Reduced ischemia and reperfusion injury following exercise training

Cardiomyocyte Adaptation to Exercise: K+ Channels, Contractility and Ischemic Injury

Cardiovascular disease is a leading cause of morbidity and mortality, and exercise-training (TRN) is known to reduce risk factors and protect the heart from ischemia and reperfusion injury. Though the cardioprotective effects of exercise are well-documented, underlying mechanisms are not well understood. This review highlights recent findings and focuses on cardiac factors with emphasis on K+ channel control of the action potential duration (APD), β-adrenergic and adenosine regulation of cardiomyocyte function, and mitochondrial Ca2+ regulation. TRN-induced prolongation and shortening of the APD at low and high activation rates, respectively, is discussed in the context of a reduced response of the sarcolemma delayed rectifier potassium channel (IK) and increased content and activation of the sarcolemma KATP channel. A proposed mechanism underlying the latter is presented, including the phosphatidylinositol-3kinase/protein kinase B pathway. TRN induced increases in cardiomyocyte contractility and the response to adrenergic agonists are discussed. The TRN-induced protection from reperfusion injury is highlighted by the increased content and activation of the sarcolemma KATP channel and the increased phosphorylated glycogen synthase kinase-3β, which aid in preventing mitochondrial Ca2+ overload and mitochondria-triggered apoptosis. Finally, a brief section is presented on the increased incidences of atrial fibrillation associated with age and in life-long exercisers.

Myokine Musclin Is Critical for Exercise-Induced Cardiac Conditioning

This study investigates the role and mechanisms by which the myokine musclin promotes exercise-induced cardiac conditioning. Exercise is one of the most powerful triggers of cardiac conditioning with proven benefits for healthy and diseased hearts. There is an emerging understanding that muscles produce and secrete myokines, which mediate local and systemic "crosstalk" to promote exercise tolerance and overall health, including cardiac conditioning. The myokine musclin, highly conserved across animal species, has been shown to be upregulated in response to physical activity. However, musclin effects on exercise-induced cardiac conditioning are not established. Following completion of a treadmill exercise protocol, wild type (WT) mice and mice with disruption of the musclin-encoding gene, Ostn, had their hearts extracted and exposed to an ex vivo ischemia-reperfusion protocol or biochemical studies. Disruption of musclin signaling abolished the ability of exercise to mitigate cardiac ischemic injury. This impaired cardioprotection was associated with reduced mitochondrial content and function linked to blunted cyclic guanosine monophosphate (cGMP) signaling. Genetic deletion of musclin reduced the nuclear abundance of protein kinase G (PKGI) and cyclic adenosine monophosphate (cAMP) response element binding (CREB), resulting in suppression of the master regulator of mitochondrial biogenesis, peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α), and its downstream targets in response to physical activity. Synthetic musclin peptide pharmacokinetic parameters were defined and used to calculate the infusion rate necessary to maintain its plasma level comparable to that observed after exercise. This infusion was found to reproduce the cardioprotective benefits of exercise in sedentary WT and Ostn-KO mice. Musclin is essential for exercise-induced cardiac protection. Boosting musclin signaling might serve as a novel therapeutic strategy for cardioprotection.

Overexpression of Neuron-Derived Orphan Receptor 1 (NOR-1) Rescues Cardiomyocytes from Cell Death and Improves Viability after Doxorubicin Induced Stress

Following myocardial infarction, reperfusion injury (RI) is commonly observed due to the excessive formation of, e.g., reactive oxygen species (ROS). Doxorubicin (DOX), a widely used anti-cancer drug, is also known to cause cardiotoxicity due to excessive ROS production. Exercise training has been shown to protect the heart against both RI- and DOX-induced cardiotoxicity, but the exact mechanism is still unknown. Neuron-derived orphan receptor 1 (NOR-1) is an important exercise-responsive protein in the skeletal muscle which has also been reported to facilitate cellular survival during hypoxia. Therefore, we hypothesized that NOR-1 could protect cardiomyocytes (CMs) against cellular stress induced by DOX. We also hypothesized that NOR-1 is involved in preparing the CMs against a stress situation during nonstimulated conditions by increasing cell viability. To determine the protective effect of NOR-1 in CMs stressed with DOX challenge, we overexpressed NOR-1 in AC16 human CMs treated with 5 µM DOX for 12 h or the respective vehicle control, followed by performing Lactate dehydrogenase (LDH) activity, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), and caspase-3 activity assays to measure cell death, cell viability, and apoptosis, respectively. In addition, Western blotting analysis was performed to determine the expression of key proteins involved in cardioprotection. We demonstrated that NOR-1 overexpression decreased cell death (p < 0.105) and apoptosis (p < 0.01) while increasing cell viability (p < 0.05) in DOX-treated CMs. We also observed that NOR-1 overexpression increased phosphorylation of extracellular signal-regulated kinase (ERK) (p < 0.01) and protein expression levels of B cell lymphoma extra-large (Bcl-xL) (p < 0.01). We did not detect any significant changes in phosphorylation of protein kinase B (Akt), glycogen synthase kinase-3β (GSK-3β) and signal transducer and activator of transcription 3 (STAT3) or expression levels of superoxide dismutase 2 (SOD2) and cyclin D1. Furthermore, we demonstrated that NOR-1 overexpression increased the cell viability (p < 0.0001) of CMs during nonstimulated conditions without affecting cell death or apoptosis. Our findings indicate that NOR-1 could serve as a potential cardioprotective protein in response to Doxorubicin-induced cellular stress.

A Mitochondrial Approach to Cardiovascular Risk and Disease

BACKGROUND

Cardiovascular diseases (CVDs) are a leading risk factor for mortality worldwide and the number of CVDs victims is predicted to rise through 2030. While several external parameters (genetic, behavioral, environmental and physiological) contribute to cardiovascular morbidity and mortality; intrinsic metabolic and functional determinants such as insulin resistance, hyperglycemia, inflammation, high blood pressure and dyslipidemia are considered to be dominant factors.

METHODS

Pubmed searches were performed using different keywords related with mitochondria and cardiovascular disease and risk. In vitro, animal and human results were extracted from the hits obtained.

RESULTS

High cardiac energy demand is sustained by mitochondrial ATP production, and abnormal mitochondrial function has been associated with several lifestyle- and aging-related pathologies in the developed world such as diabetes, non-alcoholic fatty liver disease (NAFLD) and kidney diseases, that in turn can lead to cardiac injury. In order to delay cardiac mitochondrial dysfunction in the context of cardiovascular risk, regular physical activity has been shown to improve mitochondrial parameters and myocardial tolerance to ischemia-reperfusion (IR). Furthermore, pharmacological interventions can prevent the risk of CVDs. Therapeutic agents that can target mitochondria, decreasing ROS production and improve its function have been intensively researched. One example is the mitochondria-targeted antioxidant MitoQ10, which already showed beneficial effects in hypertensive rat models. Carvedilol or antidiabetic drugs also showed protective effects by preventing cardiac mitochondrial oxidative damage.

CONCLUSION

This review highlights the role of mitochondrial dysfunction in CVDs, also show-casing several approaches that act by improving mitochondrial function in the heart, contributing to decrease some of the risk factors associated with CVDs.

Effects of short-term high-intensity interval and continuous exercise training on body composition and cardiac function in obese sarcopenic rats

AIM

We investigated the effects of high-intensity interval and continuous short-term exercise on body composition and cardiac function after myocardial ischemia-reperfusion injury (IRI) in obese rats.

METHODS

Rats fed with a standard chow diet (SC) or high-fat diet (HFD) for 20 weeks underwent systolic blood pressure (SBP), glycemia and dual-energy X-ray absorptiometry analyses. Then, animals fed with HFD were subdivided into three groups: sedentary (HFD-SED); moderate-intensity continuous training (HFD-MICT); and high-intensity interval training (HFD-HIIT). Exercised groups underwent four isocaloric aerobic exercise sessions, in which HFD-MICT maintained the intensity continuously and HFD-HIIT alternated it. After exercise sessions, all groups underwent global IRI and myocardial infarct size (IS) was determined histologically. Fat and muscle mass were weighted, and protein levels involved in muscle metabolism were assessed in skeletal muscle.

