Reduction of experimental canine myocardial infarct size with prostaglandin E1: inhibition of neutrophil migration and activation

The ability of prostaglandin E1 (PGE1) to reduce myocardial infarct size in an anesthetized open-chest canine model of regional myocardial ischemia and reperfusion was investigated. Administration of PGE1 (100 ng/kg/min into the left atrium) to dogs beginning 10 min after left circumflex coronary artery (LCCA) occlusion and continuing up to 2 hr of reperfusion resulted in a 43% reduction in infarct size expressed as a percentage of the area at risk: control infarct, 44.3 +/- 3.2%, n = 15; PGE1, 27.3 +/- 3.2%, n = 19, P less than .0005. Regional myocardial blood flow (measured with tracer-labeled microspheres in six dogs from each group) was similar between treatment groups at base line, 5 min after LCCA occlusion, 80 min after LCCA occlusion and 1 hr after LCCA reperfusion. In another group of anesthetized dogs, PGE1 was tested for its ability to decrease neutrophil migration into skin lesions. PGE1 at the same concentration that reduced infarct size, decreased the number of neutrophils (assessed by myeloperoxidase activity) that accumulated in skin lesions after intradermal injection of C5a by 63%. In addition, PGE1 inhibited the production of superoxide anion in vitro by zymosan-stimulated canine neutrophils in a concentration-dependent manner. Thus, PGE1 reduces myocardial infarct size and inhibits neutrophil function in vitro and in vivo. These data suggest that the reduction in infarct size by PGE1 may be due to multiple mechanisms including: 1) inhibition of neutrophil migration and activation at the site of tissue injury or 2) reduction in blood pressure which reduces myocardial oxygen demand.     

Antagonism of leukotriene B4 receptors does not limit canine myocardial infarct size

Injection of leukotriene (LT)B4 (0.1-3 micrograms/kg i.v.) in normal anesthetized dogs produced dose-related leukopenia that was accompanied by arterial hypotension and tachycardia at higher tested doses. LTD4 (0.1-3 micrograms/kg i.v.), in contrast, increased arterial blood pressure, lowered cardiac rate and produced little change in arterial blood leukocyte count. Continuous infusion of LY255283 [(1-(5-ethyl-2-hydroxy-4-(6-methyl-6-(1H-tetrazol-5-yl)- heptyloxy)phenyl)ethanone] (0.33 mg/kg/min i.v.), a selective LTB4 receptor antagonist, resulted in near complete inhibition of leukopenic, hypotensive and tachycardic responses to LTB4 (3 micrograms/kg i.v.) challenge over a 6-hr test period. Persistent antagonism of canine LTB4 receptors was associated with high circulating levels of LY255283 that were bound extensively to plasma proteins. In subsequent experiments, myocardial infarct size was measured following 1 hr of occlusion of the circumflex coronary artery and 5 hr of reperfusion in control dogs infused with vehicle, and in dogs receiving LY255283 (0.33 mg/kg/min i.v.). Drug and vehicle were infused continuously beginning 15 min before coronary artery occlusion. LY255283 treatment essentially did not alter base-line cardiovascular parameters or myocardial oxygen demand when alterations were compared to time-related changes observed in control dogs. LY255283 infusion also did not alter the degree of myocardial ischemia or the intensity and duration of cardiac arrhythmias associated with coronary artery occlusion and reperfusion. Resultant infarct sizes were 43 +/- 5% of the left ventricle placed at risk in control dogs and 32 +/- 5% in dogs given LY255283; this difference was not statistically significant. The extent of left ventricle placed at risk was similar between groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of LY203647 on cardiovascular leukotriene D4 receptors and myocardial reperfusion injury.

