Regulation of pantothenic acid transport in the heart. Involvement of a Na+-cotransport system

Pantothenic acid transport was studied in the isolated perfused rat heart and isolated sheep cardiac sarcolemmal vesicles. In the perfused heart, pantothenic acid transport was significantly greater if hearts were perfused as working hearts rather than Langendorff hearts, but was unaffected by the perfusion substrates used (11 mM glucose or 1.2 mM palmitate). Uptake rates of pantothenic acid in working hearts are dependent on perfusate concentrations of pantothenic acid (a Vmax of 418 nmol/g dry weight/30 min and a Km for pantothenic acid of 10.7 mircoM were obtained). Reduction in perfusate Na+ concentration from 145 to 105 mM (the Na+ was replaced with 40 mM choline) resulted in a small but significant decrease in pantothenic acid uptake. At 145 mM Na+, addition of a mixture of amino acids, whose uptake is Na+-dependent, resulted in a significant decrease in pantothenic acid uptake by the heart (173 +/- 5 to 132 +/- 12 nmol/g dry weight). If an inward Na+ gradient in isolated, purified sarcolemmal vesicles, was imposed, a rapid uptake of pantothenic acid was observed. Uptake rates are markedly reduced if Na+ was replaced by equimolar concentrations of K+ or if external Na+ was reduced below 40 mM. In the presence of Na+, increasing pantothenic acid concentrations resulted in an increase in pantothenic acid uptake by the vesicles. Combined, these data demonstrate that pantothenic acid is transported across the myocardial sarcolemmal membrane by a Na+-dependent mechanism, which may be common to a number of small molecules.     

The relative contribution of glucose and fatty acids to ATP production in hearts reperfused following ischemia

High levels of fatty acids decrease the extent of mechanical recovery of hearts reperfused following a transient period of severe ischemia. Glucose oxidation rates during reperfusion are low under these conditions, which can result in a decreased recovery of mechanical function. Stimulation of glucose oxidation with the carnitine palmitoyl transferase I inhibitor, Etomoxir, or by directly stimulating pyruvate dehydrogenase activity with dichloroacetate (DCA) results in an improvement in mechanical function during reperfusion of previously ischemic hearts. Addition of DCA (1 mM) to hearts perfused with 11 mM glucose and 1.2 mM palmitate results in an increase in contribution of glucose oxidation to overall ATP production from 6 to 23%, with a parallel decrease in that of fatty acid oxidation from 90 to 69%. In aerobic hearts, endogenous myocardial triglycerides are an important source of fatty acids for -oxidation. Using hearts in which the myocardial triglycerides were pre-labeled, the contribution of both endogenous and exogenous fatty acid oxidation to myocardial ATP production was determined in hearts perfused with 11 mM glucose, 1.2 mM palmitate and 500 µU/ml insulin. In hearts reperfused following a 30 min period of global no flow ischemia, 91.9% of ATP production was derived from endogenous and exogenous fatty acid oxidation, compared to 87.7% in aerobic hearts. This demonstrates that fatty acid oxidation quickly recovers following a transient period of severe ischemia. Furthermore, therapy aimed at overcoming fatty acid inhibition of glucose oxidation during reperfusion of ischemic hearts appears to be beneficial to recovery of mechanical function.     

Protection of the reperfused heart by L-propionylcarnitine.

The effects of L-propionylcarnitine on mechanical function, creatine phosphate and ATP content, and lactate dehydrogenase leakage were studied in isolated perfused rat hearts exposed to global no-flow ischemia for 30 min followed by reperfusion for 20 min. Five and 10 mM L-propionylcarnitine resulted in a 100% recovery of left ventricular-developed pressure, whereas the recovery was only 40% in the hearts perfused without this agent. Ischemia-reperfusion caused a 85% loss of creatine phosphate and a 77% loss of ATP, which was prevented by 10 mM L-propionylcarnitine. Five millimolar L-propionylcarnitine protected the heart from the loss of creatine phosphate but not from the loss of ATP. Ten millimolar L-propionylcarnitine failed to improve the postischemic left ventricular-developed pressure, when it was added to the perfusate only after ischemia. L-propionylcarnitine alleviated the decrease of coronary flow in the reperfused hearts. Lactate dehydrogenase leakage was aggravated in the beginning of the reperfusion period by 10 mM L-propionylcarnitine. This adverse effect was, however, transient. L-Propionylcarnitine provides protection for the postischemic reperfused heart in a dose-dependent manner. The optimal time for administration is before the ischemic insult. High doses of this compound may perturb cell membrane integrity. Moreover, the present data point to an intracellular, metabolic, and perhaps anaplerotic mechanism of action of L-propionylcarnitine in cardiac ischemia-reperfusion injury.     

