Differential effect of physical exercise routines on ventricular myosin and peripheral catecholamine stores in normotensive and spontaneously hypertensive rats

Changes in myocardial myosin heavy chain isoform composition with exercise and post-exercise cold-water immersion

This study investigated the changes in myocardial myosin heavy chain (MHC) isoforms, MHC-α and MHC-β composition in young healthy rodents following endurance training, with and without post-exercise cold-water immersion (CWI). Male rats were either trained on a treadmill for 10 weeks with (CWI) or without (Ex) regular CWI after each running session, or left sedentary (CON). Left ventricular mRNA of MHC-α, MHC-β, thyroid receptor α1 (TR-α1) and β (TR-β) were analyzed using rt-PCR and semiquantitative PCR analysis. MHC isoform protein composition was determined using SDS-PAGE electrophoresis. MHC-α isoform protein was predominant in all groups. The relative expression of MHC-β (%MHC-β) protein was not different between groups (CWI 34.7 ± 6.9%; Ex 32 ± 5.3%; CON 35.5 ± 10%; P = 0.7). MHC-β mRNA was reduced in Ex (0.7 ± 0.3-fold) compared to CWI (1.3 ± 0.2-fold; P < 0.001) and CON (1.01 ± 0.2-fold; P = 0.03). TRα1 mRNA was lower in CWI (0.4 ± 0.05-fold) than Ex (1.02 ± 0.3-fold) and CON (1.01 ± 0.2-fold) (P < 0.001 for both). CWI exhibited greater %MHC-β mRNA (56.8 ± 4.1%) than Ex (44.4 ± 7.7%; P = 0.001) and CON (48.5 ± 7.8%; P = 0.03). Neither exercise nor post-exercise CWI demonstrated a distinct effect on myocardial MHC protein isoform composition. However, CWI increased the relative expression of MHC-β mRNA compared with Ex and CON. Although this implicates a potential negative long-term impact of post-exercise CWI, future studies should include measures of cardiac function to better understand the effect of such isoform mRNA shifts following regular use of CWI.

Guidelines for animal exercise and training protocols for cardiovascular studies

Whole body exercise tolerance is the consummate example of integrative physiological function among the metabolic, neuromuscular, cardiovascular, and respiratory systems. Depending on the animal selected, the energetic demands and flux through the oxygen transport system can increase two orders of magnitude from rest to maximal exercise. Thus, animal models in health and disease present the scientist with flexible, powerful, and, in some instances, purpose-built tools to explore the mechanistic bases for physiological function and help unveil the causes for pathological or age-related exercise intolerance. Elegant experimental designs and analyses of kinetic parameters and steady-state responses permit acute and chronic exercise paradigms to identify therapeutic targets for drug development in disease and also present the opportunity to test the efficacy of pharmacological and behavioral countermeasures during aging, for example. However, for this promise to be fully realized, the correct or optimal animal model must be selected in conjunction with reproducible tests of physiological function (e.g., exercise capacity and maximal oxygen uptake) that can be compared equitably across laboratories, clinics, and other proving grounds. Rigorously controlled animal exercise and training studies constitute the foundation of translational research. This review presents the most commonly selected animal models with guidelines for their use and obtaining reproducible results and, crucially, translates state-of-the-art techniques and procedures developed on humans to those animal models.

Regular physical activity prevents chronic pain by altering resident muscle macrophage phenotype and increasing interleukin-10 in mice

Regular physical activity in healthy individuals prevents development of chronic musculoskeletal pain; however, the mechanisms underlying this exercise-induced analgesia are not well understood. Interleukin-10 (IL-10), an antiinflammatory cytokine that can reduce nociceptor sensitization, increases during regular physical activity. Since macrophages play a major role in cytokine production and are present in muscle tissue, we propose that physical activity alters macrophage phenotype to increase IL-10 and prevent chronic pain. Physical activity was induced by allowing C57BL/6J mice free access to running wheels for 8 weeks and compared to sedentary mice with no running wheels. Using immunohistochemical staining of the gastrocnemius muscle to label regulatory (M2, secretes antiinflammatory cytokines) and classical (M1, secretes proinflammatory cytokines) macrophages, the percentage of M2-macrophages increased significantly in physically active mice (68.5% ± 4.6% of total) compared with sedentary mice (45.8% ± 7.1% of total). Repeated acid injections into the muscle enhanced mechanical sensitivity of the muscle and paw in sedentary animals, which does not occur in physically active mice; no sex differences occur in either sedentary or physically active mice. Blockade of IL-10 systemically or locally prevented the analgesia in physically active mice, ie, mice developed hyperalgesia. Conversely, sedentary mice pretreated systemically or locally with IL-10 had reduced hyperalgesia after repeated acid injections. Thus, these results suggest that regular physical activity increases the percentage of regulatory macrophages in muscle and that IL-10 is an essential mediator in the analgesia produced by regular physical activity.

Swimming exercise changes hemodynamic responses evoked by blockade of excitatory amino receptors in the rostral ventrolateral medulla in spontaneously hypertensive rats

Exercise training reduces sympathetic activity in hypertensive humans and rats. We hypothesized that the swimming exercise would change the neurotransmission in the rostral ventrolateral medulla (RVLM), a key region involved in sympathetic outflow, and hemodynamic control in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. Bilateral injections of kynurenic acid (KYN) were carried out in the RVLM in sedentary- (S-) or exercised- (E-) SHR and WKY rats submitted to swimming for 6 weeks. Rats were α-chloralose anesthetized and artificially ventilated, with Doppler flow probes around the lower abdominal aorta and superior mesenteric artery. Injections into the RVLM were made before and after i.v. L-NAME (nitric oxide synthase, NOS, inhibitor). Injections of KYN into the RVLM elicited a major vasodilation in the hindlimb more than in the mesenteric artery in E-SHR compared to S-SHR, but similar decrease in arterial pressure was observed in both groups. Injections of KYN into the RVLM after i.v. L-NAME attenuated the hindlimb vasodilation evoked by KYN and increased the mesenteric vasodilation in E-SHR. Swimming exercise can enhance the hindlimb vasodilation mediated by peripheral NO release, reducing the activation of neurons with EAA receptors in the RVLM in SHR.

