Angiotensin II receptor blockade attenuates the deleterious effects of exercise training on post-MI ventricular remodelling in rats

Strength training improves heart function, collagen and strength in rats with heart failure

BACKGROUND/OBJECTIVES

Myocardial infarction (MI) frequently leads to cardiac remodeling and failure with impaired life quality, playing an important role in cardiovascular deaths. Although physical exercise is a well-recognized effective non-pharmacological therapy for cardiovascular diseases, the effects of strength training (ST) on the structural and functional aspects of cardiac remodeling need to be further documented. In this study, we aimed to investigate the role of a linear block ST protocol in the rat model of MI.

METHODS AND RESULTS

After 6 weeks of MI induction or sham surgery, male adult rats performed ST for the following 12 weeks. The ladder-based ST program was organized in three mesocycles of 4 weeks, with one load increment for each block according to the maximal carrying load test. After 12 weeks, the infarcted-trained rats exhibited an increase in performance, associated with reduced cardiac hypertrophy and pulmonary congestion compared with the untrained group. Despite not changing MI size, the ST program partially prevented cardiac dilatation and ventricular dysfunction assessed by echocardiography and hemodynamics, and interstitial fibrosis evaluated by histology. In addition, isolated cardiac muscles from infarcted-trained rats had improved contractility parameters in a steady state, and in response to calcium or stimuli pauses.

CONCLUSIONS

The ST in infarcted rats increased the capacity to carry mass, associated with attenuation of cardiac remodeling and pulmonary congestion with improving cardiac function that could be attributed, at least in part, to the improvement of myocardial contractility.

Outcomes With Multidisciplinary Cardiac Rehabilitation in Post-acute Systolic Heart Failure Patients-A Retrospective Propensity Score-Matched Study

Background

Cardiac rehabilitation (CR) is recommended for patients with acute heart failure (HF). However, the results of outcome studies and meta-analyses on CR in post-acute care are varied. We aimed to assess the medium- to long-term impact of CR and ascertain the predictors of successful CR.

Methods

In this propensity score-matched retrospective cohort study, records of consecutive patients who survived acute HF (left ventricular ejection fraction <40) and participated in a multidisciplinary HF rehabilitation program post-discharge between May 2014 and July 2019 were reviewed. Patients in the CR group had at least one exercise session within 3 months of discharge; the others were in the non-CR group. After propensity score matching, the primary (all-cause mortality) and secondary (HF readmission and life quality assessment) outcomes were analyzed.

Results

Among 792 patients, 142 attended at least one session of phase II CR. After propensity score matching for covariates related to HF prognosis, 518 patients were included in the study (CR group, 137 patients). The all-cause mortality rate was 24.9% and the HF rehospitalization rate was 34.6% in the median 3.04-year follow-up. Cox proportional hazard analysis revealed that the CR group had a significant reduction in all-cause mortality compared to the non-CR group (hazard ratio [HR]: 0.490, 95% confidence interval [CI]: 0.308-0.778). A lower risk of the primary outcome with CR was observed in patients on renin-angiotensin-aldosterone system (RAAS) inhibitors, but was not seen in patients who were not prescribed this class of medications (interaction p = 0.014).

Conclusions

Cardiac rehabilitation participation was associated with reduced all-cause mortality after acute systolic heart failure hospital discharge. Our finding that the benefit of CR was decreased in patients not prescribed RAAS inhibitors warrants further evaluation.

Concurrent vitamin D supplementation and exercise training improve cardiac fibrosis via TGF-β/Smad signaling in myocardial infarction model of rats

Although the role of vitamin D in various types of disorders such as cancer and diabetes has been well recognized, its relation to cardiovascular diseases still remains equivocal. The present study aims to investigate the interactive effects of aerobic-resistance training (ART) and vitamin D₃ (VD₃) on both cardiac fibrosis and heart functions considering TGF-β1/Smad2, 3 (transforming growth factor-β1/mothers against decapentaplegic homolog 2/3) signaling in the myocardial infarction (MI) model of rats. Fifty-six male Wistar rats were divided into 2 groups of sham (n = 8), and MI (n = 48). Then, MI rats were divided into six groups of VD₃, ART, VD₃+ART, Veh, Veh+ART, and sedentary MI. The animals received the related treatments for 8 weeks, and then their functional exercise capacity (FEC) and strength gain (SG) were estimated through exercise tests. Ejection fraction (EF%) and fractional shortening (FS%) and serum level of VD₃ were measured by echocardiography and ELISA, respectively. Cardiac expressions of TGF-β1, Smad2/3, and collagen I/III were assessed by western blotting and fibrosis by Masson's trichrome staining. The highest EF, parallel with the lowest expression of cardiac TGF-β1, Smad2/3, collagen I, and collagen III were observed in MI + VD₃ (P = 0.021), MI + ART (P = 0.001), and MI + VD₃ + ART (P < 0.001). Furthermore, similar to FS, the highest FEC and SG were related to the groups of MI + VD₃ + ART and MI + ART compared to the MI group. In conclusion, our data indicate that concurrent vitamin D supplementation and ART, compared with monotherapy, successfully improve cardiac function and alleviate myocardial fibrosis via downregulating TGF-β1, Smad2/3 signaling, and also regulating collagen I and III expressions.

Impact of Modality and Intensity of Early Exercise Training on Ventricular Remodeling after Myocardial Infarction

The objective of this study was to analyze the impact of different modalities and intensities of exercise training on cardiac remodeling started early after experimental myocardial infarction (MI). Male Wistar rats, weighing 200-250 g, were subjected to experimental MI. After 5 days, the animals were allocated into three experimental groups and observed for three months: S (sedentary control animals), C (animals subjected to continuous low-intensity training), and HIT (animals subjected to high-intensity interval training). Low-intensity exercise training was performed at a treadmill speed corresponding to 40% VO₂ max, which was kept unchanged throughout the entire session (i.e., continuous low-intensity training). High-intensity interval training was performed in such a way that rats run during 3 min at 60% VO₂ max, followed by 4-minute intervals at 85% VO₂ max (i.e., high-intensity interval training). After the follow-up period, we studied hypertrophy and ventricular geometry, functional alterations in vivo and in vitro, oxidative stress, apoptosis, and cardiac energetic metabolism. Our data showed that both high-intensity interval and continuous low-intensity modalities improved cardiac energetic metabolism variables in comparison with sedentary infarcted animals. In addition, high-intensity interval training decreased cardiac oxidative stress, associated with improved diastolic function. On the other hand, the continuous low-intensity group showed impairment of cardiac function. Therefore, altogether, our data suggest that high-intensity interval training could be the best modality for early physical exercise after MI and should be better studied in this clinical scenario.

