Myocardial O2 Consumption Research Articles

Prone Position Impairs Oxygen Supply-Demand Balance During Systemic Hypoxia in Rabbits

Ventilation in the prone position improves the prognosis of patients with severe acute respiratory distress syndrome (ARDS). Contraindications to ventilation in this position include unstable systemic circulation. Only a few reports exist on the effects of prone ventilation in respiratory failure on systemic circulation. This animal study compared systemic hemodynamic changes between supine and prone positions in anesthetized rabbits under acute systemic hypoxia (breathing 15% O2). Cardiac output and the systemic O2 extraction ratio increased under the hypoxia, but only in the supine group. Besides, the rate pressure product was higher in the prone group than in the supine group. This study showed that prone ventilation increases myocardial O2 consumption and suppresses compensatory mechanisms to maintain aerobic metabolism during systemic hypoxia. First of all, it will be necessary to examine the effect of prone ventilation on the O2 supply-demand balance in the ARDS model.

Myocardial Energetics in Heart Failure With Preserved Ejection Fraction

The role of coronary microvascular disease and its impact on functional and energetic reserve in heart failure with preserved ejection fraction (HFpEF) remains unclear. We hypothesized that in response to submaximal pharmacologic stress (dobutamine), patients with HFpEF have impairment in left ventricular (LV) myocardial mechanical (external work [EW]), energetic (myocardial O2 consumption [MVO2]), and myocardial blood flow (MBF) reserve. We further assessed whether coupling of MBF to EW is impaired in HFpEF and associated with compensatory increases or pathological decreases in myocardial O2 extraction. Lastly, we assessed whether coupling of MVO2 to EW (mechanical efficiency) was impaired in HFpEF. In prospectively enrolled patients with HFpEF (n=19) and age/sex-matched healthy controls (n=19), we performed 11C-acetate positron emission tomography assessing MVO2 and MBF at rest and during dobutamine infusion. EW was calculated as stroke volume (echo)×end-systolic pressure×heart rate. At rest, compared with controls, patients with HFpEF had higher LV EW, MVO2, and MBF. With dobutamine, LV EW, MVO2, and MBF increased in both HFpEF and controls; however, the magnitude of increases was significantly smaller in HFpEF. In both groups, MBF increased in relation to EW, but in HFpEF, the slope of the relationship was significantly smaller than in controls. Myocardial O2 extraction was increased in HFpEF. Mechanical efficiency was similar in HFpEF and controls. In a post hoc analysis, HFpEF patients with LV hypertrophy (n=10) had significant reductions in LV mechanical efficiency relative to controls. In HFpEF during submaximal dobutamine stress, there is myocardial mechanical-, energetic- and flow-reserve dysfunction with impaired coupling of blood flow to demand and slight increases in myocardial O2 extraction. These findings provide evidence that coronary microvascular dysfunction is present in HFpEF, limits O2 supply relative to demand, and is associated with reserve dysfunction.

Abstract 562: Comprehensive Arteriovenous Metabolomics in the Human Heart

Introduction: Despite broad interest in the role of metabolism in the pathogenesis of heart failure, a definitive account of fuel use by the beating human heart in situ is lacking. We therefore determined the uptake and release of over 270 metabolites by simultaneous sampling of arterial, coronary sinus, and femoral venous blood in 100 patients. Methods: We enrolled 100 patients (60% male, 12% diabetic, age = 63.6 +/- 13.5 years, BMI = 29.75 +/- 6.1, EF = 57.14 +/- 6.48) undergoing ablation of atrial fibrillation. We used liquid chromatography-mass spectrometry to quantify over 270 metabolites in plasma from coronary sinus, femoral vein, and arterial blood. We also measured O 2 and CO 2 concentration, as well as atrial pressure. Results: We detected uptake or release of 77 metabolites by the heart and 136 metabolites across the leg (p <0.05 after Benjamini-Hochberg correction). We determined the cardiac extraction of all major fuel sources, including 29 fatty acids, 11 amino acids, lactate, acetoacetate, and 3-hydroxybutyrate. Several patterns emerge: first, while the leg extracts glucose (FV/A = 0.95, q = 4.7x10-14) and releases lactate (FV/A = 1.11, q = 2.87x10-14), the heart extracts lactate (CS/A = 0.95, q = 3.77x10-9) and neither extracts nor secretes glucose. Second, while the leg releases nearly all fatty acid and amino acid species, the heart consumes most fatty acids and certain non-essential amino acids. Third, extraction of unsaturated acylcarnitines correlates with left atrial pressure (p<0.01). Finally, we find a significant positive correlation between myocardial O2 consumption and extraction of ketones (p < 0.01), but not other major cardiac fuels. Conclusion: We present the most comprehensive study to date of metabolite use and secretion by the human heart. We find the heart to be an avid consumer of fatty acids and ketone bodies, but less so of glucose and essential amino acids. Consumption of ketones increases with O2 consumption, suggesting that ketones may be a preferential fuel source under high work loads. Extraction of certain acylcarnitines increases with left atrial pressure, indicating metabolic reprogramming under high filling pressures. In summary, we provide the first comprehensive model of fuel use by the beating human heart in situ.

