Rabbit Model Of Myocardial Infarction Research Articles

Abstract 9434: Post-infarct Treatment With Microrna145 Protects the Heart Against Myocardial Ischemia-reperfusion Injury Through Acceleration of Myocyte Autophagy

Background: We previously reported that microRNA145 (miRNA145) attenuates the ischemia-reperfusion injury. However, the mechanism how miRNA145 reduces the myocardial infarct size is still unclear. Objective: We aimed to investigate whether post-infarct treatment with miRNA145 reduces myocardial infarct size and its precise mechanism in a rabbit model of myocardial infarction. Methods: Male Japanese white rabbits underwent 30 min of coronary occlusion followed by 14 days of reperfusion. Rabbits received intravenous injection of saline (control group, n=7) or 0.035 mg/kg of miRNA145 encapsulated with liposome (miRNA145 group, n=7) immediately after reperfusion. At 14 days after reperefusion, rabbits were sacrificed and the hearts were removed. The area at risk and infarct areas were measured by evans blue dye and TTC staining, respectively. The infarct size was calculated as a percentage of the risk area of the left ventricle. Heart tissues were sampled and the morphological changes were investigated by electron microscopy, and the expression of LC3B, an indicator of autophagy, was assessed by western blot analysis. In another series of experiments, rat myoblast H9C2 were treated with 20 nM of miRNA145 and investigated the morphological changes by electron microscopy and the expression of LC3B by western blot analysis. Results: Post-infarct treatment with miRNA145 significantly reduced the myocardial infarct size (16.0±3.1 %) as compared to the control (28.7±6.1 %) group. Post-infarct treatment with miRNA145 significantly improved LV remodeling and improved ±dp/dt as compared to the control group. Both in vitro myoblast and in vivo experiments, treatment with miRNA145 induced autophagic changes such as autophagosome and autolysosome, and activated LC3B. Conclusions: It is suggested that post-infarct treatment with miRNA145 attenuated ischemia-reperfusion injury through acceleration of myocyte autophagy. The miRNA145 may be a promising strategy for treatment of acute myocardial infarction.

MSCs transplantation with application of G-CSF reduces apoptosis or increases VEGF in rabbit model of myocardial infarction

The purpose of this study was to test whether mesenchymal stem cells (MSCs) transplantation with application of granulocyte colony-stimulating factor (G-CSF) would have beneficial effects on damaged heart in a rabbit model of myocardial infarction (MI). MI was created by ligation of the left anterior descending coronary artery. After induction of MI, 40 New Zealand white rabbits were randomly divided into 8 groups: (1) MSCs injection at 3days after MI; (2) G-CSF injection at 3days after MI; (3) MSCs+G-CSF (20u/kg/day) injection at 3days after MI; (4) PBS injection at 3days after MI; (5) MSCs injection at 7days after MI; (6) G-CSF injection at 7days after MI; (7) MSCs+G-CSF(20u/kg/day) injection 7days after MI; and (8) PBS injection 7days after MI. TUNEL analysis showed that the apoptotic cells were distributed in the marginal area of MI. In both 3 and 7days after MI groups, there were less apoptotic cells in the MSCs and MSCs+G-CSF groups as compared with the PBS group (P<0.05). However, no decrease in apoptosis was observed in the G-CSF only group (P>0.05). Immunohistochemistry analysis demonstrated that the expression level of vascular endothelial growth factor was higher in the MSCs, MSCs+G-CSF and G-CSF groups as compared with the PBS group. The present study demonstrated a beneficial effect of MSCs transplantation with application of G-CSF in the treatment of rabbit MI.

Cotransplantation of human umbilical cord-derived mesenchymal stem cells and umbilical cord blood-derived CD34+ cells in a rabbit model of myocardial infarction

