Myocardial contractile effects of nitric oxide

Recent experimental and clinical research solved some of the controversies surrounding the myocardial contractile effects of NO. These controversies were: (1) does NO exert a contractile effect at baseline? (2) is NO a positive or a negative inotrope? (3) Are the contractile effects of NO similar when NO is derived from NO-donors or from the different isoforms of NO synthases (NOS)? (4) Does NO exert the same effects in hypertrophied, failing or ischemic myocardium? Transgenic mice with cardioselective overexpression of NOS revealed NO to produce a small reduction in basal developed LV pressure and a LV relaxation-hastening effect mainly through myofilamentary desensitization. Similar findings had previously been reported during intracoronary infusions of NO-donors in isolated rodent hearts and in humans. The LV relaxation hastening effect was accompanied by increased diastolic LV distensibility, which augmented LV preload reserve especially in heart failure patients. This beneficial effect on diastolic LV function always overrode the small NO-induced attenuation in LV developed pressure in terms of overall LV performance. In most experimental and clinical conditions, contractile effects of NO were similar when NO was derived from NO-donors or produced by the different isoforms of NOS. Because expression of inducible NOS (NOS2) is frequently accompanied by elevated oxidative stress, NO produced by NOS2 can lead to peroxynitrite-induced contractile impairment as observed in ischemic or septic myocardium. Finally, shifts in isoforms or in concentrations of myofilaments can affect NO-mediated myofilamentary desensitization and alter the myocardial contractile effects of NO in hypertrophied or failing myocardium.     

Matrix, cytoskeleton, or myofilaments: which one to blame for diastolic left ventricular dysfunction?

During cardiac filling, the relative contribution of distension of interstitial collagen, of distension of cytoskeletal proteins, and of low-grade diastolic cross-bridge cycling in the generation of diastolic left ventricular (LV) pressure remains unclear. In failing myocardium, interstitial collagen deposition and cross-linking are augmented. This increase in collagen deposition is accompanied by expression of a stiffer isoform of titin in the cardiomyocytes. Higher diastolic stiffness of failing myocardium is therefore not necessarily related to increased interstitial collagen content. Moreover, phosporylation of titin by protein kinase A and G, and inhibition of titin-actin interaction by cytosolic calcium allow for dynamic modulation of its diastolic tension generation and could account for acute shifts of myocardial distensibility. Acute shifts of myocardial distensibility, as occur in hypertrophy or in demand ischemia, have usually been attributed to a diastolic resurgence of cross-bridge interaction. In hypertrophied and failing myocardium, the recent demonstrations of diastolic calcium release from the ryanodine receptor, of deficient diastolic calcium removal from the cytosol, and of enhanced myofilamentary calcium sensitivity support residual diastolic cross-bridge interaction. In demand ischemia, the role of calcium overload in the reduction of diastolic LV distensibility is less clear because of correction of the reduced diastolic LV distensibility by quick stretches but not by a calcium desensitizer. Simultaneous imposition in animal models of multiple molecular changes involving interstitial, cytoskeletal, and myofilamentary proteins could elucidate their relative importance for myocardial stiffness and lead to selective correction of diastolic LV dysfunction as a novel mode of heart-failure therapy.     

Beneficial Effects of Nitric Oxide on Cardiac Diastolic Function: 'The Flip Side of the Coin'

Modulation by NO of systolic myocardial function received widespread attention but most studies focused on potential negative inotropic properties of NO. The very original observations on the effects of NO on myocardial contraction already provided evidence that NO modified myocardial contractile performance mainly through a relaxation-hastening effect (i.e. earlier onset of relaxation) and through an increase in myocardial distensibility. The present review discusses the relaxation hastening and distensibility-increasing effects of NO in experimental preparations, in the normal human heart, in left ventricular hypertrophy of aortic stenosis, in the human allograft and in dilated nonischemic cardiomyopathy. This diastolic flip side of the myocardial effects of NO appears to be beneficial especially for patients who are dependent on the LV Frank-Starling response to maintain cardiac output.     

