Myocardial Creatine Phosphate Research Articles

Cardiac Metabolic Limitations Contribute to Diminished Performance of the Heart in Aging

Changes in the myocardial energetics associated with aging—reductions in creatine phosphate/ATP ratio, total creatine, and ATP—mirror changes observed in failing hearts compared to healthy controls. Similarly, both aging and heart failure are associated with significant reductions in cardiac performance and maximal left ventricular cardiac power output compared with young healthy individuals. Based on these observations, we hypothesize that reductions in the concentrations of cytoplasmic adenine nucleotide, creatine, and phosphate pools that occur with aging impair the myocardial capacity to synthesize ATP at physiological free energy levels and that the resulting changes to myocardial energetic status impair the mechanical pumping ability of the heart. The purpose of this study is to test these hypotheses using an age-structured population model for myocardial metabolism in the adult female population and to determine the potential impact of reductions in key myocardial metabolite pools in causing metabolic/energetic and cardiac mechanical dysfunction associated with aging. To test these hypotheses, we developed a population model for myocardial energetics to predict myocardial ATP, ADP, creatine phosphate, creatine, and inorganic phosphate concentrations as functions of cardiac work and age in the adult female population. Model predictions support our hypotheses and are consistent with previous experimental observations. The major findings provide a novel, to our knowledge, theoretical and computational framework for further probing complex relationships between the energetics and performance of the heart with aging.

PP.04.32] PHOSPHORUS DEFICIENCY IN MASSRY'S PHOSPHATE DEPLETION SYNDROME CAN BE ONE OF THE CAUSE OF ACUTE LEFT HEART FAILURE

Objective: In this study we investigated serum phosphorus levels in patients with acute left heart failure.Design and method: A total of 215 participants, 115 patients with acute left heart failure and 100 controls, were enrolled in the study. Patients applied to emergency room with the complaints of heart failure were assessed by echocardiography. Ejection Fraction (EF) levels lower than 50% were accepted as heart failure. Paients with renal disorders, hyperparathyroidism, chronic hearth failure, alcoholism, intake of medications that alter phosphorus level were excluded. Mean phosphorus levels of each group were measured and compared each other. SPSS 12.0 package program (SPSS Inc., Chicago, Illinois) was used for statistical analysis. Chi square test was used to compare categorical measures between the groups. Mann Whitney U or T test was used for comparison of numerical measurements between the two groups. Level of statistical significance was considered as 0.05 in all tests. Results: There were 148 (69%) women and 67 (31%) men in present study. The mean age was 52.6 years. Demographic characteristics of participants were not significantly different between the groups. Mean EF levels of groups were 40.8 versus 60.0 respectively. The difference was statistically significant (P < 0.001). Mean phosphorus levels were 3.01 versus 4.27 mg/dl respectively. There was statistically significant difference (P = 0.041) (Table 1). Table 1: Phosphorus levels in the study and control groups. Conclusions: Phosphorus is a major intracelluler constituent. The deficiency of phosphorus can cause a variety of signs and symptoms. Myocardial creatine phosphate, ATP, and ADP levels reduce in case of phosphate deficiency. In addition to these, mitochondrial and myofibrillar creatine phosphokinase activities also reduces. Alterations occur in mitochondrial oxygen consumption, acid-extractable phospholipid precursors, and mitochondrial oxidation of long chain fatty acids due to phosphate depletion. All these effect heart muscles and can cause heart failure. Consequently phosphorus levels should be controlled in patients with acute left heart failure. Phosporus supplementation may be a supportive treatment.

Myocardial energy metabolism and ultrastructure with polarizing and depolarizing cardioplegia in a porcine model.

