Exercise training attenuates age-associated diastolic dysfunction in rats

Rejuvenation of the Aging Heart: Molecular Determinants and Applications

In Canada and worldwide, the elderly population (ie, individuals > 65 years of age) is increasing disproportionately relative to the total population. This is expected to have a substantial impact on the health care system, as increased aged is associated with a greater incidence of chronic noncommunicable diseases. Within the elderly population, cardiovascular disease is a leading cause of death, therefore developing therapies that can prevent or slow disease progression in this group is highly desirable. Historically, aging research has focused on the development of anti-aging therapies that are implemented early in life and slow the age-dependent decline in cell and organ function. However, accumulating evidence supports that late-in-life therapies can also benefit the aged cardiovascular system by limiting age-dependent functional decline. Moreover, recent studies have demonstrated that rejuvenation (ie, reverting cellular function to that of a younger phenotype) of the already aged cardiovascular system is possible, opening new avenues to develop therapies for older individuals. In this review, we first provide an overview of the functional changes that occur in the cardiomyocyte with aging and how this contributes to the age-dependent decline in heart function. We then discuss the various anti-aging and rejuvenation strategies that have been pursued to improve the function of the aged cardiomyocyte, with a focus on therapies implemented late in life. These strategies include 1) established systemic approaches (caloric restriction, exercise), 2) pharmacologic approaches (mTOR, AMPK, SIRT1, and autophagy-targeting molecules), and 3) emerging rejuvenation approaches (partial reprogramming, parabiosis/modulation of circulating factors, targeting endogenous stem cell populations, and senotherapeutics). Collectively, these studies demonstrate the exciting potential and limitations of current rejuvenation strategies and highlight future areas of investigation that will contribute to the development of rejuvenation therapies for the aged heart.

Mechanisms of Exercise-Induced Cardiac Remodeling Differ Between Young and Aged Hearts

Aging induces physiological and molecular changes in the heart that increase the risk for heart disease. Several of these changes are targetable by exercise. We hypothesize that the mechanisms by which exercise improves cardiac function in the aged heart differ from those in the young exercised heart.

Heart Failure With Preserved Ejection Fraction: Heterogeneous Syndrome, Diverse Preclinical Models

Heart failure with preserved ejection fraction (HFpEF) represents one of the greatest challenges facing cardiovascular medicine today. Despite being the most common form of heart failure worldwide, there has been limited success in developing therapeutics for this syndrome. This is largely due to our incomplete understanding of the biology driving its systemic pathophysiology and the heterogeneity of clinical phenotypes, which are increasingly being recognized as distinct HFpEF phenogroups. Development of efficacious therapeutics fundamentally relies on robust preclinical models that not only faithfully recapitulate key features of the clinical syndrome but also enable rigorous investigation of putative mechanisms of disease in the context of clinically relevant phenotypes. In this review, we propose a preclinical research strategy that is conceptually grounded in model diversification and aims to better align with our evolving understanding of the heterogeneity of clinical HFpEF. Although heterogeneity is often viewed as a major obstacle in preclinical HFpEF research, we challenge this notion and argue that embracing it may be the key to demystifying its pathobiology. Here, we first provide an overarching guideline for developing HFpEF models through a stepwise approach of comprehensive cardiac and extra-cardiac phenotyping. We then present an overview of currently available models, focused on the 3 leading phenogroups, which are primarily based on aging, cardiometabolic stress, and chronic hypertension. We discuss how well these models reflect their clinically relevant phenogroup and highlight some of the more recent mechanistic insights they are providing into the complex pathophysiology underlying HFpEF.

Heart failure with preserved ejection fraction in humans and mice: embracing clinical complexity in mouse models

Heart failure (HF) with preserved ejection fraction (HFpEF) is a multifactorial disease accounting for a large and increasing proportion of all clinical HF presentations. As a clinical syndrome, HFpEF is characterized by typical signs and symptoms of HF, a distinct cardiac phenotype and raised natriuretic peptides. Non-cardiac comorbidities frequently co-exist and contribute to the pathophysiology of HFpEF. To date, no therapy has proven to improve outcomes in HFpEF, with drug development hampered, at least partly, by lack of consensus on appropriate standards for pre-clinical HFpEF models. Recently, two clinical algorithms (HFA-PEFF and H₂FPEF scores) have been developed to improve and standardize the diagnosis of HFpEF. In this review, we evaluate the translational utility of HFpEF mouse models in the context of these HFpEF scores. We systematically recorded evidence of symptoms and signs of HF or clinical HFpEF features and included several cardiac and extra-cardiac parameters as well as age and sex for each HFpEF mouse model. We found that most of the pre-clinical HFpEF models do not meet the HFpEF clinical criteria, although some multifactorial models resemble human HFpEF to a reasonable extent. We therefore conclude that to optimize the translational value of mouse models to human HFpEF, a novel approach for the development of pre-clinical HFpEF models is needed, taking into account the complex HFpEF pathophysiology in humans.

Effects of aging and exercise training on mitochondrial function and apoptosis in the rat heart

Aging is associated with vulnerability to cardiovascular diseases, and mitochondrial dysfunction plays a critical role in cardiovascular disease pathogenesis. Exercise training is associated with benefits against chronic cardiac diseases. The purpose of this study was to determine the effects of aging and treadmill exercise training on mitochondrial function and apoptosis in the rat heart. Fischer 344 rats were divided into young sedentary (YS; n = 10, 4 months), young exercise (YE; n = 10, 4 months), old sedentary (OS; n = 10, 20 months), and old exercise (OE; n = 10, 20 months) groups. Exercise training groups ran on a treadmill at 15 m/min (young) or 10 m/min (old), 45 min/day, 5 days/week for 8 weeks. Morphological parameters, mitochondrial function, mitochondrial dynamics, mitophagy, and mitochondria-mediated apoptosis were analyzed in cardiac muscle. Mitochondrial O₂ respiratory capacity and Ca²⁺ retention capacity gradually decreased, and mitochondrial H₂O₂ emitting potential significantly increased with aging. Exercise training attenuated aging-induced mitochondrial H₂O₂ emitting potential and mitochondrial O₂ respiratory capacity, while protecting Ca²⁺ retention in the old groups. Aging triggered imbalanced mitochondrial dynamics and excess mitophagy, while exercise training ameliorated the aging-induced imbalance in mitochondrial dynamics and excess mitophagy. Aging induced increase in Bax and cleaved caspase-3 protein levels, while decreasing Bcl-2 levels. Exercise training protected against the elevation of apoptotic signaling markers by decreasing Bax and cleaved caspase-3 and increasing Bcl-2 protein levels, while decreasing the Bax/Bcl-2 ratio and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive myonuclei. These data demonstrate that regular exercise training prevents aging-induced impairment of mitochondrial function and mitochondria-mediated apoptosis in cardiac muscles.

