Effect of glucose-insulin-potassium infusions on epicardial ECG changes and on myocardial metabolic changes after coronary artery ligation in dogs.

The effect of glucose-insulin-potassium infusion (GIK) on developing myocardial infarction in dogs was evaluated, commencing infusion 30 min after coronary artery ligation (CAL). The parameters studied were: early (60 min after CAL) and late (6 and one half h after CAL) epicardial ST segment elevation, the change in Q, R, and S waves and certain myocardial metabolic determinations (glycogen, sodium, potassium, dry-wet weight ratio, adenosine triphosphate, creatine phosphate, inorganic phosphate, and lactate). 6 and one half h after coronary ligation Q wave amplitude was less, the R wave amplitude was greater and the metabolic profile in hte infarct zone was less deranged; metabolic improvement was also found in the nonischaemic zone. Sites in which early ST-segment elevation was less with GIK did not predict all the sites in which there was eventual lessened Q wave formation. R wave fall and disturbance of myocardial metabolism. This study supports others showing an effect of GIK in improving the features of developing experimental myocardial infarction. Following the rate of Q wave development in relation to the early ST segment elevation may be of value in assessing GIK effects provided that a qualitative rather than quantitative relationship between the two parameters is accepted.

Role of glycolytic flux in effect of glucose in decreasing fatty-acid-induced release of lactate dehydrogenase from isolated coronary ligated rat heart.

The mechanisms whereby glucose reduces fatty acid-induced release of enzyme from the coronary-ligated isolated perfused working rat heart are investigated. Alterations in the tissue contents of ATP, phosphocreatine, or glycogen could be excluded as possible mechanisms for the beneficial effect of glucose in this system. Provision of glycolytic ATP from increased glycolytic flux may be one important factor.

Effects of substrates on tissue metabolic changes in the isolated rat heart during underperfusion and on release of lactate dehydrogenase and arrhythmias during reperfusion.

In Langendorff-perfused rat hearts, the perfusion pressure was reduced from 100 cm H2O to 20 cm H2O for 30 minutes to produce a model of global ischemia with a residual oxygen uptake. The release of lactate dehydrogenase (LDH) and the occurrence of ventricular arrhythmias during reperfusion were dependent on the substrate. Glucose-perfused hearts had the highest rates of glycolytic ATP production (2.5 mumol/g per min) during ischemia with normal contents of tissue cyclic adenosine 3',5'-monophosphate (cAMP) and, during reperfusion, the release of LDH was lowest and severe ventricular arrhythmias did not occur. In pyruvate-perfused hearts, glycolysis was inhibited during ischemia, the rate of production of glycolytic ATP was only 0.5 mumol/g per min. and tissue cAMP doubled; during reperfusion, LDH release was 14-fold higher and ventricular arrhythmias were more severe. Total tissue contents of ATP and phosphocreatine were similar in glucose- and in pyruvate-perfused hearts. In hearts perfused with acetate, there was virtually no glycolytic ATP synthesized during the last 5 minutes of ischemia and cAMP increased further. Acetate- and palmitate-perfused hearts showed greatest release of LDH and had severest arrhythmias during reperfusion, suggesting that it was the metabolic and not the detergent effects of palmitate that were operating. Lipolysis was not a major factor in the cause of reperfusion LDH release. A role of glycolytic ATP in the maintenance of membrane integrity is postulated.

Cyclic AMP as a determinant of vulnerability to ventricular fibrillation in the isolated rat heart.

Ventricular fibrillation threshold and vulnerable period were measured in the isolated perfused rat heart to assess the influence of dibutyryl cyclic AMP on ventricular vulnerability. Doses of dibutyryl cyclic AMP of 0.6-1.6 mumol/min caused an increase in coronary flow but had no effect on vulnerability, whereas doses of 2.6-4.2 mumol/min resulted in an increase in coronary flow, a decrease in VF threshold, and an increase in the width of the vulnerable period. These experiments support the concept of a local myocardial action of catecholamines, mediated by cyclic AMP, whereby vulnerability to ventricular fibrillation is increased.

Early experimental myocardial infarction. Evaluation of histologic criteria and comparison with biochemical and electrocardiographic measurements.

Light microscopical criteria of early experimental myocardial infarction were compared with biochemical changes in glycogen content and the tissue K+/Na+ ratio in 19 mongrel dogs. Five sham-operated dogs served as controls, and seven of the 14 dogs with experimentally induced infarcts received infusions of glucose, insulin, and potassium (GIK). Infarcts were diagnosed by a scoring system based on edema formation, congestion, waviness of myofibers, myofibrillar degeneration, polymorphonucleosis, glycogen depletion, and fuchsinorrhagia. Significant histologic scores were associated with tissue K+/Na+ ratios of less than 1.2, with 30% depletion of biochemical glycogen, and with epicardial ST-segment elevation. Progression of the infarction zone to involve the surrounding border zone was prevented by GIK infusions. Routine light microscopy used in conjunction with tissue K+/Na+ ratios enabled early infarction to be diagnosed with a high degree of accuracy.

Glycolytic ATP and its production during ischemia in isolated Langendorff-perfused rat hearts.

The perfused rat heart was used to assess the possible contribution of glycolytically produced ATP to the maintenance of the action potential in the normoxic heart, and to the maintenance of membrane integrity in the underperfused, ischemic heart. During normoxia, pyruvate (10 mM) was nearly as able as glucose (10 mM) to maintain the normal action potential. During ischemia (reduction of perfusion pressure of Langerdorff heart from 100 to 20 cm H2O), total tissue values of ATP and creatine phosphate were similar in pyruvate and in glucose hearts. However, pyruvate-perfused hearts had higher tissue levels of cyclic AMP during the ischemic period, and during the reperfusion period they had an increased release of lactate dehydrogenase and an increased incidence of arrhythmias when compared with glucose hearts. It is proposed that these differences can be related to a higher rate of production of glycolytic ATP. The anatomical, biochemical, and pharmacological evidence favoring a cytoplasmic compartment of ATP located in relation to the cell membrane is reviewed.

Ventricular fibrillation threshold and vulnerable period in the isolated perfused rat heart.

Ventricular fibrillation threshold (VFT) measurements were obtained in the isolated perfused rat heart. Detailed morphology of the vulnerable period (VP) could be described by stimulating repeatedly at increasing levels of stimulus energy. Addition of lignocaine to the system caused an elevation of VGT, but also led to a delay of the VP to the end of the QT interval. The implications of these findings for the understanding of VFT measurements are discussed.