In vitro studies have shown LY203647 to be a selective antagonist of contractile responses to leukotriene (LT) D4 and LTE4 in guinea pig ileum, trachea and lung parenchyma. In pithed rat, i.v. injection of LTD4 produced pressor responses that were selectively antagonized by LY203647 in a dose-dependent manner [ED50 7.5 (6.0-9.5) mg/kg, i.v.]. In normal anesthetized rats and dogs, LTD4 reduced aortic blood flow and stroke volume in association with systemic vasoconstriction, variable blood pressure responses and no change in cardiac rate. LTD4 did not alter myocardial contractility corrected for alterations in afterload. Pretreatment of rats and dogs with LY203647 (1-10 mg/kg, i.v.) produced dose-related inhibition of the myocardial and systemic hemodynamic effects of LTD4, whereas coadministration of LY203647 reversed established myocardial depression and systemic and pulmonary vasoconstriction during continuous infusion of LTD4 in dogs. LY203647 (10 mg/kg over 90 min, i.v.) infusion in normal dogs abolished or greatly antagonized hemodynamic responses to LTD4 for 6 hr. In subsequent experiments, myocardial infarct size was measured after 1 hr of occlusion of the circumflex coronary artery and 5 hr of reperfusion. LY203647 (10 mg/kg over 90 min, i.v.) treatment did not alter cardiovascular parameters when compared to time-related alterations observed in control dogs. ST segment deviation and the intensity and duration of cardiac arrhythmias associated with coronary artery occlusion and reperfusion also were similar between groups. Resultant infarct sizes were 46 +/- 1 and 45 +/- 1% of the left ventricular mass placed at risk in control and LY203647-treated dogs, respectively. Present data illustrate the prominent cardiac and systemic hemodynamic effects of LTD4 and indicate that LY203647 produces selective and sustained antagonism of cardiovascular LTD4 receptors. Lack of containment of infarction by LY203647 suggests that endogenous cysteinyl-LT do not contribute to reperfusion injury of ischemic myocardium.     

The new K+ channel opener Aprikalim (RP 52891) reduces experimental infarct size in dogs in the absence of hemodynamic changes.

The objective of the present study was to determine the effect of a novel K+ channel opener, Aprikalim (RP 52891; [trans-(-)-N-methyl-2-(3-pyridyl)-2-tetrahydrothio-pyran carbothiamide-1-oxide]), on myocardial infarct size in barbital-anesthetized dogs subjected to 90 min of left circumflex coronary artery occlusion followed by 5 hr of reperfusion. To determine if RP 52891 is mediating its effects by opening adenosine triphosphate regulated potassium channels (KATP), glibenclamide, a KATP channel antagonist was used. Dogs were pretreated with vehicle, a nonhypotensive dose of RP 52891 (10 micrograms/kg + 0.1 microgram/kg/min i.v.), glibenclamide (1 mg/kg; i.v. bolus) or RP 52891 (10 micrograms/kg and 0.1 microgram/kg/min i.v.) after pretreatment with glibenclamide (1 mg/kg i.v. bolus). At the end of reperfusion, myocardial infarct size was determined by triphenyltetrazolium staining. There were no significant differences in systemic hemodynamics, myocardial oxygen demand, collateral blood flow or ischemic bed size among groups with the exception of an increase in coronary blood flow to the ischemic area at 3 and 5 hr of reperfusion in both RP-treated groups. However, myocardial infarct size, expressed as a percentage of the area at risk, was significantly (P less than .05) reduced (38%) by RP 52891 and significantly increased (38%) by glibenclamide (vehicle, 39 +/- 4%; RP 52891, 24 +/- 2%; and glibenclamide, 54 +/- 5%).(ABSTRACT TRUNCATED AT 250 WORDS)     

LY53857, a selective and potent serotonergic (5-HT2) receptor antagonist, does not lower blood pressure in the spontaneously hypertensive rat

LY53857 was a potent antagonist of vascular contraction to serotonin, which is mediated by serotonergic (5-HT2) receptors, with a dissociation constant in vitro of 5.4 X 10(-11) M. Unlike several other serotonin antagonists, LY53857 showed minimal affinity for vascular alpha adrenergic receptors (dissociation constant of 1.4 X 10(-5) M). Thus, LY53857 was a highly potent and selective antagonist at 5-HT2 receptors. In vivo activity paralleled the in vitro observations. In pithed spontaneously hypertensive rats (SHR), LY53857 at 0.1 and 3.0 mg/kg i.p. produced a 22-and 480-fold shift, respectively, in the pressor response to serotonin whereas LY53857 at 10 mg/kg did not alter the pressor response to the alpha receptor agonist, methoxamine. Furthermore, LY53857 administered peripherally also inhibited central serotonin receptors, as evidenced by blockade of the serum corticosterone increase produced by the central actions of the serotonin agonist, quipazine, and by antagonism of tryptamine-induced convulsions in rats. LY53857 in doses that blocked the pressor response to serotonin and that blocked central serotonin receptors did not lower mean arterial blood pressure in the SHR. Thus, the lack of effectiveness of LY53857 to lower blood pressure in the SHR indicates that blockade of both central and vascular serotonin receptors is not a sufficient mechanism to lower blood pressure in this model of hypertension.     