RESULTS

HFD-fed versus SC-fed rats reduced lean body mass by 31% (P < 0.001), while SBP, glycemia and body fat percentage were increased by 10% (P = 0.04), 30% (P = 0.006) and 54% (P < 0.001); respectively. HFD-induced muscle atrophy was restored in exercised groups, as only HFD-SED presented lower gastrocnemius (32%; P = 0.001) and quadriceps mass (62%; P < 0.001) than SC. PGC1-α expression was 2.7-fold higher in HFD-HIIT versus HFD-SED (P = 0.04), whereas HFD-HIIT and HFD-MICT exhibited 1.7-fold increase in p-mTOR^Ser2481 levels compared to HFD-SED (P = 0.04). Although no difference was detected among groups for IS (P = 0.30), only HFD-HIIT preserved left-ventricle developed pressure after IRI (+0.7 mmHg; P = 0.9).

SIGNIFICANCE

Short-term exercise, continuous or HIIT, restored HFD-induced muscle atrophy and increased mTOR expression, but only HIIT maintained myocardial contractility following IRI in obese animals.

Myocardial apoptosis and mesenchymal stem cells with acute exercise

Aerobic exercise confers many health benefits. However, numerous reports have shown that acute aerobic exercise can injure the heart. We tested the general hypothesis that acute moderate‐intensity exercise in rodents induces cardiomyocyte damage and stimulates mesenchymal stem cells (MSCs) to increase paracrine‐mediated protective effects on cardiomyocytes. A single session of treadmill running (13 m/min, 0% grade, for 45 min) in untrained C57BL/6 male mice (n = 18) increased cleaved poly ADP‐ribose polymerase (PARP), a marker of apoptosis, in the myocardium 24 h postexercise. Microarray analysis of mouse myocardium identified 11 relevant apoptotic genes and several shifts in matrix remodeling transcripts over the postexercise window. Postexercise cardiomyocyte death was recapitulated in neonatal rat cardiomyocytes (NRCMs) by culturing cells in 2% plasma harvested from exercised rats. The increased cell death observed in exercise‐treated NRCMs was attenuated by β‐adrenergic blockade, but not antioxidant treatment. MSC survival, proliferation, and chemotaxis showed no significant differences between sedentary and exercise plasma conditions, despite increased IL‐6, TNF‐α, IL‐1β, and IFN‐γ secretions from MSCs treated with exercise plasma. NRCM survival was increased nearly 500% when cocultured with MSCs, but this effect was not altered under exercise plasma culture conditions. Our results suggest acute moderate‐intensity aerobic treadmill running in exercise‐naïve rodents induces temporal cardiomyocyte death due to plasma‐borne factors, namely, catecholaminergic stress. Even though exercise conditions prompt an inflammatory response in MSCs, the exercise milieu does not alter the MSC‐protective phenotype on cardiomyocytes.

Exercise: Teaching myocytes new tricks

Endurance exercise training promotes numerous cellular adaptations in both cardiac myocytes and skeletal muscle fibers. For example, exercise training fosters changes in mitochondrial function due to increased mitochondrial protein expression and accelerated mitochondrial turnover. Additionally, endurance exercise training alters the abundance of numerous cytosolic and mitochondrial proteins in both cardiac and skeletal muscle myocytes, resulting in a protective phenotype in the active fibers; this exercise-induced protection of cardiac and skeletal muscle fibers is often referred to as "exercise preconditioning." As few as 3-5 consecutive days of endurance exercise training result in a preconditioned cardiac phenotype that is sheltered against ischemia-reperfusion-induced injury. Similarly, endurance exercise training results in preconditioned skeletal muscle fibers that are resistant to a variety of stresses (e.g., heat stress, exercise-induced oxidative stress, and inactivity-induced atrophy). Many studies have probed the mechanisms responsible for exercise-induced preconditioning of cardiac and skeletal muscle fibers; these studies are important, because they provide an improved understanding of the biochemical mechanisms responsible for exercise-induced preconditioning, which has the potential to lead to innovative pharmacological therapies aimed at minimizing stress-induced injury to cardiac and skeletal muscle. This review summarizes the development of exercise-induced protection of cardiac myocytes and skeletal muscle fibers and highlights the putative mechanisms responsible for exercise-induced protection in the heart and skeletal muscles.

Cardiac Ischemia/Reperfusion Injury: The Beneficial Effects of Exercise

Cardiac ischemia reperfusion injury (IRI) occurs when the myocardium is revascularized after an episode of limited or absent blood supply. Many changes, including free radical production, calcium overload, protease activation, altered membrane lipids and leukocyte activation, contribute to IRI-induced myocardium damage. Aerobic exercise is the only countermeasure against IRI that can be sustained on a regular basis in clinical practice. Interestingly, both short-term (3-5 days) and long-term (several weeks) exercise increase myocardial tolerance, reduce infarct size area and arrhythmias induced by IRI. Exercise protects the heart against IRI in a biphasic manner. The early phase of cardioprotection occurs between 30 min and 3 h following an acute exercise bout, whilst the late phase is achieved within 24 h after the exercise bout and persists for several days. As for the exercise intensity, although controversial data exists, it is feasible that the amount of cardioprotection is proportional to exercise intensity and only achieved above a critical threshold. It is known that aerobic exercise produces a cardioprotective phenotype, however the mechanisms responsible for this phenomenon remain unclear. Apparently, aerobic exercise-induced preconditioning is dependent on several factors that work together to protect the heart. Altered nitric oxide (NO) signaling, increased levels of heat shock proteins (HSPs), enhanced function of ATP-sensitive potassium channels, increased activation of opioids system, and enhanced antioxidant capacity may contribute to exercise-induced cardioprotection. Much has been discovered from animal models involving exercise-induced cardioprotection against cardiac IRI, however translating these findings to clinical practice still represents the major challenge in this field.

Lipid partitioning during cardiac stress

It is well documented that fatty acids serve as the primary fuel substrate for the contracting myocardium. However, extensive research has identified significant changes in the myocardial oxidation of fatty acids during acute or chronic cardiac stress. As a result, the redistribution or partitioning of fatty acids due to metabolic derangements could have biological implications. Fatty acids can be stored as triacylglycerols, serve as critical components for biosynthesis of phospholipid membranes, and form the potent signaling molecules, diacylglycerol and ceramides. Therefore, the contribution of lipid metabolism to health and disease is more intricate than a balance of uptake and oxidation. In this review, the available data regarding alterations that occur in endogenous cardiac lipid pathways during the pathological stressors of ischemia-reperfusion and pathological hypertrophy/heart failure are highlighted. In addition, changes in endogenous lipids observed in exercise training models are presented for comparison. This article is part of a Special Issue entitled: Heart Lipid Metabolism edited by G.D. Lopaschuk.

Knockout of p21-activated kinase-1 attenuates exercise-induced cardiac remodelling through altered calcineurin signalling

AIMS

Despite its known cardiovascular benefits, the intracellular signalling mechanisms underlying physiological cardiac growth remain poorly understood. Therefore, the purpose of this study was to investigate a novel role of p21-activated kinase-1 (Pak1) in the regulation of exercise-induced cardiac hypertrophy.

METHODS AND RESULTS

Wild-type (WT) and Pak1 KO mice were subjected to 6 weeks of treadmill endurance exercise training (ex-training). Cardiac function was assessed via echocardiography, in situ haemodynamics, and the pCa-force relations in skinned fibre preparations at baseline and at the end of the training regimen. Post-translational modifications to the sarcomeric proteins and expression levels of calcium-regulating proteins were also assessed following ex-training. Heart weight/tibia length and echocardiography data revealed that there was marked hypertrophy following ex-training in the WT mice, which was not evident in the KO mice. Additionally, following ex-training, WT mice demonstrated an increase in cardiac contractility, myofilament calcium sensitivity, and phosphorylation of cardiac myosin-binding protein C, cardiac TnT, and tropomyosin compared with KO mice. With ex-training in WT mice, there were also increased protein levels of calcineurin and increased phosphorylation of phospholamban.

CONCLUSIONS

Our data suggest that Pak1 is essential for adaptive physiological cardiac remodelling and support previous evidence that demonstrates Pak1 signalling is important for cardiac growth and survival.