High molecular mass proteomics analyses of left ventricle from rats subjected to differential swimming training

BACKGROUND

Regular exercises are commonly described as an important factor in health improvement, being directly related to contractile force development in cardiac cells.In order to evaluate the links between swimming exercise intensity and cardiac adaptation by using high molecular mass proteomics, isogenic Wistar rats were divided into four groups: one control (CG) and three training groups (TG's), with low, moderate and high intensity of exercises.In order to evaluate the links between swimming exercise intensity and cardiac adaptation by using high molecular mass proteomics, isogenic Wistar rats were divided into four groups: one control (CG) and three training groups (TG's), with low, moderate and high intensity of exercises.

RESULTS

Findings here reported demonstrated clear morphologic alterations, significant cellular injury and increased energy supplies at high exercise intensities. α-MyHC, as well proteins associated with mitochondrial oxidative metabolism were shown to be improved. α-MyHC expression increase 1.2 fold in high intensity training group when compared with control group. α-MyHC was also evaluated by real-time PCR showing a clear expression correlation with protein synthesis data increase in 8.48 fold in high intensity training group. Other myofibrillar protein, troponin , appear only in high intensity group, corroborating the cellular injury data. High molecular masses proteins such as MRS2 and NADH dehydrogenase, involved in metabolic pathways also demonstrate increase expression, respectily 1.5 and 1.3 fold, in response to high intensity exercise.

CONCLUSIONS

High intensity exercise demonstrated an increase expression in some high molecular masses myofibrilar proteins, α-MyHC and troponin. Furthermore this intensity also lead a significant increase of other high molecular masses proteins such as MRS2 and NADH dehydrogenase in comparison to low and moderate intensities. However, high intensity exercise also represented a significant degree of cellular injury, when compared with the individuals submitted to low and moderate intensities.

Electrophoretic mobility of cardiac myosin heavy chain isoforms revisited: application of MALDI TOF/TOF analysis

The expression of two cardiac myosin heavy chain (MyHC) isoforms in response to the thyroid status was studied in left ventricles (LVs) of Lewis rats. Major MyHC isoform in euthyroid and hyperthyroid LVs had a higher mobility on SDS-PAGE, whereas hypothyroid LVs predominantly contained a MyHC isoform with a lower mobility corresponding to that of the control soleus muscle. By comparing the MyHC profiles obtained under altered thyroid states together with the control soleus, we concluded that MyHCα was represented by the lower band with higher mobility and MyHCβ by the upper band. The identity of these two bands in SDS-PAGE gels was confirmed by western blot and mass spectrometry. Thus, in contrast to the literature data, we found that the MyHCα possessed a higher mobility rate than the MyHCβ isoform. Our data highlighted the importance of the careful identification of the MyHCα and MyHCβ isoforms analyzed by the SDS-PAGE.

Exercise changes regional vascular control by commissural NTS in spontaneously hypertensive rats

Inhibition of the commissural nucleus of the solitary tract (commNTS) induces a fall in sympathetic nerve activity and blood pressure in spontaneously hypertensive rats (SHR), which suggests that this subnucleus of the NTS is a source of sympathoexcitation. Exercise training reduces sympathetic activity and arterial pressure. The purpose of the present study was to investigate whether the swimming exercise can modify the regional vascular responses evoked by inhibition of the commNTS neurons in SHR and normotensive Wistar-Kyoto (WKY) rats. Exercise consisted of swimming, 1 h/day, 5 days/wk for 6 wks, with a load of 2% of the body weight. The day after the last exercise session, the rats were anesthetized with intravenous α-chloralose, tracheostomized, and artificially ventilated. The femoral artery was cannulated for mean arterial pressure (MAP) and heart rate recordings, and Doppler flow probes were placed around the lower abdominal aorta and superior mesenteric artery. Microinjection of 50 mM GABA into the commNTS caused similar reductions in MAP in swimming and sedentary SHR (−25 ± 6 and −30 ± 5 mmHg, respectively), but hindlimb vascular conductance increased twofold in exercised vs. sedentary SHR (54 ± 8 vs. 24 ± 5%). GABA into the commNTS caused smaller reductions in MAP in swimming and sedentary WKY rats (−20 ± 4 and −16 ± 2 mmHg). Hindlimb conductance increased fourfold in exercised vs. sedentary WKY rats (75 ± 2% vs. 19 ± 3%). Therefore, our data suggest that the swimming exercise induced changes in commNTS neurons, as shown by a greater enhancement of hindlimb vasodilatation in WKY vs. SHR rats in response to GABAergic inhibition of these neurons.

Association of hyperhomocysteinemia with left ventricular dilatation and mass in human heart

BACKGROUND

Hyperhomocysteinemia is a risk factor for ischemic heart disease. Several other mechanisms apply also to dilative types of heart failure of various, non-ischemic etiologies. We hypothesized that hyperhomocysteinemia is associated with left ventricular (LV) dilatation and hypertrophy in dilative cardiomyopathy.

METHODS

Homocysteine was measured in 66 individuals with suspected cardiomyopathy. Cardiac magnetic resonance imaging was used to assess LV volume, mass, and wall stress.

RESULTS

Hyperhomocysteinemia (> 12 micromol/L) was found in 45 patients (68%). LV mass was greater in these patients compared with individuals with normal homocysteine (83+/-27 vs. 67+/-19 g/m(2); p<0.02). Homocysteine was increased in patients with increased brain natriuretic peptide > or = 100 pg/mL (18.3+/-5.9 vs. 14.9+/-5.1 micromol/L; p=0.018). LV mass, LV end-diastolic and end-systolic volume (LVEDV, LVESV) were significantly increased in individuals in the upper quartile compared with the lower quartile (90+/-25 vs. 65+/-18 g/m(2), p=0.021; 114+/-50 vs. 71+/-23 mL/m(2), p=0.042; 76+/-51 vs. 36+/-22 mL/m(2), p=0.045). LV dilatation (LVEDV > or = 90 mL/m(2)) was more common in hyperhomocysteinemia (> 12 micromol/L, p=0.0166). Normalized LV mass was correlated with homocysteine (r=0.346, p=0.065). Homocysteine was not significantly correlated with LVEDV (r=0.229, p=0.065), LV end-diastolic wall stress (r=0.226, p=0.069) and LV ejection fraction.

