CIRCULATING LEVELS OF CATECHOLAMINES IN ACUTE MYOCARDIAL INFARCTION AND ANGINA PECTORIS

The effect of orexin-A on cardiac dysfunction mediated by NADPH oxidase-derived superoxide anion in ventrolateral medulla

Hypocretin/orexin-producing neurons, located in the perifornical region of the lateral hypothalamus area (LHA) and projecting to the brain sites of rostral ventrolateral medulla (RVLM), involve in the increase of sympathetic activity, thereby regulating cardiovascular function. The current study was designed to test the hypothesis that the central orexin-A (OXA) could be involved in the cardiovascular dysfunction of acute myocardial infarction (AMI) by releasing NAD(P)H oxidase-derived superoxide anion (O2 (-)) generation in RVLM, AMI rat model established by ligating the left anterior descending (LAD) coronary artery to induce manifestation of cardiac dysfunction, monitored by the indicators as heart rate (HR), heart rate variability (HRV), mean arterial pressure (MAP) and left intraventricular pressure. The results showed that the expressions of OXA in LHA and orexin 1 receptor (OX1R) increased in RVLM of AMI rats. The double immunofluorescent staining indicated that OX1R positive cells and NAD(P)H oxidative subunit gp91phox or p47phox-immunoreactive (IR) cells were co-localized in RVLM. Microinjection of OXA into the cerebral ventricle significantly increased O2 (-) production and mRNA expression of NAD(P)H oxidase subunits when compared with aCSF-treated ones. Exogenous OXA administration in RVLM produced pressor and tachycardiac effects. Furthermore, the antagonist of OX1R and OX2R (SB-408124 and TCS OX2 29, respectively) or apocynin (APO), an inhibitor of NAD(P)H oxidase, partly abolished those cardiovascular responses of OXA. HRV power spectral analysis showed that exogenous OXA led to decreased HF component of HRV and increased LF/HF ratio in comparison with aCSF, which suggested that OXA might be related to sympathovagal imbalance. As indicated by the results, OXA might participate in the central regulation of cardiovascular activities by disturbing the sympathovagal balance in AMI, which could be explained by the possibility that OXR and NAD(P)H-derived O2 (-) in RVLM mediates OXA-induced cardiovascular responses.

Changes in sarcolemmal PLC isoenzymes in postinfarct congestive heart failure: partial correction by imidapril

We have examined the changes in quantity and activity of cardiac sarcolemmal (SL) phosphoinositide-phospholipase C (PLC)-beta(1), -gamma(1), and -delta(1) in a model of congestive heart failure (CHF) secondary to large transmural myocardial infarction (MI). We also instituted a late in vivo monotherapy with imidapril, an ANG-converting enzyme (ACE) inhibitor, to test the hypothesis that its therapeutic action is associated with the functional correction of PLC isoenzymes. SL membranes were purified from the surviving left ventricle of rats in a moderate stage of CHF at 8 wk after occlusion of the left anterior descending coronary artery. SL PLC isoenzymes were examined in terms of protein mass and hydrolytic activity. CHF resulted in a striking reduction (to 6-17% of controls) of the mass and activity of gamma(1)- and delta(1)-isoforms in combination with a significant increase of both PLC beta(1) parameters. In vivo treatment with imidapril (1 mg/kg body wt, daily, initiated 4 wk after coronary occlusion) improved the contractile function and induced a partial correction of PLCs. The mass of SL phosphatidylinositol 4,5-bisphosphate and the activities of the enzymes responsible for its synthesis were significantly reduced in post-MI CHF and partially corrected by imidapril. The results indicate that profound changes in the profile of heart SL PLC-beta(1), -gamma(1), and -delta(1) occur in CHF, which could alter the complex second messenger responses of these isoforms, whereas their partial correction by imidapril may be related to the mechanism of action of this ACE inhibitor.

Neuropeptide Y modulation of sympathetic activity in myocardial infarction

OBJECTIVES

We examined the possible effect of neuropeptide Y in modulating central sympathetic activity after myocardial infarction in rats.

BACKGROUND

Previous studies have shown the coexistence of neuropeptide Y and norepinephrine in the brain and a possible functional interaction between the two. Neuropeptide Y inhibits the release of norepinephrine at the presynaptic level and can be considered to act as a neuromodulator.