Anabolic Androgenic Steroid (AAS) related deaths: autoptic, histopathological and toxicological findings

Anabolic androgenic steroids (AASs) represent a large group of synthetic derivatives of testosterone, produced to maximize anabolic effects and minimize the androgenic ones. AAS can be administered orally, parenterally by intramuscular injection and transdermally. Androgens act by binding to the nuclear androgen receptor (AR) in the cytoplasm and then translocate into the nucleus. This binding results in sequential conformational changes of the receptor affecting the interaction between receptor and protein, and receptor and DNA. Skeletal muscle can be considered as the main target tissue for the anabolic effects of AAS, which are mediated by ARs which after exposure to AASs are up-regulated and their number increases with body building. Therefore, AASs determine an increase in muscle size as a consequence of a dose-dependent hypertrophy resulting in an increase of the cross-sectional areas of both type I and type II muscle fibers and myonuclear domains. Moreover, it has been reported that AASs can increase tolerance to exercise by making the muscles more capable to overload therefore shielding them from muscle fiber damage and improving the level of protein synthesis during recovery. Despite some therapeutic use of AASs, there is also wide abuse among athletes especially bodybuilders in order to improve their performances and to increase muscle growth and lean body mass, taking into account the significant anabolic effects of these drugs. The prolonged misuse and abuse of AASs can determine several adverse effects, some of which may be even fatal especially on the cardiovascular system because they may increase the risk of sudden cardiac death (SCD), myocardial infarction, altered serum lipoproteins, and cardiac hypertrophy. The aim of this review is to focus on deaths related to AAS abuse, trying to evaluate the autoptic, histopathological and toxicological findings in order to investigate the pathophysiological mechanism that underlines this type of death, which is still obscure in several aspects. The review of the literature allowed us to identify 19 fatal cases between 1990 and 2012, in which the autopsy excluded in all cases, extracardiac causes of death.

Endurance exercise accelerates myocardial tissue oxygenation recovery and reduces ischemia reperfusion injury in mice

Exercise training offers cardioprotection against ischemia and reperfusion (I/R) injury. However, few essential signals have been identified to underscore the protection from injury. In the present study, we hypothesized that exercise-induced acceleration of myocardial tissue oxygenation recovery contributes to this protection. C57BL/6 mice (4 weeks old) were trained on treadmills for 45 min/day at a treading rate of 15 m/min for 8 weeks. At the end of 8-week exercise training, mice underwent 30-min left anterior descending coronary artery occlusion followed by 60-min or 24-h reperfusion. Electron paramagnetic resonance oximetry was performed to measure myocardial tissue oxygenation. Western immunoblotting analyses, gene transfection, and myography were examined. The oximetry study demonstrated that exercise markedly shortened myocardial tissue oxygenation recovery time following reperfusion. Exercise training up-regulated Kir6.1 protein expression (a subunit of ATP-sensitive K(+)channel on vascular smooth muscle cells, VSMC sarc-K(ATP)) and protected the heart from I/R injury. In vivo gene transfer of dominant negative Kir6.1AAA prolonged the recovery time and enlarged infarct size. In addition, transfection of Kir6.1AAA increased the stiffness and reduced the relaxation capacity in the vasculature. Together, our study demonstrated that exercise training up-regulated Kir6.1, improved tissue oxygenation recovery, and protected the heart against I/R injury. This exercise-induced cardioprotective mechanism may provide a potential therapeutic intervention targeting VSMC sarc-K(ATP) channels and reperfusion recovery.

Mechanisms of exercise-induced cardioprotection

Myocardial ischemia-reperfusion (IR) injury can cause ventricular cell death and is a major pathological event leading to morbidity and mortality in those with coronary artery disease. Interestingly, as few as five bouts of exercise on consecutive days can rapidly produce a cardiac phenotype that resists IR-induced myocardial injury. This review summarizes the development of exercise-induced cardioprotection and the mechanisms responsible for this important adaptive response.

The effect of physical activity or exercise on key biomarkers in atherosclerosis--a systematic review

OBJECTIVE

This systematic review aimed to summarize published papers on the effect of physical activity (PA)/exercise on key atherosclerotic factors in patients with risk factors for or established cardiovascular disease (CVD).

METHODS

Studies involving PA and cytokines, chemokines, adhesion molecules, CRP and angiogenic factors were searched for in Medline and Cochrane library. Original human studies of more than 2 weeks of PA intervention were included. Study quality was assessed according to the GRADE system of evidence.

RESULTS

Twenty-eight papers fulfilled the inclusion criteria. PA decreases the cytokines, tumor necrosis factor-a (TNF-a), interleukin-6 (IL-6), and interferon-y IFN-y (high, moderate and low evidence, respectively). The effect of PA on chemokines; stromal derived factor-1 (SDF-1), interleukin-8 (IL-8) (insufficient evidence) and monocyte chemoattractant protein-1 (MCP-1) (low evidence) was inconclusive. Aerobic exercise decreased the adhesion molecules, vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) (moderate and high evidence, respectively), while effects of PA on E- and P-selectin were inconclusive. PA decreases C-reactive protein (CRP) (high evidence). The angiogenic actors, endothelial progenitor cells (EPCs) are increased (high evidence) and VEGF is decreased (moderate evidence) by PA. The effect of PA on these factors seems to depend on the type and duration of exercise intervention and patient factors, such as presence of ischemia.

CONCLUSION

As presented in this review, there is a high level of evidence that physical activity positively affects key players in atherosclerosis development. These effects could partly explain the scientifically proven anti-atherogenic effects of PA, and do have important clinical implications.

Exercise-induced cardioprotection is mediated by a bloodborne, transferable factor

Exercise protects against myocardial ischemia-reperfusion (I-R) injury but the mechanism remains unclear. Protection can be transferred from a remotely preconditioned human donor to an isolated perfused rabbit heart using a dialysate of plasma. We hypothesized that physical exercise preconditioning also confers cardioprotection through a humorally mediated effector dependent on opioid receptor activation. Thirteen male volunteers performed vigorous exercise (four 2-minute bouts of high-intensity exercise) and 1 week later they underwent remote ischemic preconditioning (four cycles of 5 min upper limb ischemia and reperfusion). Dialysates were prepared from blood collected before (control) and after the two interventions. Isolated rabbit hearts were perfused with the dialysates without and with co-administration of naloxone (opioid receptor antagonist) prior to 40 min regional ischemia and 2 h reperfusion. Exercise and remote ischemic preconditioning (rIPC) reduced infarct size from 60 ± 5 to 35 ± 5 % and from 57 ± 7 to 27 ± 3 % of the area at risk, respectively (p < 0.05 and < 0.01). Furthermore, post-ischemic left ventricular developed pressure was improved compared with controls (p = 0.08 for exercise and p = 0.04 for rIPC). Co-perfusion with naloxone abrogated the protective effects of exercise and remote ischemic preconditioned dialysates. In conclusion, high-intensity exercise preconditioning elicits cardioprotection through a humorally mediated dependent on opioid receptor activation, similar to rIPC.

Mitochondrial therapeutics for cardioprotection

Mitochondria represent approximately one-third of the mass of the heart and play a critical role in maintaining cellular function-however, they are also a potent source of free radicals and pro-apoptotic factors. As such, maintaining mitochondrial homeostasis is essential to cell survival. As the dominant source of ATP, continuous quality control is mandatory to ensure their ongoing optimal function. Mitochondrial quality control is accomplished by the dynamic interplay of fusion, fission, autophagy, and mitochondrial biogenesis. This review examines these processes in the heart and considers their role in the context of ischemia-reperfusion injury. Interventions that modulate mitochondrial turnover, including pharmacologic agents, exercise, and caloric restriction are discussed as a means to improve mitochondrial quality control, ameliorate cardiovascular dysfunction, and enhance longevity.

Acute exercise exacerbates ischemia-induced diastolic rigor in hypertensive myocardium

Previous studies have shown that acute exercise preconditions the myocardium from ischemic injury. The purpose of this study was to test whether acute exercise protects the hypertensive myocardium from ischemia-induced diastolic rigor, and to compare the response between normotensive and uncompensated hypertensive hearts. Hearts harvested from female Wistar-Kyoto (WKY; n = 24) and spontaneously hypertensive rats (SHR; n = 27) (age:10–12 weeks) were exposed to ischemia (Langendorff isovolumic preparation; 22 minutes of no flow ischemia and studied following prior conditions of: 1) no exercise (WKY-CON, n=8; SHR-CON, n=8); 2) ischemia initiated one hour post-acute exercise (WKY-1HR, n = 8; SHR-1HR, n = 11); and 3) ischemia initiated 24 hours post-acute exercise (WKY-24HR; n = 8; SHR-24HR, n = 8). Acute exercise consisted of one bout of treadmill running at 25 m/min for 60 minutes. Heart weight was similar between WKY and SHR despite elevated in vivo resting systolic blood pressure and rate pressure product in SHR (P<0.05). During normoxic perfusion, left ventricular (LV) Langendorff performance was similar between WKY and SHR over the post-exercise time course. However, during ischemia, LV diastolic rigor was less in WKY vs. SHR (P<0.05). Acute exercise augmented ischemia-induced LV dysfunction one hour post-exercise in SHR (P<0.05), with gradual recovery by 24 hours post-exercise. These data suggest that acute exercise promotes ischemic diastolic rigor in SHR, even prior to the development of cardiac hypertrophy.

