Western diet increases cardiac ceramide content in healthy and hypertrophied hearts.

BACKGROUND AND AIMS: Obesity and cardiac left ventricular hypertrophy (LVH) are recognised independent risk factors in the development of heart failure (HF). However, the combination of these factors may exacerbate the onset of cardiovascular disease by mechanisms as yet unclear. LVH leads to significant cellular remodelling, including alterations in metabolism which may result in an inappropriate accumulation of lipids and eventual lipotoxicity and apoptosis. The aim of the study was to determine the impact of dietary manipulation on cardiac metabolism in the obese and hypertrophied heart. METHODS AND RESULTS: LVH was induced via aortic constriction (AC) in an experimental model of cardiac hypertrophy and animals subjected to 9 weeks of dietary manipulation with either a standard, high fat, or a sucrose containing Western-style diet (SD, HFD and WD, respectively). This latter diet resulted in accelerated weight gain in both LVH/AC and control animals. LVH was greater in AC animals fed a WD, and both control and AC animals from this diet showed a significant reduction in cardiac fatty acid oxidation and increased triacylglycerol content. Ceramide content was significantly increased in the WD groups, with no additional effect of LVH. Comparison with a model of HF induced by exposure to Doxorubicin and WD showed exacerbated remodelling of cardiac ceramide species leading to increased C16 and C18 content. CONCLUSIONS: These findings highlight the inappropriate accumulation and re-distribution of cardiac ceramide species in a diet-induced model of obesity and LVH, potentially increasing susceptibility to cell death. The combination of increased fat and sugar leads to greater pathological remodelling and may explain why this diet pattern is consistently linked with poor cardiovascular outcomes.

Impairment of cardiac function and energetics in experimental renal failure.

Cardiac function and energetics in experimental renal failure in the rat (5/6 nephrectomy) have been investigated by means of an isolated perfused working heart preparation and an isometric Langendorff preparation using 31P nuclear magnetic resonance (31P NMR). 4 wk after nephrectomy cardiac output of isolated hearts perfused with Krebs-Henseleit buffer was significantly lower (P < 0.0001) at all levels of preload and afterload in the renal failure groups than in the pair-fed sham operated control group. In control hearts, cardiac output increased with increases in perfusate calcium from 0.73 to 5.61 mmol/liter whereas uremic hearts failed in high calcium perfusate. Collection of 31P NMR spectra from hearts of renal failure and control animals during 30 min normoxic Langendorff perfusion showed that basal phosphocreatine was reduced by 32% to 4.7 mumol/g wet wt (P < 0.01) and the phosphocreatine to ATP ratio was reduced by 32% (P < 0.01) in uremic hearts. During low flow ischemia, there was a substantial decrease in phosphocreatine in the uremic hearts and an accompanying marked increase in release of inosine into the coronary effluent (14.9 vs 6.1 microM, P < 0.01). We conclude that cardiac function is impaired in experimental renal failure, in association with abnormal cardiac energetics and increased susceptibility to ischemic damage. Disordered myocardial calcium utilization may contribute to these derangements.

Hyperthyroidism results in increased glycolytic capacity in the rat heart. A 31P-NMR study.

We have investigated the metabolic adaptations that occur in the thyroxine-treated rat heart. Rats were made hyperthyroid by daily intra-peritoneal injections of thyroxine (35 micrograms/100 g body weight) over seven days. 31P-NMR investigations of isolated glucose-perfused isometric hearts showed that thyroxine treatment caused an increase in Pi (from 4.9 mumols.(g dry wt.)-1 in control hearts to 11.7 mumols.(g dry wt.)-1 in hyperthyroid hearts), a decrease in phosphocreatine (from 36.5 mumols.(g dry wt.)-1 to 21.8 mumols.(g dry wt.)-1) with no change in ATP or ADP concentrations under the same conditions of cardiac work. The unidirectional exchange flux Pi----ATP was measured by saturation transfer NMR in hyperthyroid rat hearts. This exchange (which has been shown to contain a significant glycolytic component) increased by 2.2-fold in thyroxine-treated hearts in comparison to control hearts (to 3.6 mumols.(g dry wt.)-1.s-1, from 1.6 mumols.(g dry wt.)-1.s-1). In parallel experiments, NMR analysis of extracts from hyperthyroid rat hearts showed significantly elevated levels of glucose 6-phosphate, and fructose 6-phosphate. Measurements of enzyme activities isolated from hyperthyroid and control tissue showed a 40% increase in phosphofructokinase activity. These data together with the increased concentration of Pi show that both glycolytic and glycogenolytic fluxes are increased in the hyperthyroid rat heart. This metabolic adaptation may be necessary to cope with the increased number and activity of Na+/K(+)-ATPase pumps that occur in response to thyroxine treatment.