The objective of the study is to investigate the effect of hypoxic preconditioning on the immunomodulatory properties of human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) and the effect of cotransplantation of hUC-MSCs and human umbilical cord blood (hUCB)-derived CD34(+) cells in a rabbit model of myocardial infarction. hUC-MSCs with or without hypoxic preconditioning by cobalt chloride were plated in a 24-well plate, and then cocultured with hUCB-CD34(+) cells and PBMCs for 96 h at 37 °C in a 5% CO₂ incubator. For the negative control, hUC-MSCs were omitted. The groups were divided as follows: A1 = HP-MSCs + hUCB-CD34(+) cells + PBMC, A2 = hUC-MSCs + hUCB-CD34(+) cells + PBMC, Negative Control = hUCB-CD34(+) cells + PBMC. Culture supernatants of each group were collected, and the IL-10 and IFN-γ levels were measured by ELISA. A rabbit model of MI was established using a modified Fujita method. The animals were then randomized into three groups and received intramyocardial injections of 0.4 ml of PBS alone (n = 8, PBS group), hUC-MSCs in PBS (n = 8, hUC-MSCs group), or hUC-MSCs + CD34(+) cells in PBS (n = 8, Cotrans group), at four points in the infarct border zone. Echocardiography was performed at baseline, 4 weeks after MI induction, and 4 weeks after cell transplantation, respectively. Stem cell differentiation and neovascularization in the infracted area were characterized for the presence of cardiac Troponin I (cTnI) and CD31 by immunohistochemical staining, and the extent of myocardial fibrosis was evaluated by hematoxylin and eosin (H&E) and Masson's trichrome. IFN-γ was 27.00 ± 1.11, 14.20 ± 0.81, and 7.22 ± 0.14 pg/ml, and IL-10 was 31.68 ± 3.08, 61.42 ± 1.08, and 85.85 ± 1.80 pg/ml for the Control, A1 and A2 groups, respectively, which indicated that hUCB-CD34(+) cells induced immune reaction of peripheral blood mononuclear cells, whereas both hUC-MSCs and HP-MSCs showed an immunosuppressive effect, which, however, was attenuated by hypoxic preconditioning. The Cotrans group had less collagen deposition in the infarcted myocardium and better heart function than the hUC-MSCs or PBS group. The presence of cTnI-positive cells and CD31-positive tubular structures indicated the differentiation of stem cells into cardiomyocytes and neovascularization. The microvessel density was 12.19 ± 3.05/HP for the hUC-MSCs group and 31.63 ± 2.45/HP for the Cotrans group, respectively (P < 0.01). As a conclusion, both hUC-MSCs and HP-MSCs have an immunosuppressive effect on lymphocytes, which, however, can be attenuated by hypoxic preconditioning. Cotransplantation of hUC-MSCs and hUCB-CD34(+) cells can improve heart function and decrease collagen deposition in post-MI rabbits. Thus, a combined regimen of hUC-MSCs and hUCB-CD34(+) cells would be more desirable than either cells administered alone. This is most likely due to the increase of cardiomyocytes and enhanced angiogenesis in the infarcted myocardium.

Post-infarct Treatment with MicroRNA145 Protects the Heart Against Myocardial Ischemia-reperfusion Injury through Acceleration of Myocyte Autophagy

Background: We previously reported that microRNA145 (miR-145) significantly reduced the myocardial infarct size and improved the function of left ventricle. It has been reported that autophagy is activated in cardiomyocytes in ischemic heart disease. We investigated whether miR-145 would reduce the myocardial infarct size through acceleration of autophagy. Objective: We aimed to investigate whether administration of miR-145 would affect myocyte autophagy in a rabbit model of myocardial infarction (MI). Methods: Male Japanese white rabbits underwent 30 min of coronary occlusion followed by 2 and 14 days of reperfusion. Saline or miR-145 (0.035 mg/kg) was intravenous injected immediately after reperfusion. Some of the rabbits treated with miR-145 were administered chloroquine that acts by inhibiting vacuolar H+-ATPase and autophagosome fusion to prevent the final digestion step during autophagy immediately after reperfusion followed by 30 min of coronary ligation. On day 2 and day 14 post-MI, rabbits were sacrificed and the hearts were removed. Heart tissues were sampled and devided into three area; remote area, borderline area and infarct area. The morphological changes were assessed by electron microscopy, and the expressions of LC3B, Akt, phosphorylated (p)-Akt, ERK and p-ERK were assessed by western blot analysis. Results: The MI size as a percentage of area at risk was significantly smaller in the miR-145 group than that in the control group. Treatment with chloroquine blocked the infarct size-reducing effect of miR-145. These were observed both in 2days and 14days reperfusion groups. Electron microscopic findings showed the autophagic change in cardiomyocytes in both the control and miRNA145 groups on day 2 and day 14 post-MI. Western blot analysis showed that transition from LC3B-I to LC3B-II was significantly stronger in the miR-145 group than in the control group. The expression of p-Akt in the ischemic area was upregulated in the miR-145 group on day 2 post-MI. However, there was no significant difference in the expression of Akt, ERK and p-ERK between 2 groups on day 2 and day 14 post-MI. Conclusions: It is suggested that post-infarct treatment with miR-145 attenuated ischemia-reperfusion injury through acceleration of myocyte autophagy.

