Selected enzyme activities in mouse cardiac muscle during training and terminated training

Subcutaneous B16 melanoma impairs intrinsic pressure generation and relaxation of the heart, which are not restored by short-term voluntary exercise in mice

The aim of this study was to investigate whether subcutaneous melanoma impairs intrinsic cardiac function and hypoxia tolerance in mice. Additionally it was investigated whether these changes could be prevented by voluntary running-wheel exercise. The role of different molecular pathways were also analysed. Male mice (C57Bl/6NCrl) were divided into unexercised tumor-free group, unexercised melanoma group and exercised melanoma group. Experiment lasted 2.7±0.1 weeks (determined by the tumor size) after which the heart function was measured in different oxygen levels ex vivo using Langendorff method. All the melanoma mice had lower pressure amplitude (50.3%), rate of pressure production (54.1%) and decline (52.5%) in hearts ex vivo as compared to tumor-free group. There were no functional differences between the two melanoma groups. All the groups had similar weight change, heart weights, cardiomyocyte sizes, levels of Ca²⁺-channels, energy metabolism enzyme activities, lipid peroxidation and reactive oxygen species in their cardiac tissue homogenates. However, all the melanoma mice had 7.4% lower superoxidase dismutase activity compared to the control animals, which might reduce the ability of the heart to react to changes in oxidative stress. The exercising melanoma group had 28.6% higher average heart capillary density compared to the unexercised melanoma group. Short-term wheel running did not affect the tumor growth. In conclusion, subcutaneous melanoma seems to impair intrinsic heart function even prior to cachexia and these functional alterations were not caused by any of the measured molecular markers. Short-term voluntary running-wheel exercise was insufficient to alleviate the intrinsic cardiac impairments caused by melanoma.

Exercise Training Improves the Altered Renin-Angiotensin System in the Rostral Ventrolateral Medulla of Hypertensive Rats

The imbalance between angiotensin II (Ang II) and angiotensin 1-7 (Ang 1-7) in the brain has been reported to contribute to cardiovascular dysfunction in hypertension. Exercise training (ExT) is beneficial to hypertension and the mechanism is unclear. This study was aimed to determine if ExT improves hypertension via adjusting renin angiotensin system in cardiovascular centers including the rostral ventrolateral medulla (RVLM). Spontaneously hypertensive rats (SHR, 8 weeks old) were subjected to low-intensity ExT or kept sedentary (Sed) for 12 weeks. Blood pressure elevation coupled with increase in age was significantly decreased in SHR received ExT compared with Sed. The results in vivo showed that ExT significantly reduced or increased the cardiovascular responses to central application of sarthran (antagonist of Ang II) or A779 (antagonist of Ang 1-7), respectively. The protein expression of the Ang II acting receptor AT1R and the Ang 1-7 acting receptor Mas in the RVLM was significantly reduced and elevated in SHR following ExT, respectively. Moreover, production of reactive oxygen species in the RVLM was significantly decreased in SHR following ExT. The current data suggest that ExT improves hypertension via improving the balance of Ang II and Ang 1-7 and antioxidative stress at the level of RVLM.

Exercise training lowers the enhanced tonically active glutamatergic input to the rostral ventrolateral medulla in hypertensive rats

AIMS

It is well known that low-intensity exercise training (ExT) is beneficial to cardiovascular dysfunction in hypertension. The tonically active glutamatergic input to the rostral ventrolateral medulla (RVLM), a key region for control of blood pressure and sympathetic tone, has been demonstrated to be increased in hypertensive rats. The aim of this study was to determine the effect of ExT on the increased glutamatergic input to the RVLM in spontaneously hypertensive rat (SHR).

METHODS

Normotensive rats Wistar-Kyoto (WKY) and SHR were treadmill trained or remained sedentary (Sed) for 12 weeks and classed into four groups (WKY-Sed, WKY-ExT, SHR-Sed, and SHR-ExT). The release of glutamate in the RVLM and its contribution to cardiovascular activity were determined in WKY and SHR after treatment of ExT.