Increased expression of constitutive nitric oxide synthase III,but not inducible nitric oxide synthase II,in human heart failure

Objectives. The purpose of the present study was to examine the expression of the endothelial-type nitric oxide synthase (NOS III) and the inducible-type NOS (NOS II) in human myocardium and their regulation in heart failure from patients with different etiologies.Background. In heart failure, plasma levels of nitrates were found to be elevated. However, data on myocardial NOS expression in heart failure are conflicting.Methods. Using RNase protection analysis and Western blotting, the expression of NOS III and NOS II was investigated in ventricular myocardium from nonfailing (NF) hearts (n = 5) and from failing hearts of patients with idiopathic dilated cardiomyopathy (dCMP, n = 14), ischemic cardiomyopathy (iCMP, n = 9) or postmyocarditis cardiomyopathy (mCMP, n = 7). Furthermore, immunohistochemical studies were performed to localize NOS III and NOS II within the ventricular myocardium.Results. In failing human hearts, NOS III mRNA levels were increased to 180% in dCMP, 200% in iCMP and to 210% in mCMP as compared to NF hearts. Similarly, in Western blots (using constitutively expressed beta-tubulin as a reference) NOS III protein expression was increased about twofold in failing compared to NF hearts. Immunohistochemical studies with a selective antibody to NOS III showed no obvious differences in the staining of the endothelium of cardiac blood vessels from NF and failing human hearts. However, NOS III-immunoreactivity in cardiomyocytes was significantly more intense in failing compared to NF hearts. Low expression of NOS II mRNA was detected in only 2 of 30 failing human hearts and was not found in NF hearts. Inducible-type NOS protein was undetectable in either group.Conclusions. We conclude that the increased NOS III expression in the ventricular myocardium of failing human hearts may contribute to the contractile dysfunction observed in heart failure and/or may play a role in morphologic alterations such as hypertrophy and apoptosis of cardiomyocytes.     

Selective NOS inhibition restores myocardial contractility in endotoxemic rats; however, myocardial NO content does not correlate with myocardial dysfunction

The role of nitric oxide (NO) in lipopolysaccharide (LPS)-induced myocardial dysfunction remains controversial as some investigators concluded that inhibition of NO synthesis improves left ventricular (LV) contractility, whereas others did not. We investigated the relationship between LPS-induced LV dysfunction and LV NO production. We postulated that high myocardial NO concentrations would correspond to decreased contractility and low NO concentrations would correspond to recovery. In a rat model of endotoxemia, we used the isolated papillary preparation to assess inotropic dysfunction. We measured LV NO content and hemodynamics at baseline, 4, 16, and 48 h after LPS administration. LPS caused a decrease in LV contractility at 16 h with recovery at 48 h. Myocardial NO levels were elevated at all time periods. However, at 48 h in spite of normalization of LV contractility, myocardial NO content remained elevated. Pretreatment of LPS animals with the nonselective nitric oxide synthase (NOS) inhibitor N (G)-nitro-L-arginine methyl ester (L-NAME) worsened LV contractility, decreased LV NO content, and increased mortality. However, pretreatment with the relatively selective inducible NOS (iNOS) inhibitor S-methylisothiourea sulfate (SMT) restored LV contractility. Myocardial NO content in the SMT was lower than that of the LPS only group, but higher than the L-NAME group. We conclude that SMT is beneficial to myocardial contractility in this model of endotoxemia, whereas pretreatment with L-NAME is associated with further deterioration of contractility and increased mortality. Moreover, our data indicate that high myocardial NO concentrations do not necessarily correlate with decreased contractility.     

Cardiac myocyte neuronal nitric oxide synthase. New therapeutic target in heart failure?

Although nitric oxide-dependent regulation of contractile function is altered in the diseased and failing heart, several aspects of nitric oxide (NO) signalling in the myocardium remain poorly understood. Some apparently contrasting findings may have arisen from the use of non-isoform-specific inhibitors of NO synthase isoforms (NOS) as compared to the use of mouse models genetically deficient or overexpressing the NOS thought to be responsible for the increase in NO production in heart failure (mainly NOS2 and NOS3). In recent years, identification of the neuronal NOS (NOS1) isoform in cardiac myocytes and the recognition of the importance of its subcellular localisation have greatly advanced the understanding of the critical role of NOS1-derived NO in the control of myocardial contractility both in the normal and failing heart. The challenge is now to confirm these emerging findings on the critical role of NOS1-derived NO in human cardiac physiology and hopefully translate them into therapy.     