Post-infarct treatment with microRNA145 reduces myocardial infarct size through acceleration of myocyte autophagy in rabbits

Background: We previously reported that microRNA145 (miRNA145) attenuates the ischemia-reperfusion injury. However, it is not still unclear how miRNA145 attenuates the ischemia-reperfusion injury. Objective: We aimed to investigate whether post-infarct treatment with miRNA145 reduces myocardial infarct size and its precise mechanism in a rabbit model of myocardial infarction. Methods: Male Japanese white rabbits underwent 30 min of coronary occlusion followed by 14 days of reperfusion. Rabbits received intravenous injection of saline (control group, n=7) or 0.035 mg/kg of miRNA145 encapsulated with liposome (miRNA145 group, n=7) immediately after reperfusion. At 14 days after reperfusion, rabbits were sacrificed and the hearts were removed. The area at risk and infarct areas were measured by evans blue dye and TTC staining, respectively, and the infarct size was calculated as a percentage of the risk area of the left ventricle. In another series of experiments, rat myoblast H9C2 were treated with 20 nM of miRNA145 and investigated the morphological changes by electron microscopy and signals by western blot analysis such as LC3B. Results: Post-infarct treatment with miRNA145 significantly reduced the myocardial infarct size (16.0±3.1%) as compared to the control (28.7±6.1%) group. Post-infarct treatment with miRNA145 significantly improved LV remodeling and improved ±dp/dt as compared to the control group. In the myoblast experiment, treatment with miRNA145 caused autophagic changes such as autophagosome and autolysosome, and caused activation of LC3B. Conclusions: It is suggested that post-infarct treatment with miRNA145 attenuated ischemia-reperfusion injury through acceleration of myocyte autophagy. The miRNA145 may be a promising strategy for treatment of acute myocardial infarction.

Recovery in ERG gene expression with biventricular pacing in a rabbit model of myocardial infarction

Recovery in ERG gene expression with biventricular pacing in a rabbit model of myocardial infarction Samir Saba,* Haider Mehdi,* William Barrington, Fardeen Mehdi, Zahid Islam, Barry LondonCardiovascular Institute of the University of Pittsburgh Medical Center, Pittsburgh, PA, USA*These authors contributed equally to this workBackground: Improved clinical and echocardiographic parameters have been documented with biventricular (BIV) pacing in patients after myocardial infarction (MI). We investigated the changes in gene expression in cardiac tissue with BIV pacing, using a rabbit model of MI.Method: New Zealand White rabbits were divided into four groups: sham-operated controls, MI with no pacing, MI with right ventricle (RV) pacing (MI + RV), and MI with BIV pacing (MI + BIV). Pacing was initiated 1&ndash;2 weeks after the coronary ligation. At 5 weeks, the hearts were excised. The tissue extracted from the left ventricle (LV) and RV underwent analysis for protein and messenger ribonucleic acid (mRNA) levels.Results: The ether-a-go-go-related gene (ERG) protein levels recovered from the base of the LV away from the MI area were two- to threefold lower in the MI and the MI + RV compared with the MI + BIV groups (P = 0.07). The ERG protein levels were similar between the MI + BIV and the control groups. However, the RNA levels were comparable between the four study groups, suggesting that a posttranscriptional mechanism accounted for the difference in protein levels.Conclusion: In this rabbit model of MI, we demonstrated a recovery in ERG protein levels with BIV pacing, after MI. This recovery may underlie some of the benefits seen with BIV pacing in ischemic cardiomyopathy.Keywords: heart failure, biventricular pacing, cardiac reverse remodeling, ether-a-go-go-related gene

Aldehyde dehydrogenase-2 inhibition blocks remote preconditioning in experimental and human models