OBJECTIVES: This study investigated whether the novel St. Thomas’ Hospital polarizing cardioplegic solution (STH-POL) with esmolol/adenosine/magnesium offers improved myocardial protection by reducing demands for high-energy phosphates during cardiac arrest compared to the depolarizing St. Thomas’ Hospital cardioplegic solution No 2 (STH-2). METHODS: Twenty anaesthetised pigs on tepid cardiopulmonary bypass were randomized to cardiac arrest for 60 min with antegrade freshly mixed, repeated, cold, oxygenated STH-POL or STH-2 blood cardioplegia every 20 min. Haemodynamic variables were continuously recorded. Left ventricular biopsies, snap-frozen in liquid nitrogen or fixed in glutaraldehyde, were obtained at Baseline, 58 min after cross-clamp and 20 and 180 min after weaning from bypass. Adenine nucleotides were evaluated by high-performance liquid chromatography, myocardial ultrastructure with morphometry. RESULTS: With STH-POL myocardial creatine phosphate was increased compared to STH-2 at 58 min of cross-clamp [59.9 ± 6.4 (SEM) vs 44.5 ± 7.4 nmol/mg protein; P < 0.025], and at 20 min after reperfusion (61.0 ± 6.7 vs 49.0 ± 5.5 nmol/mg protein; P < 0.05), ATP levels were increased at 20 min of reperfusion with STH-POL (35.4 ± 1.1 vs 32.4 ± 1.2 nmol/mg protein; P < 0.05). Mitochondrial surface-to-volume ratio was decreased with polarizing compared to depolarizing cardioplegia 20 min after reperfusion (6.74 ± 0.14 vs 7.46 ± 0.13 µm2/µm3; P = 0.047). None of these differences were present at 180 min of reperfusion. From 150 min of reperfusion and onwards, cardiac index was increased with STH-POL; 4.8 ± 0.2 compared to 4.0 ± 0.2 l/min/m2 (P = 0.011) for STH-2 at 180 min. CONCLUSIONS: Polarizing STH-POL cardioplegia improved energy status compared to standard STH-2 depolarizing blood cardioplegia during cardioplegic arrest and early after reperfusion.

Abstract 18663: Myocardial Heterogeneity in Heart With Postinfarction LV Remodeling and its Response to Cell Therapy

Rationale and Objective: Human induced pluripotent stem cells (hiPSCs) hold promise for myocardial repair following injury. Here, we investigated the functional impact and myocardial heterogeneity of bioenergetics using a porcine model of post infarction LV remodeling, and 2 dimensional chemical shift imaging (2D CSI) P-31 MR spectroscopy. Methods and Results: Ischemia-reperfusion (I/R) injury was surgically induced by occlusion distal LAD (OCCL) for 60 minutes in female Yorkshire farm swine (≈15kg), then randomly assigned to experimental groups: 1) 16 million human induced pluripotent stem cells (hiPSC) derived cardio myocytes (CMs), smooth muscle cells (SMC) and Endothelia cells (ECs) were directly myocardial injected through an epicardial fibrin patch (P+Cell, n= 4), 2) open patch (fibrin patch with no cell) were placed over the injury site (P w/o Cell, n=4). Size matched normal (n=9) and OCCL only (n=5) pigs were also studied. Four weeks after I/R, 2D CSI MRS studies were performed in a 9.4T/ 65 cm bore magnet. In vivo myocardial energetic mapping was achieved using 31 P 2D CSI. To measure the forward flux rate PCr to ATP, 2D CSI data were acquired with or without saturation on ATPγ resonance. I/R injury has a heterogeneous effect on LV myocardial bioenergetics. Myocardial creatine phosphate (PCr)/ATP ratio is significantly decreased in border zone (BZ) of the infarction than the myocardial areas remote from the scar (RZ) in cell treated and patch only groups (1.54+/- 0.05 vs 2.25 +/- 0.10, 1.49+/-0.07 vs 2.34 +/- 0.07, BZ vs RZ, p&lt;0.05). The BZ PCr/ATP ratio is improved in the cell treated group compared with open patch group (1.71 +/- 0.05 vs. 1.54 +/- 0.05, p&lt;0.05). The forward flux rate constant of PCr/ATP (k pcr→ATP ) in the border zone is slightly increased in cell treated group compared with patch only group (0.29 +/- 0.02 vs 0.22 +/- 0.04 , p&lt;0.05) Conclusion: The approach of 2D CSI 31 P MRS can effectively map the heterogeneity of myocardial ATP flux rate via CK In Vivo porcine hearts. Postinfarction LV remodeling heart manifests pronounced heterogeneity in myocardial bioenergetics with most severe alterations in BZ. Cell therapy may effectively improve BZ myocardial bioenergetics.

