Temporal changes in endocardial energy metabolism following propranolol and the metabolic basis for protection against isoprenaline cardiotoxicity

Stress and the heart. Mechanisms, measurement, and management

Unrelieved physical or mental stress and repeated episodic stress are ultimately harmful to the cardiovascular system and thus can be life-threatening. In this article, Dr Eliot describes efforts to quantify the psychophysiologic responses to stress and to identify the components of stress and its clinical consequences. He also explains the importance of controlling the real-life episodic fluctuations in blood pressure that occur daily in response to stress.

The dynamics of hypertension--an overview: present practices, new possibilities, and new approaches

Contemporary clinical evaluation of hypertensive patients must include observations encompassing the impact of environment, behavior, and sociologic factors on metabolism and physiology. As evidenced by animal and human studies, catecholamines are an important mediator between psychologic factors and cardiovascular physiology, but direct measurement of catecholamine levels has not proved useful. Measurement of hemodynamic variables--blood pressure, heart rate, and stroke volume--during standardized psychophysiologic challenges is advocated. With low-challenge standardized stressors that include alpha- and beta-adrenergic stimuli, inappropriate reactors can be classified according to whether blood pressure is elevated primarily by cardiac output, total systemic resistance, or a combination of both. Hypertensive patients can be similarly distinguished, and medication can then be custom-tailored to the underlying physiology. Extensive laboratory and clinical evidence points to significant interrelationships between the central nervous system and the cardiovascular system. Furthermore, cardiovascular physiologic and metabolic perturbances are distinctly different under conditions of mental vs physical stress. Most clinical testing assesses physical performance whereas the real-life challenges of today are primarily mental.

Metabolic protection of the reperfused canine endocardium by the thromboxane synthetase inhibitor, dazoxiben

This study investigated whether dazoxiben, a thromboxane synthesis inhibitor, could reverse regional contractile dysfunction and protect against adenine nucleotide loss in the "stunned myocardium". Hearts from anesthetized dogs were "stunned" by 15 min of left anterior descending coronary artery occlusion followed by 3 hr of reperfusion. Left ventricular segment shortening (%SS) and regional myocardial blood flow (RMBF) were measured by sonomicrometry and the radioactive microsphere technique, respectively. Local coronary venous blood was withdrawn and thromboxane A2 and prostacyclin measured by radioimmunoassay. Transmural biopsies from the reperfused and nonischemic areas were taken at 3 hr following reperfusion for tissue metabolite analysis. During ischemia, %SS, RMBF and area at risk were decreased to similar levels in both control and dazoxiben-treated hearts indicating equivalent degrees of flow deprivation. During reperfusion, %SS recovered only partially and was not significantly improved by dazoxiben. Dazoxiben augmented peak prostacyclin production (123 +/- 31% vs. 292 +/- 49% of preocclusion values) following reperfusion, while it completely blocked thromboxane A2 production. Dazoxiben attenuated the decline in endocardial ATP (69 +/- 5% vs. 92 +/- 9% normalized to the nonischemic zone) and total adenine nucleotides. The results indicate that dazoxiben may elicit a cardioprotective effect on energy metabolism in the reperfused heart, but this is dissociated from any improvement in regional contractile function.

Beneficial effects of iloprost in the stunned canine myocardium

The effect of the prostacyclin-mimetic, iloprost, on the reversibly damaged ("stunned") myocardium was studied in barbital-anesthetized, open-chest dogs subjected to 15 minutes of coronary artery occlusion and 3 hours of reperfusion. Regional myocardial segment shortening (%SS) was measured in the subendocardium of nonischemic and ischemic-reperfused areas by sonomicrometry. Iloprost was infused for 30 minutes beginning 15 minutes prior to occlusion (0.05 microgram/kg/min, ILO-LOW, or 0.1 microgram/kg/min, ILO-HIGH) or immediately prior to reperfusion (0.1 microgram/kg/min, ILO-REP). %SS in the ischemic-reperfused region recovered to 3% of pretreatment values in the control (saline-treated) group by 3 hours of reperfusion. In contrast, %SS in the iloprost-treated groups was significantly enhanced versus the control group at all times of reperfusion. At 3 hours of reperfusion, %SS recovered to 43% (ILO-LOW), 58% (ILO-HIGH), and 35% (ILO-REP) of pretreatment values. The beneficial effect on functional recovery was significantly greater when iloprost was administered before occlusion versus immediately prior to reperfusion. Thus, part of the salutory effects of iloprost appear to occur prior to and/or during ischemia. Iloprost did not improve collateral blood flow to the ischemic region or myocardial high energy phosphate content at 3 hours of reperfusion. While iloprost significantly decreased mean arterial pressure during ischemia and early reperfusion, the hypotensive action did not appear to play a role in the amelioration of postischemic dysfunction, as preocclusion treatment with an equihypotensive dose of sodium nitroprusside produced no significant effect on postischemic recovery beyond 5 minutes of reperfusion. Results of in vitro experiments indicated that iloprost had no effect on the xanthine oxidase free-radical generating system including lipid peroxidation. However, iloprost decreased the neutrophil-derived superoxide burst after chemotactic stimulation. This beneficial action may, in part, explain the efficacy of iloprost in enhancing postischemic function of the stunned myocardium.