The acute effects of the creatine analogue, beta-guanidinopropionic acid, on cardiac energy metabolism and function.

1. Perfusion of isolated rat hearts with 150 mM beta GPA led to the linear accumulation of intracellular P beta GPA (approx. 150 nmol/min per g (dry wt.)) after an initial lag period of 20 min. 2. This accumulation of intracellular P beta GPA was accompanied by a decrease in PCr (30%) and an increase in total phosphagen content (20%). These results show that PCr was not equally replaced by P beta GPA, but was degraded at the expense of beta GPA phosphorylation to produce a net increase in cardiac phosphagen content. Correspondingly, total phosphate (the sum of PCr, P beta GPA, Pi and ATP) was increased, indicating that there was no cellular necrosis and that the sarcolemma remained intact throughout the perfusion. 3. An increase in Pi and decrease in ATP also occurred concomitantly with P beta GPA accumulation, indicating that ATP synthesis was not keeping up with demand. This may be due to the gradual replacement of PCr by the less efficient phosphagen, P beta GPA, resulting in inadequate transduction of energy and hence an imbalance between energy demand and supply. However, the increased hyperosmolarity of the perfusate may be partly responsible for these effects on cardiac energy metabolism, as perfusion with 150 mM mannitol produced a similar decrease in ATP, but a smaller rise in Pi. 4. Perfusion with either 150 mM beta GPA or mannitol led to a significant intracellular alkalosis (max. pHi 7.3), which was reversed on returning to normal perfusate. In addition, both hyperosmolar perfusions led to a significant reduction in cardiac frequency (40 and 15%, respectively). However, only beta GPA caused significant negative inotropism. The time-courses for the changes in cardiac frequency and pHi did parallel the increase in P beta GPA. This suggests that both hyperosmolarity and the production of P beta GPA during beta GPA perfusions determine the degree of negative chronotropism, but that hyperosmolarity alone causes alkalosis and beta GPA phosphorylation, a decrease in developed tension. 5. When hearts, acutely loaded with P beta GPA were perfused with control medium, the levels of ATP, PCr and P beta GPA stabilised to produce a new steady state. There was no decrease in P beta GPA concentration during this procedure, implying that beta GPA efflux was negligible.

A 31P-NMR study of the effects of reflow on the ischaemic rat heart.

(1) The recovery of perfused rat hearts experiencing various lengths of total global ischaemia was studied using 31P-NMR. Mechanical function was monitored by measuring left ventricular pressure. (2) Hearts exposed to a maximum of 14 min total global ischaemia regained stable contractile function on reperfusion. The concentration of phosphocreatine in these hearts rapidly exceeded its pre-ischaemic value while that of ATP rose very slowly. Pi fell on reflow to approximately its original level. These observations are interpreted as being the result of a rapid turnover of ATP stimulating phosphocreatine production by the mitochondrial isozyme of creatine kinase (ATP: creatine N-phosphotransferase, EC 2.7.3.2). (3) The recovery of intracellular pH on reperfusion does not depend upon the duration of ischaemia, nor on the pH or the percentage of ATP depletion at the end of the ischaemic period. This indicates that pH recovery is a flow-dependent phenomenon. (4) In non-recovering hearts, multiple Pi resonances are observed which arise from areas of differing myocardial pH. Phosphocreatine levels did not rise above 50% of their pre-ischaemic values. ATP levels remained depressed. This suggests that localized tissue necrosis only characterizes the failing situation.

