Post-ischemic cardiac chamber stiffness and coronary vasomotion: the role of edema and effects of dextran

Contributions of edema to left ventricular (LV) chamber stiffness and coronary resistance after ischemia were studied in isolated buffer-perfused rabbit hearts, with constant LV chamber volume, subjected to 30 min global ischemia and 60 min reperfusion. During reperfusion hearts were perfused with standard buffer or with 3% dextran to increase oncotic pressure and decrease water content. LV chamber volume was adjusted to an initial diastolic pressure (LVEDP) of 10 mmHg. In nonischemic hearts (n = 6) LVEDP was 11 +/- 0.3 mmHg and water content was 5.0 +/- 0.1 ml/g dry weight after 90 min of perfusion. In untreated ischemic hearts (n = 8) LVEDP was 51 +/- 4 mmHg and water content was 6.0 +/- 0.1 ml/g dry weight after 60 min reperfusion (P less than 0.001 v. nonischemic). In dextran-treated ischemic hearts (n = 8) LVEDP was 38 +/- 3 mmHg (P less than 0.05 v. untreated ischemic) and water content was 5.2 +/- 0.1 ml/g dry weight (P less than 0.001 v. untreated ischemic). Coronary resistance in untreated ischemic hearts increased by 26% from 2.0 +/- 0.06 to 2.6 +/- 0.06 mmHg/ml/min after 60 min reperfusion. In treated hearts coronary resistance increased by 16% from 1.9 +/- 0.09 to 2.2 +/- 0.09 mm/Hg/ml/min (P less than 0.01 v. untreated ischemic). To determine whether the decrease in coronary resistance with dextran could be ascribed to active vasodilation, dilator responses to 2 min hypoxia or 10(-4)M adenosine were tested in nonischemic and reperfused ischemic hearts. Dilator responses were stable in nonischemic hearts or hearts reperfused after 15 min ischemia but after 30 min ischemia the dilator response to hypoxia was reduced by 72% (P less than 0.025) and the dilator response to adenosine was eliminated (P less than 0.02). Thus the response to dextran was unlike that of a direct vasodilator. These data suggest that myocardial edema plays a significant role in maintaining increased ventricular chamber stiffness and coronary resistance during reperfusion after ischemia.     

Mechanism of myocardial protection with potassium arrest in isolated ischemic rat hearts]

Isolated working rat hearts were exposed to 25 min ischemia, and functional recovery was assessed by aortic flow (AoF) and rate-pressure product (RPP) to evaluate the beneficial effects of potassium (20 mM) induced arrest (K-arrest) prior to ischemia. K-arrest improved the recovery of function after 30 min of reperfusion compared with the control group (%AoF: 68 +/- 6 vs 0%, %RPP: 90 +/- 3% vs 60 +/- 3%, p less than 0.01). The accumulation of Ca++ at the end of reperfusion was less in hearts with K-arrest (2.2 +/- 0.1 vs 4.5 +/- 0.3 mumol/g dry, p less than 0.01). There was no difference between the two groups in high energy phosphate content at the end of ischemia. The increase in intracellular Na+ (Nai) during ischemia was reduced in hearts with K-arrest (delta: 19 vs 46 mumol/g dry), and the level of intracellular K+ (Ki) was higher at the end of ischemia in hearts with K-arrest (341 +/- 4 vs 318 +/- 2 mumol/g dry, p less than 0.01). During the first 5 min of reperfusion, the level of Ki in K-arrested hearts jumped to a higher level than in the control group (delta: 15 vs 2 mumol/g dry, p less than 0.01). The level of Nai was lower in hearts with K-arrest after 5 min of reperfusion. These data suggested that K-arrest might preserve the activity of Na+/K+ ATPase during ischemia and early reperfusion, and that it attenuated the increase in Nai during ischemia and reperfusion, which resulted in less Ca++ overload during reperfusion via the Na+/Ca++ exchange mechanism and led to improved recovery.     

Omapatrilat Limits Infarct Size and Lowers the Threshold for Induction of Myocardial Preconditioning Through a Bradykinin Receptor-Mediated Mechanism

Bradykinin is an important endogenous trigger of myocardial ischemic preconditioning (IPC). Through simultaneous inhibition of neutral endopeptidase and angiotensin converting enzyme, omapatrilat prevents enzymatic degradation of bradykinin. The aim of this study was to investigate if omapatrilat, through its ability to augment bradykinin levels, can augment a subthreshold IPC stimulus (Sub-IPC) and to compare the action of omapatrilat with the angiotensin-converting enzyme inhibitor, captopril. Langendorff perfused rat hearts were subjected to 35 min left coronary artery occlusion and 120 min reperfusion. Full IPC was induced with 5 min global ischemia/10 min reperfusion and substantially limited infarct size (21.5 +/- 3.5% of risk zone vs 53.4 +/- 2.0% in controls, P < 0.01). Sub-IPC (2 min global ischemia/10 min reperfusion) did not limit infarct size (48.4 +/- 3.8%). Omapatrilat (10 micromol/L) or captopril (200 micromol/L) were administered alone or in conjunction with Sub-IPC. Reduced infarct size comparable to that observed with the full IPC protocol was seen when sub-IPC was combined with either omapatrilat (19.7 +/- 2.5%) or captopril (20.3 +/- 4.9%). Omapatrilat alone caused modest reduction of infarct size (34.6 +/- 1.5%, P < 0.01 v control), an effect not observed with captopril. Hoe140, a selective kinin B(2) receptor antagonist, eliminated the cardioprotective effect of omaptrilat alone or in combination with sub-IPC. We conclude that omapatrilat elicits cardioprotection via inhibition of bradykinin degradation and that dual inhibition of angiotensin-converting enzyme and neutral endopeptidase may have beneficial effects beyond standard angiotensin-converting enzyme inhibitor therapy in patients with acute coronary syndromes who are at risk of myocardial infarction.     

