Biomedical subjects

S Hoshida

Publications and source records attributed to S Hoshida.

At least 37 records · Page 2Linked to original sources

PubMed1997

Vascular angiotensin-converting enzyme activity in cholesterol-fed rabbits: effects of enalapril.

Many reports have shown inhibitory effects of angiotensin-converting enzyme (ACE) inhibitors on the progression of atherosclerotic plaque lesions in vascular tissue of experimental models. However, no report has shown alterations of ACE activity in vascular tissue during the process of atherosclerosis. We measured ACE activity in plasma and aortic tissue in rabbits fed a cholesterol-rich (1%) or normal diet for 10 weeks. We also evaluated the blood pressure response to angiotensin (Ang) I and II. These data were compared in untreated rabbits and in rabbits receiving chronic treatment with an ACE inhibitor, enalapril (3 mg/kg/day for 10 weeks). ACE activity in aortic tissue, but not in plasma, in cholesterol-fed rabbits was gradually but significantly increased compared with that in noncholesterol-fed rabbits even after the 4-week feeding period, when no atherosclerotic lesion was observed in the aortic tissue. Treatment with enalapril for 10 weeks, but not 4 weeks, significantly reduced the ACE activity in aortic tissue in association with the reductions in the elevated Ang II level and the atherosclerotic plaque area of the aortic tissue. These results indicated that ACE activity in aortic tissue was increased during the early phase of atherosclerotic process.

Angiotensin I↗

PubMed1997

Intravascular ultrasonic evidence by constant cross-sectional area of atherosclerotic plaques during coronary vasomotion in humans.

AIMS: This study aims to visualize ultrasonically deformation of atherosclerotic plaques in human coronary arteries during vasoconstriction and vasodilatation. METHODS AND RESULTS: Intravascular ultrasound detected occult atherosclerosis in angiographically normal coronary arteries of eight patients with chest pain at rest. During the acetylcholine provocative test, intravascular ultrasound monitored deformation of the atherosclerotic plaques. At the last step of the test, intracoronary injection of isosorbide dinitrate caused vasodilation. Under control, acetylcholine-treated, and isosorbide dinitrate-treated conditions, cross-sectional areas of sonolucent circle and vessel lumen were measured. Subtraction of the latter from the former gave the area of atherosclerotic plaque. In the process of vasoconstriction and vasodilation, the plaque area did not change significantly. CONCLUSION: The cross-sectional area of the atherosclerotic plaque appeared to be constant during vasomotion of human coronary arteries.

Acetylcholine↗

PubMed1997

Long-term probucol treatment reverses the severity of myocardial injury in watanabe heritable hyperlipidemic rabbits.

We previously reported that administration of NO donors ameliorates the severity of myocardial injury in cholesterol-fed rabbits. We now evaluated the effects of probucol, a lipid-lowering antioxidant that can preserve endothelium-dependent relaxation (EDR), in the aortas of cholesterol-fed rabbits. We examined the effects of short-term (7 days) or long-term (24 weeks) administration of 1% probucol on the size of infarcts resulting from 30 minutes of coronary occlusion followed by reperfusion (for 48 hours) in Watanabe heritable hyperlipidemic (WHHL) rabbits. Infarcts in untreated WHHL rabbits were significantly larger than those in the rabbits receiving the long-term but not the short-term treatment with probucol (72.2 +/- 5.4%, 37.6 +/- 6.4%, and 66.7 +/- 3.5%, respectively). Long-term probucol treatment also significantly reduced myeloperoxidase activity in both ischemic and nonischemic myocardium and suppressed P-selectin expression in the coronary vasculature. No significant differences were observed in hemodynamic parameters during myocardial ischemia/reperfusion. Long-term probucol treatment significantly reduced the surface area of atherosclerotic plaque lesions in the aorta (24.4 +/- 3.8% vs 46.3 +/- 6.3, P < .05). Moreover, long-term probucol treatment restored acetylcholine-induced EDR in aortic rings but did not affect sodium nitroprusside-induced relaxation. Finally, long-term probucol treatment resulted in significantly elevated cGMP levels in the aorta. These results indicate that long-term probucol treatment significantly ameliorates myocardial injury in heritable atherosclerotic rabbits, perhaps by reducing the accumulation of leukocytes in the myocardium and atherosclerotic vascular lesions. Thus, long-term administration appears to suppress the progression of atherosclerotic vascular disease in this animal model.

