H(2)O(2)-induced left ventricular dysfunction in isolated working rat hearts is independent of calcium accumulation

Reactive oxygen species (ROS) and intracellular Ca²⁺ overload play key roles in myocardial ischemia-reperfusion (IR) injury but the relationships among ROS, Ca²⁺ overload and LV mechanical dysfunction remain unclear. We tested the hypothesis that H₂O₂ impairs LV function by causing Ca²⁺ overload by increasing late sodium current (I_Na), similar to Sea Anemone Toxin II (ATX-II). Diastolic and systolic Ca²⁺ concentrations (d[Ca²⁺]_i and s[Ca²⁺]_i) were measured by indo-1 fluorescence simultaneously with LV work in isolated working rat hearts. H₂O₂ (100 μM, 30 min) increased d[Ca²⁺]_i and s[Ca²⁺]_i. LV work increased transiently then declined to 32% of baseline before recovering to 70%. ATX-II (12 nM, 30 min) caused greater increases in d[Ca²⁺]_i and s[Ca²⁺]_i. LV work increased transiently before declining gradually to 17%. Ouabain (80 μM) exerted similar effects to ATX-II. Late I_Na inhibitors, lidocaine (10 μM) or R56865 (2 μM), reduced effects of ATX-II on [Ca²⁺]_i and LV function, but did not alter effects of H₂O₂. The antioxidant, N-(2-mercaptopropionyl)glycine (MPG, 1 mM) prevented H₂O₂-induced LV dysfunction, but did not alter [Ca²⁺]_i. Paradoxically, further increases in [Ca²⁺]_i by ATX-II or ouabain, given 10 min after H₂O₂, improved function. The failure of late I_Na inhibitors to prevent H₂O₂-induced LV dysfunction, and the ability of MPG to prevent H₂O₂-induced LV dysfunction independent of changes in [Ca²⁺]_i indicate that impaired contractility is not due to Ca²⁺ overload. The ability of further increases in [Ca²⁺]_i to reverse H₂O₂-induced LV dysfunction suggests that Ca²⁺ desensitization is the predominant mechanism of ROS-induced contractile dysfunction.     

Left ventricular dysfunction of isolated working rat hearts after chronic alcohol consumption.

The mechanical, haemodynamic, and energetic functions of isolated perfused working hearts from chronic alcoholic and control rats were studied. Male Long-Evans rats were fed a nutritionally-complete liquid diet containing 38% of daily calories as ethanol (isocaloric replacement with dextrin-maltose for controls) for 34 to 48 weeks. Alcoholics and controls received either 7.4% (low-fat) or 21.0% (high-fat) of calories from lipid. Animals were matched by dry heart weight for comparisons and hearts were evaluated at a constant heart rate in an improved isolated ejecting heart perfusion preparation. Ventricular function curves and the response to 10(-7) mol . litre-1 dobutamine HCl were obtained during normoxic and hypoxic perfusion. In normoxia, the hearts from the high- and low-fat alcoholic animals exhibited a significantly lower response of left ventricular maximum systolic pressure, left ventricular maximum rate of pressure rise and maximum ejection velocity to dobutamine than did the controls. In hypoxia, the left ventricular maximum systolic pressure of the low-fat alcoholic hearts was slightly, but significantly, lower than that of the low-fat control hearts at the three filling pressures studied. Also in hypoxia, the increase in left ventricular maximum rate of pressure rise with dobutamine was significantly less in the alcoholic hearts than in controls. These data suggest that long-term consumption of moderate amounts of alcohol even along with a nutritionally-adequate diet can result in depressed myocardial contractility and pump function that may be manifest when the heart is subjected to stress conditions.     

