MI Rats Research Articles

Biodegradation and heart retention of polymeric microparticles in a rat model of myocardial ischemia

Poly-lactide-co-glycolide (PLGA) microparticles emerged as one of the most promising strategies to achieve site-specific drug delivery. Although these microparticles have been demonstrated to be effective in several wound healing models, their potential in cardiac regeneration has not yet been fully assessed. The present work sought to explore PLGA microparticles as cardiac drug delivery systems. PLGA microparticles were prepared by Total Recirculation One-Machine System (TROMS) after the formation of a multiple emulsion. Microparticles of different size were prepared and characterized to select the most suitable size for intramyocardial administration. Next, the potential of PLGA microparticles for administration in the heart was assessed in a MI rat model. Particle biodegradation over time and myocardial tissue reaction were studied by routine staining and confocal microscopy. Results showed that microparticles with a diameter of 5μm were the most compatible with intramyocardial administration in terms of injectability through a 29-gauge needle and tissue response. Particles were present in the heart tissue for up to 3months post-implantation and no particle migration toward other solid organs was observed, demonstrating good myocardial retention. CD68 immunolabeling revealed 31%, 47% and below 4% microparticle uptake by macrophages 1week, 1month, and 3months after injection, respectively (P<0.001). Taken together, these findings support the feasibility of the developed PLGA microparticles as vehicles for delivering growth factors in the infarcted myocardium.

INSULIN IMPROVES POST-ISCHAEMIC CARDIAC STRUCTURAL AND FUNCTIONAL CHANGES VIA INHIBITING P38 MAPK ACTIVATION AND THUS INCREASING PLASMA BNP LEVEL

ObjectivesInsulin has been shown to possess cardioprotective effect in acute myocardial ischaemia/reperfusion (MI/R). The present study attempted to test whether long term insulin treatment influences adverse prolonged post-ischaemic cardiac structural...

Early and Delayed Tranilast Treatment Reduces Pathological Fibrosis Following Myocardial Infarction

Tranilast has been shown to inhibit TGFβ1-related fibrosis and organ failure in various disease models. We sought to examine the effects of tranilast on left ventricular (LV) remodelling post-MI. Following coronary artery ligation, Sprague Dawley rats were randomised to receive tranilast (300mg/kg/d, p.o.) or vehicle control over one of two treatment periods: (1) from 24h until seven days post-MI, (2) from seven days to 28 days post-MI. Cardiac tissue was harvested for molecular, immunohistochemical and cell culture analyses. Tranilast treatment of MI rats from 24h until seven days post-MI reduced myocardial collagen content, α1 (I) procollagen, TGFβ1 and CTGF mRNA transcripts, monocyte/macrophage infiltration and exacerbated infarct expansion compared with vehicle-treatment. Delaying the commencement of tranilast treatment to seven days post-MI attenuated myocardial fibrosis, gene expression of α1(I) procollagen, α1(III) procollagen, fibronectin, TGFβ1 and CTGF mRNA transcripts, and monocyte/macrophage infiltration at 28d compared to vehicle-treatment, without detriment to infarct healing. Extended post-MI also preserved LV infarct size. In cultures of rat cardiac fibroblasts, tranilast attenuated TGFβ1-stimulated fibrogenesis. Tranilast inhibits myocardial TGFβ1 expression, fibrosis in rat post-MI and collagen production in cardiac fibroblasts. While tranilast intervention from 24h post-MI exacerbated infarct expansion, delaying the commencement of treatment to seven days post-MI impeded LV remodelling.

Improved mesenchymal stem cell survival in ischemic heart through electroacupuncture