The effects of insulin on myocardial metabolism and acidosis in normoxia and ischaemia. A 31P-NMR study.

1. The effect of insulin on the perfused rat heart during normoxia and total ischaemia was studied by 31P-NMR. 2. During normoxic perfusion, insulin increased the phosphocreatine to ATP ratio at the expense of Pi, when glucose was the substrate. No change was observed when acetate was used as the sole substrate. the intracellular pH (as measured from the position of the 2-deoxyglucose 6-phosphate resonance peak) was unaffected by insulin treatment. 3. Infusion of insulin prior to ischaemia caused an increase in the rate and extent of acidosis during the period of no flow while the rate of ATP depletion was decreased. 4. Freeze-clamped studies showed an increase in glycogen levels upon insulin treatment of the glucose perfused rat heart. During ischaemia, a decrease in glycogen content concomitant with an increase in lactate was observed. The accessibility of glycogen to phosphorylase during ischaemia is increased as a result of insulin treatment. The control of glycolysis during ischaemia is discussed with respect to the content and structure of glycogen in heart tissue.

A protective effect of insulin on reperfusing the ischaemic rat heart shown using 31P-NMR.

The effect on the recovery of mechanical function, ATP, phosphocreatine, Pi and pH of various lengths of total global ischaemia in the insulin-treated, perfused rat heart has been studied using 31P-NMR. Insulin-treated hearts recovered stable mechanical function after 18 min ischaemia when their intracellular pH was 6.0 and 70% of the pre-ischaemic ATP remained. Hearts perfused without insulin fail to recover after 18 min ischaemia, having an intracellular pH of 6.3 and 40% of ATP remaining (Bailey, I.A., Seymour, A.-M.L. and Radda, G.K. (1981) Biochim, Biophys. Acta 637, 1-7). Thus, ATP maintenance in ischaemia is more important to recovery on reperfusion than is maintaining intracellular pH. The importance of this observation in devising biochemical strategies for the clinical protection of the myocardium is discussed.

Metabolic consequences of positive inotropy in rat and guinea-pig hearts.

The metabolic and physiological responses of hearts from male rats and guinea-pigs to isoprenaline and SK&F 94120 (a phosphodiesterase III inhibitor), have been studied. Doses which gave similar chronotropic stimulation gave different inotropic responses. In both species, isoprenaline generated a greater increase in developed tension than SK&F 94120. With both drugs the inotropic response in the rat was less than than in the guinea-pig. 31P-NMR investigation of high-energy phosphate levels showed reduction in PCr concentration and an accompanying acidosis in the isoprenaline-perfused rat heart only. In both species, lactate production was stimulated by SK&F 94120 but not by isoprenaline. These results are discussed with reference to G-protein activation of ion channels and differences in Ca2+ handling by the two species.

Creatine kinase kinetics, ATP turnover, and cardiac performance in hearts depleted of creatine with the substrate analogue beta-guanidinopropionic acid.

Rats were fed a diet containing 1% of the creatine substrate analogue beta-guanidinopropionic acid for 6-10 weeks. 31P-NMR investigation of isolated, glucose-perfused working hearts showed a 90% reduction in [phosphocreatine] from 22.2 to 2.5 mumol/g dry wt in guanidinopropionic acid-fed animals but no change in [Pi], [ATP], or intracellular pH. The unidirectional exchange flux in the creatine kinase reaction (direction phosphocreatine----ATP) was measured by saturation transfer NMR in hearts working against a perfusion pressure of 70 cm of water. This exchange was 10 mumol/g dry wt per s in control hearts and decreased 4-fold to 2.5-2.8 mumol/g dry wt per s in hearts from guanidinopropionic acid-fed animals. Oxygen consumption and cardiac performance were measured in parallel experiments at two perfusion pressures, 70 and 140 cm. No significant differences were observed in oxygen uptake or in any of the performance criteria between hearts from control and guanidinopropionic acid-fed rats at either workload. Assuming an ADP:O ratio of 3, the oxygen consumption measurements correspond to ATP turnover rates of 4.2-7.8 mumol/g dry per s. These rates are 1.5-3-times greater than the rate of the phosphocreatine----ATP exchange in hearts from guanidinopropionic acid-fed rats. These data suggest that phosphocreatine cannot be an obligate intermediate of energy transduction in the heart.