L-arginine reduces heart rate and improves hemodynamics in severe congestive heart failure

BACKGROUND: Stimulated endothelium-derived relaxing factor-mediated vasodilation and conduit artery distensibility are impaired in congestive heart failure (CHF). L-arginine could have a potentially beneficial role in CHF, acting through the nitric oxide (NO)-L-arginine pathway or by growth hormone increment. HYPOTHESIS: This study was undertaken to investigate the effects of L-arginine on heart rate, hemodynamics, and left ventricular (LV) function in CHF. METHODS: In seven patients (aged 39 +/- 8 years) with CHF, we obtained the following parameters using echocardiography and an LV Millar Mikro-Tip catheter simultaneously under four conditions: basal, during NO inhalation (40 ppm), in basal condition before L-arginine infusion, and after L-arginine intravenous infusion (mean dose 30.4 +/- 1.9 g). RESULTS: Nitric oxide inhalation increased pulmonary capillary wedge pressure from 25 +/- 9 to 31 +/- 7 mmHg (p < 0.05), but did not change echocardiographic variables or LV contractility by elastance determination. L-arginine decreased heart rate (from 88 +/- 15 to 80 +/- 16 beats/min, p<0.005), mean systemic arterial pressure (from 84 +/- 17 to 70 +/- 18 mmHg, p < 0.007), and systemic vascular resistance (from 24 +/- 8 to 15 +/- 6 Wood units, p<0.003). L-arginine increased right atrial pressure (from 7 +/- 2 to 10 +/- 3 mmHg, p<0.04), cardiac output (from 3.4 +/- 0.7 to 4.1 +/- 0.8 l/min, p < 0.009), and stroke volume (from 40 +/- 9 to 54 +/- 14 ml, p < 0.008). The ratios of pulmonary vascular resistance to systemic vascular resistance at baseline and during NO inhalation were 0.09 and 0.075, respectively, and with L-arginine this increased from 0.09 to 0.12. CONCLUSION: L-arginine exerted no effect on contractility; however, by acting on systemic vascular resistance it improved cardiac performance. L-arginine showed a negative chronotropic effect. The possible beneficial effect of L-arginine on reversing endothelial dysfunction in CHF without changing LV contractility should be the subject of further investigations.     

Inhibition of endogenous nitric oxide synthase augments contractile response to adenylyl cyclase stimulation without altering mechanical efficiency in patients with idiopathic dilated cardiomyopathy.

BACKGROUND: Increased nitric oxide (NO) in the failing heart attenuates the myocardial contractile response to beta-adrenergic receptor stimulation. However, the physiological effects of NO on the beta-adrenergic post-receptor signaling system are unknown. The objective of the present study was to examine the effects of cardiac NO synthase (NOS) inhibition on left ventricular (LV) hemodynamics and mechanoenergetics in response to adenylyl cyclase stimulation in human heart failure. METHODS AND RESULTS: The study group comprised 13 patients with heart failure because of idiopathic cardiomyopathy (IDC). Emax was examined as an index of LV contractility, LV external work (EW), pressure-volume area (PVA), myocardial oxygen consumption (MVO2), and mechanical efficiency (EW/MVO2) with the use of conductance and coronary sinus thermodilution catheters before and during colforsin daropate infusion, and during concurrent infusion of colforsin daropate with the NOS inhibitor, NG-monomethyl-L-arginine (L-NMMA; 200 micromol). Colforsin daropate increased Emax by 53% and EW by 18%, and reduced PVA by 14%, without altering MVO2 or mechanical efficiency. The combination of colforsin daropate with L-NMMA further increased Emax by 26% and reduced PVA by 9%, without altering MVO2 or mechanical efficiency. CONCLUSIONS: These findings suggest endogenous NO may modulate beta-adrenergic post-receptor pathways and preserve myocardial efficiency in patients with IDC.     