Zoniporide preserves left ventricular compliance during ventricular fibrillation and minimizes postresuscitation myocardial dysfunction through benefits on energy metabolism*

To investigate whether sodium-hydrogen exchanger isoform-1 (NHE-1) inhibition attenuates myocardial injury during resuscitation from ventricular fibrillation through effects on energy metabolism, using an open-chest pig model in which coronary perfusion was controlled by extracorporeal circulation. Randomized controlled animal study. University research laboratory. Male domestic pigs. Ventricular fibrillation was electrically induced and left untreated for 8 mins, after which extracorporeal circulation was started and its flow adjusted to maintain a coronary perfusion pressure of 10 mm Hg. After 10 mins of extracorporeal circulation, restoration of spontaneous circulation was attempted by epicardial defibrillation and gradual reduction in extracorporeal flow. Two groups of eight pigs each were randomized to receive the NHE-1 inhibitor zoniporide (3 mg.kg-1) or vehicle control immediately before starting extracorporeal circulation. Identical extracorporeal flows (approximately = 9% of baseline cardiac index) were required in zoniporide and control groups to attain the target coronary perfusion pressure, resulting in comparable left anterior descending coronary artery blood flow (9 +/- 1 and 10 +/- 1 mL.min-1) and resistance (0.10 +/- 0.01 and 0.10 +/- 0.01 dyne.sec.cm(-5)). Yet zoniporide prevented reductions in left ventricular volume and wall thickening while favoring higher myocardial creatine phosphate to creatine ratios (0.14 +/- 0.03 vs. 0.06 +/- 0.01, p < .05), lower myocardial adenosine (0.7 +/- 0.1 vs. 1.3 +/- 0.2, p < .05), and lower myocardial lactate (80 +/- 9 vs. 125 +/- 6 mmol.kg-1, p < .001). Postresuscitation, zoniporide-treated pigs had higher left ventricular ejection fraction (0.57 +/- 0.07 vs. 0.29 +/- 0.05, p < .05) and higher cardiac index (4.8 +/- 0.4 vs. 3.4 +/- 0.2 L.min-1.m-2, p < .05). Zoniporide ameliorated myocardial injury during resuscitation from ventricular fibrillation through beneficial effects on energy metabolism without effects on coronary vascular resistance and coronary blood flow.

Effects of a Pharmacologically-Induced Shift of Hemoglobin-Oxygen Dissociation on Myocardial Energetics During Ischemia in Patients with Coronary Artery Disease

Conventional strategies to treat myocardial ischemia include interventions that reduce oxygen demand and/or increase myocardial blood flow. Animal experiments suggest that right-shifting the hemoglobin-oxygen dissociation curve may also attenuate the metabolic consequences of myocardial ischemia. We evaluated whether exercise-induced myocardial ischemia can be alleviated in subjects with coronary artery disease (CAD) by enhancing oxygen release with an allosteric modifier of hemoglobin's affinity for oxygen (RSR13). Seven subjects with CAD underwent a randomized, double-blind, cross-over study of the metabolic consequences of RSR13 administration on myocardial ischemia. Myocardial high-energy phosphates were quantified with 31P nuclear magnetic resonance (NMR) spectroscopy before, during, and after isometric handgrip-exercise. Subjects underwent NMR studies at baseline and on two separate occasions following the infusion of RSR13 (100 mg/kg) or placebo. RSR13 infusion significantly increased mean p50 by 8.1 +/- 2.7 mmHg at the end of the infusion, and it was still elevated by 4.9 +/- 3.3 mmHg after the completion of the treadmill tests while placebo had no effect. The myocardial creatine-phosphate (PCr) to adenosine-triphosphate (ATP) ratio decreased during handgrip-exercise in the baseline studies (from 1.39 +/- 0.23 before exercise to 0.95 +/- 0.21 during handgrip-exercise, p = 0.0001) and in the placebo studies (from 1.29 +/- 0.16 to 0.98 +/- 0.37, p = 0.06) but not during administration of RSR13 (from 1.28 +/- 0.18 to 1.02 +/- 0.24, p = 0.12). However, the mean values of cardiac PCr/ATP during handgrip-exercise did not differ significantly among the three measurements (baseline, placebo, RSR13). A single infusion of RSR13 to subjects with CAD increased mean p50 by 4.9-8.1 mmHg but did not significantly alter myocardial PCr/ATP during exercise. This is the largest right-shift in hemoglobin-oxygen binding affinity achieved in CAD subjects, and it did not provide clear evidence of protection from cardiac ischemia.

Activation of protein kinase C contributes to the isoflurane-induced improvement of functional and metabolic recovery in isolated ischemic rat hearts.