Mitochondrial aldehyde dehydrogenase-2 (ALDH-2) is involved in preconditioning pathways, but its role in remote ischaemic preconditioning (rIPC) is unknown. We investigated its role in animal and human models of rIPC. (i) In a rabbit model of myocardial infarction, rIPC alone reduced infarct size [69 ± 5.8 % (n = 11) to 40 ± 6.5 % (n = 12), P = 0.019]. However, rIPC protection was lost after pre-treatment with the ALDH-2 inhibitor cyanamide (62 ± 7.6 % controls, n = 10, versus 61 ± 6.9 % rIPC after cyanamide, n = 10, P > 0.05). (ii) In a forearm plethysmography model of endothelial ischaemia-reperfusion injury, 24 individuals of Asian ethnic origin underwent combined rIPC and ischaemia-reperfusion (IR). 11 had wild-type (WT) enzyme and 13 carried the Glu504Lys (ALDH2*2) polymorphism (rendering ALDH-2 functionally inactive). In WT individuals, rIPC protected against impairment of response to acetylcholine (P = 0.9), but rIPC failed to protect carriers of Glu504Lys polymorphism (P = 0.004). (iii) In a second model of endothelial IR injury, 12 individuals participated in a double-blind placebo-controlled crossover study, receiving the ALDH-2 inhibitor disulfiram 600 mg od or placebo for 48 h prior to assessment of flow-mediated dilation (FMD) before and after combined rIPC and IR. With placebo, rIPC was effective with no difference in FMD before and after IR (6.18 ± 1.03 % and 4.76 ± 0.93 % P = 0.1), but disulfiram inhibited rIPC with a reduction in FMD after IR (7.87 ± 1.27 % and 3.05 ± 0.53 %, P = 0.001). This study demonstrates that ALDH-2 is involved in the rIPC pathway in three distinct rabbit and human models. This has potential implications for future clinical studies of remote conditioning.

Effects of nerve growth factor on the action potential duration and repolarizing currents in a rabbit model of myocardial infarction.

ObjectivesTo investigate the effect of nerve growth factor (NGF) on the action potential and potassium currents of non-infarcted myocardium in the myocardial infarcted rabbit model.MethodsRabbits with occlusion of the left anterior descending coronary artery were prepared and allowed to recover for eight weeks (healed myocardial infarction, HMI). During ligation surgery of the left coronary artery, a polyethylene tube was placed near the left stellate ganglion in the subcutis of the neck for the purpose of administering NGF 400 U/d for eight weeks (HMI + NGF group). Cardiomyocytes were isolated from regions of the non-infarcted left ventricular wall and the action potentials and ion currents in these cells were recorded using whole-cell patch clamps.ResultsCompared with HMI and control cardiomyocytes, significant prolongation of APD50 or APD90 (Action potential duration (APD) measured at 50% and 90% of repolarization) in HMI + NGF cardiomyocytes was found. The results showed that the 4-aminopyridine sensitive transient outward potassium current (Ito), the rapidly activated omponent of delayed rectifier potassium current (IKr), the slowly activated component of delayed rectifier potassium current (IKs), and the L-type calcium current (ICaL) were significantly altered in NGF + HMI cardiomyocytes compared with HMI and control cells.ConclusionsOur results suggest that NGF treatment significantly prolongs APD in HMI cardiomyocytes and that a decrease in outward potassium currents and an increase of inward Ca2+ current are likely the underlying mechanism of action.

Cilostazol protects the heart against ischaemia reperfusion injury in a rabbit model of myocardial infarction: Focus on adenosine, nitric oxide and mitochondrial ATP-sensitive potassium channels

1. The present study examined whether or not cilostazol reduces the myocardial infarct size, and investigated its mechanism in a rabbit model of myocardial infarction. 2. Japanese white rabbits underwent 30 min of coronary occlusion, followed by 48 h of reperfusion. Cilostazol (1 and 5 mg/kg) or vehicle was given intravenously 5 min before ischaemia. 8-p-sulfophenyl theophylline (8SPT; an adenosine receptor blocker, 7.5 mg/kg), Nω-nitro-L-arginine methylester (l-NAME; an NOS inhibitor, 10 mg/kg) or 5-hydroxydecanoic acid sodium salt (5-HD; a mitochondrial ATP-sensitive potassium (KATP) channel blocker, 5 mg/kg) was given intravenously 5 min before cilostazol injection. Infarct size was determined as a percentage of the risk area. 3. The myocardial interstitial levels of adenosine and nitrogen oxide (NOx) during ischaemia and reperfusion, and the intensity of myocardial dihydroethidium staining were determined. 4. Infarct size was significantly reduced in the cilostazol 1 mg/kg (38.4% (2.9%)) and cilostazol 5 mg/kg (30.7% (4.7%)) groups compared with that in the control group (46.5% (4.2%)). The infarct size-reducing effect of cilostazol was completely abolished by 8SPT (46.6% (3.5%)), L-NAME (49.0% (5.5%)), or 5HD (48.5% (5.1%)). 8SPT, L-NAME or 5HD alone did not affect the infarct size. Cilostazol treatment significantly increased myocardial levels of adenosine and NOx during ischaemia, and attenuated the intensity of dihydroethidium staining during reperfusion. 5. These findings show that cilostazol reduces the myocardial infarct size by increasing adenosine and NOx levels, attenuating superoxide production and opening the mitochondrial KATP channels. Cilostazol might provide a new strategy for the treatment of coronary heart disease.

