Browsing by Subject "myocardium"
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Item Mechanisms of Pyruvate Potentiation of β-adrenergic Inotropism in Stunned Myocardium(1999-05-01) Tejero DelRio, Maria Isabel; Mallet, Robert T.; Downey, H. Fred; Caffrey, James L.Tejero DelRio, M. Isabel. Mechanisms of Pyruvate Potentiation of β-adrenergic inotropism in stunned myocardium. Doctor of Philosophy (Biomedical Sciences), May, 1999; pp. 158; tables 6; illustrations 18; bibliography, 104 titles. This study tests three hypotheses: 1) the sensitivity of stunned myocardium to β-adrenergic stimulation is diminished; 2) the decreased β-adrenergic responsiveness of stunned myocardium is due in part to adenylate cyclase inactivation by oxidative stress; and 3), pyruvate could augment post-ischemic β-adrenergic responsiveness by ameliorating oxidative stress. These hypotheses were tested in isolated working guinea pig hearts perfused with Krebs-Henseleit butter fortified with 10 mM glucose. Myocardial stunning and pyruvate effects on myocardium are reviewed in the Introduction. In Chapter I, contractile function, β-adrenergic stimulation, and energy metabolism of stunned myocardium treated with pyruvate are examined. The effect of stunning, β-adrenergic stimulation, and pyruvate treatment on cellular and antioxidant defenses are examined in Chapter II. Conclusions and suggestions for future studies complete this dissertation. Results: the dose:power response curve to 0.1-100 nM isoproterenol was significantly shifted to the right in stunned hearts: EC50 (nM) increased from 0.3 ± 0.06 to 5.2 ± 1.86. Pyruvate (5 mM) and N-acetylcysteine (5 mM) restored responsiveness to isoproterenol, lowering EC50 to 1.1 ± 0.34 and 1.56 ± 0.43 nM, respectively. Cardiac power of stunned hearts treated with 2 nM isoproterenol was increased four-fold during combined treatment with pyruvate or N-acetylcysteine. Myocardium cyclic AMP content, unchanged by single treatments, increased when isoproterenol (2 nM) was combined with pyruvate by 41%, and N-acetylcysteine by 100%. Reduced antioxidant GSH/GSSG and NADPH/NADP+ ratios in stunning were restored to pre-ischemic levels with pyruvate plus isoproterenol treatment. Pyruvate did not augment power or cyclic AMP content in hearts stimulated with 30 nM isoproterenol, but lessened the decline in cytosolic phosphorylation potential. Conclusions: Both β-adrenergic inotropism and cellular antioxidant power were attenuated in the stunned myocardium. Pyruvate potentiated the effects of sub-maximal doses of attenuated energy depletion by high doses of isoproterenol. Pyruvate may allow restoration of contractile performance with lower, energetically less costly doses of β-adrenergic agents.Item Pyruvate Protection of Myocardium and Brain Following Cardiopulmonary Arrest and Resuscitation(2006-12-01) Sharma, Arti B.; Robert T. Mallet; Neeraj Agarwal; James L. CaffreySharma, Arti Bashu, Pyruvate Protection of Myocardium and Brain Following Cardiopulmonary Arrest and Resuscitation. Doctor of Philosophy (Molecular Physiology), December 2006; 167 pp; 29 figures; bibliography, 206 titles. Approximately 350,000 people experience cardiac arrest in the United States each year, and merely 4-33% of the victims survive to hospital discharge. Cardiac and neurological injuries following resuscitation are the main factors responsible for mortality. Neurodeficit and cognitive dysfunction following recovery from cardiac arrest may persist for us to two years and greatly compromise quality of life in survivors. Loss of effective circulating blood volume during cardiac arrest results in ischemia, energy depletion, ionic imbalance, calcium overload, acidosis and oxidant mediated cytotoxicity. The burst of reactive oxygen species upon reperfusion imposes an oxidant burden resulting in modification of cellular components such as membrane phospholipids and proteins, and the initiation of inflammatory and cell death cascades. This injury is most pronounced in organs with high metabolic demands such as the heart and brain. Therapies aimed at reducing metabolic impairments such as energy depletion and oxidative stress may mitigate post-resuscitation complications, improve survival and enhance quality of life. Pyruvate, a natural metabolite of the glycolytic pathway, has been shown to enhance post-ischemic energy and antioxidant reserves, and effects improvements in calcium homeostasis and metabolic acidosis. The main purpose of this investigation was to evaluate pyruvate as a corrective metabolic intervention during cardiopulmonary resuscitation and examine its cardio- and neuroprotective effects following recovery from cardiopulmonary arrest. To address these objectives as a canine model of 5 min cardiopulmonary arrest, open chest cardiac compressions (OCCC) and resuscitation was developed. In the first study intravenous sodium pyruvate or control NaCl was administered during the first 30 min of resuscitation and its effects on cardiac function and metabolites examined through the first 3 h following return of spontaneous circulation. Cardiac arrest resulted in a severe collapse of myocardial phosphocreatine phosphorylation potential and antioxidant redox state. Pyruvate treatment substantially enhanced recovery of energy and antioxidant reserves during early reperfusion. Pyruvate also enhanced contractile performance and carotid blood flow at 15-25 min return of spontaneous circulation (ROSC), and better maintained cardiac function at 3 h ROSC. Thus a