Alterations in endocardial vascular resistance after reperfusion in a low flow, high demand model of ischemia: effects of dipyridamole and WEB-2086, a platelet-activating factor antagonist

To determine if alterations in regional coronary vascular resistance could occur in the type of myocardial ischemia present in severe angina pectoris, regional perfusion and function were studied in 35 conscious sedated dogs. A stenosis producing severe hypokinesia of the perfused segment was created for 2 h on the left anterior descending coronary artery and 10 episodes of 1 min of high demand ischemia (atrial pacing at a rate sufficient to induce dyskinesia in the hypoperfused segment) were superimposed before reperfusion. The dogs were randomized into three treatment groups: control (n = 13), dipyridamole (n = 10) or WEB-2086 (n = 12), an antagonist of the effects of the endogenous platelet-activating factor. During stenosis, residual endocardial blood flow in the ischemic but nonnecrotic area averaged 0.72 +/- 0.14, 0.38 +/- 0.13 and 0.68 +/- 0.17 ml/min per g in the control, WEB-2086 and dipyridamole groups, respectively. Twenty-four hours after reperfusion, endocardial blood flow in the ischemic area was significantly lower in control dogs (1.04 +/- 0.15 ml/min per g) than in dogs treated with WEB-2086 (1.44 +/- 0.28 ml/min per g; p less than 0.03) or dipyridamole (3.00 +/- 0.83 ml/min per g; p less than 0.01). Accordingly, in control dogs, endocardial coronary vascular resistance in the ischemic area was increased after reperfusion from 85 +/- 11 to 124 +/- 27 mm Hg/(ml/min per g) (p less than 0.05) after 24 h. In contrast, coronary vascular resistance in the ischemic area remained unchanged in dogs receiving WEB-2086 (77 +/- 8 to 79 +/- 9 mm Hg/(ml/min per g); p = NS) and it decreased significantly in dogs receiving dipyridamole (72 +/- 8 to 44 +/- 8 mm Hg/(ml/min per g); p less than 0.01). Regional function after 24 h remained depressed in all three groups. These data indicate that low flow, high demand ischemia induces alterations in the subendocardial microvasculature. Such alterations in regional coronary vascular resistance might play a role in several forms of ischemic heart disease such as in severe angina, but they appear susceptible to improvement by therapeutic interventions that influence granulocyte and platelet activation.     

Cardioprotection with cariporide, a sodium-proton exchanger inhibitor, after prolonged ischemia and reperfusion in senescent rats

This study investigated the effects of cariporide, an inhibitor of sodium-proton exchanger (NHE), during myocardial ischemia and reperfusion in senescence. Isolated Langendorff perfused hearts from 4 (adult) and 24 (senescent) month old male Wistar rats were submitted to prolonged low-flow ischemia (LFI) at 15% of initial coronary flow (180 min) or to 45 min of LFI (15% of initial coronary flow) followed by 30 min of reperfusion, without or with cariporide (10(-6)M). In senescent hearts, but not in adults, treatment with cariporide during prolonged LFI attenuated the elevation of coronary resistances (578 +/- 84 vs 1020 +/- 129% of baseline value after 180 min, P < 0.05) and delayed the decrease in active tension (35.6 +/- 5.1 vs 22.2 +/- 3.4% of baseline value after 60 min; P < 0.05). During reperfusion following LFI, the coronary flow impairment was more pronounced in senescents than in adults (48.4 +/- 9.4 and 75.3 +/- 4.9% of baseline value, respectively; P < 0.05) but was fully prevented in senescent hearts by cariporide treatment (95.6 +/- 17.0% of baseline value; P < 0.05 vs untreated group). This beneficial effect of cariporide on coronary tone was associated with an improvement of active and resting tensions and lower LDH release. Such functional protective effects of cariporide suggest an operative NHE during LFI at both coronary and myocardial levels in senescent heart. In addition, cariporide-associated improvement of post-ischemic recovery of coronary and contractile function as well as the limitation of cellular injury suggests a major role of calcium overload via NHE activation during reperfusion of senescent ischemic heart.     

Angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers synergistically increase coronary blood flow in canine ischemic myocardium: role of bradykinin

OBJECTIVES: We examined whether the combination of an angiotensin-converting enzyme (ACE) inhibitor and an angiotensin II receptor blocker (ARB) synergistically mediates coronary vasodilation and improves myocardial metabolic and contractile dysfunction in ischemic hearts. BACKGROUND: Either an ACE inhibitor or ARB mediates coronary vasodilation in ischemic hearts. METHODS: In dogs with myocardial ischemia, we infused an ACE inhibitor (temocaprilat, 10 microg/kg/min) or ARB (RNH-6270, 10 microg/kg/min) into the coronary artery. RESULTS: Perfusion pressure of the left anterior descending coronary artery was reduced from 104 +/- 8 to 42 +/- 2 mm Hg, so that coronary blood flow (CBF) decreased to one-third of the baseline value. Ten minutes after starting the infusion of temocaprilat, the cardiac bradykinin level increased (from 32 +/- 6 to 98 +/- 5 pg/ml). Coronary blood flow (29 +/- 2 to 44 +/- 3 ml/100 g/min) and the cardiac level of nitric oxide (NO) (7.8 +/- 1.9 to 17.5 +/- 3.2 microm) also increased, with these changes being attenuated by either N(omega)-nitro-L-arginine methyl ester or HOE140. RNH-6270 alone caused a modest increase in CBF (34 +/- 3 ml/100 g/min), with no increase in the cardiac NO or bradykinin levels. Both temocaprilat and RNH-6270 caused a further increase in both CBF (51 +/- 4 ml/100 g/min) and cardiac NO levels, without increasing the bradykinin level, and these changes were inhibited by HOE140. In the nonischemic heart, RNH-6270 augmented bradykinin-induced increases in CBF. CONCLUSIONS: The combination of an ACE inhibitor and ARB mediates greater increases in CBF and more potent cardioprotective effects through bradykinin-dependent mechanisms than either drug alone.     

Ventricular fibrillation during partial reperfusion following severe myocardial ischemia in the canine model

The authors examined whether partial reperfusion protects against reperfusion ventricular fibrillation (VF) following severe acute myocardial ischemia. Fifty-seven dogs were divided into two groups. In group A (n = 21), the left anterior descending coronary artery was occluded for 10 minutes, followed by full reperfusion. In the remaining 36 dogs (group B), myocardial ischemia was induced by retrograde blood flow (RBF) for 10 minutes. Thereafter, these dogs were divided into three subgroups: in group B1 (n = 10), full reperfusion was made by a carotid-left anterior descending coronary artery bypass; in group B2 (n = 13), partial reperfusion was achieved by collateral flow into the ischemic zone due to stopping RBF; in group B3 (n = 13), RBF was continued for an additional 5 minutes. During 10 minute ischemia, the myocardial blood flow at the ischemic zone measured by the H2 gas-clearance method was 12.3 +/- 2.0 ml/min/100 g in A, 3.4 +/- 0.9 ml/min/100 g in B1, 4.7 +/- 0.6 ml/min/100 g in B2, and 4.7 +/- 0.6 ml/min/100 g in B3 (A vs B1, p less than 0.02; A vs B2 and B3, p less than 0.01). Maximal ST-segment elevation was 11.4 +/- 1.8 mV in A, 28.2 +/- 2.7 mV in B1, 25.1 +/- 3.0 mV in B2, and 27.0 +/- 1.9 mV in B3 (A vs B1, B2, and B3, p less than 0.001). Maximal conduction delay was 48.6 +/- 9.4 ms in A, 106.4 +/- 5.2 ms in B1, 101.6 +/- 9.9 ms in B2, and 91.2 +/- 5.1 ms in B3 (A vs B1, B2, and B3, p less than 0.001). The incidence of reperfusion VF was 14% (3/21) in A, 80% (8/10) in B1, and 69% (9/13) in B2 (A vs B1, p less than 0.001; A vs B2, p less than 0.005). In group B3, VF occurred in only 1 of 13 dogs for the additional 5 minutes. It is concluded that reperfusion VF occurred frequently when ischemia was severe even though the duration of ischemia was short (B1), and that reperfusion VF was not prevented by partial reperfusion when the ischemia was severe (B2).     

Deferoxamine, an iron chelator, reduces myocardial injury and free radical generation in isolated neonatal rabbit hearts subjected to global ischaemia-reperfusion.

The protective action of deferoxamine, an iron chelator, against functional and metabolic deteriorations of ventricular muscle, induced by ischaemia-reperfusion, was investigated in Langendorff-perfused hearts of neonatal rabbits in comparison with superoxide dismutase (SOD) plus catalase. The perfused hearts were subjected to normothermic (37 degrees C) global ischaemia for 45 min following cardiac arrest with St Thomas cardioplegic solution and then reperfused with oxygenated Krebs-Henseleit solution. In control hearts, the recovery of the left ventricular developed pressure (LVDP) after 30 min reperfusion was 50.7 +/- 3.1% (mean +/- SE, n = 5) of the pre-ischaemic value. The LVDP recovery was significantly improved in the hearts treated with deferoxamine at 10-100 microM (89.4 +/- 1.4% at 30 microM, P < 0.01 vs. control). The improvement in LVDP was less prominent when treated with 30 x 10(4) U/l SOD plus 30 x 10(4) U/l catalase (67.9 +/- 2.0%, P < 0.01 vs. deferoxamine at 30 microM). CPK leakage into the coronary effluent during the initial 5 min of reperfusion was reduced to around half of the control value with 30 microM deferoxamine (P < 0.05 vs. control), while unaffected by the addition of SOD plus catalase. Free radicals in the coronary effluent were measured with electron spin resonance spectroscopy in separate experiments by using a spin-trapping agent, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). A burst of DMPO-OH signal was detected during the initial minutes of reperfusion. The intensity of DMPO-OH signal was significantly reduced by 30 microM deferoxamine to about one-third of control.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of an endothelin receptor antagonist and an angiotensin converting enzyme inhibitor on metabolism and contraction in the ischemic and reperfused rabbit heart.