Myocardial triglyceride turnover during reperfusion of isolated rat hearts subjected to a transient period of global ischemia.

Triglyceride turnover in reperfused/ischemic rat hearts was investigated. Hearts were initially perfused under aerobic conditions for a 1-h "pulse" perfusion with 1.2 mM [1-14C]palmitate to label the endogenous lipid pools, followed by a 30-min period of no-flow ischemia or a 10-min period of retrograde perfusion (control). Hearts were then reperfused under aerobic conditions with buffer containing 1.2 mM [9,10-3H]palmitate. All buffers contained 11 mM glucose and 500 microunits/ml insulin. Rates of endogenous triglyceride lipolysis and synthesis were measured during reperfusion, whereas rates of exogenous palmitate oxidation were measured both prior to ischemia and during reperfusion following ischemia. During reperfusion of ischemic hearts, a 20% increase in exogenous fatty acid oxidation rates was seen compared with pre-ischemic rates. Despite an initial burst of endogenous fatty acid oxidation, no acceleration of steady state endogenous triglyceride lipolysis was seen compared with their nonischemic hearts. In contrast, a significant increase in triglyceride synthesis was observed. Triglyceride turnover was also measured in a series of hearts reperfused following ischemia in the absence of exogenous fatty acids. A significant enhancement of functional recovery was seen compared with hearts reperfused with 1.2 mM palmitate. In addition, a significant increase in fatty acid oxidation from endogenous triglyceride lipolysis was observed. We conclude that the heart quickly recovers its ability to oxidize exogenous fatty acids during reperfusion and that although triglyceride lipolysis is not accelerated during reperfusion of ischemic hearts in the presence of 1.2 mM palmitate, a significant increase in triglyceride synthesis does occur.     

Glucose oxidation is stimulated in reperfused ischemic hearts with the carnitine palmitoyltransferase 1 inhibitor,Etomoxir

Summary The effect of the carnitine palmitoyltransferase 1(CPT1) inhibitor, Etomoxir, on glucose oxidation rates was determined in ischemic hearts reperfused in the presence of fatty acids. Isolated working rat hearts were perfused with 11 mM (¹⁴C)-glucose and 1.2 mM palmitate at a 15 cm H₂O preload, 80 mm Hg afterload. Hearts were subjected to either 60 min aerobic perfusion, or 15 min work followed by 25 min global ischemia then 60 min of aerobic reperfusion. Steady state glucose oxidation rates in reperfused ischemic hearts were not significantly different from non-ischemic hearts. If 10^–9 M Etomoxir was added immediately prior to reperfusion no significant change in glucose oxidation occurred. Addition of 10^–8 M and 10^–6 M Etomoxir, however, significantly increased glucose oxidation. Etomoxir also significantly improved recovery of mechanical function at a concentration of 10^i–8 M or greater. As we previously reported, no significant improvement of function was seen when 10^–9 M Etomoxir was added to the perfusate (Lopaschuk GD et al., Circ Res 63: 1036–1043, 1988). Long chain acylcarnitine levels were significantly reduced in the presence of both 10^–9 M and 10^–8 M Etomoxir. These data demonstrate that the beneficial effect of Etomoxir on reperfusion recovery of ischemic hearts is not due to a lowering of long chain acylcarnitine levels. Etomoxir may improve recovery of function by overcoming fatty acid inhibition of glucose oxidation.     