To investigate whether electroacupuncture (EA) can promote cell survival and enhance heart function of mesenchymal stem cells (MSCs) therapy. MSCs were isolated from bone marrow and expanded in Minimum Essential Medium Alpha (α-MEM). MI was induced in 72 Sprague-Dawley (S-D) rats by ligation of the left anterior descending coronary artery (LAD) for 30 min and reperfusion. MI rats randomly received injection of 1×10(6) DiI-labeled MSCs alone (n =24, MSC group), or plus electroacupuncture (EA) at Neiguan (PC6, n=24, EA+MSC group), or saline (n =24, saline group). EA treatment was performed for 4 days. Another 24 rats were subjected to chest-open surgery without LAD occlusion and treatment (sham group). Three time points, 4, 14 and 28 days (n =8 for each group) were included in this study. The survival of transplanted MSCs and the protective gene expression were analyzed by reverse transcriptase polymerase chain reaction (RT-PCR) and Western blot at day 4 and 14. Left ventricular remodeling, cardiac function, infarction area, fibrosis and capillary density were analyzed at day 28. EA can enhance MSC survival (2.6-fold up) at day 4. Big capillary density was 53% higher in EA+MSC treated group than MSC alone group. Furthermore, the rats treated by EA reduced the fibrosis and had 36% smaller infarct size comparing to MSC alone. EA also attenuated left ventricular remodeling and enhanced the functional recovery of infarcted hearts at week 4. EA at Neiguan acupoint can promote the stem cell survival and improve ischemic heart function. EA could become a useful approach in stem cell therapy for ischemia heart diseases.

Effects of sildenafil and/or muscle derived stem cells on myocardial infarction

BackgroundPrevious studies have shown that long-term oral daily PDE 5 inhibitors (PDE5i) counteract fibrosis, cell loss, and the resulting dysfunction in tissues of various rat organs and that implantation of skeletal muscle-derived stem cells (MDSC) exerts some of these effects. PDE5i and stem cells in combination were found to be more effective in non-MI cardiac repair than each treatment separately. We have now investigated whether sildenafil at lower doses and MDSC, alone or in combination are effective to attenuate LV remodeling after MI in rats.MethodsMI was induced in rats by ligature of the left anterior descending coronary artery. Treatment groups were: “Series A”: 1) untreated; 2) oral sildenafil 3 mg/kg/day from day 1; and “Series B”: intracardiac injection at day 7 of: 3) saline; 4) rat MDSC (106 cells); 5) as #4, with sildenafil as in #2. Before surgery, and at 1 and 4 weeks, the left ventricle ejection fraction (LVEF) was measured. LV sections were stained for collagen, myofibroblasts, apoptosis, cardiomyocytes, and iNOS, followed by quantitative image analysis. Western blots estimated angiogenesis and myofibroblast accumulation, as well as potential sildenafil tachyphylaxis by PDE 5 expression. Zymography estimated MMPs 2 and 9 in serum.ResultsAs compared to untreated MI rats, sildenafil improved LVEF, reduced collagen, myofibroblasts, and circulating MMPs, and increased cardiac troponin T. MDSC replicated most of these effects and stimulated cardiac angiogenesis. Concurrent MDSC/sildenafil counteracted cardiomyocyte and endothelial cells loss, but did not improve LVEF or angiogenesis, and upregulated PDE 5.ConclusionsLong-term oral sildenafil, or MDSC given separately, reduce the MI fibrotic scar and improve left ventricular function in this rat model. The failure of the treatment combination may be due to inducing overexpression of PDE5.

Abstract 106: A Novel Small Molecule Protects Against Myocardial Ischemia and Doxorubicin-Induced Cardiomyopathy Through Heat Shock Response and Proteostasis Regulation In Vivo

Background: A potentially new non-cell-based therapy is the systemic delivery of small molecules to revive or protect injured myocardium. By screening a drug library, we identified a novel small molecule, sk421, and tested its effectiveness in two myocardial injury models in vivo: a myocardial infarction model and doxorubicin (DOX)-induced cardiomyopathy model. Results: Sk421 significantly increased cellular viability of DOX-injured cardiomyocytes by preventing apoptosis in vitro, demonstrated by assays for MTT (p=0.042), annexin-V, and active caspase-3 (p=0.004). Sk421 increased the concentrations of the GATA4 and the heat shock proteins (HSPs) in cardiomyocytes (by 1.5-fold), and fibroblasts (by 1.2-fold), but was unable to rescue DOX-injured fibroblast cells depleted of HSPs. Sk421 maintained the total proteosome by a 3.5-fold inhibition of ubiquitinized GATA4 degradation, as shown by immunoprecipitation assays. Oral administration of sk421(4mg/kg) rescued DOX-injured mice by significantly preserving cardiac function, weight gain, cardiomyocyte lesion size and abundance, and by reducing overall mortality (20% in treated groups) compared to control DOX-injured mice (80% in untreated groups, p&lt;0.03). The levels of GATA4 and HSPs were increased in the sk421-rescued mice. In the MI model, (n=5/group), sk421 reduced myocardial infarct size, and protected heart function evaluated by ejection fraction 45.8 ± 2.4 vs. 34.8 ± 3.3, p=0.005 (day7), and 44.3 ± 2.8 vs. 34.4 ± 4.1, p=0.011 (day28). Sk421 treatment of MI rats resulted in a higher fraction of viable tissue (within the LV (70.20 ± 0.5024, n=3) as compared to only MI group (56.38 ± 3.879%, n=3) and the infiltration of CD68+ cells was found to be more in the infarct region of LV of MI group rats as compared to MI+CEL. Quantitative analysis showed a significantly higher proportion of TUNEL positive cells and mRNA levels of IL-1β, IL-6, TNF-α and MMP2 in the myocardium of MI rats compared to MI+SK421 rats. Conclusion: This study demonstrates the broad therapeutic benefit of sk421 in animal model of myocardial injury by mechanism of inducing the heat shock response and preserving GATA levels. The ease of oral delivery makes sk421 a potentially clinically useful adjunct for myocardial preservation.