CONCLUSIONS

Hyperhomocysteinemia appears to be, at least in part, involved in a disproportional LV dilatation, where the ensuing hypertrophy is not sufficient to compensate for the increased wall stress. A potential mechanism is the hyperhomocysteinemia associated increase in oxidative stress that favors muscle fiber slippage.

Selecting exercise regimens and strains to modify obesity and diabetes in rodents: an overview

Exercise is part of a healthy lifestyle and frequently is an important component in combating chronic diseases, such as obesity and diabetes. Understanding the molecular events initiated by regular exercise is best studied in laboratory animals, with mice and rats being favoured for a number of reasons. However, the wide variety of rodent strains available for biomedical research often makes it challenging to select an animal strain suitable for studying specific disease outcomes. In the present review we focus on exercise as a management strategy for obesity and diabetes and we discuss: (i) exercise paradigms in humans shown to ameliorate signs and symptoms of obesity and diabetes; (ii) different rodent strains in terms of their advantages, disadvantages and limitations when using specific forms of exercise; (iii) the strengths and weaknesses of commonly used laboratory methods for rodent exercise; and (iv) the unintended consequences of exercise that are often manifested by increased hormonal and oxidative stress responses.

Voluntary wheel running and pacing-induced dysfunction in hypertension

PURPOSE

We examined how voluntary wheel running in the female, spontaneously hypertensive rat (SHR) impacts myocardial tolerance to pacing stress and determined whether direct adenylyl cyclase agonism via forskolin infusion improved myocardial performance during pacing.

METHODS

Twenty-five 16-week-old female Wistar Kyoto (WKY, n = 8) and SHR (n = 17) were utilized. Animals within the SHR group were randomly assigned to a sedentary (SHR-SED, n = 8) or a voluntary wheel running (SHR-WHL, n = 9) group. The SHR-WHL had free access to a running wheel 24 h/day. Resting heart rates and blood pressures were collected immediately prior to sacrifice utilizing a tail cuff apparatus. Left ventricular (LV) function was measured in a Langendorff, isovolumic preparation during pacing stress (8.5 Hz) and during pacing stress + forskolin (5 micromol/L).

RESULTS

SHR-WHL showed cardiac enlargement without alterations in heart rate, systolic blood pressure, or rate-pressure product. Pacing stress impaired inotropic and lusitropic performance to a similar extent in all groups (p < 0.05), while forskolin infusion improved LV function to a similar extent in all groups (p < 0.05).

CONCLUSIONS

These data suggest that voluntary wheel running in SHR does not protect from pacing-induced myocardial dysfunction, and adenylyl cyclase agonism during pacing stress can functionally protect the heart. These data reiterate the importance of a competent myocardial beta-adrenergic signaling cascade.

B-type natriuretic peptide and wall stress in dilated human heart

Background Although B-type natriuretic peptide (BNP) is used as complimentary diagnostic tool in patients with unknown thoracic disorders, many other factors appear to trigger its release. In particular, it remains unresolved to what extent cellular stretch or wall stress of the whole heart contributes to enhanced serum BNP concentration. Wall stress cannot be determined directly, but has to be calculated from wall volume, cavity volume and intraventricular pressure of the heart. The hypothesis was, therefore, addressed that wall stress as determined by cardiac magnetic resonance imaging (CMR) is the major determinant of serum BNP in patients with a varying degree of left ventricular dilatation or dysfunction (LVD). Methods A thick-walled sphere model based on volumetric analysis of the LV using CMR was compared with an echocardiography-based approach to calculate LV wall stress in 39 patients with LVD and 21 controls. Serum BNP was used as in vivo marker of a putatively raised wall stress. Nomograms of isostress lines were established to assess the extent of load reduction that is necessary to restore normal wall stress and related biochemical events. Results Both enddiastolic and endsystolic LV wall stress were correlated with the enddiastolic LV volume (r = 0.54, P < 0.001; r = 0.81, P < 0.001). LV enddiastolic wall stress was related to pulmonary pressure (capillary: r = 0.69, P < 0.001; artery: r = 0.67, P < 0.001). Although LV growth was correlated with the enddiastolic and endsystolic volume (r = 0.73, P < 0.001; r = 0.70, P < 0.001), patients with LVD exhibited increased LV wall stress indicating an inadequately enhanced LV growth. Both enddiastolic (P < 0.05) and endsystolic (P < 0.01) wall stress were increased in patients with increased BNP. In turn, BNP concentration was elevated in individuals with increased enddiastolic wall stress (>8 kPa: 587 +/- 648 pg/ml, P < 0.05; >12 kPa: 715 +/- 661 pg/ml, P < 0.001; normal < or =4 kPa: 124 +/- 203 pg/ml). Analysis of variance revealed LV enddiastolic wall stress as the only independent hemodynamic parameter influencing BNP (P < 0.01). Using nomograms with "isostress" curves, the extent of load reduction required for restoring normal LV wall stress was assessed. Compared with the CMR-based volumetric analysis for wall stress calculation, the echocardiography based approach underestimated LV wall stress particularly of dilated hearts. Conclusions In patients with LVD, serum BNP was increased over the whole range of stress values which were the only hemodynamic predictors. Cellular stretch appears to be a major trigger for BNP release. Biochemical mechanisms need to be explored which appear to operate over this wide range of wall stress values. It is concluded that the diagnostic use of BNP should primarily be directed to assess ventricular wall stress rather than the extent of functional ventricular impairment in LVD.

Effects of swimming exercise and soybean supplementation on the immune functions of rats fed a high-fat diet

1. In the present study, the effects of swimming exercise and soybean supplementation on the immune functions of rats fed a high-fat diet were examined. 2. Thirty-four male rats were randomly divided into four groups: (i) HS, a high-fat diet sedentary group (n = 8); (ii) HE, a high-fat diet exercised group (n = 9); (iii) SS, a soybean diet sedentary group (n = 8); and (iv) SE, a soybean diet exercised group (n = 9). The high-fat diet was composed of 35% carbohydrate, 20% protein and 35% fat. For the soybean diet, 3% crude soybean extract was substituted for the protein, carbohydrate and fat according to the energy content of the diet. In the exercise groups, rats swam for 60 min/day, 5 days/week for 4 weeks. 3. The subpopulation of CD4(+) cells and the CD4(+)/CD8(+) ratio did not differ significantly between the high-fat diet and soybean diet groups. However, the subpopulation of CD8(+) cells in the spleens of SS rats was significantly higher than that in the spleens of HS rats (P < 0.05). In addition, splenic interferon-gamma secretion in the SE group, with or without conconavalin A stimulation, was significantly increased compared with the SS group (P < 0.05 and P < 0.01, respectively). 4. These results show that regular endurance exercise training with soybean supplementation ameliorates splenic T cell-mediated immunity.

