Disseminated cytomegalovirus disease in hosts without acquired immunodeficiency syndrome and without an organ transplant.

We describe 7 histologically proven cases of cytomegalovirus disease in patients without human immunodeficiency virus and without organ transplants, all of whom had associated comorbid conditions. Therapy with ganciclovir generally resulted in a favorable outcome.

Molecular basis of anthracycline-induced cardiotoxicity and its prevention.

Anthracyclines are a class of highly potent antitumor antibiotics utilized against hematologic and solid tumors in children and in adults. Their use has been limited primarily by their cardiotoxic side effects, which may lead to congestive heart failure. Although there is a linear relationship between the cumulative dose received and the incidence of cardiotoxicity, in some patients cardiotoxicity may develop at doses below the generally accepted threshold level. Anthracycline-induced cardiotoxicity is believed to be related to the generation of highly reactive oxygen species, which, by means of membrane lipid peroxidation, cause direct damage to cardiac myocyte membranes. Another important factor may be the relatively poor antioxidant defense system of the heart. In an attempt to circumvent these toxic effects, a wide variety of antioxidants have been used in cell culture, animal, and human studies without consistent beneficial effects. Moreover, none of the agents used to date are designed to act selectively upon the heart. If the cardiac complications resulting from anthracyclines could be reduced and/or prevented, higher doses could potentially be used, thereby increasing cancer cure rates. Furthermore, the incidence of cardiac toxicity resulting in congestive heart failure or even heart transplantation would be reduced, therefore increasing the quality and extent of life for cancer survivors. This article will review the basic science of free radical biology, the biology of oxygen-derived free radicals and antioxidant proteins, and explore some new and innovative approaches to limiting and/or preventing anthracycline-induced cardiotoxicity.

Epicardial temperature is a major predictor of myocardial infarct size in dogs.

To determine whether epicardial temperature varies among anesthetised, open-chest dogs, and, if so, whether such variation has a measurable effect on myocardial infarct size, 35 open-chest mongrel dogs underwent 60 min of circumflex coronary artery occlusion and 3 h of reperfusion. Infarct size was measured using triphenyl tetrazolium chloride (TTC) macrochemistry. Known predictors of infarct size including area-at-risk (AAR) and collateral blood flow (CBF) were measured. Epicardial temperature was monitored using a temperature probe placed in the pericardial space adjacent to the posterior surface of the heart. In each individual dog, epicardial temperature was nearly constant throughout the period of coronary occlusion. Amongst dogs, however, epicardial temperature ranged from 35.5-41.0 degrees C. By multiple regression analysis, infarct size was better predicted by the combination of temperature and CBF than by CBF alone. "Low-T" (35.5-38.0 degrees C, n = 17) and "high-T" (38.1-41.0 degrees C, n = 18) subgroups were compared by analysis of covariance (ANCOVA), using infarct size as the dependent variable and CBF as the independent variable. Following adjustment of infarct size for CBF, infarct size in the low-T subgroup was only 53% v that in the high-T subgroup (16.9 +/- 2.7% v 31.9 +/-5.0% of AAR, P < 0.001). Thus, in open-chest dogs, relatively minor variation in epicardial temperature had major effects on myocardial infarct size. We conclude that myocardial temperature is an independent predictor of infarct size in dogs. Although such variation could confound studies of the therapeutic efficacy of proposed cardioprotective interventions, controlling for temperature variation in such studies should reduce the likelihood of false positive or negative results.

Effect of adenosine therapy at reperfusion on myocardial infarct size in dogs.