Abstract 240: Interruption of Ivabradine Treatment in Middle-Aged Post-MI Rats May Lead to Heart Failure

Background: We have previously demonstrated that heart rate reduction (HRR) with the selective cardiac pacemaker I f current inhibitor ivabradine (IVA) improved LV function and coronary perfusion reserve in post-MI middle-aged rats. The beneficial effects of IVA treatment were associated with attenuated collagen accumulation in the surviving LV myocardium and inhibition of the circulatory renin-angiotensin system. However, sustainability of these positive changes after a period of IVA treatment interruption remains to be determined. Methods: MI was induced in 12-month-old male Sprague-Dawley rats by left coronary artery ligation. Twenty four hours later, the rats with a confirmed large transmural MI were randomly assigned in two experimental groups. In a first group, rats were treated with IVA i.p. via osmotic pumps in a dose of 10.5 mg/kg/d for 4 weeks followed by a 4-week period without treatment (MI+IVA). In a second group, rats received placebo for 4 weeks (MI). Sham-operated rats served as a control. Eight weeks after MI, the various LV parameters were examined. Results: During 4 weeks of treatment, heart rate in MI+IVA rats was consistently reduced compared to untreated MI rats (mean of HRR was 27%). After IVA withdrawal, heart rate increased to the levels of the placebo group. Eight weeks after MI, the IVA treated group demonstrated smaller LV free wall infarct size (57.5 ± 2.7% vs. 72.5 ± 2.5%, p&lt;0.01) and greater LV weight/body weight ratio (2.54 ± 0.06 vs. 2.26 ± 0.11 mg/g, p&lt;0.05), indicating greater myocardial compensatory hypertrophy. Furthermore, the interstitial collagen content was significantly lower in the remote LV myocardium of MI+IVA rats compared to MI rats (7.5 ± 0.7% vs. 13.3 ± 1.0% in free wall and 7.3 ± 0.8% vs. 11.2 ± 0.9% in septum, p &lt; 0.01). However, compared to non-infarcted controls, rats of both MI groups had markedly lower LV ejection fraction and coronary perfusion reserve. Conclusions: Our data demonstrate that although beneficial structural changes induced by IVA in post-MI myocardium can be sustainable for a long period of time they cannot prevent deterioration of LV function after withdrawal of treatment. Therefore, we believe that continuous treatment with IVA may be essential for attenuation of heart failure after a large MI.

Abstract 234: Transcriptional Profiling of Neuregulin-Induced Myocardial Recovery After Infarction in Rats and Swine

Neuregulin-1 (NRG-1) mediates cell-cell interactions and is a critical growth and developmental signaling molecule in the heart. We have been examining whether the recombinant NRG-1 isoform known as glial growth factor 2 (GGF2) has therapeutic potential for heart failure. In rats and swine with experimental myocardial infarction we have found that GGF2 treatment improves myocardial function and limits progressive myocardial remodeling. To understand potential mechanisms for this effect, we compared gene expression in these animals using microarrays. In rats we compared Sham operated, MI treated with vehicle, and MI treated with GGF2 at a single dose. We found that GGF2 treatment was associated with correction of mitochondrial and metabolic genes altered by MI compared to Sham-operated rats. When compared to 9 published datasets of ∼400 samples from rodents and human heart failure, we identified 563 genes associated with heart failure that were also reversed in expression in response to GGF2. Ingenuity pathway analysis demonstrated clusters of genes associated with energy production and cardiovascular tissue development as particularly enriched in GGF2-treated versus untreated MI rats. In swine our analysis was confined to animals with MI +/- GGF2 treatment at two doses. There were 527 genes altered by GGF2 at both doses compared to untreated controls, with a clear GGF2 dose response. Transcripts altered in response to GGF2 treatment were mainly those associated with extracellular matrix structure and function, MAPK signaling, and p53-mediated apoptosis. Electron microscopy of remote infarct left ventricular tissue from swine confirmed extreme morphological differences in mitochondria from GGF2-treated and vehicle-treated control pigs. Most striking was recovery of intercalated discs in response to GGF2, compared to severe disruption of intercalated disc structures in vehicle-treated control animals.

