Iloprost inhibits neutrophil function in vitro and in vivo and limits experimental infarct size in canine heart

The prostacyclin analogue iloprost (ZK 36374) inhibits neutrophil activation in vitro, reduces neutrophil accumulation in inflammatory skin lesions, and reduces ultimate infarct size in an anesthetized open-chest canine model of regional ischemia and reperfusion. Iloprost (0.1-100 microM) inhibited the in vitro production of superoxide anion by canine neutrophils in a concentration-dependent manner. Iloprost (100 ng/kg/min i.v.) inhibited C5a-induced neutrophil migration into inflammatory skin lesions as assessed by the neutrophil-specific enzyme marker, myeloperoxidase. The myeloperoxidase activity determined 2 hours after the intradermal administration of C5a in each of the groups was control 13.3 +/- 1.8 units/g tissue (n = 12) and iloprost 6.5 +/- 0.9 units/g (n = 12), p less than 0.01. Iloprost was administered to anesthetized open-chest dogs (100 ng/kg/min) 10 minutes after left circumflex coronary artery (LCCA) occlusion and continued during the 90-minute occlusion period and the first 2 hours of reperfusion. Regional myocardial blood flow was similar between treatment groups at baseline, 5 minutes and 80 minutes after LCCA occlusion, and after 1 hour of reperfusion. Infarct size, assessed 6 hours after reperfusion, was reduced by iloprost treatment: 22.4 +/- 3.1% of the area at risk (n = 15) compared with 42.4 +/- 3.3% of control (n = 13), p less than 0.01. Iloprost treatment reduced the accumulation of neutrophils (measured by myeloperoxidase activity) in the ischemic myocardium at the interface between infarcted and noninfarcted tissue: control (n = 9) 9.0 +/- 1.8 units/g tissue, iloprost (n = 6) 2.0 +/- 0.4 units/g, p less than 0.01.(ABSTRACT TRUNCATED AT 250 WORDS)     

Identification of a time window for therapy to reduce experimental canine myocardial injury: suppression of neutrophil activation during 72 hours of reperfusion

The cardio-protective effects of neutrophil depletion or inhibition of neutrophil activation early in the course of myocardial reperfusion has been established. Whether these treatments would be effective during extended periods of reperfusion has not been ascertained. Open-chest anesthetized dogs were subjected to left circumflex artery (LCX) occlusion for 90 minutes followed by 72 hours of reperfusion. Dogs were randomized into one of four groups: 1) control; 2) Ilo-2 (iloprost 100 ng/kg/min administered via the left atrium beginning 10 minutes after LCX occlusion and continuing 2 hours into reperfusion); 3) Ilo-48 (iloprost 100 ng/kg/min administered as above until 1 hour after reperfusion then 25 ng/kg/min for 48 hours of reperfusion; or 4) antibody (neutrophil antibody administered before occlusion and 1/2 hourly for 2 hours of reperfusion and then every 24 hours). Myocardial infarct size, as a percentage of the area at risk assessed after 72 hours of reperfusion, was significantly smaller in the antibody-treated group (32.1 +/- 5.0% mean +/- SEM) or Ilo-48 (22.6 +/- 4.0%) treatment group compared with control (48.7 +/- 5.6%) or Ilo-2 (57.6 +/- 5.2%) groups. Regional myocardial blood flow studies demonstrated that all groups developed similar degrees of ischemia. The iloprost-treated groups had lower mean arterial blood pressures during occlusion and reperfusion than groups 1 and 4 (p less than 0.05). Circulating neutrophil counts were increased in groups 1 and 2 at 24 and 48 hours after reperfusion compared to groups 3 and 4 (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Short-term treatment with synchronized coronary venous retroperfusion before full reperfusion significantly reduces myocardial infarct size.

The efficacy of short-term synchronized coronary venous retroperfusion (SRP) before full arterial reperfusion was studied in a canine model. A control group (n = 6) was subjected to 90 minutes of occlusion of the left anterior descending coronary artery, which was followed by 6 hours of reperfusion. In another group (n = 6) the left anterior descending coronary artery was occluded for 2 hours followed by 5.5 hours of reperfusion. In this group SRP was applied for 30 minutes before full reperfusion. Myocardial regional blood flow was measured with the use of colored microspheres. During occlusion of the left anterior descending coronary artery, there was severe myocardial ischemia in both groups. Blood flow in the subendocardial area was, however, significantly better in the SRP group (0.51 +/- 0.17 ml/min/gm after 3.5 hours of reperfusion) than in the control group (0.29 +/- 0.16 ml/min/gm) after 4 hours of reperfusion (p less than 0.05). Left ventricular function was assessed as global ejection fraction from a left ventriculogram. Ejection fraction was reduced during ischemia in both groups (control = 38% +/- 3%, SRP = 32% +/- 8%). This dysfunction remained after 4 hours of reperfusion. Infarct size was assessed by means of triphenyltetrazolium chloride staining. The myocardial area at risk was similar in the two groups (control = 33.1% +/- 5.3%, SRP = 30.6% +/- 6.5%). Infarct size, which was expressed as the percent of the area at risk, was significantly smaller in the SRP group (17.2% +/- 14.6%) than in the control group (36.0% +/- 8.1%; p = 0.0197).(ABSTRACT TRUNCATED AT 250 WORDS)     