Nitric oxide synthase inhibition impairs myocardial efficiency and ventriculo-arterial matching in acute ischemic heart failure

BACKGROUND AND AIMS: The effect of nitric oxide (NO) manipulation in acute heart failure has not been sufficiently investigated. Therefore, we assessed the impact of NO-synthase (NOS) inhibition on left ventricular (LV) function and energetics as well as overall hemodynamics, in a porcine model of acute ischemic LV failure. METHODS: Acute heart failure was induced by left coronary artery microembolization in fourteen anesthetized pigs. LV pressure-volume relationships and mechanical work (PVA) were assessed 30 min after stable heart failure, using pressure-conductance catheters. Myocardial oxygen consumption (MVO(2)) was determined from coronary flow and coronary arteriovenous oxygen difference. Microembolization led to a significant decrease in cardiac output, arterial pressure and LV systolic and diastolic performance. Animals were then randomized to a control group (n=7) or to receive 15 mg/kg N(omega)-Nitro-L-arginine-metyl ester (n=7), an inhibitor of NO synthase (NOS). RESULTS: Measurements 15 min later revealed that NOS inhibited animals had significantly reduced cardiac output (1.53+/-0.45 vs. 2.13+/-0.49 l/min, P=0.003) and stroke work (1054+/-461 vs. 1296+/-348 mmHg ml, P=0.03), and also displayed a significant increase in the slope of the MVO(2)-PVA relationship (2.57+/-0.53 vs. 1.92+/-0.15, P=0.008), i.e. an inefficient chemomechanical coupling. NOS inhibition did not alter contractility, diastolic function or arterial pressure, but afterload was significantly increased compared to controls (arterial elastance 6.03+/-1.48 vs. 2.74+/-0.34 mmHg/ml, P=0.009). CONCLUSION: Inhibition of NOS in experimental acute heart failure increased afterload without altering left ventricular systolic and diastolic function. Consequently, cardiac output was reduced. Furthermore, mechanoenergetic efficiency was severely impaired. NOS inhibition in acute heart failure and cardiogenic shock warrants further investigations.     

犬急性心肌缺血时循环内皮素和一氧化氮的变化及其相关酶的基因表达

目的：探讨急性心肌缺血犬循环内皮素和一氧化氮的浓度变化以及内皮素转换酶（ＥＣＥ）、一氧化氮合酶（ＮＯＳ）基因在缺血心肌的表达和分布情况。方法：结扎麻醉犬冠状动脉左前降支中段，造成实验性急性心肌缺血模型。采用放射免疫法测定血浆内皮素含量，比色法测定血清一氧化氮代谢产物水平，以原位杂交技术检测缺血心肌中ＥＣＥ和ＮＯＳ信使核糖核酸（ｍＲＮＡ）的表达。结果：随着缺血时间的延长，血中内皮素含量显著升高，而一氧化氮代谢产物水平逐渐下降；缺血３小时后，心肌中ＥＣＥｍＲＮＡ呈高表达，而ＮＯＳｍＲＮＡ呈低表达。结论：心肌缺血时循环内皮素和一氧化氮的浓度变化与ＥＣＥｍＲＮＡ、ＮＯＳｍＲＮＡ表达水平一致，提示内皮素与一氧化氮两者的平衡失调可能参与了心肌缺血性损伤的发生和发展过程。     

17 Beta-estradiol stimulates expression of endothelial and inducible NO synthase in rat myocardium in-vitro and in-vivo

OBJECTIVES: NO production has been attributed to play a major role in cardiac diseases such as cardiac hypertrophy and cardiac remodeling after myocardial infarction which display significant gender-based differences. Therefore we assessed the effect of 17 beta-estradiol (E2) on estrogen receptor (ER) alpha and beta and endothelial and inducible NO synthase in neonatal and adult rat cardiomyocytes. METHODS: The presence of ER alpha and ER beta was demonstrated by immunofluorescence and western blot analysis as well as the expression pattern of inducible NO synthase (iNOS) and endothelial NOS (eNOS) in isolated cardiomyocytes from neonatal and adult rats. Furthermore, regulation of myocardial iNOS and eNOS expression by estrogen was evaluated in the myocardium from ovariectomized or sham-operated adult Wistar-Kyoto rats. RESULTS: Incubation with E2 led to translocalization of the ER into the nucleus and increased receptor protein expression. E2 stimulated expression of iNOS and eNOS in both neonatal and adult cardiac myocytes. Coincubation with the pure anti-estrogen ICI 182,780 inhibited upregulation of ER and NOS expression. In ovariectomized rats myocardial iNOS and eNOS protein levels were significantly lower compared to sham-operated female animals. CONCLUSION: Taken together, these results show that E2 stimulates the expression of iNOS/eNOS in neonatal and adult cardiomyocytes in-vivo and in-vitro. These novel findings provide a potential mechanism of how estrogen may modulate NOS expression and NO formation in the myocardium.     