Relation of B-type natriuretic peptide to left ventricular wall stress as assessed by cardiac magnetic resonance imaging in patients with dilated cardiomyopathy

Ventricular loading conditions are crucial determinants of cardiac function and prognosis in heart failure. B-type natriuretic peptide (BNP) is mainly stored in the ventricular myocardium and is released in response to an increased ventricular filling pressure. We examined, therefore, the hypothesis that BNP serum concentrations are related to ventricular wall stress. Cardiac magnetic resonance imaging (MRI) was used to assess left ventricular (LV) mass and cardiac function of 29 patients with dilated cardiomyopathy and 5 controls. Left ventricular wall stress was calculated by using a thick-walled sphere model, and BNP was assessed by immunoassay. LV mass (r = 0.73, p < 0.001) and both LV end-diastolic (r = 0.54, p = 0.001) and end-systolic wall stress (r = 0.66, p < 0.001) were positively correlated with end-diastolic volume. LV end-systolic wall stress was negatively related to LV ejection fraction (EF), whereas end-diastolic wall stress was not related to LVEF. BNP concentration correlated positively with LV end-diastolic wall stress (r = 0.50, p = 0.002). Analysis of variance revealed LV end-diastolic wall stress as the only independent hemodynamic parameter influencing BNP (p < 0.001). The present approach using a thick-walled sphere model permits determination of mechanical wall stress in a clinical routine setting using standard cardiac MRI protocols. A correlation of BNP concentration with calculated LV stress was observed in vivo. Measurement of BNP seems to be sufficient to assess cardiac loading conditions. Other relations of BNP with various hemodynamic parameters (e.g., EF) appear to be secondary. Since an increased wall stress is associated with cardiac dilatation, early diagnosis and treatment could potentially prevent worsening of the outcome.

Factors controlling cardiac myosin-isoform shift during hypertrophy and heart failure

Myosin is a molecular motor, which interacts with actin to convert the energy from ATP hydrolysis into mechanical work. In cardiac myocytes, two myosin isoforms are expressed and their relative distribution changes in different developmental and pathophysiologic conditions of the heart. It has been realized for a long time that a shift in myosin isoforms plays a major role in regulating myocardial contractile activity. With the recent evidence implicating that alteration in myosin isoform ratio may be eventually beneficial for the treatment of a stressed heart, a new interest has developed to find out ways of controlling the myosin isoform shift. This article reviews the published data describing the role of myosin isoforms in the heart and highlighting the importance of various factors shown to influence myosin isofrom shift during physiology and disease states of the heart.

Rat models of caloric intake and activity: relationships to animal physiology and human health

Every rodent experiment is based on important parameters concerning the levels of caloric intake and physical activity. In many cases, these decisions are not made consciously, but are based on traditional models. For experimental models directed at the study of caloric intake and activity, the selection of parameters is usually aimed at modeling human conditions, the ultimate goal of which is to gain insight into the pathophysiology of the disease process in man. In each model, it is important to understand the influence of diet, exercise, and genetic background on physiology and the development of disease states. Along the continuum of energy intake from caloric restriction to high-fat feeding, and of energy output from total inactivity to forced exercise, a number of models are used to study different disease states. In this paper, we will evaluate the influence of the quantity and composition of diet and exercise in several animal models, and will discuss how each model can be applied to various human conditions. This review will be limited to traditional models using the rat as the experimental animal, and although it is not an exhaustive list, the models presented are those most commonly represented in the literature. We will also review the mechanisms by which each affects rat physiology, and will compare these to the analogous mechanisms in the modeled human disease state. We hope that the information presented here will help researchers make choices among the available models and will encourage discussion on the interpretation and extrapolation of results obtained from traditional and novel rodent experiments on diet, exercise, and chronic disease.

Voluntary exercise protects against acute doxorubicin cardiotoxicity in the isolated perfused rat heart

The clinical use of doxorubicin (DOX) is limited by a dose-dependent cardiotoxicity. The purpose of this study was to determine whether voluntary exercise training would confer protection against DOX cardiotoxicity in the isolated perfused rat heart. Female Sprague-Dawley rats were randomly assigned to standard holding cages or cages with running wheels for 8 wk. Twenty-four hours after the sedentary (SED) or voluntary exercise (VEX) running period, rats were anesthetized with pentobarbital sodium, and hearts were isolated and perfused with oxygenated Krebs-Henseleit (KH) buffer at a constant flow of 15 ml/min. After a 20-min stabilization period, hearts were paced at 300 beats per minute and perfused with KH buffer containing 10 μM DOX for 60 min. A set of control hearts from SED and VEX rats were perfused under identical conditions without DOX for the same period. DOX perfusion led to significant decreases in left ventricular developed pressure, +dP/d t, and −dP/d t, and significant increases in LV lipid peroxidation in sedentary rats compared with non-DOX controls ( P < 0.05). Prior voluntary exercise training attenuated these DOX-induced effects and was associated with a significant increase (78%, P < 0.05) in heat shock protein (HSP72), but not mitochondrial isoform of SOD (MnSOD) or CuZnSOD protein expression in the hearts of wheel-run animals. These data indicate that chronic physical activity may provide resistance against the cardiac dysfunction and oxidative damage associated with DOX exposure and provide novel evidence of HSP72 induction in the heart after voluntary exercise.