Effects of deferoxamine on H2O2-induced oxidative stress in isolated rat heart

During myocardial reperfusion injury, iron has been implicated in the Fenton based generation of hydroxyl radical, ·OH, leading to further organ injury. Although previous studies have investigated the protective effect of iron chelators including deferoxamine (DFX) in myocardial reperfusion injury, there is little information regarding the role of iron chelation during oxidative stress produced by H₂O₂ on the heart. Isolated hearts from male Sprague-Dawley rats were retrograde-perfused with Krebs-Henseleit solution at 5 ml/min. After a 60-min equilibration, oxyradical challenge was instituted by the addition of H₂O₂ (200–600 M) to the perfusate for 60 min. A subgroup of animals received DFX (400 M) in the perfusate prior to challenge with 400 M H₂O₂. Contractility was continuously monitored; perfusate samples for glutathione (GSH) and lactate dehydrogenase (LDH) estimations were collected at 30-min intervals. Headspace ethane, an indicator of lipid peroxidation, was estimated at 30-min intervals by gas chromatography. Control hearts maintained contractility during the perfusion period. H₂O₂ perfusion caused a dose dependent decrease in myocardial contractility; DFX pretreatment was partialy protective. Headspace ethane slowly accumulated in control hearts; perfusion with H₂O₂ caused dose dependent increase in ethane accumulation indicative of enhanced lipid peroxidation. GSH and LDH in the perfusate remained low in control hearts. In contrast, H₂O₂ treated hearts had a dose dependent inclease in the efflux of GSH and LDH which was markedly increased by perfusion with 600 M H₂O₂. Pretreatment with DFX did not significantly reduce GSH or LDH efflux from hearts perfused with peroxide. While H₂O₂ perfused with peroxide. While H₂O₂ perfusion causes a dose dependent decrease in myocardial contractility with a corresponding increase in headspace ethane release with GSH & LDH efflux indicative of oxidative stress, concurrent treatment with DFX reduces myocardial dysfunction and ethane generation. However, sublethal damage of plasma membrane still continues as reflected by continuous enhancement of LDH efflux, possibly indicating involvement of other reactive species besides hydroxyl radical.     

Influence of calcium preconditioning and streptomycin on ventricular dilation-induced arrhythmias in isolated rat hearts

Objective To investigate the mechanism of ventricular dilation-induced arrhythmias by dilating isolated rat hearts. Methods Isolated rat hearts were perfused by Langerdorff method. After equilibration,80 hearts were randomly divided into four groups as follows:(1) control group(n=20) ,(2) Ca2 preconditioning(CPC) group(n=20) ,(3) streptomycin group(n=20) ,and(4) CPC streptomycin group(n=20) . A latex balloon which can be filled with fluid was anchored in the left ventricle through the left atrium and mitral valve. Epicardial ECG of the left ventricle,left ventricular pressure,coronary flow and heart rate were recorded before and during ventricular dilation by injecting fluid into the latex balloon. The rate and duration of ventricular dilation-induced arrhythmias were recorded. Results Under the same increase in ventricular end-diastolic pressure made by inflation of the balloon,the rate of arrhythmias was 100% and duration of arrhythmias was 2. 56±0.46s in the control group. Both the rates of premature ventricular beat(90%) and ventricular tachycardia 70%) were high. Compared with the control group,the total rate(60%) of arrhythmias was lower,and duration(1.67±0.61s) of arrhythmias was shorter in the CPC group. Both the rates of premature ventricular beat(60%) and ventricular tachycardia(40%) were low comparatively. The rate of arrhythmias(45%) was lower and duration(1.64±0.42s) of arrhythmias was shorter,and the rates of premature ventricular beat(30%) or ventricular tachycardia(35%) were lower in the streptomycin group than in the control one. The least ventricular dilation-induced arrhythmias occurred in the CPC streptomycin group. The rate of arrhythmias(10%) was the lowest and duration(1.01±0.37s) of arrhythmias was the shortest;both the rates of premature ventricular beat(5%) and ventricular tachycardia(10%) were the lowest. Conclusions Ventricular dilation may induce arrhythmias in isolated rat hearts. Stretch-activated ion channel and the increase in [Ca2 ]i are supposed to play important roles in the pathological mechanism.     