Administration, Oral↗

PubMed1997

Effects of preconditioning with ebselen on glutathione metabolism and stress protein expression.

Selenium induces several proteins, including glutathione and stress proteins. These proteins have been shown to be cardioprotective against oxidative injury. To determine whether ebselen, a seleno-organic compound, can also induce these proteins and exert cardioprotective action, we examined the effects of preconditioning with ebselen on glutathione metabolism and stress protein expression and on myocyte injury induced by oxidative stress. Treatment of cultured cardiac myocytes with ebselen (0.3-30 microM) for 24 hr increased the reduced glutathione content. Glutathione reductase activity, but not glutathione peroxidase activity, was significantly elevated in a dose-dependent manner. Pretreatment with ebselen increased the expression of such stress proteins as heat shock protein 70 and heme oxygenase-1 (heat shock protein 32) in cardiac myocytes, as assessed by Western blotting. Expression of heat shock protein 70 was increased only at a higher dose of ebselen (30 microM), whereas expression of heme oxygenase-1 was markedly increased at a lower dose of ebselen (3 microM). Under these conditions, the myocyte injury induced by hydrogen peroxide or simulated ischemia/reperfusion, assessed by the release of lactate dehydrogenase into the culture medium, was reduced by ebselen pretreatment in a dose-dependent manner. Results indicated that cardiac myocytes pharmacologically preconditioned with ebselen for 24 hr exhibited resistance to oxidative injury, possibly via the up-regulation of glutathione metabolism and the expression of stress proteins.

Animals↗

PubMed1996

Amelioration of severity of myocardial injury by a nitric oxide donor in rabbits fed a cholesterol-rich diet.

OBJECTIVES: This study compared the effect of a nitric oxide donor on limiting the size of infarct resulting from myocardial ischemia-reperfusion between atherosclerotic and nonatherosclerotic models. BACKGROUND: Endothelial-derived relaxation in coronary arteries affected by ischemia is substantially impaired after reperfusion, and this impairment may exacerbate the myocardial ischemia-reperfusion injury. In animals with experimental atherosclerosis, release of endothelial-derived relaxing factor is also decreased, and the propagation of myocardial infarction could be exacerbated. METHODS: We examined the extent of myocardial injury induced by ischemia (30 min) and reperfusion (48 hr) in rabbits fed a cholesterol-rich (1%) or normal diet for 10 weeks. We also evaluated the effect of a nitric oxide donor (S-nitroso-N-acetylpenicillamine [SNAP], a nitric oxide precursor (L-arginine) or a degradation product of SNAP (N-acetylpenicillamine) on infarct size in these models. RESULTS: Severity of myocardial injury was significantly exacerbated in cholesterol-fed rabbits (75.2 +/- 4.4% [mean +/- SEM]) compared with that in non-cholesterol-fed rabbits (53.2 +/- 5.2%). This exacerbation was prevented by treatment with SNAP (50.2 +/- 6.4%) but not with L-arginine (70.5 +/- 6.0%) or N-acetylpenicillamine (70.4 +/- 4.8%) in cholesterol-fed-rabbits. However, SNAP did not limit infarct size in non-cholesterol-fed rabbits (60.8 +/- 4.2%). The rate-pressure product was similar during the course of the experiment in all the groups. CONCLUSIONS: Myocardial damage induced by ischemia-reperfusion was significantly exacerbated in rabbits fed a long-term cholesterol-rich diet but was effectively reversed by treatment with a nitric oxide donor. However, this agent did not limit infarct size in normal rabbits. Thus, a nitric oxide donor reduces myocardial infarct size in atherosclerotic but not in nonatherosclerotic rabbits.