The effect of an endothelin (ET) A/ETB receptor antagonist, TAK-044, and/or an angiotensin converting enzyme (ACE) inhibitor, temocaprilat, on myocardial metabolism and contraction during ischemia and reperfusion was examined by phosphorus 31-nuclear magnetic resonance (31P-NMR) in Langendorff rabbit hearts. After normothermic 15 min global ischemia, 60min of postischemic reperfusion was carried out. TAK-044 and/or temocaprilat was administered from 40 min prior to the global ischemia. Adenosine triphosphate (ATP), creatine phosphate, inorganic phosphate, pH, left ventricular systolic developed pressure (LVDev.P), left ventricular end-diastolic pressure (LVEDP) and coronary flow were measured. Twenty-eight hearts were divided into 4 experimental groups consisted of seven hearts each: Group I consisted of controls, Group II was perfused with TAK-044 (10(-6) mol/L), Group III was perfused with temocaprilat (10(-6) mol/L), and Group IV was perfused with TAK-044 (10(-6) mol/L) in combination with temocaprilat (10(-6) mol/L). Group II showed a more early recovery of ATP during postischemic reperfusion (82+/-3%) compared with Group I (71+/-3%). Group III showed a significant inhibition of the decrease in ATP during global ischemia (54+/-3%) compared with Group I (45+/-3%). Group IV also showed a significant marked inhibition of the decrease in ATP during global ischemia (59+/-5%) and a more significant improvement on recovery of ATP during postischemic reperfusion (86+/-3%) compared with the other 3 groups. There were no differences in LVDev.P, LVEDP and coronary flow among these groups. In conclusion, TAK-044 in combination with temocaprilat had a significant potentiation on myocardial metabolism during both ischemia and reperfusion.     

Regulation of myocardial glycogenolysis during post-ischemic reperfusion

Myocardial glycogen and the factors which primarily regulate its metabolism were studied during post-ischemic reperfusion. Myocardial [13C]glycogen was continuously monitored by 13C-NMR spectroscopy in beating rat hearts perfused with oxygenated solutions containing [1-13C]glucose (5 mM) and insulin, during normal flow at 15 ml/min (n = 5), and during reperfusion after 30 min of 1 ml/min (n = 5), or 0 ml/min (n = 4) ischemia. Mean myocardial [13C]glycogen fell during reperfusion from 1.1 +/- 0.6 at the end of zero-flow ischemia to 0.4 +/- 0.4 mumol of [13C]glucosyl units/g wet wt (P less than 0.02) over the first 7 min of reperfusion; it also fell during reflow following 1 ml/min ischemia, from 2.3 +/- 1.4 to 1.7 +/- 1.0 mumol (P less than 0.03) over the same interval. In parallel experiments, glycogen phosphorylase % a (GPA%) content was higher at the end of 30 min of 0 ml/min (37.3 +/- 7.3%, P less than 0.01), and trended higher after 1 ml/min flow (30.8 +/- 12.1%, P = 0.18) than under baseline conditions (20.1 +/- 7.4%). However GPA% returned to baseline values within 1 min of reflow after both 0 and 1 ml/min ischemic periods (20.6 +/- 3.0% and 19.0 +/- 8.0%, respectively). Inorganic phosphate, as determined by simultaneous 31P-NMR, remained elevated during early reperfusion relative to baseline, and significantly correlated with the extent of decline in [13C]glycogen during reperfusion (r = 0.79, P less than 0.01). Thus, glycogen breakdown continues to occur during early post-ischemic reperfusion, but the mechanism is not related to elevated GPA%, and may be due to persistently increased inorganic phosphate at that time.     

Prostacyclin analogue iloprost decreases thrombolytic potential of tissue-type plasminogen activator in canine coronary thrombosis.

Platelets play an important role in the formation of a coronary thrombus and reocclusion after thrombolysis. Therefore, we examined the thrombolytic potential of concomitant intravenous administration of potent platelet inhibitor iloprost, a prostacyclin analogue, with tissue-type plasminogen activator (t-PA; n = 8) and t-PA alone (n = 9) in dogs with an electrically induced occlusive coronary artery thrombus. t-PA (0.75 mg/kg) was given over 20 minutes, and iloprost (4 micrograms/kg) was given over 40 minutes. Reperfusion rate was 63% (five of eight dogs) in the t-PA plus iloprost group and 67% (six of nine dogs) in the t-PA alone group (p = NS). The time to thrombolysis (or reperfusion) in the t-PA plus iloprost group was almost twice as great as in the t-PA alone group (33.0 +/- 13.3 vs. 18.5 +/- 6.7 minutes, mean +/- SD, p less than 0.02), and the duration of reperfusion was much shorter (3.4 +/- 1.8 vs. 39.3 +/- 17.4 minutes, p less than 0.005). Peak coronary artery blood flow after reperfusion in the t-PA plus iloprost group was also less (20 +/- 17 ml/min) than in the t-PA alone group (58 +/- 21 ml/min, p less than 0.005). Reocclusion occurred in all dogs given t-PA with iloprost despite potent synergistic platelet inhibitory effects of t-PA and iloprost, whereas four of six dogs given t-PA alone reoccluded. Neither regimen exerted a significant beneficial effect on regional myocardial shortening during coronary reperfusion. Plasma levels of t-PA were lower when iloprost was given with t-PA (1,022 +/- 360 vs. 1,459 +/- 270 ng/ml in t-PA alone group, p less than 0.05). The detrimental effects of iloprost identified in this study may relate to the reduction in plasma t-PA concentrations by its degradation in the liver caused by the prostacyclin analogue iloprost.     