Irisin vs. Treadmill Exercise in Post Myocardial Infarction Cardiac Rehabilitation in Rats

BACKGROUND

Irisin is an exercise-induced myokine that could play a role in post-myocardial infarction (MI) cardiac rehabilitation.

AIM OF THE STUDY

We investigated the ability of dihydromyricetin to mimic the effects of exercise on raising serum irisin and on enhancing cardiac function and remodeling following MI in rats.

METHODS

MI was induced in albino rats by subcutaneous injection of isoproterenol (85 mg/kg) for 2 consecutive days at an interval of 24 h. One week post-MI, rats either underwent physical exercise by running on a motor-driven treadmill at 25 m/min, 30 min/d, 5 d/week or received orally dihydromyricetin 100 mg/kg/d, for 8 weeks.

RESULTS

Exercise and dihydromyricetin raised serum irisin 1.8 and 1.9 folds as compared to sedentary rats (p <0.001) with no difference between both regimens (p = 0.992). There was an improvement of cardiac remodeling where β-myosin heavy chain level was not different in exercise and dihydromyricetin groups from normal group (p = 0.695, p = 0.470). The heart rate variability domains increased back to normal. However, exercise was superior to dihydromyricetin in improving cardiac contractility by increasing carotid blood flow, stroke volume and cardiac output to be insignificant from normal rats (p = 0.899, p = 0.850, p = 0.912). Meanwhile, treatment with dihydromyricetin showed reduction by 29% of carotid blood flow, 24% of stroke volume and 25% of cardiac output compared to normal rats (p <0.001).

CONCLUSIONS

DHM could mimic the effect of exercise in stimulating irisin secretion but it is not as effective as exercise in improving myocardial contractility.

Alda‑1, an aldehyde dehydrogenase‑2 agonist, improves long‑term survival in rats with chronic heart failure following myocardial infarction

Alda‑1, an aldehyde dehydrogenase 2 (ALDH2) agonist, has been demonstrated to reduce injury caused by acute myocardial infarction (MI) and ischemia/reperfusion. The present study aimed to investigate whether oral administration of Alda‑1 improved long‑term survival of rats with chronic heart failure (CHF) post‑MI. MI model rats treated daily with Alda‑1 exhibited an increase in 20‑week survival rate compared with untreated MI rats. Alda‑1 treatment decreased the heart weight/body weight ratio, collagen volume, left ventricular (LV) internal diameter at the end of diastole and LV internal diameter at the end of systole, while increasing LV ejection fraction with evident LV fractional shortening. Myocardial cell apoptosis index, the activity of caspase‑3 and the expression of cleaved‑caspase‑3 were also reduced by Alda‑1 treatment. The protective effects of Alda‑1 were associated with reduced 4‑hydroxynonenal accumulation. The results of the present study revealed that the long‑term treatment with Alda‑1 prevented the progression of ventricular remodeling and improved the long‑term survival of rats with CHF post‑MI.

Fibulin-2 is essential for angiotensin II-induced myocardial fibrosis mediated by transforming growth factor (TGF)-β

Fibrosis is an ominous pathological process in failing myocardium, but its pathogenesis is poorly understood. We recently reported that loss of an extracellular matrix (ECM) protein, fibulin-2, protected against ventricular dysfunction after myocardial infarction (MI) in association with absence of activation of transforming growth factor (TGF)-β signaling and suppressed upregulation of ECM protein expression during myocardial remodeling. Here we investigated the role of fibulin-2 in the development of myocardial hypertrophy and fibrosis induced by continuous pressor-dosage of angiotensin II (Ang II) infusion. Both wild type (WT) and fibulin-2 null (Fbln2KO) mice developed comparable hypertension and myocardial hypertrophy by Ang II infusion. However, myocardial fibrosis with significant upregulation of collagen type I and III mRNA was only seen in WT but not in Fbln2KO mice.Transforming growth factor (TGF)-β1 mRNA and its downstream signal, Smad2, were significantly upregulated in WT by Ang II, whereas there were no Ang II-induced changes in Flbn2KO, suggesting fibulin-2 is necessary for Ang II-induced TGF-β signaling that induces myocardial fibrosis. To test whether fibulin-2 is sufficient for Ang II-induced TGF-β upregulation, isolated Flbn2KO cardiac fibroblasts were treated with Ang II after transfecting with fibulin-2 expression vector or pretreating with recombinant fibulin-2 protein. Ang II-induced TGF-β signaling in Fbln2KO cells was partially rescued by exogenous fibulin-2, suggesting that fibulin-2 is required and probably sufficient for Ang II-induced TGF-β activation. Smad2 phosphorylation was induced just by adding recombinant fibulin-2 to KO cells, suggesting that extracellular interaction between fibulin-2 and latent TGF-β triggered initial TGF-β activation. Our study indicates that Ang II cannot induce TGF-β activation without fibulin-2 and that fibulin-2 has an essential role in Ang II-induced TGF-β signaling and subsequent myocardial fibrosis. Fibulin-2 can be considered as a critical regulator of TGF-β that induces myocardial fibrosis.

An experimental model of myocardial infarction and controlled reperfusion using a miniaturized cardiopulmonary bypass in rats

OBJECTIVES

Different revascularization strategies for patients with acute myocardial infarction (AMI) exist. It remains unclear whether ventricular unloading using cardiopulmonary bypass (CPB) or extracorporeal life support (ECLS) has an impact on early postischaemic ventricular function. Here, we report on the results of an approach using a miniaturized CPB in a well-established animal model of AMI.

METHODS

In a randomized fashion, 30 male Wistar rats were assigned to temporary left anterior descending (LAD) ligation (30 min) followed by 180 min of reperfusion either with or without 60 min of CPB (70 ml/min, 36°C). The CPB circuit consisted of a venous reservoir, a peristaltic roller pump and a membrane oxygenator with heat exchanger. Cardiac function was measured at 60 and 120 min after reperfusion (F60, F120) using a conductance catheter.