METHODS

Two groups of rats were examined in this study-an experimental group, defined as those rats undergoing left coronary artery ligation, and a sham group without coronary artery ligation, serving as the control group. The animal in both groups underwent microdialysis in the paraventricular nucleus at 2, 4 and 8 weeks after operation. Microdialysis samples were collected with and without injecting neuropeptide Y in the paraventricular nucleus. The concentration of norepinephrine was determined by injecting purified microdialysate samples during high performance liquid chromatography. To explore the receptor's possible role, autoradiographic localization of neuropeptide Y receptors in the paraventricular nucleus was also carried out in the experimental and sham groups.

RESULTS

The concentration of norepinephrine measured in the samples was decreased by 50% with neuropeptide Y in 2- and 4-week old rats after infarction, but by only 20% (p < 0.05) in 8-week old rats after infraction. The diminished inhibitory effects of neuropeptide Y on norepinephrine release was associated with increased sympathetic activity, as reflected by plasma norepinephrine; 8-week old rats after infarction had almost a 100% (p < 0.05) increase in their plasma norepinephrine level compared with the sham group. Autoradiography revealed a significant decrease in density of neuropeptide Y receptors in the paraventricular nucleus in 8-week old rats after infarction (p < 0.05).

CONCLUSIONS

The data presented in this report suggest that the reduction of the inhibitory activation of neuropeptide Y on sympathetic release may contribute to elevated norepinephrine levels after myocardial infarction.

Glucose requirement for postischemic recovery of perfused working heart

The quantitative importance of glycolysis in cardiomyocyte reenergization and contractile recovery was examined in postischemic, preload-controlled, isolated working guinea pig hearts. A 25-min global but low-flow ischemia with concurrent norepinephrine infusion to exhaust cellular glycogen stores was followed by a 15-min reperfusion. With 5 mM pyruvate as sole reperfusion substrate, severe contractile failure developed despite normal sarcolemmal pyruvate transport rate and high intracellular pyruvate concentrations near 2 mM. Reperfusion dysfunction was characterized by a low cytosolic phosphorylation potential [( ATP]/[( ADP][Pi]) due to accumulations of inorganic phosphate (Pi) and lactate. In contrast, with 5 mM glucose plus pyruvate as substrates, but not with glucose as sole substrate, reperfusion phosphorylation potential and function recovered to near normal. During the critical ischemia-reperfusion transition at 30 s reperfusion the cytosolic creatine kinase appeared displaced from equilibrium, regardless of the substrate supply. When under these conditions glucose and pyruvate were coinfused, glycolytic flux was near maximum, the glyceraldehyde-3-phosphate dehydrogenase/3-phosphoglycerate kinase reaction was enhanced, accumulation of Pi was attenuated, ATP content was slightly increased, and adenosine release was low. Thus, glucose prevented deterioration of the phosphorylation potential to levels incompatible with reperfusion recovery. Immediate energetic support due to maximum glycolytic ATP production and enhancement of the glyceraldehyde-3-phosphate dehydrogenase/3-phosphoglycerate kinase reaction appeared to act in concert to prevent detrimental collapse of [ATP]/[( ADP][Pi]) during creatine kinase dysfunction in the ischemia-reperfusion transition. Dichloroacetate (2 mM) plus glucose stimulated glycolysis but failed fully to reenergize the reperfused heart; conversely, 10 mM 2-deoxyglucose plus pyruvate inhibited glycolysis and produced virtually instantaneous de-energization during reperfusion. The following conclusions were reached. (1) A functional glycolysis is required to prevent energetic and contractile collapse of the low-flow ischemic or reperfused heart (2). Glucose stabilization of energetics in pyruvate-perfused hearts is due in part to intensification of glyceraldehyde-3-phosphate dehydrogenase/3-phosphoglycerate kinase activity. (3) 2-Deoxyglucose depletes the glyceraldehyde-3-phosphate pool and effects intracellular phosphate fixation in the form of 2-deoxyglucose 6-phosphate, but the cytosolic phosphorylation potential is not increased and reperfusion failure occurs instantly. (4) Consistent correlations exist between cytosolic ATP phosphorylation potential and reperfusion contractile function. The findings depict glycolysis as a highly adaptive emergency mechanism which can prevent deleterious myocyte deenergization during forced ischemia-reperfusion transitions in presence of excess oxidative substrate.

