Myocardial mitochondrial injury induced by pulmonary exposure to particulate matter in rats.

Exposure to air pollution has been associated with acute myocardial ischemia, impaired myocardrial function, and ST-segment depression. Particulate matter (PM)-associated metals, especially vanadium and nickel, have been implicated in observed cardiovascular impairments. We aimed to assess the effect of single intratracheal pulmonary exposure to vanadium-rich respirable oil combustion PM (HP-10) on the intrinsic myocardial ischemic tolerance and mitochondrial integrity in rats. The authors subjected isolated heart tissue slices derived from saline or PM-exposed rats to low glucose low oxygen induced ischemia followed by oxygenated condition with glucose supplementation. Mitochondrial structural integrity was determined by TEM (transmission electron microscopy) and functionality by the 3-(4, 5 dimethylthiazol-2yl)-2, 5 diphenyltetrazolium bromide (MTT) assay. Rats exposed to PM exhibited no apparent inhibition of mitochondrial dehydrogenase activity in oxygenated conditions at 24 or 48 hr post-PM exposure. However, in conditions of simulated ischemia/reoxygenation, these heart slices showed a delayed but consistent and significant decrease in dehydrogenase activity compared to controls at 48 hr after exposure to PM. Electron microscopy revealed significant myocardial mitochondrial injury upon exposure to PM characterized by mitochondrial swelling and fusion. The authors conclude that exposure to soluble vanadium-rich PM induces mitochondrial functional impairment and structural abnormality, which compromises mitochondrial respiration and results in decreased tolerance to ischemia/reoxygenation in rats.

Blood pressure modulation following activation of mast cells by cationic cell penetrating peptides.

Short cell penetrating peptides (CPP) are widely used in vitro to transduce agents into cells. But their systemic effect has not been yet studied in detail. We studied the systemic effect of the cell penetrating peptides, penetratin, transportan and pro-rich, on rat hemodynamic functions. Intra-arterial monitoring of blood pressure showed that injection of the positively charged penetratin and transportan in a wide range of concentrations (2.5-320 µg/kg) caused highly significant transient decrease in the systolic and diastolic blood pressure in a dose dependent manner (p<0.01). Pretreatment with histamine receptors blockers or with cromolyn, a mast cell stabilizing agent, significantly attenuated this effect. Furthermore, in vitro incubation of these both peptides with mast cells line, LAD2, caused a massive mast cell degranulation. In vitro studies showed that these CPP in a wide range of concentrations were not cytotoxic without any effect on the survival of LAD2 mast cell line. In contrast, the less positively charged and proline-rich CPP, pro-rich, had no systemic effects with no effect on mast cell degranulation. Our results indicate that intravenously administrated positively charged CPP may have deleterious consequences due to their induced BP drop, mediated by mast cell activation. Therefore, the major effect of mast cell activation on BP should be considered in developing possible future drug therapies based on the injection of membrane-permeable and positively charged CPP. Nevertheless, lower levels of such CPP may be considered as a treatment of systemic high BP through moderate systemic mast cell activation.

Mast cell activation by fibrinogen-related homologous c-terminal peptides (haptides) modulates systemic blood pressure.

BACKGROUND: Haptides are a family of short peptides homologous to C-termini sequences of fibrinogen chains ß and γ (haptides Cß and preCγ, respectively) which were previously shown to penetrate and bind cells. OBJECTIVES: This work investigates the systemic effect of the haptides with possible clinical implications. METHODS: Intra-arterial monitoring in rats recorded the haptides' effects on systemic blood pressure. In parallel, their effect was also tested in vitro on isolated rat peritoneal mast cells and on human mast cells. RESULTS: Intra-arterial monitoring in rats showed that intravenous administration of low haptides concentrations (35-560 µg/kg rat) caused a shocklike behavior with transient decrease in the systolic and diastolic blood pressure by up to 55% (P < .05) in a dose-dependent manner and a minor increase in their heart rate. Randomly scrambled sequences of the haptides had no such effect, suggesting a specific interaction with receptors. Intravenous administration of blockers to histamine receptors H1 and H2 before haptides administration attenuated this effect. Furthermore, in vitro incubation of human LAD2 mast cell line or isolated rat peritoneal mast cells with the haptides caused degranulation of the mast cells. We found that the haptides Cß and preCγ activated mast cells causing histamine release, resulting in a steep decrease in blood pressure, comparable to anaphylactic shock. CONCLUSION: In treating vascular occlusive diseases, massive fibrinolysis is induced, and haptide-containing sequences are released. We suggest that treatment with histamine receptor blockers or with mast cell stabilizing agents in such pathological conditions may overcome this effect.

