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V J Richard

Publications and source records attributed to V J Richard.

14 recordsLinked to original sources
PubMed1993

Reperfusion in acute myocardial infarction: effect of timing and modulating factors in experimental models.

Timely reperfusion of ischemic myocardium in experimental animals halts the advancing transmural "wavefront" of ischemic cell death and thereby limits myocardial infarct size by limiting its transmural extent. The time window of opportunity for such salvage in most experimental models of regional ischemia is the first 3 hours. The number of myocytes that can be salvaged by reperfusion decreases exponentially during this period, such that at 3 hours, reperfusion limits infarct size by only about 10%. The rate of lethal ischemic cell injury and therefore the amount of myocardium that can be salvaged by reperfusion after a particular duration of ischemia is dependent both on the degree of blood flow deficit and the rate of ischemic metabolism. In experimental animal models, several interventions, including hypothermia, calcium antagonists, and "ischemic preconditioning," have been shown to reduce the rate of ischemic metabolism and to limit myocardial infarct size when assessed after a defined period of ischemia and reperfusion. Hypothetically, interventions that could prevent additional myocyte necrosis caused by some deleterious aspects of reperfusion ("lethal reperfusion injury") also could serve as valuable adjunctive therapy. However, studies of therapies designed to prevent lethal reperfusion injury have produced conflicting results. Thus, the concept that lethal reperfusion injury occurs remains controversial. Experimental evidence indicates that reperfusion accelerates both the initial inflammatory response and later process of infarct repair. Late reperfusion of infarcts in dogs, which does not limit myocardial infarct size, appears to accelerate the replacement of necrotic myocardium by scar without altering the size of the final scar.

Animals↗
PubMed1993

Superoxide dismutase plus catalase therapy delays neither cell death nor the loss of the TTC reaction in experimental myocardial infarction in dogs.

Studies to test whether superoxide dismutase (SOD), with or without catalase, limits myocardial infarct size have produced conflicting results. Positive results following short periods of reperfusion vs negative results following longer periods of reperfusion could be explained if either: (1) myocytes, initially salvaged by SOD, are killed by continued production of free radicals after the administered SOD have been excreted, or (2) false positive results occur because SOD transiently preserves the TTC reaction, despite loss of cellular viability. To evaluate these two possibilities, we measured infarct size after 90 min of ischemia and 4 h of reperfusion in SOD+catalase treated and untreated dogs. Treated dogs received a 60 min intra-arterial infusion of SOD (15,000 U/kg) plus catalase (CAT) (55,000 U/kg) beginning 25 min before reperfusion. Infarct size was measured using triphenyl tetrazolium (TTC) macrochemistry and was compared with the extent of necrosis assessed semi-quantitatively by light microscopy. Mean infarct size was similar in the control and treated groups. In addition, there was a positive linear correlation (r = 0.95) between the extent of necrosis estimated by microscopy and that estimated by TTC in both groups, and treatment did not alter the regression line. These current results were compared with results from the control dogs from our previous study (Richard et al., 1988) in which 90 min of ischemia was followed by 4 days of reperfusion. TTC-based infarct size at 4 days of reperfusion was similar to that observed in both groups at 4 h. These data indicate that oxygen free radicals, accessible to intravascular SOD and catalase, are not a cause of myocyte death detectable by measurement of infarct size after 4 h of reperfusion. Moreover, neither an "early protection, delayed death" hypothesis nor a specific preservation of the TTC reaction explain the positive results of other studies. TTC macrochemistry provides reliable estimates of myocardial infarct size, provided that sufficient magnification is used to permit resolution of interdigitating peninsulas of viable and necrotic tissue.

Animals↗
PubMed1993

Effect of anti-CD18 antibody on myocardial neutrophil accumulation and infarct size after ischemia and reperfusion in dogs.