Lipid Peroxidation, Tissue Necrosis, and Metabolic and Mechanical Recovery of Isolated Reperfused Rat Heart as a Function of Increasing Ischemia

Isolated Langendorff-perfused rat hearts, after 30 min of preperfusion, were submitted to increasing times of global normothermic ischemia (1, 2, 5, 10, 20 and 30 min) or to the same times of ischemia followed by 30 min of reperfusion. Analysis of malondialdehyde, ascorbic acid, oxypurines, nucleosides, nicotinic coen-zymes and high-energy phosphates was carried out by HPLC on neutralized perchloric acid extracts of freeze-clamped tissues. In addition, maximum rate of intra-ventricular pressure development and cardiac output of malondialdehyde, lactate dehydrogenase, oxypurines and nucleosides were monitored during both preperfusion and reperfusion. Besides decreasing energy metabolites and nicotinic coenzyme pool, prolonged ischemia produced oxidation of significant amounts of hypoxanthine and xanthine to uric acid and generation of detectable levels of malondialdehyde (0.002 μmollg dry weight). After oxygen and substrate readmission, tissue and perfusate malondialdehyde increased only if previous ischemia was longer than 5 min, while lactate dehydrogenase was detected in perfusate of reperfused hearts following 10, 20, and 30 min of ischemia. Highest values of tissue malondialdehyde and total malondialdehyde output were recorded in reperfused hearts subjected to 30 min of ischemia (0.043 μmol/g dry weight and 0.069 μmol/ 30 min/g dry weight, respectively). Since tissue malondialdehyde was observed without detectable lactate dehydrogenase release in perfusate, it might be stated that malondialdehyde generation (i.e., lipid peroxidation) temporally preceded lactate dehydrogenase release (i.e., tissue necrosis). In reperfused hearts, evaluation of myocardial energy state and of mechanical recovery allowed us to determine times of ischemia beyond which reperfusion did not positively affect these metabolic and functional parameters. Main findings are that, under these experimental conditions, lipid peroxidation might be the cause and not the consequence of tissue necrosis and that duration of ischemia might be the factor deciding effectiveness of reperfusion.     

Effects of L-carnitine and its derivatives on postischemic cardiac function,ventricular fibrillation and necrotic and apoptotic cardiomyocyte death in isolated rat hearts

The study aimed to examine whether L-carnitine and its derivatives, acetyl-L-carnitine and propionyl-L-carnitine, were equally effective and able to improve postischemic cardiac function, reduce the incidence of reperfusion-induced ventricular fibrillation, infarct size, and apoptotic cell death in ischemic/reperfused isolated rat hearts. There are several studies indicating that L-carnitine, a naturally occurring amino acid and an essential cofactor, can improve mechanical function and substrate metabolism not only in hypertrophied or failing myocardium but also in ischemic/reperfused hearts. The effects of L-carnitine, acetyl-L-carnitine, and propionyl-L-carnitine, on the recovery of heart function, incidence of reperfusion-induced ventricular fibrillation (VF), infarct size, and apoptotic cell death after 30 min ischemia followed by 120 min reperfusion were studied in isolated working rat hearts. Hearts were perfused with various concentrations of L-carnitine (0.5 and 5 mM), acetyl-L-carnitine (0.5 and 5 mM), and propionyl-L-carnitine (0.05, 0.5, and 5 mM), respectively, for 10 min before the induction of ischemia. Postischemic recovery of CF, AF, and LVDP was significantly improved in all groups perfused with 5 mM of L-carnitine, acetyl-L-carnitine, and propionyl-L-carnitine. Significant postischemic ventricular recovery was noticed in the hearts perfused with 0.5 mM of propionyl-L-carnitine, but not with the same concentration of L-carnitine or L-acetyl carnitine. The incidence of reperfusion VF was reduced from its control value of 90 to 10% (p < 0.05) in hearts perfused with 5 mM of propionyl-L-carnitine only. Other doses of various carnitines failed to reduce the incidence of VF. The protection in CF, AF, LVDP, and VF reflected in a reduction in infarct size and apoptotic cell death in hearts treated with various concentrations of carnitine derivatives. The difference between effectiveness of various carnitines on the recovery of postischemic myocardium may be explained by different membrane permeability properties of carnitine and its derivatives.     