Short homologous peptides based on C-terminal sequences of fibrinogen ß- and γ-chains (Haptides) affect cardiovascular function by eNOS inhibition.

Haptides are a family of 19-21-mer cell-binding and permeating peptides homologous to sequences in the C termini on both fibrinogen ß- and γ-chain (Cß and preCγ, respectively). The effect of the Haptides on the cardiovascular system was studied by different assays, including the activity of isolated perfused rat heart and blood vessels in the organ bath. Haptides (50-80 µg/ml) decreased the hemodynamic functions of perfused rat hearts by up to 60% (p < 0.05) in a dose-dependent manner. Whole fibrinogen or a control nonrelated peptide (Cα) did not show such an effect. The NO donor, sodium nitroprusside, reversed the inhibitory effects of Haptides. L-NAME, an endothelial nitric oxide synthase (eNOS) inhibitor, did not further augment the effect of the Haptides. Perfused (FITC)Haptides were attached to the coronary endothelium. In myocardial homogenates and HUVEC, Haptides significantly decreased eNOS activity, but had no effect on the contraction of isolated cultured adult cardiomyocytes. Haptides also significantly enhanced the contraction of rings of rat aorta and human mammary artery vessels ex vivo only when the endothelium was intact. Haptides seem to affect the coronary endothelium, but not the cardiomyocytes, by inhibiting eNOS activity, causing vasoconstriction, temporary ischemia and impaired myocardial function that seem to be related to the amino acid composition of the Haptides.

Occult cardiotoxicity--toxic effects on cardiac ischemic tolerance.

The outcome of cardiac ischemic events depends not only on the extent and duration of the ischemic stimulus but also on the myocardial intrinsic tolerance to ischemic injury. Cardiac ischemic tolerance reflects myocardial functional reserves that are not always used when the tissue is appropriately oxygenated. Ischemic tolerance is modulated by ubiquitous signal transduction pathways, transcription factors and cellular enzymes, converging on the mitochondria as the main end effector. Therefore, drugs and toxins affecting these pathways may impair cardiac ischemic tolerance without affecting myocardial integrity or function in oxygenated conditions. Such effect would not be detected by current toxicological studies but would considerably influence the outcome of ischemic events. The authors refer to such effect as "occult cardiotoxicity." In this review, the authors summarize current knowledge about main mechanisms that determine cardiac ischemic tolerance, methods to assess it, and the effects of drugs and toxins on it. The authors offer a view that low cardiac ischemic tolerance is a premorbid status and, therefore, that occult cardiotoxicity is a significant potential source of cardiac morbidity. The authors propose that toxicologic assessment of compounds would include the assessment of their effect on cardiac ischemic tolerance.

Successful restoration of function of frozen and thawed isolated rat hearts.