Ventricular fibrillation threshold and local dispersion of refractoriness in isolated rabbit hearts with left ventricular dysfunction

Patients with congestive heart failure or left ventricular dysfunction (LVD) have a high incidence of ventricular tachyarrhythmias and sudden cardiac death. In addition to structural, metabolic and neuroendocrine changes, mechano-electrical feedback may play a role in arrhythmogenesis in heart failure. Three groups of rabbits (n = 10 for each) were studied: chronic coronary ligation with ejection fraction (EF) ≥ 0.45 or < 0.45, and sham-operated controls. Ventricular fibrillation (VF) thresholds were measured at LV pressures of 0 and 40 mmHg during modified Langendorff perfusion. Intervals between local activations during VF (VFI) were used as an index of refractoriness. Global dispersion was expressed as coefficient of variation of VFI; local dispersion by maximum difference in VFI between adjacent sites. Median VF threshold was lower at 0mmGH in the lower EF group compared to controls (30 vs. 67.5 mA, P<0.05). VF threshold in control hearts was lower at 40 mmHG than at 0 mmHg (P<0.01), but there was no further reduction in threshold in LVD hearts at 40mmHg. Global dispersion of VFI in the lower EF group was greater than in controls at 0mmHg in the infarct border zone (P<0.05). At 40 mmHg, local dispersion of VFI in zones bordering and remot from the infarct were greater in both LVD groups than in controls (P<0.05). Local inhomogeneity of refractoriness is more marked in the infarct border zone, but latent abnormalities are evident in normal myocardium of rabbits with left ventricular dysfunction and are revealed by left ventricular distension. Received: 7 October 1999 Returned for revision: 2 December 1999 Revision received: 19 January 2000 Accepted: 14 February 2000     

Coronary endothelial dysfunction increases the severity of ischaemia-induced ventricular arrhythmias in rat isolated perfused hearts

In order to determine the role of coronary vascular endothelial cells in generating cardioprotective substances during myocardial ischaemia, rat isolated hearts, perfused at constant flow by the Langendorff technique, were subjected to treatment with the detergent Triton X100 and the responses of these hearts to a 30 or 60 min period of coronary artery occlusion was determined. Endothelial damage or denudation was shown both by histological examination and by the altered vasodilator response to the endothelium-dependent vasodilator bradykinin (100 nM), which was reversed to vasoconstriction in hearts treated with Triton X100. In contrast, the responses to sodium nitroprusside (100 μM) were unimpaired in these hearts and were not different from control responses. Ventricular ectopic activity was much more pronounced in hearts with endothelial dysfunction (e.g., 3329±361 ventricular premature beats over a 30 min occlusion period compared to 243±34 in controls; P<0.01), and the duration of ventricular tachycardia was greatly increased (1162±391 s v 9±12 s in the controls; P<0.01). Ventricular ectopic activity was still marked when the occlusion was prolonged to 1 h and was still apparent at the end of this 1 h occlusion period. Reperfusion arrhythmias (ventricular tachycardia and ventricular fibrillation) were marked in endothelium-damaged hearts (50%); whereas there were no such arrhythmias after a 30 or 60 min occlusion period in control hearts. Hearts were also preconditioned by a 3 min coronary artery occlusion period 10 min prior to a 30 min coronary artery occlusion. This reduced ventricular ectopic activity in both control and endothelium-damaged hearts to about the same extent (between 80 and 90% suppression). The results suggest that under normal conditions substances generated from endothelial cells protect the myocardium against ventricular arrhythmias both during ischaemia and reperfusion. However, in this species, preconditioning is still possible in hearts from which the coronary vascular endothelium has been removed. If these results can be extrapolated to the clinical situation, it suggests that in patients with endothelial dysfunction ventricular arrhythmias may be more pronounced following a period of ischaemia and especially of reperfusion. Received: 8 July 1997, Returned for revision: 31 July 1997, Revision received: 3 November 1997, Accepted: 2 December 1997     

Contrast effects of isoproterenol and ouabain on left ventricular diastolic relaxation dysfunction in isolated, blood-perfused rabbit hearts