Failure of nitroglycerin introduced after prolonged myocardial ischemia to improve collateral blood flow and function in tranquilized dogs

This study investigated whether nitroglycerin can improve ischemic zone blood flow and function when its infusion is delayed following left anterior descending (LAD) occlusion. Nitroglycerin (200 micrograms/min, 11 dogs) or saline (six dogs) was infused for 2 hours starting 2 hours after occlusion. Regional myocardial blood flow (MBF) was measured (9 +/- 1 micron radioactive microspheres) before and at 2 and 4 hours after occlusion. Segmental contraction was determined by cineroentgenography of implanted tantalum markers. For all ischemic samples (defined as MBF less than or equal to 0.4 ml/min/gm), the average improvement in MBF in the epicardial half (EPI) was 0.05 +/- 0.02 ml/min/gm (mean +/- SEM) with nitroglycerin vs 0.06 +/- 0.06 with saline (p greater than 0.5). Improvement in the endocardial half (ENDO) averaged 0.03 +/- 0.03 ml/min/gm with nitroglycerin vs 0.09 +/- 0.08 with saline (p = 0.5). Contraction in the ischemic zone ceased following occlusion and was unaffected by nitroglycerin or saline. Control blood flows in the ischemic region were 22% less in the ENDO (p less than 0.001) and 19% less in the EPI (p less than 0.005) than in nonischemic myocardium. These results indicate that 2 hours after LAD occlusion in dogs, nitroglycerin was unable to improve ischemic zone collateral flow or contractile function compared to untreated controls. Lower ischemic zone control flows indicate that infarct volume expansion may occur within 4 hours after coronary occlusion.     

Failure of iloprost to protect the regionally ischemic, reperfused porcine heart.

The effect of iloprost (Schering AG, Berlin), a stable prostacyclin analogue, was investigated in ischemic, reperfused porcine hearts. The left anterior descending coronary artery (LAD) was distally occluded in 18 pigs for 45 min followed by 3-d of reperfusion. Nine pigs were continuously treated with iloprost at a dose of 25 ng/kg per min. Treatment was started as intracoronary infusion into the proximal LAD 10 min before occlusion. The intercoronary infusion was replaced by an intravenous infusion after 45 min of reperfusion, which was continued until the end of the experiment. Infarct size was determined as the ratio of infarcted (tetrazolium stain) to ischemic myocardium (dye technique). Regional systolic shortening was assessed by sonomicrometry. Myocardial concentrations of adenosine triphosphate were evaluated at the end of the experiment. Generation of free radicals by stimulated polymorphonuclear neutrophils was determined by luminol-enhanced chemiluminescence. Histologic and immunohistologic techniques were applied to characterize the myocardial inflammatory response. Global hemodynamics did not differ between the two groups. Neither infarct size (control group 68 +/- 18%, treated group 74 +/- 14%), recovery of systolic shortening (control group 3 +/- 6%, treated group 6 +/- 6%), nor myocardial adenosine triphosphate concentrations were improved by iloprost treatment. Myocardial inflammatory response remained unaffected by this treatment. The capacity of coronary venous, stimulated polymorphonuclear neutrophils to generate free radicals was slightly suppressed in the treated group before ischemia, at the end of ischemia and during early reperfusion. In this preparation, iloprost did not exhibit any beneficial effect on infarct size, recovery of systolic shortening and myocardial adenosine triphosphate concentrations.     