RESULTS

Blood pressure and sympathetic tone were significantly reduced in SHR after treatment with ExT. Bilateral microinjection of the glutamate receptor antagonist kynurenic acid (2.7 nmol in 100 nL) into the RVLM significantly decreased resting blood pressure, heart rate, and renal sympathetic nerve activity in SHR-Sed but not in WKY groups (WKY-Sed and WKY-ExT). However, the degree of reduction in these cardiovascular parameters evoked by KYN was significantly blunted in SHR-ExT compared with SHR-Sed group. The concentration of glutamate and the protein expression of vesicular glutamate transporter 2 in the RVLM were significantly increased in SHR-Sed compared with WKY-Sed, whereas they were reduced after treatment with ExT.

CONCLUSION

Our findings suggest that ExT attenuates the enhancement in the tonically acting glutamatergic input to the RVLM of hypertensive rats, thereby reducing the sympathetic hyperactivity and blood pressure.

Development of aerobic and anaerobic metabolism in cardiac and skeletal muscles from harp and hooded seals

In diving animals, skeletal muscle adaptations to extend underwater time despite selective vasoconstriction include elevated myoglobin (Mb) concentrations, high acid buffering ability (beta) and high aerobic and anaerobic enzyme activities. However, because cardiac muscle is perfused during dives, it may rely less heavily on Mb, beta and anaerobic pathways to support contractile activity. In addition, because cardiac tissue must sustain contractile activity even before birth, it may be more physiologically mature at birth and/or develop faster than skeletal muscles. To test these hypotheses, we measured Mb levels, beta and the activities of citrate synthase (CS), beta-hydroxyacyl-CoA dehydrogenase (HOAD) and lactate dehydrogenase (LDH) in cardiac and skeletal muscle samples from 72 harp and hooded seals, ranging in age from fetuses to adults. Results indicate that in adults cardiac muscle had lower Mb levels (14.7%), beta (55.5%) and LDH activity (36.2%) but higher CS (459.6%) and HOAD (371.3%) activities (all P<0.05) than skeletal muscle. In addition, while the cardiac muscle of young seals had significantly lower [Mb] (44.7%) beta (80.7%) and LDH activity (89.5%) than adults (all P<0.05), it was relatively more mature at birth and weaning than skeletal muscle. These patterns are similar to those in terrestrial species, suggesting that seal hearts do not exhibit unique adaptations to the challenges of an aquatic existence.

Exercise-mediated regulation of Hsp70 expression following aerobic exercise training

An issue central to understanding the biological benefits associated with regular exercise training is to elucidate the intracellular mechanisms governing exercise-conferred cardioprotection. Heat shock proteins (HSPs), most notably the inducible 70-kDa HSP family member Hsp70, are believed to participate in the protection of the myocardium during cardiovascular stress. Following acute exercise, activation of PKA mediates the suppression of an intermediary protein kinase, ERK1/2, which phosphorylates and suppresses the activation of the heat shock transcription factor 1 (HSF1). However, following exercise training, ERK1/2 has been reported to regulate the transcriptional activation of several genes involved in cell growth and proliferation and has been shown to be associated with training-mediated myocardial hypertrophy. The present project examined the transcriptional activation of hsp70 gene expression in acutely exercised (60 min at 30 m/min) naïve sedentary and aerobically trained (8 wk, low intensity) male Sprague-Dawley rats. Following acute exercise stress, no significant differences were demonstrated in the expression of myocardial Hsp70 mRNA and activation of PKA between sedentary and trained animals. However, trained animals elicited expression of the hsp70 gene (P < 0.05) in the presence of elevated ERK1/2 activation. Given the association of ERK1/2 and the suppression of hsp70 gene expression following acute exercise in naïve sedentary rats, these results suggest that training results in adaptations that allow for the simultaneous initiation of both proliferative and protective responses. While it is unclear what factors are associated with this training-related shift, increases in HSF1 DNA binding affinity (P < 0.05) and posttranscriptional modifications of the Hsp70 transcript are suggested.