Murine Models of Heart Failure with Preserved Ejection Fraction: a "Fishing Expedition"

Heart failure with preserved ejection fraction (HFpEF) is characterized by signs and symptoms of HF in the presence of a normal left ventricular (LV) ejection fraction (EF). Despite accounting for up to 50% of all clinical presentations of HF, the mechanisms implicated in HFpEF are poorly understood, thus precluding effective therapy. The pathophysiological heterogeneity in the HFpEF phenotype also contributes to this disease and likely to the absence of evidence-based therapies. Limited access to human samples and imperfect animal models that completely recapitulate the human HFpEF phenotype have impeded our understanding of the mechanistic underpinnings that exist in this disease. Aging and comorbidities such as atrial fibrillation, hypertension, diabetes and obesity, pulmonary hypertension and renal dysfunction are highly associated with HFpEF. Yet, the relationship and contribution between them remains ill-defined. This review discusses some of the distinctive clinical features of HFpEF in association with these comorbidities and highlights the advantages and disadvantage of commonly used murine models, used to study the HFpEF phenotype.

Exercise training reverses age-induced diastolic dysfunction and restores coronary microvascular function

KEY POINTS

In a rat model of ageing that is free of atherosclerosis or hypertension, E/A, a diagnostic measure of diastolic filling, decreases, and isovolumic relaxation time increases, indicating that both active and passive ventricular relaxation are impaired with advancing age. Resting coronary blood flow and coronary functional hyperaemia are reduced with age, and endothelium-dependent vasodilatation declines with age in coronary resistance arterioles. Exercise training reverses age-induced declines in diastolic and coronary microvascular function. Thus, microvascular dysfunction and inadequate coronary perfusion are likely mechanisms of diastolic dysfunction in aged rats. Exercise training, initiated at an advanced age, reverses age-related diastolic and microvascular dysfunction; these data suggest that late-life exercise training can be implemented to improve coronary perfusion and diastolic function in the elderly.

ABSTRACT

The risk for diastolic dysfunction increases with advancing age. Regular exercise training ameliorates age-related diastolic dysfunction; however, the underlying mechanisms have not been identified. We investigated whether (1) microvascular dysfunction contributes to the development of age-related diastolic dysfunction, and (2) initiation of late-life exercise training reverses age-related diastolic and microvascular dysfunction. Young and old rats underwent 10 weeks of exercise training or remained as sedentary, cage-controls. Isovolumic relaxation time (IVRT), early diastolic filling (E/A), myocardial performance index (MPI) and aortic stiffness (pulse wave velocity; PWV) were evaluated before and after exercise training or cage confinement. Coronary blood flow and vasodilatory responses of coronary arterioles were evaluated in all groups at the end of training. In aged sedentary rats, compared to young sedentary rats, a 42% increase in IVRT, a 64% decrease in E/A, and increased aortic stiffness (PWV: 6.36 ± 0.47 vs.4.89 ± 0.41, OSED vs. YSED, P < 0.05) was accompanied by impaired coronary blood flow at rest and during exercise. Endothelium-dependent vasodilatation was impaired in coronary arterioles from aged rats (maximal relaxation to bradykinin: 56.4 ± 5.1% vs. 75.3 ± 5.2%, OSED vs. YSED, P < 0.05). After exercise training, IVRT, a measure of active ventricular relaxation, did not differ between old and young rats. In old rats, exercise training reversed the reduction in E/A, reduced aortic stiffness, and eliminated impairment of coronary blood flow responses and endothelium-dependent vasodilatation. Thus, age-related diastolic and microvascular dysfunction are reversed by late-life exercise training. The restorative effect of exercise training on coronary microvascular function may result from improved endothelial function.

The Role of Exercise in Cardiac Aging: From Physiology to Molecular Mechanisms

Aging induces structural and functional changes in the heart that are associated with increased risk of cardiovascular disease and impaired functional capacity in the elderly. Exercise is a diagnostic and therapeutic tool, with the potential to provide insights into clinical diagnosis and prognosis, as well as the molecular mechanisms by which aging influences cardiac physiology and function. In this review, we first provide an overview of how aging impacts the cardiac response to exercise, and the implications this has for functional capacity in older adults. We then review the underlying molecular mechanisms by which cardiac aging contributes to exercise intolerance, and conversely how exercise training can potentially modulate aging phenotypes in the heart. Finally, we highlight the potential use of these exercise models to complement models of disease in efforts to uncover new therapeutic targets to prevent or treat heart disease in the aging population.

Voluntary stand-up physical activity enhances endurance exercise capacity in rats

Involuntary physical activity induced by the avoidance of electrical shock leads to improved endurance exercise capacity in animals. However, it remains unknown whether voluntary stand-up physical activity (SPA) without forced simulating factors improves endurance exercise capacity in animals. We examined the eff ects of SPA on body weight, cardiac function, and endurance exercise capacity for 12 weeks. Twelve male Sprague-Dawley rats (aged 8 weeks, n=6 per group) were randomly assigned to a control group (CON) or a voluntary SPA group. The rats were induced to perform voluntary SPA (lifting a load equal to their body weight), while the food height (18.0 cm) in cages was increased progressively by 3.5 every 4 weeks until it reached 28.5 cm for 12 weeks. The SPA group showed a lower body weight compared to the CON group, but voluntary SPA did not affect the skeletal muscle and heart weights, food intake, and echocardiography results. Although the SPA group showed higher grip strength, running time, and distance compared to the CON group, the level of irisin, corticosterone, genetic expression of mitochondrial biogenesis, and nuclei numbers were not affected. These findings show that voluntary SPA without any forced stimuli in rats can eff ectively reduce body weight and enhance endurance exercise capacity, suggesting that it may be an important alternative strategy to enhance endurance exercise capacity.

Altered left ventricular performance in aging physically active mice with an ankle sprain injury

We assessed the impact of differing physical activity levels throughout the lifespan, using a musculoskeletal injury model, on the age-related changes in left ventricular (LV) parameters in active mice. Forty male mice (CBA/J) were randomly placed into one of three running wheel groups (transected CFL group, transected ATFL/CFL group, SHAM group) or a SHAM Sedentary group (SHAMSED). Before surgery and every 6 weeks after surgery, LV parameters were measured under 2.5 % isoflurane inhalation. Group effects for daily distance run was significantly greater for the SHAM and lesser for the ATLF/CFL mice (p = 0.013) with distance run decreasing with age for all mice (p < 0.0001). Beginning at 6 months of age, interaction (group × age) was noted with LV posterior wall thickness-to-radius ratios (h/r) where h/r increased with age in the ATFL/CFL and SHAMSED mice while the SHAM and CFL mice exhibited decreased h/r with age (p = 0.0002). Passive filling velocity (E wave) was significantly greater in the SHAM mice and lowest for the ATFL/CFL and SHAMSED mice (p < 0.0001) beginning at 9 months of age. Active filling velocity (A wave) was not different between groups (p = 0.10). Passive-to-active filling velocity ratio (E/A ratio) was different between groups (p < 0.0001), with higher ratios for the SHAM mice and lower ratios for the ATFL/CFL and SHAMSED mice in response to physical activity beginning at 9 months of age. Passive-to-active filling velocity ratio decreased with age (p < 0.0001). Regular physical activity throughout the lifespan improved LV structure, passive filling velocity, and E/A ratio by 6 to 9 months of age and attenuated any negative alterations throughout the second half of life. The diastolic filling differences were found to be significantly related to the amount of activity performed by 9 months and at the end of the lifespan.