BACKGROUND: Polymorphonuclear neutrophils (PMNs) accumulate in postischemic myocardium and may cause injury to myocardium or to vessels by production of oxygen free radicals or by release of proteases and lipases. PMN accumulation is dependent on adherence to endothelium, which is mediated by a family of glycoproteins on the PMN surface, each of which has a common beta-subunit (CD18). The purpose of this study was to determine whether an antibody (IB4) against the CD18 protein could attenuate PMN accumulation and limit myocardial infarct size. METHODS AND RESULTS: F(ab')2 fragments of a mouse monoclonal antibody to human adherence-promoting leukocyte glycoprotein (CD18) were used. Infarct size after 90 minutes of ischemia and 3 hours of reperfusion was compared in dogs with (n = 8) and without (n = 8) the anti-CD18 treatment. Myocardial PMN accumulation was assessed with 111In-labeled autologous PMNs. Anti-CD18 treatment significantly reduced the number of PMNs in the ischemic region (19,123 +/- 5,352/mg versus 5,204 +/- 927/mg in the control and treated groups, respectively; p < 0.05). In addition, the ratio of myocardial blood flow (ischemic/nonischemic wall) at 45 minutes into reperfusion was higher in the treated than in the control group (1.18 +/- 0.18 versus 0.69 +/- 0.09; p < 0.05). Nevertheless, infarct size was similar between the control and treated groups (40.5 +/- 7.4% versus 48.5 +/- 4.4% of the area at risk; p = NS). Transmural mean collateral blood flow to the ischemic myocardium was similar between the two groups, and the inverse relation between infarct size and collateral blood flow was not shifted by anti-CD18 therapy. CONCLUSIONS: Although PMN accumulation contributed to reduced postischemic microvascular perfusion, it caused insufficient additional myocardial cell death to measurably affect infarct size in this model.

Animals↗
PubMed1991

Hypoxic reperfusion to remove ischaemic catabolites prior to arterial reperfusion does not limit the size of myocardial infarcts in dogs.

STUDY OBJECTIVE: Although timely reperfusion limits myocardial infarct size, it has been postulated that reperfusion itself may kill some myocytes which were alive at the end of an episode of ischaemia (lethal reperfusion injury). The aim of this study was to test the hypothesis that ischaemic catabolites may "prime" myocardium for such injury and that preliminary hypoxic washout of such catabolites, prior to arterial reperfusion, would limit myocardial infarct size. DESIGN: Dogs underwent a 40 min occlusion of the left circumflex coronary artery, followed by 4 d reperfusion. In a treated group, a 5 min episode of coronary artery perfusion with hypoxic buffer was instituted at the end of this ischaemic episode, before blood reperfusion was restored. Control dogs received a similar volume of hypoxic buffer intravenously. Systemic fluid overload was attenuated by haemofiltration. The effect of this preliminary hypoxic washout on myocardial infarct size was assessed. EXPERIMENTAL MATERIAL: 18 anaesthetised, open chest dogs were used. After the acute study they recovered from surgery for 4 d and were then killed for further study. MEASUREMENTS AND MAIN RESULTS: Infarct size, determined by microscopic evaluation, was not significantly different in the two groups, at (control) 31.3 (SEM 6.2)% v (hypoxic reperfusion) 25.8(3.9)% of the vascular area at risk. In control dogs, infarct size was inversely related to the amount of collateral blood flow (measured using microspheres); hypoxic reperfusion did not shift this relation (analysis of covariance, F = 0.236, NS). CONCLUSIONS: The washout of ischaemic catabolites by hypoxic perfusate prior to reoxygenation did not limit infarct size.

Animals↗
PubMed1991

Myocardial protection is lost before contractile function recovers from ischemic preconditioning.

Preconditioning myocardium with brief episodes of ischemia reduces energy demand and delays cell death during a subsequent ischemic episode. We hypothesized that postischemic contractile dysfunction after the brief ischemic episodes ("stunning") causes this reduced energy demand. If this hypothesis is correct, then cardioprotection should persist as long as mechanical function still is depressed at the onset of sustained ischemia. To analyze the temporal relationship between preconditioning and stunning, infarct size was compared in two groups of open-chest anesthetized dogs that were preconditioned with a 15-min coronary occlusion followed by a sustained 40-min occlusion. One group received 5 min of reperfusion and the second group received 120 min of reperfusion between occlusions. Nonpreconditioned controls received a single 40-min occlusion. A 15-min occlusion caused severe stunning, which did not improve during 2 h of reperfusion. In the 5-min reflow group, preconditioning resulted in dramatically smaller infarcts, averaging 2.2 +/- 0.9% of the area at risk vs. 26.5 +/- 4.2% in controls (P less than 0.01), confirmed by a marked shift in the inverse relationship between collateral blood flow and infarct size. Despite persistently severe stunning in the 120-min reflow group, infarct size was intermediate, averaging 12.3 +/- 2.7% (P less than 0.05 vs. 5-min reflow; P less than 0.01 vs. control), and the infarct vs. flow regression had returned toward control. Thus the cardioprotective effect of preconditioning was attenuated when the intervening reperfusion time was extended, even though severe contractile dysfunction persisted. We conclude that myocardial stunning, per se, is insufficient to cause preconditioning.