Effects of thoracic epidural anaesthesia on central haemodynamics compared to cardiac beta adrenoceptor blockade in conscious rats with acute myocardial infarction

The study aimed to compare the effects of thoracic epidural anaesthesia (TEA) with those of the beta-adrenoceptor blocker, metoprolol, on central haemodynamics in conscious rats with acute myocardial infarction. During methohexital anaesthesia, appropriate vascular catheters were inserted, a thoracic epidural catheter was implanted and the left coronary artery was ligated. A recovery period of 1-2 h elapsed after termination of surgery and anaesthesia. Experiments were performed on four separate groups of animals (A-D). In Group A (n = 10) mean arterial pressure (MAP), heart rate (HR), and cardiac output (CO) were measured, and stroke volume (SV) and systemic vascular resistance (SVR) were calculated before and 10-15 min after the induction of TEA (bupivacaine 5 mg.ml-1). In Group B (n = 6) left ventricular end-diastolic pressure (LVEDP) and maximal dP/dt were recorded as in Group A. In Group C (n = 10) central haemodynamics were measured 10 min after i.v. metoprolol (0.5 mg.kg-1) and again 10-15 min after the addition of TEA. In Group D (n = 6) LVEDP and max dP/dt were measured as in Group C. The reduction in CO, SV, HR and max dP/dt was of the same magnitude with TEA and metoprolol. TEA lowered MAP by 17%, while metoprolol did not change MAP. Metoprolol caused an increase in LVEDP from 20.8 +/- 1.8 to 27.5 +/- 2.7 mmHg (2.8 +/- 0.2 to 3.7 +/- 0.4 kPa) (P less than 0.01), while TEA induced a decrease in LVEDP from 24.2 +/- 1.4 to 17.8 +/- 1.6 mmHg (3.2 +/- 0.2 to 2.4 +/- 0.2 kPa) (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Functional significance of hypertrophy of the noninfarcted myocardium after myocardial infarction in humans

Hypertrophy of the noninfarcted left ventricle as a chronic response to myocardial infarction has been demonstrated in animals and at autopsy in humans. However, the functional significance of postmyocardial infarction hypertrophy is a subject of dispute. The purpose of this study was to determine the time course of development of postmyocardial infarction hypertrophy of the noninfarcted myocardium in humans and to assess its functional significance. Subcostal view, two-dimensional echocardiograms were recorded at rest and during peak exercise, 6 and 40 weeks postmyocardial infarction in 45 patients (16 anterior, 20 inferior, nine non-Q wave infarcts), for measurement of left ventricular mass and ejection fraction. The left ventricular mass index increased from 94 +/- 30 to 118 +/- 27 g/m2 (p less than 0.01) during the time of the two studies. There was a significant correlation between the change in left ventricular mass index and improved resting ejection fraction (r = 0.48, p less than 0.001) and exercise ejection fraction (r = 0.48, p less than 0.001) at the follow-up study. Of the 32 patients who increased their left ventricular mass index greater than 7%, 18 improved their rest ejection fraction greater than 0.05 units and 17 improved their exercise ejection fraction greater than 0.05 units. Conversely, of the 13 patients who failed to increase their left ventricular mass index, only three improved their rest ejection fraction and one improved the exercise ejection fraction (Fisher's exact test, p less than 0.05). We reached three conclusions. First, in humans, significant hypertrophy of the noninfarcted myocardium can be detected by two-dimensional echocardiography, 9 months postmyocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)

Pyruvate-enhanced phosphorylation potential and inotropism in normoxic and postischemic isolated working heart. Near-complete prevention of reperfusion contractile failure

Bioenergetic and hemodynamic consequences of cellular redox manipulations by 0.2-20 mM pyruvate were compared with those due to adrenergic stress (0.7-1.1 microM norepinephrine) using isolated working guinea-pig hearts under the conditions of normoxia, low-flow ischemia, and reperfusion. 5 mM glucose (+ 5 U/l insulin) + 5 mM lactate were the basal energy-yielding substrates. To stabilize left ventricular enddiastolic pressure, ventricular filling pressure was held at 12 cmH2O under all conditions; this preload control minimized Frank-Starling effects on ventricular inotropism. Global low-flow ischemia was induced by reducing aortic pressure to levels (20-10 cmH2O) below the coronary autoregulatory reserve. Reactants of the creatine kinase, including H+ and other key metabolites, were measured by enzymatic, HPLC, and polarographic techniques. In normoxic hearts, norepinephrine stimulations of inotropism, heart rate x pressure product, and oxygen consumption (MVO2) were associated with a fall in the cytosolic phosphorylation potential [( ATP]/[( ADP].[Pi]] as judged by the creatine kinase equilibrium. In contrast, infusion of excess pyruvate (5 mM) markedly increased [ATP]/[( ADP].[Pi]) and ventricular work output, while intracellular phosphate decreased; MVO2 remained constant under the same conditions. During reperfusion following ischemia, pyruvate effected striking and concentration-dependent increases in MVO2, phosphorylation potential, and inotropism. Pyruvate dehydrogenase flux was augmented during reperfusion hyperemia followed by near-complete recoveries of [ATP]/([ADP].[Pi]), contractile force, heart rate x pressure product, and MVO2 in the presence of 5-10 mM pyruvate. Pyruvate also attenuated ischemic adenylate degradation. Omission of glucose from the perfusion medium rendered pyruvate ineffective in postischemic hearts. Similarly, excess lactate (5-15 mM) or acetate (5 mM) failed to reenergize reperfused hearts and severe depressions of MVO2 and inotropism developed despite the presence of glucose. Apparently, subcellular redox manipulations by pyruvate dissociated stimulated mitochondrial respiration and increased inotropism from low cytosolic phosphorylation potentials. This was evidence against the extramitochondrial [ADP].[Pi]/[ATP] ratio being the primary factor in the control of mitochondrial respiration. The mechanism of pyruvate enhancement of inotropism during normoxia and reperfusion is probably multifactorial. Thermodynamic effects on subcellular [NADH]/[NAD+] ratios are coupled with a rise in the cytosolic [ATP]/[( ADP].[Pi]) ratio at constant (normoxia) or increased (reperfusion) MVO2.(ABSTRACT TRUNCATED AT 400 WORDS)