Effect of the thromboxane A2 receptor antagonist SQ 30,741 on ultimate myocardial infarct size, reperfusion injury and coronary flow reserve

We determined if the thromboxane A2 antagonist SQ 30,741 can reduce ultimate myocardial infarct size and reperfusion injury. Anesthetized dogs were subjected to left circumflex coronary artery occlusion for 90 min at which time reperfusion was instituted. In one study, SQ 30,741 (1 mg/kg + 1 mg/kg/hr) was given either 10 min postocclusion (n = 7) or 2 min (n = 9) before reperfusion along with their appropriate vehicle controls in a model of 90 min of occlusion and 5 hr of reperfusion. Infarct size was reduced 50% (P less than .05) when SQ 30,741 was given 10 min postocclusion and 30% (P less than .05) when given only during reperfusion. Flow reserve using maximally dilating doses of adenosine was determined 3 hr postreperfusion in vehicle (10 min postocclusion, n = 10), SQ 30,741 (10 min postocclusion, n = 6) and nonischemic (n = 5) animals. Maximal subendocardial flow was reduced during reperfusion in ischemic animals, but SQ 30,741 improved this compared to vehicle animals (400 +/- 95, 88 +/- 25 and 208 +/- 48 ml/min/100 g; nonischemic, vehicle, SQ 30,741 groups, respectively). To determine if myocardial salvage can be observed 24 hr postocclusion with SQ 30,741 or the cyclooxygenase inhibitor aspirin, dogs were given vehicle (n = 9), SQ 30,741 (10 min postocclusion up to 4 hr postreperfusion) or aspirin (n = 9, 40 mg/kg 30 min preocclusion) and infarct size was determined 24 hr postocclusion (90 min left circumflex coronary artery occlusion + reperfusion).(ABSTRACT TRUNCATED AT 250 WORDS)     

Reduction of experimental canine myocardial reperfusion injury by a monoclonal antibody (anti-Mo1, anti-CD11b) that inhibits leukocyte adhesion.

A monoclonal antibody (904) that binds to a leukocyte cell adhesion-promoting glycoprotein, (Mo1; CD11b/CD18) was administered (1 mg/kg, iv.) to open chest anesthetized dogs 45 min after the induction of regional myocardial ischemia. Ischemia was produced by occluding the left circumflex coronary artery (LCX) for 90 min and then reperfusing for 6 h. There was no difference between control and antibody treated groups with respect to arterial blood pressure, heart rate, or LCX blood flow. Administration of antibody produced no observable effect on circulating neutrophil counts, suggesting that antibody-bound neutrophils were not cleared from the circulation. The mean size of myocardial infarct expressed as percentage of the area at risk of infarction that resulted was reduced by 46% with anti-Mo1 treatment (25.8 +/- 4.7%, n = 8) compared to control (47.6 +/- 5.7%, n = 8; P less than 0.01). The area at risk of infarction was similar between groups. Circulating (serum) antibody excess was confirmed in all 8 anti-Mo1 treated dogs by immunofluorescence analysis. Analysis of ST segment elevation on the electrocardiogram as an indicator of the severity of ischemia suggests that the anti-Mo1 reduces infarct size independent of the severity of ischemia. An additional group of dogs (n = 5) was tested with a control monoclonal antibody of the same subtype (murine IgG1) and was found to produce no significant reduction in myocardial infarct size. Accumulation of neutrophils within the myocardium was significantly attenuated with 904 treatment when analyzed by histological methods. These data demonstrate that administration of anti-Mo1 monoclonal antibody after the induction of regional myocardial ischemia results in reduced myocardial reperfusion injury as measured by ultimate infarct size.     