E0372 Post-operative observation of the safety and angiogenesis effect of direct current stimulation in a myocardial infarction rabbit model

IntroductionThe purpose of the current study was to evaluate the safety of low voltage direct current (DC) electric stimulation and its angiogenesis effect in a rabbit myocardial infarction (MI) model...

Postinfarct Treatment With Oxytocin Improves Cardiac Function and Remodeling via Activating Cell-survival Signals and Angiogenesis

We investigated whether postinfarct treatment with oxytocin (OT) improves left ventricular (LV) function and remodeling via cardiac repair of myocardial ischemia-reperfusion injury. Experiments were performed with 30 minutes of coronary occlusion and 2 or 14 days of reperfusion rabbit model of myocardial infarction. LV function and remodeling were significantly improved in the OT group. The infarct size was significantly reduced in the OT group. The number of CD31-positive microvessels was increased significantly in the OT group. There were no Ki67-positive myocytes in either group. The expression of the OT receptor, phosphorylated (p)-Akt protein kinase, p-extracellular signal-regulated protein kinase, p-enodthelial NO synthase, p-signal transducer and activator of transcription 3, vascular endothelial growth factor, B-cell lymphoma 2, and matrix metalloproteinase-1 (MMP-1) were markedly increased in the OT group days 2 and 14 post myocardial infarction. Postinfarct treatment with OT reduces myocardial infarct size and improves LV function and remodeling by activating OT receptors and prosurvival signals and by exerting antifibrotic and angiogenic effects through activation of MMP-1, endothelial NO synthase, and vascular endothelial growth factor. These findings provide new insight into therapeutic strategies for ischemic heart disease.

Antidiabetic drug pioglitazone protects the heart via activation of PPAR-γ receptors, PI3-kinase, Akt, and eNOS pathway in a rabbit model of myocardial infarction

The insulin-sensitizing drug pioglitazone has been reported to be protective against myocardial infarction. However, its precise mechanism is unclear. Rabbits underwent 30 min of coronary occlusion followed by 48 h of reperfusion. Rabbits were assigned randomly to nine groups (n = 10 in each): the control group (fed a normal diet), pioglitazone group (fed diets containing 1 mg.kg(-1).day(-1) pioglitazone), pioglitazone + 5-hydroxydecanoic acid (HD) group [fed the pioglitazone diet + 5 mg/kg iv 5-HD, a mitochondrial ATP-sensitive K(+) (K(ATP)) channel blocker], pioglitazone + GW9662 group [fed the pioglitazone diet + 2 mg/kg iv GW9662, a peroxisome proliferator activated receptor (PPAR)-gamma antagonist], GW9662 group (fed a normal diet + iv GW9662), pioglitazone + wortmannin group [fed the pioglitazone diet + 0.6 mg/kg iv wortmannin, a phosphatidylinositol (PI)3-kinase inhibitor], wortmannin group (fed a normal diet + iv wortmannin), pioglitazone + nitro-l-arginine methyl ester (l-NAME) group [fed the pioglitazone diet + 10 mg/kg iv l-NAME, a nitric oxide synthase (NOS) inhibitor], and l-NAME group (fed a normal diet + iv l-NAME). All groups were fed the diets for 7 days. The risk area and nonrisk area of the left ventricle (LV) were separated by Evans blue dye, and the infarct area was determined by triphenyltetrazolium chloride staining. The infarct size was calculated as a percentage of the LV risk area. Western blotting was performed to assess levels of Akt and phospho-Akt and phospho-endothelial NOS (eNOS) in the myocardium following reperfusion. The infarct size was significantly smaller in the pioglitazone group (21 +/- 2%) than in the control group (43 +/- 3%). This effect was abolished by GW9662 (42 +/- 3%), wortmannin (40 +/- 3%), or l-NAME (42 +/- 7%) but not by 5-HD (24 +/- 5%). Western blotting showed higher levels of phospho-Akt and phospho-eNOS in the pioglitazone group. Pioglitazone reduces the myocardial infarct size via activation of PPAR-gamma, PI3-kinase, Akt, and eNOS pathways, but not via opening the mitochondrial K(ATP) channel. Pioglitazone may be a novel strategy for the treatment of diabetes mellitus with coronary artery disease.