OBJECTIVE: Long-term organ preservation for transplantation may allow optimal donor-recipient matching with potential reduction in the incidence and severity of rejection. Complete cessation of metabolism may be obtained by freezing. Previous attempts to freeze intact mammalian hearts were limited to -3.6 degrees C, restricting tissue ice content to 34%. We hypothesized that our method will allow recovery of function of the intact rat heart after freezing to -8 degrees C, a temperature at which most of the tissue water is frozen. METHODS: Isolated rat hearts were attached to a Langendorff apparatus. After normothermic perfusion, cold cardioplegia was induced followed by perfusion with a cryoprotecting agent. Hearts were than frozen to -8 degrees C (45 +/- 8 minutes), thawed, and reperfused (60 minutes). RESULTS: All frozen and thawed hearts regained normal electric activity. At -8 degrees C, ice content was 64.36% +/- 13%. The use of 10% ethylene glycol for cryoprotection (n = 13) resulted in recovery (mean +/- standard deviation) of 49.7% +/- 21.8% of +dP/dt, 48.0% +/- 23.5% of -dP/dt, 65.2% +/- 30.8% of coronary flow, and 50.4% +/- 23.9% of left ventricular developed pressure. Hearts in this group (n = 4) maintained 81.3% +/- 10% viability compared with 69.3% +/- 14% (not significant) in control hearts kept at 0 degrees C for the same duration. Energy stores, represented by adenosine triphosphate and phosphocreatine, were depleted to 12.2 +/- 6.1 micromol/g dry weight and 22.5 +/- 6.4 micromol/g dry weight, respectively, compared with 19.0 +/- 2.5 micromol/g dry weight and 36.6 +/- 3.0 micromol/g dry weight, respectively (P < .05) in the control hearts. The integrity of muscle fibers and intracellular organelles after thawing and reperfusion was demonstrated by electron microscopy. CONCLUSION: We demonstrate for the first time the feasibility of functional recovery after freezing and thawing of the isolated rat heart while maintaining structural integrity and viability.

Ozone administration reduces reperfusion injury in an isolated rat heart model.

BACKGROUND: Accumulating clinical experience with ozone administration for conditions associated with ischemia has been encouraging. The aim of our study was to determine the effect of ozone on reperfusion injury in an isolated rat heart model. METHODS: Isolated rat hearts were perfused with modified Krebs-Henseleit buffer solution via ascending aorta cannulation. After 15 minutes, perfusion was stopped and global ischemia was maintained for 30 minutes, following which perfusion was restarted, and continued for 40 minutes. Baseline hemodynamic measurements (heart rate, left ventricular developed pressure (LVDP), dP/dt, and coronary flow) were taken prior to ischemia, and every 10 minutes after reperfusion was started. Eleven hearts were treated with ozone during reperfusion and eight hearts served as controls. In the treatment group, after 5 minutes of reperfusion, ozone was administered in distilled water via a side arm for 5 minutes. RESULTS: Preischemic baseline hemodynamic measurements and coronary flow were similar in the two groups. Hearts treated with ozone during reperfusion exhibited better recovery than did controls. Mean (+/-SE) percent recovery for treatment and control groups, respectively, was: LVDP 69 +/- 2% vs 51 +/- 6% (p = 0.04); dP/dt 68.9 +/- 13.3% vs 53.7 +/- 20.4% (p = 0.05); and LVDPxHR 61.4 +/- 3.3% vs 44.4 +/- 3.5% (p = 0.02). CONCLUSION: In the isolated rat heart model, treatment with ozone during reperfusion enables better recovery than in controls. Although the mechanism by which ozone exerts its beneficial effect is not identified, it is possibly due to reduction in reperfusion injury.

Occult cardiotoxicity: subtoxic dosage of Bis(2-chloroethoxy)methane impairs cardiac response to simulated ischemic injury.

The effect of Bis(2-chloroethoxy)methane (CEM) on myocardial response to ischemia was tested in rats. CEM was dermally applied for 3 days to F344/N male rats, at 0, 100, 400, or 600 mg/kg/d. Subsequently, left ventricular sections were prepared from each rat heart. Part of the sections from each heart were exposed to 90 minutes of simulated ischemia, followed by 90 minutes of reoxygenation. The rest of the sections were continuously oxygenated. Mitochondrial activity was assessed in the sections by the MTT colorimetric assay, reflecting dehydrogenases redox activity. Myocardial toxicity occurred in response to 400 and 600 mg/kg, characterized by myofiber vacuoles, necrosis, and mononuclear infiltrates. The latter dose was lethal. In sections from rats treated with 400 mg/kg CEM, redox activity was decreased by 21% (p<0.01) in oxygenated conditions and by 45% (p<0.01) in ischemia-reoxygenation, compared to controls. Hearts of rats treated with 100 mg/kg/d CEM showed normal histology. Their mitochondrial activity did not differ from that of untreated rat hearts in oxygenated conditions. However, in ischemia-reoxygenation, their redox activity was significantly lower (by 46%, p<0.01) than that of untreated rat hearts. These results demonstrate that subtoxic dosage of a cardiotoxic agent may cause occult cardiotoxicity, reflected by impaired response to ischemia.