Determination of free creatine and phosphocreatine concentrations in the isolated perfused rat heart by 1H- and 31P-NMR.

To measure free creatine in the isolated perfused rat heart, the concentration of phosphocreatine, and phosphocreatine plus creatine (sigma Cr) were measured by 31P- and 1H-NMR, respectively. Quantification was performed in the presence and absence of an intraventricular balloon filled with a known amount of PCr, which acted as an external standard. Total (free plus bound) phosphocreatine and creatine were measured by HPLC analysis of extracts from the same hearts, freeze-clamped at the end of the perfusions. A greater concentration of creatine (mumol/g dry wt.) in the perfused rat heart was measured by HPLC analysis (40.3 +/- 2.38 (11)) as compared to NMR (34.6 +/- 1.95 (11)), whilst no significant difference was observed in the measurement of phosphocreatine between the two assay methods. Consequently, a greater sigma Cr was measured by HPLC. This work suggests that the majority of Cr in the heart is NMR visible and unbound, so available to interact with creatine kinase. The lower free ADP concentration calculated from NMR measurements (53.3 +/- 3.80 microM (9)) was not significantly different from that determined by HPLC analysis (56.9 +/- 5.90 microM (9)). This suggests that the concentration of free ADP in the heart is higher than values where it can regulate oxidative phosphorylation most effectively.

A 31P-NMR study of some metabolic and functional effects of the inotropic agents epinephrine and ouabain, and the ionophore R02-2985 (X537A) in the isolated, perfused rat heart.

1. Some metabolic effects of increased mechanical activity by the Langendorff-perfused rat heart have been characterized using 31P-NMR. Mechanical activity was increased by infusion of ouabain (0.9-7.0.10(-5) M), the ionophore R02-2985 (1.10(-5) M) or epinephrine (5.10(-8) M). 2. Similar metabolic changes accompanied infusion of each of the positive inotropic agents into hearts perfused with buffer containing 11 mM glucose as the substrate. In each case phosphocreatine concentrations decreased. During the period of epinephrine infusion the phosphocreatine began to recover its original concentration, although there were no significant changes in mechanical activity. 3. Comparisons of the metabolic changes accompanying the positive inotropic and chronotropic effects of epinephrine were made between hearts perfused with either glucose (11 mM), acetate (5 mM) or lactate (5 mM). A time-dependent decrease in phosphocreatine concentrations also accompanied infusion of epinephrine into hearts perfused with lactate as the sole exogenous substrate, but no statistically significant metabolite changes were observed after identical epinephrine infusions with acetate as the substrate. 4. Calculations of the concentration of free ADP assuming equilibrium in the creatine phosphokinase reaction allows estimation of the cytosolic phosphate potential ([ATP]/[ADP][Pi]), which appears to be dependent on the number of factors, including the nature of the exogenous substrate and the level of mechanical activity. 5. Thus, we conclude that there is no general correlation between the phosphate potential and the mitochondrial respiratory rate in the perfused rat heart.

Decreased GLUT-4 mRNA content and insulin-sensitive deoxyglucose uptake show insulin resistance in the hypertensive rat heart.