Atenolol, but not mexiletine, protects against stimulus-induced ventricular tachycardia in a chronic canine model

1. In a placebo-controlled study of the antiarrhythmic and electrophysiological properties of atenolol and mexiletine, programmed electrical stimulation (PES) was performed in three groups of six conscious greyhounds, 7-30 days after coronary artery ligation. 2. In the placebo group, repeated PES challenge resulted in the consistent induction of ventricular tachycardias (VT) in 4/6 dogs and ventricular fibrillation in 2/6. Atenolol prevented arrhythmia induction in 4/6 dogs, one continued to demonstrate a VT and one died (P less than 0.05 compared with placebo). In the mexiletine group 5/6 dogs continued to demonstrate a VT and one died. 3. Electrocardiographic parameters were not affected by any treatment. There was no change in blood pressure in any group but when compared with placebo, heart rate fell (P less than 0.05) after atenolol (256 micrograms kg-1) and increased (P less than 0.05) after mexiletine (16 mg kg-1). Effective (ERP) and functional (FRP) refractory periods did not change after mexiletine, but ERP was prolonged (P less than 0.05) after atenolol. 4. The results indicate that atenolol but not mexiletine is effective in preventing re-entrant arrhythmias in this conscious canine model. Antiarrhythmic efficacy may be related to a fall in heart rate and/or a prolongation of refractoriness.

Thoracic epidural anaesthesia decreases the incidence of ventricular arrhythmias during acute myocardial ischaemia in the anaesthetized rat

The aim of the present investigation was to study the effect of high thoracic epidural anaesthesia (TEA) on the incidence of ventricular arrhythmias after ligation of the left coronary artery in chloralose-anaesthetized rats. Forty animals were randomly assigned to receive either 40-50 microliter of bupivacaine (5 mg/ml) or saline in implanted thoracic epidural catheters. TEA decreased mean arterial pressure (MAP) from 118 +/- 5 mmHg to 72 +/- 4 mmHg and heart rate (HR) from 450 +/- 9 to 387 +/- 8 beats/min, while epidural saline did not affect MAP and HR. In both groups coronary artery ligation induced a transient decrease in MAP within the first 5-10 min after ligation. In the control group HR increased, during the 30-min post-ligation period, from 453 +/- 9 to 474 +/- 10 beats/min (P less than 0.05) while no significant change was seen in the TEA group. In both groups the mortality rate was 10%. In the TEA group 30% and in the control group 0% had normal sinus rhythm during the recording period (P less than 0.001). The incidence of ventricular fibrillation and/or tachycardia was significantly lower (P less than 0.05) in the TEA group (20%) compared to the control group (53%). The incidence of ventricular extrasystoles did not differ between the two groups. We conclude that TEA-induced blockade of sympathetic afferents and efferents may offer protection against malignant ventricular arrhythmias in the early phase of acute myocardial infarction.