Influence of myocardial oxygen demand on the coronary vascular response to arterial blood gas changes in humans.

It remains unclear if the human coronary vasculature is inherently sensitive to changes in arterial Po2 and Pco2 or if coronary vascular responses are the result of concomitant increases in myocardial O2 consumption/demand ([Formula: see text]). We hypothesized that the coronary vascular response to Po2 and Pco2 would be attenuated in healthy men when [Formula: see text] was attenuated with β1-adrenergic receptor blockade. Healthy men (age: 25 ± 1 yr, n = 11) received intravenous esmolol (β1-adrenergic receptor antagonist) or volume-matched saline in a double-blind, randomized crossover study and were exposed to poikilocapnic hypoxia, isocapnic hypoxia, and hypercapnic hypoxia. Measurements made at baseline and after 5 min of steady state at each gas manipulation included left anterior descending coronary blood velocity (LADV; Doppler echocardiography), heart rate, and arterial blood pressure. LADV values at the end of each hypoxic condition were compared between esmolol and placebo. The rate-pressure product (RPP) and left ventricular mechanical energy (MELV) were calculated as indexes of [Formula: see text]. All gas manipulations augmented RPP, MELV, and LADV, but only RPP and MELV were attenuated (4-18%) after β1-adrenergic receptor blockade ( P < 0.05). Despite attenuated RPP and MELV responses, β1-adrenergic receptor blockade did not attenuate the mean LADV vasodilatory response compared with placebo during poikilocapnic hypoxia (29.4 ± 2.2 vs. 27.3 ± 1.6 cm/s) and isocapnic hypoxia (29.5 ± 1.5 vs. 30.3 ± 2.2 cm/s). Hypercapnic hypoxia elicited a feedforward coronary dilation that was blocked by β1-adrenergic receptor blockade. These results indicate a direct influence of arterial Po2 on coronary vascular regulation that is independent of [Formula: see text]. NEW & NOTEWORTHY In humans, arterial hypoxemia led to an increase in epicardial coronary artery blood velocity. β1-Adrenergic receptor blockade did not diminish the hypoxemic coronary response despite reduced myocardial O2 demand. These data indicate hypoxemia can regulate coronary blood flow independent of myocardial O2 consumption. A plateau in the mean left anterior descending coronary artery blood velocity-rate-pressure product relationship suggested β1-adrenergic receptor-mediated, feedforward epicardial coronary artery dilation. In addition, we observed a synergistic effect of Po2 and Pco2 during hypercapnic hypoxia.

Methods for the Preparation of an Excised, Cross-Circulated Rat Heart.