Regional differences in postischemic recovery in the stunned canine myocardium

To determine if differences exist in the degree of ischemic damage and in postischemic recovery when different coronary arteries are occluded and reperfused, 40 barbital-anesthetized dogs were subjected to brief 15-minute periods of coronary artery occlusion followed by 3 hours of reperfusion ("stunned" myocardium) of the left anterior descending (LAD) or the left circumflex (LCX) coronary arteries. Myocardial segment shortening (%SS) in the subendocardium of nonischemic and ischemic reperfused areas was measured by sonomicrometry, and regional myocardial blood flow was measured by radioactive microspheres. Transmural tissue biopsies were taken at the end of reperfusion for the measurement of adenine nucleotides and total tissue water content. Arterial and local coronary venous blood samples were collected during preocclusion, during occlusion, and at 30 and 180 minutes of reperfusion for determination of blood oxygen content and oxygen consumption in the ischemic area. During occlusion, subendocardial blood flow (LAD flow = 0.11 +/- 0.02; LCX flow = 0.15 +/- 0.04 ml/min/gm), myocardial oxygen consumption (LAD = 2.4 +/- 0.7; LCX = 2.7 +/- 0.7 ml/min/100 gm), and areas of the left ventricle at risk (LAD = 27.4 +/- 2.3%; LCX = 32.4 +/- 2.4) were similar in both groups, thus indicating equivalent degrees of ischemia. There were no differences between groups in hemodynamics throughout the experiment or in the loss of myocardial high-energy phosphates or increase in total tissue water in the ischemic reperfused area at 3 hours of reperfusion. There was a significantly greater loss (p less than 0.05) of systolic wall function during LAD versus LCX occlusion and a greater recovery of segment function from 5 minutes throughout 1 hour of reperfusion after LCX occlusion (p less than 0.05), with no difference in %SS at 2 and 3 hours following reperfusion. Thus, although similar changes occurred in blood flow, metabolite parameters, tissue edema, wall function, and overall hemodynamics when either the LAD or LCX perfusion territories were occluded and reperfused, the loss of systolic wall function and recovery of segment shortening were more variable after regional stunning of the LCX perfusion bed. These data suggest that evaluation of pharmacologic or surgical interventions to improve postischemic functional recovery may be more reliably performed when the LAD coronary artery is the vessel occluded.

Salient effects of L-carnitine on adenine-nucleotide loss and coenzyme A acylation in the diabetic heart perfused with excess palmitic acid. A phosphorus-31 NMR and chemical extract study

The beneficial effects of L-carnitine perfusion on energy metabolism and coenzyme A acylation were studied in isolated hearts from control and diabetic rats. All hearts were perfused at a constant flow rate with a glucose/albumin buffer which contained 2.0 mM palmitate. 31P-NMR was utilized to assess sequential phosphocreatine and ATP metabolism during 1 h of recirculation perfusion. L-Carnitine (5.0 mM final concentration) was added after 12 min of baseline recirculation perfusion. Frozen samples were taken after 1 h of recirculation perfusion for spectrophotometric analysis of high-energy phosphates and the free and acylated fractions of coenzyme A. L-Carnitine perfusion of diabetic hearts attenuated or prevented the reduction of ATP observed in untreated diabetic hearts. It also attenuated the accumulation of long-chain fatty-acyl coenzyme A. Although L-carnitine improved myocardial function in diabetic hearts, this was independent of any direct effect on physiological indices. Thus, the salutory effect of acute perfusion with L-carnitine on energy metabolism in the isolated perfused diabetic rat heart appears to be a direct effect on lipid metabolism.

Lipid-mediated impairment of normal energy metabolism in the isolated perfused diabetic rat heart studied by phosphorus-31 NMR and chemical extraction

The relationship between extracellular palmitate and the accumulation of long-chain fatty-acyl coenzyme A with that of high-energy phosphate metabolism was investigated in the isolated perfused diabetic rat heart. Hearts were perfused with a glucose/albumin buffer supplemented with 0, 0.5, 1.2 or 2.0 mM palmitate. 31P-NMR was used to analyze phosphocreatine and ATP metabolism during 1 h of constant-flow recirculation perfusion. At the end of perfusion, frozen samples were taken for chemical analysis of high-energy phosphates and the free and acylated fractions of coenzyme A and carnitine. Perfusion of diabetic hearts with palmitate, unlike control hearts, caused a time-dependent and concentration-dependent reduction in ATP, despite normal and constant phosphocreatine. Concentrations of acid-soluble coenzyme A, long-chain-acyl coenzyme A and total tissue coenzyme A were elevated in palmitate-perfused diabetic hearts, while the total tissue carnitine pool was decreased. Increases in long-chain-acyl coenzyme A correlated with the reduction in myocardial ATP. This reduction in ATP could not be adequately explained by alterations in heart rate, perfusion pressure or vascular resistance.