J.C.N. Kotzé

Normothermic ischemic cardiac arrest of the isolated working rat heart. Effects of time and reperfusion on myocardial ultrastructure, mitochondrial oxidative function, and mechanical recovery.

The ischemic state of the myocardium of the isolated working rat heart after induction of normothermic ischemic cardiac arrest was assessed by the interrelationship among changes in myocardial ultrastructure, mitochondrial oxidative phosphorylation, and tissue high energy phosphate contents. At all time intervals (10-40 minutes) studied, the ultrastructural changes were more severe in the subendocardium than in the subepicardium. After 25-40 minutes of normothermic ischemic cardiac arrest, the mitochondrial oxygen uptake (state 3) became increasingly depressed, particularly in mitochondria isolated from the subendocardium. Mitochondrial oxidative function, as measured in vitro, did not correlate well with mitochondrial ultrastructural damage. In addition, the effects of coronary reperfusion on the ability of the ischemic heart to recover in terms of ultrastructure, mechanical, and metabolic function were evaluated. Hearts subjected to 10-40 minutes of normothermic ischemic cardiac arrest showed almost complete ultrastructural recovery of the subepicardium upon reperfusion; regression of ultrastructural changes occurred to a lesser extent in the subendocardium. Reperfusion for 30 minutes did not alleviate the depression in mitochondrial oxidative function, while tissue ATP levels did not return to control, preischemic levels. After 20 minutes of normothermic ischemic cardiac arrest, the mechanical performance of the working heart during reperfusion was significantly depressed, compared with pre-ischemic control values. Normal ultrastructure of the subendocardium always accompanied mechanical recovery, while improvement of mitochondrial oxidative function was not essential.

Mitochondrial oxidative phosphorylation in myocardial anoxia: Effects of albumin

Abstract The mechanism whereby albumin exerts its protective action on the oxidative phosphorylation process of mitochondria prepared from anoxic tissue was investigated. Albumin has a beneficial effect on the parameters of mitochondrial function studied, whether present in the mitochondrial isolation medium, mitochondrial incubation medium or perfusate of the isolated anoxic rat heart. The effects of albumin could be removed by perfusing the isolated rat heart with albumin-free Ringer. Albumin may act by binding of free fatty acids, which are uncouplers of oxidative phosphorylation. Mitochondria prepared from hearts perfused with palmitate showed a depression of oxidative phosphorylation.

Mitochondrial Acyl-CoA, adenine nucleotide translocase activity and oxidative phosphorylation in myocardial ischaemia

Abstract The hypothesis that inhibition of mitochondria) adenine nucleotide translocase activity by accumulation of long-chain acyl-CoA esters might be responsible for the depression in mitochondria) energy metabolism in myocardial ischaemia was reinvestigated. Hypoxic, low-flow perfusion (substrate-free) of the isolated rat heart resulted in increases in tissue and mitochondria) acyl-CoA contents together with a reduction in adenine nucleotide translocase activity and oxidative phosphorylation function of mitochondria isolated from the tissue. Addition of exogenous substrates together with insulin or propranolol to the perfusate (glucose and insulin glucose, glycerol and insulin; glucose, propranolol and insulin) caused significant further increases in tissue and mitochondria) acyl-CoA contents. In contrast, the mitochondria) adenine nucleotide translocase activity and oxidative phosphorylation function improved and were similar to those of control perfused hearts. The difference between the in vivo and in vitro effects of acyl-CoA on mitochondria) adenine nucleotide translocase and oxidative phosphorylation could be due to in vivo binding to intracellular fatty acid binding proteins.

Work Performance of the Isolated Perfused Beating Heart in the Hereditary Myocardiopathy of the Syrian Hamster

The work performance of the isolated beating heart of control Syrian hamsters and hamsters suffering from an inbred myocardiopathy was studied in a system using a myographic differential force transducer. A stretch force of either 3.75 or 8.75 g was applied to the hearts. Myocardial metabolism of pyruvate-3-14C and palmitate-1-14C was studied with and without a stretch force. A definite reduction in work performance of the myopathic heart could be demonstrated. Peak height of contraction, tension-time index, tension time per minute and heart rate were significantly lower. The progressive myocardial fiber lengthening, caused by the stretch force, was less in the myopathic hearts. No difference was observed between the uptake and oxidation of pyruvate-3-14C and palmitate-1-14C by control and myopathic hearts. The presence of a stretch force affected metabolism of both hearts in a similar manner. Two mechanisms for explaining the reduction in work performance by the myopathic heart were observed, namely, a reduction in heart rate and a relative inability of the myopathic muscle fibers to lengthen. The depressed mechanical performance could not be related directly with altered substrate metabolism or with reduction in total muscle mass.

Mitochondrial oxidative phosphorylation in myocardial ischaemia: effects of glycerol, glucose and insulin on anoxic hearts perfused at low pressure.

Abstract To determine whether metabolic intervention could prevent the depression in mitochondrial oxidative phosphorylation resulting from ischaemic perfusion of the isolated rat heart, hearts were perfused with glucose alone, glucose plus insulin, glycerol alone and a combination of glycerol, glucose and insulin. Addition of glucose, as well as glucose plus insulin to perfusates of ischaemic hearts improved mitochondrial oxidative phosphorylation. Perfusions of ischaemic hearts with glycerol, glucose and insulin were most effective: all parameters of mitochondrial function studied were significantly increased.