Animals↗
PubMed1990

Oxygen-derived free radicals and postischemic myocardial reperfusion: therapeutic implications.

Oxygen-derived free radicals have been implicated in the pathogenesis of various disease states, including myocardial ischemia and reperfusion. In this article, we review 1) the evidence linking free radical production and myocardial injury during myocardial ischemia and reperfusion and 2) results of studies of the effects of the pharmacological therapies available potentially to prevent free radical-mediated injury. Free radicals can be produced during ischemia and reperfusion by several different biochemical pathways. Of these, the xanthine oxidase reaction and the output of free radicals by neutrophils that have accumulated in damaged tissue have been studied extensively. When produced, free radicals can potentially damage myocytes or endothelial cells through peroxidation of membrane lipids or damage to proteins or nucleic acids. Using electron spin resonance spectroscopy, several studies have shown a 'burst' of oxygen free radicals immediately after reperfusion. Moreover, exogenous generation of intravascular free radicals has been shown to produce marked vascular and myocyte damage, as well as contractile dysfunction. 'Anti-free radical' interventions, such as xanthine oxidase inhibitors and free radical scavengers have been reported to prevent contractile dysfunction and reperfusion-induced arrhythmias after an episode of reversible ischemic injury. However, after more severe episodes of ischemia, such interventions have had conflicting effects on myocardial infarct size. 'Anti-free radical' interventions could be of potential use in situations where reversible ischemic injury occurs. In situations where reperfusion is achieved after irreversible ischemic injury has occurred, the potential beneficial effect of these treatments on infarct size is more doubtful.

Animals↗
PubMed1990

Electrophysiological effects of monophasic and biphasic stimuli in normal and infarcted dogs.

Though some biphasic waveforms significantly decrease the energy required for defibrillation, little is known about the effect of biphasic stimulation on the determination of other electrophysiological parameters in normal and infarcted hearts. To evaluate this, nine normal dogs and 12 dogs with myocardial infarction had activation threshold (AT), effective refractory period (ERP), strength-interval curves, and ventricular fibrillation threshold (VFT) determined with constant current stimulation to a pair of right ventricular plunge electrodes, and upper limit of vulnerability (ULV) and defibrillation threshold (DFT) determined with truncated exponential shocks delivered to a pair of wire electrodes coiled to contour the right and left ventricular epicardium. Each electrophysiological parameter was determined with a 5.5 msec monophasic and 5.5-msec biphasic (3.5 msec first phase) waveform. Though AT and VFT were not significantly different for the two waveforms, the ERP was significantly longer, the strength-interval curve shifted rightward, and the threshold for repetitive responses higher for biphasic stimuli. Compared to the monophasic waveform, the ULV and DFT were significantly decreased in a parallel fashion for the biphasic waveform. Neither the presence nor size of myocardial infarction significantly affected any of the measured electrophysiological parameters. In six additional dogs, sigmoid defibrillation probability curves were constructed from biphasic shocks of four energies including that of the DFT and ULV. The ULV energy predicted an effective dose that defibrillated 97% of the time (range 90%-100%). In conclusion, the increased defibrillation efficacy of the biphasic waveform is independent of its ability to activate fully repolarized myocardium and cannot be explained by a greater ability of biphasic waveforms to activate partially depolarized tissue. The parallel decrease in the ULV and DFT for biphasic stimulation and the finding that the ULV energy defibrillates with a high probability of success suggest similar underlying mechanisms for the ULV and defibrillation.

Animals↗
PubMed1990

Ischemic preconditioning slows energy metabolism and delays ultrastructural damage during a sustained ischemic episode.