RESULTS

The mortality rate was 37% (11/30). Thus, 19 animals could be included into the analysis (8 CPB). The mean cardiac output did not differ between the groups at F60 [63 ± 29 vs 54 ± 25 ml/min (CPB), P = 0.56] and F120 [73 ± 27 vs 53 ± 24 ml/min (CPB), P = 0.21]. During reperfusion, the mean left ventricular ejection fraction (LVEF) was stable in both the control (F60 37 ± 5% vs F120 33 ± 8%, P = 0.42) and the CPB groups (F60 52 ± 11% vs F120 51 ± 13%, P = 0.71). CPB animals had a significantly better LVEF after reperfusion (F60 P = 0.007, F120 P = 0.01).

CONCLUSIONS

In this animal model of AMI, the establishment of CPB resulted in a significantly better LVEF in comparison with conventional reperfusion only. This beneficial effect may have an impact on revascularization strategies and timing in patients presenting with AMI in the future.

AT1 receptor blockade for the prevention of cardiovascular events after myocardial infarction

Myocardial infarction is associated with high morbidity and mortality. Multiple therapeutic modalities have been shown to be effective in reducing adverse postmyocardial infarction outcomes. The most prominent drugs that have been used in this group of patients are those that oppose the effects of the renin-angiotensin-aldosterone system. These drugs include beta-blockers, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers and aldosterone blockers. Following initial success with angiotensin-converting enzyme inhibitors in reducing mortality and cardiac remodeling in postmyocardial infarction patients, recent focus has been on adjunctive or alternative use of angiotensin II-receptor antagonists. Multiple large-scale, randomized trials have been conducted in order to compare angiotensin II-receptor antagonists with a combination of angiotensin II-receptor antagonists and angiotensin-converting enzyme inhibitors, and with angiotensin-converting enzyme inhibitors alone in postmyocardial infarction patients and also in heart failure. Although some results are conflicting, the weight of evidence is towards equivalency of these two groups of medicines, provided that the maximum effective dose of the angiotensin II-receptor antagonists is used. The combination of an angiotensin-converting enzyme inhibitor and an angiotensin II-receptor antagonist may have additional benefits for some, but not all, patients; for example, reducing morbidity and mortality in patients with chronic heart failure but not in postmyocardial infarction patients. Indeed, in the postmyocardial infarction setting, the combination appears simply to increase the side effects, without conferring additional benefits. Use of aldosterone antagonists as adjunctive therapy in postmyocardial infarction patients is associated with added benefits in terms of mortality reduction and will become the standard of care in this group of patients.

Prevention of remodeling in congestive heart failure due to myocardial infarction by blockade of the renin–angiotensin system

Ventricular remodeling subsequent to myocardial infarction (MI) is a complex process and is considered to be a major determinant of the clinical course of congestive heart failure (CHF). Emerging evidence suggests that activation of the renin-angiotensin system (RAS) plays an important role in post-MI ventricular remodeling; however, it is becoming clear that this is one of several neurohumoral systems that are activated in CHF. Blockade of RAS by angiotensin-converting enzyme inhibitors or angiotensin II type 1 receptor antagonists attenuates the ventricular dysfunction, but the effects of individual drugs in reducing the morbidity and mortality in CHF patients are variable. Furthermore, there is a difference of opinion as to the time of initiation of therapy with RAS blockers after the onset of MI. Since blockade of RAS partially improves cardiac function, it is suggested that a combination therapy involving RAS blockers (angiotensin-converting enzyme inhibitors or angiotensin II type 1 receptor antagonists) and agents that affect other neurohumoral systems may prove useful for improved treatment of CHF. Although activation of RAS has been shown to promote oxidative stress in experimental studies, the use of antioxidant therapy in CHF patients is controversial. Recent experimental studies have shown that ventricular remodeling in CHF is associated with remodeling of subcellular organelles such as sarcolemma, sarcoplasmic reticulum, myofibrils and extracellular matrix in terms of their molecular structure and composition. Since attenuation of remodeling in one and/or more subcellular organelles by different agents may prevent the progression of CHF, it is a challenge to develop specific drugs affecting molecular mechanisms associated with subcellular remodeling for the improved therapy of CHF.

Fibulin-2 deficiency attenuates angiotensin II-induced cardiac hypertrophy by reducing transforming growth factor-β signalling

AngII (angiotensin II) is a potent neurohormone responsible for cardiac hypertrophy, in which TGF (transforming growth factor)-β serves as a principal downstream mediator. We recently found that ablation of fibulin-2 in mice attenuated TGF-β signalling, protected mice against progressive ventricular dysfunction, and significantly reduced the mortality after experimental MI (myocardial infarction). In the present study, we investigated the role of fibulin-2 in AngII-induced TGF-β signalling and subsequent cardiac hypertrophy. We performed chronic subcutaneous infusion of AngII in fibulin-2 null (Fbln2-/-), heterozygous (Fbln2+/-) and WT (wild-type) mice by a mini-osmotic pump. After 4 weeks of subpressor dosage of AngII infusion (0.2 μg/kg of body weight per min), WT mice developed significant hypertrophy, whereas the Fbln2-/- showed no response. In WT, AngII treatment significantly up-regulated mRNAs for fibulin-2, ANP (atrial natriuretic peptide), TGF-β1, Col I (collagen type I), Col III (collagen type III), MMP (matrix metalloproteinase)-2 and MMP-9, and increased the phosphorylation of TGF-β-downstream signalling markers, Smad2, TAK1 (TGF-β-activated kinase 1) and p38 MAPK (mitogen-activated protein kinase), which were all unchanged in AngII-treated Fbln2-/- mice. The Fbln2+/- mice consistently displayed AngII-induced effects intermediate between WT and Fbln2-/-. Pressor dosage of AngII (2 mg/kg of body weight per min) induced significant fibrosis in WT but not in Fbln2-/- mice with comparable hypertension and hypertrophy in both groups. Isolated CFs (cardiac fibroblasts) were treated with AngII, in which direct AngII effects and TGF-β-mediated autocrine effects was observed in WT. The latter effects were totally abolished in Fbln2-/- cells, suggesting that fibulin-2 is essential for AngII-induced TGF-β activation. In conclusion our data indicate that fibulin-2 is essential for AngII-induced TGF-β-mediated cardiac hypertrophy via enhanced TGF-β activation and suggest that fibulin-2 is a potential therapeutic target to inhibit AngII-induced cardiac remodelling.

Exercise training post-MI favorably modifies heart extracellular matrix in the rat

PURPOSE

In order to assess the effect of daily exercise on extracellular matrix remodeling in the heart after myocardial infarction (MI), we measured collagen concentration (%COL) and nonreducible collagen cross-linking (hydroxylysylpyridinoline, HP) in the right ventricle (RV), and regionally within the infarcted (INF) and viable left ventricular free wall (LVF) and septum (LVS), using a rodent MI training model.