Reduction of plasma norepinephrine levels in response to brief coronary occlusion in experimental dogs

Although an increased plasma norepinephrine (NE) level is sometimes observed during angina pectoris, it is difficult to say whether sympathetic overflow is its cause. The left anterior descending coronary artery was occluded by intracoronary balloon for 3 minutes in 12 closed-chest anesthetized dogs. During occlusion, heart rate did not change but aortic pressure slightly decreased. Occlusion caused a significant reduction in both NE levels in the aorta (177 +/- 17 to 134 +/- 16 pg/ml, p less than 0.01) and in the great cardiac vein (GCV) 296 +/- 44 to 249 +/- 44 pg/ml, p less than 0.01). After surgical vagotomy, the occlusion increased NE levels in the aorta (227 +/- 44 to 278 +/- 43 pg/ml, p less than 0.01) and in GCV (384 +/- 76 to 444 +/- 81 pg/ml, p less than 0.01), showing the release of vagal inhibition. These results may be applicable to patients with transient anterior myocardial ischemia; if plasma NE increases without marked hemodynamic changes, it is suggested that the sympathetic overflow is not a result but a possible cause of the ischemia.

Apparent superiority of H2-receptor stimulation and simultaneous beta-blockade over conventional treatment with beta-sympathomimetic drugs in post-acute myocardial infarction: cardiac effects of impromidine--a new specific H2-receptor agonist-in the surviving catecholamine-insensitive myocardium

Left ventricular infarction (AMI) was produced in experimental animals and the contractile response to beta-adrenergic and H2-histaminergic stimulation by isoproterenol and impromidine tested in the isolated perfused heart preparation. Adenylate cyclase activity as well as binding characteristics of [3H]-dihydroalprenolol ([3H]-DHA), [3H]-methyl-tiotidine ([3H]-TIOT) and [3H]-quinuclidinyl benzilate ([3H]-QNB) to cardiac beta 1-, H2- and cholinergic muscarinic receptors were determined in sarcolemmal membrane preparations of the right ventricle of the same hearts. In addition, an attempt was made to elucidate the therapeutic value of post-AMI treatment with impromidine in the presence and absence of beta-blockade, in contrast to administration of prenalterol and the conventional therapy with beta-sympathomimetic drugs, e.g. dobutamine. Three days post-AMI the dose-response curve for isoproterenol of right ventricular dP/dtmax was significantly depressed, while the inotropic effect of impromidine was not impaired. Stimulation of adenylate cyclase activity by isoproterenol was reduced by 80% whereas impromidine and NaF stimulation rates were unaltered. Receptor-binding studies indicated a 90% loss and 10-times lowered affinity (KD) of the remaining beta-receptors while specific [3H]-TIOT- and [3H]-QNB-binding was unchanged. Administration of dobutamine increased mortality rates and extension of infarct size, led to a further decrease in contractile response to isoproterenol, induced complete insensitivity of adenylate cyclase to isoproterenol stimulation and caused pronounced additional reduction of number and affinity of [3H]-DHA-binding sites. In contrast, all above alterations were prevented by treatment with either prenalterol or combined administration of impromidine plus metoprolol. It is concluded, that these alterations in the non-ischemic, uninvolved myocardium post-AMI are the result of catecholamine-induced specific damage of sarcolemmal beta-receptors. Furthermore, treatment with H2-agonists in combination with beta-blocking agents may have beneficial effects, whereas conventional therapy with beta-sympathomimetic drugs tends to worsen the already depressed function of the beta-adrenergic stimulation mechanism.

Morphology and mitochondrial function of the surviving myocardium following myocardial infarction in the cat

The surviving myocardium of the cat was studied 7 days and 6 weeks following experimental infarction. Seven days after infarction, ultrastructural alterations of the mitochondria indicative of slight hypoxic injury--clearing of the matrix and loss of dense matrix granules--were found. Together with intracellular edema and glycogen depletion this result was considered as a sign of relative hypoxia in the surviving myocardium 7 days after infarction. At the same time beta-glucuronidase activity of tissue homogenates was found to be elevated. Focal ischemic lesions in remote myocardium which have been described by other authors (5, 6, 23) were not detected in our experiments. Six weeks after infarction, the fractional volume occupied by myofibrils had increased whereas the fractional volume of mitochondria had remained unchanged (left ventricle) resp. had decreased (right ventricle). There were no qualitative changes detectable at the ultrastructural level. Based on the morphometric investigation of Anversa (1, 2), our results were regarded indicative of mild compensatory hypertrophy of the surviving myocardium. Glutamate dehydrogenase activity of tissue homogenates was shown to be increased when compared to control values. Furthermore our morphometric results showed that the unit mass of mitochondria has to render an enhanced amount of energy six weeks after infarction which might leave the surviving myocardium with a higher susceptibility to future hypoxic injury.