Regional differences in postischemic recovery in the stunned canine myocardium

To determine if differences exist in the degree of ischemic damage and in postischemic recovery when different coronary arteries are occluded and reperfused, 40 barbital-anesthetized dogs were subjected to brief 15-minute periods of coronary artery occlusion followed by 3 hours of reperfusion ("stunned" myocardium) of the left anterior descending (LAD) or the left circumflex (LCX) coronary arteries. Myocardial segment shortening (%SS) in the subendocardium of nonischemic and ischemic reperfused areas was measured by sonomicrometry, and regional myocardial blood flow was measured by radioactive microspheres. Transmural tissue biopsies were taken at the end of reperfusion for the measurement of adenine nucleotides and total tissue water content. Arterial and local coronary venous blood samples were collected during preocclusion, during occlusion, and at 30 and 180 minutes of reperfusion for determination of blood oxygen content and oxygen consumption in the ischemic area. During occlusion, subendocardial blood flow (LAD flow = 0.11 +/- 0.02; LCX flow = 0.15 +/- 0.04 ml/min/gm), myocardial oxygen consumption (LAD = 2.4 +/- 0.7; LCX = 2.7 +/- 0.7 ml/min/100 gm), and areas of the left ventricle at risk (LAD = 27.4 +/- 2.3%; LCX = 32.4 +/- 2.4) were similar in both groups, thus indicating equivalent degrees of ischemia. There were no differences between groups in hemodynamics throughout the experiment or in the loss of myocardial high-energy phosphates or increase in total tissue water in the ischemic reperfused area at 3 hours of reperfusion. There was a significantly greater loss (p less than 0.05) of systolic wall function during LAD versus LCX occlusion and a greater recovery of segment function from 5 minutes throughout 1 hour of reperfusion after LCX occlusion (p less than 0.05), with no difference in %SS at 2 and 3 hours following reperfusion. Thus, although similar changes occurred in blood flow, metabolite parameters, tissue edema, wall function, and overall hemodynamics when either the LAD or LCX perfusion territories were occluded and reperfused, the loss of systolic wall function and recovery of segment shortening were more variable after regional stunning of the LCX perfusion bed. These data suggest that evaluation of pharmacologic or surgical interventions to improve postischemic functional recovery may be more reliably performed when the LAD coronary artery is the vessel occluded.     

Acute ethanol does not protect against ischemic/ reperfusion injury in rabbit myocardium

Moderate use of alcohol has shown protective effects in coronary artery disease, while excessive use has been associated with cardiomyopathy and hypertension. Since alcohol is a vasodilator, we postulated that it might have protective effects when administered acutely in the setting of ischemia/reperfusion. Therefore, we studied the acute effects of alcohol on myocardial infarction in a rabbit model. Anesthetized, open chest rabbits were subjected to a 30 minute coronary artery occlusion followed by 4 hours of reperfusion. Rabbits were randomized to a control group (n = 20), receiving an infusion of 10 ml normal saline, intravenously, over 10 minutes via a Harvard pump, or an alcohol group (n = 20), receiving a diluted solution of 100% ethanol (1 ml/kg diluted in normal saline to 10 ml total solution) infused in a similar fashion. This infusion regimen resulted in an average blood alcohol level of 110 mg/dl (range 77–129) tested in five rabbits within the study. Ten minutes after infusion, a marginal branch of the circumflex artery was occluded. Regional myocardial blood flow during coronary occlusion and reperfusion was measured using radioactive microspheres. Myocardial ischemic area at risk (AR) was assessed by blue dye injection and myocardial necrosis (AN) by triphenyltetrazolium chloride (TTC) staining. The mean regional coronary blood flow in ischemic tissue was 0.04 ± 0.01 ml/min/g in the control group versus 0.03 ± 0.01 ml/min/g in the experimental group (p = NS) and averaged 1.74 ml/min/g (control) to 1.98 ml/min/g (alcohol) in the nonischemic tissue. All rabbits received comparable ischemic insult: Collateral blood flow and AR were similar in both groups. An overall analysis showed no significant reduction in infarct size (expressed as the percent of necrotic tissue within the area at risk) in the alcohol group (23 ± 3%) compared with the control group (27 ± 4%). In conclusion, alcohol did not reduce infarct size in the rabbit model.     

Sustained limitation of myocardial reperfusion injury by a monoclonal antibody that alters leukocyte function