The Emax-Pressure-Volume Area (PVA)-VO2 framework proposed by Dr. Suga for canine hearts has dramatically advanced the field of cardiac mechanical work and energetics, i.e., mechanoenergetics. He and his collaborators investigated mechanoenergetics in the left ventricle (LV) of excised, cross-circulated canine heart preparations. We instituted the excised cross-circulated rat whole heart preparations and found a curvilinear end-systolic pressure-volume relation (ESPVR) in the rat LV, in contrast to the linear ESPVR in canine, rabbit, and human LVs. Although Emax, the slope of the linear ESPVR, could be used as an index of LV contractility, it was not applicable for evaluating LV contractility in the rat LV. Thus, we proposed a new index of contractility, equivalent Emax (eEmax) in the rat LV. We also found a linear VO2-PVA relationship in the rat LV. Here, we introduce the methods for the preparation of excised, cross-circulated rat whole hearts and the eEmax-PVA-VO2 framework in the rat LV. Using this method, we can obtain accurate LV volume and myocardial O2 consumption in real time for estimating cardiac mechanoenergetics, which is very challenging in in vivo experiments.

Exercise of obese mice induces cardioprotection and oxygen sparing in hearts exposed to high-fat load.

Exercise training is a potent therapeutic approach in obesity and diabetes that exerts protective effects against the development of diabetic cardiomyopathy and ischemic injury. Acute increases in circulating fatty acids (FAs) during an ischemic insult can challenge the heart, since high FA load is considered to have adverse cardiac effects. In the present study, we tested the hypothesis that exercise-induced cardiac effects in diet-induced obese mice are abrogated by an acute high FA load. Diet-induced obese mice were fed a high-fat diet (HFD) for 20 wk. They were exercised using moderate- and/or high-intensity exercise training (MIT and HIT, respectively) for 10 or 3 wk, and isolated perfused hearts from these mice were exposed to a high FA load. Sedentary HFD mice served as controls. Ventricular function and myocardial O2 consumption were assessed after 10 wk of HIT and MIT, and postischemic functional recovery and infarct size were examined after 3 wk of HIT. In addition to improving aerobic capacity and reducing obesity and insulin resistance, long-term exercise ameliorated the development of diet-induced cardiac dysfunction. This was associated with improved mechanical efficiency because of reduced myocardial oxygen consumption. Although to a lesser extent, 3-wk HIT also increased aerobic capacity and decreased obesity and insulin resistance. HIT also improved postischemic functional recovery and reduced infarct size. Event upon the exposure to a high FA load, short-term exercise induced an oxygen-sparing effect. This study therefore shows that exercise-induced cardioprotective effects are present under hyperlipidemic conditions and highlights the important role of myocardial energetics during ischemic stress.NEW & NOTEWORTHY The exercise-induced cardioprotective effects in obese hearts are present under hyperlipidemic conditions, comparable to circulating levels of FA occurring with an ischemic insult. Myocardial oxygen sparing is associated with this effect, despite the general notion that high fat can decrease cardiac efficiency. This highlights the role of myocardial energetics during ischemic stress.

The effect of endotoxin on general and coronary haemodynamics and metabolism, and its relation in certain infectious diseases.

Shock occurs in gram-negative septicaemia, dengue, and other infections: to understand the situation better, a study was made of the effects of endotoxin on the general and coronary circulation of intact animals. Cardiac output (Fick), coronary flow (N2O Fick), vascular pressures, glucose lactate, pyruvate, non-esterified fatty acid (NEFA), and C14 palmitate levels, were measured before and after the injection of Serratia marcescens endotoxin into healthy anaesthetized dogs.Cardiac output, vascular pressures, and cardiac work fell precipitously. Coronary blood flow, myocardial O2 consumption, and cardiac efficiency decreased by 50%.Whole-body glucose, lactate, pyruvate, and NEFA increased, but no change occurred in the myocardial extraction of these substances. The myocardial oxidation of C14 palmitate increased.The general haemodynamic changes are similar to those occurring in patients; it is suggested that the changes in the coronary circulation seen in animals may also occur in the clinical situation. Other animal studies with a histamine releaser (Tween 20), gave results similar to those of endotoxin. Anaphylotoxins may then also be relevant to the "shock" state of certain infections.

Selective Heart Rate Reduction Improves Metabolic Syndrome-related Left Ventricular Diastolic Dysfunction.