METHODS

Infarcts (19%-24% of LV) were surgically induced in adult rats that were assigned to either trained (MI-TR) or sedentary (MI-SED) groups and compared to sham-surgery sedentary controls (SHAM).

RESULTS

In LVF, 10 wk of treadmill running had no effect on the increase (P < 0.001) in %COL seen with MI (MI-SED = 7.14% ± 0.15%, MI-TR = 7.61% ± 0.19%, SHAM = 3.55% ± 0.19%). However, it normalized the increase (P < 0.05) in HP cross-linking (MI-SED = 0.43 ± 0.02, MI-TR = 0.27 ± 0.03, SHAM = 0.30 ± 0.04 mol HP·mol(-1) collagen). The INF scar in MI-SED rats showed a sevenfold increase in %COL (P < 0.001) compared to SHAM LVF myocardium, an increase that was attenuated by training (MI-SED = 26% ± 1% vs MI-TR = 21% ± 2%; P < 0.05). However, training had no effect on MI-induced increases in cross-linking in the INF scar (1.01 ± 0.22 vs 0.84 ± 0.14 mol HP·mol(-1) collagen). In LVS, although a small but significant increase in %COL was seen in both MI groups, HP cross-linking was unaltered compared to SHAM rats. Training also normalized the increase observed in cross-linking in RV after MI.

CONCLUSIONS

Because increased HP cross-linking in the heart is associated with decreased chamber compliance, these findings may help to explain the improved heart function seen after daily exercise in cardiac rehabilitation patients.

Effects of buyang huanwu decoction on ventricular remodeling and differential protein profile in a rat model of myocardial infarction

Buyang Huanwu decoction (BYHWD) is a well-known and canonical Chinese medicine formula from “Correction on Errors in Medical Classics” in Qing dynasty. Here, we show that BYHWD could alleviate the ventricular remodeling induced by left anterior descending (LAD) artery ligation in rats. BYHWD treatment (18 g/kg/day) decreased heart weight/body weight (HW/BW), left ventricle (LV) dimension at end diastole (LVDd) and increased LV ejection fraction (LVEF) and LV fractional shortening (LVFS) significantly compared to model group at the end of 12 weeks. The collagen volume of BYHWD group was more significantly decreased than that of model group. Proteomic analysis showed that atrial natriuretic factor (ANF) was downregulated; heat shock protein beta-6 (HSPB6) and peroxiredoxin-6 (PRDX6) were upregulated in BYHWD-treated group among successfully identified proteins. The apoptotic index (AI) was reduced by BYHWD accompanied by decreased expression of Bax and caspase 3 activity, increased Bcl-2/Bax ratio, and phosphorylation of HSPB6 compared to that of model group. Taken together, these results suggest that BYHWD can alleviate ventricular remodeling induced by LAD artery ligation. The antiremodeling effects of BYHWD are conferred by decreasing AI through affecting multiple targets including increased Bcl-2/Bax ratio and decreased caspase 3 activity that might be via upregulated PRDX6, phosphorylation of HSPB6 and subsequently reduction of ANF.

Cardiac remodeling and function following exercise and angiotensin II receptor antagonism

The purpose of this study was to test the impact of chronic exercise training combined with selective angiotensin II receptor (AT1) antagonism on systolic blood pressure (SBP) and the left-ventricular pressure-volume relationship in normotensive, non-infarcted rat hearts. Wistar rats (N = 19) were randomly assigned to either a sedentary control group (N = 8) or an exercise-trained group (N = 11). Losartan was administered to individually caged rats via the drinking water (10 mg/kg/d). Exercise training consisted of running on a motorized driven treadmill for 6 weeks at 30 m/min, 60 min/day, 5 days/week. Tail cuff SBP was measured weekly. Left ventricular performance was assessed in an ex vivo Langendorff isovolumic mode. One week of losartan treatment significantly reduced SBP in both groups by 13% relative to baseline (P < 0.05). SBP was lower in exercise-trained animals versus sedentary animals in the later weeks of the protocol (P < 0.05) Body weight was significantly lower in exercise-trained animals versus sedentary animals, but heart weight, heart to body weight ratio, atrial weight, and absolute left ventricular mass and length were similar between groups. The LV systolic pressure-volume relationship (PV) and systolic elastance were significantly greater in exercise-trained animals versus sedentary controls (P < 0.05). The left ventricular end-diastolic PV and diastolic stiffness were similar between exercise-trained and sedentary animals. These data suggest that chronic aerobic exercise training can improve the Starling response in the presence of AT1 receptor blockade without altering absolute cardiac size.

Potential role of renin-angiotensin system blockade for preventing myocardial ischemia/reperfusion injury and remodeling after myocardial infarction

Experimental and clinical studies have demonstrated that myocardial ischemia induces activation of various components of the renin-angiotensin system (RAS), including angiotensinogen, renin, angiotensin-converting enzyme (ACE), angiotensins, and angiotensin receptors, in the acute phase of myocardial infarction and the postinfarction remodeling process. Pharmacological inhibition of the RAS by administration of renin inhibitors, ACE inhibitors, and angiotensin receptor blockers has shown beneficial effects on the pathological processes of myocardial infarction in both experimental animal studies and clinical trials. However, the potential mechanisms responsible for the cardioprotection of RAS inhibition remain unclear. In this review, we discuss roles of RAS blocking in the prevention of myocardial ischemia/reperfusion injury and postinfarction remodeling.

Divergent effects of losartan and metoprolol on cardiac remodeling, c-kit+ cells, proliferation and apoptosis in the left ventricle after myocardial infarction

There is strong evidence for the use of angiotensin converting enzyme inhibitors and beta-blockers to reduce morbidity and mortality in patients with myocardial infarction (MI), whereas the effect of angiotensin receptor blockers is less clear. We evaluated the effects of an angiotensin receptor blocker losartan and a beta-blocker metoprolol on left ventricular (LV) remodeling, c-kit+ cells, proliferation, fibrosis, apoptosis, and angiogenesis using a model of coronary ligation in rats. Metoprolol treatment for 2 weeks improved LV systolic function. In contrast, losartan triggered deleterious structural remodeling and functional deterioration of LV systolic function, ejection fraction being 41% and fractional shortening 47% lower in losartan group than in controls 2 weeks after MI. The number of c-kit+ cells as well as expression of Ki-67 was increased by metoprolol. Losartan-induced thinning of the anterior wall and ventricular dilation were associated with increased apoptosis and fibrosis, while losartan had no effect on the expression of c-kit or Ki-67. Metoprolol or losartan had no effect on microvessel density. These results demonstrate that beta-blocker treatment attenuated adverse remodeling via c-kit+ cells and proliferation, whereas angiotensin receptor blocker-induced worsening of LV systolic function was associated with increased apoptosis and fibrosis in the peri-infarct region.