Exercise-induced cardiac preconditioning: how exercise protects your achy-breaky heart

The ability of exercise to protect the heart against ischemia-reperfusion (I/R) injury is well known in both human epidemiological studies and experimental animal models. In this review article, we describe what is currently known about the ability of exercise to precondition the heart against infarction. Just 1 day of exercise can protect the heart against ischemia/reperfusion damage, and this protection is upheld with months of exercise, making exercise one of the few sustainable preconditioning stimuli. Exercise preconditioning depends on the model and intensity of exercise, and appears to involve heightened oxidant buffering capacity, upregulated subunits of sarcolemmal ATP-sensitive potassium channels, and adaptations to cardiac mitochondria. We review the putative mechanisms involved in exercise preconditioning and point out many areas where future research is necessary to advance our understanding of how this stimulus confers resistance against I/R damage.

Exercise-induced cardioprotection against myocardial ischemia-reperfusion injury

Myocardial ischemia-reperfusion (IR) injury is a major contributor to the morbidity and mortality associated with coronary artery disease. Muscular exercise is a countermeasure to protect against IR-induced cardiac injury in both young and old animals. Specifically, regular bouts of endurance exercise protect the heart against all levels of IR-induced injury. Proposed mechanisms to explain the cardioprotective effects of exercise include alterations in coronary circulation, expression of endoplasmic reticulum stress proteins, increased cyclooxygenase-2 activity, induction of myocardial heat shock proteins, improved cardiac antioxidant capacity, and/or elevation of ATP-sensitive potassium channels on both the sarcolemmal and the mitochondrial inner membranes. Moreover, it seems possible that other, yet to be defined, mechanisms of exercise-induced cardioprotection may also exist. Of the known putative cardioprotective mechanisms, current evidence suggests that elevated myocardial levels of antioxidants and increased expression of sarcolemmal ATP-sensitive potassium channels are both contributors to exercise-induced cardioprotection against IR injury. At present, it is unclear if these two protective mediators act independently or interact to contribute to exercise-induced cardioprotection. Understanding the molecular basis for exercise-induced cardioprotection will provide the required knowledge base to develop therapeutic approaches to protect the heart during an IR insult.

Exercise-induced cardioprotection: endogenous mechanisms

It is now well established that exercise can result in cardioprotection against ischemia-reperfusion (I-R) injury; however, the adaptations within the heart that provide the protection are still in doubt. The cytoprotective proteins receiving the most attention to date are antioxidant enzymes and heat shock proteins. The extent of I-R injury is dependent on the interactions of several events, including energy depletion, metabolite accumulation, oxidant stress, and calcium overload. Adaptations that directly influence any of these could affect I-R outcome. Thus, the exercise-induced cardioprotective phenotype is likely to include additional cytoprotective proteins beyond antioxidant enzymes or heat shock proteins. In this review, we will consider evidence for some of these in the cytosol, mitochondria, and sarcolemma of the cardiomyocyte. We will not consider potentially important adaptations within vascular tissue or the autonomic nervous system. Results of recent studies support the hypothesis that exercise leads to cardioprotective adaptations that are unique from other forms of preconditioning against I-R injury.

Exercise induces a cardiac mitochondrial phenotype that resists apoptotic stimuli

Ischemia-reperfusion-induced calcium overload and production of reactive oxygen species can trigger apoptosis by promoting the release of proapoptotic factors via the mitochondrial permeability transition pore. While it is clear that endurance exercise provides cardioprotection against ischemia-reperfusion-induced injury, it is unknown if exercise training directly alters mitochondria phenotype and confers protection against apoptotic stimuli in both subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria. We hypothesized that exercise training increases expression of endogenous antioxidant enzymes and other antiapoptotic proteins, resulting in a SS and IMF mitochondrial phenotype that resists apoptotic stimuli. Mitochondria isolated from hearts of sedentary (n = 8) and exercised-trained (n = 8) adult male rats were studied. Endurance exercise increased the protein levels of primary antioxidant enzymes in both SS and IMF mitochondria. Furthermore, exercise increased the levels of antiapoptotic proteins in the heart, including the apoptosis repressor with a caspase recruitment domain and inducible heat shock protein 70. Importantly, our findings reveal that endurance exercise training attenuates reactive oxygen species-induced cytochrome c release from heart mitochondria. These changes are accompanied by a lower maximal rate of mitochondrial permeability transition pore opening (V(max)) and prolonged time to V(max) in both SS and IMF cardiac mitochondria. These novel findings reveal that endurance exercise promotes biochemical alterations in cardiac SS and IMF mitochondria, resulting in a phenotype that resists apoptotic stimuli. Furthermore, these results are consistent with the concept that exercise-induced mitochondrial adaptations contribute to exercise-induced cardioprotection.

Long-term aerobic exercise protects the heart against ischemia/reperfusion injury via PI3 kinase-dependent and Akt-mediated mechanism

OBJECTIVE

Physical activity has been shown to improve cardiovascular function and to be beneficial to type 2 diabetic patients. However, the effects of aerobic exercise (AE) on myocardial ischemia/reperfusion (MI/R) are largely unclear. Therefore, the aims of the present study were to determine whether long-term AE can protect the heart against I/R injury, and if so, to investigate the underlying mechanism.

METHODS

Adult male Sprague-Dawley rats were randomly subjected to 8 weeks of either sedentary or free-loading swimming exercise (3 h/day, 5 d/week). Then the animals were subjected to 30 min MI followed by 4 h R. Arterial blood pressure and left ventricular pressure (LVP) were monitored throughout the whole MI/R procedure. Plasma creatine kinase (CK) and lactate dehydrogenase (LDH) activities were measured spectrophotometrically. Myocardial infarction and myocardial apoptosis (TUNEL analysis) were determined in a blinded manner.

RESULTS

MI/R caused significant cardiac dysfunction and myocardial apoptosis (strong TUNEL-positive staining). Compared with sedentary group, rats subjected to 8 weeks of AE showed protection against MI/R as evidenced by reduced myocardial infarction (26.8 +/- 1.5% vs. 35.3 +/- 2.4%, n = 8, P < 0.05), inhibited cardiomyocyte apoptosis (decreased apoptotic index (12.4 +/- 1.1% vs. 21.0 +/- 1.7%, n = 8, P < 0.01) and decreased myocardial caspase-3 activity), decreased plasma CK and LDH activities and improved recovery of cardiac systolic/diastolic function (including LVSP and +/-LVdP/dt) at the end of R. Moreover, exercise resulted in 1.7-fold, 2.5-fold and 2.5-fold increases in Akt expression, Akt phosphorylation and glycogen synthase kinase-3beta phosphorylation in I/R myocardium, respectively (n = 3, all P < 0.05). More importantly, treatment with wortmannin, a PI3 kinase inhibitor, 15 min before R not only significantly blocked Akt phosphorylation (P < 0.05) in exercise rats, but also abolished long-term AE-induced cardioprotection for the I/R heart as manifested by increased apoptosis and myocardial infarction, and reduced cardiac function.

CONCLUSION

Long-term AE exerts cardioprotective effect against MI/R injury, including anti-cardiomyocyte apoptosis, which is at least partly via PI3 kinase-dependent and Akt-mediated mechanism.

Calcineurin inhibition normalizes beta-adrenergic responsiveness in the spontaneously hypertensive rat

Calcineurin, a Ca(2+)-regulated protein phosphatase, links myocardial Ca(2+) signaling with hypertrophic gene transcription. Calcineurin abundance increases in pressure-overload hypertrophy and may reduce agonist-mediated phospholamban (PLB) phosphorylation to underlie blunted beta-adrenergic receptor (beta-AR) responsiveness in hypertension. This hypothesis was tested by measuring the effects of calcineurin inhibition on changes in cardiac contractility caused by beta-adrenergic stimulation in spontaneously hypertensive rats (SHR). Female SHR (age: 7 mo) and age-matched female Wistar-Kyoto rats (WKY) were studied. Heart weight-to-body weight ratio (P < 0.01) and systolic blood pressure (P < 0.01) were greater in SHR compared with WKY and were associated with increased myocardial calcineurin mRNA (CnAbeta) and activity (P < 0.05). beta-AR stimulation with isoproterenol (Iso) increased calcineurin activity (P < 0.05) in both WKY and SHR hearts, and this activity was suppressed with cyclosporin A (CsA) treatment. In SHR, CsA improved left ventricular whole heart and isolated myocyte beta-AR responsiveness by normalizing PLB phosphorylation at Ser(16) and Thr(17) (P < 0.05). These CsA-induced, PLB-mediated effects were associated with an augmentation in cardiomyocyte peak Ca(2+) and a reduced rate (time constant of isovolumic pressure relaxation, tau) and magnitude of diastolic Ca(2+) during beta-AR stimulation. In conclusion, CsA normalized the blunted beta-AR responsiveness associated with hypertension, in part, by mitigating calcineurin activity while improving PLB phosphorylation and subsequent sarcoplasmic reticulum Ca(2+) regulation.