Impaired beta-adrenergic stimulation in the uninvolved ventricle post-acute myocardial infarction: reversible defect due to excessive circulating catecholamine-induced decline in number and affinity of beta-receptors

Left ventricular infarction (AMI) was produced in experimental animals and the contractile response to isoproterenol was tested in the isolated perfused heart preparation. Adenylate cyclase activity, phosphodiesterase activity, and beta-receptor binding characteristics were determined in a sarcolemmal preparation of the right ventricle of the same hearts. Three days post-AMI the dose-response curve for isoproterenol of right ventricular dP/dtmax was significantly depressed, while the inotropic effect of histamine was not impaired. Stimulation of adenylate cyclase activity by isoproterenol was reduced by 70% in the membrane preparation, whereas histamine and NaF stimulation rates were unaltered; phosphodiesterase activity was unchanged. In contrast, beta-receptor binding studies with [3H]-DHA1 indicated 74% loss and 10 times lowered affinity (KD) of the remaining beta-receptors, while specific [3H]-QNB1 binding was unchanged. All of the above alterations were prevented by pretreatment with reserpine or metoprolol. It is concluded that these abnormalities in the nonischemic surviving myocardium post-AMI are the result of specific reversible damage of sarcolemmal beta-receptors due to excessive levels of circulating catecholamines.

Cardiac contractile and metabolic effects mediated via the myocardial H2-receptor adenylate cyclase system. Characterization of two new specific H2-receptor agonists, impromidine and dimaprit, in the guinea pig and human myocardium

The present study chartacterizes myocardial effects of two new histaminergic H2-receptor specific compounds, impromidine, and dimaprit, on cardiac contractile and metabolic parameters of the guinea pig heart and human papillary muscle in comparison to the well-known effects of catecholamines. Impromidine and dimaprit produced a dose-dependent stimulation of the right and left ventricular contractile force in the isolated perfused biventricular catheterized guinea pig heart with maximal stimulation rates equal to those of isoproterenol. Hemodynamic equieffective doses of isoproterenol (2.8X10(-9) mol/l), histamine (1.1X10(-5) mol/l), impromidine (4.6X10(-7) mol/l, and dimaprit (8.5X10(-6) mol/l) induced nearly identical increases in tissue concentrations of c-AMP. All compounds dose-dependently enhanced the activity of the myocardial adenylate cyclase with very similar KA-values in a particulate sarcolemmal membrane preparation of both guinea pig ventricles and human papillary muscles. No effect of either compound was seen on cardiac phosphodiesterase activity. Selective administration of the beta1-blocking agent metoprolol and the H2-receptor antagonist cimetidine clearly discriminates two independent receptors linked to the sarcolemmal adenylate cyclase system in the guinea pig and human myocardium. This is further supported by results obtained from beta-receptor-binding studies in which an interference of impromidine and dimaprit with the stereospecific binding of (-)[3H]-dihydroalprenolol to cardiac beta-receptors could be definitely excluded. The possible therapeutic role of both H2-agonists on the non-ischemic, surviving myocardium, which is transiently refractory to beta-adrenergic stimulation by catecholamines after myocardial infarction, will be discussed.

Time-dependent changes in canine cardiac mitochondrial function and ultrastructure resulting from coronary occlusion and reperfusion

Time-dependent changes in mitochondrial function and structure resulting from 1 hr of left circumflex coronary artery occlusion followed by 2 to 24 hr of reperfusion were examined. These changes were correlated with changes in myocardial ultrastructure, tissue water content, infarct size and mitochondrial calcium content. The heart was removed after different periods of reperfusion, and mitochondria were isolated from ischemic and nonischemic regions of the left ventricle. Tissue samples from ischemic and nonischemic myocardium also were taken for electron microscopy and tissue water content determinations. Infarct size was measured by the nitroblue tetrazolium staining method. Oxygen consumption by mitochondria isolated from ischemic and nonischemic myocardium was measured in vitro. Mitochondria from ischemic myocardium showed time-dependent decreases in rates of oxygen consumption and tightness of coupling. Electron microscopy revealed progressive ultrastructural deterioration in ischemic myocardium, including accumulation of calcium deposits within mitochondria, a finding corroborated by elevated concentrations of calcium in mitochondria isolated from the same area. Tissue wet-to-dry weight ratios were increased significantly in ischemic myocardium. A small, but significant, decrease in respiratory function was observed in mitochondria isolated from nonischemic myocardium several hrs after reperfusion; however, normal respiration was observed 24 hrs after release of occlusion. This latter observation indicates that the nonischemic zone also is affected by regional ischemia. The results obtained indicate that temporary left circumflex artery occlusion and reperfusion result in progressively decreasing mitochondrial function and structure within the ischemic myocardium, and that these changes are accompanied by cellular electrolyte alterations.