Dopamine 4-sulfate: effects on isolated perfused rat heart and role of atria

We studied the effects of sulfate conjugate of dopamine on the isolated perfused rat heart (Langendorff preparation). In the experimental group, we removed atria from half number of the hearts. In the hearts with intact atria, dopamine 4-sulfate significantly improved the DT (developed tension), +dT/dt max (maximal rate of contraction), -dT/dt max (maximum rate of relaxation) over baseline values. But when atria were removed, dopamine 4-sulfate had no effect on the mechanical functions of heart. We analysed the effluent perfusate for the free and conjugated catecholamines. In the control group (no drug), and when atria were excised, the free catecholamine levels were negligible. But when the atria were kept intact, the effluent contained significant amount of free dopamine (DA), and norepinephrine (NE). These data suggested that dopamine sulfate had no direct effect on the ventricular muscle of rat heart, but was converted within the atrial tissues into free catecholamines which might be responsible for the positive inotropic actions.     

The influence of lactate,pyruvate and glucose as exogenous substrates on free radical defense mechanisms in isolated rat hearts during ischaemia and reperfusion

Previous studies have shown that exogenous lactate impairs mechanical function of reperfused ischaemic hearts, while pyruvate improves post-ischaemic recovery. The aim of this study was to investigate whether the diverging influence of exogenous lactate and pyruvate on functional recovery can be explained by an effect of the exogenous substrates on endogenous protecting mechanisms against oxygen-derived free radicals. Isolated working rat hearts were perfused by a Krebs-Henseleit bicarbonate buffer containing glucose (5 mM) as basal substrate and either lactate (5 mM) or pyruvate (5 mM) as cosubstrate. In hearts perfused with glucose as sole substrate the activity of glutathione reductase was decreased by 32% during 30 min of ischaemia (p<0.10 versus control value), while the activity of superoxide dismutase and catalase was reduced by 27 and 35%, respectively, during 5 min of reperfusion (p<0.10 versus control value). The GSH level in the glucose group was reduced by 29% following 30 min of ischaemia and 35 min of reperfusion (p<0.10). In lactate- and pyruvateperfused hearts there were no significant decreases of superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase activity during 30 min of ischaemia, 5 min of reperfusion or 35 min of reperfusion. In pyruvate-perfused hearts the glutathione peroxidase activity was even increased by 43% during 30 min of ischaemia (p<0.05). Glutathione levels (reduced and oxidized) did not markedly change in the lactate and pyruvate groups. Thus, the endogenous defense mechanism against oxygen-derived free radicals is compromised at the onset of reperfusion when glucose as sole substrate is present, while addition of lactate or pyruvate prevents reduction of the endogenous capacity to scavenge oxygen-derived free radicals. The equivocal relationship between endogenous scavenging enzyme activity and haemodynamic recovery indicates that involvement of the endogenous antioxidants, if any, in functional recovery of the post-ischaemic heart is complex. Pyruvate may exert protective effects on mechanical function after mild ischaemia by functioning as exogenous scavenger in itself, as pyruvate is able to react with hydrogen peroxide.     

Leptin activates cardiac fatty acid oxidation independent of changes in the AMP-activated protein kinase-acetyl-CoA carboxylase-malonyl-CoA axis