Analysis of Variance↗

PubMed1996

Heme oxygenase-1 expression and its relation to oxidative stress during primary culture of cardiomyocytes.

The inducible form of heme oxygenase (heme oxygenase-1) is a heat shock protein 32 (HSP32) whose expression is induced by numerous agents, including heme compounds and heavy metals, and during oxidative stress. The purpose of this study was to examine whether heme oxygenase-1 is induced during primary cell culture of cardiomyocytes and the relation of heme oxygenase-1 expression to oxidative stress levels. Western blot analysis and reverse transcription-polymerase chain reaction analysis showed heme oxygenase-1 expression 12-48 h after isolation of rat neonatal cardiomyocyte for culture. Its expression was barely detected immediately after isolation. Actinomycin D or cycloheximide completely suppressed such expression. Myocardial cells were exposed to oxidative stress during the first 12 h after isolation as assessed by their glutathione redox state; the ratio of reduced glutathione/oxidized glutathione was less than 10. The expression of heme oxygenase-1 was significantly reduced by treatment with reduced glutathione (58% reduction, P < 0.05), but markedly increased by treatment with hydrogen peroxide (65% increase, P < 0.05) 12 h after isolation. Expression of heat shock protein 70 was not significantly changed during primary culture incubation. Results indicate that heme oxygenase-1 is expressed during primary culture of cardiomyocytes. Its expression is closely related to the oxidative stress level of the cultured cells.

Animals↗

PubMed1996

Alpha 1-adrenergic stimulation induces cardiac tolerance to hypoxia via induction and activation of Mn-SOD.

We examined whether or not alpha 1-adrenergic stimulation increases the tolerance of the heart to ischemia using a hypoxia-reoxygenation model of cardiac myocytes. After exposure to norepinephrine (NE; 0.2 microM) for 24 h, the manganese superoxide dismutase (Mn-SOD) content and activity in the cells were increased from 0.61 +/- 0.03 to 0.87 +/- 0.04 microgram/dish and 22 +/- 1 to 55 +/- 4 U/dish, respectively. The specific activity of Mn-SOD was also increased from 36 to 63 U/microgram Mn-SOD protein after the stimulation with NE. Prazosin (2 microM) abolished the increase in Mn-SOD activity (U/mg total protein). Creatine kinase (CK) release after hypoxia (PO2 7 mmHg; 3 h)-reoxygenation (1 h) from cells pretreated with NE in the presence of propranolol and yohimbine for 24 h was attenuated by 48% compared with that from cells without NE stimulation. When antisense oligodeoxyribonucleotides to Mn-SOD were added to myocyte cultures, the increase in Mn-SOD activity (U/mg total protein) and the attenuation of CK release after the addition of NE in the presence of propranolol and yohimbine were not observed. These results suggest that alpha 1-adrenergic stimulation increases the tolerance of myocytes to hypoxia through induction and activation of Mn-SOD.

Adrenergic alpha-Agonists↗

PubMed1996

A nitric oxide donor reverses myocardial injury in rabbits with acute hypercholesterolemia.