Exercise training decreases rat heart mitochondria free radical generation but does not prevent Ca2+-induced dysfunction

Exercise provides cardioprotection against ischemia-reperfusion injury, a process involving mitochondrial reactive oxygen species (ROS) generation and calcium overload. This study tested the hypotheses that isolated mitochondria from hearts of endurance-trained rats have decreased ROS production and improved tolerance against Ca(2+)-induced dysfunction. Male Fischer 344 rats were either sedentary (Sed, n = 8) or endurance exercise trained (ET, n = 11) by running on a treadmill for 16 wk (5 days/wk, 60 min/day, 25 m/min, 6 degrees grade). Mitochondrial oxidative phosphorylation measures were determined with glutamate-malate or succinate as substrates, and H(2)O(2) production and permeability transition pore (PTP) opening were determined with succinate. All assays were carried out in the absence and presence of calcium. In response to 25 and 50 microM CaCl(2), Sed and ET displayed similar decreases in state 3 respiration, respiratory control ratio, and ADP:O ratio. Ca(2+)-induced PTP opening was also similar. However, H(2)O(2) production by ET was lower than Sed (P < 0.05) in the absence of calcium (323 +/- 12 vs. 362 +/- 11 pmol.min(-1).mg protein(-1)) and the presence of 50 microM CaCl(2) (154 +/- 3 vs. 197 +/- 7 pmol.min(-1).mg protein(-1)). Rotenone, which blocks electron flow from succinate to complex 1, reduced H(2)O(2) production and eliminated differences between ET and Sed. Mitochondrial superoxide dismutase and glutathione peroxidase were not affected by exercise. Catalase activity was extremely low but increased 49% in ET (P < 0.05). In conclusion, exercise reduces ROS production in myocardial mitochondria through adaptations specific to complex 1 but does not improve mitochondrial tolerance to calcium overload.

Reduced susceptibility to ventricular tachyarrhythmias in rats selectively bred for high aerobic capacity

Reperfusion after a brief period of cardiac ischemia can lead to potentially lethal arrhythmias. Human epidemiological studies and experimental work with animals indicate that regular physical activity is associated with reductions in cardiovascular disease (CVD) risk factors and sudden cardiac death. Similarly, artificial selection of rats for high aerobic treadmill-running capacity (high-capacity runners; HCR) has been shown to reduce CVD risk factors relative to rats selected as low-capacity runners (LCR). Therefore, we tested the hypothesis that HCR, relative to LCR rats, would be less susceptible to ischemia-reperfusion-mediated ventricular tachyarrhythmias. To test this hypothesis, we measured the susceptibility to ventricular tachyarrhythmias produced by 3 min of occlusion and reperfusion of the left main coronary artery in conscious LCR and HCR rats. Results document a significantly lower incidence of ventricular tachyarrhythmias in HCR (3 of 11, 27.3%) relative to LCR (6 of 7, 85.6%) rats. The decreased susceptibility to tachyarrhythmias in HCR rats was associated with a reduced cardiac metabolic demand during ischemia (lower rate-pressure product and ST segment elevation) as well as a wider range for the autonomic control of heart rate. The HCR and LCR represent a unique substrate for evaluation of the mechanisms underlying ischemia-mediated cardiac arrhythmogenesis.

Myocardial hypoperfusion/reperfusion tolerance with exercise training in hypertension

The purpose of this study was to examine whether exercise training, superimposed on compensated-concentric hypertrophy, could increase myocardial hypoperfusion-reperfusion (H/R) tolerance. Female Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) (age: 4 mo; N = 40) were placed into a sedentary (SED) or exercise training (TRD) group (treadmill running; 25 m/min, 1 h/day, 5 days/wk for 16 wk). Four groups were studied: WKY-SED ( n = 10), WKY-TRD ( n = 10), SHR-SED ( n = 10), and SHR-TRD ( n = 10). Blood pressure and heart rate were determined, and in vitro isolated heart performance was measured with a retrogradely perfused, Langendorff isovolumic preparation. The H/R protocol consisted of a 75% reduction in coronary flow for 17 min followed by 30 min of reperfusion. Although the rate-pressure product was significantly elevated in SHR relative to WKY, training-induced bradycardia reduced the rate-pressure product in SHR-TRD ( P < 0.05) without an attenuation in systolic blood pressure. Heart-to-body weight ratio was greater in both groups of SHR vs. WKY-SED ( P < 0.001). Absolute and relative myocardial tolerance to H/R was greater in WKY-TRD and both groups of SHR relative to WKY-SED ( P < 0.05). Endurance training superimposed on hypertension-induced compensated hypertrophy conferred no further cardioprotection to H/R. Postreperfusion 72-kDa heat shock protein abundance was enhanced in WKY-TRD and both groups of SHR relative to WKY-SED ( P < 0.05) and was highly correlated with absolute left ventricular functional recovery during reperfusion ( R2= 0.86, P < 0.0001). These data suggest that both compensated hypertrophy associated with short-term hypertension and endurance training individually improved H/R and that increased postreperfusion 72-kDa heat shock protein abundance was, in part, associated with the cardioprotective phenotype observed in this study.

Sprint training improves postischemic, left ventricular diastolic performance

We examined the effects of sprint training on left ventricular diastolic stiffness during normoxia and after ischemia-reperfusion (I/R). Thirty-seven, male Sprague-Dawley rats, weighing 150-175 g at the initiation of the experiment, were randomly assigned to a sedentary, control group (n = 20) or to a high-intensity, sprint-trained group (n = 17). Animals were trained 5 days/wk on a motor-driven treadmill for 6 wk. High-intensity sprint training consisted of running five 1-min sprints at 75 m/min, 15% grade, interspersed with 1-min active recovery runs at a speed of 20 m/min, 15% grade. Langendorff-derived isolated heart performance was measured before and after 20 min of no-flow ischemia followed by 30 min of reperfusion. Isolated myocytes were harvested from a subset of postischemic hearts. Sprint training reduced Langendorff-derived LV chamber stiffness (P < 0.05) and induced a rightward shift in the LV pressure-volume relationship during both normoxic perfusion and after I/R. LV developed pressure after I/R was also better preserved in hearts obtained from sprint-trained animals (P < 0.05), a result that is in part related to a lower postischemic LV chamber stiffness in sprint-trained hearts. The putative impact of sprint training on postischemic LV chamber stiffness was masked by glycolytic inhibition with iodoacetate, suggesting that glycolysis was involved in the better postischemic recovery observed in sprint-trained hearts. There was a tendency for enhanced postischemic cardiomyocyte shortening in sprint-trained cardiomyocytes compared with control. The rate of myocyte relaxation, i.e., time for 50% relaxation of the Ca(2+) transient amplitude, was similar between groups. These data suggest that additional mechanisms unrelated to Ca(2+) were involved in sprint-induced protection from ischemia-reperfusion-induced LV diastolic dysfunction.

Myocardial Heat Shock Protein 70 Expression in Young and Old Rats After Identical Exercise Programs

Synthesis of inducible heat shock protein 70 (HSP70) is impaired in aged animals following acute stresses including exercise. In this study we determined whether aging affects expression of this cytoprotective protein following chronic exercise participation. Male Fischer 344 rats, final ages 6 and 24 months, exercised identically for 10 weeks on a treadmill (15 degrees incline, 15 m/min for up to 60 minutes, 5 days/week). In 6-month-old animals, exercise increased HSP70 in heart (44%), liver (216%), and skeletal muscle (126%) (p <.05 vs sedentary). In 24-month-old animals, exercise increased HSP70 in muscle (69%), but not in heart or liver. In heart, antioxidant enzyme activities and HSP70 messenger RNA were measured and found to be unaffected by exercise at both ages. Our results indicate an age-related decrease in HSP70 production in heart and liver following chronic exercise. Furthermore, the aged heart does not increase its antioxidant enzyme defenses to compensate for the HSP70 deficit.