OBJECTIVES: Insulin resistance in skeletal muscle and adipose tissue often accompanies hypertension; however, it has not been shown that heart muscle is similarly affected. The aims of this study were to determine whether basal and insulin-stimulated glucose transport and glucose transporter mRNA content are altered in the spontaneously hypertensive rat (SHR) heart. METHODS: Hearts from 16-18-month-old SHRs were compared to their normotensive (WKY) controls. The accumulation of 2-deoxyglucose-6-phosphate (2DG6P), detected using 31P nuclear magnetic resonance spectroscopy, was used to assess glucose uptake before and during insulin stimulation in the isolated perfused heart. The mRNA levels of both the insulin-sensitive glucose transporter (GLUT-4) and the transporter responsible for basal glucose uptake (GLUT-1) were quantified by Northern blot analysis. RESULTS: The hypertensive rat hearts exhibited hypertrophy in that the heart/body weight ratio was increased by 59%. In these hearts, the basal rate of glucose uptake was 3-fold greater and hexokinase activity was 1.6 fold greater than that of the control rat hearts. On exposure to insulin, accumulation of 2DG6P increased 5-fold in the control hearts, but only 1.4-fold in the SHR hearts. Thus, in the presence of insulin, the rate of glucose uptake by the hypertensive rat heart was significantly (P < 0.05) reduced, being 82% of control. GLUT-4 mRNA content was decreased was no significant difference in the GLUT-1 mRNA content. CONCLUSION: We have demonstrated insulin resistance in the hypertrophied heart of the hypertensive rat that may have a molecular basis in a lower GLUT-4 content.

Alterations in the myocardial creatine kinase system during chronic anaemic hypoxia.

OBJECTIVE: The aim was to use a model of chronic anaemia in the rat, in which there is an increase in cardiac mitochondrial creatine kinase activity (mito-CK) per mitochondrion, to test the hypothesis that creatine stimulated respiration in saponin skinned fibres is correlated with mito-CK activity. In order to discuss the altered regulation of mitochondrial respiratory rate in the context of other metabolic alterations, steady state metabolite concentrations and maximum extracted activities of regulatory enzymes in glycolysis were also investigated. METHODS: Weanling male Wistar Albino rats were randomly distributed into two experimental groups. One group received a powdered diet deficient in iron (5-7 mg iron.kg-1) while the second group was placed on a standard laboratory chow diet (109 mg iron.kg-1) for 4-8 weeks. RESULTS: Total cardiac creatine kinase activity was unchanged in anaemic rats; however, a 25% increase in nascent or functional mito-CK activity per mitochondrion was detected [0.969(SEM 0.005), control group and 1.203(0.040), anaemic group, p < 0.001]. The sensitivity of creatine (40 mM creatine, VCr) and ADP (0.1 mM ADP, V0.1) stimulated respiration, as a percentage of maximum respiratory rate (2.0 mM ADP, V2.0), was increased by 48% and 52% respectively in the anaemic skinned cardiac fibres. An increase in basal respiration with glutamate and malate as substrates was detected in the anaemic group compared to the control group, at 6.77(0.74) v 4.58(0.35) ng O.min-1 x mg-1 dry weight (p < 0.025). Cytosolic ATP was decreased in isolated perfused hearts from anaemic animals, at 35.18(3.11) mumol.g-1 dry weight in control hearts versus 23.66(1.42) in anaemic hearts (p < 0.01). A significant increase in myocardial glycolytic capacity was detected in anaemic cardiac tissue, as evidenced by a 20% increase in phosphofructokinase activity (p < 0.01). Phosphorylase activity was unaltered in anaemic hearts, indicating that the increased glucose requirement originated from exogenous sources. Lactate dehydrogenase (LDH) was increased by 30% in anaemic hearts (p < 0.001). The LDH isozyme profile was shifted in favour of lactate and NAD+ production, thus supporting anaerobic glycolysis. CONCLUSIONS: In support of the phosphocreatine circuit model, the increased mito-CK per mitochondrion in the anaemic skinned fibre preparation was associated with an increase in creatine stimulated respiration. In addition, the sensitivity of mitochondrial respiratory rate to ADP and the maximum glycolytic capacity were increased in anaemic fibres. Although the net effect of these changes in metabolic capacity and regulation on in vivo high energy phosphate flux is unknown, it is likely that they are adaptive alterations that compensate for the lower steady state cytosolic nucleotide concentration.