We evaluated the propagation of myocardial injury in a model of coronary artery occlusion and reperfusion in control and hypercholesterolemic rabbits. This was done by examining the differences in the infarct size and in the extent of leukocyte accumulation resulting from coronary artery occlusion (30 min) followed by reperfusion (2 or 48 hr) in rabbits fed 1% cholesterol for 4 days vs. controls not fed cholesterol. There was no significant difference in the infarct size in the 2-hr (45.7 +/- 6.7%, n = 8) vs. 48-hr (48.8 +/- 5.8%, n = 9) models of reperfusion in control rabbits. However, infarct size in the cholesterol-fed rabbits at 2 hr (64.0 +/- 4.1%, n = 6) or 48 hr (72.3 +/- 3.0%, n = 8) of reperfusion significantly exceeded that in the corresponding controls (P < .05). The infarct in cholesterol-fed rabbits at 2 hr of reperfusion was smaller than that at 48 hr of reperfusion, but not significantly. Treatment with S-nitroso-N-acetylpenicillamine, a nitric oxide donor, effectively reduced the size of infarct in the cholesterol-fed rabbits. However, treatment with N-acetylpenicillamine had no infarct-limiting effect. When we evaluated the extent of leukocyte accumulation in the ischemic myocardium, as assessed by myeloperoxidase activity, a positive correlation was observed between myeloperoxidase activity and infarct size at 48 hr of reperfusion. Results indicate that the propagation of myocardial ischemia and reperfusion injury in acutely hypercholesterolemic rabbits differed from that in controls. An exogenous nitric oxide donor effectively reduced the size of infarct associated with the reduction in the accumulation of leukocytes 48 hr after reperfusion, which suggests that a reduction in the production of endogenous nitric oxide during ischemia and reperfusion may aggravate the severity of myocardial injury in acutely hypercholesterolemic rabbits.

Animals↗

PubMed1995

Nitric oxide synthase protects the heart against ischemia-reperfusion injury in rabbits.

The role of nitric oxide (NO) in myocardial ischemia-reperfusion injury is still controversial. To determine the role of NO in the propagation of myocardial injury in a coronary artery occlusion-reperfusion model, we examined the effect of a competitive NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), with and without L-arginine, on the size of the infarct resulting from coronary artery occlusion (30 min) followed by reperfusion (48 hr) in rabbits. L-NAME (300 micrograms/kg, as a bolus, and 100 micrograms/kg/min, i.v.) with and without L-arginine (30 mg/kg, as a bolus, and 10 mg/kg/min, i.v.) was administered immediately before coronary occlusion to 60 min after reperfusion. The infarct size in the L-NAME-treated rabbits (75.1% +/- 5.0%, n = 7), assessed as a percentage of infarcted region/ischemic region, was significantly larger than that of control rabbits (51.2% +/- 7.4%, n = 7; P < .05). The increase in infarct size was significantly attenuated by the treatment with L-NAME and L-arginine (62.0% +/- 4.0%, n = 7). However, the infarct size for the treatment with L-NAME and D-arginine (76.7% +/- 5.7%, n = 6) did not differ from that in the L-NAME-treated rabbits. There was no significant difference in the infarct size between L-arginine-treated (60.1% +/- 7.3%, n = 6) and control rabbits. Rate-pressure products, as an index of myocardial oxygen consumption, were comparable in all the groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Oxidoreductases↗

PubMed1994

gamma-Glutamylcysteine ethyl ester for myocardial protection in dogs during ischemia and reperfusion.