Dexrazoxane prevents myocardial ischemia/reperfusion-induced oxidative stress in the rat heart.

INTRODUCTION: Dexrazoxane (Dex), used clinically to protect against anthracycline-induced cardiotoxicity, possesses iron-chelating properties. The present study was designed to examine whether Dex could inhibit the ischemia/reperfusion (I/R) induced damage to the rat heart. MATERIALS AND METHODS: Isolated perfused rat hearts were exposed to global ischemia (37 degrees C) and 60 min reperfusion. Dex was perfused for 10 min prior to the ischemia, or administered intraperitoneally (150 mg) 30 min prior to anesthesia of the rats. I/R caused a significant hemodynamic function decline in control hearts during the reperfusion (e.g., the work index LVDP X HR declined to 42.7+/-10%). Dex (200 microM) applied during the preischemia significantly increased the hemodynamic recovery following reperfusion (LVDP X HR recovered to 55.7+/-8.8%, p<0.05 vs. control). Intraperitoneal Dex, too, significantly increased the hemodynamic recovery of the reperfused hearts. I/R caused an increase in oxidation of cytosolic proteins, while Dex decreased this oxidation. DISCUSSION: The decrease in proteins carbonylation and correlative hemodynamic improvement suggests that Dex decreases I/R free radical formation and reperfusion injury.

Apomorphine-induced myocardial protection is due to antioxidant and not adrenergic/dopaminergic effects.

Apomorphine (Apo), a dopaminergic agonist used for treatment of Parkinson disease, is a potent antioxidant. In addition to its antioxidative effects, the dopaminergic and adrenergic effects of Apo were studied. Isolated perfused rat hearts were exposed to 25 min of no-flow global ischemia (37 degrees C) and 60 min of reperfusion (I/R, control). Drugs were introduced for the first 20 min of reperfusion. The LVDP of the control group recovered to 54.6 +/- 3.3%. Apo-treated hearts had significantly improved recovery (61.6 +/- 5%, p < 0.05). The recovery of the work index LVDP x HR was even bigger: 67.8 +/- 3.7% (Apo treatment) vs 41.7 +/- 4.6% (control, p < 0.001). Haloperidol, a dopaminergic antagonist, did not affect the recovery with Apo. Propranolol, a beta-adrenergic blocker, initially inhibited the effect of Apo. However, the recovery of the combined group (Apo + propranolol) increased and reached significance (LVDP, p < 0.05 vs control group) after cessation of propranolol perfusion. At 60 min of reperfusion this group was superior to Apo-treated hearts (LVDP, p < 0.05). Propranolol (without Apo) did not improve the hemodynamic recovery. The same pattern of recovery applies also to the recovery of the +dP/dt during the reperfusion. L-DOPA was less effective than Apo. I/R caused significant increase in carbonylation of proteins. Apomorphine inhibited the increase in carbonylation. Haloperidol did not affect this beneficial effect of Apo. L-DOPA significantly decreased the carbonylation of proteins. We conclude that the antioxidative effect of Apo is its main mechanism of cardioprotection.

Oxidized and ubiquitinated proteins may predict recovery of postischemic cardiac function: essential role of the proteasome.

This study examined the hypothesis that postischemic levels of oxidized and/or ubiquitinated proteins may be predictive of functional recovery as they may be indicative of activity of the 20S and/or 26S proteasomes, respectively. Subjecting isolated rat hearts to 15 min of ischemia had no effect on 20S- and 26S-proteasome activities; however, both were significantly (p < 0.05) decreased by 70% and 54%, respectively, following 30 min of ischemia and 60 min of reperfusion, changes associated with increased levels of protein carbonyls and ubiquitinated proteins. Preischemic treatment of hearts with the proteasome inhibitor, MG132, resulted in dose-dependent decreases (p < 0.05) in recovery of postischemic function [MG132 (microM), heart rate x pressure product: 0, 11,158 +/- 2,423; 6, 11,400 +/- 3,009; 12, 5,513 +/- 2,225; 25, 2,325 +/- 992] and increased accumulation of ubiquitinated proteins. Preconditioning with repetitive ischemia (IP) or preischemic treatment with nicorandil (Nic) resulted in a significant increase in postischemic 20S-proteasome activity after 60 min of reperfusion (control, 95 +/- 4; IP, 301 +/- 65; Nic, 242 +/- 61 fluorescence units). Only Nic had similar effects on 26S-proteasome activity. These results support the conclusion that a correlation exists between eventual recovery of postischemic function and levels of oxidized and/or ubiquitinated proteins, a phenomenon that may be dependent on activity of the 20S and 26S proteasomes.