Effects of exercise training on contractile function in myocardial trabeculae after ischemia-reperfusion

Potential protective effects of aerobic exercise training on the myocardium, before an ischemic event, are not completely understood. The purpose of the study was to investigate the effects of exercise training on contractile function after ischemia-reperfusion (Langendorff preparation with 15-min global ischemia/30-min reperfusion). Trabeculae were isolated from the left ventricles of both sedentary control and 10- to 12-wk treadmill exercise-trained rats. The maximal normalized isometric force (force/cross-sectional area; Po/CSA) and shortening velocity ( Vo) in isolated, skinned ventricular trabeculae were measured using the slack test. Ischemia-reperfusion induced significant contractile dysfunction in hearts from both sedentary and trained animals; left ventricular developed pressure (LVDP) and maximal rates of pressure development and relaxation (±dP/d tmax) decreased, whereas end-diastolic pressure (EDP) increased. However, this dysfunction (as expressed as percent change from the last 5 min before ischemia) was attenuated in trained myocardium [LVDP: sedentary −60.8 ± 6.4% (32.0 ± 5.5 mmHg) vs. trained −15.6 ± 8.6% (64.9 ± 6.6 mmHg); +dP/d tmax: sedentary −54.1 ± 4.7% (1,058.7 ± 124.2 mmHg/s) vs. trained −16.7 ± 8.4% (1,931.9 ± 188.3 mmHg/s); −dP/d tmax: sedentary −44.4 ± 2.5% (−829.3 ± 52.0 mmHg/s) vs. trained −17.9 ± 7.2% (−1,341.3 ± 142.8 mmHg/s); EDP: sedentary 539.5 ± 147.6%; (41.3 ± 6.0 mmHg) vs. trained 71.6 ± 30.6%; 11.4 ± 1.2 mmHg]. There was an average 26% increase in Po/CSA in trained trabeculae compared with sedentary controls, and this increase was not affected by ischemia-reperfusion. Ischemia-reperfusion reduced V0 by 39% in both control and trained trabeculae. The relative amount of the β-isoform of myosin heavy chain (MHC-β) was twofold greater in trained trabeculae as well as in the ventricular free walls. Despite a possible increase in the economy in the trained heart, presumed from a greater amount of MHC-β, ischemia-reperfusion reduced Vo, to a similar extent in both control and trained animals. Nevertheless, the trained myocardium appears to have a greater maximum force-generating ability that may, at least partially, compensate for reduced contractile function induced by a brief period of ischemia.

Improved myocardial beta-adrenergic responsiveness and signaling with exercise training in hypertension

BACKGROUND

Cardiac responses to beta-adrenergic receptor stimulation are depressed with pressure overload-induced cardiac hypertrophy. We investigated whether exercise training could modify beta-adrenergic receptor responsiveness in a model of spontaneous hypertension by modifying the beta-adrenergic receptor desensitizing kinase GRK2 and the abundance and phosphorylation of some key Ca2+ cycling proteins.

METHODS AND RESULTS

Female spontaneously hypertensive rats (SHR; age, 4 months) were placed into a treadmill running (SHR-TRD; 20 m/min, 1 h/d, 5 d/wk, 12 weeks) or sedentary group (SHR-SED). Age-matched Wistar Kyoto (WKY) rats were controls. Mean blood pressure was higher in SHR versus WKY (P<0.01) and unaltered with exercise. Left ventricular (LV) diastolic anterior and posterior wall thicknesses were greater in SHR than WKY (P<0.001) and augmented with training (P<0.01). Langendorff LV performance was examined during isoproterenol (ISO) infusions (1x10(-10) to 1x10(-7) mol/L) and pacing stress (8.5 Hz). The peak LV developed pressure/ISO dose response was shifted rightward 100-fold in SHR relative to WKY. The peak ISO LV developed pressure response was similar between WKY and SHR-SED and increased in SHR-TRD (P<0.05). SHR-TRD showed the greatest lusitropic response to ISO (P<0.05) and offset the pacing-induced increase in LV end-diastolic pressure and the time constant of isovolumic relaxation (tau) observed in WKY and SHR-SED. Improved cardiac responses to ISO in SHR-TRD were associated with normalized myocardial levels of GRK2 (P<0.05). SHR displayed increased L-type Ca2+ channel and sodium calcium exchanger abundance compared with WKY (P<0.001). Training increased ryanodine receptor phosphorylation and phospholamban phosphorylation at both the Ser16 and Thr17 residues (P<0.05).

CONCLUSIONS

Exercise training in hypertension improves the inotropic and lusitropic responsiveness to beta-adrenergic receptor stimulation despite augmenting LV wall thickness. A lower GRK2 abundance and an increased phosphorylation of key Ca2+ cycling proteins may be responsible for the above putative effects.

Antioxidants and ecto-5'-nucleotidase are not involved in the training-induced cardioprotection against ischaemia-reperfusion injury

Isolated Langendorff-perfused hearts from sedentary and prolonged (24 weeks) treadmill-trained rats were subjected to 30 min of normoxic perfusion either alone or followed by 20 min of global ischaemia, or by 20 min of global ischaemia and 15 min of normoxic reperfusion. Pre-ischaemic values of antioxidant enzyme activities and ecto-5'-nucleotidase activity were not different in sedentary and trained hearts but a 5-fold increase of 72-kDa heat shock protein (HSP72) levels was detected in trained myocardium. After ischaemia and reperfusion (I/R), metabolic recovery was better in trained than in sedentary hearts as indicated by higher ATP and creatine phosphate levels. However, antioxidant enzymatic activities, glutathione reductase, and total and mitochondrial superoxide dismutase decreased in trained rats after I/R, whereas they remained unchanged in the sedentary ones. Ecto-5'-nucleotidase activity was modified by I/R in sedentary as well as in trained hearts while HSP72 content did not change. Ecto-5'-nucleotidase activity and HSP72 content increased in parallel by the 30-min perfusion period. In conclusion, the cardioprotection induced by long-term training could be mediated by the exercise-induced increase in HSP72 levels and is not related to enhanced antioxidant systems or ecto-5'-NT activity.

MnSOD antisense treatment and exercise-induced protection against arrhythmias

Exercise provides protection against ischemia-reperfusion (I-R)-induced arrhythmias, myocardial stunning, and infarction. An exercise-induced increase in myocardial manganese superoxide dismutase (MnSOD) activity has been reported to be vital for protection against infarction. However, whether MnSOD is essential for exercise-induced protection against ventricular arrhythmias is unknown. We determined the effects of preventing the exercise-induced increase in MnSOD activity on arrhythmias during I-R resulting in myocardial stunning. Male rats remained sedentary or were subjected to successive bouts of endurance exercise. During in vivo myocardial I-R, the incidence of arrhythmias was significantly lower in the exercise-trained rats than in the sedentary rats as evidenced by the arrhythmia. When exercised rats were pretreated with antisense oligonucleotides directed against MnSOD, protection from arrhythmias was attenuated. Moreover, I-R resulted in significant increases in nitro-tyrosine (NT) in the sedentary group. Exercise abolished this I-R-induced NT formation but this protection was unchanged by antisense treatment. Protein carbonyls were increased by I-R, but neither exercise nor antisense treatment impacted carbonyl formation. These data demonstrate that an exercise-induced increase in MnSOD activity is important for protection against arrhythmias. The mechanism by which MnSOD provides protection does not appear to be linked to protein nitrosylation or oxidation.

Exercise and myocardial tolerance to ischaemia-reperfusion

It is well established that both short-term (1-5 days) and long-term (weeks to months) high intensity exercise (i.e. 70-75%VO2max) provides cardioprotection against ischaemia-reperfusion injury. However, it is unclear if moderate intensity exercise will also provide cardioprotection.

AIM

Therefore, these experiments compared the protective effects of moderate vs. high intensity exercise in providing defense against ischaemia-reperfusion injury.

METHODS

Male Sprague-Dawley rats were randomly assigned to one of three-experimental groups: (1) sedentary (control); (2) moderate intensity treadmill exercise (60 min day(-1) at approximately 55%VO2max); or (3) high intensity treadmill exercise (60 min day(-1) at approximately 75%VO2max). Hearts were exposed to 20 min of global ischaemia followed by 30 min reperfusion in an isolated working heart preparation.

RESULTS

Compared with sedentary rats, both moderate and high intensity exercised rats maintained a higher (P < 0.05) percentage of pre-ischaemia cardiac output and cardiac work (cardiac output x systolic blood pressure) during reperfusion. No differences in the percent recovery of cardiac output and heart work existed (P > 0.05) between the two exercise groups.