Left ventricular systolic and diastolic function in the hypertrophied ventricle

To investigate left ventricular (LV) systolic and diastolic function in cardiac hypertrophy, we analysed LV pressure (catheter tip-manometer) and simultaneously performed cineangiography in 24 patients with systemic hypertension (HT), 25 patients with hypertrophic cardiomyopathy (HCM) and 25 normal subjects. We digitized LV cineangiograms frame by frame and computed volume and its derivatives, wall thickness and circumferential wall stress. LV systolic pump function was normal or supernormal in HT and HCM. However, myocardial contractility assessed by end-systolic wall stress-volume relation was depressed in HCM whereas it is normally maintained in HT. LV diastolic function was also impaired in HCM and even in HT despite normal systolic function. The LV hypertrophy group showed significantly prolonged time constant of isovolumic relaxation, increased time from end-systole to the peak filling rate, and upward shift of the diastolic pressure-volume relationship. The characteristic findings of LV diastolic function in LV hypertrophy, therefore, can be summarized as impaired isovolumic relaxation, delayed early diastolic filling and decreased diastolic distensibility. The mechanisms of abnormal systolic and diastolic function may include myocardial ischemia and/or calcium overload in hypertrophied myocardium, but further study will be needed to clarify these problems.     

Inhibition of NOS2 ameliorates cardiac remodeling,improves heart function after myocardial infarction in rats

Abstract. Objective: Previous studies have shown increased expression of nitric oxide synthase 2 (NOS2) in rat heart several weeks after myocardial infarction (MI). The aim of this study was to examine the effect of chronic administration of S-methylisothurea (SMT), a selective NOS2 inhibitor, commenced one week after MI on hemodynamic parameters and left ventricular (LV) remodeling in rats. Methods: Rats with MI induced by left coronary ligation were given SMT (0.5 mg/kg/d) or saline by gavage starting one week after MI. After chronic administration for five weeks, hemodynamic and cardiac morphologic studies were performed, and lung water content, plasma NO_x concentration, NOS2 protein level, myocyte size and collagen volume fraction of noninfarct LV area were quantified. Results: The NO_x concentration in plasma and the NOS2 protein level in noninfarct myocardium in MI rats were higher than controls. When compared with the MI rats receiving saline, chronic administration of SMT reduced myocyte size (15.1 ± 1.6 µm vs 16.9 ± 2.3 µm, P < 0.05), collagen volume fraction of noninfarct LV area (4.4% ± 1.1% vs 5.7% ± 1.2%, P < 0.01) and lung water content (77.4% ± 1.4% vs 79.3% ± 0.9%, P < 0.01), without affecting infarct size. Administration of SMT had no significant effect on heart rate and mean arterial pressure, but decreased LV end-diastolic pressure (8.7 ± 2.1 mmHg vs 13.4 ± 3.1 mmHg, P < 0.01), central venous pressure (0.9 ± 0.3 mmHg vs 1.5 ± 0.5 mmHg, P < 0.01) and inner LV diameter (6.9 ± 0.3 mm vs 7.2 ± 0.3 mm, P < 0.05) in the MI rats. Plasma level of NO_x in the MI rats receiving SMT was reduced to control level. Conclusions: Chronic administration of SMT had beneficial effects on LV remodeling and cardiac dysfunction in MI rats, suggesting the possibility that inhibition of NOS2 could be a therapeutic tool for cardiac dysfunction after MI.     

抑制诱生型一氧化氮合酶对大鼠心肌梗死后左心室形态及心功能的影响

目的 :探讨抑制诱生型一氧化氮合酶 (iNOS)对大鼠心肌梗死后左心室形态及心功能的影响。方法 :结扎大鼠左冠状动脉建立心肌梗死模型。免疫组化检测心肌iNOS表达水平。分别于心肌梗死发生前、心肌梗死 7d后开始iNOS抑制剂S methylisothiourea (SMT)干预 ,于心肌梗死 6周后测定血浆一氧化氮 (NO)、心肌iNOS表达、左心室形态变化和心功能。结果 :心肌梗死 6周后心肌iNOS表达增加 ,血浆NO水平上升。于心肌梗死发生前、心肌梗死 7d后开始SMT干预均可降低血浆NO水平 ,减轻心室扩张 ,减轻心室重量 ,改善心功能。心肌梗死发生前开始SMT干预尚可提高存活率。结论 :iNOS在心肌梗死后心功能障碍的发生发展过程中起促进作用 ,抑制iNOS可以改善左心室功能 ,其机制与减轻心肌梗死后左心室重构有关。     