Impaired mitochondrial response to simulated ischemic injury as a predictor of the development of atrial fibrillation after cardiac surgery: in vitro study in human myocardium.

OBJECTIVE: Atrial fibrillation occurs in 20% to 40% of patients after cardiac surgery, but its pathophysiology remains unclear. Recent studies demonstrated preexisting histologic markers that portend the development of postoperative atrial fibrillation. In this prospective study, we focused on mitochondrial dysfunction in response to ischemic stress as a potential predictor for postoperative atrial fibrillation. METHODS: Slices of right atrial trabeculae from 50 patients undergoing elective cardiac surgery were surperfused with oxygenated glucose-containing phosphate-buffered saline solution. After 30 minutes of stabilization, the sections were exposed to 90 minutes of simulated ischemia (nitrogenated phosphate-buffered saline solution without glucose) followed by 90 minutes of reoxygenation (reintroduction of the oxygenated solution). Mitochondrial viability and response were measured by staining with 3-[4.5 dimethylthiazol 2-yl]-2,5-diphenyltetrazolium bromide. The magnitudes of mitochondrial recovery after simulated ischemia and 28 possible risk factors for postoperative atrial fibrillation were entered into univariate and multivariate models. RESULTS: There were no deaths in this group of patients. Nineteen patients (38%) had postoperative atrial fibrillation. Interestingly, no difference in baseline (before simulated ischemia) mitochondrial function was documented between patients who had postoperative atrial fibrillation and those who did not. An independent predictor for postoperative atrial fibrillation was the degree of mitochondrial dysfunction in response to simulated ischemia, as measured by the intensity of the staining. CONCLUSION: This study has identified for the first time an association between mitochondrial dysfunction in response to ischemia and postoperative atrial fibrillation. This finding improves our understanding of the pathophysiology of postoperative atrial fibrillation and may eventually lead us to identify candidates for selective preoperative or early postoperative prophylactic treatment.

Apomorphine prevents myocardial ischemia/reperfusion-induced oxidative stress in the rat heart.

This study examined the hypothesis that low-concentration apomorphine improves postischemic hemodynamic and mitochondrial function in the isolated rat heart model by attenuating oxidation of myocardial proteins. Control and apomorphine-treated hearts were subjected to 35 min of perfusion, 25 min of normothermic global ischemia, and 60 min of reperfusion. Apomorphine (2 microM) was introduced into the perfusate for 20 min starting from the onset of reperfusion. Apomorphine significantly (p <.05) improved postischemic hemodynamic function: work index of the heart (product of LVDP and heart rate) was twice as high in apomorphine-treated hearts compared to controls at the end of reperfusion (p <.01). After isolation of cardiac mitochondria, the respiratory control ratio (RCR) was calculated from the oxygen consumption rate of State 3 and State 4 respiration. Apomorphine significantly improved postischemic RCR (87% of preischemic value vs. 39% in control, p <.05). Using an immunoblot technique, carbonyl content of multiple unidentified myocardial proteins (mitochondrial and nonmitochondrial) was observed to be elevated after global ischemia and reperfusion. Apomorphine significantly attenuated the increased protein oxidation at the end of reperfusion. These results support the conclusion that apomorphine is capable of preventing ischemia/reperfusion-induced oxidative stress and thereby attenuating myocardial protein oxidation and preserving mitochondrial respiration function.

Preconditioning improves postischemic mitochondrial function and diminishes oxidation of mitochondrial proteins.