We have shown previously that preconditioning myocardium with four 5-minute episodes of ischemia and reperfusion dramatically limited the size of infarcts caused by a subsequent 40-minute episode of sustained ischemia. The current study was undertaken to assess whether the same preconditioning protocol slowed the loss of high energy phosphates, limited catabolite accumulation, and/or delayed ultrastructural damage during a sustained ischemic episode. Myocardial metabolites and ultrastructure in the severely ischemic subendocardial regions were compared between control and preconditioned canine hearts. Hearts (four to 10 per group) were excised after 0, 5, 10, 20, or 40 minutes of sustained ischemia. All groups had comparable collateral blood flow. Preconditioned hearts developed ultrastructural injury more slowly than controls; evidence of irreversible injury was observed after 20 minutes in controls but not until 40 minutes in preconditioned hearts. Furthermore, after 40 minutes of ischemia, irreversible injury was homogeneous in controls but only focal in preconditioned myocardium. Preconditioning reduced starting levels of ATP by 29%. Nevertheless, it also slowed the rate of ATP depletion during the episode of sustained ischemia, so that after 10 minutes of ischemia, preconditioned hearts had more ATP than controls. However, after 40 minutes, ATP contents were not significantly different between groups. Preservation of ATP resulted from reduced ATP utilization and was not due to increased ATP production. Accumulation of purine nucleosides and bases (products of adenine nucleotide degradation) was limited in preconditioned myocardium. Accumulation of glucose-1-phosphate, glucose-6-phosphate, and lactate also was reduced markedly by preconditioning, due to reduced rates of glycogen breakdown and and anaerobic glycolysis. We propose that preconditioning reduces myocardial energy demand during ischemia, which results in a reduced rate of high energy phosphate utilization and a reduced rate of anaerobic glycolysis. Either preservation of ATP or reduction of the cellular load of catabolites may be responsible for delaying ischemic cell death.

Adenine Nucleotides↗
PubMed1990

Evaluation of free radical injury in myocardium.

Abundant evidence now is available that free radicals are produced in excess when myocardium is reperfused following an episode of ischemia and that free radicals can injure myocytes and endothelial cells. Free radicals may contribute to either reversible or irreversible manifestations of cell injury from ischemia and reperfusion. Several investigators have observed that post-ischemic contractile dysfunction (myocardial stunning) can be attenuated by a variety of anti-free radical therapies, and there seems to be general agreement that free radical injury contributes to stunning. Whether free radicals are an important cause of lethal myocyte injury ("lethal reperfusion injury") remains controversial. Using similar interventions and animal models, both positive and negative results have been reported from a growing number of studies done to test the effect of anti-free radical therapies on infarct size. Proposed explanations include differences in: 1) dose of drug and onset or duration of treatment, 2) duration of occlusion or reperfusion, 3) methods of measuring infarct size or area at risk, and 4) failure of some studies to control for baseline variation in the major determinants of infarct size, e.g., collateral blood flow. At present, none of these explanations seems sufficient to resolve the question.

Animals↗
PubMed1989

Effect of a critical coronary stenosis on myocardial neutrophil accumulation during ischemia and early reperfusion in dogs.

In many experimental models of ischemia and reperfusion, reperfusion is performed abruptly, allowing full reactive hyperemia to occur. In the clinical setting, however, reperfusion after thrombolysis is often limited by residual stenosis. Some experimental models attempt to mimic this situation with a "critical stenosis" (defined as a coronary constriction sufficient to abolish reactive hyperemia without altering baseline flow). The purpose of this study was to determine whether preventing reactive hyperemia during the initial phase of reperfusion would modify the transmural distribution of myocardial blood flow or the myocardial accumulation of polymorphonuclear leukocytes (PMNs). The left circumflex artery was occluded for 90 minutes and then reperfused for 60 minutes in anesthetized, open-chest dogs. Autologous PMNs were isolated, labeled with 111In, and reinjected 1 hour before coronary occlusion. 125I-labeled albumin was injected simultaneously to correct for 111In associated with plasma proteins and to permit calculation of the number of PMNs in the inner, middle, and outer thirds of nonischemic and ischemic-reperfused tissue. The presence of a critical stenosis abolished reactive hyperemia during the first 5 minutes of reperfusion, but did not substantially affect blood flow measured after 55 minutes of reperfusion. In both groups, there was a significant accumulation of PMNs in all layers of the ischemic-reperfused bed compared with the nonischemic bed, and the magnitude of this PMN accumulation was not altered by the presence of a critical stenosis. Moreover, infarct size, estimated by triphenyl tetrazolium chloride (TTC) loss after 60 minutes of reperfusion, was not affected by the presence of a critical stenosis. Thus, the presence of a critical stenosis abolished the hyperemic blood flow after reperfusion but did not influence the early PMN response to ischemia and reperfusion or the early loss of TTC staining.

Animals↗
PubMed1988

The xanthine oxidase inhibitor oxypurinol does not limit infarct size in a canine model of 40 minutes of ischemia with reperfusion.