Pentobarbital anesthetized dogs were subjected to 90 minutes of left circumflex coronary artery (LCCA) occlusion followed by 72 hours of reperfusion. Control or anti-Mo1 (904) F(ab')2 fragments of monoclonal antibodies were administered intravenously at a dose of 1 mg/kg beginning 45 minutes after occlusion and at a dose of 0.5 mg/kg at 12, 24, 36, and 48 hours after reperfusion. Myocardial infarct size expressed as a percentage of the area at risk (IN/AR) measured postmortem after 72 hours of reperfusion was significantly reduced by 904 F(ab')2 (21.6 +/- 2.8%, n = 8) compared with control F(ab')2 (37.4 +/- 5.8%, n = 8; p less than 0.025). There were no significant differences between groups in heart rate, mean arterial blood pressure, rate-pressure product, or LCCA blood flow that could account for a reduced infarct size. Regional myocardial blood flow (RMBF) was determined with 15-microns radiolabeled microspheres. Transmural blood flows (ml/min/g) within the region of myocardium at risk were not statistically different between treatment groups. Infarct size in both groups was related to regional myocardial blood flow, and the relation was shifted downward in the group treated with the anti-Mo1 F(ab')2 antibody (analysis of covariance, p = 0.01). Thus, anti-Mo1 F(ab')2 produces a sustained limitation of myocardial infarct size compared with controls under similar hemodynamic conditions and a similar degree of myocardial ischemia as determined by RMBF. These data suggest that inhibition of neutrophil adhesive interactions (as suggested by the inhibitory effect of anti-Mo1 on canine neutrophil aggregation) may be an effective mechanism for protection against myocardial injury secondary to myocardial ischemia and reperfusion.     

Intracoronary adenosine administration during reperfusion following 3 hours of ischemia: effects on infarct size, ventricular function, and regional myocardial blood flow

Previous studies have demonstrated that adenosine significantly enhances myocardial salvage after 90 minutes of regional ischemia. To determine its effect after prolonged ischemia, closed-chest dogs underwent 3 hours of left anterior descending artery occlusion followed by 72 hours of reperfusion. Intracoronary adenosine (3.75 mg/min; at 1.5 ml/min:total volume = 90 ml; n = 10) or an equivalent volume of saline (1.5 ml/min: total volume = 90 ml; n = 9) was infused into the left main coronary artery during the first 60 minutes of reperfusion. Regional myocardial blood flow was assessed serially with microspheres and regional ventricular function was assessed by contrast ventriculography. Infarct size was determined histologically. Light and electron microscopy were utilized to assess neutrophil infiltration and microvascular injury. Adenosine failed to reduce infarct size expressed as a percentage of the area at risk (38.0 +/- 4.9% versus 34.8 +/- 4.6%; p = NS) or to improve regional ventricular function as measured by the radial shortening method (3.2 +/- 1.8% versus 2.2 +/- 3.1%; p = NS) at 72 hours after reperfusion. Vasodilatory effects were not observed in the endo- and midmyocardial regions of the ischemic zone during adenosine administration. This was associated with a similar extent of capillary endothelial changes and neutrophil infiltration in both adenosine-treated and saline control groups. These results suggest that severe functional abnormalities are present in the vasculature after 3 hours of ischemia and that adenosine therapy is ineffective in enhancing myocardial salvage.     

Treatment of hypertension in diabetes mellitus

We have previously reported that regional wall motion abnormalities in a canine model of acute myocardial infarction may show substantial improvement in the first 6 weeks after infarction. To determine whether the mechanism of this improvement in function is the result of scar contraction within the infarct, we studied the relationship between changes in regional wall motion defined by cross-sectional echocardiography and the regional concentration of radioactive microspheres injected immediately before coronary occlusion and sampled 6 weeks after occlusion. Eight dogs underwent serial echocardiographic and microsphere blood flow measurements immediately before and 30 minutes, 48 hours, 1 week, 3 weeks, and 6 weeks after ligation of the left anterior descending or the left circumflex coronary artery. Wall motion and blood flow were measured in the short-axis section of the left ventricle at the level of the midpapillary muscle in each 10-degree radial segment around the circumference of the ventricle. Infarct histology was assessed at 6 weeks by means of the same radial coordinate system. Control data were collected in a similar manner from four dogs that underwent sham operations and had no histologic evidence of infarction. In all of the animals with infarcts, but not in the sham animals, the calculated preocclusion endocardial and epicardial blood flow values in the histologic infarct zone (252 +/- 44 and 168 +/- 17 ml/min/100 gm, respectively, mean +/- SEM) were significantly higher than those in the normal opposite wall (endocardial: 106 +/- 3 ml/min/100 gm, p less than 0.01); epicardial: 108 +/- 3 ml/min/100 gm, p less than 0.01. The location and circumferential extent of myocardium showing this elevation of preocclusion blood flow correlated well (r = 0.93, p less than 0.001) with the location and circumferential extent of the histologic infarct. The amount of wall motion abnormality, measured from the "correlation plot area," decreased significantly from its maximum value of 39 +/- 3 degrees at 48 hours after coronary occlusion to 3 +/- 1 degrees (p less than 0.001) at 6 weeks after occlusion. The ratio of the preocclusion transmural blood flow in the infarct zone to that in the noninfarct zone, a measure of the condensation of the microspheres injected before coronary occlusion, and therefore of the degree of scar contraction at 6 weeks, correlated well (r = 0.83, p less than 0.01) with the recovery of wall motion 6 weeks after infarction.(ABSTRACT TRUNCATED AT 400 WORDS)     