This study examines the hypothesis that ischemic or pharmacologic preconditioning improves postischemic mitochondrial function by attenuating oxidation of mitochondrial proteins. Isolated rat hearts were perfused for 38 min preischemia, followed by 25 min global ischemia and then 60 min reperfusion. Hearts were preconditioned by two episodes of 3 min global ischemia, followed by 2 min of reflow (IP), or by perfusion with 50 micromol/l nicorandil (Nic) for 10 min, followed by 10 min washout. IP and Nic significantly (p <.05) improved postischemic function, which was abolished by bracketing the protocols with 200 micromol/l 5-hydroxydecoanate (5HD) or 300 micromol/l alpha-mercaptopropionylglycine (MPG). After isolation of cardiac mitochondria, the respiratory control index (RCI) was calculated from State 3 and State 4 respiration. Both IP and Nic significantly (p <.05) improved postischemic RCI, which was depressed 71% from preischemic values in control hearts. The protective effects of IP and Nic were partially abolished by bracketing with 5HD or MPG. Furthermore, mitochondria from ischemic hearts had significantly (p <.05) less ability to resist swelling on Ca2+ loading, which was improved by both IP and Nic. By use of an immunoblot technique, carbonyl content of multiple bands of mitochondrial proteins was observed to be elevated after 25 min ischemia, and still elevated by the end of 60 min reperfusion. Both IP and Nic attenuated the increased protein oxidation observed at the end of ischemia. The protective effect of IP was almost completely abolished by MPG and partially by 5HD, which also partially abolished the protective effect of Nic. These studies support the conclusion that one mechanism for enhanced postischemic function in the preconditioned heart is improved mitochondrial function as a result of decreased oxidation of mitochondrial proteins.

Protection of myocardium by cyclosporin A and insulin: in vitro simulated ischemia study in human myocardium.

BACKGROUND: The efficacy of myocardial protection by cyclosporin A (CSA) and insulin was tested in human right atrial myocardial slices subjected to simulated ischemia and reoxygenation. METHODS: Slices of right atrial trabeculae were obtained from patients undergoing elective cardiac surgery. Trabeculae were incubated with oxygenated glucose containing phosphate buffered saline (O(2), G-PBS). After 30 minutes of stabilization the sections were exposed to 90 minutes of simulated ischemia (N(2), PBS without glucose) followed by 90 minutes reoxygenation (O(2), G-PBS). Cyclosporin A (0.2 micromol/L) or insulin (5 mU/mL) was added during the stabilization period prior the ischemia. Cell viability was measured by using 3-[4.5 dimethylthiazol 2-yl]-2,5-diphenyltetrazolium bromide (MTT), which is cleaved by active mitochondrial dehydrogenases of living cells. RESULTS: The viability of untreated slices (control) was 30.45% +/- 2.5% versus 52.65% +/- 4.4% in the CSA treated slices, p less than 0.001. The extent of protection by CSA was affected by oral antiglycemic drugs (glibenclamide). The effect obtained by CSA was inhibited by 5-hydroxydecanoate (5HD), a specific blocker of mitochondrial K(ATP) channels. Protection of the myocardial slices with insulin appears to be superior and not affected by the medication before surgery. This protection was maximal when insulin was present during both preischemic equilibration and reoxygenation periods (68.9% +/- 9.3% viability with insulin versus 33.2% +/- 6.9% in the control, p < 0.001). CONCLUSIONS: Protection of right atrial trabeculae slices with insulin is superior to that obtained with CSA and is independent of preoperative medication.

Effect of nitric oxide and nitroxide SOD-mimic on the recovery of isolated rat heart following ischemia and reperfusion.