Myocardial protection by intracoronary nicardipine administration during percutaneous transluminal coronary angioplasty

To determine if the calcium antagonist nicardipine protects the myocardium against ischemia, myocardial lactate, hypoxanthine and prostanoid function was studied in 12 patients during percutaneous transluminal coronary angioplasty (PTCA). Values were obtained before balloon inflation and during 4 minutes after deflation. Intracoronary injection of 0.2 mg of nicardipine distal to the stenosis was done randomly before the first or second inflation; the other inflation served as a control. One minute after deflation, coronary sinus flow levels were similar during the nicardipine and control procedure (161 +/- 61 vs 159 +/- 72 ml/min); lactate (-9 +/- 21% vs -17 +/- 21%, p less than 0.025) and hypoxanthine production (-107 +/- 85% vs -218 +/- 153%, p less than 0.05) were less severe after nicardipine pretreatment than after control. All patients reverted to lactate extraction 4 minutes after inflation plus nicardipine infusion, whereas lactate was still produced 4 minutes after control inflation. No significant changes in thromboxane B2 or prostacyclin levels were observed in the coronary sinus 1 minute after inflation, but higher arterial thromboxane B2 values were observed after control inflation than after inflation with nicardipine infusion (median values 169 vs 78 pg/ml, p less than 0.05). In conclusion, intracoronary infusion of nicardipine reduced signs of ischemia and alterations in prostanoid handling after coronary occlusion. The mechanisms of myocardial protection appeared unrelated to coronary sinus blood flow changes or to a systemic effect of nicardipine.     

Comparative effects of pacing-induced and flow-limited ischemia on left ventricular function

We compared left ventricular (LV) myocardial blood flow and function accompanying severe demand ischemia (rapid atrial pacing in the presence of critical bilateral coronary stenoses) and supply ischemia (complete bilateral coronary occlusion) of the same ischemic regions in 14 pentobarbital-anesthetized dogs. Pacing-induced ischemia resulted in pronounced reductions in average regional epicardial blood flow (0.8 +/- 0.4 vs. control 1.2 +/- 0.4 [+/- SD] ml/g/min, p less than 0.05) and endocardial blood flow (0.4 +/- 0.1 vs. control 1.3 +/- 0.3 ml/g/min, p less than 0.05). More severe reductions in average regional epicardial and endocardial blood flow were seen after bilateral coronary occlusion (BCO) (0.3 +/- 0.3 and 0.1 +/- 0.1 vs. control 1.3 +/- 0.3 ml/g/min, p less than 0.05, respectively). Hemodynamics of postpacing ischemia (PPi) were consistently characterized by systolic impairment including depressed systolic contractile performance [(+)dP/dtmax 1,281 +/- 442 vs. control 2,173 +/- 775 mm Hg/sec, p less than 0.05], ventricular dilation (left ventricular [LV] end-diastolic dimension [EDD] 47.6 +/- 7.8 vs. control 44.7 +/- 8.6 mm, p less than 0.05), and an increase in LV end-diastolic pressure (EDP) (14.4 +/- 2.8 vs. control 4.2 +/- 2.8 mm Hg, p less than 0.05). Abnormalities in early and late diastolic function with PPi included increased time constant of isovolumic relaxation (78.0 +/- 40.4 vs. control 46.4 +/- 20.5 msec, p less than 0.05) and increased chamber stiffness (1.9 +/- 0.77 vs. control 0.81 +/- 0.55 mm Hg/mm, p less than 0.05), respectively. The LV diastolic pressure-dimension relation, however, shifted upward and to the right in eight of nine animals, whereas an upward shift was observed in only one animal. Thus, in this model of postpacing ischemia, we observed contractile failure and passive changes in diastolic function. Alterations in ventricular function occurred consistently earlier and to a greater extent during BCO than PPi, including higher LVEDP (25.3 +/- 8.1 vs. 14.9 +/- 6.6 mm Hg, p less than 0.05), greater ventricular dilation (delta LVEDD 4.9 +/- 2.5 vs. 3.5 +/- 2.8 mm, p less than 0.05), and reduced minor-axis dimension shortening (3.3 +/- 3.1% vs. 6.5 +/- 3.6%, p less than 0.05). To detect potential qualitative differences in ventricular function between the two types of ischemia, we evaluated hemodynamics at comparable loading conditions (30 seconds to 1 minute of BCO).(ABSTRACT TRUNCATED AT 400 WORDS)     

Evidence for a reversible oxygen radical-mediated component of reperfusion injury: reduction by recombinant human superoxide dismutase administered at the time of reflow