Expression of MHC-beta and MCT1 in cardiac muscle after exercise training in myocardial-infarcted rats

To evaluate the hypothesis that increasing the potential for glycolytic metabolism would benefit the functioning of infarcted myocardium, we investigated whether mild exercise training would increase the activities of oxidative enzymes, expression of carbohydrate-related transport proteins (monocarboxylate transporter MCT1 and glucose transporter GLUT4), and myosin heavy chain (MHC) isoforms. Myocardial infarction (MI) was produced by occluding the proximal left coronary artery in rat hearts for 30 min. After the rats performed 6 wk of run training on a treadmill, the wall of the left ventricle was dissected and divided into the anterior wall (AW; infarcted region) and posterior wall (PW; noninfarcted region). MI impaired citrate synthase and 3-hydroxyacyl-CoA dehydrogenase activities in the AW (P < 0.01) but not in the noninfarcted PW. No differences in the expression of MCT1 were found in either tissues of AW and PW after MI, whereas exercise training significantly increased the MCT1 expression in all conditions, except AW in the MI rats. Exercise training resulted in an increased expression of GLUT4 protein in the AW in the sham rats and in the PW in the MI rats. The relative amount of MHC-beta was significantly increased in the AW and PW in MI rats compared with sham rats. However, exercise training resulted in a significant increase of MHC-alpha expression in both AW and PW in both sham and MI rats (P < 0.01). These findings suggest that mild exercise training enhanced the potential for glycolytic metabolism and ATPase activity of the myocardium, even in the MI rats, ensuring a beneficial role in the remodeling of the heart.

Short- and long-term swimming exercise training increases myocardial insulin-like growth factor-I gene expression

OBJECTIVES. We investigated the effect of short- and long-term swimming exercise, with or without insulin-like growth factor (IGF)-I administration, on the expression of myocardial IGFs and contractile proteins.

METHODS

Sprague-Dawley male rats (n=36) were subjected to swimming exercise for 2 or 6 weeks. IGF-I (0.5mg/rat) was administered continuously for 1 week, using alzet osmotic pumps. Control groups remained sedentary. IGF-I, IGF-I receptor (IGF-IR), IGF-II, skeletal alpha-actin (sk-actin), and beta myosin heavy chain (beta MHC) mRNAs were measured using Northern blot analysis and RT-PCR.

RESULTS

A significant 2-fold increase in myocardial IGF-I mRNA was found after 2 and 6 weeks of swimming in both IGF-I treated and untreated rats (p<0.001). IGF-IR mRNA was significantly (p<0.05) increased after 6 weeks of training only in the IGF-I treated animals. IGF-II mRNA remained unchanged at all time points. While beta MHC mRNA was significantly decreased (p=0.003) at 2 and 6 weeks, sk-actin mRNA remained unchanged.

CONCLUSIONS

Short- and long-term swimming exercise training increase myocardial expression of IGF-I mRNA. Exogenous administration of IGF-I, during the first week of the exercise session, did not produce any effect on myocardial IGF-I but was associated with increased IGF-IR signal after the long-term exercise training. These data suggest a relationship between IGF-I expression and cardiac adaptation to exercise training.

Age-related differences in the effect of running training on cardiac Myosin isozyme composition in rats

We examined the effect of running training on age-related changes in cardiac myosin isozyme composition in rats. Female Fischer 344 rats (6, 12, 20, and 27 months old) were divided into two groups: sedentary control and trained. The trained group rats were trained by treadmill running for up to 60 minutes per day, 5 days per week for 8 weeks at up to 30 m per minute. In sedentary control rats, the proportion of V1 myosin, that is, alpha-myosin heavy chain (MyHC) isoform, decreased progressively from 6 to 27 months of age. In the younger age groups (6 or 12 months old), there was a shift from V1 myosin to V3 myosin (beta-MyHC isoform) in trained hearts. However, the training program did not induce a cardiac myosin isozyme transition in older rats (20 or 27 months old). These results suggest that the mechanisms mediating the responses of cardiac muscle to running training alter during aging.

Different regional effects of voluntary exercise on the mechanical and electrical properties of rat ventricular myocytes

Short-term (6 weeks) voluntary wheel running exercise in young female rats that were in an active growth phase resulted in whole-heart hypertrophy and myocyte concentric hypertrophy, when compared to sedentary controls. The cross-sectional area of ventricular myocytes from trained rats was significantly greater than for those isolated from sedentary rats, with the greatest change in morphology seen in sub-endocardial cells. There was no statistically significant effect of training on cell shortening in the absence of external mechanical loading, in [Ca2+](i) transients, or in myofilament Ca2+ sensitivity (assessed during re-lengthening following tetanic stimulation). Under the external mechanical load of carbon fibres, absolute force developed in myocytes from trained rats was significantly greater than in those from sedentary rats. This suggests that increased myocyte cross-sectional area is a major contractile adaptation to exercise in this model. Training did not alter the passive mechanical properties of myocytes or the relative distribution of titin isomers, which was exclusively of the short, N2B form. However, training did increase the steepness of the active tension-sarcomere length relationship, suggesting an exercise-induced modulation of the Frank-Starling mechanism. This effect would be expected to enhance cardiac contractility. Training lengthened the action potential duration of sub-epicardial myocytes, reducing the transmural gradient in action potential duration. This observation may be important in understanding the cellular causes of T-wave abnormalities found in the electrocardiograms of some athletes. Our study shows that voluntary exercise modulates the morphological, mechanical and electrical properties of cardiac myocytes, and that this modulation is dependent upon the regional origin of the myocytes.

TGF-beta(1) and prepro-ANP mRNAs are differentially regulated in exercise-induced cardiac hypertrophy

The induction of transforming growth factor (TGF)-beta and prepro-atrial natriuretic peptide (ANP) mRNAs represent hallmark features of pathological cardiac hypertrophy. The present study examined whether this pattern of mRNA expression was conserved in a physiological model of cardiac hypertrophy. To address this thesis, female Sprague-Dawley rats were individually housed and permitted to run freely. Voluntary exercise for 3 and 6 wk resulted in biventricular hypertrophy and increased cytochrome c oxidase activity in the triceps muscle. In the hypertrophied left ventricle, the steady-state mRNA level of the cardiac fetal gene prepro-ANP and the extracellular matrix proteins preprocollagen-alpha(1) and fibronectin were similar in exercise-trained and sedentary rats. By contrast, an increased expression of TGF-beta(1) mRNA was observed, whereas TGF-beta(3) mRNA level was unchanged in the hypertrophied left ventricle of exercise-trained compared with sedentary rats. These data highlight a heterogeneity in the regulation of TGF-beta isoforms, and the increased expression of ventricular TGF-beta(1) mRNA in physiological cardiac hypertrophy may contribute to myocardial remodeling.