Echinochrome A Improves Exercise Capacity during Short-Term Endurance Training in Rats

Echinochrome A (Echi A) improves mitochondrial function in the heart; however, its effects on skeletal muscle are still unclear. We hypothesized that Echi A administration during short-term exercise may improve exercise capacity. Twenty-four male Sprague-Dawley rats were randomly divided into the following groups: control group (CG), Echi A-treated group (EG), aerobic exercise group (AG), and aerobic exercise treated with Echi A group (AEG) (n = 6 per group). Echi A was administered intra-peritoneally (0.1 mg/kg of Echi A in 300 µL phosphate-buffered saline) daily 30 min before each exercise training. The AG and AEG groups performed treadmill running (20 m/min, 60 min/day) five days/week for two weeks. The exercise capacity was significantly higher in the AG and AEG groups compared to other groups. Interestingly, the exercise capacity increased more effectively in the AEG group. The body weight in the EG tended to be slightly lower than that in the other groups. There were no significant changes in the plasma lipids among the groups. However, the gastrocnemius muscle mitochondria content was greater in the EG and AEG groups. These findings show that Echi A administration after short-term endurance training enhances exercise capacity, which was associated with an increase in skeletal muscle mitochondrial content.

Acute exercise modifies titin phosphorylation and increases cardiac myofilament stiffness

Titin-based myofilament stiffness is largely modulated by phosphorylation of its elastic I-band regions N2-Bus (decreases passive stiffness, PT) and PEVK (increases PT). Here, we tested the hypothesis that acute exercise changes titin phosphorylation and modifies myofilament stiffness. Adult rats were exercised on a treadmill for 15 min, untrained animals served as controls. Titin phosphorylation was determined by Western blot analysis using phosphospecific antibodies to Ser4099 and Ser4010 in the N2-Bus region (PKG and PKA-dependent. respectively), and to Ser11878 and Ser 12022 in the PEVK region (PKCα and CaMKIIδ-dependent, respectively). Passive tension was determined by step-wise stretching of isolated skinned cardiomyocytes to sarcomere length (SL) ranging from 1.9 to 2.4 μm and showed a significantly increased PT from exercised samples, compared to controls. In cardiac samples titin N2-Bus phosphorylation was significantly decreased by 40% at Ser4099, however, no significant changes were observed at Ser4010. PEVK phosphorylation at Ser11878 was significantly increased, which is probably mediated by the observed exercise-induced increase in PKCα activity. Interestingly, relative phosphorylation of Ser12022 was substantially decreased in the exercised samples. Surprisingly, in skeletal samples from acutely exercised animals we detected a significant decrease in PEVK phosphorylation at Ser11878 and an increase in Ser12022 phosphorylation; however, PKCα activity remained unchanged. In summary, our data show that a single exercise bout of 15 min affects titin domain phosphorylation and titin-based myocyte stiffness with obviously divergent effects in cardiac and skeletal muscle tissues. The observed changes in titin stiffness could play an important role in adapting the passive and active properties of the myocardium and the skeletal muscle to increased physical activity.

Effect of exercise training on post-translational and post-transcriptional regulation of titin stiffness in striated muscle of wild type and IG KO mice

Exercise has beneficial effects on diastolic dysfunction but the underlying mechanisms are not well understood. Here we studied the effects of exercise on the elastic protein titin, an important determinant of diastolic stiffness, in both the left ventricle and the diaphragm. We used wild type mice and genetically engineered mice with HFpEF symptoms (IG KO mice), including diastolic dysfunction. In the diaphragm muscle, exercise increased the expression level of titin (increased titin:MHC ratio) which is expected to increase titin-based stiffness. This effect was absent in the LV. We also studied the constitutively expressed titin residues S11878 and S12022 that are known targets of CaMKIIδ and PKCα with increased phosphorylation resulting in an increase in titin-based passive stiffness. The phosphorylation level of S11878 was unchanged whereas S12022 responded to exercise with a reduction in the phosphorylation level in the LV and, interestingly, an increase in the diaphragm. These changes are expected to lower titin's stiffness in the LV and increase stiffness in the diaphragm. We propose that these disparate effects reflect the unique physiological needs of the two tissue types and that both effects are beneficial.

Pathophysiological defects and transcriptional profiling in the RBM20-/- rat model

Our recent study indicated that RNA binding motif 20 (Rbm20) alters splicing of titin and other genes. The current goals were to understand how the Rbm20(-/-) rat is related to physiological, structural, and molecular changes leading to heart failure. We quantitatively and qualitatively compared the expression of titin isoforms between Rbm20(-/-) and wild type rats by real time RT-PCR and SDS agarose electrophoresis. Isoform changes were linked to alterations in transcription as opposed to translation of titin messages. Reduced time to exhaustion with running in knockout rats also suggested a lower maximal cardiac output or decreased skeletal muscle performance. Electron microscopic observations of the left ventricle from knockout animals showed abnormal myofibril arrangement, Z line streaming, and lipofuscin deposits. Mutant skeletal muscle ultrastructure appeared normal. The results suggest that splicing alterations in Rbm20(-/-) rats resulted in pathogenic changes in physiology and cardiac ultrastructure. Secondary changes were observed in message levels for many genes whose splicing was not directly affected. Gene and protein expression data indicated the activation of pathophysiological and muscle stress-activated pathways. These data provide new insights on Rbm20 function and how its malfunction leads to cardiomyopathy.

Rodent models of heart failure: an updated review

Heart failure (HF) is one of the major health and economic burdens worldwide, and its prevalence is continuously increasing. The study of HF requires reliable animal models to study the chronic changes and pharmacologic interventions in myocardial structure and function and to follow its progression toward HF. Indeed, during the past 40 years, basic and translational scientists have used small animal models to understand the pathophysiology of HF and find more efficient ways of preventing and managing patients suffering from congestive HF (CHF). Each species and each animal model has advantages and disadvantages, and the choice of one model over another should take them into account for a good experimental design. The aim of this review is to describe and highlight the advantages and drawbacks of some commonly used HF rodents models, including both non-genetically and genetically engineered models, with a specific subchapter concerning diastolic HF models.

Update on diastolic heart failure or heart failure with preserved ejection fraction in the older adults

Nearly half of all heart failure (HF) patients have diastolic HF (DHF) or clinical HF with normal or near-normal left ventricular ejection fraction (LVEF). Although the terminology has not been clearly defined, it is increasingly being referred to as HF with preserved ejection fraction (HFPEF). The prevalence of HFPEF increases with age, especially among older women. Identifying HFPEF is important because the etiology, pathogenesis, prognosis, and optimal management may differ from that for systolic HF (SHF) or HF with reduced ejection fraction. The clinical presentation of HF is similar for both SHF and HFPEF. As in SHF, HFPEF is a clinical diagnosis. Once a clinical diagnosis of HF has been made, the presence of HFPEF can be established by confirming a normal or near-normal LVEF, often by an echocardiogram. HFPEF is often associated with a history of hypertension, concentric left ventricular hypertrophy, vascular stiffness, and left ventricular diastolic dysfunction. As in SHF, HFPEF is also associated with poor outcomes. While therapies with angiotensin-converting enzyme inhibitors and beta-blockers improve outcomes in SHF, there is currently no such evidence of their benefits in older HFPEF patients. In this review recent advances in the diagnosis and management of HFPEF in older adults are discussed.