We studied the influence of inotropic agents on prompt and transient left ventricular (LV) diastolic relaxation dysfunction produced by superimposition of pacing tachycardia on low-flow ischemia, using an isolated, blood-perfused and isovolumic (balloon-in-LV) rabbit heart preparation. The LV balloon volume was adjusted to produce an LV end-diastolic pressure (EDP) of 15 mmHg and was held constant thereafter. Coronary perfusion pressure was adjusted to 100 mmHg during baseline and to 20 mmHg during low-flow ischemia of 6 min. At baseline, isoproterenol and ouabain were administered to cause moderate and similar rises (14 +/- 3 and 16 +/- 4% above baseline values, respectively) in maximum + dp/dt of LVP with no change in LVEDP. In control hearts which received no drug, superimposition of 5-min pacing tachycardia on low-flow ischemia produced a significant and transient increase in LVEDP under constant LV volume (from 13.4 +/- 0.4 to 24.7 +/- 3.3 mmHg, p less than 0.01). In the hearts which received isoproterenol it did not change LVEDP (from 14.0 +/- 0.4 to 16.2 +/- 1.0 mmHg, NS). In contrast, the ouabain hearts showed a further increase in LVEDP (from 13.7 +/- 0.8 to 29.9 +/- 4.6 mmHg, p less than 0.01). LV developed pressure, myocardial oxygen consumption or myocardial lactate production during pacing tachycardia superimposed on the low-flow ischemia did not differ significantly among the 3 groups. Thus, isoproterenol markedly improved transient LV relaxation dysfunction produced by superimposition of pacing tachycardia on low-flow ischemia, in which an equipotent inotropic dose of ouabain exaggerated the relaxation dysfunction. These results suggest that calcium overload rather than ATP depletion per se contributes to transiently impaired diastolic relaxation by pacing tachycardia and low-flow ischemia.     

Proteomic analysis of left ventricular diastolic dysfunction hearts in renovascular hypertensive rats

Abnormalities of diastolic function are common to virtually all forms of cardiac failure. However, the molecular events leading to diastolic dysfunction have not been fully elucidated. We performed a differential proteomic profiling study on diastolic dysfunction hearts induced by renovascular hypertension. Left ventricular diastolic dysfunction induced by renovascular hypertension (2K1C, two-kidneys, one clip) was performed in twelve Sprague-Dawley rats. 2D echocardiographic and cardiac protein patterns (2D-electrophoresis and mass spectroscopy) were compared with the sham operated rats. We described sixteen altered protein spots in 2K1C rats with left ventricular diastolic dysfunction. Calsarcin-1 (CS-1) was significantly down-regulated in 2K1C rats and it showed a negative correlation with calcineurin enzymatic activity (r(2)=0.72 p=0.03). We also showed changes in cellular energy metabolism in 2K1C rats, and these changes go in parallel with alterations of the thin filament proteome responsible for actin-myosin cross-bridge. In conclusion, this study provides a new insight into the left ventricular proteome profile associated with systemic hypertension induced diastolic dysfunction in a renovascular hypertension rat model. The decreased CS-1 protein with a concomitant increased enzymatic activity of calcineurin, suggests an important role of CS-1 in the calcineurin-mediated left ventricular hypertrophy.     

The effects of calcium antagonists on extracellular potassium accumulation during global ischaemia in isolated perfused rat hearts

Summary The effects of equipotent concentrations of diltiazem, verapamil, and nifedipine upon the accumulation of extracellular potassium [K⁺]_out and the left ventricular pressure (LVP) were studied during global ischemia in isolated perfused rat hearts. Measurement of [K⁺]_out and LVP were performed in two series of experiments. Diltiazem (2×10^-6, 3×10^-6, and 10^-5M), verapamil (3×10^-8, 10^-7, and 3×10^-7 M), and nifedipine (3×10^-8, 10^-7, and 1.5×10^-7 M) were able to slow, in a concentration-dependent manner, the initial rate of rise of [K⁺]_out without affecting the final plateau value of [K⁺]_out reached at t=5 to t=10 minutes. Notably, at the lowest concentrations, which slightly influenced LVP diltiazem, verapamil, and to a lesser degree nifedipine, were still able to slow the rise in [K⁺]_out. In addition, after preper-fusion with low-calcium media ([Ca²⁺] from 1.8 to 1.3 or 0.9 mM), inducing similar negative inotropic effects as those of the calcium antagonists, the rise in [K⁺]_out was not significantly influenced. Our data indicate that the ability to slow the rise in [K⁺]_out is a specific characteristic of calcium antagonists that is independent of their negative inotropic effects.     

