Anne-Marie L. Seymour

Metabolic alterations in the chronically denervated dog heart

OBJECTIVEnPrevious 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.nnnMETHODSnTwelve 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.nnnRESULTSnThe 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.nnnCONCLUSIONnThe 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.

Reduced purine catabolite production in the postischemic rat heart: a31P NMR assessment of cytosolic metabolites

Ischemia can cause release of adenosine and purine catabolites from the heart, through the breakdown of ATP. If repeated periods of ischemia are induced, the efflux of purines is markedly reduced, although it is not clear if this is beneficial for the long-term survival of the heart. We have investigated changes in high-energy phosphates and purine release in the isolated perfused rat heart using31P NMR spectroscopy and high-performance liquid chromatography. Hearts were subjected to one of the following protocols: Group A—1 min of total global ischemia (TGI) after 40 min, 60 min, and 85 min of perfusion (a total of 3 × 1 min ischemia); Group B—1 min of TGI after 40 min of perfusion, 10 min of TGI after 50 min of perfusion, and a final 1 min of TGI after 85 min of perfusion. The profile of high-energy phosphate metabolites, Pi accumulation and purine release was similar for each 1-min period of TGI in Group A, whereas phosphocreatine content was increased and ATP content reduced by an extended period of TGI in Group B, leading to a less severe acidosis and purine efflux in the final 1 min of TGI at 85 min of perfusion. In conclusion, the reduced purine release observed in Group B may be related to the preischemic ATP pool size and accessibility and the increased myocardial energy reserve in the form of phosphocreatine.

Adenosine Uptake and Metabolism in Human Endothelial Cells

The handling of adenosine by the endothelium is crucial for the effects of this nucleoside in the vascular system. Strategic location of endothelial cells at the vessel wall border indicate its important role in the turnover of adenosine. High endothelial activity of ecto 5’nucleotidase1 implies predominant role in the extracellular formation of adenosine from secreted nucleotides. However, the capacity to release intracellularly produced adenosine, phosphorylation of extracellular adenosine and to some extent adenosine transit between interstitial and intravascular space depend on the membrane transport capacity in this type of cells.

1017-69 Preconditioning Human Myocardium –– Reduced Hypoxanthine Production During PTCA

Brief episodes of myocardial ischaemia and reperfusion protect against subsequent prolonged ischaemic insults. This adaptive response termed preconditioning has been observed with successive coronary occlusions at PTCA based on recordings of anginal intensity and ECG changes. The aim of this study was to evaluate myocardial release of Hypoxanthine (HX) (an ATP catabolite and a sensitive marker of ischaemia) in coronary sinus blood immediately after successive balloon inflations. Nine male patients mean age 50xa0±xa02.1 with isolated left anterior descending artery stenoses and normal left ventricular function were studied. Collateral channels filling diseased arterial segment were absent on the diagnostic angiogram, PTCA consisted of three balloon inflations, durations of which were: (1) 60–90 seconds, (2) 90–180 seconds, (3) 180–300 seconds with 5 minutes of intervening reperfusion between each. Paired aortic and coronary sinus blood samples were taken immediately after each deflation and deproteinized with 1.3xa0M HCI0 4 and neutralized supernatant fractions analysed by HPLC for HX content. The arteriovenous differences (meanxa0±xa0SEM) were: Before PTCA Reperfusion 1 2 3 Hypoxanthine ( μ moles/litre of blood) -0.01xa0±xa00.37 -3.41xa0±xa02.05 -1.54xa0±xa00.64 -2.42xa0±xa00.56 Hypoxanthine release is reduced after second and third prolonged balloon inflations when compared to the first shorter inflation reflecting an adaptive response of the myocardium to ischaemia. These results show metabolic evidence for preconditioning in the human myocardium.

Enzymes of Adenosine Metabolism in the Heart, Cardiomyocytes and Endothelium

Adenine nucleotide metabolism in the heart has important physiological implications for the regulation of the high energy phosphate pool and the production of adenosine, a “retaliatory” metabolite of the heart (Newby, 1984). The extent of operation of metabolic pathways within various cell types in a single organ may differ substantially. Two cell types are of particular importance in the heart; cardiomyocytes which represent the majority of weight of the heart and the endothelium contributing only 3% to the weight of heart (Gerlach et al., 1985), but strategically localized in the vessel wall.

High-Energy Phosphate Changes in the Normal and Hypertrophied Heart During Cardioplegic Arrest and Ischemia

The profile of metabolic changes in the ischemic heart following repeated infusions of cardioplegic solution has not been well characterized in cardiac hypertrophy. In this study we evaluated the effect of mild cardiac hypertrophy on the changes in phosphocreatine (PCr) and ATP throughout a cardioplegic arrest/ischemia/reperfusion experimental protocol (see Fig. 1). In addition to metabolic status, mechanical recovery of systolic and diastolic function was evaluated in the same hearts.

The Effect of Ischemic Preconditioning on Nucleotide Metabolism and Function of Rat Heart after Prolonged Cold Storage

Experimental data suggests that brief periods of myocardial ischemia followed by reperfusion induced by coronary artery occlusion or global ischemia enhances myocardial tolerance to subsequent, more prolonged ischemic episodes (Ischemic Preconditioning)1. However, the effect of ischemic preconditioning on the contractility and metabolism of the heart subjected to prolonged cold storage induced by a single use of cold cardioplegia as in clinical heart transplantation has not been determined. In this study we evaluated the effect of 5 min ischemia and 10 min reperfusion on the recovery of myocardial mechanical function and metabolism following 6 hours of 4°C preservation using an isolated rat heart preparation.