OBJECTIVES: The concept of lethal reperfusion injury in ischemic myocardium has been the subject of controversy. Adenosine administered during reperfusion has been reported to limit lethal reperfusion injury in several studies. On the contrary, it has been reported that cardioprotection may not be achieved with adenosine alone but may occur if adenosine is co-administered with lidocaine. Still other investigators have reported no beneficial effect of adenosine, given with or without lidocaine. If the positive reports are reproducible, they are important both because they provide evidence for the existence of reperfusion injury and establish a rationale for preventing it. Thus, the present study was done to determine if adenosine could limit lethal reperfusion injury in a canine model of regional myocardial ischemia and reperfusion, carefully controlled for baseline predictors of infarct size. METHODS: Dogs (n = 37) of either sex were subjected to 90 min of coronary occlusion followed by 3 h of reperfusion. Two groups of dogs received adenosine (150 micrograms/kg/min) intravenously for 155 min starting 5 min prior to the reperfusion. One treated group received adenosine only and a second group received adenosine plus lidocaine (2 mg/kg). Control dogs received a saline infusion. After 3 h of reflow, hearts were excised and infarct size was measured and expressed as a percentage of the ischemic area at risk (AAR). To control for variation in infarct size due to variation in collateral blood flow (CBF), infarct size among groups was compared using ANCOVA, using CBF as the independent variable and infarct size as the dependent variable. RESULTS: Transmural collateral blood flow and AAR were not significantly different between any of the groups. Mean infarct size (adjusted by ANCOVA) in control dogs (n = 9) was 38.1 +/- 5.3% of the AAR. Neither adenosine (n = 9) nor adenosine plus lidocaine (n = 7) significantly limited infarct size (35.6 +/- 5.6% AAR and 38.1 +/- 7.7% AAR, respectively; both P = NS). CONCLUSIONS: Intravenous adenosine therapy (150 micrograms/kg/min) during reperfusion, whether administered alone or in dogs previously treated with lidocaine, did not limit infarct size after 90 min of regional ischemia in canine myocardium.

Reducing lactate accumulation does not attenuate lethal ischemic injury in isolated perfused rat hearts.

The role of lactate accumulation in lethal ischemic myocardial cell injury was assessed by partially depleting hearts of glycogen before ischemia by using glucagon. Isolated adult rat hearts were perfused with glucose-free Krebs-Henseleit buffer containing acetate as substrate. After stabilization, treated hearts were perfused briefly (3 min) with buffer containing 2 micrograms/ml glucagon to reduce tissue glycogen stores, followed by 10 min of perfusion with control buffer, and 60 or 90 min of global ischemia. Before the onset of ischemia, glucagon-treated hearts contained 40% less glycogen than untreated hearts, but myocardial function and tissue levels of high-energy phosphates, lactate, and glucose 6-phosphate were similar. Lactate production during ischemia in the glucagon-treated hearts was 50% less than in untreated hearts. However, there was no decrease in the amount of creatine kinase release during reperfusion after either 60 or 90 min of ischemia. Thus although partial glycogen depletion reduced lactate accumulation during ischemia, this did not decrease the amount of lethal myocardial cell injury.

Effect of reversible ischemia on the activity of the mitochondrial ATPase: relationship to ischemic preconditioning.

The mitochondrial ATPase enzyme accounts for roughly 35-50% of the overall energy demand that leads to ATP depletion under conditions of severe myocardial ischemia. In larger mammalian hearts, this energy squandering action of the ATPase is modulated by an endogenous inhibitor protein. The present studies were undertaken to characterize the time course of inhibition of the mitochondrial ATPase in canine myocardium under conditions of severe regional ischemia in vivo. In addition, we determined if the energy sparing effects of ischemic preconditioning (PC) can be explained by persistent inhibition of the mitochondrial ATPase enzyme. The circumflex coronary artery was ligated for 1.5 min (n = 4), 5 min (n = 6), or 15 min (n = 5). In a separate group (n = 7), hearts were preconditioned by four 5-min periods of ischemia each followed by 5 min of reperfusion. Sub-mitochondrial particles were prepared from the sub-endocardial zone of the ischemic and non-ischemic regions and were assayed for oligomycin-sensitive ATPase activity. ATPase activity was reduced to about 79% at 1.5 min and to approximately 55% at 5 and 15 min of ischemia, relative to non-ischemic tissue from the same heart. The rate of HEP utilization slowed concurrently with the development of ATPase inhibition. In preconditioned myocardium, ATPase activity was not significantly different from control myocardium from the same heart. We conclude that the early inhibition of the mitochondrial ATPase activity slows the utilization of high energy phosphate and thereby serves as an important endogenous cardioprotective mechanism. Nevertheless, altered activity of the ATPase is not the explanation of the energy sparing effect of ischemic preconditioning.

Effect of catecholamine depletion on myocardial infarct size in dogs: role of catecholamines in ischemic preconditioning.