Stroke and ventricular dysfunction in a patient with isolated left ventricular noncompaction

A 44-year-old woman developed a cardioembolic stroke. Transthoracic echocardiography demonstrated isolated noncompaction of the ventricular myocardium. Left ventricular systolic function was mildly depressed, which severely decreased during 3 months after discharge. The embolic stroke might occur when the ventricular systolic function had begun to deteriorate. The proper time to start anticoagulation in isolated noncompaction of ventricular myocardium patients may be when left ventricular systolic function decreases below normal.     

Dobutamine-induced hypotension is an independent predictor for mortality in patients with left ventricular dysfunction following myocardial infarction

Dobutamine echocardiography was performed on 297 patients after acute myocardial infarction to assess the prognostic value of dobutamine-induced hypotension in patients with left ventricular dysfunction. Patients were divided into two groups according to ejection fraction (group I, ejection fraction <0.45, n = 123; group II, ejection fraction > or =0.45, n = 174) and were followed for 20+/-8 months. Hypotension was defined as a decrease in systolic blood pressure > or =20 mm Hg, compared with baseline values. The incidence of hypotension was similar in groups I and II (23.6% vs. 18.4%, P = 0.28), and the hypotension was not related to positive dobutamine echocardiography. Univariate analysis showed that the development of hypotension was associated with a higher incidence of cardiac death in group I but not in group II. Multivariate analysis showed that dobutamine-induced hypotension was an independent predictor only for cardiac death in group I and was not related to any other cardiac events in either group. In conclusion, the development of hypotension during dobutamine stress can identify a subgroup with poor ventricular functional reserve and at high risk for cardiac death among patients complicated with left ventricular dysfunction.     

Paradoxical contributions of non-compacted and compacted segments to global left ventricular dysfunction in isolated left ventricular noncompaction

The pathophysiologic mechanisms of left ventricular (LV) dysfunction in isolated ventricular noncompaction (IVNC) remain unclear. Evaluating global and segmental systolic LV function in 65 patients with IVNC, this study found that normal wall motion was more common in noncompacted than in compacted segments. The number of noncompacted segments per patient correlated positively with the LV ejection fraction and negatively with LV end-diastolic volume index. These paradoxical findings support the concept that noncompaction represents a marker of a more generalized (cardio)myopathy rather than the direct pathophysiologic substrate of this still little-understood disease.     

Melatonin prevents H2O2-induced activation of rat hepatic stellate cells

Considerable evidence shows therapeutic effects of melatonin on liver injury and the involvement of hepatic stellate cells (HSCs) in vivo. In the present studies, we investigate the protective effect of melatonin on H2O2-induced activation of HSCs in vitro. Compared with that in control HSCs, synthesis of collagen type I was increased in H2O2-treated cells. Melatonin pretreatment significantly inhibited the above effects of H2O2 in HSCs. CCAAT/enhancer-binding protein alpha (C/EBP-alpha), which could partially reverse the phenotype of activated HSCs, augmented in HSCs pretreated with melatonin. Moreover, secretion of the most important fibrotic cytokine transforming growth factor beta 1 (TGF-beta1) diminished in melatonin-pretreated HSCs. These results suggest that melatonin prevents H2O2-induced activation of HSCs and that the mechanism involves, at least in part, differential regulation of TGF-beta1 and C/EBP-alpha gene expression.     

H(+)-induced vasodilation of rat aorta is mediated by alterations in intracellular calcium sequestration