Metabolic alterations in the chronically denervated dog heart.

OBJECTIVE: Previous studies have shown that chronic cardiac denervation impairs myocardial glucose oxidation. To investigate this further we tested whether the tissue content of glucose transporters, activity of glycolytic enzymes or metabolic capacity of pyruvate dehydrogenase were altered. Moreover, we investigated whether the decline in glucose utilization was associated with an upregulation of proteins and enzymes involved in fatty acid handling. Chronic cardiac denervation results also in decreased left ventricular efficiency. We explored whether alterations in mitochondrial properties could be held responsible for this phenomenon. METHODS: Twelve adult dogs were included in the study. In 6 of them chronic cardiac denervation was accomplished by surgical ablation of the extrinsic nerve fibers. The other 6 dogs were sham-operated. Biopsies were obtained from the left ventricle after 4-5 weeks of denervation. The content or enzymatic activity of proteins involved in fatty acid and glucose handling was assessed. Features of glutamate oxidation were measured in freshly isolated mitochondria. RESULTS: The content or activity of a set of fatty acid handling proteins did not change during chronic cardiac denervation. In contrast GLUT1 content significantly increased in the chronically denervated left ventricle, while the active form of pyruvate dehydrogenase declined (p < 0.05). Glutamate oxidation characteristics in freshly isolated mitochondria were not affected by chronic denervation. CONCLUSION: The impairment of glucose oxidation in the chronically denervated myocardium is most likely caused by a decline of pyruvate dehydrogenase in its active form. It is unlikely that the decrease in work efficiency is caused by alterations in mitochondrial properties.

Intracellular Ca2+ transients in isolated perfused rat heart: measurement using the fluorescent indicator Fura-2/AM.

We have investigated the nature of Fura-2/AM loading into isolated perfused rat heart and the temporal and kinetic relationship between left ventricular [Ca2+]i dependent fluorescence and isovolumic pressure. The contribution of hydrolysed mitochondrial matrix Fura-2 fluorescence to that measured from the surface of the heart was estimated to be 43.9 +/- 5.5% by the addition of 100 microM Mn2+ to the perfusate. Maximum endothelial Fura-2 fluorescence ratio, estimated by the addition of 3 microM bradykinin to the perfusate, was found to constitute 33.6 +/- 2.7% of the maximum myocardial Fura-2 fluorescence ratio. Approximately 11.2% of the 340 nm surface fluorescence was insensitive to 20 mM Mn2+ in the presence of ionomycin (3 microM) and therefore indicates the degree of partial hydrolysis of Fura-2/AM. Thus, depending on the contribution of endothelial Fura-2 fluorescence at a physiological endothelial calcium concentration, cytosolic fluorescence may comprise between 11-45% of the total cellular fluorescence at 340 nm. Net tissue interference of the Fura-2 fluorescence ratio by NADH emission and myoglobin absorption remained unaltered, providing the oxygenation state of the tissue was unaltered throughout the experiment. The [Ca2+]i dependent fluorescence decay from peak systole was best fitted to a biexponential decay with fast and slow rate constants of 18.08 +/- 1.97 s-1 and 0.23 +/- 0.02 s-1, respectively. In addition, a phase shift was observed between temporal and kinetic measurements of the left ventricular isovolumic pressure and calcium dependent fluorescence traces during a contraction-relaxation cycle. We conclude that despite imperfect Fura-2/AM loading, the temporal and kinetic characteristics of intracellular [Ca2+] transients in normal isolated perfused rat heart are similar to those reported in more controlled preparations such as isolated myocytes and cardiac trabeculae.

87Rb NMR studies of the perfused rat heart.

We have studied 87Rb+ fluxes in the perfused rat heart using nuclear magnetic resonance spectroscopy (NMR). A simple model for the interpretation of the data is presented. A comparison of radioactively measured K+ fluxes and the K+ fluxes deduced from the 87Rb+ measurements shows them to be very similar. This method provides a means of noninvasively measuring uni-directional K+ fluxes in the heart.

