Biomedical subjects

L D Horwitz

Publications and source records attributed to L D Horwitz.

At least 37 records · Page 2Linked to original sources

PubMed1996

Efficacy of lipid soluble, membrane-protective agents against hydrogen peroxide cytotoxicity in cardiac myocytes.

We examined the efficacy of a group of drugs that stabilize the cell membrane and can potentially prevent cytotoxicity in cultured fetal chick cardiac myocytes exposed to hydrogen peroxide (H2O2). The effects of various membrane-protective agents were determined by analysis of the kinetics of lactic dehydrogenase (LDH) release. The kinetic parameters calculated from the data include a rate constant for release of LDH (kb) and the fraction of total LDH that is released from the cells (CIIMax). The CIIMaxs derived from a range of H2O2 concentrations reveal that the mean toxic concentration of H2O2 is 1.1 mM and that the pattern of toxicity is consistent with the damage being directly proportional to the concentration of the free radicals generated from the H2O2. Maximum nontoxic concentrations of three amphiphilic membrane protective agents had no effect upon cytotoxicity from H2O2. The slightly polar lipophilic agent, Trolox C, a vitamin E derivative, was also without protective effect at a maximum nontoxic concentration. The highly lipophilic agent, probucol, had a small protective effect at 50 microM, the maximum concentration we succeeded in solubilizing in the culture medium. However, the lipophilic 21-aminosteroid U74500, delivered to the cells in an emulsion, markedly reduced cytotoxicity from H2O2. The CII Max was significantly reduced and the protection was concentration dependent over a range of concentrations from 50-400 nmol/ml. Furthermore, the inhibition by U74500 was fully consistent with a mechanism of scavenging of free radicals formed during lipid peroxidation. In support of this hypothesis, a dose of 400 nmoles/ml completely prevented an increase in lipid peroxides due to H2O2 exposure, whereas there was a sixfold increase during exposure to H2O2 in untreated myocytes. Thus, a lipid soluble 21-aminosteroid prevented lipid peroxidation and reduced cardiac myocyte injury during exposure to H2O2, probably by scavenging of free radicals formed during lipid peroxidation in the cell membrane, whereas amphiphilic agents, which probably altered the physicochemical structure of the cell membrane but did not scavenge free radicals, were not protective.

Animals↗

PubMed1995

Catalase and hydrogen peroxide cytotoxicity in cultured cardiac myocytes.

We examined the role of intracellular catalase activity in modulating hydrogen peroxide (H2O2)-induced cytotoxicity in cultured chick embryo cardiac myocytes. Injury was quantitated by release of lactate dehydrogenase (LDH). Application of 1.5 mM H2O2 to myocytes caused LDH release beginning at 2 h. Inactivation or inhibition of catalase with aminotriazole or sodium azide increased LDH release but did not cause earlier release. Free catalase which entered or became associated with myocytes, but not catalase bound to agarose beads, which did not enter or become associated with myocytes, was protective. Separate experiments demonstrated that myocyte catalase activity decreased by 27% between 1 and 4 h of H2O2 exposure. Treatment with aprotinin, a protease inhibitor, prevented the H2O2-induced fall in catalase activity at 4 h but treatment with deferoxamine, an iron chelator, had no effect on catalase activity. Thus, with exposure of cardiac myocytes to H2O2, the magnitude of the cytotoxicity is modulated by endogenous or cell associated exogenous catalase. It is proposed that in addition to excessive accumulation of H2O2, a reduction intracellular catalase activity may be required before substantial cell injury occurs during H2O2 exposure. Activation of proteases may cause the reduction in catalase activity in this setting.

Animals↗

PubMed1995

Multiple growth factors are released from mechanically injured vascular smooth muscle cells.