Moderate intensity, but not high intensity, treadmill exercise training alters power output properties in myocardium from aged rats

Aging is characterized by a progressive decline in cardiac function, but endurance exercise training has been shown to retard a number of deleterious effects of aging. However, underlying mechanisms by which exercise training improves age-related decrements in myocardial contractile function are not well understood. The purpose of this study was to determine the effects of exercise training on power output properties in permeablized (skinned) myocytes of old rats. Thirty-month-old rats were divided into sedentary control (C) and groups undergoing 11 weeks of treadmill exercise training at moderate intensity (MI) and at high intensity (HI). Peak power output normalized to maximal force was significantly increased in MI but not in HI compared to C with significant increases in atrial myosin light chain 1 in ventricle. These results suggest that MI exercise training is beneficial as a significant increase was seen in the ability of the myocardium to do work, but this effect was not seen with HI training.

Combined exercise training in asymptomatic elderly with controlled hypertension: effects on functional capacity and cardiac diastolic function

Background

Aging is associated with changes in cardiac structure and function that are associated with left ventricular diastolic dysfunction. Whether diastolic functional alterations during senescence are manifestations of the intrinsic aging process or related to cardiac adaptations to a more sedentary lifestyle is still unsettled. This was a prospective study evaluating the effects of a 6-month combined exercise training period on functional capacity and diastolic function in sedentary elderly patients with controlled arterial hypertension.

Material/Methods

Functional capacity was assessed by exercise stress test and muscle strength was evaluated by the one-repetition maximum test. Cardiac structures and function were analyzed by transthoracic echocardiography.

Results

Fifteen patients, 68±8 years old, completed the training program. Exercise training significantly improved physical capacity (distance walked: 551±92 vs. 630±153 m, P<0.05; work load: 7.2±1.7 vs. 8.5±3.0 METs, P<0.05) and upper and lower extremity muscle strength (P<0.001). Arterial blood pressure significantly decreased after training (systolic blood pressure: 134±9 vs. 128±8 mmHg; diastolic blood pressure: 82±7 vs. 77±6 mmHg; P<0.05). Cardiac structures and left and right systolic and diastolic function did not change after combined training (P>0.05).

Conclusions

Combined and supervised training for a 6-month period increases physical capacity and muscle strength in elderly patients with controlled arterial hypertension without changing resting left ventricular diastolic function.

Differential effects of late-life initiation of low-dose enalapril and losartan on diastolic function in senescent Fischer 344 x Brown Norway male rats

No proven pharmacological therapies to delay or reverse age-related diastolic dysfunction exist. We hypothesized that late-life low-dose (non-blood-pressure-lowering) angiotensin-converting enzyme inhibition vs. angiotensin II receptor blockade would be equally efficacious at mitigating diastolic dysfunction in the senescent Fischer 344 × Brown Norway rat. Enalapril (10 mg/kg/day; n = 9) initiated at 24 months of age and continued for 6 months, increased myocardial relaxation (e'), reduced Doppler-derived indices of filling pressure (E/e'), favorably lowered the ratio of phospholamban-SERCA2 and reduced oxidative stress markers, Rac1 and nitrotyrosine, in aged hearts. Treatment with losartan (15 mg/kg/day; n = 9) similarly mitigated signs of cardiac oxidative stress, but impairments in diastolic function persisted when compared with untreated rats (n = 7). Our findings favor the idea that the lusitropic benefit of low-dose angiotensin-converting enzyme inhibitor initiated late in life may be related to an antioxidant-mediated modulation of SERCA2, resulting in improved relaxation rather than via overt effects on cardiac structure or blood pressure.

The larger exercise stroke volume in endurance-trained men does not result from increased left ventricular early or late inflow or tissue velocities

AIM

To determine whether the larger exercise stroke volume in senior endurance-trained athletes results from an attenuation of age-related alterations in left ventricular (LV) early diastolic filling or a more vigorous late filling.

METHODS

Body composition (DEXA), VO(2)peak, stroke volume (CO(2) rebreathing) and Doppler measures of early and late mitral inflow and mitral annular velocities were collected at seated upright rest and heart rate-matched exercise (100 and 120 bpm) in trained and untrained younger (18-30 years) men and trained and untrained older (60-80 years) healthy men.

RESULTS

Ageing had a greater effect than training status on seated rest mitral inflow and tissue Doppler imaging parameters, as shown by a lower peak early-to-late mitral inflow velocity ratio (E/A ratio) and slower peak early mitral annular velocity (Em) in older compared with younger men. Exercise stroke volume was unaffected by healthy ageing; however, Em, an index of early LV lengthening rate and relaxation, was slower (P < 0.001), while measures of atrial systole were increased (P < 0.001) during exercise in older men. Stroke volume during exercise was larger in the trained men (P < 0.001); however, early and late mitral inflow and tissue velocities were not different between trained and untrained men.

CONCLUSION

The larger exercise stroke volume in trained older male athletes does not seem to be related to faster filling or lengthening velocities during early or late filling. Thus, a larger, more compliant left ventricle in combination with an increased blood volume may explain the larger LV filling volumes in trained seniors.

Alagebrium in combination with exercise ameliorates age-associated ventricular and vascular stiffness

Advanced glycation end-products (AGEs) initiate cellular inflammation and contribute to cardiovascular disease in the elderly. AGE can be inhibited by Alagebrium (ALT), an AGE cross-link breaker. Moreover, the beneficial effects of exercise on aging are well recognized. Thus, we investigated the effects of ALT and exercise (Ex) on cardiovascular function in a rat aging model. Compared to young (Y) rats, in sedentary old (O) rats, end-systolic elastance (Ees) decreased (0.9±0.2 vs 1.7±0.4mmHg/μL, P<0.05), dP/dt(max) was attenuated (6054±685 vs 9540±939mmHg/s, P<0.05), ventricular compliance (end-diastolic pressure-volume relationship (EDPVR)) was impaired (1.4±0.2 vs 0.5±0.4mmHg/μL, P<0.05) and diastolic relaxation time (tau) was prolonged (21±3 vs 14±2ms, P<0.05). In old rats, combined ALT+Ex (4weeks) increased dP/dt(max) and Ees (8945±665 vs 6054±685mmHg/s, and 1.5±0.2 vs 0.9±0.2 respectively, O with ALT+Ex vs O, P<0.05 for both). Diastolic function (exponential power of EDPVR and tau) was also substantially improved by treatment with Alt+Ex in old rats (0.4±0.1 vs 0.9±0.2 and 16±2 vs 21±3ms, respectively, O with ALT+EX vs O, P<0.05 for both). Pulse wave velocity (PWV) was increased in old rats (7.0±0.7 vs 3.8±0.3ms, O vs Y, P<0.01). Both ALT and Ex alone decreased PWV in old rats but the combination decreased PWV to levels observed in young (4.6±0.5 vs 3.8±0.3ms, O with ALT+Ex vs Y, NS). These results suggest that prevention of the formation of new AGEs (with exercise) and breakdown of already formed AGEs (with ALT) may represent a therapeutic strategy for age-related ventricular and vascular stiffness.