Enhanced heart rate observed in metabolic syndrome (MS) contributes to the deterioration of left ventricular (LV) function via impaired LV filling and relaxation, increased myocardial O2 consumption, and reduced coronary perfusion. However, whether heart rate reduction (HRR) opposes LV dysfunction observed in MS is unknown. We assessed in Zucker fa/fa rats, a rat model of MS, the cardiovascular effects of HRR induced by the If current inhibitor S38844 (3 mg · kg(-1) · d(-1)). Delayed short-term (4 days) and long-term (90 days) HRR induced by S38844 reduced LV end-diastolic pressure and LV end-diastolic pressure-volume relation, increased myocardial tissue perfusion, decreased myocardial oxidized glutathione levels, and preserved cardiac output, without modifying LV end-systolic pressure and LV end-systolic pressure-volume relation, although only long-term S38844 opposed LV collagen accumulation. Long-term S38844 improved flow-induced endothelium-dependent dilatation of mesenteric arteries, while metabolic parameters, such as plasma glucose levels, and Hb1c, were never modified. In rats with MS, HRR induced by the If inhibitor S38844 improved LV diastolic function and endothelium-dependent vascular dilatation, independent from modifications in metabolic status. Moreover, this improvement in cardiac function involves not only immediate effects such as improved myocardial perfusion and reduced oxidative stress but also long-term effects such as modifications in the myocardial structure.

Progressively heterogeneous mismatch of regional oxygen delivery to consumption during graded coronary stenosis in pig left ventricle.

In normal hearts, myocardial perfusion is fairly well matched to regional metabolic demand, although both are distributed heterogeneously. Nonuniform regional metabolic vulnerability during coronary stenosis would help to explain nonuniform necrosis during myocardial infarction. In the present study, we investigated whether metabolism-perfusion correlation diminishes during coronary stenosis, indicating increasing mismatch of regional oxygen supply to demand. Thirty anesthetized male pigs were studied: controls without coronary stenosis (n = 11); group I, left anterior descending (LAD) coronary stenosis leading to coronary perfusion pressure reduction to 70 mmHg (n = 6); group II, stenosis with perfusion pressure of about 35 mmHg (n = 6); and group III, stenosis with perfusion pressure of 45 mmHg combined with adenosine infusion (n = 7). [2-(13)C]- and [1,2-(13)C]acetate infusion was used to calculate regional O2 consumption from glutamate NMR spectra measured for multiple tissue samples of about 100 mg dry mass in the LAD region. Blood flow was measured with microspheres in the same regions. In control hearts without stenosis, regional oxygen extraction did not correlate with basal blood flow. Average myocardial O2 delivery and consumption decreased during coronary stenosis, but vasodilation with adenosine counteracted this. Regional oxygen extraction was on average decreased during stenosis, suggesting adaptation of metabolism to lower oxygen supply after half an hour of ischemia. Whereas regional O2 delivery correlated with O2 consumption in controls, this relation was progressively lost with graded coronary hypotension but partially reestablished by adenosine infusion. Therefore, coronary stenosis leads to heterogeneous metabolic stress indicated by decreasing regional O2 supply to demand matching in myocardium during partial coronary obstruction.

Acute High-Intensity Intermittent Aerobic Exercise Reduces Plasma Angiopoietin-Like 2 in Patients With Coronary Artery Disease

BackgroundCirculating levels of angiopoietin-like 2 (ANGPTL2), a proinflammatory and proatherogenic protein, are elevated in patients with coronary artery disease (CAD). We hypothesized that high-intensity intermittent exercise (HIIE), known to be beneficial in patients with CAD, would reduce circulating ANGPTL2 levels. MethodsPlasma levels of ANGPTL2 were measured before and 20 minutes, 24 hours, and 72 hours after an acute exercise session in a crossover study comparing HIIE to moderate-intensity continuous exercise (MICE) in 14 patients with CAD and 20 age-matched and 20 young healthy controls. ResultsPre-exercise ANGPTL2 levels were 3-fold higher in patients with CAD than in age-matched controls (P < 0.05) and correlated negatively with Vo2max/lean body mass (P < 0.0001). In healthy controls, ANGPTL2 levels were low and not affected by HIIE or MICE. In patients with CAD, ANGPTL2 levels decreased significantly by 41% after 20 minutes of HIIE, a reduction that was maintained after 24 and 72 hours (P < 0.05). In contrast, although ANGPTL2 levels decreased by 47% after 20 minutes of MICE, they increased by 104% after 24 hours and returned to baseline values after 72 hours (P < 0.05). A negative correlation was observed between this increase in ANGPTL2 levels and the mean rate-pressure product (heart rate × systolic blood pressure; index of myocardial O2 consumption) measured during MICE, suggesting that subclinical ischemia might promote ANGPTL2 expression. ConclusionsIn patients with CAD, circulating ANGPTL2 levels are acutely reduced after HIIE and transiently increased after MICE. A sustained reduction in circulating ANGPTL2 levels could contribute to the chronic beneficial cardiometabolic effects of HIIE in patients with CAD.