Effects of exercise and L-arginine on ventricular remodeling and oxidative stress

OBJECTIVE

Our aim was to characterize the changes in messenger RNA (mRNA) abundance, protein, and activity levels of the enzymatic antioxidants, superoxide dismutase (SOD), glutathione peroxidase, and catalase by exercise training combined with L-arginine after myocardial infarction (MI).

METHODS

L-Arginine (1 g x kg(-1) x d(-1)) and N(G)-nitro-L-arginine methyl ester (L-NAME; 10 mg x kg(-1) x d(-1)) were administered in drinking water for 8 wk. Sprague-Dawley rats were randomized to the following groups: sham-operated control (Sham); MI sedentary (Sed); MI exercise (Ex); MI sedentary + L-arginine (Sed + LA); MI exercise + L-arginine (Ex + LA); MI sedentary + L-NAME (Sed + L-NAME); and MI exercise + L-NAME (Ex + L-NAME).

RESULTS

The glutathione peroxidase, catalase, and gp91(phox) mRNA levels were comparable among all the groups. The SOD mRNA level was significantly increased in the Ex group (5.43 +/- 0.87) compared with the Sed group (1.74 +/- 0.29), whereas this effect was pronouncedly down-regulated by the L-NAME intervention (2.51 +/- 1.17, P < 0.05). The protein levels of SOD in the Sed and Ex groups were both significantly decreased with the administration of L-NAME. The protein levels of catalase were significantly higher in the Ex and Ex + LA groups than that in the Sed, Sed + LA, and L-NAME-treated groups. The collagen volume fraction was significantly lowered by the exercise and/or L-arginine treatment when compared with the Sed group. Fractional shortening was significantly preserved in the trained groups compared with their corresponding sedentary groups with or without drug treatments. However, the beneficial effect was not further improved by L-arginine treatment.

CONCLUSIONS

Our results suggest that exercise training exerts antioxidative effects and attenuates myocardial fibrosis in the MI rats. These improvements, in turn, alleviate cardiac stiffness and preserve post-MI cardiac function. In addition, L-arginine appears to have no additive effect on cardiac function or expression of enzymatic antioxidants.

Effect of early versus late AT(1) receptor blockade with losartan on postmyocardial infarction ventricular remodeling in rabbits

To characterize the temporal activation of the renin-angiotensin system after myocardial infarction (MI) in rabbits, we examined cardiac ANG II type 1 receptor (AT(1)R) expression and ANG II levels from 3 h to 35 days. The effects of losartan (12.5 mg.kg(-1).day(-1)) on functional and histomorphometric parameters when treatment was initiated early (3 h) and late (day 15) post-MI and maintained for different periods of time [short term (4 days), midterm (20 days), and long term (35 days)] were also studied. AT(1)R expression increased in the MI zone at 15 and 35 days (P < 0.05). ANG II levels increased (P < 0.05) in the non-MI zone at 24 h and in the MI zone as well as in plasma at 4 days and then progressively decreased until 35 days. The survival rate was significantly lower in untreated MI and early long-term-treated animals. Diastolic pressure-volume curves in MI at 35 and 56 days shifted to the right (P < 0.05). This shift was even more pronounced in long-term-treated groups (P < 0.05). Contractility decreased (P < 0.05 vs. sham) in the untreated and long-term-treated groups and was attenuated in the midterm-treated group. The early administration of losartan reduced RAM 11-positive macrophages from 4.15 +/- 0.05 to 3.05 +/- 0.02 cells/high-power field (HPF; P < 0.05) and CD45 RO-positive lymphocytes from 2.23 +/- 0.05 to 1.48 +/- 0.01 cells/HPF (P < 0.05) in the MI zone at 4 days. Long-term treatment reduced the scar collagen (MI: 70.50 +/- 2.35% and MI + losartan: 57.50 +/- 2.48, P < 0.05), determined the persistency of RAM 11-positive macrophages (3.02 +/- 0.13 cells/HPF) and CD45 RO-positive lymphocytes (2.77 +/- 0.58 cells/HPF, P < 0.05 vs. MI), and reduced the scar thinning ratio at 35 days (P < 0.05). Consequently, the temporal expressions of cardiac AT(1)R and ANG II post-MI in rabbits are different from those described in other species. Long-term treatment unfavorably modified post-MI remodeling, whereas midterm treatment attenuated this harmful effect. The delay in wound healing (early reduction and late persistency of inflammatory infiltrate) and adverse remodeling observed in long-term-treated animals might explain the unfavorable effect observed in rabbits.

Left ventricle radio-frequency ablation in the rat: a new model of heart failure due to myocardial infarction homogeneous in size and low in mortality

BACKGROUND

The purpose of the current study was to create a model of myocardial infarction (MI) that is homogeneous in size with a low immediate (24 hours) mortality.

METHODS AND RESULTS

Male and female rats (n = 256) underwent left ventricle (LV) ablation (Ab) by a radiofrequency current (1000 kHz; 12 watts for 12 seconds) to promote a MI. A transmural MI occurred in all rats. Post-Ab complex arrhythmias were frequent (atrioventricular block, ventricular tachycardia, and fibrillation), which rapidly and spontaneously reverted to sinus rhythm. Among 66 male rats, immediate mortality occurred in 7.5%. Small MI size dispersion was characterized by smaller variability following Ab (x +/- SD: 45 +/- 8%) when compared with coronary occlusion (Oc; 40 +/- 19%). The histopathologic evaluations identified lesions similar to those which occurred following Oc, with scarring complete at 4 weeks. The hemodynamic and Doppler echocardiograms showed comparable increases in LV dimension, end-diastolic pressure, and pulmonary water content 1 and 4 weeks post-MI. Papillary muscle mechanics 6 weeks post-MI had matched inotropic and lusitropic dysfunction.

