared to controls (i.e., lower amplitude of contraction, longer duration of contraction and relaxation). The STP attenuated the reduced amplitude of contraction (SC, 11 ± 0.2% vs ED, 11.6 ± 0.2%), time to peak contraction (SC, 319 ± 5.8 ms vs ED, 333 ± 4.8 ms) and time to 50.0% of relaxation (SC, 619 ± 22.2 ms vs ED 698 ± 18.6 ms) of cardiomyocytes of diabetic rats. Diabetes reduced the size of cardiomyocytes, however, the STP minimized the reduction of cell volume and width, without changing length. CONCLUSION: The swimming training program attenuated the contractile dysfunction of the LV myocytes of rats with experimental diabetes.

Short-term in vivo inhibition of nitric oxide synthase with L-NAME influences the contractile function of single left ventricular myocytes in rats.

The main purpose of this study was to investigate the effects of short-term L-NAME treatment on the contractile function of left ventricle (LV) myocytes and the expression of proteins related to Ca(2+) homeostasis. Data from Wistar rats treated with L-NAME (L group, n = 20; 0.7 g/L in drinking water; 7 days) were compared with results from untreated controls (C group, n = 20). Cardiomyocytes from the L group showed increased (p < 0.05) fractional shortening (23%) and maximum rate of shortening (20%) compared with the C group. LV from the L group also showed increased (p < 0.05) expression of the ryanodine receptor 2 and Na(+)/Ca(2+) exchanger proteins (76% and 83%, respectively; p < 0.05). However, the L and C groups showed similar in vivo hemodynamic parameters of cardiac function. In conclusion, short-term NOS inhibition determines an increased expression of Ca(2+) regulatory proteins, which contributes to improving cardiomyocyte contractile function, preserving left ventricular function.