Effects of experimental type 1 diabetes and exercise training on angiogenic gene expression and capillarization in skeletal muscle

Diabetes alters microvascular structure and function and is a major risk factor for cardiovascular diseases. In diabetic skeletal muscle, impaired angiogenesis and reduced VEGF-A expression have been observed, whereas in healthy muscle exercise is known to have opposite effects. We studied the effects of type 1 diabetes and combined exercise training on angiogenic mRNA expression and capillarization in mouse skeletal muscle. Microarray and real-time PCR analyses showed that diabetes altered the expression of several genes involved in angiogenesis. For example, levels of proangiogenic VEGF-A, VEGF-B, neuropilin-1, VEGFR-1, and VEGFR-2 were reduced and the levels of antiangiogenic thrombospondin-1 and retinoblastoma like-2 were increased. Exercise training alleviated some of these changes, but could not completely restore them. VEGF-A protein content was also reduced in diabetic muscles. In line with the reduced levels of VEGF-A and other angiogenic factors, and increased levels of angiogenesis inhibitors, capillary-to-muscle fiber ratio was lower in diabetic mice compared to healthy controls. Exercise training could not restore capillarization in diabetic mice. In conclusion, these data illustrate that type 1 diabetes is associated with reduced skeletal muscle capillarization and the dysregulation of complex angiogenesis pathways.

Effects of streptozotocin-induced diabetes and physical training on gene expression of extracellular matrix proteins in mouse skeletal muscle

Diabetes induces changes in the structure and function of the extracellular matrix (ECM) in many tissues. We investigated the effects of diabetes, physical training, and their combination on the gene expression of ECM proteins in skeletal muscle. Mice were divided to control (C), training (T), streptozotocin-induced diabetic (D), and diabetic training (DT) groups. Training groups (T, DT) performed 1, 3, or 5 wk of endurance training on a treadmill. Gene expression of calf muscles was analyzed using microarray and quantitative PCR. Training group samples were collected 24 h after the last training session. Diabetes affected the gene expression of several collagens (types I, III, IV, V, VI, and XV), some noncollagenous glycoproteins, and proteoglycans (e.g., elastin, thrombospondin-1, laminin-2, decorin). Reduced gene expression of collagens in diabetic skeletal muscle was partially attenuated as a result of physical training. In diabetes, mRNA expression of the basement membrane (BM) collagens decreased and that of noncollagenous glycoproteins increased. This may change the structure of the BM in a less collagenous direction and affect its properties.

Regular exercise is associated with a protective metabolic phenotype in the rat heart

Adaptation of myocardial energy substrate utilization may contribute to the cardioprotective effects of regular exercise, a possibility supported by evidence showing that pharmacological metabolic modulation is beneficial to ischemic hearts during reperfusion. Thus we tested the hypothesis that the beneficial effect of regular physical exercise on recovery from ischemia-reperfusion is associated with a protective metabolic phenotype. Function, glycolysis, and oxidation of glucose, lactate, and palmitate were measured in isolated working hearts from sedentary control (C) and treadmill-trained (T: 10 wk, 4 days/wk) female Sprague-Dawley rats submitted to 20 min ischemia and 40 min reperfusion. Training resulted in myocardial hypertrophy (1.65 +/- 0.05 vs. 1.30 +/- 0.03 g heart wet wt, P < 0.001) and improved recovery of function after ischemia by nearly 50% (P < 0.05). Glycolysis was 25-30% lower in T hearts before and after ischemia (P < 0.05), whereas rates of glucose oxidation were 45% higher before ischemia (P < 0.01). As a result, the fraction of glucose oxidized before and after ischemia was, respectively, twofold and 25% greater in T hearts (P < 0.05). Palmitate oxidation was 50-65% greater in T than in C before and after ischemia (P < 0.05), whereas lactate oxidation did not differ between groups. Alteration in content of selected enzymes and proteins, as assessed by immunoblot analysis, could not account for the reduction in glycolysis or increase in glucose and palmitate oxidation observed. Combined with the studies on the beneficial effect of pharmacological modulation of energy metabolism, the present results provide support for a role of metabolic adaptations in protecting the trained heart against ischemia-reperfusion injury.