CONCLUSIONS

LV Ab gave rise to a MI within a narrow size limit and with a low immediate mortality. LV Ab resulted in histopathologic evolution, ventricular dilation, and dysfunction, impairment in myocardial mechanics, and congestive outcome that reproduced a MI from Oc.

Effects of exercise training on cardiac function and myocardial remodeling in post myocardial infarction rats

To test the hypothesis that early exercise training after myocardial infarction (MI) could preserve cardiac function, alleviate left ventricular (LV) remodeling and induce a protective effect on morphology, male Sprague-Dawley rats underwent coronary ligation or sham operation, and were assigned to 3 groups: Sham, sedentary MI (SedMI), and exercise MI (ExMI). We measured the changes in collagen volume fraction, matrix metalloproteinase (MMP) 1, tissue inhibitor matrix metalloproteinase 1 (TIMP-1), angiotensin II receptor type 1 (AT1), and angiotensin converting enzyme (ACE) at gene and protein levels after 8 weeks of exercise training. Cardiac functions were determined by echocardiographic and hemodynamic measurements. Early exercise training after MI had no effect on LV wall thinning. Cardiac function was significantly preserved in the ExMI group in comparison to the SedMI group. The collagen volume fraction in the ExMI group was significantly lower than in the SedMI group. Compared to the SedMI group, the ExMI group showed a markedly decrease at both the gene and protein levels in TIMP-1 (P<0.05). No significant differences were found in MMP-1 among the three groups. MMP-1/TIMP-1 ratio in the ExMI group was significantly higher than in the SedMI group. In addition, the expression of AT1 protein in the ExMI group was significantly lower than in the SedMI group. Furthermore, both ACE mRNA expression and ACE binding in the ExMI group are significantly decreased compared to the SedMI group. Our results suggest that early exercise training after MI reduces TIMP-1 expression, improves the balance between MMPs and TIMPs, and mitigates the expressions of ACE and AT1 receptor. These improvements, in turn, attenuate myocardial fibrosis and preserve post-MI cardiac function.

Additive effects of combined blockade of AT1receptor and HMG-CoA reductase on left ventricular remodeling in infarcted rats

Both angiotensin receptor antagonists and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors have been shown to attenuate cardiomyocyte hypertrophy after myocardial infarction. Whether combination treatment may be superior to either drug alone on cardiomyocyte hypertrophy remains unclear. After ligation of the left anterior descending artery, rats were randomized to both, one, or neither of the angiotensin receptor antagonists olmesartan (0.01, 0.1, 1, and 2 mg·kg−1·day−1) and HMG-CoA reductase inhibitor pravastatin (5 mg·kg−1·day−1) for 4 wk. Each drug, when given alone, decreased cardiomyocyte sizes isolated by enzymatic dissociation at the border zone when compared with vehicles. However, compared with either drug alone, combined olmesartan and pravastatin prevent cardiomyocyte hypertrophy to a larger extent, which was further confirmed by downregulation of the left ventricular atrial natriuretic peptide mRNA. The myocardial endothelin-1 levels at the border zone were 6.5-fold higher ( P <0.0001) in the vehicle group compared with the sham group, which can be inhibited after pravastatin administration. Combination treatment significantly attenuated cardiomyocyte hypertrophy in a dose-dependent manner, although tissue endothelin-1 levels remained stable in combination groups of different olmesartan doses. Measurements of the arrhythmic score mirrored those of cardiomyocyte hypertrophy. Dual therapy with pravastatin and olmesartan, which produced an additive reduction in cardiomyocyte hypertrophy and cardiac fibrosis after myocardial infarction through different mechanisms, decreases the propensity of the heart to arrhythmogenesis. Pravastatin administration provided favorable ventricular remodeling, probably through decreased tissue endothelin-1 level. In contrast, olmesartan-related attenuated cardiomyocyte hypertrophy is independent of endothelin-1 pathway.

Role of angiotensin receptor blockers in the prevention and treatment of arrhythmias

The renin-angiotensin system is a key regulatory system that is activated in many forms of cardiovascular disease. It is well established that angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) are important therapeutic agents in the treatment of hypertension, myocardial infarction, and congestive heart failure. More recent research has suggested that renin-angiotensin system activation may also play a critical role in the genesis of atrial and ventricular arrhythmias. The possible role of renin-angiotensin system activation in arrhythmogenesis suggests that ACE inhibitors and ARBs may be important therapeutic agents in the prevention and treatment of arrhythmias. This review summarizes the current evidence for the use of ARBs in the treatment of atrial and ventricular arrhythmias.

Effects of the early administration of losartan on the functional and morphological aspects of postmyocardial infarction ventricular remodeling in rabbits

BACKGROUND

The effects of losartan (Los) on ventricular remodeling (VR) remain controversial. The objective was to determine whether early administration of Los to rabbits with myocardial infarction (MI) modifies VR.

METHODS

New Zealand rabbits underwent left coronary artery ligation. Four groups were analyzed: Sham (G(1); n = 13), MI (G(2); n = 13), Sham+Los (G(3); n = 13), and MI+Los (G(4); n = 13). Los (12.5 mg/kg/day) was administered from 3 h post-MI and during 35 days. At the end of the protocol, the hearts were isolated and perfused to determine pressure-volume curves (P/V). Hearts were weighed, cut, and stained with picrosirius red. The heart weight (HW)/body weight (BW) ratio was determined. Infarct size (IS;%), septum (SeT, mm) and scar thickness (ST, mm), myocyte area (microm(2)), and width (mum) were measured. RESULTS (X +/- S.E.M.): Los shifted the diastolic left ventricular (LV) P/V relationship to the right in sham and MI (P < .05 vs. sham), with no changes in the systolic relation. IS was G(2) = 25.38 +/- 5.31 and G(4) = 21.85 +/- 4.13 (NS); HW/BW was 0.34+/-0.01, 0.35 +/- 0.02, 0.29 +/- 0.02 (P < .05 vs. G(1) and G(2)), and 0.32 +/- 0.02 in G(1), G(2), G(3), and G(4), respectively. Scar collagen concentration (%) was lower in G(4) (P < .05 vs. G(2)). SeT was lower in G(3) and G(4) (P < .05 vs. G(2)). The width and area of the septum myocytes increased in the untreated infarct, and Los suppressed that increase.

CONCLUSION

The early administration of Los unfavorably modified post-MI VR, increasing ventricular dilation, reducing scar collagen concentration and thickness, and inhibiting myocytes width and area increase. The dilation observed in sham animals' hearts suggests that infarct was not the main factor in the dilation of the cavity.