Isoflurane enhances myocardial functional recovery and improves energy levels after ischemia. We sought to determine whether isoflurane-induced cardioprotection is mediated by protein kinase C (PKC). The Langendorff model was used, and isolated perfused rat hearts were separated into untreated, isoflurane, chelerythrine (PKC inhibitor) plus isoflurane, and chelerythrine groups. All hearts were subjected to treatment before ischemia, followed by 30 min of ischemia and 60 min of reperfusion. We recorded hemodynamic variables, measured metabolites by high-performance liquid chromatography, and analyzed subcellular localization of PKC isoforms by Western blot analysis. Isoflurane significantly improved the recovery of left ventricular developed pressure, attenuated the depletion of myocardial adenosine triphosphate (ATP) and creatine phosphate at 15 min of ischemia, enhanced the recovery of myocardial ATP and creatine phosphate concentrations after ischemia, and was associated with the translocation of PKC-delta and -epsilon to the membrane. Chelerythrine suppressed the translocation of PKC-delta and -epsilon and blocked the improvement of cardiac function and ATP. We conclude that isoflurane delays the decrease in ATP during ischemia and improves the recovery of mechanical function and the energy state 60 min after ischemia. These effects of isoflurane are dependent on the activation of PKC.

Adenine Nucleotide and Creatine Phosphate Pool in Adult and Old Rat Heart during Immobilization Stress

Background: Disturbances in the heart energy provision is important in the stress-induced injury of myocardium. In order to learn the causes of age-dependent differences in myocardial sensitivity to stress, we determined the level of adenylates, creatine and creatine phosphate in adult and old rat heart during an immobilization stress. Methods: Fifty male Wistar rats were used to study the myocardial adenine nucleotides, creatine and creatine phosphate pool and creatine kinase activity during an immobilization period. Results: The concentration of adenine nucleotides in old and adult rat hearts was similar. The total concentration of adenylate pool, ATP and ADP in the heart of both age groups was reduced during stress. However, in old rats under stress the concentration of ATP in a less measure and ADP in a greater measure is decreased against that observed in adult animals. The level of inorganic phosphate in old rat heart remains the same as in adult rats. Conclusion: The creatine kinase system may be important in stabilizing the ATP level in myocardium of adult rats during stress. The role of this system in heart energy metabolism during stress is decreased in old rats. Disturbances of isoenzyme creatine kinase activity are responsible for these disorders.

Effect of massive sympathetic nervous system activation on coronary blood flow and myocardial energy pool.

Our previous work indicates that myocardial ischemia could be the mechanism responsible for the left ventricular (LV) dysfunction that frequently develops after massive sympathetic nervous system (SNS) activation. In this study, coronary blood flow (CBF) and myocardial ATP, creatine phosphate, and lactate concentrations were measured after massively activating the SNS of anesthetized rabbits with an intracisternal injection of veratrine. CBF was measured at time 0 (baseline), and at 2, 10, and 20 min after SNS activation in one group, and at 0, 45, 90, and 150 min in a second group. Myocardial ATP, creatine phosphate, and lactate were measured at 0, 2, 10, 20, 90, and 150 min in separate groups of rabbits. SNS activation caused LV dysfunction in approximately 60% of the rabbits. SNS-related increases in CBF kept pace with the increases in myocardial energy demand as determined from the systolic pressure-heart rate product. The subendocardial-to-subepicardial blood flow ratio did not change significantly. Myocardial creatine phosphate concentration was depressed 2 min after SNS activation and remained depressed for at least 20 min. ATP fell continuously and was significantly lower than baseline by 20 min. Tissue lactate concentration was elevated at this time. By 90 min, the concentrations of all three metabolites had recovered. These results indicate that myocardial high-energy phosphate compounds fall after massive SNS activation, but ischemia does not appear to be the underlying mechanism.

Role of TNF-α in myocardial dysfunction after hemorrhagic shock and lower-torso ischemia

Ruptured abdominal aortic aneurysm (RAAA) repair, a combination of hemorrhagic shock and lower-torso ischemia, is associated with a 50-70% mortality. Myocardial dysfunction may contribute to the high rate of mortality after aneurysm repair. We attempted to determine whether RAAA repair results in cardiac dysfunction mediated by tumor necrosis factor-alpha (TNF-alpha). We modeled aortic rupture and repair in the rat by inducing hemorrhagic shock to a mean blood pressure of 50 mmHg for 1 h, followed by supramesenteric clamping of the aorta for 45 min. After 90 min of reperfusion, cardiac contractile function was assessed with a Langendorff preparation. Myocardial TNF-alpha, ATP and creatine phosphate (CP) levels, and markers of oxidant stress (F(2)-isoprostanes) were measured. Cardiac function in the combined shock and clamp rats was significantly depressed compared with sham-operated control rats but was similar to that noted in animals subjected to shock alone. Myocardial TNF-alpha concentrations increased 10-fold in the combined shock and clamp rats compared with sham rats, although there was no difference in myocardial ATP, CP, or F(2)-isoprostanes. TNF-alpha neutralization improved cardiac function by 50% in the combined shock and clamp rats. Hemorrhagic shock is the primary insult inducing cardiac dysfunction in this model of RAAA repair. An improvement in cardiac contractile function after immunoneutralization of TNF-alpha indicates that TNF-alpha mediates a significant portion of the myocardial dysfunction in this model.