OBJECTIVES: The aim of this study was to examine the infarct-limiting effects of gamma-glutamylcysteine ethyl ester, a newly discovered synthetic precursor of glutathione biosynthesis, in a canine model of myocardial infarction. BACKGROUND: Reduced glutathione plays an important role in protecting cells against damage induced by reactive oxygen species during myocardial ischemia and reperfusion. Gamma-glutamylcysteine ethyl ester is capable of penetrating into cells in its intact form and increasing intracellular glutathione levels. METHODS: Dogs were subjected to a 90-min coronary occlusion followed by 5 h of reperfusion. An intravenous bolus injection of gamma-glutamylcysteine ethyl ester (3 or 10 mg/kg body weight) was administered immediately before reperfusion. Regional myocardial blood flow was measured with the use of colored microspheres. RESULTS: Gamma-glutamylcysteine ethyl ester effectively reduced infarct size in a dose-dependent manner (mean +/- SEM 26.4 +/- 3.5% in the low dose group [3 mg/kg, n = 10] and 19.0 +/- 3.4% in the high dose group [10 mg/kg, n = 10]; each p < 0.05 vs. the value in the control group [40.6 +/- 4.8%, n = 10]). There were no differences between the control and treated groups in hemodynamic variables or regional myocardial blood flow either during the ischemic period or after reperfusion. The reduced glutathione content of ischemic myocardium in the control group (0.62 +/- 0.11 mumol/g, p < 0.01) was significantly lower than that in nonischemic myocardium (1.46 +/- 0.07 mumol/g), and it was preserved by treatment in a dose-dependent manner (3 mg/kg, 0.83 +/- 0.06 mumol/g; 10 mg/kg, 0.92 +/- 0.14 mumol/g; each p < 0.05 vs. control level). There were no differences in oxidized glutathione content between nonischemic and ischemic myocardium or among the three groups. CONCLUSIONS: Gamma-glutamylcysteine ethyl ester, a precursor of glutathione, significantly attenuates myocardial ischemia and reperfusion injury when administered immediately before reperfusion.

Animals↗

PubMed1994

Polymorphonuclear leukocytes-induced injury in hypoxic cardiac myocytes.

Growing evidence suggests that free radicals derived from polymorphonuclear leukocytes (PMNs) play an important role in myocardial ischemia-reperfusion injury. To elucidate the cellular mechanism by which activated PMNs exacerbate ischemic myocardial damage, we investigated the extent of cell injury, assessed by the morphological deterioration, free radical generation, and lipid peroxidation in mouse embryo myocardial cells coincubated with activated PMNs. The generation of PMN-derived free radicals was related to the extent of myocardial cell injury. When myocardial cell sheets were subjected to hypoxia and glucose-free media, myocardial cells were injured (cristalysis in the mitochondria and disruption of the sarcolemma) after adding various PMN activators, and the injury extended to the adjacent cells. Chemiluminescent emission and production of thiobarbituric acid-reactive substances in the coincubated cells increased markedly compared with myocardial cells or PMNs alone. The augmented lipid peroxidation coincided with the progression of myocardial cell injury. Catalase inhibited the myocardial cell injury by 52%, the chemiluminescence by 46%, and lipid peroxidation by 50%, whereas superoxide dismutase exhibited less pronounced inhibition. These results indicate that a chain reaction of lipid peroxidation in myocardial cells induced by PMN-derived free radicals closely correlates with membrane damage and contributes to the propagation of irreversible myocardial cell damage.

Animals↗

PubMed1994

Adenosine blockade during reperfusion reverses the infarct limiting effect in preconditioned canine hearts.

OBJECTIVES: The aim was to investigate whether adenosine release after reperfusion contributes to infarct limitation by ischaemic preconditioning. METHODS: Dogs underwent preconditioning with four 5 min cycles of left anterior descending coronary artery (LAD) occlusion and reperfusion, followed by 90 min LAD occlusion and 5 h reperfusion with or without the non-specific adenosine receptor blocker, 8-phenyltheophylline (8-PT). Infarct size was assessed by a dual staining method with triphenyltetrazolium chloride and Evans blue. Blood flow measurements in the subendocardial region were made by infusion of coloured microspheres before occlusion and midway through the sustained occlusion. Transcardiac alteration of neutrophillic function was assessed by luminol-enhanced whole blood chemiluminescence induced by zymosan. RESULTS: Infarct size was significantly reduced in the preconditioned dogs [12.5(SEM 4.0)%, n = 10, p < 0.01] compared with the control dogs [40.5(6.1)%, n = 10], an effect significantly reduced by the 8-PT treatment [23.4(4.9)%, n = 8]. Treatment with 8-PT without ischaemic preconditioning had no effect on infarct size [42.8(6.3)%, n = 7]. There was no difference in myocardial blood flow in the ischaemic or non-ischaemic subendocardial tissue between any pair of the four groups. The ratio of whole blood chemiluminescence in the cardiac vein to that in the carotid artery was considerably reduced in preconditioned dogs compared with that in control dogs after reperfusion. Myeloperoxidase activity in the ischaemic myocardium and the peripheral neutrophil count at the end of the experiment were both also decreased compared with control dogs. In preconditioned dogs treated with 8-PT, neutrophillic function in the coronary circulation after reperfusion was increased compared with that in both controls and preconditioned dogs with no 8-PT treatment. There was no difference in neutrophillic function between the 8-PT-treated dogs with or without ischaemic preconditioning. Treatment with 8-PT increased myeloperoxidase activity in the ischaemic myocardium of the preconditioned dogs, and no difference was seen in activity between dogs treated with 8-PT with or without ischaemic preconditioning. CONCLUSIONS: An adenosine receptor blocker caused a moderate but significant reversal of infarct limitation by ischaemic preconditioning associated with a significant increase of neutrophillic function in the coronary circulation during early reperfusion.