Local release of mitogenic and chemotactic signals during angioplasty-induced vascular injury may initiate restenosis. We investigated whether mechanical injury to vascular smooth muscle cells (VSMC) results in the release of biologically active peptide growth factors. Monolayers of bovine SMC cultures were mechanically injured by cell scraping. Conditioned medium (CM) from control and injured SMC cultures was collected, and the mitogenic activity was measured by [3H]thymidine incorporation in recipient SMC cultures. Mitogenic activity from injured CM was detected within 15 min after injury. When the CM from injured cells was removed 15 min after injury and replaced with serum-free media, there was no detectable mitogenic activity in the replacement CM assessed 1-6 days postinjury. Suramin, a nonspecific peptide growth factor antagonist, significantly inhibited the mitogenic activity of injured CM. Basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF A chain), and epidermal growth factor (EGF) were detected in CM from injured cells by immunoblot analysis. The mitogenic activity of injured CM was significantly inhibited with neutralizing antibodies to bFGF (34%), PDGF-AA (32%), PDGF-BB (25%), and EGF (25%). A neutralizing antibody to transforming growth factor (TGF)-beta had no effect. In conclusion, bFGF, PDGF, and EGF are immediately released from mechanically injured VSMC. VSMC likely contain preformed, biologically active growth factors that are efficiently released from the cell cytoplasm following mechanical injury. Conditioned medium from injured VSMC is highly mitogenic, and this activity is probably due to multiple growth factors interacting synergistically.

Animals↗

PubMed1994

Hydrogen peroxide cytotoxicity in cultured cardiac myocytes is iron dependent.

Because of its potential importance in injury during myocardial ischemia and reperfusion, we assessed mechanisms of hydrogen peroxide (H2O2) cytotoxicity in cultured chick embryo cardiac myocytes. Injury was quantitated by release of lactate dehydrogenase (LDH) or 51Cr, both of which correlated with loss of cell viability assessed by trypan blue exclusion. The iron chelator deferoxamine (0.25-2 mM), but not equimolar iron-loaded deferoxamine, markedly reduced LDH and 51Cr release. Injury was also prevented or attenuated by the diffusible reactive oxygen metabolite scavengers dimethylthiourea (10-20 mM) and N-(2-mercaptopropionyl)-glycine (20 mM). The hydroxyl radical scavenger, dimethyl sulfoxide (200-400 mM), also reduced injury. Other scavengers that probably remained extracellular, superoxide dismutase and mannitol, were ineffective. Thus, with exposure of cardiac myocytes to H2O2, cytotoxicity requires reactions catalyzed by intracellular iron.

Animals↗

PubMed1994

Prevention of lipid peroxidation does not prevent oxidant-induced myocardial contractile dysfunction.

We tested whether, with exposure to an extraneous iron-catalyzed free radical-generating system, prevention of lipid peroxidation with U74006F, a 21-aminosteroid, could also prevent myocardial contractile dysfunction. Rabbits received either U74006F (10 mg/kg iv) or vehicle (V). Thirty minutes later the hearts were excised and perfused by a non-recirculating Langendorff technique. Six U74006F- and six V-treated hearts were exposed for 7.5 min to a .OH-generating system (H2O2 and Fe(2+)-ADP chelate). Myocardial lipid peroxides were measured by glutathione peroxidase-catalyzed oxidation of exogenous glutathione. With exposure to .OH, cytosolic lipid peroxide levels were increased threefold in V-treated hearts, but there was no increase in U74006F-treated hearts. After 30 min of recovery, developed pressure and maximum first derivative of left ventricular pressure were greater in U74006F-treated hearts than in V-treated hearts but were still 50 and 44% of levels in saline hearts, respectively. Coronary flow was markedly reduced after exposure to free radicals and was only slightly less depressed when U74006F was administered. When coronary flow following oxidant exposure was increased by nitroglycerin, U74006F again only modestly improved systolic function. Thus, although U74006F blocked lipid peroxidation, it only slightly improved the ventricular dysfunction caused by .OH. Therefore, factors other than lipid peroxidation play a major role in oxidant-induced myocardial stunning.

Adenosine Diphosphate↗

PubMed1994

Marked reduction in myocardial infarct size due to prolonged infusion of an antioxidant during reperfusion.