Subnormothermic Preservation in Somah: A Novel Approach for Enhanced Functional Resuscitation of Donor Hearts for Transplant

Organ preservation at 4°C results in temporally irreversible injury to cellular structure and function. This study was designed to evaluate the possibility of storing hearts at ambient temperatures in novel organ preservation solution Somah to prevent damage and preserve optimum function by maintaining cellular energy over the temperature range of storage. Porcine hearts were stored in Celsior at 4°C and Somah at 4°C, 13°C and 21°C for 5 h thereafter reperfused and reanimated in vitro for 3 h. Heart weights, histopathology, ultrastructure and 2-dimensional echocardiography (2D-Echo) assessments showed preservation of structure in Somah groups. Tissue high-energy phosphate levels in Somah groups after storage were significantly greater than the Celsior hearts (p < 0.05) and highest in the 21°C Somah hearts. Upon reperfusion, myocardial O2 consumption and lactate levels quickly achieved steady state in 21°C hearts, but were delayed in Somah 4/13°C groups and severely depressed in the Celsior group. Inotrope and electroconversion requirements were inversely related to storage temperature. In vitro 2D Echo demonstrated a discordantly attenuated function in the Celsior group, moderate functionality in 4°C Somah group and superior reestablishment of performance in the Somah higher temperature groups. Hearts stored in Somah at 21°C were metabolically and functionally superior to any other groups.

Impaired left ventricular mechanical and energetic function in mice after cardiomyocyte-specific excision of Serca2

Sarco(endo)plasmic reticulum Ca2+ -ATPase (SERCA)2 transports Ca2+ from the cytosol into the sarcoplasmic reticulum of cardiomyocytes and is essential for maintaining myocardial Ca2+ handling and thus the mechanical function of the heart. SERCA2 is a major ATP consumer in excitation-contraction coupling but is regarded to contribute to energetically efficient Ca2+ handling in the cardiomyocyte. Previous studies using cardiomyocyte-specific SERCA2 knockout (KO) mice have demonstrated that decreased SERCA2 activity reduces the Ca2+ transient amplitude and induces compensatory Ca2+ transport mechanisms that may lead to more inefficient Ca2+ transport. In this study, we examined the relationship between left ventricular (LV) function and myocardial O2 consumption (MVo2) in ex vivo hearts from SERCA2 KO mice to directly measure how SERCA2 elimination influences mechanical and energetic features of the heart. Ex vivo hearts from SERCA2 KO hearts developed mechanical dysfunction at 4 wk and demonstrated virtually no working capacity at 7 wk. In accordance with the reported reduction in Ca2+ transient amplitude in cardiomyocytes from SERCA2 KO mice, work-independent MVo2 was decreased due to a reduced energy cost of excitation-contraction coupling. As these hearts also showed a marked impairment in the efficiency of chemomechanical energy transduction (contractile efficiency, i.e, work-dependent MVo2), hearts from SERCA2 KO mice were found to be mechanically inefficient. This ex vivo evaluation of mechanical and energetic function in hearts from SERCA2 KO mice brings together findings from previous experimental and mathematical modeling-based studies and demonstrates that reduced SERCA2 activity not only leads to mechanical dysfunction but also to energetic dysfunction.