Topographic correspondence of contrast echocardiographic perfusion mapping and myocardial infarct extent after varying durations of coronary occlusion

After acute coronary occlusion, the extent of dysfunction exceeds the extent of infarction by a variable amount. Contrast echocardiography has been shown to be a good predictor of the extent of acute infarction after permanent occlusion. We used hydrogen peroxide contrast echocardiography to study the temporal and topographic relationship between contrast enhancement and tissue viability during acute myocardial infarction in 32 dogs undergoing 1, 2, 3, or 4 hours of circumflex occlusion before reperfusion. To account for changes in collateral blood flow, contrast studies were performed by aortic root injection immediately before reperfusion. The area, circumference, and transmural extent of the region at risk in vivo by contrast echocardiography were statistically unchanged regardless of the duration of occlusion before reperfusion. Echo contrast defect analysis of the risk region predicted the area, circumference, and transmural extent of infarcts reperfused at 2 or more hours (r = 0.81, 0.84, 0.71, respectively). For the 1-hour occlusion group, contrast defect analysis predicted the circumference at risk but markedly overestimated the area and transmural extent of infarction. These data indicate that the circumferential extent of infarction can be identified by contrast echo and is fixed by 1 hour of occlusion. Infarction progression transmurally within the circumferential boundaries had nearly reached the transmural contrast extent by 2 hours of occlusion in this model. Assuming the development of a similar high contrast agent safe for human injection, aortic root contrast echocardiography could be useful to predict myocardium at risk of infarction early after occlusion. Late after occlusion it could be of value to predict the presence of still viable myocardial layers within the dysfunctional infarct region.     

Comparison of three different A1 adenosine receptor antagonists on infarct size and multiple cycle ischemic preconditioning in anesthetized dogs

A(1) adenosine receptor (AR) antagonists are effective diuretic agents that may be useful for treating fluid retention disorders including congestive heart failure. However, antagonism of A(1)ARs is potentially a concern when using these agents in patients with ischemic heart disease. To address this concern, the present study was designed to compare the actions of the A(1)AR antagonists CPX (1,3-dipropyl-8-cyclopentylxanthine), BG 9719 (1,3-dipropyl-8-[2-(5,6-epoxynorbornyl)]xanthine), and BG 9928 (1,3-dipropyl-8-[1-(4-propionate)-bicyclo-[2,2,2]octyl]xanthine) on acute myocardial ischemia/reperfusion injury and ischemic preconditioning (IPC) in an in vivo dog model of infarction. Barbital-anesthetized dogs were subjected to 60 min of left anterior descending coronary artery occlusion followed by 3 h of reperfusion, after which infarct size was assessed by staining with triphenyltetrazolium chloride. IPC was elicited by four 5-min occlusion/5-min reperfusion cycles produced 10 min before the 60-min occlusion. Multiple-cycle IPC produced a robust reduction ( approximately 65%) in infarct size; this effect of IPC on infarct size was not abrogated in dogs pretreated with any of the three AR antagonists. Surprisingly, in the absence of IPC, pretreatment with CPX or BG 9928 before occlusion or immediately before reperfusion resulted in significant reductions ( approximately 40-50%) in myocardial infarct size. However, treatment with an equivalent dose of BG 9719 had no similar effect. We conclude that the A(1)AR antagonists BG 9719, BG 9928, and CPX do not exacerbate cardiac injury and do not interfere with IPC induced by multiple ischemia/reperfusion cycles. We discuss the possibility that the cardioprotective actions of CPX and BG 9928 may be related to antagonism of A(2B)ARs.     

Deferoxamine pretreatment reduces canine infarct size and oxidative injury

To test whether iron-catalyzed processes contribute to myocardial necrosis during ischemia and reperfusion, we administered the iron chelator, deferoxamine, to chloralose-anesthetized dogs subjected to 90 min of left anterior descending artery occlusion followed by 360 min of reperfusion. Deferoxamine blocks iron-catalyzed hydroxyl radical formation in vitro. Groups of dogs received either pretreatment with deferoxamine or iron-loaded deferoxamine (15 mg/kg over 30 min preocclusion and 2.5 mg/kg/hr during the first 120 min of reperfusion), equal volumes of saline or deferoxamine treatment during reperfusion (15 mg/kg over 30 min beginning at 75 min of occlusion followed by 2.5 mg/kg/hr during the remainder of the first 120 min of reperfusion). Infarct size as a percentage of area at risk was reduced (P less than .05) by deferoxamine pretreatment (29.8 +/- 4.8%, n = 7, +/- S.E.) compared to saline control (46.8 +/- 4.7%, n = 8), deferoxamine reperfusion (50.5 +/- 6.7%, n = 8) or iron-loaded deferoxamine (60.2 +/- 8.6%, n = 3)-treated dogs. Deferoxamine pretreatment also decreased (P less than .05) the release of oxidized glutathione into the coronary sinus during early reperfusion compared to the other groups. There were no differences between groups in area at risk, risk zone blood flow during ischemia or in heart rate-blood pressure product. Deferoxamine did not decrease hydrogen peroxide concentration, neutrophil superoxide anion production or neutrophil adherence in vitro. We conclude that iron-mediated processes, possibly including iron-catalyzed hydroxyl radical formation, contribute to myocardial necrosis during regional ischemia and reperfusion.     