BACKGROUND: There has been controversy about whether early reperfusion of myocardial infarcts causes further necrosis mediated by reactive oxygen species or other mechanisms. Unequivocal evidence that therapeutic agents given only during reperfusion can prevent, rather than delay or modify, injury has been sparse. Failure to account for variables, such as collateral blood flow, that influence infarct size independently and attempts to measure infarct size too early in reperfusion may have limited the sensitivity and specificity of some previous studies. METHODS AND RESULTS: After 90 minutes of coronary occlusion and 48 hours of reperfusion in a canine model, we examined the effect on infarct size of intravenous infusion of N-(2-mercaptopropionyl)-glycine (MPG), a diffusible antioxidant. Infarct size and region at risk were measured by post-mortem dual perfusion with triphenyl tetrazolium chloride and Evans blue dyes, and regional myocardial blood flow was measured with radioactive microspheres. Infusion of MPG 100 mg.kg-1.h-1, beginning either 15 minutes before the onset of reperfusion or 30 minutes after the onset of reperfusion and continued until 4 hours of reperfusion and followed by an intramuscular dose, reduced infarct size, normalized for both region at risk and the level of collateral blood flow, by 60% and 45%, respectively. When infusion of MPG was limited to the last 15 minutes of ischemia and the first hour of reperfusion only, the normalized infarct size was reduced by 26%. Heart rate, blood pressure, and their product did not differ among the four groups studied. The plasma half-time of MPG was < 10 minutes. In in vitro experiments MPG was a scavenger of hydrogen peroxide but not of superoxide radical. CONCLUSIONS: After 90 minutes of coronary ligation, infusion of the diffusible hydrogen peroxide scavenger, MPG, for several hours, beginning as late as 30 minutes after the onset of reperfusion, substantially reduced infarct size measured 48 hours later. In this model, necrosis caused by processes during reperfusion may be more extensive than necrosis caused by ischemia alone. Since infusion of this agent for only the first hour of reperfusion was considerably less effective, it appears that most of the oxidant injury leading to necrosis occurred after the first 60 minutes but within the first 4 hours of reperfusion.

Animals↗

PubMed1994

Platelet-induced vascular smooth muscle cell proliferation is modulated by the growth amplification factors serotonin and adenosine diphosphate.

BACKGROUND: Platelet-mediated mechanisms have been implicated in intimal lesion formation following vascular injury. Although the participation of peptide growth factors has been suspected in this process, little has been known about the possible mitogenic role of other platelet factors that are released at sites of vascular injury. METHODS AND RESULTS: We tested the hypothesis that platelet products, which are not peptide growth factors, are important modulators of the platelet-induced smooth muscle cell (SMC) proliferative response by acting as growth amplification factors. In these studies, cell proliferation was assessed by [3H]thymidine incorporation, flow cytometry, and direct cell counting. We examined the potential mitogenicity of several platelet products, including serotonin, ADP, norepinephrine, histamine, platelet-activating factor, the thromboxane A2 mimetic U46619, and bradykinin. Of the platelet products tested, serotonin and ADP induced a synergistic response with peptide growth factors. This synergy was greatest at low growth-factor concentrations. Addition of nonaggregated platelets to quiescent SMC cultures strongly stimulated cell proliferation. Since the addition of suramin to platelet-treated cultures markedly inhibited SMC proliferation, peptide growth factors are most likely the primary mitogens mediating this response. However, platelet-induced proliferation was also markedly reduced by the serotonin antagonists ketanserin and LY53857 (44%), and by the ADP antagonist apyrase (35%). CONCLUSIONS: Therefore, serotonin and ADP contribute significantly, in synergy with peptide growth factors, to the platelet-induced SMC proliferative response. We propose that in vivo serotonin and ADP act as amplification factors for SMC proliferation at sites of vascular injury.

Adenosine Diphosphate↗

PubMed1994

Time course of coronary endothelial healing after injury due to ischemia and reperfusion.