It has been suggested that the beneficial effects of reperfusing ischemic myocardium might be in part reversed by the occurrence of "reperfusion injury." One possible mechanism could be the generation of oxygen free radicals. Superoxide dismutase enzymatically scavenges superoxide radicals by dismutation to hydrogen peroxide. This study tested the hypothesis that administration of recombinant human superoxide dismutase (h-SOD) at the time of reflow after a period of prolonged global ischemia would result in improved recovery of myocardial metabolism and function by preventing or reducing a potentially harmful component of reperfusion. We also sought to determine whether catalase, an enzymatic scavenger of hydrogen peroxide, was a necessary addition for optimal benefit. Langendorff perfused rabbit hearts were subjected to 30 min of normothermic (37 degrees C) total global ischemia. At the moment of reperfusion, 12 control hearts received a 10 ml bolus of normal perfusate followed by 15 min of reperfusion with normal perfusate (group I), 12 hearts received 60,000 IU of h-SOD as a bolus followed by a continuous infusion of 100 IU/ml for 15 min (group II), and 12 hearts received 60,000 IU of h-SOD and 60,000 IU of catalase as a bolus followed by 100 IU/ml of both enzymes for 15 min (group III). Myocardial ATP and phosphocreatine (PCr) content and intracellular pH during ischemia and reperfusion were continuously monitored with 31P nuclear magnetic resonance (NMR) spectroscopy. During 30 min of normothermic global ischemia intracellular pH dropped from 7.11-7.18 to 5.58-5.80 in all three groups of hearts. Likewise myocardial PCr content fell rapidly to 7% to 8% and ATP fell more slowly to 29% to 36% of preischemic control content. After 45 min of reperfusion PCr recovered to 65 +/- 5% of control in untreated (group I) hearts compared with 89 +/- 8% in h-SOD-treated (group II) hearts (p less than .01 vs group I) and with 83 +/- 6% of control in h-SOD/catalase-treated (group III) hearts (p less than .05 vs group I). Recovery of isovolumic left ventricular developed pressure was 68 +/- 5% of control in h-SOD-treated (group II) hearts and 66 +/- 6% of control in h-SOD/catalase-treated (group III) hearts after 45 min of reflow, compared with 48 +/- 6% of control in untreated (group I) hearts (p less than .005 for groups II and III vs group I). The NMR data confirmed equal depletion of ATP and PCr content in all three groups of hearts.(ABSTRACT TRUNCATED AT 400 WORDS)     

Protective effect of PEG-SOD against early coronary reperfusion injury assessed in reperfused and non-reperfused ischaemic areas of the same heart

OBJECTIVE: In order to investigate the salvage of ischaemic myocardium by polyethylene glycol-conjugated superoxide dismutase (PEG-SOD), we compared reperfused and non-reperfused regions in the same canine heart and measured regional myocardial blood flow (RMBF) and myocardial CPK during coronary occlusion and reperfusion using non-radioactive, coloured microspheres. METHODS AND RESULTS: The chests of 17 mongrel dogs were opened under anaesthesia, and the left circumflex coronary artery was occluded for 90 min and then reperfused for 5 min. During this procedure, polystyrene microspheres of different colours were infused at four different times: prior to occlusion (orange), 10 min (red) and 90 min (blue) after occlusion, and 5 min after reperfusion (yellow). Thereafter, the heart was excised, cut in slices along the left circumflex coronary artery, and flow rates at the various times were assessed as a function of microsphere counts. In the control group (n=9), there are significant differences in the myocardial CPK level between reperfused and non-reperfused areas.The myocardial CPK level in reperfused area was significantly reduced compared to non-reperfused area in the outer layers (54 +/- 8 IU/g vs. 74 +/- 9 IU/g, P < 0.05), and also reduced in the inner layers (59 +/- 9 IU/g vs. 74 +/- 13 IU/g), however, it was not significantly different. In the PEG-SOD group (n=8), there was no significant difference in the myocardial CPK level between reperfused and non-reperfused areas in both inner and outer layers (inner layers; 68 +/- 11 IU/g vs. 68 +/- 6 IU/g, outer layer; 69 +/- 17 IU/g vs. 67 +/- 18 IU/g), indicating a significant protective effect of PEG-SOD. In the control group, transmural necrosis of the reperfused areas was 22.4 +/- 10.0%, which showed no significant difference compared with non-reperfused areas (23.1 +/- 9.9%). In the PEG-SOD group, transmural necrosis of the reperfused areas by TTC staining was 8.1 +/- 8.1%, which showed no significant difference compared with non-reperfused areas (8.5 +/- 7.1%). CONCLUSIONS: PEG-SOD prevents infarct extension during early coronary reperfusion.     

Reperfusion-induced arrhythmias are critically dependent upon occluded zone size: relevance to the mechanism of arrhythmogenesis