Reduction of Myocardial Infarct Size in the Rabbit by a Carbohydrate Analog of Sialyl Lewis(x)

BACKGROUND: Available data suggest that the accumulation of neutrophils within the myocardium following an ischemic event plays an important role in the pathogenesis of myocardial ischemia/reperfusion injury. It is of interest, therefore, to develop pharmacologic agents designed to inhibit neutrophil adhesion to the endothelium. METHODS AND RESULTS: A synthetic carbohydrate analog to the P-selectin ligand sialyl Lewis(x) (sLe(x)) was evaluated for its ability to protect the myocardium from ischemia/reperfusion injury. Open chest anesthetized rabbits were subjected to 30 minutes occlusion of the left circumflex artery followed by 5 hours of reperfusion. Vehicle or sLe(x) analog (10 mg/kg) was administered intravenously before the onset of reperfusion and every hour during the reperfusion period. Myocardial infarct size in rabbits treated with the sLe(x) analog (10 mg/kg) was administered intravenously before the onset of reperfusion and every hour during the reperfusion period. Myocardial infarct size in rabbits treated with the sLe(x) analog was significantly reduced when compared to rabbits treated with vehicle (28 +/- 9% vs 57 +/- 10% of the area at risk, p <.05). The compound did not alter circulating neutrophil counts or myocardial oxygen demand as determined by the rate-pressure product. Furthermore, neutrophil accumulation within the ischemic region was decreased by 44% (P <.05) in the hearts of animals receiving sLe(x) analog as compared to vehicle. CONCLUSIONS: Carbohydrate derivatives of sLe(x) may be effective in reducing the degree of myocardial injury after ischemia/reperfusion.     

Effect of diltiazem on infarct size, reperfusion flow and flow reserve: the effect of timing of treatment

This study was performed to determine if improved subendocardial reflow seen with diltiazem pretreatment after left circumflex coronary (LCX) occlusion is due to a direct vasodilatory effect of diltiazem on the reperfused bed or due to an increased flow maximum or reserve. In the first part of this study anesthetized dogs were subjected to saline or diltiazem (infused starting before, 10 min after LCX occlusion or 2 min before reperfusion; 0.18 mg/kg + 0.45 mg/kg/hr i.v. for all groups) treatment with a 90-min LCX occlusion and 5-hr reperfusion and myocardial blood flow and infarct size were determined at the end of the experiment. In the second part, maximal flow using intracoronary adenosine was determined at 1 and 3 hr postreperfusion in the ischemic bed when pretreated with saline or diltiazem. Myocardial infarct size was reduced significantly only in animals pretreated with diltiazem compared to saline-treated animals. At 1-hr postreperfusion, subendocardial flow (microspheres) was significantly higher only with diltiazem pretreatment compared to the saline group (100 +/- 17 vs. 54 +/- 8 ml/min/100 g, respectively) and subendocardial reperfusion flows were negatively correlated to infarct size (r = 0.97, P less than .05). Thus, diltiazem only improves reflow and infarct size when infused before occlusion and this improved reflow does not occur via a direct vasodilator action of diltiazem. When maximal vasodilating doses of adenosine were given, flow in the ischemic region was nearly identical for saline and diltiazem pretreated groups despite higher preadenosine flows in the diltiazem group (higher resting flow occurred at the expense of the existing flow reserve).(ABSTRACT TRUNCATED AT 250 WORDS)     

The antianginal agent, ranolazine, reduces myocardial infarct size but does not alter anatomic no-reflow or regional myocardial blood flow in ischemia/reperfusion in the rabbit