The xanthine oxidase inhibitor oxypurinol does not limit infarct size in a canine model of 40 minutes of ischemia with reperfusion

Free radicals such as superoxide (.O2-) produced by xanthine oxidase might cause cell death during reperfusion after myocardial ischemia. The effect of the xanthine oxidase inhibitor allopurinol on infarct size in ischemia-reperfusion models has been variable, possibly because of differences in treatment duration. Adequate inhibition of xanthine oxidase may require a sufficient pretreatment period to permit conversion of allopurinol to oxypurinol, the actual inhibitor of superoxide production. To test more definitively whether xanthine oxidase-derived free radicals cause cell death during reperfusion, the effect of oxypurinol on infarct size was evaluated in an ischemia-reperfusion model. Open chest dogs underwent 40 min of circumflex coronary artery occlusion followed by reperfusion for 4 days. Twelve dogs were treated with oxypurinol (10 mg/kg body weight intravenously 10 min before occlusion and 10 mg/kg intravenously 10 min before reperfusion) and 11 control dogs received drug vehicle alone (pH 10 normal saline solution). Nine control dogs from a concurrent study also were included. Infarct size was measured histologically and analyzed with respect to its major baseline predictors, including anatomic area at risk and collateral blood flow (measured with radioactive microspheres). Infarct size as a percent of the area at risk averaged 23.8 +/- 2.7% (mean +/- SEM) in the oxypurinol group (n = 10) and 23.1 +/- 4.2% in the control group (n = 17) (p = NS). Collateral blood flow to the inner two thirds of the ischemic wall averaged 0.08 +/- 0.01 ml/min per g in the oxypurinol group and 0.09 +/- 0.02 ml/min per g in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Myocardial reperfusion injury in the canine model after 40 minutes of ischemia: effect of intracoronary adenosine

To explore the contribution of reperfusion injury to final infarct size after a short duration of ischemia, closed-chest dogs underwent 40 minutes of proximal left anterior descending artery occlusion followed by 3 days of reperfusion. Animals randomly received intracoronary adenosine (n = 8) at 3.75 mg/min during the first hour of reperfusion or no therapy (control, n = 9). Infarct size was measured histologically. Regional ventricular function was determined with contrast ventriculography. The risk region was similar and collateral blood flow in the inner two thirds of the ischemic zone was markedly reduced in both groups (adenosine: 0.05 +/- 0.07 ml/min/gm; control: 0.02 +/- 0.07 ml/min/gm; p = NS). Infarct size as a percent of the area at risk was significantly reduced in the adenosine group (5.0 +/- 1.3% versus 13.5 +/- 3.2%; p = 0.03), associated with a trend for improved recovery of regional ventricular function. Relative endothelial preservation was seen in the adenosine group. These results suggest that reperfusion injury contributes to final myocardial cell necrosis in the closed-chest canine model subjected to 40 minutes of regional ischemia.     

Acceleration of cell necrosis following reperfusion after ischemia in the pig heart without collateral circulation

A study of whether reperfusion accelerates cell death was performed in 35 pig hearts without collateral circulation. In 15 animals, the distal one-third of the left anterior descending coronary artery was occluded for 1 hour followed by 1-, 3-, or 7-hour reperfusion in 5 animals each. As controls, 5 hearts each were examined after 1, 2, 4 and 8 hours of occlusion of the artery without reperfusion. Heart rate and aortic pressure before and during occlusion and reperfusion did not change in any group. The subepicardial and subendocardial regional blood flow decreased to almost zero in all hearts after occlusion (85 +/- 1 to 2 +/- 2) but recovered during reperfusion (65 +/- 15 ml/100 g/min). Specimens were histologically examined by an enzyme method using nitrotetrazolium blue, an immunohistochemical method using myoglobin antibody, by staining with hematoxylin-eosin and Masson's trichrome. In the control hearts, clear demarcation of the infarct area was observed 4 hours after occlusion. However, in the reperfusion group, clear demarcation of the infarct was seen after 1-hour reperfusion, namely, 2 hours after the onset of infarct. Demarcation was seen not only in the tissue with contraction band necrosis, but also in the tissue with coagulation necrosis. Therefore, it is concluded that reperfusion accelerates cell death due to both contraction band necrosis and coagulation necrosis.     