BACKGROUND: Although it has been demonstrated in short-term preparations that ischemia with early reperfusion results in coronary vascular injury manifested by abnormal endothelium-dependent relaxation and increased permeability to plasma proteins, it has not been clear whether these abnormalities are permanent or reversible. METHODS AND RESULTS: In a canine model, regional coronary ischemia was accomplished by 1 hour of left anterior descending coronary artery ligation, and follow-up studies were performed after reperfusion for 1 hour, 48 hours, 2 weeks, or 9 weeks. Vasorelaxation was measured in vitro with preconstricted epicardial coronary artery rings subjected to increasing concentrations of the endothelium-dependent vasodilator ADP and the endothelium-independent vasodilator nitroprusside. At 1 and 48 hours of reperfusion, relaxation of rings from the ischemic reperfused artery to ADP was blunted, but relaxation to nitroprusside was normal. At 2 weeks there was a nonsignificant trend toward a blunted response to ADP in the ischemic/reperfused rings, and at 9 weeks a completely normal response to ADP was observed. Coronary microvascular permeability was assessed by measurement of protein leak index (PLI), by using a double-isotope technique with autologous radiolabeled transferrin and erythrocytes. At 1 and 48 hours of reperfusion there were substantial increases in PLI in the previously ischemic regions, indicative of increased extravascular transferrin. There was a small increase in PLI at 2 weeks but a completely normal measurement at 9 weeks. Electron microscopy of ischemic/reperfused vessels demonstrated endothelial cell swelling and other abnormalities in epicardial arteries and the microcirculation at 48 hours of reperfusion but normal endothelium at 2 weeks of reperfusion. CONCLUSIONS: After 1 hour of regional coronary ischemia, coronary endothelial injury occurs early in reperfusion with abnormalities in epicardial coronary artery endothelium-dependent relaxation, coronary microvascular permeability, and both epicardial coronary artery and microvascular histology. This pattern of injury persists for at least 48 hours, but there is partial functional and complete histological recovery within 2 weeks and complete functional recovery within 9 weeks.

Animals↗

PubMed1993

Peripheral bypass-induced pulmonary and coronary vascular injury. Association with increased levels of tumor necrosis factor.

BACKGROUND: Although cardiopulmonary bypass is associated with systemic complement activation and neutrophil sequestration, it is unclear whether bypass-induced vascular injury is localized and dependent on organ ischemia. We hypothesized that other factors perhaps related to placement of a bypass circuit or to blood perfusion of a pump-oxygenator system may produce vascular injury caused by systemically circulating mediators. In dogs, we determined whether application of a systemic venoarterial bypass circuit with pump-oxygenator perfusion but without pulmonary or cardiac flow diversion (peripheral bypass) leads to vascular injury. Since several features of the postperfusion syndrome after bypass resemble sequelae of endotoxin exposure, we also measured circulating endotoxin and tumor necrosis factor levels. METHODS AND RESULTS: Anesthetized dogs underwent 2 hours of exposure to a pump-oxygenator with peripheral venoarterial bypass. We used a double indicator measurement of pulmonary and coronary vascular permeability (protein leak index [PLI]) as indexes of vascular injury. Compared with controls (n = 7), the pulmonary PLI of dogs undergoing bypass (n = 11) increased more than threefold (18.8 +/- 2.3 vs 63.3 +/- 7.6 x 10(-4) min-1; P < .05) and the coronary PLI increased more than twofold (P < .05). The rate of disappearance of intravascular radiolabeled protein increased threefold after bypass (disappearance t1/2, 241 +/- 35 vs 84 +/- 15 minutes, control vs bypass; P < .05), suggesting a generalized increase in vascular permeability. Circulating endotoxin was detectable in blood samples from 8 of 8 bypass animals (range, 0.24 to 4.56 ng/mL) compared with 2 of 5 controls (P < .05). Tumor necrosis factor levels increased significantly with bypass (6.7 +/- 3.8 vs 146.7 +/- 33.6 U/mL, baseline vs bypass; P < .05) and were only slightly and nonsignificantly increased in controls (7.0 +/- 4.4 vs 18.2 +/- 5.9 U/mL; P = NS). Peak tumor necrosis factor but not peak endotoxin levels correlated with pulmonary and with coronary protein leak. As expected, circulating complement (CH50) levels decreased significantly during bypass, reflecting systemic complement activation. However, the levels correlated poorly with the severity of vascular injury. CONCLUSIONS: We conclude that peripheral pump-oxygenator bypass causes coronary and pulmonary vascular injury that is independent of blood flow diversion and is associated with the appearance of circulating levels of endotoxin and tumor necrosis factor, which may play a role in bypass-induced vascular injury.

Animals↗

PubMed1992

Iron-catalyzed reactions cause lipid peroxidation in the intact heart.