Effects of pre-, peri-, and postmyocardial infarction treatment with losartan in rats: effect of dose on survival, ventricular arrhythmias, function, and remodeling

Angiotensin receptor blockers (ARBs) reduce adverse left ventricular (LV) remodeling and improve LV function and survival when started postmyocardial infarction (MI). ARBs also reduce ventricular arrhythmias during ischemia-reperfusion injury when started pre-MI. No information exists regarding their efficacy and safety when started pre-MI and continued peri- and post-MI. We evaluated whether the ARB losartan improves the outcome when started pre-MI and continued peri- and post-MI. Male Wistar rats (n = 502) were treated for 7 days pre-MI with losartan at a high dose (30 mg.kg(-1).day(-1)), progressively increasing dose (3 mg.kg(-1).day(-1) increased to 10 mg.kg(-1).day(-1) 10 days and 30 mg.kg(-1).day(-1) 20 days post-MI), or no treatment. Ambulatory systolic blood pressure and Holter monitoring were performed for 24 h post-MI. Echocardiography was done 30 days post-MI, and LV remodeling, cardiac hemodynamics, and fetal gene expression were assessed 38 days post-MI. High-dose losartan reduced 24-h post-MI survival compared with the progressive dose and control (21.9% vs. 36.6% and 38.1%, P = 0.033 and P = 0.009, respectively). This was associated with greater hypotension in the high dose and no change in ventricular arrhythmias in all groups. In 24-h post-MI survivors, the progressive dose group had reduced mortality from 24 h to 38 days (8.5% vs. 28.6% for control vs. 38.9% for high dose, P = 0.032 and P = 0.01, respectively). Survivors of both losartan groups demonstrated improved LV remodeling, cardiac hemodynamics, preserved GLUT-4, and reduced cardiac fetal gene expression. Pretreatment with ARBs does not reduce 24-h post-MI ventricular arrhythmias or survival, and high doses increase mortality by causing excessive hypotension. In 24-h post-MI survivors, progressively increasing doses of losartan have multiple beneficial effects, including improved survival.

Effects of differential blockade of the renin-angiotensin system in postinfarcted rats

The present study compared short-term effects of the AT(1)-receptor antagonist, irbesartan with the angiotensin-converting enzyme (ACE) inhibitor, enalapril on systemic haemodynamics and cardiac remodelling in post-myocardia-infarcted (MI) rats. MI Sprague-Dawley rats were orally treated for 4 weeks with irbesartan (50 mg/kg/day) or enalapril (10 mg/kg/day). Then, cardiac and systemic haemodynamics were measured. Compared with the sham-operated group, left ventricular end-diastolic pressure (LVEDP), diastolic pressure (LVDP), heart weight to body weight ratio were all significantly increased in the MI group while the LV contractility (dP/dt) and pulsatile arterial pressure were significantly reduced. Both drugs reduced the elevated LVEDP and LVDP and prevented cardiac hypertrophy. Furthermore, irbesartan attenuated the right shift of the pressure-volume curves, prevented postinfarction-induced increase in urinary cyclic guanosine monophosphate and reduced urinary aldosterone excretion. Although both drugs were able to prevent further cardiac hypertrophy and improved cardiac filling pressure, only irbesartan limited LV dilatation. These data indicate that blockade of the renin-angiotensin system at the level of AT1 receptors may have a better cardioprotective benefit than reducing angiotensin II levels by ACE inhibition.

Prevention of Sympathetic and Cardiac Dysfunction After Myocardial Infarction in Transgenic Rats Deficient in Brain Angiotensinogen

To provide evidence for the role of angiotensin II locally produced in the brain in the development of sympathetic hyperactivity and heart failure after myocardial infarction (MI), transgenic rats (TGR) were used, which express an antisense RNA against angiotensinogen. In TGR and control Sprague-Dawley (SD) rats, an MI was induced by acute coronary artery ligation. At 8 weeks after MI, MI sizes were similar in TGR and SD rats. In the groups with MI > or =25% of left ventricle (LV), LV peak systolic pressure decreased in SD rats but not in TGR. LV end-diastolic pressure increased substantially more in SD-MI than TGR-MI rats (from 2+/-1 to 15+/-2 mm Hg, and 2+/-1 to 8+/-1 mm Hg, respectively; P<0.05). LV dP/dtmax decreased from approximately 5400 to 3573+/-187 in SD-MI rats, but only to 4353+/-180 mm Hg/sec in TGR-MI (P<0.05). LV pressure volume curves in vitro showed a marked shift to the right in SD-MI rats. This shift was significantly attenuated by -70% in TGR versus SD rats with MI. Both RV weight and interstitial fibrosis in the LV increased clearly in the SD-MI rats, but not or significantly less in the TGR-MI rats. In SD-MI rats, arterial baroreflex control of heart rate and renal sympathetic nerve activity was markedly impaired but was not affected in the TGR-MI. Plasma angiotensin II levels tended to be higher in SD versus TGR rats, both in sham and MI-groups. This study provides the major new finding that in rats after MI, angiotensin II locally produced in the brain plays a dominant role in the development of LV dysfunction after MI, possibly through its effects on sympathetic function and on circulatory/cardiac renin-angiotensin system.

Comparative effects of carvedilol and losartan alone and in combination for preventing left ventricular remodeling after acute myocardial infarction in rats