Regional effects of voluntary exercise on cell size and contraction-frequency responses in rat cardiac myocytes

A model of voluntary exercise, in which rats are given free access to a running wheel over a 14-week period, led to left ventricular hypertrophy. To test whether the hypertrophic response to exercise was uniformly distributed across the ventricular wall, single ventricular myocytes were isolated from the sub-epicardium (EPI) and sub-endocardium (ENDO) of exercised rats and from sedentary rats for comparison. Cellular hypertrophy (approximately 20 % greater cell volume) was seen in ENDO cells from exercised animals, but no significant changes were observed in EPI cells when compared with sedentary controls. This regional effect of exercise may be a response to transmural changes in ventricular wall stress and/or strain. Cell contraction was measured as cell shortening in ENDO and EPI cells at stimulation frequencies between 1 and 9 Hz at 37 degrees C. Exercise training had no effect on cell shortening. Positive and negative contraction-frequency relationships (CFRs) were found in both EPI and ENDO cells between 1 and 5 Hz; at higher frequencies (5–9 Hz), all myocytes displayed a negative CFR. The CFR of a myocyte was, therefore, independent of regional origin and unaffected by exercise. These results suggest that, in vivo, the rat heart displays a negative CFR. We conclude that increased cell size may be a more important adaptive response to exercise than a modification of excitation-contraction coupling.

Lack of effect of running training at two intensities on cardiac myosin isozyme composition in rats

Little information is available regarding the influence of the intensity of endurance training over biochemical profiles in cardiac muscle. We assessed the effect of running training at two different intensities on cardiac myosin isozyme composition in rats. Male Sprague-Dawley rats (4 weeks old) were divided into four groups: sedentary control (SC), trained at 20 m/min (T20), trained at 40 m/min (T40), and weight-matched sedentary control (WMSC) groups. The T20 and T40 group rats were trained by treadmill running for 60 min/d, 5 d/week at 20 or 40 m/min, respectively, for 11 to 12 weeks. In both groups the left ventricle was significantly heavier than in WMSC animals. The ratio of left ventricle weight to body weight was significantly greater in T40 rats than in either the untrained (SC and WMSC) or trained T20 rats. Thus the extent of exercise-induced cardiac hypertrophy appears to be influenced by the intensity of running training. However, neither of the training programs (1) induced a change in cardiac myosin isozyme composition or (2) had any effect on myocardial succinate dehydrogenase or citrate synthase activity. These results suggest that although the intensity of running training may play an important role in cardiac morphological adaptation, it does not modulate the cardiac biochemical adaptation to running training.

Excess catecholamine syndrome. Pathophysiology and therapy

In addition to genetic factors, lifestyle has a predominant influence on primary hypertension and noninsulin-dependent diabetic mellitus (NIDDM). We initiated studies using radiotelemetry for characterizing molecular events linked with excess calorie intake and psychologic stress. An increased calorie intake was associated with raised (p < 0.05) systolic and diastolic blood pressure as well as heart rate independent of day-night cycle. Sympathetic activity was in excess when related to the unchanged motility. The hyperkinetic hypertension is expected to result in adverse remodeling of resistance vessels and to aggravate insulin resistance. To examine adverse effects of psychological stress, rats were subjected to intermittent food pellet feeding. Urinary catecholamines and cardiac norepinephrine stores were increased (p < 0.05). The depressed (p < 0.05) rate of Ca2+ uptake of sarcoplasmic reticulum is expected to contribute to cellular Ca2+ overload. These lifestyle influences strengthen the notion of an excess catecholamine syndrome which requires selective reduction of sympathetic outflow of the brain by I1-receptor agonists.

Training in swimming reduces blood pressure and increases muscle glucose transport activity as well as GLUT4 contents in stroke-prone spontaneously hypertensive rats

Exercise improves muscle insulin sensitivity and GLUT4 contents. We investigated the beneficial effects of swimming training on insulin sensitivity and genetic hypertension using stroke-prone hypertensive rats (SHRSP). We studied the relationship between genetic hypertension and insulin resistance in SHRSP and Wistar Kyoto rats (WKY) as a control. The systolic blood pressure of SHRSP was significantly reduced by 4-week swimming training (208.4 +/- 6.8 mmHg vs. 187.2 +/- 4.1 mmHg, p < 0.05). The swimming training also resulted in an approximately 20% increase in the insulin-stimulated glucose transport activity (p < 0.05) of soleus muscle strips and an approximately 3-fold increase in the plasma membrane GLUT4 protein expression (p < 0.01) in SHRSP. However, basal and insulin-stimulated glucose transport activity and GLUT4 contents were not significantly different between WKY and SHRSP. There was no difference in insulin resistance in skeletal muscle of SHRSP as compared with WKY. Our results indicated swimming training exercise improved not only hypertension but also muscle insulin sensitivity and GLUT4 protein expression in SHRSP.

The effects of voluntary running on cardiac mass and aortic compliance in Wistar-Kyoto and spontaneously hypertensive rats

OBJECTIVE

To investigate the effects of voluntary running exercise from 4-20 weeks of age on aortic compliance in Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR).

DESIGN

For each species we made comparisons between rats housed with an exercise wheel locked (10 rats) and unlocked (10 rats).

METHODS

Rats were killed using CO2 asphyxia and the aorta and heart of each rat were rapidly removed. The heart was dissected and weighed. A 4 mm descending proximal aortic ring was mounted on wires in an organ bath for determination of static compliance from the slope of the diameter-pressure relationship derived using Laplace's equation.

RESULTS

During the final 2 weeks of training WKY rats ran an average of 7.9 +/- 1.0 km/24 h compared with 1.0 +/- 0.2 km/24 h for SHR. Body weights of WKY rats and SHR and of animals housed with locked and unlocked exercise wheels did not differ. The septum, left ventricle and total heart weights and left ventricular:body weight ratios of sedentary SHR were greater than those of sedentary WKY rats. Trained WKY rats had significantly higher atrial, left and right ventricular and total heart weights and left ventricular:body weight ratios than did untrained WKY rats. Aortic compliance was higher in trained than it was in sedentary WKY rats (12.3 +/- 0.4 versus 14.2 +/- 0.5 microm/mmHg, P < 0.05). There was no difference between heart weights and aortic compliances of SHR housed with exercise wheels locked and unlocked.