The effects of endurance training and exhaustive exercise on mitochondrial enzymes in tissues of the rat (Rattus norvegicus)

The aim of the present study was to ascertain the effects of training and exhaustive exercise on mitochondrial capacities to oxidize pyruvate, 2-oxoglutarate, palmitoylcarnitine, succinate and ferrocytochrome c in various tissues of the rat. Endurance capacity was significantly increased (P<0.01) by an endurance training program over a period of 5-6 weeks. The average run time to exhaustion was 214.2+/-23.8 min for trained rats in comparison with 54.5+/-11.7 min for their untrained counterparts. Oxidative capacities were reduced in liver (P<0.05) and brown adipose tissue (P<0.05) as a result of endurance training. On the contrary, the oxidative capacity of skeletal muscle was slightly increased and that of heart almost unaffected except for the oxidation of palmitoylcarnitine, which was significantly reduced (P<0.05) as a result of training.

Dissociation of the effects of training on oxidative metabolism, glucose utilisation and GLUT4 levels in skeletal muscle of streptozotocin-diabetic rats

The effects of long-term, moderate physical exercise on in vivo glucose uptake, levels of two glucose transporter proteins (GLUT1 and GLUT4) and activities of various key enzymes of energy metabolism were measured in skeletal muscle from streptozotocin-diabetic rats. Diabetes (12-16 weeks) reduced the in vivo glucose uptake (glucose metabolic index, GMI) in muscle containing mainly type I fibres by 55% but had no effect in muscles containing mainly type IIa and IIb fibres. GMI was increased in the diabetic white skeletal muscle (mainly type IIb fibres) by more than 120%. In contrast to the complex changes in GMI, GLUT4 levels were reduced in all types of skeletal muscle from diabetic rats with no change in GLUT1 levels. Exercise training had no effects on GMI or the glucose transporter levels. Streptozotocin induced diabetes significantly reduced the oxidative capacity of skeletal muscle assayed as the activities of citrate synthase, succinate dehydrogenase and cytochrome c oxidase. Training increased the activities of oxidative enzymes, with this increase being more prominent in the diabetic animals. The present data indicate that long-term streptozotocin-induced diabetes decreases oxidative metabolic capacity and GLUT4 protein levels in skeletal muscle, but that the changes of glucose transport largely depend on the fibre type composition. Moderate training fully reverses the effect of insulinopenia and hyperglycaemia on muscle oxidative metabolism. In contrast to the previous suggestions, the expression of GLUT4 is not correlated with the capacity of oxidative metabolism in skeletal muscle of streptozotocin-diabetic rats.

Regional differences of substrate oxidation capacity in rat hearts: effects of extra load and endurance training

Male rats, aged 17 weeks at the end of experiments, were divided into four groups. Two groups lived in normal cage conditions with or without extra load (20% of the body weight) and two groups were trained by running with or without extra load for 8 weeks. Oxidation rates of succinate, glutamate + malate, palmitoylcarnitine, and pyruvate, and the activities of lactate dehydrogenase, citrate synthase, isocitrate dehydrogenase and cytochrome oxidase were measured in homogenates of the right ventricle and in those of the subendocardial and subepicardial layers of the left ventricle. Oxidation rates of succinate and palmitoylcarnitine tended to be higher in the subendocardium than in the subepicardium of sedentary control animals (p less than 0.1 and p less than 0.05, respectively). Transmural differences of succinate and palmitoylcarnitine oxidation rates were even more clear after running training (p less than 0.01 and p less than 0.05, respectively), after carrying extra load (p less than 0.001 and p less than 0.001, respectively) and after training carrying extra load (p less than 0.001 and p less than 0.05, respectively). Training also enhanced pyruvate oxidation rate in the subendocardium. Oxidation rates of all substrates were lower in the right ventricle than in the left ventricle. In control animals there were no regional differences in the myocardial enzyme activities and the training- or extra-load-induced changes were modest compared with the changes in the oxidation rates. The most significant change was the training-induced enhancement in the lactate dehydrogenase activity of the subendocardium (p less than 0.001 vs subepicardium). These results show greater subendocardial than subepicardial oxidation rates of certain substrates in the normal heart. These results also suggest that the myocardium adapts to increased work by increasing the subendocardial oxidation rate of some but not all substrates, indicating further that there may be qualitative mitochondrial differences in the different regions of the heart.