Effects of propranolol on myocardial ultrastructure, mitochondrial function and high energy phosphates of isolated working rat hearts with coronary artery ligation

The effects of coronary artery ligation on myocardial ultrastructure, high energy phosphate contents and mitochondrial oxidative phosphorylation were studied in the isolated, perfused working rat heart model. The changes in ultrastructure, mitochondrial function and high energy phosphate contents of the ischaemic tissue were characteristic of severe ischaemic damage, showing a good correlation between ultrastructural and functional changes. To determine whether these changes could be prevented, reduced or delayed by beta-blockade, propranolol (3 × 10−7 and 3 × 10−6 m) was added to the perfusate. In our model propranolol did not exert a protective effect on the ultrastructure, tissue high energy phosphate contents and mitochondrial oxidative function except for a significant increase in QO2 (State 3) with propranolol at a concentration of 3 × 10−7 m.

Normothermic ischaemic cardiac arrest and reperfusion of the isolated working heart: Effect of chlorpromazine on functional, metabolic and morphological recovery

The effects of chlorpromazine, an inhibitor of both Ca2+ flux and phospholipase activity, on myocardial ultrastructure, function and metabolism were assessed during normothermic ischaemic cardiac arrest and reperfusion of the isolated working rat heart. Normothermic ischaemic cardiac arrest produced significant changes in myocardial ultrastructure, high energy phosphate contents and mitochondrial oxidative phosphorylation within 20 min. Reperfusion of untreated hearts subjected to 20 and 25 min ischaemia failed to restore mitochondrial function, mechanical activity and ATP content to control, pre-ischaemic levels. Morphological signs of ischaemic injury regressed, especially in the subendocardial layer. Pretreatment of hearts with chlorpromazine did not prevent the ischaemia-induced changes in myocardial ultrastructure and mitochondrial function. However, during reperfusion the chlorpromazine-treated, totally ischaemic heats (20 to 25 min) exhibited improved coronary flow rates, and ultrastructural and mechanical recovery. The mitochondrial oxidative phosphorylation process and tissue high energy phosphate contents were not affected by the drug.

Substrate effects on mitochondrial function and tissue lipids in low-flow hypoxia of isolated perfused rat hearts

SummaryA possible causal relationship between tissue FFA contents and the depression in mitochondrial oxidative phosphorylation in myocardial ischaemia has been suggested. To test this hypothesis, the effects of different substrates added to the perfusates of hypoxic, low-flow perfused hearts were examined on oxidative phosphorylation catalysed by mitochondria isolated from such tissue. In an additional series of experiments tissue neutral glyceride and FFA levels were analysed and correlated with changes in mitochondrial function. Mitochondria isolated from hearts with a high tissue FFA content exhibited the lowest ADP/O ratios, RCI and QO2 values. On the other hand, mitochondria isolated from hearts with reduced FFA contents, performed significantly better with respect to these parameters of mitochondrial function studied.ZusammenfassungAufgrund früherer Untersuchungen wurde eine kausale Beziehung zwischen dem Gehalt des Gewebes an freien Fettsäuren und der Depression der oxidativen Phosphorylierung in den Mitochondrien bei Myokadischämie vermutet. Um diese Hypothese zu testen, wurden dem Perfusat hypoxischer, mangelperfundierter Herzen verschiedene Substrate zugefügt und deren Einfluß auf die oxidative Phosphorylierung der aus solchen Geweben isolierten Mitochondrien untersucht. In weiteren Experimenten wurde der Gewebsspiegel der neutralen Glyzeride und freien Fettsäuren analysiert und mit Änderungen der Mitochondrienfunktion korreliert. Mitochondrien, die aus Herzen mit einem hohen Gehalt an freien Fettsäuren isoliert worden waren, zeigten die geringsten Werte für das Verhältnis ADP/0, sowie für den respiratorischen Kontrollindex (RCI) und die mitochondriale Sauerstoffaufnahme (QO2). Andererseits war die Funktion-gemessen an diesen Parametern-eindutig besser bie Mitochondrien, die von Herzen mit reduziertem Gehalt an freinen Fettsäuren gewonnen wurden.

Normothermic ischaemic cardiac arrest of the isolated perfused rat heart: effects of trifluoperazine and lysolecithin on mechanical and metabolic recovery.

SummaryTo evaluate the hypothesis that maintenance of the integrity of myocardial membrane systems and prevention of Ca2+ influx into the cell are significant in the survival of ischaemic tissue, the effect of trifluoperazine and lysolecithin, were tested on the recovery of globally ischaemic rat hearts. Trifluoperazine increases membrane stabilization, inhibits calmodulin and binds to other Ca2+-dependent proteins. Lysolecithin, on the other hand, has a detergent action on myocardial cell membranes and facilitates Ca2+ ingress in ischaemic tissue. With trifluoperazine (2.45 μM), added before induction of ischaemia or during reperfusion only, hearst subjected to 40 min normothermic ischaemic cardiac arrest recovered mechanically. Untreated hearts failed after 20 min of ischaemia. The drug had no effect on tissue high energy phosphate levels or mitochondrial oxidative phosphorylation. Conversely, lysolecithin (2.5–10 μM) caused all hearts to fail after being subjected to 15 min ischaemia. Mechanical failure during reperfusion of such hearts was associated with a significant reduction in tissue ATP and CrP levels. Trifluoperazine counteracted the harmful effects of lysolecithin to a limited extent.