Effect of aging on power output properties in rat skinned cardiac myocytes

Aging is generally associated with a decline in several indices of cardiac function. The cellular mechanisms for this decline are not completely understood. The ability of the myocardium to perform external work (power output) is a critical aspect of ventricular function. The purpose of this study was to determine the effect of aging on loaded shortening and power output properties. We measured force-velocity properties in permeabilized (skinned) myocytes from the hearts of 9-, 24-, and 33-month-old male Fisher 344 × Brown Norway F1 hybrid rats (F344BN) during loaded contractions using a force-clamp technique. Power output was calculated by multiplying force and shortening velocity values. We found that peak power output normalized to maximal force was significantly decreased by 18% and 31% in myocytes from 24- and 33-month-old group, respectively, compared with 9-month group (p < .05). These results suggest that aging is associated with a significant decrease in the ability of the myocardium to do work.

Modulation of sarcoplasmic reticulum Ca(2+) cycling in systolic and diastolic heart failure associated with aging

Hypertension, atherosclerosis, and resultant chronic heart failure (HF) reach epidemic proportions among older persons, and the clinical manifestations and the prognoses of these worsen with increasing age. Thus, age per se is the major risk factor for cardiovascular disease. Changes in cardiac cell phenotype that occur with normal aging, as well as in HF associated with aging, include deficits in ss-adrenergic receptor (ss-AR) signaling, increased generation of reactive oxygen species (ROS), and altered excitation-contraction (EC) coupling that involves prolongation of the action potential (AP), intracellular Ca(2+) (Ca(i)(2+)) transient and contraction, and blunted force- and relaxation-frequency responses. Evidence suggests that altered sarcoplasmic reticulum (SR) Ca(2+) uptake, storage, and release play central role in these changes, which also involve sarcolemmal L-type Ca(2+) channel (LCC), Na(+)-Ca(2+) exchanger (NCX), and K(+) channels. We review the age-associated changes in the expression and function of Ca(2+) transporting proteins, and functional consequences of these changes at the cardiac myocyte and organ levels. We also review sexual dimorphism and self-renewal of the heart in the context of cardiac aging and HF.

Exercise training augments the dynamic heart rate response to vagal but not sympathetic stimulation in rats

We examined the transfer function of autonomic heart rate (HR) control in anesthetized sedentary and exercise-trained (16 wk, treadmill for 1 h, 5 times/wk at 15 m/min and 15-degree grade) rats for comparison to HR variability assessed in the conscious resting state. The transfer function from sympathetic stimulation to HR response was similar between groups (gain, 4.2 ± 1.5 vs. 4.5 ± 1.5 beats·min(-1)·Hz(-1); natural frequency, 0.07 ± 0.01 vs. 0.08 ± 0.01 Hz; damping coefficient, 1.96 ± 0.55 vs. 1.69 ± 0.15; and lag time, 0.7 ± 0.1 vs. 0.6 ± 0.1 s; sedentary vs. exercise trained, respectively, means ± SD). The transfer gain from vagal stimulation to HR response was 6.1 ± 3.0 in the sedentary and 9.7 ± 5.1 beats·min(-1)·Hz(-1) in the exercise-trained group (P = 0.06). The corner frequency (0.11 ± 0.05 vs. 0.17 ± 0.09 Hz) and lag time (0.1 ± 0.1 vs. 0.2 ± 0.1 s) did not differ between groups. When the sympathetic transfer gain was averaged for very-low-frequency and low-frequency bands, no significant group effect was observed. In contrast, when the vagal transfer gain was averaged for very-low-frequency, low-frequency, and high-frequency bands, exercise training produced a significant group effect (P < 0.05 by two-way, repeated-measures ANOVA). These findings suggest that, in the frequency domain, exercise training augments the dynamic HR response to vagal stimulation but not sympathetic stimulation, regardless of the frequency bands.

Exercise training improves age-related myocardial metabolic derangement: proton magnetic resonance spectroscopy study in the rat model

BACKGROUND AND OBJECTIVES

The objective of this study was to determine whether long-term exercise training will improve age-related cardiac metabolic derangement using proton magnetic resonance (MR) spectroscopy.

MATERIALS AND METHODS

Young and old male Fischer 344 rats were assigned to sedentary controls groups {young control (YC) group-3 months of age: YC, n=10; old control (OC) group-22 months of age: OC, n=10}, and an exercise training group (OT, n=5). After 12-week of treadmill exercise training, MR spectroscopy at 4.7 T was performed to assess myocardial energy metabolism: measurements of myocardial creatine-to-water ratio (Scr/Sw) were performed using the XWIN-NMR software.

RESULTS

Exercise capacity was 14.7 minutes greater in OT than that in OC (20.1±1.9 minutes in OT, 5.4±2.3 minutes in OC; p<0.001). The 12-week exercise training rendered the old rats a maximum exercise capacity matching that of untrained YC rats (17.9±1.5 minutes in YC, 20.1±1.9 minutes in OT; p>0.05). The creatine-to-water ratios in the interventricular septa of YC did not differ significantly from that of OT (0.00131±0.00025 vs. 0.00127±0.00031; p=0.37). However, OC showed significant reduction in creatine-to-water ratio compared to OT (0.00096±0.00025 vs. 0.00127±0.00031; p<0.001). Mean total creatine concentrations in the myocardium were similar between YC and OT (13.3±3.6 vs. 11.5±4.1 mmol/kg wet weight; p=0.29). In contrast, the mean total creatine concentration of OC was significantly reduced compared to OT (6.8±3.2 vs. 11.5±4.1 mmol/kg wet weight; p=0.03).

CONCLUSION

Our findings suggest that long-term exercise training in old rats induced prevention of age-related deterioration in myocardial metabolism.

Heart failure with preserved ejection fraction: pathophysiology and emerging therapies

Approximately half of patients with heart failure (HF) have a preserved ejection fraction (HFpEF). Morbidity and mortality are similar to HF with reduced EF (HFrEF), yet therapies with unequivocal benefit in HFrEF have not been shown to be effective in HFpEF. Recent studies have shown that the pathophysiology of HFpEF, initially believed to be due principally to diastolic dysfunction, is more complex. Appreciation of this complexity has shed new light into how HFpEF patients might respond to traditional HF treatments, while also suggesting new applications for novel therapies and strategies. In this review, we shall briefly review the pathophysiologic mechanisms in HFpEF, currently available clinical trial data, and finally explore new investigational therapies that are being developed and tested in ongoing and forthcoming trials.