CONCLUSIONS

These data reveal that both moderate and high intensity exercise training provide equivalent protection against ischaemia-reperfusion injury.

Elevated MnSOD is not required for exercise-induced cardioprotection against myocardial stunning

Endurance exercise provides cardioprotection against ischemia-reperfusion-induced myocardial stunning and infarction. A recent study demonstrates that an exercise-induced increase in myocardial manganese superoxide dismutase (MnSOD) activity is essential to protect the heart against infarction. It is unknown if an elevation in cardiac MnSOD is also a prerequisite to achieve exercise-induced protection against myocardial stunning. Therefore, this study determined if an exercise-induced increase in myocardial MnSOD activity is a requirement to achieve protection against myocardial stunning. Adult male rats remained sedentary or performed successive bouts of endurance exercise. Hearts were exposed to 25 min of global ischemia followed by reperfusion in an isolated working heart preparation. Postischemic recovery of cardiac external work during reperfusion was significantly higher (84 +/- 3 vs. 67 +/- 4%) in exercised animals compared with sedentary controls. Furthermore, prevention of exercise-induced expression of myocardial MnSOD via antisense oligonucleotides did not retard this exercise-induced protection against myocardial stunning. These data demonstrate that exercise-induced increases in cardiac MnSOD activity are not essential to achieve exercise-mediated protection against myocardial stunning. Therefore, we conclude that different mediators are responsible for exercise-induced cardioprotection against myocardial stunning and infarction.

Improved coronary vascular function evoked by high-intensity treadmill training is maintained in arteries exposed to ischemia and reperfusion

We hypothesized that myocardial contractile function and coronary arterial function are greater after ischemia and reperfusion in high-intensity treadmill-trained vs. sedentary rats. Rats performed 10 x 4-min bouts of treadmill running consisting of 2 min at 13 m/min + 2 min at 45-60 m/min (Etr) or were sedentary (Sed) for 12 wk. Animals then were instrumented to measure left ventricular (LV) contractility in response to three 15-min coronary occlusion (O) and 5-min reperfusion (R) cycles (Isc) or a sham operation (Sham). After the Isc and Sham protocols, hearts were excised and coronary arterial ( approximately 105 microm ID) function was evaluated by using isometric techniques. LV developed pressure, the first derivative of LV pressure at a developed pressure of 40 mmHg, and systolic blood pressure were not different between Etr (n = 14) and Sed (n = 7) rats before or after the Sham protocol. Furthermore, hemodynamic variables were similar in Etr (n = 14) and Sed (n = 13) animals before the Isc protocol and were depressed to the same degree by the three O-R cycles. Therefore, Etr did not alter myocardial contractile function in rats that were (i.e., Isc) or were not (i.e., Sham) exposed to ischemia and reperfusion. Acetylcholine-evoked relaxation (10-8 to 3 x 10-5 M) was greater (P < 0.05) in coronary arteries from Sham-Etr vs. Sham-Sed animals (5 of 8 doses tested) and Isc-Etr vs. Isc-Sed rats (3 of 8 doses tested). Maximal relaxation produced by sodium nitroprusside (10-4 M) was similar among groups. Vasocontractile responses produced by KCl (10-100 mM) and endothelin-1 (10-11-10-4 M) were greater (P < 0.05) in the presence vs. the absence of nitric oxide synthase inhibition (10-6 M NG-monomethyl-l-arginine) in vessels from Sham-Etr but not Sham-Sed rats and from Isc-Etr but not Isc-Sed rats. These findings suggest that Etr-evoked improvements in coronary function are maintained in small arteries even when exposed to ischemia and reperfusion.

Differential effects of exercise training on skeletal muscle SERCA gene expression

INTRODUCTION

Exercise training induces significant changes in the performance of skeletal muscle.

PURPOSE

To determine whether changes in the gene expression of rat hind-limb muscle sarcoplasmic reticulum Ca2+ -ATPase isoforms (SERCA1a and SERCA2a) in response to either moderate- or high-intensity exercise training underlie the functional remodeling.

METHODS

SERCA1a and SERCA2a isoform mRNA expression was determined in predominantly fast-twitch, gastrocnemius muscle and predominantly slow-twitch, soleus muscle with northern analysis. SERCA mRNA was normalized by the 18S rRNA measured in the same sample.

RESULTS

Significant increases in the gastrocnemius SERCA2a mRNA expression were observed after both moderate- and high-intensity training. No significant change in SERCA1a expression was found under any conditions.

CONCLUSION

These results indicate that both moderate and high intensity exercise increase the relative SERCA2a expression in the gastrocnemius.

Exercise training alters an anoxia-induced, glibenclamide-sensitive current in rat ventricular cardiocytes

The effect of training on properties of a sarcolemmal ATP-sensitive K+ current (I(K(ATP))) was examined in left ventricular cardiocytes isolated from sedentary (Sed) and trained (Tr) female Sprague-Dawley rats. Whole cell patch-clamp techniques were used to characterize I(K(ATP)), an anoxia-inducible, glibencamide-sensitive current. An anoxic condition was induced by superfusing cells with a buffer that was equilibrated with 100% N(2), maintained under a layer of argon, and that contained 2-deoxy-D-glucose. Over a 1-h period of anoxia, 59% of Tr cells and 85% Sed cells expressed I(K(ATP)). In those cells that did express I(K(ATP)), the time to expression of the current during the anoxic period occurred significantly later in cells from the Tr group compared with the Sed. Peak I(K(ATP)) density was significantly lower in the Tr cells compared with the Sed cells. These results indicate that the onset and magnitude of I(K(ATP)) were altered by training. These alterations in I(K(ATP)) may be reflective of processes that contribute to training-induced cardioprotection against ischemia-reperfusion damage.

Short-term exercise improves myocardial tolerance to in vivo ischemia-reperfusion in the rat

These experiments examined the independent effects of short-term exercise and heat stress on myocardial responses during in vivo ischemia-reperfusion (I/R). Female Sprague-Dawley rats (4 mo old) were randomly assigned to one of four experimental groups: 1) control, 2) 3 consecutive days of treadmill exercise [60 min/day at 60-70% maximal O2 uptake (VO2 max)], 3) 5 consecutive days of treadmill exercise (60 min/day at 60-70% VO2 max), and 4) whole body heat stress (15 min at 42 degrees C). Twenty-four hours after heat stress or exercise, animals were anesthetized and mechanically ventilated, and the chest was opened by thoracotomy. Coronary occlusion was maintained for 30-min followed by a 30-min period of reperfusion. Compared with control, both heat-stressed animals and exercised animals (3 and 5 days) maintained higher (P < 0.05) left ventricular developed pressure (LVDP), maximum rate of left ventricular pressure development (+dP/dt), and maximum rate of left ventricular pressure decline (-dP/dt) at all measurement periods during both ischemia and reperfusion. No differences existed between heat-stressed and exercise groups in LVDP, +dP/dt, and -dP/dt at any time during ischemia or reperfusion. Both heat stress and exercise resulted in an increase (P < 0.05) in the relative levels of left ventricular heat shock protein 72 (HSP72). Furthermore, exercise (3 and 5 days) increased (P < 0.05) myocardial glutathione levels and manganese superoxide dismutase activity. These data indicate that 3-5 consecutive days of exercise improves myocardial contractile performance during in vivo I/R and that this exercise-induced myocardial protection is associated with an increase in both myocardial HSP72 and cardiac antioxidant defenses.

Glibenclamide improves postischemic recovery of myocardial contractile function in trained and sedentary rats

In this study, we sought to determine whether there was any evidence for the idea that cardiac ATP-sensitive K+ (K(ATP)) channels play a role in the training-induced increase in the resistance of the heart to ischemia-reperfusion (I/R) injury. To do so, the effects of training and an K(ATP) channel blocker, glibenclamide (Glib), on the recovery of left ventricular (LV) contractile function after 45 min of ischemia and 45 min of reperfusion were examined. Female Sprague-Dawley rats were sedentary (Sed; n = 18) or were trained (Tr; n = 17) for >20 wk by treadmill running, and the hearts from these animals used in a Langendorff-perfused isovolumic LV preparation to assess contractile function. A significant increase in the amount of 72-kDa class of heat shock protein was observed in hearts isolated from Tr rats. The I/R protocol elicited significant and substantial decrements in LV developed pressure (LVDP), minimum pressure (MP), rate of pressure development, and rate of pressure decline and elevations in myocardial Ca(2+) content in both Sed and Tr hearts. In addition, I/R elicited a significant increase in LV diastolic stiffness in Sed, but not Tr, hearts. When administered in the perfusate, Glib (1 microM) elicited a normalization of all indexes of LV contractile function and reductions in myocardial Ca(2+) content in both Sed and Tr hearts. Training increased the functional sensitivity of the heart to Glib because LVDP and MP values normalized more quickly with Glib treatment in the Tr than the Sed group. The increased sensitivity of Tr hearts to Glib is a novel finding that may implicate a role for cardiac K(ATP) channels in the training-induced protection of the heart from I/R injury.