Abstract 1612: Pharmacological Postconditioning Effect of G-csf Is Mediated through Activation of Pi3k-akt-enos Pathway and Opening the Mitochondrial Katp Channels in a Rabbit Model of Myocardial Infarction

It has been reported that granulocyte-colony-stimulating factor(G-CSF) improves cardiac function after myocardial infarction (MI). However, its direct effect on the myocardium and its signaling pathway remain unclear. We examined the acute beneficial effect of G-CSF on myocardial infarct size and its precise mechanisms in a rabbit model of myocardial infarction. In 80 Japanese white rabbits, MI was induced by 30 min of ischemia and 48 hours of reperfusion. Rabbits were intravenously injected with 10 μg/kg of G-CSF (G-CSF group, n=10) or saline (control group, n=10) immediately after reperfusion. The G-CSF+5HD group (n=10) was injected with 5-HD(5-hydroxydecanoate, a mitochondrial KATP channel blocker) 5 min before G-CSF injection. The G-CSF +wortmaninn group (n=10) was injected wortmaninn (0.6mg/kg) 5 min before G-CSF injection. G-CSF+L-NAME group (n=10) was injected with L-NAME (10mg/kg) 5 min before G-CSF injection. The 5HD alone (n=10), wortmannin alone (n=10), L-NAME alone (n=10) groups were respectively injected 5HD, wortmannin and L-NAME immediately after reperfusion. Myocardial infarct size was calculated as a percentage of the risk area of the left ventricle. Western blot analysis was performed to examine the Akt and phospho-Akt and phospho-eNOS in the ischemic myocardium at 48 hours of reperfusion. The infarct size was significantly smaller in the G-CSF group (26.7±2.7%) than in the control group (42.3±4.6%). The infarct size-reducing effect of G-CSF was completely blocked by 5-HD (42.5±1.66%), wortmaninn(44.7±4.81) and L-NAME (42.1±4.2%). Wortmannin, L-NAME or 5HD alone did not affect the infarct size. Western blotting showed higher expression of phospho-Akt and phosho-eNOS in the infarct area in the G-CSF group than in the control group. G-CSF administered immediately after reperfusion reduces myocardial infarct size via activation of PI3K, Akt, eNOS and opening the mitochondrial KATP channels.

Prevention of adverse electrical and mechanical remodeling with biventricular pacing in a rabbit model of myocardial infarction

Biventricular (BIV) pacing can improve cardiac function in heart failure (HF). This study sought to investigate the mechanisms of benefit of BIV pacing using a rabbit model of myocardial infarction (MI). New Zealand White rabbits were divided into 4 groups (sham-operated [C], MI with no pacing [MI], MI with right ventricular pacing [MI+RV], and MI with BIV pacing [MI+BIV]) and underwent serial electrocardiograms and echocardiograms. At 4 weeks, hearts were excised and tissue was extracted from various areas of the left ventricle (LV). Four weeks after coronary ligation, BIV pacing prevented systolic and diastolic dilation of the LV as well as the reduction in its fractional shortening, restored the QRS width and the rate-dependent QT intervals to their baseline values, and prevented the decline of the ether-a-go-go (Erg) protein levels. This prevention of remodeling was not documented in the MI+RV groups. In this rabbit model of BIV pacing and MI, we show prevention of adverse mechanical and electrical remodeling of the heart. These changes may underlie some of the benefits seen with BIV pacing in HF patients with more severe LV dysfunction.