It has been suggested that ranolazine protects the ischemic/reperfused heart by reducing diastolic wall pressure during ischemia. However, there is limited information regarding the effect of ranolazine on the anatomic zone of no-flow in a model of acute myocardial occlusion/reperfusion. Before coronary artery occlusion (CAO), open-chest anesthetized rabbits were assigned to vehicle or ranolazine. Hearts received 60 minutes of CAO and 3 hours reperfusion. Ischemic risk zone was comparable in the 2 groups. Ranolazine significantly reduced infarct size. There was a non-significant trend for the no-reflow defect to be smaller in the ranolazine group. Regional myocardial blood flow was similar in both groups in the risk zone during ischemia and at 3 hours reperfusion. Heart rates were similar in both groups, whereas mean arterial pressure was reduced in the ranolazine group. While ranolazine was effective in reducing myocardial infarct size, the mechanism by which it did this was independent of improving perfusion during either ischemia or reperfusion, suggesting that ranolazine's effect of reducing infarct size involves alternative mechanisms.     

Sustained reduction in myocardial reperfusion injury with an adenosine receptor antagonist: possible role of the neutrophil chemoattractant response

Recent studies have demonstrated that three membrane-permeant A(1) receptor antagonists reduced infarct size in a model of ischemia followed by brief reperfusion. However, it was not determined whether cardioprotection was mediated by nonspecific intracellular effects of these highly lipophilic drugs and whether the antagonists only delayed myocardial necrosis without affecting the ultimate infarct size. In the present study, closed-chest dogs were subjected to 90 min of left anterior descending coronary artery occlusion and 72 h of reperfusion and received either a nonmembrane-permeant adenosine receptor blocker that is devoid of direct intracellular effects and is 6-fold selective for the A(1) receptor [1, 3-dipropyl-8-p-sulfophenylxanthine (DPSPX); n = 11] or vehicle (n = 12). DPSPX was administered as three 200-mg boluses 60 min before and 30 and 120 min after reperfusion. The area of necrosis was determined histologically and expressed as a percentage of the area at risk. Baseline predictors of infarct size were similar in the two groups. The ratio of the area of necrosis to the area at risk was less in the DPSPX group (17.8 +/- 4.3% versus 35.0 +/- 1.9%; P =. 012), and DPSPX improved regional ventricular function. Under both basal and stimulated (formyl-Met-Leu-Phe) conditions, suspensions of human neutrophils generated extracellular adenosine levels (approximately 50 nM) sufficient to activate A(1) receptors. Moreover, both DPSPX and 1,3-dipropyl-8-cyclopentylxanthine, a selective A(1) receptor antagonist, significantly reduced the chemoattractant response of neutrophils to formyl-Met-Leu-Phe. We conclude that blockade of A(1) adenosine receptors attenuates myocardial ischemic/reperfusion injury, possibly in part by decreasing the chemoattractant response of neutrophils.     

Role of leukocytes in acute myocardial infarction in anesthetized dogs: relationship to myocardial salvage by anti-inflammatory drugs

The invasion of leukocytes into and around a myocardial infarct was studied in chloralose-anesthetized dogs subjected to 1-hr occlusion of the left anterior descending coronary artery and reperfused for periods up to 5 hr. Polymorphonuclear leukocytes adhering to the endothelium of blood vessels within the ischemic area are evident at the end of the occlusion period. During reperfusion, the leukocytes migrate into the myocardium and large groups of cells can be observed "streaming" toward the irreversibly damaged area after 5 hr reperfusion. Infarcted tissue produces 10 times more 12-hydroxyeicosatetraenoic acid (a metabolite attributed to the invading leukocytes) from arachidonic acid than adjacent "normal" areas of the ventricle. BW755C (10 mg/kg-1 i.v.), which inhibits both the lipoxygenase and cyclooxygenase pathways of arachidonic metabolism, attenuates leukocyte infiltration into the infarcted myocardium, prevents 12-hydroxyeicosatetraenoic acid formation and significantly reduces infarct size (P less than .005). BW755C also significantly diminishes the incidence of cardiac arrhythmias during infarction. In animals where circulating white cells are reduced 60% by treatment with hydroxyurea (20 mg/kg-1 i.v./day for 5 days), there is also a smaller infarct (P less than .01). Indomethacin (5 mg/kg-1 i.v.) and dexamethasone (0.2 mg/kg-1 i.v.), which do not affect leukocyte migration into the ischemic myocardium, do not reduce infarct size. It is proposed that migrating leukocytes contribute to the tissue injury accompanying myocardial ischemia, possibly by the release of proinflammatory mediators such as lipoxygenase products, free radicals (oxygen metabolites) and hydrolytic enzymes. Drugs which reduce the migration and/or activation of leukocytes may be useful in reducing infarct size.     