Preservation of mitochondrial function by diazoxide during sustained ischaemia in the rat heart.

1. A possible mechanism for the action of the K(ATP) channel opener diazoxide on the improvement of energy metabolism of ischaemic/reperfused hearts was examined. 2. Isolated, perfused rat hearts were subjected to 40 min ischaemia followed by 60 min reperfusion. Diazoxide at concentrations of 3 to 30 microM was present in the perfusion buffer for the last 15 min of pre-ischaemia. 3. Treatment of the perfused heart with diazoxide enhanced the post-ischaemic recovery of rate-pressure product, attenuated the post-ischaemic rise in left ventricular end-diastolic pressure, and suppressed the release of creatine kinase and purine nucleosides and bases from the reperfused heart. Treatment of the heart with diazoxide also restored myocardial ATP and creatine phosphate and attenuated the decrease in mitochondrial oxygen consumption rate after reperfusion. This attenuation was maintained at the end of ischaemia as well as at the end of reperfusion. 4. In another set of experiments, myocardial skinned bundles were incubated for 30 min under hypoxic conditions in the presence and absence of diazoxide, and then the mitochondrial oxygen consumption rate was determined. Hypoxia induced a decrease in the mitochondrial oxygen consumption rate of the skinned bundles to approximately 40% of the pre-hypoxic value. In contrast, treatment of the bundles with 30 microM diazoxide preserved the normal mitochondrial oxygen consumption rate during hypoxia. This effect was abolished concentration-dependently by the combined treatment with either the K(ATP) channel blocker glibenclamide or 5-hydroxydecanoate. 5. These results suggest that diazoxide is capable of attenuating ischaemia/reperfusion injury of isolated perfused hearts due to preservation of mitochondrial function during ischaemia.

Low-potassium University of Wisconsin solution for cardioplegia: improved protection of the isolated ischemic neonatal rabbit heart

Recovery of cardiac function and high-energy phosphates following ischemia and reperfusion were determined for hearts perfused with low potassium University of Wisconsin solution, high potassium University of Wisconsin solution, St Thomas' solution, or subjected to hypothermia alone. Isolated hearts were arrested for either 3 h at 15°C or 6 h at 20°C ( n=7 for each group) with one of the four solutions and then reperfused. Aortic flow after ischemic arrest at 20°C was 40.3±13.3%, 79.3±10.0%, 64.3±11.9% and 43.9±15.9% of control values for high potassium University of Wisconsin solution, low potassium University of Wisconsin solution, St Thomas' solution and hypothermia alone, respectively. Similar results were observed in hearts subjected to ischemic arrest at 15°C. Myocardial adenosine triphosphate and creatine phosphate after reperfusion tended to be higher in the low potassium University of Wisconsin solution group. It is concluded that low potassium University of Wisconsin solution may provide reliable cardioplegia during surgery that requires prolonged cardiac arrest in neonates and infants.

Relationships between myocardial bioenergetic and left ventricular function in hearts with volume-overload hypertrophy.

Left ventricular (LV) hypertrophy secondary to volume overload can result in alterations in myocardial bioenergetics and LV dysfunction. This study examined whether bioenergetic abnormalities contribute to the pump dysfunction. Severe mitral regurgitation (MR) was produced in 10 dogs by disruption of the chordal apparatus. Hemodynamics and ventricular function were examined 11.7 months later under baseline conditions and during treadmill exercise. Myocardial high-energy phosphates were measured by using magnetic resonance spectroscopy at rest, during coronary vasodilation with adenosine, and during oxidative stress induced by rapid pacing and dobutamine. Chronic MR caused a 30% increase in LV mass and a 65% increase in LV volume. In MR animals, the hemodynamic and LV function were normal at rest, but abnormalities developed during beta-blockade and exercise. Myocardial creatine phosphate-to-ATP ratios were significantly lower in each layer across the LV wall in MR hearts than normal hearts. Myocardial blood flow and coronary reserve were normal in MR hearts. Moreover, hyperperfusion did not correct the abnormal bioenergetics. Despite altered bioenergetics at rest, the MR hearts tolerated rapid pacing and dobutamine infusion well. In volume-overloaded LV hypertrophied hearts, alterations in myocardial high-energy phosphate levels do not induce abnormal mechanical performance at rest but may be related to a decreased contractile reserve during exercise.