Animals↗

PubMed1994

Calcium overload and cardiac myocyte cell damage induced by arachidonate lipoxygenation.

The accumulation of arachidonic acid and lipoxygenase metabolites of arachidonate occurs in ischemic-reperfused myocardium. Although lipoxygenase inhibitors have been shown to attenuate myocardial infarct size after ischemia-reperfusion, the relationship between arachidonate lipoxygenation and myocardial injury remains unclear. To investigate the direct effect of arachidonate lipoxygenation on cardiac myocytes, isolated rat cardiac myocytes loaded with indo 1 were superfused with Tyrode solution containing arachidonic acid mixed with soybean lipoxygenase. Although neither arachidonic acid nor lipoxygenase alone had any effects, arachidonic acid plus lipoxygenase induced an increase in the twitch amplitude associated with an increased intracellular Ca2+ concentration ([Ca2+]i) and irreversible hypercontracture. Nordihydroguaiaretic acid, a lipoxygenase inhibitor, blocked these effects. Linolenic acid, which is also a lipoxygenase substrate, caused the same effects as arachidonic acid in the presence of lipoxygenase, whereas oleic and stearic acid, which do not function as lipoxygenase substrates, did not. Both ascorbic acid and alpha-tocopherol attenuated an increase in [Ca2+]i and the cellular damage, whereas nicardipine and superoxide dismutase had no effects. These results suggest that lipoxygenase metabolites of arachidonic acid cause intracellular Ca2+ overload and cellular damage to cardiomyocytes, probably through augmentation of lipid peroxidation of the cell membranes by free radicals.

Animals↗

PubMed1994

Ebselen protects against ischemia-reperfusion injury in a canine model of myocardial infarction.

We investigated the infarct-limiting effect of a selenoorganic compound, ebselen [2-phenyl-1,2-benzisoselenazol-3(2H)-one], in a canine coronary artery occlusion-reperfusion model of myocardial infarction. Ebselen, administered 1 h before coronary artery occlusion (50 mg/kg po), significantly reduced infarct size resulting from 90-min coronary artery occlusion followed by 5-h reperfusion (P < 0.05). When we examined the relation between infarct size and plasma ebselen level, infarct size in dogs with plasma ebselen level > 5 microM before reperfusion was significantly smaller (P < 0.05) than that in dogs with plasma ebselen level < or = 5 microM or in the control dogs. This infarct limitation produced by ebselen treatment was associated with an increase in reduced glutathione content and a reduction in myeloperoxidase activity in the ischemic myocardium. No differences between the control and treated groups were found in hemodynamic parameters or regional myocardial blood flow in the course of the experiment. The findings of this study demonstrate that ebselen effectively reduced the myocardial ischemia-reperfusion injury associated with preservation of the glutathione redox state and a reduction in neutrophil infiltration into the ischemic myocardium.