The chemical targets and mechanisms of iron-catalyzed oxidative injury in myocardium are poorly understood. Oxygen metabolites, in the presence of iron, can initiate free-radical chain reactions in unsaturated membrane lipids, generating lipid peroxides and causing membrane injury. We examined whether exposure to iron-catalyzed oxidative injury would increase myocardial lipid peroxide levels as injury evolved in the intact heart. Isolated, buffer perfused rabbit hearts were exposed for 30 min to 100 uM Fe2+/500 uM ADP and 10 uM H2O2 (IRON group, n = 5), saline vehicle (CON group, n = 6) or 500 uM ADP and 10 uM H2O2 without iron (ADP, n = 5). Lipid peroxides were measured in cytosol and membrane fractions by a new method, using the lipid peroxide-induced oxidation of exogenous GSH to GSSG, catalyzed by the enzyme glutathione peroxidase. The results indicated that iron-catalyzed lipid peroxidation occurs in the intact heart during chemically-mediated oxidative injury.

Animals↗

PubMed1992

Trolox C, a lipid-soluble membrane protective agent, attenuates myocardial injury from ischemia and reperfusion.

The lipophilic antioxidant Trolox C, a vitamin E analog, was administered to isolated, buffer-perfused rabbit hearts subjected to 25 min of global stop-flow ischemia and 30 min of reperfusion. In six hearts, Trolox C (200 microM) was infused for 15 min immediately prior to ischemia and for the first 15 min of reperfusion. Six control hearts received only vehicle. Gas chromatography analysis confirmed that effective myocardial levels of Trolox were attained. At 30 min reperfusion, the recovery of left ventricular developed pressure was 56 +/- 3% of baseline in control hearts versus 70 +/- 4% in Trolox-treated hearts (p < .01). There was also significant improvement in recovery of Trolox-treated hearts in diastolic pressure and both maximum and minimum values of the first derivative of left ventricular pressure (dP/dt). Creatine phosphokinase release into the coronary effluent at 30 min of reperfusion was 16.5 +/- 8.4 IU/min in untreated and 6.3 +/- 1.0 IU/min (p < .05) in Trolox-treated hearts. Thus Trolox C, a lipophilic antioxidant, attenuated myocardial injury during stop-flow ischemia and reperfusion.

Animals↗

PubMed1992

The lazaroid U74006F, a 21-aminosteroid inhibitor of lipid peroxidation, attenuates myocardial injury from ischemia and reperfusion.

U74006F, a novel new 21-aminosteroid inhibitor of lipid peroxidation, has been effective in preventing free-radical-mediated injury in central nervous system models. To assess its ability to diminish myocardial injury due to ischemia and reperfusion, U74006F (n = 11) or its vehicle (n = 11) were administered intravenously to New Zealand white rabbits. After allowing for distribution, the hearts were excised and exposed to 30 min of stop-flow ischemia and 30 min of reperfusion on a nonrecirculating Langendorf apparatus. There was diminished creatine phosphokinase release; improved peak positive dP/dt, developed pressure, and peak negative dP/dt; and diminished diastolic pressure in the group treated with U74006F. Thus, pretreatment with U74006F diminished myocardial injury and enhanced systolic and diastolic functional recovery, probably by protecting the lipid component of cell membranes from peroxidation by reactive oxygen metabolites.

Animals↗

PubMed1992

Coronary vascular injury due to ischemia-reperfusion is reduced by pentoxifylline.