Up-to-date access to cardiovascular problems

The regulatory systems that control the pump function of the heart are the mechanisms that modulate the level of myocardial contractility and the lenght-tension relationship. The Frank-Starling relationship is important in balancing -- beat-to-beat -- the outputs of both ventricles. More drastic changes in circulatory dynamics, as during exercise and in old age, are accompanied by changes in myocardial contractility. The young heart normally becomes smaller during exercise, even though the cardiac output is markedly increased. The increased myocardial contractility and the normal distensibility make it possible that the length-tension curve moves to the left and upward. The old heart and the failing heart tend to a relative dilation, even though the cardiac output is markedly decreased. Because of the diminished myocardial contractility in combination with the decreased distensibility, the length-tension curve is moved to the right and downward.     

脓毒症时各型一氧化氮合酶在大鼠心脏中的表达及其可能机制

目的研究脓毒症时各型一氧化氮合酶(NOS)在心脏中的损伤作用及其机制。方法成年雄性Wistar大鼠腹腔注射脂多糖(LPS)制备脓毒症模型。应用多导生理仪监测大鼠心功能变化;用分光光度计法测定大鼠心肌组织NOS的活性;用RT-PCR和Western blot对大鼠心肌组织各型NOS的表达进行半定量分析。结果给予LPS后6h大鼠心肌收缩和舒张功能受损下降,心肌中iNOS的活性明显升高,eNOS和nNOS(合称cNOS)活性减弱;RT-PCR和Western blot结果显示,给予LPS后cNOS的表达减少,给予LPS后iNOS表达量明显增加。结论脓毒症时,iNOS、nNOS和eNOS的表达和活性发生改变;心肌细胞上iNOS表达及活性升高,这些变化可能在心功能降低中发挥作用。     

Deoxyribonucleic acid damage/repair proteins are elevated in the failing human myocardium due to idiopathic dilated cardiomyopathy

OBJECTIVES: The study investigated the expression and relationship of deoxyribonucleic acid (DNA) repair enzymes with hemodynamic and nitric oxide (NO)-mediated stress in the failing myocardium. BACKGROUND: The role of apoptosis in human heart failure is controversial. Experimental studies suggested that NO-mediated stress modulates apoptosis of the cardiac myocytes. Of note, DNA repair enzymes such as redox factor/apurinic/apyridimine endonuclease Ref-1 protein, proliferative cell nuclear antigen (PCNA), the poly (ADP-ribose) polymerase (PARP), and DNA-protein kinase (DNA-PK) determine the cell fate after the DNA damage. METHODS: Left ventricular (LV) endomyocardial biopsies from 23 patients with dilated cardiomyopathy were analyzed by immunohistochemistry. RESULTS: Terminal deoxynucleotidyltransferase-mediated biotin-dUTP nick-end labeling (TUNEL) or cleaved caspase-3 and cleaved PARP could not be detected. The number of Ref-1-positive myocytes tended to be higher in patients with LV ejection fraction (EF) < or =35% versus LV EF >35% (21.23 +/- 4.8% vs. 13.8 +/- 5.8%, p = 0.1). The PCNA (7.1 +/- 2.8% vs. 0.9 +/- 0.6%, p = 0.05) and DNA-PK expressions (39.5 +/- 5.4% vs. 8.6 +/- 5.5%, p < 0.01) were higher in patients with LVEF < or =35% vs. LVEF >35%. The PCNA, Ref-1, and DNA-PK expression correlated with the LV end-systolic wall stress (r = 0.61, p < 0.01; r = 0.52, p < 0.01; and r = 0.73, p < 0.001, respectively). In addition, the PCNA and DNA-PK expression correlated with inducible NO synthase (r = 0.41, p = 0.05, and r = 0.53, p < 0.01, respectively). CONCLUSION: In this study, apoptosis could not be detected in the failing myocardium owing to idiopathic dilated cardiomyopathy. In contrast, failing myocardium was characterized by active DNA repair that was associated with elevated LV wall stress and activation of the inducible NO synthase.