Metabolomic profiles of myocardial ischemia under treatment with salvianolic acid B

BackgroundRadix Salvia miltiorrhiza (Danshen) has been used as a principal herb in treating cardiovascular diseases in Chinese medicine. Salvianolic acid B (SA-B), a water-soluble active component of Danshen, was found to have anti-myocardial ischemia (anti-MI) effect. This study aims to investigate mechanisms of SA-B on MI.MethodsFive conventional Western medicines (isosorbide dinitrate, verapamil, propranolol, captopril and trimethazine) with different mechanisms for treating cardiovascular diseases were selected as positive references to compare with SA-B in changing of the metabolomic profiles in MI rats under treatment. Potential mechanisms of SA-B were further investigated in H9C2 cell line.ResultsThe metabolomic profiles between SA-B- and propranolol-treated MI rats were similar, since there was a big overlap between the two groups in the PLS-DA score plot. Finally, it was demonstrated that SA-B exhibited a protective effect on MI mainly by decreasing the concentration of cyclic adenosine monophosphate (cAMP) and Ca2+ and inhibiting protein kinase A (PKA).ConclusionSA-B and propanolol exhibited similar metabolomic profiles, indicating that the two drugs might have a similar mechanism.

Long‐term treatment with ivabradine in post‐myocardial infarcted rats counteracts f‐channel overexpression

Recent clinical data suggest beneficial effects of ivabradine, a specific heart rate (HR)-lowering drug, in heart failure patients. However, the mechanisms responsible for these effects have not been completely clarified. Thus, we investigated functional/molecular changes in I(f), the specific target of ivabradine, in the failing atrial and ventricular myocytes where this current is up-regulated as a consequence of maladaptive remodelling. We investigated the effects of ivabradine (IVA; 10 mg·kg(-1) ·day(-1) for 90 days) on electrophysiological remodelling in left atrial (LA), left ventricular (LV) and right ventricular (RV) myocytes from post-mycardial infarcted (MI) rats, with sham-operated (sham or sham + IVA) rats as controls. I(f) current was measured by patch-clamp; hyperpolarization-activated cyclic nucleotide-gated (HCN) channel isoforms and microRNA (miRNA-1 and miR-133) expression were evaluated by reverse transcription quantitative PCR. Maximal specific conductance of I(f) was increased in MI, versus sham, in LV (P < 0.01) and LA myocytes (P < 0.05). Ivabradine reduced HR in both MI and sham rats (P < 0.05). In MI + IVA, I(f) overexpression was attenuated and HCN4 transcription reduced by 66% and 54% in LV and RV tissue, respectively, versus MI rats (all P < 0.05). miR-1 and miR-133, which modulate post-transcriptional expression of HCN2 and HCN4 genes, were significantly increased in myocytes from MI + IVA. The beneficial effects of ivabradine may be due to the reversal of electrophysiological cardiac remodelling in post-MI rats by reduction of functional overexpression of HCN channels. This is attributable to transcriptional and post-transcriptional mechanisms.

Antioxidant N-acetyl cysteine reverses cigarette smoke-induced myocardial infarction by inhibiting inflammation and oxidative stress in a rat model