Myocardial ischemia and reperfusion cause coronary vascular injury involving both the large epicardial arteries and the microcirculation. Although the mechanisms are unclear, leukocytes appear to play an important role. Since the methylxanthine derivative pentoxifylline (PTX) decreases neutrophil activity in vitro, we hypothesized that it might diminish coronary vascular injury due to ischemia and reperfusion. We investigated the effects of PTX on coronary microvascular and epicardial artery injury in open chest, anesthetized dogs undergoing moderate (60 min) or more prolonged (90 min) ischemia due to left anterior descending coronary artery occlusion followed by 60 min of reperfusion. As an index of microvascular injury, we assessed regional permeability with a dual radioisotope protein leak index (PLI) method. Both ischemic periods with reperfusion increased the PLI of severely ischemic (flow less than or equal to 20/ml/min/100 g) myocardium by 2.5- and 3-fold, respectively, compared to nonischemic (flow greater than or equal to 100 ml/min/100 g) myocardium. Treated dogs received PTX (20 mg/kg bolus plus 0.1 mg/kg/min infusion) before ischemia. PTX reduced the increase in the PLI by 40% after 60 min of ischemia (PLI = 5.87 +/- 0.48 vs. 4.10 +/- 0.52 untreated vs. PTX-treated; P less than .05), and by 25% after 90 min of ischemia (6.84 +/- 0.49 vs. 4.84 +/- 0.42; P less than .05). The amount of protein leak was inversely related to ischemic blood flow, and the magnitude of this relationship was significantly reduced in PTX-treated animals. In arterial rings from untreated dogs exposed to 90 min of ischemia followed by reperfusion, there was impaired relaxation to ADP and acetylcholine, but not to sodium nitroprusside.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Hydrogen peroxide decreases effective refractory period in the isolated heart.

Although previous investigations have concluded that reactive oxygen metabolites contribute to reperfusion arrhythmias, the experimental models employed also had a significant amount of tissue injury, which may have contributed to the observed electrophysiologic effects. We studied whether exposure of the intact heart to a reactive oxygen metabolite at doses that are not associated with histologic evidence of cell necrosis would alter myocardial refractoriness, suggesting that subtle and reversible oxidative stress could alter myocardial electrophysiologic properties and perhaps contribute to ventricular arrhythmias. Isolated rabbit hearts were perfused for 30 min with low doses of hydrogen peroxide (H2O2), either 10(-5), 5 x 10(-6), or 10(-6)-M H2O2 versus vehicle alone; followed by a 30-min washout period without H2O2. Infusion of H2O2 for 30 min decreased ventricular epicardial effective refractory period (ERP) in a dose-dependent manner compared to saline controls (delta ERP). The delta ERP versus time curves during the last 10 min of H2O2 infusion were different (p less than 0.01) for each of the three H2O2 doses. Creatine phosphokinase and reversible oxidized glutathione release occurred during 10(-5)-M H2O2 infusion, but not with lower H2O2 doses. Exposure of the intact heart to low concentrations of H2O2, in a range that caused subtle oxidative injury, decreased ventricular ERP in a dose-dependent manner. Thus, H2O2 generation could contribute to ventricular arrhythmias, even in settings of sublethal and potentially reversible oxidative injury.

Animals↗

PubMed1991

Reactive oxygen metabolite scavengers decrease functional coronary microvascular injury due to ischemia-reperfusion.

The role of reactive oxygen metabolites in ischemia-reperfusion coronary microvascular injury is unclear. To investigate this problem, we tested the effects of the reactive oxygen metabolite scavengers superoxide dismutase (SOD) and dimethylthiourea (DMTU) on ischemia-reperfusion-induced coronary microvascular dysfunction. As an index of vascular function, we assessed microvascular permeability with a double radioisotope protein leak index (PLI) method. Anesthetized dogs underwent 60 min of ischemia via left anterior descending (LAD) occlusion followed by 60 min of reperfusion. Untreated animals (n = 7) received saline. SOD-treated animals (n = 6) received 140 U.kg-1.min-1 (6.6 mg.kg-1.min-1) bovine SOD throughout ischemia and reperfusion. DMTU-treated animals (n = 5) received a 500 mg/kg bolus 30 min before ischemia. At the beginning of reperfusion, radiolabeled autologous protein (113mIn transferrin) and red blood cells (99mTc) were given intravenously for the assessment of permeability. In untreated dogs, ischemia-reperfusion increased the PLI of ischemic (flow less than 20 ml.min-1.100 g-1) myocardium more than threefold compared with that of nonischemic (flow greater than 100 ml.min-1.100 g-1) myocardium (ischemic-to-nonischemic PLI ratio = 3.49 +/- 0.48). SOD reduced the PLI of ischemic myocardium by 45% and DMTU reduced it by 66% (PLI = 9.25 +/- 1.30, 5.04 +/- 1.18, and 3.16 +/- 0.94, untreated, SOD, and DMTU, respectively). The PLI was increased proportional to the regional severity of ischemic blood flow. Both SOD and DMTU reduced the increase in protein leak at all levels of regional ischemic blood flow. Neither SOD nor DMTU increased regional myocardial blood flow to the occluded LAD zone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Existence and participation of xanthine oxidase in reperfusion injury of ischemic rabbit myocardium.