Effect of long term and intensive endurance training in athletes on the age related decline in left and right ventricular diastolic function as assessed by Doppler echocardiography

The aim of this study was to evaluate (1) the effect of endurance training on left ventricular and right ventricular diastolic function and (2) whether the normal aging effect on left ventricular and right ventricular diastolic function is slowed by endurance training. A total of 269 healthy subjects were prospectively enrolled for echocardiographic evaluation. Five groups were defined on the basis of age and athletic activities: (1) young (18 to 39 years) nonathletes (n = 62), (2) veteran (>or=40 years) nonathletes (n = 33), (3) young regular athletes (9 to 18 hours of sports/week; n = 58), (4) young elite athletes (>18 hours of sports/week; n = 63), and (5) veteran athletes (>or=40 years and >or=9 hours of sports/week; n = 53). Pulsed-wave Doppler indexes for diastolic function in the left and right ventricles were obtained at rest. No significant differences were found among the young controls, regular athletes, and elite athletes in left ventricular and right ventricular pulsed-wave and tissue Doppler diastolic parameters. These were also comparable between the veteran athletes and controls. In athletes and controls, similar and significant correlations were found between age and diastolic parameters. Age was the most important determinant in almost all parameters in multivariate analysis, while the influence of the amount of training did not account for >2% of the observed variance in any of these parameters. In conclusion, the amount of endurance training did not alter diastolic parameters in either ventricle in the young. Furthermore, the biventricular decreases in diastolic function observed in healthy, nonathletic subjects with age was also observed in aging athletes' hearts.

Long-term exercise training attenuates age-related diastolic dysfunction: association of myocardial collagen cross-linking

The incidence of diastolic heart failure increases dramatically with age. We investigated the impact of long-term exercise training on age-related diastolic dysfunction. Old (25-month-old) male Fischer 344 rats were studied after 12 weeks of treadmill exercise training or sedentary cage life (N=7, in each group). We determined cardiac performance using a pressure-volume conductance catheter and magnetic resonance imaging. Collagen volume fraction (CVF) and myocardial collagen solubility by pepsin as an index of advanced glycation end products (AGEs) cross-linked collagen were measured. The maximal slope of systolic pressure increment (+dP/dt) and the slope of end-systolic pressure-volume relation were higher, and end diastolic volume (EDV), Delta EDV (the percentage of the EDV increment-to-baseline EDV) and the slope of end-diastolic pressure-volume relation were lower in training group. The maximal slope of diastolic pressure decrement (-dP/dt) and time constant of LV pressure decay (tau) had no difference. AGEs cross-linked collagen, not CVF was reduced by exercise training. Long-term exercise training appears to attenuate age-related deterioration in cardiac systolic function and myocardial stiffness and could be reduce in pathologic AGEs cross-linked collagen in myocardium.

Silent cardiac dysfunction and exercise intolerance in HIV+ men receiving combined antiretroviral therapies

Resting and exercise cardiac function, skeletal muscle oxygenation and whole-body aerobic exercise capacities were evaluated prospectively in cardiac symptom-free HIV men receiving antiretroviral therapies and in healthy controls matched for age, physical activity, smoking and body surface area. HIV patients showed resting cardiac dysfunction, altered cardiac responses to exercise and depressed exercise tolerance. Exercise stroke volume kinetics and muscle oxygenation were impaired in HIV patients, especially in those with resting diastolic dysfunction.

Effects of short-term treadmill exercise training or growth hormone supplementation on diastolic function and exercise tolerance in old rats

Whether the lusitropic potential of short-term exercise in aged rats is linked to an augmentation in the growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis and an alteration in the cardiac renin angiotensin system (RAS) is unknown. Old (28-month-old) male, Fischer 344xBrown Norway rats were randomized to 4 weeks of GH supplementation (300 microg subcutaneous, twice daily) or 4 weeks of treadmill running, or were used as sedentary controls. Six-month-old rats, sedentary or exercised, were used as young controls. Training improved exercise capacity in old animals. Exercise and GH attenuated age-related declines in myocardial relaxation despite an exercise-induced suppression of IGF-1. The regulatory protein, sarcoplasmic Ca2+ adenosine triphosphatase (SERCA2), increased with exercise but not GH. Among aged rats, the cardiac RAS was not altered by training or GH. Thus, the signaling pathway underlying the lusitropic benefit of short-term habitual exercise in the aged rat may be distinct from GH-mediated benefits and independent of the cardiac RAS.

Myocardial alterations in senescent mice and effect of exercise training: a strain rate imaging study

BACKGROUND

Aging is accompanied by an alteration in myocardial contractility. However, its noninvasive detection is difficult. The effect of chronic exercise on this decrease is unknown. Murine models of senescence are increasingly used to test therapies in aging. We tested whether strain rate imaging detected left ventricular (LV) systolic dysfunction in aging mice and was able to assess a potential improvement after exercise.

METHODS AND RESULTS

Young (3 weeks), adult (2 to 3 months), and old (6 to 18 months) C57BL6 male mice underwent echocardiograms with strain rate imaging, either in sedentary conditions or before, 2 weeks and 4 weeks after chronic swimming. Hemodynamic parameters of LV function including maximal and end-systolic elastance were obtained before euthanizing. LV fibrosis was measured using Sirius red staining. Conventional echocardiography was unable to detect LV systolic dysfunction in old mice, whereas both systolic strain rate and load-independent hemodynamic parameters such as preload recruitable stroke work and end-systolic elastance were significantly decreased. Both strain rate and load-independent hemodynamic parameters normalized after 4 weeks of exercise. Both endocardial and epicardial fibrosis were increased in the LV of aging mice. Endocardial fibrosis decreased in exercised aged mice.

CONCLUSIONS

Strain rate noninvasively detects LV systolic dysfunction associated with aging in mice, whereas conventional echocardiography does not. Chronic exercise normalizes LV systolic function and decreases fibrosis in old mice. Strain rate imaging in mice may be a useful tool to monitor the effect of new therapeutic strategies preventing the myocardial dysfunction associated with aging.

Differential protein expression during aging in ventricular myocardium of Fischer 344 x Brown Norway hybrid rats

The aging heart undergoes well characterized structural changes associated with functional decline, though the underlying mechanisms are not understood. The aim of this study was to determine to what extent ventricular myocardial protein expression was altered with age and which proteins underwent protein nitration. Fischer 344 x Brown Norway F1 hybrid (FBN) rats of four age groups were used, 4, 12, 24, and 34 months. Differential protein expression was determined by 2-DE and proteins were identified by peptide mass fingerprinting. Altered protein nitration with age was assessed by immunoblotting. Over 1000 protein spots per sample were detected, and 255 were found to be differentially expressed when all aged groups were compared to young rats (4 months) (p0.05). A strong positive correlation between differential protein expression and increasing age (p=0.03, R(2)=0.997) indicated a progressive, rather than abrupt, change with age. Of 46 differentially expressed proteins identified, seventeen have roles in apoptosis, ten in hypertrophy, seven in fibrosis, and three in diastolic dysfunction, aging-associated processes previously reported in both human and FBN rat heart. Protein expression alterations detected here could have beneficial effects on cardiac function; thus, our data indicate a largely adaptive change in protein expression during aging. In contrast, differential protein nitration increased abruptly, rather than progressively, at 24 months of age. Altogether, the results suggest that differential myocardial protein expression occurs in a progressive manner during aging, and that a proteomic-based approach is an effective method for the identification of potential therapeutic targets to mitigate aging-related myocardial dysfunction.