The contribution of chronic tobacco exposure in determining post-myocardial infarction (MI) left ventricular (LV) remodeling and possible therapeutic strategies has not been investigated systematically. In this small animal investigation, we demonstrate that chronic tobacco smoke exposure leading up to acute MI in rats is associated with greater histological extent of myocardial necrosis and consequent worse LV function. These findings are associated with increased transcriptomic expression of pro-inflammatory cytokines, tissue repair molecules and markers of oxidative stress in the myocardium. The results demonstrate that an N-acetyl cysteine (NAC) treatment significantly reduced tobacco-exposed induced infarct size and percent fractional shortening. A significantly increased LV end-systolic diameter was observed in tobacco-exposed sham compared to tobacco-naïve sham (4.92±0.41 vs 3.45±0.33; P<0.05), and tobacco-exposed MI compared to tobacco-naïve MI (8.24±0.3 vs 6.1±0.49; P<0.01) rats. Decreased intracardiac mRNA expression of the markers of inflammation, tissue repair and oxidative stress and circulating levels of pro-inflammatory cytokines accompanied these positive effects of NAC. The treatment of tobacco-exposed MI rats with NAC resulted in significantly increased levels of intracardiac mRNA expression of antioxidants, including superoxide dismutase, thioredoxin and nuclear factor-E2-related factor 2, as well as circulating levels of glutathione (7±0.12 vs 10±0.18; P⩽0.001), where the levels were almost identical to the tobacco-naïve sham rats. These findings identify a novel post-infarction therapy for amelioration of the adverse effects of tobacco exposure on the infracted myocardium and advocate the use of dietary supplement antioxidants for habitual smokers to prevent and reverse cardiovascular adverse effects in the absence of successful achievement of cessation of smoking.

The serum metabolomic study of intervention effects of the traditional Chinese medicine Shexiang Baoxin Pill and a multi-component medicine polypill in the treatment of myocardial infarction in rats

A metabolomic approach based on liquid chromatography coupled with quadrupole time-of-flight detector (LC-Q-TOF/MS) was developed to investigate the therapeutic mechanism of a traditional Chinese medicine (TCM) formula Shexiang Baoxin Pill (SBP) and a multi-component medicine polypill (consisting of simvastatin (Sim), atenolol (Ate), ramipril (Ram), hydrochlorthiazide (Hyd) and aspirin (Asp), named as SARHA). Twenty-seven biomarkers were identified in the serum of MI rats. Thirteen related pathways and 4 main pathological processes including oxidative injury, energy metabolism dysfunction, amino acid metabolism dysfunction and inflammation are involved in MI development. Our study revealed that SBP showed better therapeutic effectiveness than the polypill on MI through regulation of the energy metabolism dysfunction, oxidative injury and inflammation. The combination agent polypill had only certain therapeutic effects on inhibiting oxidative injury and inflammation induced by MI. The reverse effect of the polypill on biomarkers related to MI was much better than mono-therapy groups.

Effect of simvatatin and atorvastatin on Fox03a expression and ventricular remolding in post-myocardial infarction rats

ObjectiveAccumulating evidence suggests non-phosphorylation FoxO3a play a role in cardiovascular diseases. Therefore we examined the expression of non-phosphorylation FoxO3a in Post-myocardial Infarction Rats, to investigate the effect of simvastatin and...

A long‐term efficacy of allogeneic bone marrow mesenchymal stem cells in myocardial repair

Allogeneic mesenchymal stem cells (AMSCs) are currently undergoing clinical trials for myocardial repair. However, their long‐term therapeutic efficacy has not been established. We conducted a six month comparative study on allogeneic and syngeneic MSCs using a MI rat model. We found AMSCs were immunoprivileged soon after implantation and produced a robust cardiac functional improvement similar to syngeneic MSCs in the first three months after treatment. After two weeks implantation, the differentiated AMSCs acquired immunogenic phenotype associated with increased cell surface expression of MHC class I and II molecules, rendering them immune rejected and diminishing their ability to prevent heart failure after 6 months of treatment. These results suggest that AMSCs have short‐term benefits for heart repair, and reconcile inconsistent findings from earlier studies by identifying the unknown biphasic immune response to AMSCs. Differentiation induced immune rejection supports the need for future studies to modify the late immunogenic phenotype of MSCs to prevent rejection and achieve long term benefits of AMSCs for cardiac repair. Supported by HSFO and CIHR.