A single-blind, randomised, vehicle-controlled dose-finding study of recombinant human granulocyte colony-stimulating factor (lenograstim) in patients undergoing chemotherapy for solid cancers and lymphoma.

This study evaluated the effect of glycosylated recombinant human granulocyte colony-stimulating factor (rHuG-CSF; lenograstim) on neutrophil granulocyte counts and on cells of other haematopoietic lineages in 66 patients with solid cancer or lymphoma who received myelosuppressive chemotherapy. Beginning 1 day after completion of chemotherapy, patients received lenograstim (at dosages of 0.5, 2, 5 or 10 micrograms/kg) or vehicle subcutaneously once daily for 14 consecutive days. Compared with vehicle, lenograstim significantly accelerated neutrophil recovery after chemotherapy in a dose-dependent manner. Mean neutrophil counts recovered to > 1.0 x 10(9) cells/l by day 13 in the vehicle group compared with days 11, 10, 8 and 7 in the 0.5, 2, 5 and 10 micrograms/kg lenograstim groups, respectively. Doses of 0.5 and 2 micrograms/kg of lenograstim had a significant effect on the duration of neutropenia (< 1.0 x 10(9) cells/l), the area under the absolute neutrophil count (ANC) curve and the time to ANC nadir. The dose of 5 micrograms/kg additionally decreased the total area of neutropenia and gave the narrowest range of values for all neutrophil parameters, while the 10 micrograms/kg dose brought no added benefit. A dose-response effect of lenograstim on time to neutrophil recovery was observed both for patients who received chemotherapy on a single day (n = 35) and for those who received chemotherapy over several days (n = 29). Based on these findings, a dose of 5 micrograms/kg/day was chosen for further trials.

Dynamics of energy metabolism in the transplanted human heart during reperfusion.

Reperfusion after ischemia of the heart generates further damage to the myocardium through a variety of mechanisms including free radical generation, calcium overload, and abnormalities of energetics. In this study, the uptake and release of metabolites involved in energy metabolism were investigated during 45 minutes of reperfusion of donor human heart after transplantation to evaluate the nature of the metabolic abnormalities and the time course of recovery. Analysis of coronary sinus and arterial blood samples in 11 transplant recipients showed the following: (1) In the first minute of reperfusion, lactate release was observed accompanied by an uptake of pyruvate, resulting in a markedly elevated lactate/pyruvate ratio. The pH value of coronary sinus blood was lower than that of arterial blood by 0.1 unit, inorganic phosphate was released, and a massive efflux of nucleotide catabolites was observed. Hemoglobin oxygen saturation of coronary sinus blood was almost equal to that of arterial blood, showing minimal myocardial oxygen extraction. Coronary flow was approximately 300 ml/min at reperfusion with minor changes in the first minute. (2) From the second minute onward, pyruvate was released for over 45 minutes, contrasting with the first minute of reperfusion. Lactate was significantly released for up to 10 minutes of reperfusion, but myocardial uptake of lactate was not restored by the end of the observation period. However, the lactate/pyruvate ratio in coronary sinus blood recovered at the onset of this phase. Both pH changes in coronary sinus blood and phosphate release were restored within 5 minutes, but release of nucleotide catabolites was still significant after 30 minutes of reperfusion. The oxygen saturation of hemoglobin in coronary sinus blood decreased gradually in a biphasic mode over the 45 minutes, indicating gradual restoration of myocardial oxygen uptake. Coronary flow measured for up to 10 minutes of reperfusion decreased to a minimal value of 200 ml/min in the third minute, followed by restoration of initial flow. These data highlight the profound alterations in energy metabolism that occur during reperfusion of the transplanted heart. These changes, which may result from the preceding ischemia and impaired oxidative metabolism at the onset of reperfusion, were partially reversed in the first minutes. However, impaired pyruvate and lactate use and underperfusion reflected by the release of purine catabolites persisted for a period of more than 30 minutes of reperfusion.