Short-term exercise training can improve myocardial tolerance to I/R without elevation in heat shock proteins

We examined the effects of 3 days of exercise in a cold environment on the expression of left ventricular (LV) heat shock proteins (HSPs) and contractile performance during in vivo ischemia-reperfusion (I/R). Sprague-Dawley rats were divided into the following three groups (n = 12/group): 1) control, 2) exercise (60 min/day) at 4 degrees C (E-Cold), and 3) exercise (60 min/day) at 25 degrees C (E-Warm). Left anterior descending coronary occlusion was maintained for 20 min, followed by 30 min of reperfusion. Compared with the control group, both the E-Cold and E-Warm groups maintained higher (P < 0.05) LV developed pressure, first derivative of pressure development over time (+dP/dt), and pressure relaxation over time (-dP/dt) throughout I/R. Relative levels of HSP90, HSP72, and HSP40 were higher (P < 0.05) in E-Warm animals compared with both control and E-Cold. HSP10, HSP60, and HSP73 did not differ between groups. Exercise increased manganese superoxide dismutase (MnSOD) activity in both E-Warm and E-Cold hearts (P < 0.05). Protection against I/R-induced lipid peroxidation in the LV paralleled the increase in MnSOD activity whereas lower levels of lipid peroxidation were observed in both E-Warm and E-Cold groups compared with control. We conclude that exercise-induced myocardial protection against a moderate duration I/R insult is not dependent on increases in myocardial HSPs. We postulate that exercise-associated cardioprotection may depend, in part, on increases in myocardial antioxidant defenses.

Glutathione supplementation and training increases myocardial resistance to ischemia-reperfusion in vivo

The present study examined the effects of oral reduced glutathione (GSH) supplementation in conjunction with endurance training on contractile function, antioxidant defense, and oxidative damage in response to ischemia-reperfusion (I/R) in rat hearts. Female Sprague-Dawley rats (age 4 mo, n = 72) were randomly assigned to a treadmill-trained (T; 25 m/min, 15% grade, for 75 min/day, 5 days/wk, for 10 wk) or untrained (U) group. Each group was further divided into rats receiving 5 g GSH/kg diet during the final 17 days of training (GSH-S) and control (C) groups. One-half of each group of rats was subjected to I/R by surgical occlusion of the main coronary artery for 45 min, followed by 30-min reperfusion or sham operation. Left ventriclar (LV) peak systolic pressure (LVSP) and contractility (+dP/dt), measured with a catheter inserted into the LV via the carotid artery, decreased with I/R in all groups (P < 0.05). However, LVSP with I/R in the T/GSH-S group was 9.5%, 17%, and 18% higher (P < 0.05) than that in the U/GSH-S, T/C, and U/C groups, respectively. +dP/dt with I/R was 19%, 27%, and 29% (P < 0.05) greater in the T/GSH-S group versus the T/C, U/GSH-S, and U/C groups, respectively. I/R decreased heart GSH content by 12-17% (P < 0.05) and increased oxidized glutathione (GSSG) by 20-27% (P < 0.05). T/GSH-S hearts showed 15% higher GSH (P < 0.05) and a 32% higher GSH-to-GSSG ratio (P < 0.05) than the U/C group at the end of I/R. Myocardial superoxide dismutase, GSH peroxidase, glutathione reductase, and gamma-glutamyl transpeptidase activities were increased with treadmill training in both GSH-S and C rats. I/R induced myocardial lipid peroxidation and lactate dehydrogenase release were attenuated with T/GSH-S treatment. The present data indicate that training in conjunction with dietary GSH supplementation can increase myocardial GSH content and antioxidant defense capacity, thereby protecting the intact heart against oxidative damage and functional retardation caused by I/R.

Exercise, heat shock proteins, and myocardial protection from I-R injury

Heat shock proteins (HSPs) play a critical role in maintaining cellular homeostasis and protecting cells during episodes of acute stress. Specifically, HSPs of the 70 kDa family (i.e., HSP72) are important in preventing ischemia-reperfusion induced apoptosis, necrosis, and oxidative injury in a variety of cell types including the cardiac myocyte. Evidence indicates that HSP72 may contribute to cellular protection against a variety of stresses by preventing protein aggregation, assisting in the refolding of damaged proteins, and chaperoning nascent polypeptides along ribosomes. Endurance exercise is a physiological stress that can be used to elevate myocardial levels of HSP72. It is now clear that endurance exercise training can elevate myocardial HSP72 by 400-500% in young adult animals. Importantly, an exercise-induced elevation in myocardial HSPs is associated with a reduction in ischemia-reperfusion (I-R) injury in the heart. Although it seems likely that exercise-induced elevations in myocardial levels of HSPs play an important role in this protection against an I-R insult, new evidence suggests that other factors may also be involved. This is an important area for future research.

Epinephrine upregulates superoxide dismutase in human coronary artery endothelial cells

Regular exercise resulting in release of catecholamines is an oxidant stress, and yet it protects humans from acute cardiac events. We designed this study to examine the effect of epinephrine on free radical release and endogenous superoxide dismutase (SOD) gene and protein expression in human coronary artery endothelial cells (HCAECs). HCAECs were incubated with epinephrine (10(-9) to 10(-5) M) alone or with the water-soluble analog of vitamin E (trolox) (10(-5) M), the lipid-soluble vitamin E (5 x 10(-5) M), or the beta(1)-adrenergic blocker atenolol (10(-5) M). At 1 and 24 h of incubation with epinephrine, superoxide anion generation increased by 102 and 81% in the HCAECs. There was a marked increase in both MnSOD and Cu/ZnSOD mRNA and protein, as determined by RT-PCR and Western Analysis, respectively. Both MnSOD and Cu/ZnSOD activities were also increased. Pretreatment of HCAECs with trolox and vitamin E decreased superoxide anion generation (p <.05 vs. epinephrine alone) and blocked the subsequent upregulation of SOD mRNA and protein. Treatment of cells with the beta-blocker atenolol also blocked the upregulation of SOD (p <.05 vs. epinephrine alone). These observations suggest that epinephrine via beta(1)-adrenoceptor activation causes superoxide anion generation, and the superoxide subsequently upregulates the endogenous antioxidant species SOD. These observations may be the basis of long-term benefits of exercise.

Exercise training improves left ventricular isovolumic relaxation

PURPOSE

Left ventricular (LV) diastolic function is an important determinant of aerobic fitness. The purpose of this paper was to investigate the relationship between aerobic fitness and the rate and extent of isovolumic LV relaxation.

METHODS

Two series of experiments were performed utilizing both human and animal models. In the first series of experiments, the relationship between LV diastolic time intervals and exercise capacity was assessed in two groups of collegiate men (N = 18) with variable peak run times (Bruce protocol). In the second series of experiments, the extent of LV relaxation was examined in sedentary and exercise-trained rats (treadmill running), using an isolated, isovolumic heart preparation. Subsequent morphological assessment was also performed in rats.

RESULTS

At rest, men with greater peak treadmill time had a shorter resting LV isovolumic relaxation time (R-R interval adjusted 1000 ms) (long duration runners, 84+/-5 ms vs short duration runners, 105+/-7 ms, P < 0.05) despite a similar LV diastolic interval. Peak treadmill time was inversely correlated to LV isovolumic relaxation time (R-R interval adjusted 1000 ms) (r = -0.55; P < 0.02). In animal studies (N = 26), the LV pressure-volume relationship was shifted rightward in exercise-trained rats (P = 0.003). Exercise-trained rats had an increased LV inner diameter (sedentary, 5.1+/-0.35 mm vs exercise-trained, 6.1+/-0.28 mm, P < 0.05) and a thicker interventricular septum (sedentary, 1.52+/-0.06 mm vs exercise-trained, 1.72+/-0.09 mm, P < 0.05).

CONCLUSION

This study suggests that both the rate and extent of LV isovolumic relaxation is enhanced with exercise training. Further study is required to understand the interrelationship between exercise and diastolic function.