CONCLUSION

Exercise-trained WKY rats had greater intrinsic aortic compliance when it was measured statically in vitro, which supports results of previous human work revealing a blood-pressure-independent component in the elevation of arterial compliance with training. The lower physical activity of the SHR strain used in this study could contribute to their higher blood pressures and lack of change in aortic compliance with exercise training.

Spontaneous running increases aortic compliance in Wistar-Kyoto rats

OBJECTIVE

Previous studies in humans have found, using non-invasive methodology, that arterial compliance is elevated with exercise training. Forced exercise in animals has corroborated these findings, but the association of this type of exercise with psychological stressors limits its relevance to humans. We have investigated the effects of spontaneous running exercise from 4-20 weeks of age on aortic and mesenteric compliance and vascular reactivity in Wistar-Kyoto (WKY) rats.

METHODS

Animals were killed using CO2 asphyxia and the aorta, mesentery and heart rapidly removed. The heart was dissected and weighed. The aorta was separated into 3 4-mm rings which were mounted on wires in organ baths for determination of compliance and vascular reactivity to noradrenaline, acetylcholine and sodium nitroprusside. The slope of diameter-pressure relationship derived using Laplace's equation was used as an index of compliance.

RESULTS

During the final 2 weeks of training WKY rats ran an average of 7.9 +/- 1.0 km/24 h. Body weight was not affected by training. Training significantly increased the weight of the atria, left and right ventricles as well as total heart weight and left ventricular/body weight ratio. Aortic compliance was increased from 12.3 +/- 0.4 to 14.2 +/- 0.5 microns/mmHg (P < 0.05) after training. There was no effect of training on aortic reactivity to noradrenaline, acetylcholine or sodium nitroprusside.

CONCLUSION

Exercise training increased intrinsic aortic compliance in WKY rats which provides evidence for a structural basis for the elevated compliance reported previously with 4 weeks of aerobic exercise in man.

Plasma catecholamine response in trained rats following hemorrhage

The purpose of this study was to evaluate the effect of physical training on hemorrhage-induced catecholamine release in rats. The training program consisted of swimming 5 days a week from 15 min in the first week to 2.5 hours in the 14th week. The rats were divided into four groups. Two groups (one trained and the other untrained) were studied during hemorrhage. The third and fourth groups (one trained and the other untrained) were not subjected to hemorrhage. After 14 weeks, trained rats had a lower heart rate than untrained animals at rest (311.86 +/- 8.9 vs. 361.33 +/- 12.13 bpm, p < .002) for a similar body weight. The trained and untrained groups had the same blood pressure, hematocrit, and norepinephrine responses following hemorrhage. However, plasma epinephrine concentration was lower in the trained rats 15 and 25 min following hemorrhage. These results suggest a decrease of the hemorrhage-induced epinephrine secretion in trained rats. An alteration of the relationship of arterial baroreflexes and of their hormonal effectors is a potential mechanism for the reduced plasma epinephrine level in trained hemorrhaged rats.

Sympathoadrenergic overactivity and lipid metabolism

Epidemiological studies have identified high heart rates as a risk factor for coronary heart disease mortality, and heart rate was found to correlate with the severity of coronary atherosclerosis. Heart rate was positively correlated with serum concentrations of total cholesterol, triglycerides, and non-HDL cholesterol. Since heart rate responds sensitively to sympathoadrenergic activity, it was hypothesized that catecholamines play a crucial role in the unfavorable lipid alterations. In addition to influences on circulating lipids, the question arose whether catecholamines have more specific effects on molecular species of structural lipids. Of particular importance is the question of the involvement of catecholamines in the recently suggested correlation between arachidonic acid and stroke mortality. It is therefore attempted to delineate the possible effects of catecholamines on the fatty acid composition of the phospholipids of heart muscle and vasculature. This was achieved in rats by either catecholamine injection or by swimming, a condition known to be associated with marked sympatho-adrenergic stimulation. In swimming rats, linoleic acid was decreased by up to 40% in heart phospholipids, whereas stearic acid and arachidonic acid were increased. Similarly, chronic norepinephrine treatment in rats resulted in a net decrease in linoleic acid and an increase in arachidonic acid and docosahexaenoic acid, which was particularly pronounced when rats were fed an n-3 polyunsaturated fatty acid (PUFA)-rich oil diet. Thus, catecholamines do affect the PUFA composition of heart membranes, mainly through an increase in arachidonic acid content. To further define the action of catecholamines on structural lipids, isolated rat ventricular myocytes in culture were subjected four times to 30 minutes of isoproterenol (10(-6) M) stimulation over 48 hours. No changes in membrane lipid parameters were observed, although the beating rate was increased by 30% during the stimulation. When the cell membranes were enriched in n-3 PUFAs (in association with a decrease in arachidonic acid), the positive chronotropic effect elicited by isoproterenol was raised to + 50%, indicating the modulation of adrenergic function by membrane PUFAs. However, isoproterenol treatment again had no effect on the phospholipid fatty acid composition. Thus, the effect of catecholamines on membrane lipids observed in intact organism appears to be indirect and to involve most probably organs such as the liver and adipose tissue. Catecholamines are expected to induce a lipolysis-linked quantitative and qualitative alteration in circulating fatty acids, which in turn alter the heart membrane composition, similar to the composition changes elicited by diet lipid alterations. Since there is increasing evidence that such fatty acid changes affect the activity of membrane proteins, the possibility emerges that this mechanism may contribute to the catecholamine-linked cardiovascular mortality.