Preischemic bradykinin and ischaemic preconditioning in functional recovery of the globally ischaemic rat heart.

Substantial release of bradykinin has been demonstrated to occur during short periods of myocardial ischaemia in various species. The aim of the present study was to investigate the protective effect of bradykinin in ischaemia and whether bradykinin could be involved in ischaemic preconditioning in the rat heart. Isolated, buffer-perfused hearts were subjected to 30 min of global ischaemia, followed by 30 min of reperfusion. Postischaemic functional recovery was recorded in the following groups: (1) control; (2) treatment with 0.1 microM bradykinin for 10 min before ischaemia (BK); (3) bradykinin treatment combined with pretreatment with the specific bradykinin B2-receptor antagonist, HOE 140; (4) ischaemic preconditioning by 5 min ischaemia +5 min reperfusion prior to sustained ischaemia (i.p.); and (5) ischaemic preconditioning combined with HOE 140 administration. Postischaemic myocardial function was significantly improved in both BK and i.p. groups (developed pressure 66.9 +/- 6.8 and 67.6 +/- 7.1 mmHg, respectively, vs. 43.1 +/- 5.9 mmHg in controls, P < 0.05). Pretreatment with 1 microM HOE 140 completely abolished the effect of bradykinin, while protection achieved by i.p. was unaltered by this drug. None of the protective interventions was associated with any significant improvement in myocardial adenosine triphosphate, creatine phosphate, glycogen, lactate or glucose tissue levels, detected either at the end of ischaemia or after 30 min of reperfusion. Bradykinin, acting via B2-receptors, can protect against postischaemic contractile dysfunction to a similar extent as i.p.. An involvement of B2-receptors in the ischaemic preconditioning phenomenon could, however, not be demonstrated.

Functional and bioenergetic consequences of postinfarction left ventricular remodeling in a new porcine model. MRI and 31 P-MRS study.

The underlying mechanisms by which left ventricular remodeling (LVR) leads to congestive heart failure (CHF) are unclear. This study examined the functional and bioenergetic abnormalities associated with postinfarction ventricular remodeling in a new, large animal model. Remodeling was induced by circumflex coronary artery ligation in young pigs. LV mass, volume, ejection fraction (EF), the ratio of scar surface area to LV surface area, and LV wall stresses were calculated from magnetic resonance imaging anatomic data and simultaneously measured LV pressure. Hemodynamics, transmural blood flow, and high-energy phosphates (spatially localized 31P-nuclear magnetic resonance) were measured under basal conditions, during hyperperfusion induced by pharmacological vasodilation with adenosine, and during pyruvate infusion (11 mg/kg per minute IV). Six of 18 animals with coronary ligation developed clinical CHF while the remaining 12 animals had LV dilation (LVR) without CHF. The results were compared with 16 normal animals. EF decreased from 55.9 +/- 5.6% in normals to 34.6 +/- 2.3% in the LVR group (P < .05) and 24.2 +/- 2.8% in the CHF group (P < .05 versus LVR). The infarct scar was larger in CHF hearts than in LVR hearts (P < .05). In normals, LV myocardial creatine phosphate (CP)/ATP ratios were 2.10 +/- 0.10, 2.06 +/- 0.16, and 1.92 +/- 0.12 in subepicardium (EPI), mid myocardium (MID), and subendocardium (ENDO), respectively. In LVR hearts, the corresponding ratios were decreased to 1.99 +/- 0.13, 1.80 +/- 0.14, and 1.57 +/- 0.15 (ENDO P < .05 versus normal). In CHF hearts, CP/ATP ratios were 1.41 +/- 0.14, 1.33 +/- 0.15, and 1.25 +/- 0.15; (P < .05 versus LVR in EPI and MID). The calculated myocardial free ADP levels were significantly increased only in CHF hearts. Bioenergetic abnormalities in remodeled myocardium are related to the severity of LV dysfunction, which, in turn, is dependent on the severity of the initiating myocardial infarction.