The relationship between reperfusion-induced arrhythmias and the size of the occluded zone was examined. The isolated perfuse rat heart was used because its negligible collateral flow maximizes susceptibility to arrhythmias and reduces variability. Ischemia lasting 10 min was followed by 10 min of reperfusion. A constant-pressure perfusion system (which precludes coronary steal) permitted measurement of the rapidity of restoration of coronary flow. Mean occluded zone sizes of 0, 7.2 +/- 1.1, 19.5 +/- 1.5, 45.8 +/- 1.7, 30.1 +/- 4, and 100% of the total ventricular weight were obtained by sham ligation, distal, medial and proximal ligation of the left main coronary artery, right arterial ligation and the induction of global ischemia, respectively. Occluded zone size correlated positively (r = 0.86, P less than 0.001) with a linearly-additive arrhythmia score irrespective of the site of ischemia (left versus right ventricle). In globally ischemic hearts, ventricular fibrillation (VF) depended upon ventricular beating rate during ischemia, occurring only if the rate exceeded 150 beats/min. If this factor were taken into consideration, VF incidence exhibited a sigmoidal relationship with occluded zone size. During the first min of reperfusion, the rapidity of restoration of coronary flow was inversely related to occluded zone size (P less than 0.001) and had a small but significant effect on the severity of arrhythmias; slow recovery of flow increased susceptibility. We conclude that when reperfusion is elicited at the moment of peak susceptibility to arrhythmias, VF incidence is determined principally by occluded zone size. Heart rate during ischemia becomes relevant at rates less than 150 beats/min, when a protective effect is seen. Since VF incidence was 100% in hearts reperfused after global ischemia, an interface between non-ischemic tissue and reperfused tissue is therefore unnecessary for arrhythmogenesis during reperfusion, and flow of injury current between non-ischemic and reperfused tissue can be ruled out as a mechanism of arrhythmogenesis. The initiation of reperfusion-induced arrhythmias must therefore take place within the reperfused tissue.     

Myocardial release of nitric oxide during ischaemia and reperfusion: effects of L-arginine and hypercholesterolaemia

AIMS: Nitric oxide (NO) may modulate myocardial ischaemia/reperfusion (I/R) injury, but effects of hypercholesterolaemia on myocardial NO release during I/R are unknown. METHODS: A NO-specific carbon fibre electrode continuously measured coronary sinus [NO] during 60 min low-flow ischaemia (1 ml/min) and 60 min free reperfusion (I/R) in isolated rabbit hearts. Experimental groups (n=7 per group) were control, L-arginine supplement (200 microM), N-nitro-L-arginine methyl ester (L-NAME) treatment (8 microM) and hypercholesterolaemic. RESULTS: During early I, NO release decreased markedly in control (-1356+/-286 pmol/min/g) and L-arginine (-1972+/-172) groups, but less in L-NAME (-441+/-89) and hypercholesterolaemic (-602+/-164) groups (both p<0.01 vs. controls). No increase in NO release during I was seen in any group. After R, NO release increased above baseline in control (+2333+/-591 pmol/min/g) and L-arginine (+1048+/-278) groups and hypercholesterolaemic (+1100+/-478) (p<0.05 vs. pre-ischaemia each group). There was little increase in NO release in the L-NAME group (+436+/-247 pmol/min/g, p<0.05 vs. controls). In each group, myocardial NO release declined towards pre-ischaemic levels during 60 min R. Hearts treated with L-arginine had similar NO release but better functional recovery than controls (p<0.01). Treatment with L-NAME was also associated with better functional recovery than in controls or hypercholesterolaemic hearts. CONCLUSION: Myocardial NO release declines rapidly during ischaemia, but increases above baseline during early reperfusion. Improved function after L-arginine treatment appears to be independent of effects upon NO release. Hypercholesterolaemia is associated with reduced myocardial NO release, under both baseline conditions and during ischaemia and reperfusion.     

Effect of angiotensin converting enzyme inhibitor and angiotensin II type 1 receptor antagonist on metabolism and contraction in ischemia-reperfused rabbit heart

The effect of angiotensin converting enzyme (ACE) inhibitor, temocaprilat and/or angiotensin II type 1 (AT1) receptor antagonist, CV-11974 on myocardial metabolism and contraction during ischemia and reperfusion was examined by phosphorus 31-nuclear magnetic resonance (31P-NMR) in Langendorff rabbit hearts. After normothermic 15 min global ischemia, postischemic reperfusion of 60min was carried out. Temocaprilat and/or CV-11974 were administered from 40 min prior to the global ischemia. Adenosine triphosphate (ATP), creatine phosphate (PCr), inorganic phosphate (Pi), intracellular pH (pHi), left ventricular developed pressure (LVDevP), left ventricular end-diastolic pressure (LVEDP) and coronary flow were measured. Twenty-eight hearts were divided into 4 experimental groups consisting of 7 hearts each: group I consisted of controls, group II was perfused with temocaprilat (10(-6)mol/L), group III was perfused with CV-11974 (10(-6)mol/L), and group IV was perfused with temocaprilat (10(-6)mol/L) in combination with CV-11974 (10(-6) mol/L). Groups II and III showed a significant (p<0.05) inhibition of an overshoot phenomenon of PCr during postischemic reperfusion compared with group I. Group IV also showed a more pronounced significant (p<0.01) inhibition of the overshoot of PCr during reperfusion compared with group I. Groups II, III and IV showed a significant (p<0.05) inhibition of the decrease in ATP during global ischemia (59+/-2, 54+/-3 and 54+/-7%, respectively) compared with group I (45+/-3%). Groups II and IV showed a significant (p<0.05) early recovery of ATP during reperfusion (81+/-2, 80+/-6%) compared with group I (71+/-3%) and group II (73+/-2%). Group IV showed no more significant recovery in ATP than group III. There were no differences in LVDevP, LVEDP and coronary flow among these groups. In conclusion, temocaprilat in combination with CV-11974 has significant potential for improving myocardial energy metabolism during both myocardial ischemia and reperfusion.     