Cardiac dysfunction in aging conscious rats: altered cardiac cytoskeletal proteins as a potential mechanism

The objective of this study was to test the hypothesis that the mechanism mediating left ventricular (LV) dysfunction in the aging rat heart involves, in part, changes in cardiac cytoskeletal components. Our results show that there were no significant differences in heart rate, LV pressure, or LV diameter between conscious, instrumented young [5.9 +/- 0.3 mo (n = 9)] and old rats [30.6 +/- 0.1 mo (n = 10)]. However, the first derivative of LV pressure (LV dP/dt) was reduced (8,309 +/- 790 vs. 11,106 +/- 555 mmHg/s, P < 0.05) and isovolumic relaxation time (tau) was increased (8.7 +/- 0.7 vs. 6.3 +/- 0.6 ms, P < 0.05) in old vs. young rats, respectively. The differences in baseline LV function in young and old rats, which were modest, were accentuated after beta-adrenergic receptor stimulation with dobutamine (20 mug/kg), which increased LV dP/dt by 170 +/- 9% in young rats, significantly more (P < 0.05) than observed in old rats (115 +/- 5%). Volume loading in anesthetized rats demonstrated significantly impaired LV compliance in old rats, as measured by the LV end-diastolic pressure and dimension relationship. In old rat hearts, there was a significant (P < 0.05) increase in the percentage of LV collagen (2.4 +/- 0.2 vs. 1.3 +/- 0.2%), alpha-tubulin (92%), and beta-tubulin (2.3-fold), whereas intact desmin decreased by 51%. Thus the cardiomyopathy of aging in old, conscious rats may be due not only to increases in collagen but also to alterations in cytoskeletal proteins.

Exercise training in late middle-aged male Fischer 344 x Brown Norway F1-hybrid rats improves skeletal muscle aerobic function

The Fischer 344 x Brown Norway F1-hybrid (F344BN) rat has become an increasingly popular and useful strain for studying age-related declines in skeletal muscle function because this strain lives long enough to experience significant declines in muscle mass. Since exercise is often considered a mechanism to combat age-related declines in muscle function, determining the utility of this strain of rat for studying the effects of exercise on the ageing process is necessary. The purpose of this study was to evaluate the plasticity of skeletal muscle aerobic function in late middle-aged male rats following 7 weeks of treadmill exercise training. Training consisted of 60 min per day, 5 days per week with velocity gradually increasing over the training period according to the capabilities of individual rats. The final 3 weeks involved 2 min high-intensity intervals to increase the training stimulus. We used in situ skeletal muscle aerobic metabolic responses and in vitro assessment of muscle mitochondrial oxidative capacity to describe the adaptations of aerobic function from the training. Training increased running endurance from 11.3 +/- 0.6 to 15.5 +/- 0.8 min, an improvement of approximately 60%. Similarly, distal hindlimb muscles from trained rats exhibited a higher maximal oxygen consumption in situ (23.2 +/- 1.3 versus 19.7 +/- 0.8 mumol min(-1) for trained versus sedentary rats, respectively) and greater citrate synthase and complex IV enzyme activities in gastrocnemius (29 and 19%, respectively) and plantaris muscles (24 and 28%, respectively) compared with age-matched sedentary control animals. Our results demonstrate that skeletal muscles from late middle-aged rats adapt to treadmill exercise by improving skeletal muscle aerobic function and mitochondrial enzyme activities. This rat strain seems suitable for further investigations using exercise as an intervention to combat ageing-related declines of skeletal muscle aerobic function.

Local delivery of PKCepsilon-activating peptide mimics ischemic preconditioning in aged hearts through GSK-3beta but not F1-ATPase inactivation

In adult heart, selective PKCepsilon activation limits ischemia (I)-reperfusion (R) damage and mimics the protection associated with ischemic preconditioning. We sought to determine whether local delivery of PKCepsilon activator peptide psiepsilon-receptor for activated C-kinase (psiepsilon-RACK) is sufficient to produce a similarly protected phenotype in aged hearts. Langendorff-perfused hearts isolated from adult (5 mo; n = 9) and aged (24 mo; n = 9) male Fisher 344 rats were perfused with psiepsilon-RACK conjugated to Tat (500 nM) or Tat only (500 nM) for 10 min before global 31-min ischemia. Western blotting was used to measure mitochondrial targeting of PKCepsilon, PKCdelta, phospho (p)-GSK-3beta (Ser(9)) and GSK-3beta in hearts snap-frozen during I. Recovery of left ventricular developed pressure was significantly improved by psiepsilon-RACK (P < 0.01) and infarct size reduced in 24-mo rats vs. age-matched controls (60% vs. 34%; P < 0.01). Mitochondrial PKCepsilon levels were 30% greater during I with psiepsilon-RACK in aged vs. control rats (P < 0.01). Interestingly, mitochondrial GSK-3beta levels were threefold greater in aged vs. adult rats during I, and psiepsilon-RACK prevented this increase (P < 0.01). Mitochondrial p-GSK-3beta levels were also greater in aged rats after psiepsilon-RACK (P < 0.01), and subsequent inhibition of GSK-3beta with SB-216763 (3 muM) before I/R elicited protection similar to that of psiepsilon-RACK (n = 3/group). Mitochondrial proteomic analysis further identified group differences in the F(1)-ATPase beta-subunit, and coimmunoprecipitation studies revealed a novel interaction with PKCepsilon. F(1)-ATPase-PKCepsilon association was affected by psiepsilon-RACK in adult but not aged rats. Our results provide evidence, for the first time, for PKCepsilon-mediated protection in aged rat heart after I/R and suggest a central role for mitochondrial GSK-3beta but not F(1)-ATPase as a potential target of PKCepsilon to limit I/R damage with aging.

Growth hormone replacement attenuates diastolic dysfunction and cardiac angiotensin II expression in senescent rats

We tested the hypothesis that long-term growth hormone (GH) replacement in aged rats would preserve diastolic function and attenuate left ventricular remodeling associated with normal aging. Male Brown Norway x F344 rats were randomized to receive twice daily injections of porcine GH (200 microg/injection, subcutaneous) or saline from 24 to 30 months of age. Adult rats (6- to 9-months old) received saline injections throughout the study. Thirty-month-old, saline-treated rats exhibited low levels of insulin-like growth factor 1 (IGF-1), impaired diastolic left ventricular filling (Doppler), increased cardiac angiotensin II (Ang II), reduced plasma Ang II, and increased cardiac collagen. GH administration in old rats restored IGF-1 and diastolic indices to values comparable to those of adults. These effects were associated with reduced cardiac Ang II and attenuations in cardiac collagen. Age-related decreases in GH and IGF-1 may contribute to the decline in diastolic function of aging, in part through alterations in renin-angiotensin system-mediated ventricular remodeling.