[The Contractile Function of the Surviving Heart Muscle Following Coronary Occlusion (author's transl)]

Following acute myocardial infarction the functional load of the surviving heart muscle does increase considerably, leading to an increased release of adrenergic neurotransmitters with a consequent decrease in endogenous catecholamine stores. Within the first 24 h following infarction, a temporary decline in the high-energy phosphate content is observed in the surviving heart muscle; futhermore, a reduction in lactate extraction is noted. In the intact organism an increased shortening of the surviving heart muscle is noted as a consequence of the altered ventricular geometry and the increased release of catecholamines. If these effects are excluded by means of isolation and analysis in vitro, a decrease in contractile function could be demonstrated in the surviving heart muscle in the early phase following infarction; the response to positive inotropic interventions was depressed as well. These changes are reversible; six weeks following infarction a normal contractile behaviour is observed.

Experimental myocardial infarction in the cat. I. Reversible decline in contractility of noninfarcted muscle

The contractile state of the noninfarcted myocardium was examined in adult cats after myocardial infarction produced by ligation of several branches of the left coronary artery. At 2 days, 7 days, and 6 weeks after infarction, and after determination of intracardiac pressures, papillary muscles were exicised from the noninfarcted segment of the right ventricle and attached to a myograph for analysis of contractile function. One week after infarction there was a decline in actively developed force at Lmax, caused by a decrease in the rate of force development. In addition, the response to procedures that augment myocardial contractility, such as paired stimulation and increasing the frequency of electrical stimulation, was significantly depressed. Two days after infarction, changes were less significant, although similar in direction. Six weeks after infarction, developed force at Lmax had returned to normal values. The response to procedures augmenting contractility also had returned to normal. There appears to be a distinct, reversible loss of contractility in the remaining viable myocardium in the early phase after experimental infarction.

Consequences of coronary arterial occlusion on remote myocardium: effects of occlusion and reperfusion

Focal necrosis (microinfarcts) and regional lactate derangements were observed in closed chest dogs in the nonoccluded (remote) posterior segments of the left and right ventricles after acute occlusion of the proximal left anterior descending coronary artery. Focal infarcts in the remote areas were observed in five of the six dogs with 7 days of occlusion of the left anterior descending artery and in six of seven dogs with 7 days of reperfusion after 3 hours of occlusion. There was a good correlation between the finding of microinfarcts and myocardial lactate derangements in the corresponding remote myocardium. No significant lactate derangements or microinfarcts were found in sham experiments. These findings suggest that ischemia of the remote myocardium frequently accompanies an acute coronary occlusion and may result in irreversible focal lesions.

Effects of sustained isometric handgrip on praecordial accelerocardiogram in normal subjects and in patients with heart disease

The effects of isometric exercise on the maximum amplitude of the praecordial accelerocardiogram (as represented by the DE deflection) have been compared in 6 normal subjects (group 1), 12 patients with aortic stenosis (group 2), and 16 patients with myocardial disease (group 3). Whereas the tachycardia and pressor effects of isometric exercise were identical in all three groups, the normal subjects showed a significant decrease in DE during handgrip of 10 +/- 4 per cent (P less than 0.05) as compared with the insignificant increases of 8.5 +/- 6 per cent (P greater than 0.5), and 4 +/- 3.5 per cent (P greater 0.3) observed in the patients in groups 2 and 3. This response in the normal subjects differed significantly from the responses observed in the patients in groups 2 (P less than 0.02) and 3 (P less than 0.01). Of the patients in each of groups 2 and 3, 50 per cent responded abnormally to handgrip in that they showed a significant increase in DE. In the patients with aortic stenosis this subgroup of patients differed from the remainder in that they had a higher resting cardiac index (P less than 0.05). In the patients with myocardial disease this subgroup was characterized by a significantly lower resting left ventricular end-diastolic pressure (P less than 0.02). It seems, therefore, that those patients who increase DE in response to handgrip tend to have better left ventricular function at rest than those who do not. We suggest that this may be because of increased beta adrenergic activity at rest and during isometric exercise in the subgroup who respond to handgrip with an increase in DE.