The intracoronary infusion of superoxide dismutase during the initial liberation of oxygen free radicals induced by reperfusion. The effect on the infarct size after 60 minutes of coronary occlusion in the pig model]

The role of oxygen free radicals (OFR) generated early during myocardial reperfusion in the genesis of myocardial necrosis was studied in 26 pigs submitted to transient coronary occlusion followed by one of three different reperfusion protocols. In group A, a selective intracoronary infusion of a Ringer solution was started after 60 min of coronary occlusion, and reperfusion was performed 4 min later. The infusion was maintained during the first 6 min of reperfusion at a rate of 3 ml/min. In group B, the Ringer solution administered during reperfusion contained a high concentration (2.778 U/ml) of superoxide dismutase (SOD). In group C, reperfusion was performed after 60 min of coronary occlusion with no intracoronary infusion. Twenty-four hours later the heart was excised and the area at risk and infarct size were measured by in vivo fluorescein injection and triphenyl-tetrazolium chloride staining respectively. The area at risk was similar in the 3 groups: 15.03 +/- 2.6%, 13.26 +/- 3.3% and 16.34 +/- 6.7% of ventricular mass in groups A, B, and C, respectively (p = 0.42). No differences between groups were observed in infarct size, either when measured as a percent of ventricular mass (10.04 +/- 3.8%, 9.31 +/- 3.8% and 10.1 +/- 2.4% in groups A, B, and C, p = 0.91) or as a percent of the area at risk (64.63 +/- 18.5%, 67.81 +/- 16.1%, and 61.35 +/- 6.7%, respectively, p = 0.72). Thus, the intracoronary administration of SOD during the early reperfusion has not beneficial effect on infarct size. This results suggest that the early burst of OFR is not a major determinant of infarct size in the pig.     

Reduction of myocardial reperfusion injury by intravenous adenosine administered during the early reperfusion period

Adenosine influences the function of several cell types thought to be involved in the pathogenesis of myocardial reperfusion injury. We have previously demonstrated that intracoronary administration of adenosine enhances myocardial salvage 24 hours after reperfusion. To determine if these beneficial effects could be obtained during a prolonged period of reperfusion using an intravenous route of administration, 22 closed-chest dogs were subjected to 90 minutes of proximal left anterior descending coronary artery occlusion and 72 hours of reperfusion. Animals randomly received either intravenous adenosine (0.15 mg/kg/min) or an equal volume of Ringer's lactate during the first 150 minutes of reperfusion. The area at risk was defined in vivo with Monastral blue, and infarct size was measured histologically with Mallory's trichrome stain. Serial global and regional ventricular function were determined with contrast ventriculography and analyzed using a computerized radial shortening method. Biopsies were obtained from the central ischemic zone to assess endothelial ultrastructure and capillary obstruction. No significant effects in heart rate or blood pressure were noted during adenosine infusion. Transmural collateral blood flow during ischemia was similar in the groups. Infarct size expressed as a percentage of the anatomical area at risk was significantly less in the adenosine-treated group (35.3 +/- 4.3% in controls versus 17.1 +/- 4.3% in treated animals, p less than 0.01). A progressive decrease in transmural blood flow was noted in control animals during reperfusion, resulting in a significant reduction at 3 hours compared with the preocclusion value (0.69 +/- 0.11 ml/min/g [at baseline versus 0.45 +/- 0.10 ml/min/g at 3 hours, p less than 0.05]). In contrast, flow in adenosine animals at 3 hours was similar to baseline values (0.91 +/- 0.15 ml/min/g at baseline versus 0.98 +/- 0.14 ml/min/g at 3 hours, p = NS) and was significantly higher (p less than 0.05) than the control group. Radial shortening in the ischemic zone was significantly improved at 3 (-2.6 +/- 2.8% in controls versus 11.6 +/- 3.3% in treated animals, p less than 0.01) and 72 hours (5.5 +/- 2.0% in controls versus 17.3 +/- 3.5% in treated animals, p less than 0.01) after reperfusion in treated animals. Electron microscopy showed reduced neutrophil and erythrocyte plugging of capillaries with relative preservation of endothelial cell structure in the adenosine group.(ABSTRACT TRUNCATED AT 400 WORDS)     

Preconditioning does not attenuate myocardial stunning.