Nitric oxide synthesized from L-arginine in cells has important salutary physiological roles, but can also exert deleterious effects. Nitric oxide (NO) can ameliorate post-ischemic reperfusion myocardial injury, yet formation from NO and O(2)z*(-) of peroxynitrite and its downstream toxic products, such as *OH, *NO(2) and CO(3)*(-), can ultimately exacerbate reperfusion damage. Nitroxide stable radicals, such as 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TPL), unlike SOD, readily penetrate cells and catalytically remove intracellular O(2)*(-). Hence, nitroxides by virtue of catalytic removal of O(2)*(-) would be expected to diminish the adverse effect of NO and lower post-ischemic reperfusion cardiac damage. We show that post-ischemic recovery of hemodynamic functions of isolated perfused rat hearts treated with L-arginine or TPL alone did not differ from that of the control hearts. However, the recovery of hearts treated with the combined regimen of L-arginine and TPL was significantly improved, e.g. the Work Index=(left ventricular developed pressure x heart rate) recovered to 92+/-1.6% (L-arginine and TPL) vs. 59.4+/-5.4% (Control), 60+/-2.9% (L-arginine) and 53.3+/-4.3% (TPL) of the pre-ischemic value; mean+/-SEM, N=10, P<0.001. The enhanced recovery of hemodynamic function of hearts treated with L-arginine and TPL was accompanied by an increased recovery of oxygen consumption during the reperfusion. The combined regimen of L-arginine and TPL reduces the negative effects of NO by either inhibiting the production of ONOO(-) or through reaction with CO(3)z.rad;(-) and *NO(2) radicals formed during the decomposition of peroxynitrite in the presence of bicarbonate, thus promoting cardioprotection following post-ischemic reperfusion.

Cardioprotective and antioxidant effects of apomorphine.

Apomorphine is a potent antioxidant that infiltrates through biological membranes. We studied the effect of apomorphine (2 microM) on myocardial ischemic-reperfusion injury in the isolated rat heart. Since iron and copper ions (mediators in formation of oxygen-derived free radicals) are released during myocardial reperfusion, apomorphine interaction with iron and copper and its ability to prevent copper-induced ascorbate oxidation were studied. Apomorphine perfused before ischemia or at the commencement of reperfusion demonstrated enhanced restoration of hemodynamic function (i.e. recovery of the work index (LVDP x HR) was 69.2 +/- 4.0% with apomorphine pre-ischemic regimen vs. 43.4 +/- 9.01% in control hearts, p < 0.01, and 76.3 +/- 8.0% with apomorphine reperfusion regimen vs. 30.4 +/- 11.1% in controls, p < 0.001). This was accompanied by decreased release of proteins in the effluent and improved coronary flow recovery in hearts treated with apomorphine after the ischemia. Apomorphine forms stable complexes with copper and with iron, and inhibits the copper-induced ascorbate oxidation. It is suggested that these iron and copper chelating properties and the redox-inactive chelates formed by transition metals and apomorphine play an essential role in post-ischemic cardioprotection.

Glucose metabolism, energetics, and function of rat hearts exposed to ischemic preconditioning and oxygenated cardioplegia.

We examined changes induced during ischemia-reperfusion on myocardial metabolism and function by oxygenated warm cardioplegia (CP) and ischemic preconditioning (IP). The postischemic hemodynamic recovery was comparable and significantly better in IP and CP groups, than in untreated hearts (e.g., LVDP recovery was threefold that of the control). The IP hearts reached a pH plateau earlier during ischemia and at considerably higher pH value (pH approximately 6) compared to the other groups (pH approximately 5.5). Postischemic phosphocreatine (PCr) and ATP recoveries were comparable and better in protected groups (approximately 72% and approximately 30% vs approximately 25% and approximately 10% in control, p < 0.0001). Preischemic glycogen was significantly reduced in IP to 49% and increased in CP hearts to 127%. However, the lactate levels at the end of ischemia were similar in all the groups, indicating glucose utilization from extracellular space during ischemia in IP hearts. Thus, similar hemodynamic protection by CP and IP is observed despite increased energy depletion during ischemia in IP. IP and CP protection is expressed through better energetic status and by higher recovery of the TCA cycle activity or enhanced mitochondria-cytosol transport of alpha-ketoglutarate on reperfusion in addition to metabolic changes during ischemia. Glycogen store recovered significantly better in IP than in CP and Control. These results exhibit similar and improved postischemic hemodynamic protection by CP and IP. Increased recovery of postischemic glycogen pool is a protective feature of IP, whereas slightly higher lactate metabolism during reperfusion is a protection component of CP.