latent effect of temporary metabolic correction by intravenous pyruvate therapy during early resuscitation was manifest as improved cardiac function, 3 h after the acute insult. Oxidative stress during resuscitation can modify membrane lipids and proteins. Inactivation of myocardial enzymes may exacerbate ischemic derangements of myocardial metabolism. To study the impact of cardiac arrest on left ventricular enzymes, beagles were subjected to cardiac arrest and myocardial enzyme activities were measured in snap-frozen left ventricle. Severe depletion of glutathione (GSH) antioxidant redox state occurred during cardiac arrest, which recovered partially following cardiac massage and then completely during early ROSC. Concomitant with oxidant stress, activities of phosphofructokinase, citrate synthase, aconitase, malate dehydrogenase, creatine kinase, glucose 6-phosphate dehydrogenase and glutathione reductase fell sharply during arrest, and recovered gradually after resuscitation and ROSC, in parallel with GSH redox state. We then tested whether oxidative stress is responsible for the loss of enzyme activity during cardiac arrest. Metabolic (pyruvate) or pharmacological (N-acetylcysteine) antioxidants were infused iv for 30 min immediately before cardiac arrest. Antioxidant pretreatments augmented phosphofructokinase, aconitase and malate dehydrogenase activities before arrest, and enhanced these activities, as well as citrate synthase and glucose 6-phosphate dehydrogenase, during arrest. Cardiac arrest thus reversibly inactivates several important myocardial metabolic enzymes, while protection of these enzymes by antioxidants implicates oxidative stress as a principal mechanism of enzyme inactivation. The third part of this investigation was directed towards addressing the question whether metabolic correction with pyruvate therapy during ROSC, would extend protection and enhance neurological recovery over an extended period of 3 days following cardiac arrest-resuscitation. Neurological evaluation in the days following recovery from cardiac arrest revealed considerable impairment of function. Activation of matrix metalloproteinases and increased myeloperoxidase activity were also detected in frozen brain tissue. Loss of viable neuronal structure and cell death as indicted by histological evidence and TUNEL were detected 3 days following arrest. Treatment with pyruvate for the first hour of reperfusion prevented neurological deficit on days 1 and 2 of recovery, partially mitigated the inflammatory response and prevented neuronal loss. By preventing early metabolic disturbances during resuscitation and immediate reperfusion, intravenous pyruvate therapy protected the heart and brain from dysfunction and injury. The following figure summarizes these major findings. [see dissertation] Figure: Pyruvate mediated metabolic protection following cardiopulmonary arrest-resuscitation.Item Role of Adenosine in Acute Hibernation of Guinea-Pig Myocardium(1995-08-01) Gao, Zhi-Ping; H. Fred Downey; James L. Caffrey; Patricia A. GwirtzGao, Zhi-Ping, Role of Adenosine in Acute Hibernation of Guinea-Pig Myocardium Doctor of Philosophy (Biomedical Sciences), August, 1995; 111 pp; 3 tables; 15 figures, bibliography, 158 titles. Myocardial hibernation is a state of depressed contractile function and energy demand during chronic ischemia. When coronary flow is restored, depressed contractile function can partially or completely recover to the pre-ischemic level, and ischemic injury of the myocardium in not evident. This project tested the hypothesis that endogenous adenosine mediates hibernation in guinea-pig myocardium. Isolated working guinea-pig hearts, perfused with glucose fortified Krebs-Henseleit buffer, were subjected to global low-flow ischemia. Left ventricular performance and cytosolic energy level were assessed. Lactate and purine nucleotides were measured in venous effluent. Heart were perfused with [U-14C]glucose to investigate the role of adenosine on glucose metabolism in myocardium. Left ventricular function in untreated hearts decreased by 80% and remained stable during ischemia, and completely recovered upon reperfusion. Neither adenosine receptor blockade with 8-p-sulfophenyl theophylline (8-SPT; 20 μM) nor ecto 5’-nucleotidase inhibitor αβ-methylene adenosine 5’-diphosphonate (AOPCP; 50μM) affected left ventricular function either ischemia or during reperfusion. Cytosolic energy level fell by 67% at 10 min ischemia in untreated hearts, but subsequently recovered to the pre-ischemic level despite continued ischemia. Adenosine receptor blockade increased cytosolic energy level at 10 min ischemia relative to untreated hearts, but blunted the subsequent rebound of phosphorylation potential. Moreover, 8-SPT doubled ischemic lactate release. Adenosine receptor blockade also increased glucose uptake during pre-ischemia and hypoperfusion, but did not stimulate glucose oxidation. Crossover plots of glycolytic intermediates revealed that phosphofructokinase, a key rate-controlling step in glycolysis, was activated by adenosine receptor blockade in both pre-ischemic and hibernating myocardium. We conclude that 1) activation of adenosine receptors results in recovery of cytosolic energy level of moderately ischemic working myocardium, but this energetic recover is not solely responsible for post-ischemic contractile recovery; 2) endogenous adenosine attenuates anaerobic glycolysis during myocardial hibernation by blunting phosphofructokinase activity.