Leptin regulates fatty acid metabolism in liver, skeletal muscle, and pancreas by partitioning fatty acids into oxidation rather than triacylglycerol (TG) storage. Although leptin receptors are present in the heart, it is not known whether leptin also regulates cardiac fatty acid metabolism. To determine whether leptin directly regulates cardiac fatty acid metabolism, isolated working rat hearts were perfused with 0.8 mm [9,10-(3)H]palmitate and 5 mm [1-(14)C]glucose to measure palmitate and glucose oxidation rates. Leptin (60 ng/ml) significantly increased palmitate oxidation rates 60% above control hearts (p < 0.05) and decreased TG content by 33% (p < 0.05) over the 60-min perfusion period. In contrast, there was no difference in glucose oxidation rates between leptin-treated and control hearts. Although leptin did not affect cardiac work, oxygen consumption increased by 30% (p < 0.05) and cardiac efficiency was decreased by 42% (p < 0.05). AMP-activated protein kinase (AMPK) plays a major role in the regulation of cardiac fatty acid oxidation by inhibiting acetyl-CoA carboxylase (ACC) and reducing malonyl-CoA levels. Leptin has also been shown to increase fatty acid oxidation in skeletal muscle through the activation of AMPK. However, we demonstrate that leptin had no significant effect on AMPK activity, AMPK phosphorylation state, ACC activity, or malonyl-CoA levels. AMPK activity and its phosphorylation state were also unaffected after 5 and 10 min of perfusion in the presence of leptin. The addition of insulin (100 microunits/ml) to the perfusate reduced the ability of leptin to increase fatty acid oxidation and decrease cardiac TG content. These data demonstrate for the first time that leptin activates fatty acid oxidation and decreases TG content in the heart. We also show that the effects of leptin in the heart are independent of changes in the AMPK-ACC-malonyl-CoA axis.     

Palmitic and erucic acid metabolism in isolated perfused hearts from weanling pigs

Hearts from 4 week-old weanling pigs were capable of continuous work output when perfused with Krebs-Henseleit buffer containing 11 mM glucose. Perfused hearts metabolized either glucose or fatty acids, but optimum work output was achieved by a combination of glucose plus physiological concentrations (0.1 mM) of either palmitate or erucate. Higher concentrations of free fatty acids increased their rate of oxidation but also resulted in a large accumulation of neutral lipids in the myocardium, as well as a tendency to increased acetylation and acylation of coenzyme A and carnitine. When hearts were perfused with 1 mM fatty acids, the work output declined below control values. Erucic acid is known to be poorly oxidized by isolated rat heart mitochondria and, to a lesser degree, by perfused rat hearts. In addition, it has been reported that erucic acid acts as an uncoupler of oxidative phosphorylation. In isolated perfused pig hearts used in the present study, erucic acid oxidation rates were as high as palmitate oxidation rates. When energy coupling was measured by 31P-NMR, the steady-state levels of ATP and phosphocreatine during erucic acid perfusion did not change noticeably from those during glucose perfusion. It was concluded that the severe decrease in oxidation rates and ATP production resulting from the exposure of isolated pig and heart mitochondria to erucic acid are not replicated in the intact pig heart.     

An improved isolated working rabbit heart preparation using red cell enhanced perfusate

The performance of isolated working rabbit hearts perfused with Krebs-Henseleit (KH) buffer was compared with those in which the buffer was supplemented with washed human red blood cells (KH + RBC) at a hematocrit of 15 percent. When perfused with KH alone at 70 cm H2O afterload and paced at 240 beats/minute, coronary flow was more than double, whereas aortic flow was 40-60 percent of that in hearts perfused with KH + RBC, regardless of left atrial filling pressures (LAFP). Peak systolic pressure reached a plateau at 120 mm Hg in KH + RBC, but at 95 mm Hg in the KH group. Stroke work, however, was similar in the two groups. Despite the high coronary flow, oxygen uptake by hearts perfused with KH was substantially less and did not respond to increases in LAFP as in those perfused with KH + RBC. There was a 20 percent drop in ATP and glycogen content after 90 minutes' perfusion. In contrast, isolated hearts perfused with RBC-enriched buffer remained stable for at least 150 minutes. Irrespective of the perfusate, triacylglycerol content of the muscle remained at similar levels throughout the course of study. Increasing RBC in the perfusate from 15 percent to 25 percent had no additional effect on cardiac performance or oxygen consumption. Our findings demonstrate that in the isolated working rabbit heart inclusion of RBC in the perfusate improves mechanical and metabolic stability by providing an adequate oxygen supply.     