The role of accumulation of sodium and calcium on contractile failure of the hypoxic/reoxygenated heart.

The present study was undertaken to determine whether myocardial energy or ion levels are related to oxygen-replenishment-induced recovery of cardiac contractile force after hypoxia. Isolated rat hearts were perfused for 3 to 40 min under hypoxic conditions, followed by 45 min of reoxygenation. Hypoxia induced a cessation of cardiac contractile force, a rise in resting tension, a decrease in high energy phosphates, and an increase in lactate. Myocardial ATP, creatine phosphate (CP) and lactate reached steady-state levels after 15, 10 and 5 min of hypoxia, respectively. Hypoxic conditions in the present study also caused an increase in sodium content and a decrease in potassium content, but not changes in calcium content, along with a prolonged hypoxic period. When the hearts were perfused for more than 25 min under hypoxic conditions, no recovery of contractile force was observed following 45-min of reoxygenation. Hypoxic perfusion for more than 25 min induced an accumulation of tissue sodium content approximately 3 fold higher than the pre-hypoxic value at the end of hypoxia, and also induced a marked increase in myocardial calcium content upon reoxygenation. When tissue sodium content accumulated by less than 300% of the pre-hypoxic value, cardiac contractile function was partially reversed by reoxygenation and calcium-overload was not observed. The recovery of post-hypoxic cardiac contractility correlated with tissue sodium content during hypoxia rather than with myocardial high energy phosphate content at the end of hypoxia. These results suggest that accumulation of tissue sodium content in the hypoxic myocardium and calcium content in the reoxygenated myocardium may be indicative of hypoxia/reoxygenation-induced cardiac contractile failure.

Myocardial β-Adrenergic Receptor Function and High-Energy Phosphates in Brain Death– Related Cardiac Dysfunction

Cardiac failure remains an important problem after heart transplantation and may be associated with events that occur during brain death (BD) before transplantation. In this study, cardiac function is studied after BD, and biochemical evaluation of myocardial high-energy phosphates and the beta-adrenergic receptor system is presented. The hearts of 17 mongrel dogs (23 to 31 kg) were instrumented with flow probes, micromanometers, and ultrasonic dimension transducers to measure ventricular pressure and volume relationships. In a validated canine BD model, systolic right and left ventricular (RV/LV) function was analyzed by load-insensitive measurements during caval occlusion (preload-recruitable stroke work, PRSW). The beta-adrenergic receptor (BAR) density, adenylate cyclase (AC) activity, and myocardial ATP and creatine phosphate (CP) were measured before and 6 to 7 hours after BD. Results are expressed as mean +/- SEM (*P < .05 versus baseline, paired two-tailed Student's t test). Myocardial function deteriorated significantly from baseline PRSW (RV, 22 +/- 1 erg x 10(3); LV, 75 +/- 4 erg x 10(3)) by 37 +/- 10% for the RV (P < .001) and 22 +/- 7% for the LV (P < .001). BAR density increased from 282 +/- 42 to 568 +/- 173 fmol/mg for the RV and from 291 +/- 64 to 353 +/- 56 fmol/mg for the LV. Isoproterenol-stimulated AC activity was also significantly enhanced after BD. ATP and CP, however, remained unchanged after BD compared with baseline values before BD. BD causes significant systolic biventricular dysfunction. The loss of ventricular function after BD was more prominent in the right ventricle and may contribute to early postoperative RV failure in the recipient. These injuries occurred despite BAR system upregulation after BD. Global myocardial ischemia is unlikely, since ATP and CP remained normal before and after BD.

Regional short-term myocardial hibernation in swine does not involve endogenous adenosine or KATP channels.