Evaluation of reperfusion hyperemia with myocardial contrast echocardiography

In this study we used myocardial contrast echocardiography to evaluate reperfusion hyperemia in an open-chest canine model of temporary coronary artery occlusion. Eight dogs had coronary occluders and electromagnetic flow probes on the left circumflex coronary artery. Aortic root injections of agitated sodium diatrizoate and saline solution were used for myocardial contrast. Data were collected at baseline (n = 16), during coronary occlusion (n = 18), immediately after coronary release (n = 18), and 5 minutes after coronary artery release (n = 12). Baseline coronary flow was 23.8 +/- 5.9 ml/min, decreasing to 0 ml/min during coronary occlusion. Immediately after coronary release flow was 96.6 +/- 41 ml/min (p less than 0.001 compared with baseline), and 5 minutes after coronary release flow was 68.2 +/- 27.9 ml/min (p less than 0.001 compared with baseline). The myocardial image intensity change after injection of contrast material was 74.25 +/- 30.6 ml/min at baseline and declined to 10.4 +/- 10.9 ml/min during coronary occlusion (p less than 0.001 compared with baseline). During reperfusion hyperemia image intensity change was 102.3 +/- 33.3 ml/min (p less than 0.001 compared with occlusion, p less than 0.02 compared with baseline, p less than 0.001 compared with remote regions). Considering all observations, myocardial image intensity change after contrast injection correlated positively with coronary flow (r = 0.67, p less than 0.001). Correlations within individual dogs ranged from r = 0.70 to 0.98. We conclude that image intensity change after aortic root injection of echocardiographic contrast correlates with coronary blood flow. Objective measurements of contrast intensity reflect increases in coronary flow associated with reactive hyperemia after coronary occlusion and release.     

Tissue kallikrein is involved in the cardioprotective effect of AT1-receptor blockade in acute myocardial ischemia

Angiotensin-converting enzyme inhibitors limit infarct size in animal models of myocardial ischemia reperfusion injury. This effect has been shown to be due to inhibition of bradykinin degradation rather than inhibition of angiotensin II formation. The purpose of this study was to determine whether angiotensin AT1 receptor blockade by losartan or its active metabolite EXP3174 protects against myocardial ischemia-reperfusion injury in mice and whether this protection is mediated by the kallikrein kinin system. We subjected anesthetized mice to 30 min of coronary artery occlusion followed by 3 h of reperfusion and evaluated infarct size immediately after reperfusion. Losartan (Los) or EXP3174 [2-n-butyl-4-chloro-1-[(2'-(1H-tetrazol-5-yl)biphenyl-4-yI)methyl]imidazole-5-carboxylic acid] were administered 5 min before starting reperfusion at dosages determined by preliminary studies of blood pressure effect and inhibition of angiotensin pressor response. Compared with saline, both drugs significantly reduced myocardial infarct size by roughly 40% (P < 0.001). Pretreatment of mice with the selective AT2 receptor antagonist PD123,319 [S-(+)-1-([4-(dimethylamino)-3-methylphenyl]methyl)-5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazo(4,5-c)pyridine-6-carboxylic acid] did not affect infarct size in the absence of losartan but abolished the reduction in infarct size provided by losartan. In tissue kallikrein gene-deficient mice (TK-/-), losartan no longer reduced infarct size. Pretreatment of wild-type mice with the B2 receptor antagonist icatibant reproduced the effect of TK deficiency. We conclude that AT1 receptor blockade provides cardioprotection against myocardial ischemia-reperfusion injury through stimulation of AT2 receptors. Kallikrein and B2 receptor are major determinants of this cardioprotective effect of losartan. Our results support the hypothesis of a coupling between AT2 receptors and kallikrein during AT1 receptor blockade, which plays a major role in cardioprotection.     