Effects of dichloroacetate on the metabolism of glucose, pyruvate, acetate, 3-hydroxybutyrate and palmitate in rat diaphragm and heart muscle in vitro and on extraction of glucose, lactate, pyruvate and free fatty acids by dog heart in vivo

1. The extractions of glucose, lactate, pyruvate and free fatty acids by dog heart in vivo were calculated from measurements of their arterial and coronary sinus blood concentration. Elevation of plasma free fatty acid concentrations by infusion of intralipid and heparin resulted in increased extraction of free fatty acids and diminished extractions of glucose, lactate and pyruvate by the heart. It is suggested that metabolism of free fatty acids by the heart in vivo, as in vitro, may impair utilization of these substrates. These effects of elevated plasma free fatty acid concentrations on extractions by the heart in vivo were reversed by injection of dichloroacetate, which also improved extraction of lactate and pyruvate by the heart in vivo in alloxan diabetes. 2. Sodium dichloroacetate increased glucose oxidation and pyruvate oxidation in hearts from fed normal or alloxan-diabetic rats perfused with glucose and insulin. Dichloroacetate inhibited oxidation of acetate and 3-hydroxybutyrate and partially reversed inhibitory effects of these substrates on the oxidation of glucose. In rat diaphragm muscle dichloroacetate inhibited oxidation of acetate, 3-hydroxybutyrate and palmitate and increased glucose oxidation and pyruvate oxidation in diaphragms from alloxan-diabetic rats. Dichloroacetate increased the rate of glycolysis in hearts perfused with glucose, insulin and acetate and evidence is given that this results from a lowering of the citrate concentration within the cell, with a consequent activation of phosphofructokinase. 3. In hearts from normal rats perfused with glucose and insulin, dichloroacetate increased cell concentrations of acetyl-CoA, acetylcarnitine and glutamate and lowered those of aspartate and malate. In perfusions with glucose, insulin and acetate, dichloroacetate lowered the cell citrate concentration without lowering the acetyl-CoA or acetylcarnitine concentrations. Measurements of specific radioactivities of acetyl-CoA, acetylcarnitine and citrate in perfusions with [1-(14)C]acetate indicated that dichloroacetate lowered the specific radio-activity of these substrates in the perfused heart. Evidence is given that dichloroacetate may not be metabolized by the heart to dichloroacetyl-CoA or dichloroacetylcarnitine or citrate or CO(2). 4. We suggest that dichloroacetate may activate pyruvate dehydrogenase, thus increasing the oxidation of pyruvate to acetyl-CoA and acetylcarnitine and the conversion of acetyl-CoA into glutamate, with consumption of aspartate and malate. Possible mechanisms for the changes in cell citrate concentration and for inhibitory effects of dichloroacetate on the oxidation of acetate, 3-hydroxybutyrate and palmitate are discussed.     

Transport and metabolism of pantothenic acid by rat kidney

Transport of [14C]pantothenic acid was studied using brush-border membrane vesicles prepared from rat kidney. In the presence of a Na+ gradient an accumulation of pantothenic acid 3-fold above equilibrium was observed. The Km and Vmax found were 7.30 microM and 23.8 pmol/mg protein per min, respectively. Isolated perfused rat kidneys were employed to study excretion of pantothenic acid at various concentrations in the perfusate. At physiological plasma concentrations, the filtered pantothenic acid was largely reabsorbed by the active process observed in the vesicles. At higher concentrations, pantothenic acid was found to undergo tubular secretion. Penicillin inhibited this secretory process indicating that both compounds share a secretory mechanism. Live animal studies indicated that the only compound excreted after injection of [14C]pantothenic acid was free pantothenic acid. After 1 week only 38% of the administered dose was excreted in the urine, indicating that effective conservation was taking place in the whole animal.     

Effects of increased mechanical work by isolated perfused rat heart during production or uptake of ketone bodies. Assessment of mitochondrial oxidized to reduced free nicotinamide-adenine dinucleotide ratios and oxaloacetate concentrations.