OBJECTIVES: Cardioprotective adaptation to brief periods of ischemia and reperfusion is termed ischemic preconditioning (PC). Limitation of infarct size by preconditioning is associated with marked slowing of ischemic metabolism. The cause of metabolic slowing has not been determined but may involve either pro- or anti-adrenergic mechanisms. Hypothetically, adrenergic stimulation could signal the adaptive response. Alternatively, metabolic slowing during the sustained ischemic challenge could occur through a reduction in beta-adrenergic stimulation. This study was designed to test the role of cardiac norepinephrine (NE) in PC. METHODS: The effect of PC on myocardial infarct size was studied in control dogs and dogs depleted of catecholamines by pretreatment with reserpine (RES; 0.25 mg/kg i.v.). PC was induced by four cycles of 5 min of ischemia and 5 min of reperfusion. Infarcts were produced by 60 min of ischemia and 3 h of reperfusion. Cardiac NE depletion was verified by radioimmunoassay of tissue samples and by absence of hemodynamic response to a tyramine bolus (1.4 mg/kg) administered at the end of each experiment. Infarct size, expressed as percent of area at risk, was controlled for variation in collateral blood flow using analysis of covariance (ANCOVA). RESULTS: Adjusted mean infarct size was 25.5 +/- 3.2% in untreated controls vs. 19.1 +/- 3.3% in RES-treated controls (P = NS). PC limited infarct size in untreated dogs (7.4 +/- 1.8 vs. 25.5 +/- 3.2%; PC vs. control; P < 0.01) but not in RES-treated dogs (15.7 +/- 3.0% vs. 19.1 +/- 3.3%; RES + PC vs. RES; P = NS). Infarct size was larger in dogs with RES + PC than with PC alone, even though there was a trend toward a slight beneficial effect with RES alone. CONCLUSION: The cardioprotective effect of ischemic preconditioning cannot be explained entirely as an anti-adrenergic effect. On the contrary, adrenergic receptor stimulation may be required for the full expression of ischemic preconditioning in canine myocardium.

The novel calcium antagonist Ro 40-5967 limits myocardial infarct size in the dog.

OBJECTIVE: The aim was to compare the infarct limiting effect of Ro 40-5967 (Ro40), a new calcium antagonist with little negative inotropic activity, with that of verapamil and with ischaemic preconditioning, a potent endogenous cardioprotective mechanism. METHODS: Dogs (n = 53) of either sex were subjected to 60 min of coronary occlusion followed by 3 h of reperfusion. Drug treated dogs received either verapamil (1.0 mg.kg-1) or Ro40 (3.0 mg.kg-1) intravenously for 100 min starting 15 min prior to the occlusion. Control dogs received a saline infusion. Ischaemic preconditioning consisted of four 5 min cycles of ischaemia alternating with four 5 min cycles of reperfusion. After 3 h of reflow, hearts were excised and infarct size was measured using tripheyltetrazolium chloride macrochemistry and expressed as percent of the ischaemic area at risk (AAR). To control for variation in infarct size due to variation in collateral blood flow, infarct size among groups was compared using ANCOVA, in which infarct size and collateral blood flow, measured at 30 min of occlusion, were dependent and independent variables, respectively. RESULTS: Transmural collateral blood flow and AAR were not significantly different between any of the groups. Mean infarct size (adjusted by ANCOVA for slight differences in collateral blood flow among groups) in control dogs (n = 13) was 25.9(SEM 3.2)% of the AAR. Both verapamil (n = 11) and Ro40 (n = 9) limited infarct size [14.2(3.2)% AAR and 16.7(2.9)% AAR, respectively; both p < 0.05]. Preconditioning (n = 17) also significantly limited infarct size [8.1(1.8)%; p < 0.01]. CONCLUSIONS: The new calcium antagonist, Ro 40-5967, was as effective as verapamil in limiting infarct size after 60 min of regional ischaemia followed by 3 h of reperfusion, although neither calcium antagonist was as effective as ischaemic preconditioning.

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.

Cardiac protection by ischaemic preconditioning is not mediated by myocardial stunning.