Influence of preconditioning on rat heart subjected to prolonged cardioplegic arrest.

BACKGROUND: Ischemic preconditioning (IP) can reduce lethal injury to the myocardium induced by prolonged ischemia. However, little is known about the effect of preconditioning on the heart subjected to cardioplegic arrest and hypothermic preservation. We evaluated the effect of IP on myocardial metabolism, mechanical performance, and coronary endothelial function after cardioplegic arrest and prolonged hypothermic preservation. METHODS: An isovolumic Langendorff perfused rat heart model was used, and hearts were divided into two groups. The first group (IP, n = 14) was preconditioned by 5 minutes of global normothermic (37 degrees C) ischemia followed by 10 minutes of normothermic reperfusion before 6 hours of cold (4 degrees C) preservation, followed by 60 minutes of reperfusion. The second group (control, n = 15) was subjected to 6 hours of cold preservation followed by 60 minutes of reperfusion without preconditioning. Mechanical function was assessed using left ventricular balloon by constructing pressure-volume curves in two ways: at defined left ventricular volumes or at defined left ventricular end-diastolic pressures. Initially, the volume of the balloon was increased incrementally from 0 to 150 microL in 25-microL steps. Measurements were then repeated with loading balloon to achieve left ventricular end-diastolic pressure of 5, 10, 15, or 20 mm Hg. Myocardial function was assessed before ischemia and at 15 or 60 minutes of reperfusion. Metabolic status of the heart was evaluated by measuring the release of purine catabolites during the initial 15 minutes of reperfusion and concentrations of myocardial nucleotides at the end of reperfusion. Endothelium-mediated vasodilatation was evaluated using 10 mumol/L 5-hydroxytryptamine before and after ischemia. RESULTS: Left ventricular end-diastolic pressure values were significantly lower in the IP group, by 20% to 40%, during the reperfusion phase at each volume of the balloon compared with the control group. The rate-pressure product was more favorable during reperfusion in the IP than in the control group because of a 15% increased heart rate in the IP group. The release of purine catabolites from the heart during the reperfusion phase was reduced (p < 0.01) in the IP group (0.66 +/- 0.04 mumol) relative to the control group (0.92 +/- 0.06 mumol). No difference in the recovery of systolic function, myocardial adenosine triphosphate concentration, or endothelial function was observed between the groups. CONCLUSIONS: Under conditions of cardioplegic arrest and hypothermic preservation, IP can offer additional protection for the heart by preventing an increase in diastolic stiffness. However, metabolic improvement or better preservation of the systolic or endothelial function was not observed in this model.

Value of carnitine therapy in kidney dialysis patients and effects on cardiac function from human and animal studies.

Cardiovascular complications are the leading cause of mortality, accounting for 50% of all deaths among patients with end-stage renal disease (ESRD). The majority of these deaths are from cardiac causes. The mechanisms underlying the enhanced susceptibility to myocardial ischaemia and subsequent morbidity in ESRD remain ill-defined. Numerous metabolic derangements accompany myocardial ischaemia and reperfusion and play a pivotal role in the development of concurrent myocardial dysfunction. Carnitine plays a critical role in myocardial energy metabolism, as the transporter of long chain fatty acyl intermediates across the inner mitochondrial membrane for ß oxidation and as a central regulator of carbohydrate metabolism. Myocardial carnitine is significantly depleted during ischaemia and more particularly in uraemic patients and those on dialysis therapy. Carnitine treatment has cardiovascular benefits including modulation of myocardial metabolism, reduction in necrotic cell death and infarct size, decrease in the incidence of arrhythmias and preservation of mechanical function. This review details the profile of substrate metabolism in the uraemic heart and the impact of carnitine supplementation on metabolism and function of the reperfused heart and finally the experimental and clinical evidence for carnitine replacement therapy, in particular its impact on the uraemic heart via modulation of function and energetics.