Acidosis induces vasodilation both in vivo and in vitro. Although it is commonly surmised that acidosis alters contractility by affecting contractile proteins and calcium entry, the exact role of these mechanisms in acidosis-induced vasodilation has not been determined. In the present study, we demonstrated that a novel mechanism, involving increased calcium sequestration into intracellular sites sensitive to norepinephrine, mediates the vasodilation associated with relatively modest decreases in pH. The effects of changing pH from 7.4 to 7.0 on tension development, 45Ca fluxes, and the norepinephrine-releasable intracellular calcium stores were studied in isolated rat aorta. Acute acidification produced marked endothelium-independent dilations of aortic rings that had been precontracted with norepinephrine. In contrast, this maneuver had only modest effects on contractions elicited by 80 mM KCl or phorbol ester. Acidification in this range did not alter basal or norepinephrine-stimulated undirectional 45Ca influx, nor did it reduce the norepinephrine-induced net gain in 45Ca content. Furthermore, neither norepinephrine-stimulated 45Ca efflux nor the peak contractile response to norepinephrine in calcium-free buffer was affected, although in this setting, the duration of the phasic contractile response was shortened. When calcium was restored to tissues exposed to norepinephrine in calcium-free buffer, acidification slowed the rate of tension development without altering 45Ca uptake, thus changing the relation between tension development and calcium entry. These effects of acidification were shown to be associated with an increase in the amount of calcium sequestered into the norepinephrine-sensitive intracellular calcium store. These findings clearly indicate that acidification, within a range that has no effect on other aspects of smooth muscle activation, elicits vasodilation by stimulating intracellular calcium sequestration. This action may represent a predominant mechanism whereby acidosis alters vascular smooth muscle contractility.     

The natural history of isolated left ventricular diastolic dysfunction.

STUDY OBJECTIVE: To assess the natural history of isolated left ventricular diastolic dysfunction. PATIENTS AND METHODS: Follow-up (average duration, 68 months) was obtained in 51 patients with isolated left ventricular diastolic dysfunction at cardiac catheterization, characterized by (1) an elevated left ventricular end-diastolic pressure; (2) normal left ventricular end-diastolic and end-systolic volumes; (3) normal left ventricular ejection fraction; (4) no coronary artery disease; and (5) no valvular disease. RESULTS: During follow-up, seven patients died, but only one died of cardiac causes. Of the 44 living subjects, 20 (45%) noted new-onset symptoms of congestive heart failure, with 11 (25%) of these requiring hospitalization, and 12 (27%) required hospitalization for recurrent chest pain. CONCLUSIONS: Isolated left ventricular diastolic dysfunction is associated with a low cardiac mortality; at the same time, however, it is associated with substantial morbidity.     

Metabolic syndrome is associated with abnormal left ventricular diastolic function independent of left ventricular mass

Aim To characterize the extent to which metabolic syndrome criteriapredict left ventricular (LV) structure and function. Methods and results Metabolic syndrome criteria were assessedin 607 adults with normal LV function. The cohort was groupedaccording to the number of criteria satisfied: (1) Absent (0criteria, n = 110); (2) Pre-Metabolic Syndrome (1–2 criteria,n = 311); and (3) Metabolic Syndrome (3 criteria, n = 186).Echocardiography was used to assess LV structure (LV mass) andsystolic (LVEF, Vs) and diastolic function, by pulse-wave Doppler(E/A ratio) and tissue Doppler imaging (Ve). LV volumes andLVEF were similar between groups. However, LV mass increasedsignificantly and progressively (LVM/Ht^2.7, in g/m^2.7: 34.9± 6.7, 41.0 ± 9.5, 46.3 ± 11.0, P <0.001); LV relaxation decreased progressively (Ve_global', incm/s: 13.5 ± 2.8, 12.1 ± 3.0, 10.5 ± 2.2,P < 0.001) from Absent to Pre-Metabolic Syndrome to MetabolicSyndrome groups, respectively. Multiple variable analyses showedthat diastolic blood pressure, waist circumference, and triglyceridelevels were independent predictors of Ve after adjustment forLV mass. Conclusion Patients with metabolic syndrome have LV diastolicdysfunction independent of LV mass. These functional abnormalitiesmay partially explain the increased cardiovascular morbidityand mortality associated with metabolic syndrome.     

Anaemia is an independent predictor of mortality in patients with left ventricular systolic dysfunction following acute myocardial infarction

BACKGROUND: In patients with chronic heart failure (HF), mortality is inversely related to haemoglobin (hgb) concentration. We investigated the prognostic importance of anaemia in patients with acute myocardial infarction (AMI) and left ventricular systolic dysfunction (LVSD) with and without HF. METHODS AND RESULTS: We studied 1731 patients with AMI and left ventricular ejection fraction 相似文献