Impairment of Cardiac Function and Remodeling Induced by Myocardial Infarction in Rats are Attenuated by the Nonpeptide Angiotensin‐(1–7) Analog AVE 0991

We evaluated effects of the nonpeptide angiotensin (ANG)-(1-7) analog AVE 0991 (AVE) on cardiac function and remodeling as well as transforming growth factor-beta1 (TGF-β1)/tumor necrosis factor-alpha (TNF-α) expression in myocardial infarction rat models. Sprague-Dawley rats underwent either sham surgery or coronary ligation. They were divided into four groups: sham, control, AVE, and AVE+A-779 [[D-Ala(7) ]-ANG-(1-7), a selective antagonist for the ANG-(1-7)] group. After 4 weeks of treatment, the AVE group displayed a significant elevation in left ventricular fractional shorting (LVFS) (25.5 ± 7.3% vs. 18.4 ± 3.3%, P < 0.05) and left ventricular ejection fraction (LVEF) (44.8 ± 7.6% vs. 32.7 ± 6.5%, P < 0.05) when compared to the control group, but no effects on the left ventricular end-diastolic and end-systolic diameters (LVDd and LVDs, respectively) were observed. In addition, we found that the myocyte diameter (18 ± 2 μm vs. 22 ± 4 μm, P < 0.05), infarct size (42.6 ± 3.6% vs. 50.9 ± 4.4%, P < 0.001) and collagen volume fraction (CVF) (16.4 ± 2.2% vs. 25.3 ± 3.2%, P < 0.001) were significantly reduced in the AVE group when compared to the control group. There were no differences in LVFS, LVEF, myocyte diameter, and infarct size between the control and AVE+A-779 groups. AVE also markedly attenuated the increased mRNA expression of collagen I (P < 0.001) and collagen III (P < 0.001) and inhibited the overexpression of TGF-β1 (P < 0.05) and TNF-α (P < 0.05) compared to the control group. AVE could improve cardiac function and attenuate ventricular remodeling in MI rat models. It may involve the inhibition of inflammatory factors TGF-β1/TNF-α overexpression and the action on the specific receptor Mas of ANG-(1-7).

Heart rate reduction with ivabradine prevents the global phenotype of left ventricular remodeling

The aim of this study was to investigate the effect of chronic heart rate (HR) reduction with the hyperpolarization-activated current inhibitor ivabradine on the global phenotype of left ventricular (LV) remodeling in a ligated rat model. Seven days after coronary artery ligation, Wistar rats received ivabradine (10 mg · kg(-1) · day(-1) administered in drinking water) [myocardial infarction + ivabradine (MI+IVA), n = 22] or vehicle only (drinking water) (MI, n = 20) for 90 days. A sham group (n = 20) was included for model validation. MI+IVA rats had 12% lower HR (P < 0.01), improved LV volumes, 15% higher LV ejection fraction (LVEF, P < 0.01) than MI rats, and 33% reductions in both plasma atrial natriuretic peptide (ANP, P = 0.052) and cardiac hydroxyproline. Using patch-clamp, action potential duration was reduced and transient outward current density increased (P < 0.05). Cardiac energy metabolism was also improved (+33% creatine phosphate, P < 0.001; +15% ATP; and +9% energy charge, P < 0.05). Significant correlations were found between HR and parameters of cardiac metabolism, ANP, and LVEF (all P < 0.05). The HR-reducing properties of ivabradine prevent changes in the global phenotype of LV remodeling in the rat, optimize energy consumption, and avoid electrophysiological and structural remodeling.

Use of afterload hemodynamic stress as a practical method for assessing cardiac performance in rats with heart failure

After myocardial infarction, the hemodynamics under basal conditions might appear to be unaltered, which makes it difficult to identify cardiac dysfunction by the usual approaches. Thus, we tested the response to sudden afterload stress in infarcted rats with apparently normal ejection function. Control (CT) and infarcted (MI) Wistar rats with various MI sizes were submitted to echocardiography 30 days after coronary occlusion, followed by assessment of hemodynamics under basal conditions and during a pharmacologically induced sudden pressure overload (phenylephrine 15-25 microg/kg, i.v.). Coronary occlusion resulted in cardiac remodeling proportional to MI size, although several functional parameters such as systolic pressure (SP), stroke volume (SV), and stroke work (SW) of all MI rats were similar to those of CT rats. However, the afterload stress that was produced led to a relative preservation of SV and an increase of SW in CT rats; MI rats exhibited a significant reduction in SV and SW generation, although global cardiac function was normal under basal conditions, as indicated by regular echocardiography and hemodynamics assessment. Thus, we propose the use of sudden pharmacologically induced afterload stress as a practical and efficient procedure for identifying impaired performance of the heart in anesthetized rats, providing an additional physiological variable to be evaluated in experimental therapeutic studies.