Inducible nitric oxide synthase inhibits oxygen consumption in collateral-dependent myocardium

Following coronary artery occlusion growth of collateral vessels can provide an effective blood supply to the dependent myocardium. The ischemia, which results in growth of collateral vessels, recruits an inflammatory response with expression of cytokines and growth factors, upregulation of endothelial nitric oxide (NO) synthase (eNOS) in vascular endothelial cells, and expression of inducible nitric oxide synthase (iNOS) in both vessels and cardiac myocytes. Because NO is a potent collateral vessel dilator, this study examined whether NO derived from iNOS or constitutive NOS regulates myocardial blood flow (MBF) in the collateral region. Nonselective NOS inhibition with N(G)-nitro-l-arginine (LNA) caused vasoconstriction with a significant decrease in MBF to the collateral region during exercise. In contrast, the highly selective iNOS inhibitor 1400W caused a 21 ± 5% increase of MBF in the collateral region. This increase in MBF following selective iNOS blockade was proportionate to an increase in myocardial O2 consumption (MVo2). The results suggest that NO produced by iNOS inhibits MVo2 in the collateralized region, so that the increase in MBF following iNOS blockade was the result of metabolic vasodilation secondary to an increase in MVo2. Thus the coordinated expression of iNOS to restrain MVo2 and eNOS to maintain collateral vasodilation act to optimize the O2 supply-demand relationship and protect the collateralized myocardium from ischemia.

Inhibition of murine cardiomyocyte respiration by amine local anesthetics

The hydrophobic amino acyl amide-linked local anesthetics (e.g., lidocaine and bupivacaine) impose potent cardiac toxicity and direct mitochondrial dysfunction. To investigate these adverse events, an in vitro system was employed to measure their effects on O2 consumption (cellular respiration) by murine myocardium. Specimens were collected from the ventricular myocardium and immediately immersed in ice-cold Krebs-Henseleit buffer saturated with 95% O2:5% CO2. O2 concentration was determined as a function of time from the phosphorescence decay rates of Pd(II)-meso-tetra-(4-sulfonatophenyl)-tetrabenzoporphyrin. Myocardial O2 consumption was linear with time (zero-order kinetics); its rate (k, in μMO2min(-1)), thus, was the negative of the slope of [O2] vs. time. Cyanide inhibited O2 consumption, confirming the oxidation occurred in the respiratory chain. Lidocaine and bupivacaine produced immediate and sustained inhibition of cellular respiration at plasma concentrations of the drugs (low micromolar range). Bupivacaine was twice as potent as lidocaine. The inhibition was dose-dependent, saturating at concentrations ≥30μM. At saturating doses, lidocaine produced ~20% inhibition and bupivacaine ~40% inhibition. Cellular ATP was also decreased in the presence of 30μM lidocaine or bupivacaine. The studied amines inhibited myocardial cellular respiration. This effect is consistent with their known adverse events on mitochondrial function. The described approach allows accurate assessments and comparisons of the toxic effects of local anesthetics on heart tissue bioenergetics.

Biphasic Change of Tau (τ) in Mice as Arterial Load Acutely Increased with Phenylephrine Injection

BackgroundDiastolic dysfunction is the hemodynamic hallmark of hypertensive heart disease. Tau (τ) has been used to describe left ventricle relaxation. The relationship between τ and afterload has been controversial. Our goal was to demonstrate this relationship in mice, because genetically-modified mouse models have been used extensively for studies in cardiovascular diseases.MethodsIncreased arterial load was produced by phenylephrine administration (50 µg/kg iv) (n = 10). A series of pressure-volume loops was recorded with a Millar conductance catheter in vivo as the left ventricle pressure reached the maximum. The arterial load was expressed as Ea (effective arterial elastance). Tau values were computed using three mathematical methods: τWeiss, τGlantz, and τLogistic.ResultsA correlation plot between τ and Ea showed a biphasic relationship a flat phase I and an inclined phase II. The existence of an inflection point was proved mathematically with biphasic linear regression. Pressure-volume area (PVA), a parameter linearly related to myocardial O2 consumption (MVO2), was found to be directly proportional to Ea. The plot of τ versus PVA was also biphasic.ConclusionWe concluded that a small increase of the arterial load by phenylephrine increased PVA (index of MVO2) but had little effect on τ. However, after an inflection point, further increase of arterial load and PVA resulted in the linear increase of τ.