Animals↗

PubMed1994

Induction of manganese superoxide dismutase in rat cardiac myocytes increases tolerance to hypoxia 24 hours after preconditioning.

Manganese superoxide dismutase (Mn-SOD) is induced in ischemic hearts 24 h after ischemic preconditioning, when tolerance to ischemia is acquired. We examined the relationship between Mn-SOD induction and the protective effect of preconditioning using cultured rat cardiac myocytes. Exposure of cardiac myocytes to brief hypoxia (1 h) decreased creatine kinase release induced by sustained hypoxia (3 h) that follows when the sustained hypoxia was applied 24 h after hypoxic preconditioning (57% of that in cells without preconditioning). The activity and content of Mn-SOD in cardiac myocytes were increased 24 h after hypoxic preconditioning (activity, 170%; content, 139% compared with cells without preconditioning) coincidentally with the acquisition of tolerance to hypoxia. Mn-SOD mRNA was also increased 20-40 min after preconditioning. Antisense oligodeoxyribonucleotides corresponding to the initiation site of Mn-SOD translation inhibited the increases in the Mn-SOD content and activity and abolished the expected decrease in creatine kinase release induced by sustained hypoxia after 24 h of hypoxic preconditioning. Sense oligodeoxyribonucleotides did not abolish either Mn-SOD induction or tolerance to hypoxia. These results suggest that the induction of Mn-SOD in myocytes by preconditioning plays a pivotal role in the acquisition of tolerance to ischemia at a later phase (24 h) of ischemic preconditioning.

Adaptation, Physiological↗

PubMed1993

Brief myocardial ischemia affects free radical generating and scavenging systems in dogs.

This study examined whether brief repeated myocardial ischemia altered free radical generating and scavenging activity in a dog model. In dogs preconditioned with four 5-min left anterior descending coronary artery (LAD) occlusions and reperfusions, we examined transcardiac changes in both the function of neutrophils, cells which are major free radical generators, and in myocardial antioxidant enzyme activity, as an indication of free radical scavenging. Neutrophil function was assessed by determining luminol-enhanced whole blood chemiluminescence (CL) induced by zymosan. Blood was taken simultaneously from the carotid artery and the cardiac vein running along the occluded LAD. Preconditioning with sublethal ischemia significantly reduced whole blood CL in the cardiac vein compared with the carotid artery after the first and fourth 5-min reperfusions, while there was no difference in neutrophil count between these sampling sites. Immediately after brief repeated ischemia and reperfusion, manganese-superoxide dismutase (SOD) activity was significantly enhanced, and glutathione reductase activity was markedly reduced in the ischemic, compared with the non-ischemic, myocardium. There were no differences in the myocardial activities of copper, zinc-SOD, glutathione peroxidase, and glutathione S-transferase between the ischemic and non-ischemic regions. Also, no difference was observed between the reduced myocardial glutathione levels in these regions, although the oxidized glutathione level was significantly higher in the ischemic regions of the subepicardial and subendocardial areas. We demonstrated that brief repeated ischemia affects free radical generating and scavenging systems in the ischemic myocardium.

Animals↗

PubMed1993

Transcardiac alteration of neutrophil function relates to myocardial ischaemia/reperfusion injury.