Free radicals such as superoxide (.O2-) produced by xanthine oxidase might cause cell death during reperfusion after myocardial ischemia. The effect of the xanthine oxidase inhibitor allopurinol on infarct size in ischemia-reperfusion models has been variable, possibly because of differences in treatment duration. Adequate inhibition of xanthine oxidase may require a sufficient pretreatment period to permit conversion of allopurinol to oxypurinol, the actual inhibitor of superoxide production. To test more definitively whether xanthine oxidase-derived free radicals cause cell death during reperfusion, the effect of oxypurinol on infarct size was evaluated in an ischemia-reperfusion model. Open chest dogs underwent 40 min of circumflex coronary artery occlusion followed by reperfusion for 4 days. Twelve dogs were treated with oxypurinol (10 mg/kg body weight intravenously 10 min before occlusion and 10 mg/kg intravenously 10 min before reperfusion) and 11 control dogs received drug vehicle alone (pH 10 normal saline solution). Nine control dogs from a concurrent study also were included. Infarct size was measured histologically and analyzed with respect to its major baseline predictors, including anatomic area at risk and collateral blood flow (measured with radioactive microspheres). Infarct size as a percent of the area at risk averaged 23.8 +/- 2.7% (mean +/- SEM) in the oxypurinol group (n = 10) and 23.1 +/- 4.2% in the control group (n = 17) (p = NS). Collateral blood flow to the inner two thirds of the ischemic wall averaged 0.08 +/- 0.01 ml/min per g in the oxypurinol group and 0.09 +/- 0.02 ml/min per g in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Myocardial neutrophil accumulation during reperfusion after reversible or irreversible ischemic injury.

Recent studies suggest that polymorphonuclear leukocytes (PMNs) may cause additional myocyte injury during reperfusion of ischemic myocardium. The present study was done to investigate whether PMNs accumulate in myocardium during early reperfusion after reversible or irreversible ischemic injury. Open-chest anesthetized dogs underwent circumflex coronary occlusions for 12 min (n = 5), 40 min (n = 8), or 90 min (n = 8), followed by 1 h of reperfusion. Autologous PMNs were radiolabeled with 111In and reinjected to quantitate myocardial PMN influx during reflow. 125I-labeled albumin was injected simultaneously to correct for 111In associated with plasma proteins in myocardial tissue. The number of PMNs was determined in the inner, middle, and outer one-third of nonischemic and ischemic-reperfused myocardium. In the 12-min group, 40% fewer PMNs were present in the reperfused than in the nonischemic control tissue. In contrast, in both the 40- and 90-min groups, PMN accumulation was two- to sixfold greater in the ischemic-reperfused than nonischemic myocardium, with a transmural gradient of PMN influx increasing from the outer to inner layers. Collateral blood flow, measured with radioactive microspheres, was not significantly different among the three groups. The failure of PMNs to accumulate during reperfusion after 12 min of ischemia does not support the hypothesis that PMNs contribute to postischemic dysfunction of reversibly injured myocytes. Whether PMNs caused cell death during early reperfusion after longer ischemic episodes remains unknown; however, the rapidity of PMN accumulation in the zones of predicted infarction is consistent with this possibility.

Animals↗
PubMed1988

Therapy to reduce free radicals during early reperfusion does not limit the size of myocardial infarcts caused by 90 minutes of ischemia in dogs.

It has been postulated that oxygen-centered free radicals are produced in significant quantities upon reperfusion of ischemic myocardium and could cause the death of myocytes that are still reversibly injured at the end of ischemia ("reperfusion injury"). However, we have shown previously that anti-free radical therapies including superoxide dismutase (SOD) and inhibitors of xanthine oxidase did not limit infarct size after 40 minutes of ischemia and 4 days of reperfusion in dogs. To test whether 40 minutes of ischemia is too brief a period to produce the prerequisite conditions for free radical-mediated necrosis upon reperfusion, we studied infarcts produced by 90 minutes of ischemia followed by reperfusion. Dogs in an SOD-catalase group received a 60-minute infusion of SOD (15,000 units/kg) and catalase (55,000 units/kg) beginning 25 minutes before and ending 35 minutes after reperfusion. A second group of dogs received a single injection of the xanthine oxidase inhibitor oxypurinol (20 mg/kg) 25 minutes before reperfusion. Infarct size was assessed histologically relative to the size of the area at risk and to collateral blood flow to the ischemic region. Infarct size as a percentage of the area at risk was similar in the control group (40.7 +/- 5.5%, n = 11), the SOD-catalase group (38.0 +/- 6.4%; n = 8), and the oxypurinol-treated group (41.4 +/- 6.1%; n = 7) [p = not significant (NS) by analysis of variance]. In controls, there was an inverse relation between infarct size and collateral blood flow; neither of the treatments altered this relation (p = NS by analysis of covariance).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