BACKGROUND. Despite numerous reports that one or more episodes of brief coronary artery occlusion preconditions the myocardium and dramatically reduces myocardial infarct size produced by a subsequent prolonged ischemia, we recently demonstrated that preconditioning does not attenuate contractile dysfunction in the peri-infarct tissue. However, the specific effects of preconditioning on myocardium in which wall motion has not been compromised by the preconditioning regimen per se and is further submitted to a short ischemic insult (that is, not confounded by necrosis) remain unknown. METHODS AND RESULTS. We addressed these issues in the canine model of myocardial stunning. Eighteen anesthetized dogs underwent 15 minutes of coronary occlusion followed by 3 hours of reperfusion. Before the 15-minute coronary occlusion, each dog received one of three treatments: no intervention (control group, n = 6), one episode of 5-minute coronary occlusion/5-minute reperfusion (PC5 group, n = 6), or one episode of 2.5-minute coronary occlusion/5-minute reperfusion (PC2.5 group, n = 6). Segment shortening (SS) in the ischemic/reperfused midmyocardium was monitored by sonomicrometry, and myocardial blood flow was assessed by injection of radiolabeled microspheres. All three groups were equally ischemic during the 15-minute coronary occlusion: Midmyocardial blood flow averaged 0.05 +/- 0.02, 0.07 +/- 0.04, and 0.08 +/- 0.03 ml/min/g in control, PC2.5, and PC5 groups, respectively. Before the 15-minute coronary occlusion, PC5 dogs exhibited significant stunning (SS = 55% baseline; p less than 0.01 versus control), whereas PC2.5 dogs did not (SS = 91% baseline; p = NS versus control). However, segment shortening during the subsequent 15-minute coronary occlusion was equally depressed at -25% to -42% of baseline values among the three groups. Furthermore, all three groups demonstrated a similar degree of stunning after reperfusion: SS at 3 hours after reflow averaged 24 +/- 12%, 34 +/- 16%, and 48 +/- 12% of baseline in control, PC2.5, and PC5 groups, respectively (p = NS). The degree of recovery of function after reperfusion correlated with the amount of midmyocardial blood flow during coronary artery occlusion. However, this relation was not different among the three groups: Specifically, for any given collateral flow during ischemia, preconditioning did not reduce the degree of stunning. CONCLUSIONS. Preconditioning neither preserves contractile function during a reversible ischemic insult nor prevents myocardial stunning during the initial hours of reflow.     

Combined treatment with vitamins E and C in experimental myocardial infarction in pigs

The effect of two different combined treatments with vitamin E acetate and vitamin C on infarct size and recovery of regional myocardial function was investigated in ischemic, reperfused porcine hearts. The left anterior descending coronary artery was distally ligated in 30 thoracotomized pigs for 45 minutes followed by 3 days of reperfusion. Infarct size was determined as the ratio of infarcted (tetrazolium stain) to ischemic (dye technique) myocardium. Regional myocardial function was assessed by sonomicrometry. Ten pigs received vitamin E acetate (12 gm intravenously three times for 1 week) before ischemic and vitamin C (4.4 gm intravenously) before reperfusion (therapy A). Another 10 pigs were treated with vitamin E acetate (12 gm intraarterially) and vitamin C (4.4 gm intravenously) during ischemia (therapy B). An additional 10 pigs served as a control group. Global hemodynamics did not differ significantly among the groups before and during ischemia. Mean plasma concentrations of vitamin E amounted to 107 micrograms/ml in group A, 16 micrograms/ml in group B, and 0.9 micrograms/ml in the control group at the onset of reperfusion. Therapy A reduced the size of the infarct from 73 +/- 12% to 47 +/- 16% of the region at risk (p less than 0.005) and improved regional systolic shortening from 0 +/- 7% to 11 +/- 6% at 3 days after reperfusion (p less than 0.01). Therapy B decreased the size of the infarct to 64 +/- 9% of the region at risk (p = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of noncoronary sources of left ventricular perfusion to intercoronary collateral-dependent myocardium due to chronic major vessel occlusion: absent contribution of luminal and extracardiac channels

Liminal contribution to perfusion of collateral-dependent left ventricular (LV) myocardium was evaluated in six dogs. A portion of LV free wall was rendered collateral-dependent by gradual occlusion of left circumflex artery with Ameroid constrictor. Eight to 10 weeks after implantation of constrictor, measurements of LV myocardial flow were made by left atrial injections of 9-10 micro radioactive microspheres. To measure total collateral flow, microspheres were injected under control conditions, and to measure luminal contribution to collateral flow, microspheres were injected after ligation of right coronary artery during extracorporeal perfusion of left common coronary artery (LCCA) with microsphere-free arterial blood, and during stoppage of flow through LCCA. Under control conditions, myocardial blood flow in collateral-dependent region, 1.01 +/- 0.31 ml/min/gm, was not significantly different from that in normal region, 1.06 +/- 0.32 ml/min/gm. Flow from luminal collateral vessels was negligible (less than 0.005 ml/min/gm) in both collateral-dependent and normal myocardium, and was not affected by stoppage of flow through LCCA. These results indicate that luminal collateral vessels, as well as collateral vessels originating from other noncoronary sources, do not contribute significantly to perfusion of normal or collateral-dependent LV myocardium.     