Using a highly specific assay that minimizes enzyme inactivation in vitro, we found that rabbit myocardial tissue contained low levels of xanthine oxidase (XO) and xanthine dehydrogenase (XD) activity that were effectively inhibited by pretreatment of hearts with allopurinol. In parallel, allopurinol treatment also improved ventricular developed pressure, peak systolic pressure, and coronary flow in isolated hearts subjected to 30 min of normothermic global ischemia and 30 min of reperfusion. Although function was protected by allopurinol treatment, creatine kinase (CK) release was not altered by allopurinol. Inhibition of myocardial XO with allopurinol did not increase myocardial ATP or phosphocreatine. In addition, allopurinol did not scavenge superoxide anion or hydrogen peroxide in vitro. The results support the possibility that relatively low amounts of XO activity, similar to levels reported in human myocardium, may contribute to cardiac ischemia-reperfusion injury.

Allopurinol↗

PubMed1991

Effects of phorbol esters on canine coronary artery constriction and dilation in vitro.

The influence of protein kinase C (PKC) activation on canine coronary vasoreactivity was assessed in vitro. Activation of PKC by phorbol 12,13-dibutyrate (PDBu) or phorbol 12-myristate 13-acetate (PMA) caused slow sustained constriction of isolated coronary artery rings. PDBu was a more potent and efficacious constrictor than PMA (169 +/- 21 vs. 81 +/- 7% of maximum KCl constriction). Constriction to PDBu was reduced slightly by deendothelialization and by meclofenamate. Pretreatment with threshold concentrations of PDBu increased constriction to serotonin from 3 +/- 1 to 48 +/- 4% of maximum KCl constriction whether or not the endothelium was present but had no effect on response to the thromboxane analogue U-46619. In addition, in arteries constricted with PDBu, dilations to ADP, thrombin, acetylcholine, and sodium nitroprusside were impaired when compared with arteries constricted with U-46619. These results suggest that activation of PKC in coronary arteries 1) produces potent constriction mediated only in small part by the endothelium and by cyclooxygenase products, 2) potentiates markedly the constrictor response to serotonin by an endothelium-independent mechanism, and 3) attenuates both endothelium-dependent and endothelium-independent vasodilation.

6-Ketoprostaglandin F1 alpha↗

PubMed1991

Myocardial sulfhydryl pool alterations occur during reperfusion after brief and prolonged myocardial ischemia in vivo.

Myocardial sulfhydryl (SH)-containing compounds, including reduced glutathione (GSH), are both defenses against and potential markers of reactive oxygen metabolite injury during ischemia and reperfusion. We examined the alterations in GSH and other myocardial SH pools during reperfusion in anesthetized dogs exposed to brief (15 minutes, n = 7) or prolonged (90 minutes, n = 6) regional ischemia caused by occlusion of the left anterior descending artery. Ninety minutes of ischemia followed by 5 hours of reperfusion, which resulted in myocardial necrosis of 43.9 +/- 4.0% of the area at risk, caused a 22% reduction in total myocardial SH groups (p less than 0.01), a 57% decrease in nonprotein myocardial SH groups (p less than 0.01), a 56% decrease in GSH (p less than 0.01), and a 62% decrease in non-GSH, nonprotein SH groups (p less than 0.02). However, protein SH groups were not significantly reduced (12% decrease, p = NS). Also, myocardial release of GSH and oxidized glutathione (GSSG) into the coronary venous effluent occurred during early reperfusion. In contrast, 15 minutes of ischemia, followed by 30 minutes of reperfusion, did not alter myocardial total SH groups, protein SH groups, or GSH (9% decrease, p = NS); nor was there reperfusion release of GSH or GSSG. However, even with brief ischemia, nonprotein SH groups decreased 23% (p less than 0.05), due mainly to a 59% decrease in the non-GSH, nonprotein SH pool (p less than 0.05). These changes after brief ischemia occurred without alterations in myocardial GSSG or the GSH/GSSG ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