OBJECTIVE: The aim was to define the relation between transcardiac changes in neutrophil function in myocardial ischaemia and the progression of myocardial necrosis. METHODS: Samples of blood from carotid artery, jugular vein, and cardiac vein streaming from the ischaemic area were taken simultaneously in a canine coronary occlusion-reperfusion model of myocardial infarction. Neutrophil function was evaluated by neutrophil count, whole blood chemiluminescence and leucocyte infiltration into the ischaemic myocardium. Myocardial necrosis was assessed by plasma creatine kinase and dual staining technique using Evans blue dye and triphenyltetrazolium chloride. Effects of a free radical scavenger, N-2-mercaptopropionyl glycine (MPG), initiated 15 min before reperfusion and continued during the reperfusion phase, were also examined. RESULTS: Whole blood chemiluminescence of the cardiac vein was reduced at 90 min after coronary artery occlusion as compared to carotid artery [5.8(SEM 0.5) v 7.5(0.7) count x 10(3) cell neutrophil-1 x 10 min-1, p < 0.05], and then increased abruptly after reperfusion to peak after 10 min of reperfusion [7.1(0.7) count x 10(3) cell neutrophil-1 x 10 min-1]. The neutrophil count in cardiac venous blood was significantly reduced within 5 min of reperfusion. MPG significantly attenuated the reperfusion associated increase in cardiac vein whole blood chemiluminescence and the decrease in the cardiac venous blood neutrophil count. The increase in myocardial free radical generation 1-3 h after reperfusion, as assessed by the electron paramagnetic resonance spin trapping technique, was reduced markedly, as was the extent of leucocyte infiltration into the ischaemic myocardium. Under these conditions, administration of MPG significantly reduced myocardial infarct size [40.3(4.5)% v 21.4(4.2)%, p < 0.05]. A marked increase in transcardiac creatine kinase release after reperfusion observed in control dogs was also reduced significantly. CONCLUSIONS: A transient alteration of neutrophil function occurs in the coronary circulation immediately after reperfusion, which may augment neutrophil infiltration and free radical generation in the ischaemic myocardium, leading to the propagation of myocardial ischaemia/reperfusion injury.

Animals↗

PubMed1993

Free radical generation coupled with arachidonate lipoxygenase reaction relates to reoxygenation induced myocardial cell injury.

OBJECTIVE: The role of arachidonate lipoxygenase activity in reoxygenation induced cell injury in adult canine cardiac myocytes was investigated. METHODS: The production of hydroxyeicosatetraenoic acids (HETEs), which are lipoxygenase metabolites, was measured with high pressure liquid chromatography in canine cardiac myocytes cultured under hypoxic conditions and then reoxygenated. Free radical generation was evaluated by electron paramagnetic resonance spectroscopy with a spin trapper, 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and luminol enhanced chemiluminescence emission. Cell injury was estimated in terms of morphological changes and release of intracellular enzymes. Morphological damage to myocytes was quantified in terms of the percentage of hypercontracted "round" cells. The effects of nordihydroguaiaretic acid, AA-861, mepacrine, indomethacin, aspirin, alpha tocopherol, and 2-0-octadecylascorbic acid (CV-3611) on lipoxygenase metabolism, free radical generation and cell injury were also assessed. RESULTS: Cardiac myocytes produced 5-HETE and 12-HETE at less than 0.1 ng.mg-1 protein under normoxic conditions. Production of HETE was greatly increased at five hours of reoxygenation after 45 minutes of hypoxia [5-HETE = 12.0(SEM 0.5), 12-HETE = 23.6(1.1) ng.mg-1 protein]. Both DMPO-OH adduct generation and chemiluminescence emission were considerably increased after one to three hours of reoxygenation, although they increased only slightly after 45 minutes of hypoxia. After five hours of reoxygenation, long rod cells gradually became deformed; 92.0% of the cells were converted to hypercontracted "round" cells. Cell injury and HETE production were significantly suppressed by nordihydroguaiaretic acid (10 microM), AA-861 (2 microM), and mepacrine (10 microM). Indomethacin (10 microM) and aspirin (50 microM) enhanced cell injury and HETE production. alpha Tocopherol and CV-3611 greatly suppressed cell injury and free radical generation, but not HETE production. CONCLUSION: The arachidonate lipoxygenase metabolic pathway may have an important role in reoxygenation induced myocardial cell injury in adult cardiac myocytes, possibly because of the generation of free radicals.

Animals↗