OBJECTIVE: Previous studies have shown that cardiac protection by ischaemic preconditioning wanes before contractile function recovers; thus stunning is insufficient to cause preconditioning. To test whether reduced contractile effort is necessary for preconditioning induced protection, the effect on myocardial infarct size of restoring contractile function with dobutamine was examined in preconditioned and control dogs. METHODS: In two experimental groups (groups P and P+D), preconditioning was produced by four 5 min occlusions of the left anterior descending coronary artery, each separated by 5 min of reperfusion. Contractile function was assessed by sonomicrometry 5 min after completion of the preconditioning protocol. In group P+D, dobutamine (average dose = 5 micrograms.kg-1.min-1) was then infused intravenously to restore systolic shortening to baseline. The artery then was reoccluded for 40 min of sustained ischaemia followed by 4 d of reperfusion. Two additional groups of non-preconditioned control dogs (groups C and C+D) also underwent 40 min of coronary occlusion and 4 d of reperfusion. Group C+D received a dobutamine infusion beginning 15 min before and during the 40 min occlusion to match the dobutamine received in group P+D, whereas group C received normal saline. RESULTS: Preconditioning caused mild postischaemic contractile dysfunction (50% decrease in systolic shortening) which was easily reversed by dobutamine treatment. Dobutamine also increased both the rate-pressure product and the left ventricular dP/dt in both treated groups (C+D and P+D). Histological infarct size was 12.3(SEM 2.0)% of the area at risk in the untreated control group (n = 11), and was reduced to 4.4(1.7)% in the untreated preconditioning group (n = 8; p < 0.05). Dobutamine increased non-preconditioned infarct size (group C+D) to 22.1(3.4)% (n = 7; p < 0.05). Infarct size in the dobutamine treated preconditioning group (P+D) was not significantly different from infarct size in group P (n = 8), at 6.1(2.5%). CONCLUSIONS: In preconditioned hearts, dobutamine restored postischaemic contractile function but did not increase infarct size significantly. Thus reduced contractile effort is not required for the cardioprotective effect on ischaemic preconditioning.

Adenosine slows ischaemic metabolism in canine myocardium in vitro: relationship to ischaemic preconditioning.

OBJECTIVE: Studies in rabbits suggest that the cardioprotective effects of adenosine against lethal cell injury may be related to production of adenosine and subsequent activation of adenosine A1 receptors. However, it is not known whether intracoronary adenosine therapy can mimic the metabolic sparing effects of preconditioning in rabbits or dogs. The purpose of this study was to determine the effect of intracoronary adenosine on ischaemic metabolism in totally ischaemic canine myocardium. METHODS: Dog hearts (n = 13) were excised and the coronary arteries were perfused with an oxygenated Krebs' buffer containing glucose. Adenosine was added to the buffer perfusing the circumflex (treated) region. Following perfusion, control and treated beds from each heart were subjected to 90 min total ischaemia at 37 degrees C. Tissue levels of ATP and glycolytic intermediates were determined at several time points during the ischaemic incubation. RESULTS: Adenosine significantly slowed the rate of ATP depletion, glycogen utilisation, and lactate accumulation during the first 20 minutes of total ischaemia. CONCLUSIONS: The results suggest that adenosine is capable of slowing ischaemic metabolism and they are consistent with the hypothesis that adenosine may mediate ischaemic preconditioning.

An in vitro model of myocardial ischemia utilizing isolated adult rat myocytes.

Isolated adult rat myocytes were used to develop an in vitro model of myocardial ischemia. Freshly isolated myocytes were spun into a cell pellet to limit extracellular volume. Excess supernatant was removed and the pellet was covered with mineral oil and incubated in a temperature controlled water bath. After various periods of incubation, cells were analyzed for adenine nucleotide levels, lactate accumulation, rate of cell death, and cell morphology. Adenine nucleotide profiles after 60 min incubation at 37 degrees C showed marked depletion of adenosine triphosphate (ATP) and large increases in adenosine monophosphate (AMP), adenosine, inosine, and lactate and no significant difference in levels of inosine monophosphate. These results are consistent with ischemic conditions. Reduction of the incubation temperature to 34 and 30 degrees C slowed the rate of cell squaring and the onset of cell death. Resuspension of ischemic cells after 30, 45, 60 and 90 min incubation in hypotonic buffer (170 mosmol) to induce acute cell swelling caused an increase in the number of non-viable cells at each time point. Control cells and ischemic cells incubated less than 30 min did not show increases in non-viable cells when subjected to hypotonic swelling. Morphological analysis revealed that isolated myocytes respond to ischemia in a heterogeneous fashion and exhibit changes at both light and electron microscopic levels similar to those seen in other ischemic models. These results indicate that pelleted isolated adult rat myocytes may be a useful in vitro model to study myocardial ischemic cells injury.