Metabolic effects of increased mechanical work were studied by comparing isolated pumping rat hearts perfused by the atrial-filling technique with aortic-perfused non-pumping hearts perfused by the technique of Langendorff. The initial medium usually contained glucose (11 mm) and palmitate (0.6 mm bound to 0.1 mm albumin). During increased heart work (comparing pumping with non-pumping hearts) the uptake of oxygen and glucose increased threefold, but that of free fatty acids was unchanged. Tissue contents of alpha-oxoglutarate, NH4+, malate, lactate, pyruvate and Pi rose with increased heart work, but contents of ATP, phosphocreatine and citrate fell. Ketone bodies were produced with a ratio of beta-hydroxybutyrate/acetoacetate of about 3:1 in both pumping and non-pumping hearts but with higher net production rates in non-pumping hearts. When ketone bodies were added in relatively high concentrations (total 4 mm) to a glucose (11 mm) medium the medium, ratios of beta-hydroxybutyrate/acetoacetate were not steady even after 60 min of perfusion. The validity of calculating mitochondrial free NAD+/NADH ratios from the tissue contents of the reactants of the glutamate dehydrogenase system or the beta-hydroxybutyrate dehydrogenase system is assessed. The activities of these enzymes are considerably less in the rat heart than in the rat liver, introducing reservations into the application to the heart of the principles used by Williamson et al. (1967) for calculation of mitochondrial free NAD+/NADH ratios of liver mitochondria...     

Effects of L-carnitine on mechanical recovery of isolated rat hearts in relation to the perfusion with glucose and palmitate

The purpose of this study was to investigate the effects of L-carnitine on the hemodynamic parameters of Langendorff hearts. Isolated rat hearts were perfused with various solutions containing high or low concentrations of fatty acids, additional glucose or no glucose, and L-carnitine or no L-carnitine. The most interesting part of the experiments was the behaviour of the hearts in the reperfusion period after no-flow ischemia of 20 min. The results were: (1) With glucose and high fatty acid concentrations the hearts showed an improved recovery of the left ventricular functions in the reperfusion period compared with low fatty acid concentrations. Without glucose the left ventricular pressure is much lower in the reperfusion period. (2) Addition of L-carnitine improved the recovery of the ischemically damaged hearts. This improvement is especially impressive at low fatty acid concentrations. L-carnitine addition at high fatty acid concentrations but without glucose strongly improved reperfusion behaviour. (3) The coronary flow is increased by 2 experimental conditions: (i) perfusion at low levels of fatty acids, carnitine and with glucose and (ii) high levels of fatty acids and carnitine but without glucose. These findings suggest that supplementation of L-carnitine has a beneficial effect on the isolated heart under various conditions, and possibly on specific human heart diseases.     

Oxygen reperfusion is limited in the postischemic hypertrophic myocardium

Studies have shown that hypertrophied hearts are unusually vulnerable to ischemia. Compromised O2 supply has been postulated as a possible explanation for this phenomenon on the basis of elongated O2 diffusion distance and altered coronary vasculature found in hypertrophied myocardium. To examine the postulate, perfused heart experiments followed the metabolic and functional responses of hypertrophic myocardium to ischemia. 1H/31P NMR was used to measure cellular oxygenation and energy level during ischemia-reperfusion. The left ventricles from spontaneously hypertensive rats (SHR) were enlarged by 48%. With this moderate degree of hypertrophy, cellular O2 and energy levels were normal during baseline perfusion. After an ischemic episode, however, cellular O2 was severely deprived in the SHR hearts compared with the normal hearts. Depressed postischemic O2 reperfusion correlated well with depressed energetic and functional recovery. The results from the current study thus demonstrate a critical relationship between reperfused O2 level and functional recovery in hypertrophic myocardium. The role of reperfused O2, however, is time dependent. During early reperfusion, factor(s) other than O2 appear to limit functional recovery. It is when the mechanical function of the heart approaches a new steady state that O2 becomes a dominant factor. Meanwhile, the finding of a normal O2 level in preischemic SHR hearts defies the notion of preexisting hypoxia as a primer of ischemic damage.     