Effects of prolonged metoprolol treatment on neural remodeling and inducible ventricular arrhythmias after myocardial infarction in rabbits

Background Neural remodeling is part of the pathophysiology of ventricular arrhythmias after myocardial infarction (MI). In this study, we developed a rabbit model of MI to investigate the effect of the β-blocker metoprolol on ventricular neural remodeling and susceptibility to ventricular arrhythmias. Methods MI was induced by ligation of the left anterior descending coronary artery in 30 rabbits, and sham operations were performed in 12 control animals. Metoprolol was then administered to 15 of the MI animals. After electrophysiological recordings, the expression of nerve markers was studied at the infarct border and the non-infarct left ventricle free wall (LVFW) by immunostaining or RT-PCR. Results Eight weeks after MI, the incidence of inducible ventricular arrhythmias was significantly ( P < 0.01) higher in the MI group than in the sham group. However, metoprolol treatment decreased incidence of post-MI ventricular arrhythmias (8.3%) compared to those without treatment (58.3%, P < 0.001). The density of nerve fibers was increased in MI group (3889 ± 521 μm 2/mm 2) compared to the sham group (1727 ± 304 μm 2/mm 2). Treatment of MI rabbits with metoprolol resulted in a partial reduction (2725 ± 283 μm 2/mm 2). However, the shape and imbalance of nerve fibers appeared to be normalized by the metoprolol treatment. The expression levels of TH mRNA were reduced ( P < 0.01) by metoprolol treatment. Conclusion Metoprolol reduces post-MI ventricular arrhythmias, partly by altering the neural remodeling process.

A64. Total liquid ventilation rapidly cools the heart to protect it from infarction

Decreasing myocardial temperature during ischemia is a powerful cardioprotective strategy, but application in the setting of acute myocardial infarction has been impaired by the lack of a practical methodology to quickly cool the heart. We investigated whether total liquid ventilation with a temperature-controlled mixture of perfluorocarbons could elicit rapid cardioprotective cooling in a rabbit model of myocardial infarction. We performed a 30-min coronary artery occlusion followed by 3 h of reperfusion in pentobarbital-anesthetized open-chest rabbits.

Na+/Ca2+ Exchanger Expression and Function in a Rabbit Model of Myocardial Infarction

In general, sarcolemmal Na(+)/Ca(2+) exchanger (NCX) protein and activity is increased in hearts with ventricular dysfunction. However, in a subset of studies, reduced activity of NCX has been reported. Left ventricular dysfunction (LVD) was induced in the rabbit eight weeks after an apical myocardial infarction. Using single microelectrode voltage clamp to assess the NCX activity in isolated ventricular cells, a decrease in NCX activity by approximately 30% was observed. Immunoblot analysis indicated increased NCX protein levels by approximately 20% in the LVD group. The cause of this paradox is unknown. Overexpression of the protein sorcin increased the activity of NCX without affecting NCX protein levels. Sorcin protein (dimer) levels were significantly lower in the LVD group (0.67+/-0.05 n=15, P<0.05) compared to sham (1.0+/-0.16, n=15). Sorcin monomer levels were not significantly different (sham: 1.0+/-0.26, LVD: 0.83+/-0.13). Mathematical modeling of NCX suggests that a reduction of NCX activity during diastole to that in LVD could be achieved by holding the diastolic membrane potential at -60 mV instead of -80 mV. Holding E(m) at -60 mV decreased NCX-mediated Ca(2+) efflux rates to values comparable to those seen in LVD and increased SR Ca(2+) content and peak systolic [Ca(2+)] in sham and LVD cardiomyocytes. In conclusion, reduced sorcin expression may be linked to the lower NCX activity in the rabbit model of LVD. Reduced NCX activity during diastole increases SR Ca(2+) content and Ca(2+) transient amplitude.

Hepatocyte growth factor gene transfer improves cardiac function and remodeling via enhancing angiogenesis and bcl-2 expression and decreasing hydroxyl radicals