Irreversible injury of isolated adult rat myocytes. Osmotic fragility during metabolic inhibition.

Isolated myocytes can be established as a valid model for studying changes in cytoskeletal proteins during the development of irreversible injury only if isolated cells develop lesions similar to those that occur during irreversible injury to intact hearts, specifically osmotic fragility and subsarcolemmal blebs. In the first experiment, isolated cells were irreversibly injured by metabolic inhibition with 5 mM Iodoacetic acid (IAA) and 6 mM amobarbital (Amy). Osmotic fragility of control and injured cells was determined by comparing the rates of development of trypan blue permeability during 60 minutes of isotonic or hypotonic (50% reduction in osmolality) incubations. Cell morphology was monitored by light and electron microscopy. Control cells remained elongated and excluded trypan blue. Metabolically inhibited cells rapidly contracted to a nearly square shape. The inhibited squared cells initially excluded trypan blue, but during 60 minutes of incubation became permeable to trypan blue. Cells in hypotonic buffer developed blue staining at a more rapid rate than cells in isotonic buffer, indicating increased osmotic fragility. In a second experiment, control and inhibited cells were first incubated for 25 minutes in isotonic buffer and then in either isotonic or hypotonic buffer. In this experiment, inhibited cells also developed more extensive and rapid permeability increases when transferred to the hypotonic buffer than cells maintained in the isotonic buffer. In both experiments, increased permeability of cells to trypan blue was accompanied by formation of subsarcolemmal blebs along the lateral cell border and at the intercalated disks. The results show that metabolically inhibited, isolated myocytes do exhibit morphologic lesions and increased osmotic fragility properties similar to those reported during anoxic or ischemic injury to intact hearts. Therefore, isolated myocytes may be a useful model with which to study cytoskeletal-sarcolemmal membrane changes during development of irreversible injury.

Increased myocyte fragility following anoxic injury.

The ability of cells in anoxic-perfused hearts to withstand two types of physical stresses (stretching and swelling), in the absence of reoxygenation was determined. Isolated rat hearts were perfused for 20, 40, or 60 mins with anoxic buffer after which hearts were either reoxygenated for 20 mins or exposed for 15 s to a physical stress caused by inflation of a intraventricular balloon to an appropriate volume (0.35 ml), while maintaining anoxic perfusion for an additional 20 mins. At 20, 40, or 60 mins of anoxic perfusion, reoxygenation induced CK releases of (n = 5) 14.13 +/- 13.15, 62.42 +/- 2.87, and 83.22 +/- 6.41 IUCK/g wet wt, respectively. After 0.35 ml balloon inflation, in the absence of reoxygenation, corresponding CK releases were respectively 8.10 +/- 1.63, 39.13 +/- 8.27, and 59.64 +/- 2.57 IUCK/g wet wt. Increasing the volume of balloon inflation from 0.2 to 0.6 ml at a constant (60 mins) duration of anoxic perfusion resulted in a corresponding increase in CK release. Control hearts released no CK even following 0.6 ml balloon inflation. In the second experimental protocol, hearts were perfused for 30, 45, 60, or 75 mins with isotonic (300 mOsm) anoxic buffer followed by 15 mins with hypotonic (150, 200, or 250 mOsm) anoxic buffer. At each time interval there was a graded increase in cell injury as the duration of anoxia was increased. Control hearts perfused for 75 mins with oxygenated buffer released no CK when perfused with 150 mOsm buffer. Electron microscopy revealed that injured cells contained lesions in sarcomere attachment sites (balloon) and/or in sarcomere-sarcolemmal membrane connections (osmotic). These results suggest that hearts develop latent injury during prolonged anoxic perfusion which can be exposed by application of a physical stress. The extent of injury increases with both the duration of anoxic perfusion and with the degree of stress. It is hypothesized that following prolonged anoxic perfusion, myocardial cells become fragile and respond abnormally to a variety of stresses including the ventricular distensions hypotonic cell swelling, or the effects of reoxygenation.