Effect of chronic exercise on glucose uptake and activities of glycolytic enzymes measured regionally in rat heart

Regional glucose uptake in perfused hearts, and the activities of several glycolytic enzymes contributing to the glucose metabolism in perfused and nonperfused hearts were studied in male and female rats after 8-9 weeks of swimming training. The left ventricular glucose uptake showed a transmural gradient in the sedentary animals, the subendocardial uptake being 30% and 12% higher than that of the subepicardial layer in the males and females, respectively. Swimming exercise abolished the left ventricular glucose uptake gradient in male rats, and in female rats an opposite gradient was found, the subepicardial uptake being 23% higher than the subendocardial uptake. The activities of phosphofructokinase and 3-phosphoglyceraldehyde dehydrogenase also showed transmural gradients in the left ventricles. Training did not abolish these gradients. Training-induced changes in the activities of phosphofructokinase, 3-phosphoglyceraldehyde dehydrogenase, pyruvate kinase, lactate dehydrogenase, glucose-6-phosphate dehydrogenase, citrate synthase, and malate dehydrogenase were found in certain sites of the myocardium. Perfusion of isolated hearts for 50 min with insulin-containing Krebs-Ringer buffer especially affected the activities of phosphofructokinase, lactate dehydrogenase, and citrate synthase, increasing these activities in the left ventricles and decreasing them in the atria. These results indicate that there are regional differences between male and female rats in the cardiac glucose uptake rate after swimming training.

Total muscle mitochondrial volume in relation to aerobic capacity of horses and steers

The relationship between maximal oxygen consumption rate (VO2max) and mitochondrial content of skeletal muscles was examined in horses and steers (n = 3 each). Samples of the heart left ventricle, diaphragm, m. vastus medialis, m. semitendinosus, m. cutaneous thoracicus and m. masseter, as well as samples of muscles collected in a whole-body sampling procedure, were analyzed by electron microscopy. VO2max per kilogram body mass was 2.7 x greater in horses than steers. This higher VO2max was in proportion to the higher total volume of mitochondria in horse versus steer muscle when analyzed from the whole-body samples and from the locomotor muscle samples. In non-locomotor muscles, total mitochondrial volume was greater in horses than steers, but not in proportion to their differences in VO2max. The VO2max of the mitochondria was estimated to be close to 4.5 ml O2.ml-1 mitochondria in both species. It is concluded that in a comparison of a highly aerobic to a less aerobic mammalian species of similar body size, a higher oxidative potential may be found in all muscles of the more aerobic species. This greater oxidative potential is achieved by a greater total volume of skeletal muscle mitochondria.

Ouabain-binding site of (Na+ + K+)-ATPase in right-side-out vesicles has not an externally accessible SH group

The fluorescing sulfhydryl reagent N-(7-dimethylamino-4-methylcoumarinyl)maleimide (DACM) inactivates purified (Na+ + K+)-ATPase at 20 microM. This inactivation results in a decrease of the ouabain-binding capacity of the enzyme. Treatment of (Na+ + K+)-ATPase, embedded in right-side-out-oriented vesicles, by DACM does not affect ouabain binding to the enzyme. Incorporation of DACM into the alpha subunit of (Na+ + K+)-ATPase embedded in right-side-out vesicles is also not affected by the presence or absence of 100 microM ouabain. It is therefore concluded that a sulfhydryl group does not reside within the ouabain-binding site of (Na+ + K+)-ATPase.

Testosterone application influences sympathetic activity of intracardiac nerves in non-trained and trained mice

Application of testosterone and/or physical exercise causes degenerative and then regenerative patterns of intracardiac sympathetic neurons. Observations in 3 stages (1, 3 and 6 weeks) illustrate the adaptative changes of sympathetic neurons as a response to these stimuli and show that the effects following testosterone application or physical exercise are comparable. Ultrastructural investigations indicate that the sympathetic neurons are more sensitive to testosterone than to physical exercise. The combination of testosterone plus training indicates overlapping effects of these two stimuli. The system of adrenergic nerve fibers seems to be overstimulated. Its reaction pattern is found not only to depend on time but also on the intensity of the stimuli.