Myoglobin-dependent O2 consumption of the hypoxic trout heart

Myoglobin (Mb) plays a well-established role in facilitated O2 diffusion to sustain mitochondrial O2 consumption during hypoxia in the mammalian heart. To better understand the function of Mb in the fish heart, we have measured the effects of adding 20% carbon monoxide (CO), which inhibits Mb function, compared to inert 20% N2 on the O2 consumption and twitch force in hypoxic rainbow trout (Oncorhynchus mykiss) ventricle ring preparations. Results showed that O2 consumption was significantly reduced upon addition of CO, whereas twitch force was not affected. Control experiments at 40% CO did not decrease O2 consumption further, showing that CO was not inhibiting cytochrome c oxidase in the mitochondria. Because myocardial O2 consumption can be depressed by endogenous nitric oxide (NO) in the trout myocardium and because Mb is a scavenger of NO, CO inhibition experiments were also made in the presence of the NO synthase inhibitor, asymmetric dimethylarginine (ADMA). O2 consumption decreased to a similar extent upon CO addition, regardless of NO synthase inhibition, indicating that under hypoxic conditions Mb-dependent NO scavenging plays a minor role. Taken together, these results show that O2 consumption of the hypoxic rainbow trout heart is dependent on the function of Mb as intracellular O2 carrier.

582 DECOMPENSATED CARDIAC HYPERTROPHY IS RELATED TO LOWER PLASMA HIF-1α AND SVEGF LEVELS IN PATIENTS WITH HYPERTENSIVE HEART DISEASE

Background: Chronic hypertension causes cardiac pressure overload leading to increased myocardial O2-consumption. Previous animal studies showed that inhibition of HIF-1α and VEGF resulted in cardiac decompensation following fibrosis and hypertrophy, due to its failure to maintain myocardial capillary density in response to hypoxia. However, it is still not clear whether this mechanism applied in human. Therefore, we sought to measure plasma HIF-1α and sVEGF level among chronic hypertensive patients with structural and functional cardiac changes. Methods: Eighty hypertensive subjects participated in this study. Echocardiographic study, plasma HIF-1α and sVEGF measurement were performed in hypertensive (n=30); compensated hypertrophy (n=25); decompensated hypertrophy (n=25) patients. Results: There were no significant differences in the SBP and DBP between groups, however decompensated patients were significantly older and were longer to suffer from hypertension. The LVMI was significantly higher in decompensated as compared to compensated and hypertensive group (157±5.2 and137±2.2 vs.98±2.3gr/m2 p<0.05). Furthermore, there was higher proportion of diastolic dysfunction in decompensated group compared with compensated one (44vs.96%; p<0.05); with significantly lower systolic function (64±1.2vs70±1.7%; p<0.05). Interestingly, the plasma HIF-1α was significantly lower (1038.2±363vs.261±113pg/L; p<0.01) followed by decreased in sVEGF level (427.8±56.2vs.240.3±20.5pg/L; p<0.05) in decompensated group; which might explain the inadequate response to persistent hypoxia. Conclusion: Our study revealed that there was a reduction in plasma HIF-1α and sVEGF level among hypertensive subjects with decompensated cardiac hypertrophy. This implies that preservation of cardiac function requires adequate response to chronic hypoxia to maintain myocardial capillary function and that strategy for anti-hypertensive therapy should be considered for that purpose.