The influence of isotonic exercise on cardiac hypertrophy in arterial hypertension: impact on cardiac function and on the capacity for aerobic work

Intense physical training through isotonic exercises has controversial effects in individuals with moderate to severe hypertension. In this study, normotensive Wistar rats and rats with renovascular hypertension (Goldblatt II) were subjected to intense physical exercise involving two 50-min swimming sessions per day for a period of 12 weeks. At the end of the study, we evaluated the effect of training on arterial pressure, the capacity for aerobic work and cardiac function. Our results demonstrate that intense physical training has no effect on the arterial blood pressure of normotensive rats or of animals with moderate renovascular hypertension. Hypertensive animals with cardiac hypertrophy require a greater period of training in order to attain the same capacity for aerobic work as normotensive rats. This difference may result from an inability of the former animals to increase cardiac compliance, thereby impeding more extensive usage of the Frank-Starling mechanism to subsequently increase the systolic cardiac performance. Cardiac hypertrophy induced by exercise did not summate with that induced by arterial hypertension. Physical exercise normalized the end-diastolic left ventricular pressure in hypertensive animals without any corresponding increase in the compliance of the chamber. The first derivative of left ventricular pulse pressure (+/- dP/dt) was greater in the hypertensive trained group than in the hypertensive sedentary rats. These observations suggest that a systolic dysfunction of the left ventricle involving an elevated residual volume secondary to arterial hypertension may be corrected by physical exercise such as swimming.

Antioxidant enzyme activities and lipid peroxidation levels in exercised and hypertensive rat tissues

Previous studies have shown that exercise-induced changes in muscle antioxidant status occur shortly after exercise. The present studies were designed to determine if longer-term exercise-related changes in antioxidant enzyme activities in both normotensive (WKY) and hypertensive rats (SHR) occurred, and if these changes were related to the levels of lipid peroxidation. WKY and SHR rats were exercised over a 10-week period using a progressive treadmill regimen. After a 1-week detraining period, the animals were euthanized and measurements of tissue antioxidant enzyme activities and lipid peroxide levels were determined in both exercised and cage-sedentary groups. Decreases in antioxidant activities (particularly glutathione peroxidase and catalase) in liver, kidney, skeletal and cardiac were associated with exercise training in both WKy and SHR rats (e.g. left ventricular glutathione peroxidase specific activity in WKY rats was decreased from 234 +/- 25 [SD, n = 12] to 187 +/- 17 [SD, n = 11] units/mg protein). Elevations in activities of antioxidant enzymes were generally associated with hypertension in these tissues (e.g. left ventricular glutathione peroxidase specific activity in SHR rats was 275 +/- 30 [SD, n = 12] units/mg protein), but changes in activities were more variable than those seen in response to exercise. Exercise-related changes in tissue levels of thiobarbituric acid-reactive substances (an indirect measure of tissue lipid peroxide levels) generally did not correlate with exercise-related antioxidant enzyme activity changes, and hypertension had no effect on these levels except in liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of endurance training on left ventricular performance: a study in anaesthetized rabbits

Endurance training is known to increase ventricular performance during exercise and to decrease resting heart rate. The aim of this study was to evaluate a model for endurance training in rabbits and to study the effects of endurance training on local myocardial performance in the left ventricle during resting conditions. One group of rabbits underwent a 10-week exercise training programme. The rabbits trained 5 days a week on a treadmill. Training periods increased gradually from 15 min to 1 h with increments in speed from 0.5 to 1.2 km h-1. After the training programme the rabbits were anaesthetized and studied as acute open-chest preparations. A micro-tip pressure transducer was introduced via apex to the left ventricle and two pairs of ultrasonic crystals were implanted in the left anterior wall to measure segment lengths. One pair measured shortening in the circumferential direction whereas the other pair measured shortening in the longitudinal direction. Heart rate was lower in the trained group (n = 5), 172 +/- 9 beats min-1 (mean +/- SEM), compared with 235 +/- 19 beats min-1 in the control group (n = 8) (P < 0.02). Stroke volume, measured by radio-nuclidelabelled microspheres, was greater in the trained rabbits compared with controls (P < 0.03). Shortening in both segments was of similar magnitude for the trained and control groups. End-systolic pressure-length relations (ESPLR) obtained by occlusion of the descending aorta (balloon catheter) showed reduced slopes for longitudinal segments in the trained group compared with the control group (P < 0.05). We conclude that this endurance training programme in rabbits can be used to study myocardial effects of endurance training. Furthermore, the less steep slope of ESPLRs for the longitudinal segment in the trained animals might indicate a structural myocardial remodelling and increased contractile reserve that might be recruited during adrenergic stimulation in the trained group.

Excess catecholamines and the metabolic syndrome: should central imidazoline receptors be a therapeutic target?

A sympathetic overactivity plays a major role in the pathogenesis of cardiovascular diseases in Westernized affluent societies. Of importance is an increased caloric intake and psychosocial stress which are associated with a raised central sympathetic outflow and unfavourable changes in metabolic parameters. Normalization of central sympathetic outflow could thus be a major therapeutic target. The newly developed antihypertensive drugs moxonidine and rilmenidine reduce the excitatory activity of neurons of the rostral ventrolateral medulla (RVLM) via binding to imidazoline receptors. Using radio telemetry, it is shown that, in contrast to the first generation centrally acting drug clonidine, moxonidine did not result in rebound of blood pressure after drug withdrawal in rats with spontaneous hypertension. In accordance, moxonidine is characterized by a low affinity for alpha-adrenoceptors and exhibits few side-effects. It is proposed that normalization of central sympathetic outflow represents a causal approach for improving crucial features of the metabolic syndrome.

Diabetes-like action of intermittent fasting on sarcoplasmic reticulum Ca2+-pump ATPase and myosin isoenzymes can be prevented by sucrose

Experimental diabetes results in a reduction of the sarcoplasmic reticulum (SR) Ca2+-stimulated ATPase activity and a redirection of myosin isoenzymes from V1 to V3. Similar, but less pronounced, changes were induced by subjecting rats to intermittent fasting for 6 weeks. Low amounts of sucrose (0.8%) in the drinking water prevented the subcellular changes in fasted rats; however, sucrose neither affected the levels of plasma thyroid hormones nor normalized the reduced body weight. Plasma glucose was lowered without any changes in plasma insulin in the fasted rats receiving sucrose; this suggested an enhanced peripheral glucose utilization. Thus, the signals in the diabetic heart leading to changes in SR and myosin can be mimicked by intermittent fasting and seem to be linked to a shift in fuel utilization by the myocytes.