Progressive failure of coronary flow during reperfusion of myocardial infarction: documentation of the no reflow phenomenon with positron emission tomography

During reperfusion of a myocardial infarct, development of microvascular occlusion may result in regional hypoperfusion ("no reflow") despite a patent infarct-related artery. This study examined the extent and time course of no reflow with use of rubidium-82 positron emission tomography. In 12 anesthetized dogs, the left anterior descending coronary artery was occluded for 90 min and then freely reperfused. Regional myocardial perfusion was imaged by serial rubidium-82 positron emission tomography during coronary occlusion and every 30 min during reperfusion. After 4 h of reperfusion, infarct size and no reflow zone were measured postmortem by triphenyltetrazolium and thioflavin staining, respectively. Perfusion defects evident on rubidium-82 images during coronary occlusion rapidly resolved during the early reflow period. However, a recurrent perfusion defect appeared after 1 to 2 h of reflow in all dogs. The severity of recurrent perfusion defects progressed with time; after 5 min of reflow, relative perfusion in the left anterior descending artery territory was 97 +/- 6% of that in the normal circumflex artery region, but perfusion decreased progressively to 68 +/- 5% after 2 h (p less than 0.05) and to 55 +/- 4% after 4 h of reperfusion (p less than 0.05 versus 2 h). As measured by radioactive tracer microspheres, endocardial blood flow decreased similarly in the postischemic left anterior descending artery region from 1.2 +/- 0.2 ml/min per g after 5 min of reflow to 0.4 +/- 0.1 ml/min per g after 3 h of reflow (p less than 0.01). Residual infarct perfusion, measured by rubidium-82 after 4 h of reflow, was related to both infarct size (r = -0.88) and the extent of the no reflow zone (r = -0.84) in the postmortem left ventricular sections. Thus, serial positron emission tomography with rubidium-82 demonstrates a progressive loss of infarct perfusion, beginning 1 to 2 h after initial restoration of blood flow despite patency of the infarct-related artery. This phenomenon is probably a manifestation of progressive microvascular occlusion within the reperfused myocardium.     

Streptokinase improves reperfusion blood flow after coronary artery occlusion

Streptokinase is an effective thrombolytic agent which, with early restoration of coronary blood flow, has the potential for limiting infarct size. Distinct from thrombolysis, we studied the effects of streptokinase on reperfusion coronary blood flow and infarct size. Open-chest anesthetized canines underwent a 90 minute snare occlusion of the left circumflex coronary artery followed by release and reperfusion through a critical stenosis for 6 hours. The animals were assigned randomly to two groups. Intracoronary streptokinase [group 1 (n = 8): 6000 IU/kg in 3 ml of saline] or saline [group 2 (n = 8): 3 ml of saline] was infused at 0.05 ml/min for 60 minutes beginning 30 minutes before reperfusion. Coronary blood flow was stable in group 1 during reperfusion, while in group 2 it fell during 6 hours of reperfusion (30 +/- 4 ml/min to 18 +/- 2 ml/min, P = 0.05). The ST-segment elevation on the limb lead II electrocardiogram 15 minutes after coronary artery occlusion was similar in both groups (group 1: 3.9 +/- 0.6 mV, group 2: 2.3 +/- 0.5 mV), suggesting the extent of myocardial ischemia was also similar in both groups. The infarct sizes were similar when expressed both as a percent of the total left ventricular mass [(IZ/LV) group 1: 17 +/- 2.5%, group 2: 17.5 +/- 2.5%] or as a percent of the area at risk of infarction [(IZ/AR) group 1: 39 +/- 6%, group 2: 39 +/- 5%]. In both groups, the mass of left ventricle dependent on the blood flow distribution of the left circumflex coronary artery was similar when compared to total left ventricular mass [(AR/LV) group 1: 41 +/- 3%, group 2: 44 +/- 4%]. These results demonstrate that streptokinase maintains reperfusion coronary blood flow through a critical stenosis at a rate similar to baseline levels. Despite the fact that coronary blood flow remained stable with streptokinase during reperfusion, infarct size was not limited after 90 minutes of fixed coronary artery occlusion in this canine model of myocardial injury.