Effects of myocardial infarction on adrenergic nerves of the rat heart muscle, a histochemical study

The anterior branch of the left coronary artery of the rat heart was ligated and the effects of anoxia on adrenergic nerves were studied histochemically using formaldehyde-induced fluorescence for localization of norepinephrine. Greenish catecholamine fluorescence was associated in the normal or infarcted myocardium only with adrenergic nerves. Constant but not prominent changes were seen in adrenergic nerve fibers 2 or 4 h after ligation of the coronary artery; the number of dilicate adrenergic fibers was reduced and some diffusion of the histochemical reaction was seen in small areas of the infarcted myocardium. Strong effects of anoxia were seen 8 h or more after ligation of the coronary artery. These were characterized by a prominent diffusion of the histochemical reaction and gradual disappearance of adrenergic structures in 2 to 4 days of anoxia. During the healing phase the appearance of numerous adrenergic nerve fibers was closely connected with the ingrowth of a new vascular bed into the infarction area. The observations indicate that adrenergic nervous structures of the myocardium resist the effects of anoxia, which may indicate the viability of sympathetic nerves in the infarcted area during long periods of anoxia.

Plasma catecholamine response of coronary-prone subjects (type A) to a specific challenge

Plasma norepinephrine (NE) and epinephrine (E) were assayed in 15 men prone to develop coronary heart disease (type-A behavior pattern) and in 15 coronary-disease-resistant men (type-B behavior pattern) under resting, noncompetitive conditions and also immediately before, during, and after participation in a nonphysical competitive struggle. The average concentration of catecholamines was virtually the same in both groups under resting conditions. Under competitive conditions the NE concentration of the coronary-susceptible group rose an average of 30%, while that of the resistant group remained essentially unchanged. E concentration remained unchanged in both groups.

Apex cardiogram and systolic time intervals in acute myocardial infarction

Images

Effect of heparin on serum free-fatty-acids, plasma catecholamines, and the incidence of arrhythmias following acute myocardial infarction

The effect of intravenous heparin in a therapeutic dosage on cardiac arrhythmias in patients with indubitable acute myocardial infarction was investigated. The value of serum free-fatty-acids (F.F.A.s) and plasma catecholamines in the prediction of patients vulnerable to serious arrhythmias was also studied.Heparin produced a significant rise in F.F.A., maximal within 10 minutes of injection, but did not increase the incidence of cardiac arrhythmias.No relationship was found between the incidence of arrhythmias and the initial levels of F.F.A. or adrenaline. No correlation was obtained between F.F.A. and plasma catecholamine levels. Heparin did not have a consistent effect on plasma catecholamines. Initial control plasma noradrenaline concentrations, however, were found to be significantly correlated with the incidence of subsequent arrhythmias. It is suggested that the level of plasma noradrenaline may be a valuable predictive guide to those patients likely to develop significant arrhythmias after acute myocardial infarction.

Effects of propranolol and isosorbide dinitrate on exercise performance and adrenergic acitivity in patients with angina pectoris

Twelve patients with angina pectoris were evaluated in a single blind crossover study with respect to objective changes in exercise performance on the treadmill and subjective, clinical improvement on oral administration of propranolol, isosorbide dinitrate (ISD), and a combination of propranolol and ISD. Combined objective and subjective evaluations showed that nine of 12 patients improved on propranolol, seven of 10 on ISD, and all 10 on the combination of drugs. The differences in objective improvement between the various drug regimens were not significant. However, subjectively all patients on the combination of drugs improved markedly. The patients on propranolol or the combination had a decrease in pressure-rate index of about 30% both at rest and during exercise, while these values did not change on ISD. A significant reduction in exercise-induced S-T depression was observed with propranolol alone and in combination with ISD at grade 3+ pain. Adrenergic activity, estimated from plasma and urinary catecholamines, appeared to be increased in these patients before drug treatment and was not altered during treatment. It is concluded that propranolol, ISD, and the combination of these drugs all improve exercise performance in patients with angina. Although the combination of drugs could not be shown to produce a greater increase in exercise performance than either drug alone, the combination effected a greater overall clinical improvement.

Myocardial infarction following coronary ligation in dogs. Hemodynamic effects of isoproterenol and acetylstrophanthidin

In the subacute phase of myocardial infarction following coronary ligation in dogs, a relationship was noted between the extent of infarction and the degree of elevation of left ventricular end-diastolic pressure. Left ventricular filling pressure was consistently increased when 25% or more of the left ventricle was infarcted. Isoproterenol infusion resulted in enhanced left ventricular function in both control and infarcted dogs, but the response was clearly weakened in those animals in which more than 20% of the left ventricle was infarcted. Acetylstrophanthidin caused no improvement in left ventricular function in infarcted dogs as judged by the relationship between filling pressure and cardiac output. The peak rate of rise of left ventricular pressure did increase in animals with infarcts, but was less than that in controls. Animals with infarcts had a lowered threshold for production of ventricular tachycardia by acetylstrophanthidin. These results in dogs suggest the need for further assessment of the role of digitalis in the treatment of heart failure following acute myocardial infarction.