Incomplete oxidation of palmitate and leakage of intermediary products during anoxia

Surviving isolated rat hearts were perfused utilizing the Langendorff technique with [1-¹⁴C]palmitate or [16-¹⁴C]palmitate. During anoxia it was possible to isolate shorter-chain fatty acids and hydroxylated intermediates in the perfusate. When the heart was well oxygenated this was not the case. During oxygenation most of the palmitate was utilized and some of its labeled fragments were used for elongation of other fatty acids. During anoxia this was not observed. The fatty acid composition of the heart did not show a statistically significant change during anoxia, but the perfusate was enriched with some metabolites. It is suggested that changes in permeability in the cell membrane which occur during anoxia may cause leakage or transport of lipids, including short fatty acids and hydroxy intermediates.     

硫辛酸抗再灌期心律失常与外源性自由基所致动作电...

By means of Langendorff method the isolated rat heart was perfused with Krebs Henseleit solution. Following ligation of the left descending coronary artery for 10 min the heart was reperfused for 3 min. The incidence of ventricular fibrillation in the reperfusion period was 100%, and the normal sinus rhythm time was shortened to 29 s within 3 min of reperfusion. Administration of lipoic acid (6.8 X 10(-6)-1.7 X 10(-4) mol/L) to the perfusate significantly reduced the incidence of ventricular fibrillation to 33-50% and prolonged the normal sinus rhythm time to 97-107 s. APA, RP, and Vmax recorded from the guinea pig papillary muscle were depressed due to the deleterious effect of xanthine oxidase and hypoxanthine free radical generating system. Under the treatment of lipoic acid (3.5 X 10(-5) mol/L), the depression of APA, RP, and Vmax were significantly relieved. This confirms that lipoic acid treatment, owing to its free radical scavenger effect, is able to protect myocardium from free radical induced electrophysiological abnormalities, and consequently decrease the incidence of malignant arrhythmias.     

Carnitine stimulation of glucose oxidation in the fatty acid perfused isolated working rat heart.

The effects of L-carnitine on myocardial glycolysis, glucose oxidation, and palmitate oxidation were determined in isolated working rat hearts. Hearts were perfused under aerobic conditions with perfusate containing either 11 mM [2-3H/U-14C]glucose in the presence or absence of 1.2 mM palmitate or 11 mM glucose and 1.2 mM [1-14C]palmitate. Myocardial carnitine levels were elevated by perfusing hearts with 10 mM L-carnitine. A 60-min perfusion period resulted in significant increases in total myocardial carnitine from 4376 +/- 211 to 9496 +/- 473 nmol/g dry weight. Glycolysis (measured as 3H2O production) was unchanged in carnitine-treated hearts perfused in the absence of fatty acids (4418 +/- 300 versus 4547 +/- 600 nmol glucose/g dry weight.min). If 1.2 mM palmitate was present in the perfusate, glycolysis decreased almost 2-fold compared with hearts perfused in the absence of fatty acids. In carnitine-treated hearts this drop in glycolysis did not occur (glycolytic rates were 2911 +/- 231 to 4629 +/- 460 nmol glucose/g dry weight.min, in control and carnitine-treated hearts, respectively. Compared with control hearts, glucose oxidation rates (measured as 14CO2 production from [U-14C]glucose) were unaltered in carnitine-treated hearts perfused in the absence of fatty acids (1819 +/- 169 versus 2026 +/- 171 nmol glucose/g dry weight.min, respectively). In the presence of 1.2 mM palmitate, glucose oxidation decreased dramatically in control hearts (11-fold). In carnitine-treated hearts, however, glucose oxidation was significantly greater than control hearts under these conditions (158 +/- 21 to 454 +/- 85 nmol glucose/g dry weight.min, in control and carnitine-treated hearts, respectively). Palmitate oxidation rates (measured as 14CO2 production from [1-14C]palmitate) decreased in the carnitine-treated hearts from 728 +/- 61 to 572 +/- 111 nmol palmitate/g dry weight.min. This probably occurred secondary to an increase in overall ATP production from glucose oxidation (from 5.4 to 14.5% of steady state myocardial ATP production). The results reported in this study provide direct evidence that carnitine can stimulate glucose oxidation in the intact fatty acid perfused heart. This probably occurs secondary to facilitating the intramitochondrial transfer of acetyl groups from acetyl-CoA to acetylcarnitine, thereby relieving inhibition of the pyruvate dehydrogenase complex.