Lifestyle and Prevention of Cardiovascular Disease in the Elderly: An Italian Perspective

The life span of human beings is partially influenced by genetic factors, but outcomes of aging are profoundly influenced by lifestyle and other environmental factors. Age-related modifications of the cardiovascular system are preserved by antiaging lifestyle interventions such as physical activity and caloric restriction. Accordingly, physical activity and low body mass index reduce mortality in older men with cardiovascular diseases. Several mechanisms have been proposed to explain the protective effect of lifestyle interventions against cardiovascular diseases in the elderly, including a reduction of vulnerability (i.e., the age-related reduction of endogenous mechanisms protective against pathologic insults). The age-related reduction of ischemic preconditioning, the most powerful endogenous protective mechanism against myocardial ischemia, is restored by both physical activity and caloric restriction. Thus, older persons can implement lifestyle practices that minimize their risk of death from cardiovascular diseases.

Validation of echocardiographic and Doppler indexes of left ventricular relaxation in adult hypertensive and normotensive rats

This study was performed to validate echocardiographic and Doppler techniques for the assessment of left ventricular (LV) diastolic function in spontaneously hypertensive rats (SHR) and normotensive Wistar rats. In 11 Wistar rats and 20 SHR, we compared 51 sets of invasive and Doppler LV diastolic indexes. Noninvasive indexes of LV relaxation were related to the minimal rate of pressure decline (−dP/d tmin), particularly isovolumic relaxation time (IVRT), the Tei index, the early velocity of the mitral annulus ( Em) using Doppler tissue imaging, and early mitral flow propagation velocity using M-mode color ( r = 0.28–0.56 and P < 0.05–0.0001). When the role of systolic load was considered, the correlation between Doppler indexes of LV diastolic function and relaxation rate [(−dP/d tmin)/LV systolic pressure] improved ( r = 0.48–0.86 and P = 0.004–0.0001, respectively). Similarly, Doppler indexes of LV diastolic function and the time constant of isovolumic LV relaxation (τ) correlated well ( r = 0.50–0.84 and P = 0.0002–0.0001, respectively). In addition, eight SHR and eight Wistar rats were compared; their LV end-diastolic diameters were similar, whereas the SHR LV mass was greater. Furthermore, IVRT and Tei index were significantly higher and Em was lower in SHR. Moreover, τ was higher in SHR, demonstrating impaired LV relaxation. In conclusion, LV relaxation can be assessed reliably using echocardiographic and Doppler techniques, and, using these indexes, impaired relaxation was demonstrated in SHR.

Role of exercise training on cardiovascular disease in persons who have type 2 diabetes and hypertension

Exercise training is an essential component in the medical management of patients who have type 2 diabetes and hypertension. Regular exercise improves the cardiovascular health of individuals who have these conditions through multiple mechanisms (Fig. 1). These mechanisms include improvements in endothelial vasodilator function,left ventricular diastolic function, arterial stiffness.systematic inflammation, and reducing left ventricular mass. Exercise training also reduces total and abdominal fat, which mediate improvements in insulin sensitivity and blood pressure, and possibly, endothelial function. Persons who are in a prediabetic stage or those who have the metabolic syndrome may be able to prevent or delay the progression to overt diabetes by adopting a healthier lifestyle, of which increasing habitual levels of physical activity isa vital component. Most persons who have diabetes and hypertension or are at risk for these conditions should be able to initiate an exercise program safely after appropriate medical screen-ing and the establishment of an individualized exercise prescription. Despite the increasing amount of evidence that shows the benefits of exercise training, this modality of prevention and treatment continues to be underused. Although patients' lack of knowledge of the benefits of exercise or lack of motivation contributes to this underuse, a lack of clear and specific guidelines from health care professionals also is an important factor. Clinicians need to educate patients about the benefits of exercise for managing their type 2 diabetes and assist in formulating specific advice for increasing physical activity. Specific instructions should be given to patients, rather than general advice, such as "you should exercise more often." Many cardiac re-habilitation and clinical exercise programs can accommodate patients who have type 2 diabetes and hypertension. Such programs can establish individualized exercise prescriptions and provide an environment that is conducive for "lifestyle change" that underlies long-term compliance to exercise and risk factor modification.

Tandem action of exercise training and food restriction completely preserves ischemic preconditioning in the aging heart

Ischemic preconditioning (IP) has been proposed as an endogenous form of protection against ischemia reperfusion injury. IP, however, does not prevent post-ischemic dysfunction in the aging heart but may be partially corrected by exercise training and food restriction. We investigated the role of exercise training combined with food restriction on restoring IP in the aging heart. Effects of IP against ischemia-reperfusion injury in isolated hearts from adult (A, 6 months old), sedentary 'ad libitum' fed (SL), trained ad libitum fed (TL), sedentary food-restricted (SR), trained- and food-restricted senescent rats (TR) (24 months old) were investigated. Norepinephrine release in coronary effluent was determined by high performance liquid cromatography. IP significantly improved final recovery of percent developed pressure in hearts from A (p<0.01) but not in those from SL (p=NS) vs unconditioned controls. Developed pressure recovery was partial in hearts from TL and SR (64.3 and 67.3%, respectively; p<0.05 vs controls) but it was total in those from TR (82.3%, p=NS vs A; p<0.05 vs hearts from TL and SR). Similarly, IP determined a similar increase of norepinephrine release in A (p<0.001) and in TR (p<0.001, p=NS vs adult). IP was abolished by depletion of myocardial norepinephrine stores by reserpine in all groups. Thus, IP reduces post-ischemic dysfunction in A but not in SL. Moreover, IP was preserved partially in TR and SR and totally in TR. Complete IP maybe due to full restoration of norepinephrine release in response to IP stimulus.

Eplerenone, a selective aldosterone blocker, improves diastolic function in aged rats with small-to-moderate myocardial infarction

BACKGROUND

The incidence of cardiovascular diseases increases rapidly with age, and the elderly suffer higher morbidity and mortality. Aldosterone blockers have shown benefits in patients with left ventricular (LV) dysfunction and heart failure after myocardial infarction (MI). However, aldosterone blockade efficacy has not been explored in aged animals with MI. Methods and results Small-to-moderate MI was induced by coronary artery ligation in 16-month old rats, divided into 3 groups: sham-operated (control, n = 9), MI (n = 9), and MI fed a diet containing eplerenone (120 mg/kg/day, MI+Eplerenone, n = 9) given 18 days postsurgery and up to sacrifice 3 months later. At sacrifice, untreated MI rats did not show overt systolic dysfunction but they had (1) echocardiographic evidences of impaired relaxation (increase of E wave deceleration time and of isovolumic relaxation time, decrease of peak E wave velocity), (2) hemodynamically impaired LV relaxation (LV -dP/dt from 7413 +/- 720 to 4956 +/- 475 mm Hg/s, P < .05), and (3) significant increase of collagen content in LV interstitium (from 4.27 +/- 0.23 to 5.34 +/- 0.24%, P < .01) and in aorta (from 19 +/- 1 to 24 +/- 2%, P < .05). Eplerenone normalized echocardiographic and hemodynamic evidences of diastolic dysfunction, as well as myocardial interstitial collagen and aortic fibrosis (all parameters statistically different from untreated MI).

CONCLUSION

In aged rats with small to moderate MI, eplerenone normalized diastolic relaxation, possibly through a reduction of interstitial fibrosis.