High-Resolution Optical Mapping of Ventricular Tachycardia in Rats with Chronic Myocardial Infarction

Ventricular tachycardia (VT) is a common cause of mortality in post-myocardial infarction (MI) patients, even in the current era of coronary revascularization treatment. We report a reproducible VT model in rats with chronic MI induced by ischemia-reperfusion and describe its electrophysiological characteristics using high-resolution optical mapping. An MI was generated by left anterior descending coronary ligation (25 minutes) followed by reperfusion in 20 rats. Electrophysiology study and optical mapping were performed 5 weeks later using a Langendorff-perfused preparation and compared to normal rats. The conduction velocity of the MI border zone was decreased to 53% of the normal areas remote from the infarct (0.37 +/- 0.16 m/sec vs 0.70 +/- 0.09 m/sec, P < 0.0001). The rate of VT inducibility in MI rats was significantly greater than in normal control rats (70% vs 0%, P = 0.00002). VT circuits involving the infarct area were identified with optical mapping in 83% MI rats. In addition, fixed and functional conduction block were observed in the infarct border zone. This ischemia-reperfusion MI rat model is a reliable VT model, which simulates clinical revascularization treatment. High-resolution optical mapping in this model is useful to study the mechanism of VT and evaluate the effects of therapies.

Insulin inhibits myocardial ischemia-induced apoptosis and alleviates chronic adverse changes in post-ischemic cardiac structure and function

Insulin has been shown to possess significant anti-apoptotic effect in myocardial ischemia/reperfusion (MI/R). However, the contribution by this protection of insulin to the prolonged cardiac function in rats subjected to ischemia remains unclear. The present study attempted to test whether early insulin treatment influences adverse prolonged post-ischemic cardiac structural and functional changes. Adult male rats were subjected to left anterior descending coronary artery occlusion and were randomized to receive one of the following treatments: saline (4 ml/kg/h i.v. injection beginning 10 min before the ischemia and continuing for 2 h), insulin (60 U/l, i.v. injection following the same routine, and hypodermic injection of insulin (0.5 U/ml, 1 ml/kg/d) for 3 days after the ischemia surgery) or insulin plus wortmannin (15 mug/kg i.v. injection 15 min before each insulin administration). Treatment with insulin significantly reduced infarct size, decreased plasma creatine kinase and lactate dehydrogenase activities, decreased apoptosis index and caspase-3 activity (all P < 0.01 vs. saline), and improved cardiac function 24 h after ischemia. Importantly, at the end of 4 weeks after the ischemia surgery, MI rats receiving insulin treatment showed smaller left ventricle (LV) cavity and thicker systolic interventricular septum, and increased cardiac ejection fraction and LV fractional shortening (all P < 0.05 vs. saline). Inhibition of insulin signaling with wortmannin not only blocked insulin's anti-apoptotic effect, but also almost completely abolished effects of insulin on cardiac structure and function. These data indicate that inhibition of apoptosis by early insulin treatment alleviates chronic adverse changes in post-ischemic cardiac structure and function.

Reactive Oxygen Species Promote Angiogenesis in the Infarcted Rat Heart

Cardiac reactive oxygen species (ROS) production is significantly increased following infarction (MI), particularly at early stage. Herein we sought to determine whether ROS play a role on angiogenesis in the infarcted heart. Experimental MI rats were treated with combined antioxidants, tempol and apocynin, each 120mg/kg/day. Non‐treated MI rats served as controls. Hearts were collected at day 1, 3, 7, 14, 28 and 42. We examined effect of antioxidants on angiogenesis in the infarcted myocardium. Following MI, NADPH oxidase (gp91phox subunit) was significantly increased in the infarcted myocardium at day 3, reached peak at day 7, and gradually declined thereafter. In the infarcted region, existing vessels were lost at day 1 postMI. Newly formed vessels appeared in the border zone as early as day 3, followed by the infarcted myocardium. Vascular density peaked at day 7 and 14, and progressively reduced thereafter. Antioxidants significantly reduced cardiac vascular density at day 7 and 14, but not in the later time points. Thus, angiogenesis is activated in the infarcted myocardium in the first two weeks and becomes quiescent in the late stage of MI, which is temporally and spatially coincident with increased ROS production. Our study also indicates that ROS promote angiogenesis in the infarcted myocardium. Further studies are required to determine the mechanisms responsible for ROS mediated cardiac angiogenesis.