Role of NO and Superoxide in Hyperhomocysteinemia Induced Cardiac Metabolic Dysfunction in Pregnant Cystathionine Beta‐synthase Heterozygote Mice

Genetic defects in cystathionine beta‐synthase (CBS) can cause severe hyperhomocysteinemia (HHcy). HHcy causes cardiovascular dysfunction and is associated with many complications during pregnancy related to reduced NO bioactivity. This study assessed the mechanisms of HHcy on the NO‐dependent control of cardiac O2 consumption in pregnant CBS heterozygote (HET) mice. Pregnant CBS HET mice (n=8) were fed low‐folate diet for 20 days to increase plasma Hcy (8.2±0.5 of WT to 17.9±2.2 uM of HET). As compared to wild type (WT) (n=10), while heart weight/body weight increased by 18.2%, ejection fraction decreased from 85.7±0.8% to 80.3±1.8% in HET. Systolic blood pressure was significantly increased from 92.5±3.6 mmHg of WT to 114.5±4.0 mmHg in HET, and MBP from 66.8±9.2 mmHg to 82.9±5.5 mmHg, without hypertension. The total peripheral resistance significantly increased by 42.1%. The ability of bradykinin to reduce myocardial O2 consumption in vitro was impaired by 56% in heart. The response was restored by ascorbic acid, tempol and apocynin. O2− production was increased by 2.7 folds in Hcy heart using lucigenin chemiluminescence.ConclusionCBS deficiency caused HHcy during pregnancy, impairs cardiac function, increases O2− production and reduces the ability of NO to regulate myocardial O2 consumption probably through NADPH oxidase stimulation.

DNA methylation status of cytokine biosynthesis genes during hyperhomocysteinemia in Cystathionine Beta‐synthase Heterozygote Mice

Epigenetic regulations play a role in the development and progression of cardiovascular diseases. Discovering novel epigenetically regulated genes could provide useful information in understanding hyperhomocysteinemia (HHcy). We have previously shown that HHcy causes cardiovascular dysfunction due to reduced NO bioactivity. Genetic defects in cystathionine beta‐synthase (CBS) can cause severe HHcy. We have shown that CBS deficiency caused HHcy during pregnancy and lead to impairment of cardiac function, increased O2− production and reduced the ability of NO to regulate myocardial O2 consumption probably through NADPH oxidase stimulation. DNA methylation is an epigenetic event that affects cell function by altering gene expression and could be a potential mechanism for regulating gene expression in these animals. As a preliminary study, we carried out a small scale DNA methylation analysis between wild type and CBS (+/−) mice using the Mouse Cytokine Production DNA Methylation PCR array. This array profiles the promoter methylation status of a panel of 24 genes whose role in cytokine biosynthesis has been well documented. The results showed that 8/24 genes represented (such as IL18, Ltb, Smad3&amp;4 and Igf2bp2) were hypermethylated in these animals but to a higher extend in CBS (+/−) mice. This could highlight the importance of epigenetic mechanisms in the progression of HHcy. Supported by HL‐PO1‐43023.

Impact of High‐Fructose Consumption on Gene Expression and the Cardiovascular System through NO‐Superoxide Interaction

Fructose consumption (FC) has caused much concern due to its prominence in today's diet and its link to cardiovascular disease. We hypothesized that the effects of FC are mediated by overactivation of NADPH oxidase (Nox), which increases superoxide (O2−) production, reducing NO bioavailability. SD rats were fed either a normal or a 60% fructose diet for 21 days. FC animals showed increases in blood pressure and plasma insulin (3.1 ± 0.4 to 5.4 ± 0.4 ng/mL). In pregnancy, fetal weights of FC rats were significantly lower (5.84 ± .06 to 4.71 ± .06 g, ~20%). Furthermore, the reduction of myocardial O2 consumption (MVO2) ex vivo by bradykinin was impaired in FC (28 ± 2% to 17 ± 2%), an effect reversed by apocynin or tiron, a Nox inhibitor and O2− scavenger, respectively. Finally, microarray of mRNA revealed significant changes in 237 genes (p &lt; .05, fold change &gt; ± 1.5), including upregulation of cholesterol transporter caveolin 1 and endothelin receptor B, and repression of mitochondrial protein Mrpl12, and mitochondrial ATP synthase subunit Atp5S. Analysis of miRs showed repression of miRs associated with upregulated genes and vice versa, including trends seen in heart failure: upregulation of miR126, a regulator of angiogenesis, and miR21. In conclusion, FC triggers gene expression changes in the heart with involvement of miRs, which leads to the lowering of NO bioavailability through the generation of O2−. Supported by PO43023.