It has been verified that losartan has beneficial effects on ventricular remodeling (VRM) after acute myocardial infarction (AMI), but the effects of carvedilol alone or in combination with losartan on this condition have not been defined. The present study used rats to compare the effects of carvedilol and losartan alone and in combination for preventing VRM after AMI. After ligation of the left coronary artery, 100 surviving female Sprague-Dawley rats were randomly assigned to 1 of 4 groups: (1) AMI control (n=25), (2) carvedilol (Car, 1 mg x kg(-1) x day(-1)) (n=25), (3) losartan (Los, 3 mg x kg(-1) x day (-1)) (n=25), and (4) Car (1 mg x kg (-1). day(-1)) + Los (3 mg x kg(-1) x day (-1)) (n=25). A sham-operated group (n=17) was also randomly selected. Drugs were administered by gastric gavage for 4 weeks. After hemodynamic studies, the hearts were fixed and analyzed pathologically. Exclusive of the rats that had died or had an infarct size <35% or >55%, complete data were obtained for 65 rats, comprising AMI control (n=13), Car (n=12), Los (n=13), combination (n=14), and sham (n=13) groups. There were no significant differences in the size of infarct among the 4 AMI groups (45.8 approximately 46.7%, all p>0.05). Compared with the sham group, left ventricular (LV) end-diastolic pressure (LVEDP), volume (LVV), weight (LVW) and septal thickness (STh) were all significantly increased (all p<0.001), whereas +/-dp/dt was significantly decreased (both p<0.001) in the AMI group. In comparison with the AMI group, LVEDP, LVV, LVW and STh were all significantly decreased (LVEDP: 12.7+/-2.3, 9.7+/-2.8, and 8.6+/-3.5 mmHg vs 20.6+/-2.7 mmHg, all p<0.001; LVV: 0.74+/-0.07, 0.76+/-0.07, and 0.70+/-0.09 ml vs 0.86+/-0.05 ml, all p<0.05; LVW: 668.4+/-52.0, 702.6+/-45.4, and 683.9+/-67.7 mg vs 787.3+/-76.7 mg, p<0.05 approximately 0.001; STh: 1.57+/-0.05, 1.48+/-0.07, and 1.46+/-0.07 mm vs 1.71+/-0.04 mm, all p<0.05), whereas +/-dp/dt was significantly increased (all p<0.05) in the Car, Los, and combination groups, with LVEDP decreasing more in both Los and the combination groups than in the Car group alone (p<0.05) and STh decreasing more in the combination group than in the Car group alone (p<0.05). Carvedilol and losartan alone and in combination all prevent VRM after AMI in rats, with almost equivalent effect.

Influence of gender on the response to hemodynamic overload after myocardial infarction

After myocardial infarction (MI), the left ventricle (LV) undergoes ventricular remodeling characterized by progressive global dilation, infarct expansion, and compensatory hypertrophy of the noninfarcted myocardium. Little attention has been given to the response of remodeling myocardium to additional hemodynamic overload. Studies have indicated that gender may influence remodeling and the response to both MI and hemodynamic overload. We therefore determined 1) structural and function consequences of superimposing hemodynamic overload (systemic hypertension) on remodeling myocardium after a MI and 2) the potential influence of gender on this remodeling response. Male and female Dahl salt-sensitive and salt-resistant rats underwent coronary ligation, resulting in similar degrees of MI. One week post-MI, all rats were placed on a high-salt diet. Four groups were then studied 4 wk after initiation of high-salt feeding: MI female, MI female + hypertension, MI male, and MI male + hypertension. Hypertension-induced pressure overload resulted in additional comparable degrees of myocardial hypertrophy in both females and males. In females, hypertension post-MI resulted in concentric hypertrophy with no additional cavity dilation and no measurable scar thinning. In contrast, in males, hypertension post-MI resulted in eccentric hypertrophy, further LV cavity dilation, and scar thinning. Physiologically, concentric hypertrophy in post-MI hypertensive females resulted in elevated contractile function, whereas eccentrically hypertrophied males had no such increase. Female gender influences favorably the remodeling and physiological response to hemodynamic overload after large MI.

Effects of cariporide and losartan on hypertrophy, calcium transients, contractility, and gene expression in congestive heart failure

BACKGROUND

The purpose of this study was to compare long-term effects of cariporide with those of losartan in postinfarction heart failure.

METHODS AND RESULTS

Female Sprague-Dawley rats with large myocardial infarctions and sham controls were randomized to losartan, cariporide, or placebo after 7 days and treated for 49 days. Cardiac function was assessed by echocardiography and measurement of left ventricular pressures, and gene expression was assessed by competitive reverse transcription-polymerase chain reaction. Cell dimensions, shortening, and relaxation were determined by videomicroscopy and calcium transients by fura 2. Losartan reduced postinfarction systolic and diastolic left ventricular dilation (by 24% and 31%, respectively), left and right ventricular weight (by 22% and 26%, respectively), and cardiomyocyte hypertrophy length and width (by 62% and 54%, respectively). Induction of myocardial atrial natriuretic peptide decreased 66%. Cariporide did not affect postinfarction hypertrophy or atrial natriuretic peptide. Losartan and cariporide respectively improved reduced cellular contractility (55% and 30%) and reduced elevated systolic (86% and 27%) and diastolic (49% and 43%) calcium. Losartan and cariporide respectively reduced prolonged time to 50% relaxation (66% and 25%) and time to 50% calcium reduction (55% and 53%).

CONCLUSIONS

Losartan and cariporide improve cardiomyocyte contractility and calcium regulation in chronic heart failure. Losartan has salutary effects on postinfarction remodeling and gene expression, whereas cariporide is neutral.

Cell therapy attenuates deleterious ventricular remodeling and improves cardiac performance after myocardial infarction

BACKGROUND

Myocardial infarction (MI) promotes deleterious remodeling of the myocardium, resulting in ventricular dilation and pump dysfunction. We examined whether supplementing infarcted myocardium with skeletal myoblasts would (1) result in viable myoblast implants, (2) attenuate deleterious remodeling, and (3) enhance in vivo and ex vivo contractile performance.

METHODS AND RESULTS

Experimental MI was induced by 1-hour coronary ligation followed by reperfusion in adult male Lewis rats. One week after MI, 10(6) myoblasts were injected directly into the infarct region. Three groups of animals were studied at 3 and 6 weeks after cell therapy: noninfarcted control (control), MI plus sham injection (MI), and MI plus cell injection (MI+cell). In vivo cardiac function was assessed by maximum exercise capacity testing and ex vivo function was determined by pressure-volume curves obtained from isolated, red cell-perfused, balloon-in-left ventricle (LV) hearts. MI and MI+cell hearts had indistinguishable infarct sizes of approximately 30% of the LV. At 3 and 6 weeks after cell therapy, 92% (13 of 14) of MI+cell hearts showed evidence of myoblast graft survival. MI+cell hearts exhibited attenuation of global ventricular dilation and reduced septum-to-free wall diameter compared with MI hearts not receiving cell therapy. Furthermore, cell therapy improved both post-MI in vivo exercise capacity and ex vivo LV systolic pressures.

CONCLUSIONS

Implanted skeletal myoblasts form viable grafts in infarcted myocardium, resulting in enhanced post-MI exercise capacity and contractile function and attenuated ventricular dilation. These data illustrate that syngeneic myoblast implantation after MI improves both in vivo and ex vivo indexes of global ventricular dysfunction and deleterious remodeling and suggests that cellular implantation may be beneficial after MI.