Cytoskeletal lesions in anoxic myocardial injury. A conventional and high-voltage electron-microscopic and immunofluorescence study.

The role of cell swelling in mediating myocardial injury was studied in control (normoxic) and anoxic Langendorf perfused rat hearts. Control and 45-, 75-, or 90-minute anoxic hearts were exposed to hypotonic (200 mOsm/l) perfusion media to induce osmotic swelling. Anoxic hearts, but not control hearts, released myoglobin when subjected to osmotic swelling. Control hearts, exposed to hypotonic swelling, retained an intact cytoskeletal system of intermediate filaments, microfilaments and microtubules, intact sarcoplasmic reticulum, and intact sarcolemmal membranes. In contrast, swollen anoxic hearts showed a variety of ultrastructural lesions, including formation of large subsarcolemmal blebs associated with lysis of lateral Z-, M-, and A-band intermediate filament attachments, vesiculation of sarcoplasmic reticulum, and rupture of sarcolemmal membranes. Inter-mediate filament attachments with nuclear membranes were also broken, and microtubules disappeared from the perinuclear space. Sarcomere changes included distortion of Z bands, loss of lateral Z band-sarcolemmal attachments, and separations of myofibrils from internal faces in intercalated disks. Immunofluorescence studies of control hearts showed normal staining patterns for the cytoskeletal-associated proteins vinculin, alpha-actinin, and desmin. After 90 minutes of anoxia, hearts exhibited diminished staining of vinculin and alpha-actinin and relatively little change in desmin staining. The results demonstrate that a critical period of anoxia causes lesions in the cytoskeletal apparatus of myocardial cells which correlate with the increased osmotic fragility of irreversibly injured anoxic myocardial cells.

Effects of the free radical scavenger DMTU and mannitol on the oxygen paradox in perfused rat hearts.

The oxygen paradox refers to the abrupt release of cytoplasmic enzymes and severe cellular disruption that occurs following reoxygenation of anoxic perfused hearts. In this study, the ability of a series of oxygen-derived free radical inhibitors and scavenging agents to protect isolated perfused rat hearts from the oxygen-induced enzyme release following 30 or 60 mins of anoxic perfusion (oxygen paradox) and cumene hydroperoxide-induced injury was evaluated. Malondialdehyde (MDA) release, an indicator of lipid peroxidation, and creatine kinase (CK) release, an indicator of cellular injury, were monitored. We evaluated five agents previously reported to scavenge or inhibit the formation of oxygen free radicals. The putative hydroxyl radical scavengers dimethylthiourea (DMTU) and mannitol; catalase, an agent protective against peroxide injury; allopurinol, an inhibitor of xanthine oxidase; and albumin, a non-specific protein control, were evaluated. Coronary flow rates and myocardial temperature were continuously monitored to ensure uniform perfusion conditions. The MDA assay was carefully monitored by constructing standard curves on each experimental day. Addition of 20 microM cumene hydroperoxide to oxygenated perfused hearts caused peroxidative cell injury as evidenced by significant MDA and CK release in the coronary effluent. DMTU and catalase provided near complete protection from cumene hydroperoxide-induced cell injury but did not reduce CK release from hearts subjected to either the mild (30-min) or the severe (60-min) oxygen paradox (reoxygenation-induced injury). Allopurinol caused a significant reduction in MDA release but not CK release from oxygen paradox-injured hearts. Allopurinol and albumin had no significant effect on MDA release from cumene-hydroperoxide-injured hearts. Catalase (300 U/ml) caused a mild but not statistically significant reduction in MDA release from cumene hydroperoxide injury but did not provide protection from the oxygen paradox at either injury level. Mannitol (120 mM), in contrast to DMTU, was ineffective in reducing cumene-induced injury but showed a significant protective effect against oxygen paradox-induced damage. It is concluded that the ability of mannitol to reduce reoxygenation-induced CK release in the oxygen paradox may be due to its osmotic activity and consequent ability to prevent cellular swelling rather than its activity as an oxygen-free radical scavenger.