A pharmacologic examination of receptors mediating serotonin-induced bronchoconstriction in the anesthetized guinea pig

The receptors involved in the bronchoconstriction evoked in vivo by intravenous administration to the anesthetized guinea pig of serotonin and serotonin-related agonists have been examined in this study. Animals were pretreated with indomethacin and (+/-)-propranolol to inhibit cyclooxygenase and beta adrenergic receptors, respectively, and pulmonary parameters were obtained with a Buxco pulmonary mechanics computer. Dose-dependent increases in pulmonary resistance and decreases in dynamic lung compliance were produced by serotonin, 2-methyl-serotonin, 5-methoxy-tryptamine, alpha-methyl-serotonin, 5-carboxamidotryptamine, and m-trifluoromethylphenylpiperazine (TFMPP). Responses to all agonists except 2-methyl-serotonin, a selective 5-hydroxytryptamine3 (5-HT3) agonist, were antagonized by the 5-HT2 antagonists, LY53857 and ketanserin. Zaclopride, 1 and 10 mg/kg, a selective 5-HT3 antagonist, blocked responses to 2-methyl-serotonin. A maximally effective dose of LY53857 (1 mg/kg) produced larger shifts of the dose-response curves to serotonin, 5-methoxytryptamine and alpha-methyl-serotonin than did a maximally effective dose of ketanserin (1 mg/kg). Thiorphan, 10 mg/kg, an inhibitor of neutral endopeptidase, potentiated 2-methyl-serotonin and, when studied in the presence of LY53857, also potentiated serotonin, 5-methoxytryptamine and TFMPP. After thiorphan and LY53857, responses to serotonin, but not 5-methoxytryptamine or TFMPP, were blocked by zaclopride. Capsaicin pretreatment of the animals resulted in rightward shifts of the dose-response curves to serotonin, 2-methyl-serotonin and TFMPP, but not to 5-methoxytryptamine or alpha-methyl-serotonin. Potentiation by thiorphan and antagonism by zaclopride of responses to serotonin were still evident after capsaicin pretreatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

心肌声学造影评价快速心房起搏预适应减小心肌梗死范围的实验研究

目的：探讨心肌声学造影技术评价不同频率快速心房起搏预适应减小缺血再灌注后心肌梗死范围的作用。方法：20条健康成年杂种犬随机分为三组：A组6条，为非缺血性快速心房起搏预适应组；B组7条，为缺血性快速心房起搏预适应组；C组7条，为对照组，A、B两组完成3个回合的快速起搏预适应后，与C组一道结扎阻断左前降支冠脉血流60min，随后灌注60min，在持续缺血和再灌注阶段行心肌声学造影检查（MCE），比较各组缺血再灌注后心肌梗死的面积以及心肌坏死我面积与危险区面积之比（NA／RA），并与氯化三苯四氮唑（TTC）心肌组织染色结果呈高度正相关，结论：缺血性和非缺血性快速心房起搏预应对犬心肌缺血再灌注损伤均有保护作用，缺血性快速起搏预适应的保护效力大于非缺血性起搏预适应，心肌声学造影可以准确评价快速心房起搏预应对心肌缺血再灌注损伤的保护作用。     

双羟基黄酮醇对心肌再灌注损伤中局部心肌血流量影响的实验研究

目的:评价双羟基黄酮醇对缺血后冠脉内皮功能的作用以及评价其对致死性心肌缺血再灌注损伤的防治效果。方法:测定意识清醒、无应激状态下绵羊的冠状血管对不同浓度静脉输注的乙酰胆碱的反应,闭塞冠状动脉1 h然后进行7 d的连续再灌注,再灌注的同时进行双羟基黄酮醇或vehicle的治疗,测定缺血状态下和再灌注开始后的血液动力学指数和局部心肌收缩力,评估冠脉血管对乙酰胆碱的反应,并心脏测量梗死面积。结果:(1)双羟基黄酮醇处理后可预防心率上升,显著降低左室舒张末压在再灌注过程中的升高幅度;(2)乙酰胆碱引起的浓度依赖性心率、心搏出量和外周血管传导力的上升并不受到双羟基黄酮醇的处理和心肌缺血/再灌注的影响;(3)双羟基黄酮醇处理后梗死面积显著缩小;(4)双羟基黄酮醇处理可以显著改善危险心肌边缘区域的局部心肌血流。结论:双羟基黄酮醇可显著缩小心肌梗死面积,延长缺血后心肌再灌注中可显著改善内皮功能,可显著减弱危险心肌边缘区局部血流量的进行性损伤。