Short-term hibernating myocardium is characterized by reduced contractile function during persistent ischemia, the recovery of metabolism over time, a recruitable inotropic reserve, and the lack of necrosis. The mechanisms underlying myocardial hibernation are unclear. The present study addressed the role of endogenous adenosine and that of activation of ATP-dependent potassium (KATP) channels. In 22 enflurane-anesthetized swine, coronary inflow was reduced to decrease regional myocardial work (W, measured by sonomicrometry) by 60-70% at 5 min of ischemia; this flow reduction has previously been shown to be compatible with the development of myocardial hibernation. Systemic hemodynamics, W, subendocardial blood flow (measured by microspheres), and the myocardial creatine phosphate content (measured by biopsies, mumol/g wet wt) were measured under control conditions and during 90 min of ischemia, with an intracoronary dobutamine infusion during the last 5 min of ischemia. The impact of endogenous adenosine was eliminated by infusion of intracoronary adenosine deaminase (ADA), and the impact of activation of KATP channels by glibenclamide. Creatine phosphate content recovered in the placebo-treated swine (n = 8, 3.8 +/- 1.9 to 5.8 +/- 2.0 mumol/g wet wt) as well as in swine receiving ADA (n = 7, 4.1 +/- 1.2 to 6.0 +/- 1.7 mumol/g wet wt) or glibenclamide (n = 7, 2.8 +/- 1.3 to 6.7 +/- 1.6 mumol/g wet wt) when ischemia was prolonged from 5 to 85 min. At the end of 90 min of ischemia, W increased during intracoronary dobutamine in all three groups to a comparable extent, and myocardial necrosis was absent in all three groups of swine.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of metabolic acidosis on cardiac mechanical performance during severe acute hypoxia and reoxygenation is small and transient

The aim was to determine whether the metabolic acidosis that develops during severe acute myocardial hypoxia improves or impairs the recovery of cardiac mechanical function during reoxygenation. Isolated rat hearts performed external work against a model of the rat systemic vascular impedance. Four groups of 10 hearts were used for mechanical studies. In these experiments, the hearts were subjected to normoxic ventilation for 15 min, hypoxic ventilation for 20 min, and reoxygenation for 60 min. The perfusate pH was either allowed to drift downward due to metabolic acidosis, or it was corrected to 7.4 as hypoxia or reoxygenation began. Mechanical performance was assessed by measuring heart rate and model "aortic" pressure and flow and by computing left ventricular mean, pulsatile, and total hydraulic power output and stroke work. A further four groups of 10 hearts were used for biochemical studies. In these experiments, myocardial high energy phosphates and calcium content were measured at the end of the period of hypoxia. When no attempt was made to regulate the perfusate pH, it drifted downward from 7.40(SEM 0.01) to 7.33(0.01) during hypoxia and then to 7.25(0.02) during reoxygenation. All mechanical variables measured and computed were severely depressed by hypoxia, whether the pH was regulated or not. Left ventricular total hydraulic hydraulic power output decreased to less than 10% of the control value in all experiment groups and recovered to 86.7-91.2% of the control value after 60 min of reoxygenation. Mechanical recovery was most rapid when the correction of acidosis was delayed until reoxygenation was begun. After 5 min of reoxygenation, it had recovered to 65.5% of the control value compared with a 37.0% recovery when the pH was allowed to drift and 34.9% when the pH was corrected to 7.4 during hypoxia. However, the differences in power output became non-significant after 10 min of reoxygenation. Myocardial creatine phosphate and adenosine triphosphate concentrations were decreased by hypoxia whether the pH was corrected (63.0% and 26.9% relative to the control), or not (68.9% and 35.0% relative to the control) (not statistically significant), but total cell calcium was not affected. In the isolated rat heart, correction of the moderate metabolic acidosis that developed during severe acute myocardial hypoxia improved the rate of mechanical recovery, but the effect was small and not sustained.

Intracellular and extracellular spaces and the direct quantification of molar intracellular concentrations of phosphorus metabolites in the isolated rat heart using 31P NMR spectroscopy and phosphonate markers

To quantify metabolite and cation concentrations using NMR spectroscopy, the volumes of intracellular and extracellular spaces must be known. We describe a simple 31P NMR spectroscopic method that employs dimethyl methylphosphonate (DMMP) as a marker of total water space and phenylphosphonate (PPA) as a marker of extracellular space to determine intracellular and extracellular space volumes in the isolated, perfused rat heart. In vivo and in vitro radiolabel studies were used to verify this method. The difference between the total and extracellular water spaces, determined as milliliters/heart, gave the intracellular volume and allowed direct calculation of myocardial creatine phosphate, ATP, and inorganic phosphate concentrations, which were 13.4 mM, 10.1 mM, and 3.4 mM, respectively, for the glucose-perfused rat heart. The extracellular volume decreased by 84% in hearts subjected to 28 min total, global ischemia and increased by 15% during reperfusion. The method described allows the determination of intracellular energy metabolite concentrations in perfused rat heart directly from a single, fully relaxed 31P NMR spectrum.