Background: Gene transfer of hepatocyte growth factor (HGF) is reported to protect the heart against ischemia- reperfusion injury. However, its precise mechanisms are unknown. Methods: In male Japanese white rabbits, 1 × 10 9 particles of adenovirus Ad-HGF (HGF group, n = 15) or adenovirus Ad-LacZ (control group, n = 15) was directly injected into the myocardium. Three days after viral infection, the coronary artery was occluded for 30 min and reperfused. The heart was excised at 2 or 14 days after infarction. The infarct size and cardiac function were obtained. Bcl-2 protein was detected. Myocardial interstitial 2,5-DHBA levels, an indicator of hydroxyl radicals, were also measured. Results: The infarct size was significantly reduced in the HGF group (13.4 ± 2.3 %) than in the control group (36.5 ± 2.0 %) at 2 days after infarction. Smaller LV dimension and increased LV ejection fraction and higher capillary density assessed by immunostaining of CD31 were observed in the HGF group at 14-days after infarction. Bcl-2 protein was significantly increased at 4 h of reperfusion in the HGF group than in the control group. The 2,5-DHBA levels during ischemia and reperfusion was significantly attenuated in the HGF group compared to the control group. Conclusion: In vivo adenovirus-mediated HGF gene transfer improves cardiac function and remodeling via enhancing angiogenesis and Bcl-2 expression and decreasing hydroxyl radicals in a rabbit model of myocardial infarction.

Post-ischemic cardioprotection by A2A adenosine receptors: dependent of phosphatidylinositol 3-kinase pathway.

Activation of myocardial A2A adenosine receptors during reperfusion has been shown to be cardioprotective. The intracellular mechanisms underlying this protection remain unknown. To understand the beneficial effects of activated A2A adenosine receptors in such a state, we investigated whether the enzymes phosphatidylinositol 3-kinase (PI3K) and caspase-3 can account for this post-ischemic cardioprotective effect in an anesthetized rabbit model of myocardial infarction (30 minutes ischemia; 5 hours reperfusion). Administration of the A2A agonist CGS21680 (0.2 microg/kg/min) 5 minutes before reperfusion began (Early) reduced infarct size expressed as a percentage of the area at risk (25.7 +/- 5.3% versus 46.5 +/- 5.3% for the control group; * P < 0.05). Treatment with the A2A agonist 5 minutes after the onset of reperfusion (Late) had no effect on infarct size (38.2 +/- 6.2%). In the presence of a selective inhibitor of PI3K (LY294002), the beneficial effects of CGS21680 on infarct size was no longer observed (43.9 +/- 7.9%). After 5 hours of reperfusion, higher PI3K activity in the ischemic region was observed in the Early group compared with the other experimental groups. Caspase-3 activity was not observed in these different groups. In another set of experiments, PI3K activity was significantly higher during the first 15 minutes of reperfusion in the Early group as compared with the Control group. Caspase-3 activity increased rapidly during the first 15 minutes of reperfusion in the Control group and remained stable in the Early group. These results indicated that post-ischemic cardioprotection afforded by A2A adenosine receptor activation is PI3K-dependent and modulate rapidly other signaling pathways such as caspase-3.

Manipulating cardiac contractility in heart failure: data from mice and men.

In the year 1990, cardiovascular disease surpassed infectious diseases as the leading cause of death worldwide, and by the year 2020 it is predicted to be the leading cause of all disability.1,2 In the United States, cardiovascular disease has been estimated to account for 44% of the nation’s mortality and is a leading cause of morbidity.3,4 Heart failure afflicts an estimated 5 million Americans, with ≈400 000 new individuals diagnosed each year at an annual cost of more than $20 billion.4–6 The alarming reality behind these statistics is our current lack of an effective therapy to repair or otherwise reverse severe forms of cardiac dysfunction and pathological remodeling associated with heart failure. Typically, heart failure is the final culmination of protracted disease states precipitated by underlying hypertension, ischemic disease and atherosclerosis, valvular insufficiency, viral myocarditis, or mutations in genes encoding sarcomeric proteins.6 Given these diverse etiologies, it is not surprising that the final phenotypic manifestations of heart failure can also vary considerably, although dilated cardiomyopathy is the most common. This syndrome is characterized by a progressive loss in contractility and ejection fraction, ventricular chamber dilatation, ventricular wall thinning, increased peripheral vascular resistance, and dysregulated fluid homeostasis. The predominant therapeutic strategy used over the past two decades for treating such patients has been based in pharmacological manipulation of cardiac contractility.7–9 Initially, positive inotropic agents were used as a means of enhancing cardiac pump function aimed at alleviating congestive symptomology. However, use of positive inotropes is now indicated only as a means of acutely bridging patients in severe heart failure because these agents actually worsen prognosis in individuals with somewhat more stable heart failure.8 More recently, pharmacological blockade of β-adrenergic receptors has emerged as the favored treatment for individuals in heart failure. β-Adrenergic receptor antagonists initially …