Postischemic recovery of mechanical performance and energy metabolism in the presence of left ventricular hypertrophy. A 31P-MRS study

The present study was undertaken to define the effects of left ventricular hypertrophy on postischemic recovery of myocardial performance and high energy phosphate metabolism. Hemodynamics and 31P-magnetic resonance spectra were monitored simultaneously in the isolated Langendorff-perfused rat heart during 30 minutes of ischemia and 30 minutes of reperfusion. Left ventricular hypertrophy was produced by either suprarenal aortic constriction or chronic thyroxine administration. In chronic pressure overload hypertrophy, minimal coronary resistance was significantly higher (p less than 0.001) and the loss of purine nucleosides in the coronary effluent during early reperfusion significantly larger (p less than 0.001) compared with both normal hearts and thyroxine-induced hypertrophied hearts. Postischemic recovery of the baseline values for left ventricular developed pressure and phosphorylation potential was 43 +/- 4% and 82 +/- 4%, respectively, in chronic pressure overload hypertrophied hearts; 86 +/- 4% and 91 +/- 3%, respectively, in normal hearts (chronic pressure overload hypertrophy versus normal hearts, p less than 0.001 and p less than 0.05); and 100 +/- 4% and 98 +/- 2%, respectively, in thyroxine-induced hypertrophied hearts (normal hearts versus thyroxine-induced hypertrophied hearts, p less than 0.05 and p less than 0.05). Recovery after reperfusion was not related to intracellular pH, ATP, phosphocreatine, or inorganic phosphate levels during ischemia. Also, recovery was not related to developed pressure or oxygen consumption before ischemia. However, recovery was inversely related to coronary resistance and directly related to coronary flow before ischemia. Thus, functional and/or anatomic alterations of the coronary vascular bed and a greater loss of purine nucleosides during reperfusion are likely responsible for the attenuated compensatory response to ischemia and reperfusion in left ventricular hypertrophy induced by chronic pressure overload. On the other hand, the excess muscle mass per se does not seem to alter recovery, since thyroxine-induced myocardial hypertrophied hearts responded at least as well as normal hearts.     

Acadesine and myocardial protection. Studies of time of administration and dose-response relations in the rat.

BACKGROUND. Although there are many factors that might contribute to tissue injury during ischemia and reperfusion, the loss of adenine nucleotides has long been considered to be of importance. This has led to the study of interventions designed to limit the loss of nucleotides or to enhance the rate of nucleotide resynthesis during reperfusion. Alternatively, the breakdown of adenosine triphosphate to adenosine might represent a protective response of the ischemic heart because adenosine is considered an anti-injury autocoid. Augmentation of endogenous adenosine levels might be beneficial. For these reasons, the protective properties of acadesine (AICAr: 5-amino-4-imidazole carboxamide riboside) were assessed in a rat model of myocardial ischemia and reperfusion. METHODS AND RESULTS. The protective properties of acadesine were studied in the isolated, perfused rat heart subjected to global hypothermic (20 degrees C) ischemia and reperfusion. When acadesine was given as an in vivo pretreatment (100 mg/kg i.v. 15 minutes before study) followed by being administered as an additive (20 mumol/l) to the St. Thomas' Hospital cardioplegic solution (single dose) and then as an additive (20 mumol/l) to the initial reperfusion (15 minutes) solution, the recovery of aortic flow after 2.5 hours of ischemia was improved from its control value of 16.5 +/- 3.9 ml/min to 28.9 +/- 4.1 ml/min (n = 8 per group; p less than 0.05). Similar protection was seen with other indexes of cardiac function. Analysis of hearts obtained at the end of 2.5 hours of ischemia and 35 minutes of reperfusion revealed no significant differences in metabolite content between control and drug-treated hearts with the exception of inosine monophosphate, which was increased from its drug-free control value of 0.10 +/- 0.01 mumol/g dry wt to 0.86 +/- 0.06 mumol/g dry wt (p less than 0.05). In further studies (n = 8 per group), with multidose (every 30 minutes) cardioplegia and extended periods (6 hours) of hypothermic ischemia, acadesine consistently led to higher mean recoveries of function and lower levels of creatine kinase leakage. Again, the only significant metabolic effect was an increase in tissue inosine monophosphate content. In studies (n = 12 per group) to determine whether acadesine was acting before, during, or after ischemia, the drug was given 1) only as pretreatment (100 mg/kg i.v.), 2) only during single-dose cardioplegia (20 mumol/l), or 3) only during reperfusion (20 mumol/l). Significant protection was observed in the first two groups (recovery of aortic flow increased from 10.6 +/- 2.6 ml/min in the acadesine-free control to 22.6 +/- 2.8 and 23.6 +/- 3.1 ml/min, respectively; p less than 0.05). No significant protection was observed when acadesine was given only during reperfusion. In dose-response studies, acadesine (0, 5, 20, 50, 200, and 1,000 mumol/l; n = 12 per group) was given only as a cardioplegic additive; the postischemic recoveries of aortic flow were 15.4 +/- 2.8, 16.9 +/- 3.6, 29.5 +/- 3.8, 27.4 +/- 3.8, 26.7 +/- 4.2, and 27.1 +/- 2.7 ml/min, respectively. CONCLUSIONS. Acadesine improves the ability of the heart to recover from ischemia and reperfusion when administered before ischemia or with cardioplegia. The mechanism underlying the protection remains to be resolved.