Reduction in coronary vasodilator reserve following coronary occlusion and reperfusion in anesthetized dog: role of endothelium-derived relaxing factor, myocardial neutrophil infiltration and prostaglandins

The prognostic significance of coronary flow reserve in the risk stratification of patients with chronic total occlusion of the right coronary artery and the intermediary stenosis of the left coronary artery

Introduction: Coronary Flow Reserve (CFR) is a clinically useful, non-invasive diagnostic method for assessing the functional ability of coronary arteries and it is important for their long-term follow-up in patients. However, CFR has not always been sufficiently investigated in previous studies. Objective: To examine the prognostic significance of CFR in the risk stratification of patients with chronic total occlusion of the right coronary artery (RCA) and the intermediary stenosis of the left coronary artery (LAD). Material and Methods: Number of 71 patients, mean age 64 ± 7 years, (84%) patients male, having LAD stenosis, diameter 50-70%, and CTO of RCA, were referred for noninvasive estimation of functional significance of LAD stenosis. Transthoracic Doppler echocardiography was used to obtain coronary flow velocities in the distal segment of LAD. Patients were followed for the mean period of 18.3 ± 7.1 months for the occurrence of composite end point including cardiovascular death, myocardial infarction, bypass surgery and PCI. Results: During the follow-up period, there were a total of 23 adverse events (4 deaths, 2 myocardial infarction, 7 bypass surgeries and 10 PCI). Patients with CFR < 2 had significantly more adverse events (n = 9; 56.3% vs. n = 14; 25.5%; p = 0.021), they were significantly older (68 ± 9 vs. 62 ± 6; p = 0.011), with a higher incidence of a positive family history (14; 87.5% vs. 26; 47.3%; p = 0.039), as well as a significantly higher frequency of three-dose coronary disease (14; 87.5% vs. 30; 54.5%; p = 0.017). Using Kaplan-Meier estimator, we obtained that patients with CFR < 2 have a significantly shorter average period without unwanted event (15.4 ± 2.8 months vs 23.5 ± 1.1 months, Log Rank 7.407; p = 0.008). Conclusion: CFR plays an important role in stratifying the risk of patients with CTO of RCA and the intermediary stenosis of LAD.

Noninvasive Assessment of Myocardial Perfusion in Different Blood Pressure Phenotypes and Its Association With Arterial Stiffness Indices

BACKGROUND

We investigated for the first time whether patients with recent-onset, uncomplicated hypertension and different hypertension phenotypes exhibit altered values of subendocardial viability ratio (SEVR), a surrogate measure of myocardial perfusion that correlates with the ratio of subendocardial to subepicardial blood flow. We additionally explored whether SEVR correlates with arterial stiffness in a population free from the long-term effects of essential hypertension.

METHODS

Nontreated individuals free from any known health problems were classified as true hypertensives (THs), white-coat hypertensives (WCHs), masked hypertensives (MHs), and normotensives. SEVR was noninvasively calculated with applanation tonometry in the radial artery. Carotid-femoral pulse wave velocity, central and peripheral pulse pressure (PP), augmentation index, and central systolic/diastolic blood pressure (BP) were assessed with applanation tonometry. Total arterial compliance index was calculated with impedance cardiography.

RESULTS

In a total of 150 participants, normotensive individuals exhibited the highest values of SEVR (162.9 ± 25.3%), whereas SEVR appeared to be similar in MHs (150.2 ± 22.1%), WCHs (148.1 ± 20.4%), and THs (149.9 ± 24.8%) (P = 0.017). In the univariate analysis, SEVR significantly correlated with central systolic BP, peripheral PP, and total arterial compliance index. The association between SEVR and both central (P = 0.017) and peripheral PP (P = 0.003) remained significant after adjustment for heart rate and other parameters.

CONCLUSIONS

SEVR, an alternative tool to the invasive assessment of microvascular coronary perfusion, presents different values across patients with divergent BP phenotypes and correlated with arterial stiffness, even in the absence of overt cardiovascular disease. Future studies need to address the potential utility of this easily implementable marker as a screening test for myocardial ischemia.

Cardiopulmonary Bypass-Induced Inflammatory Response: Pathophysiology and Treatment

OBJECTIVES

The objectives of this review are to discuss the pathophysiology of the pro-inflammatory response to the cardiopulmonary bypass circuit, the impact of ischemia reperfusion injury on post-operative organ function, the compensatory anti-inflammatory response and the evidence for immune-modulatory strategies and their impact on outcomes.

DATA SOURCE

MEDLINE, PubMed.

CONCLUSION

Innovations such as the development of more biocompatible surfaces and miniaturized circuits, as well as the increasing expertise of surgeons, anesthesiologists and perfusionists has transformed cardiac surgery and the use of cardiopulmonary bypass into a relatively routine procedure with favorable outcomes. Despite these refinements, the attendant inflammatory response to bypass, ischemia reperfusion injury and the compensatory anti-inflammatory response contribute to post-operative morbidity and mortality. Additional studies are needed to further delineate the impact of immunomodulatory strategies on outcomes.

Association of aortic stiffness and wave reflections with coronary flow reserve in women without obstructive coronary artery disease: An ancillary study from the National Heart, Lung, and Blood Institute-sponsored Women's Ischemia Syndrome Evaluation (WISE)

BACKGROUND

Increased aortic stiffness and reduced coronary flow reserve (CFR) independently predict adverse outcomes. But information about relationships between arterial properties and CFR in subjects without obstructive coronary artery disease (CAD) is limited.

METHODS

CFR was measured (Doppler flow wire and intracoronary adenosine) in 50 women (age 53 ± 11 years) with symptoms and signs of myocardial ischemia without obstructive CAD. Aortic pulse wave velocity (aPWV), a measure of aortic stiffness, was obtained via catheter pullback; radial artery pressure waves were measured by applanation tonometry and central aortic pressure synthesized.

RESULTS

Overall, CFR (mean 2.61 ± 0.47) was significantly correlated with aPWV (r = -0.51), pulse wave amplification (r = 0.45), augmented pressure (r = -0.48), augmentation index (AIx, r = -0.44), aortic systolic pressure (r = -0.49), left ventricular wasted energy (LVEw, r = -0.47) (all P < .001), systolic pressure time index (r = -0.37, P < .008), and rate pressure product (r = -0.29, P < .04). In the multiple regression model including aPWV, CFR was still significantly correlated with aPWV (P < .008) and aortic systolic pressure (P < .01). No other measures contributed significant additional information. Women with CFR ≤2.5 versus those with CFR >2.5 had greater aPWV (894 ± 117 vs 747 ± 93 cm/s, P < .001), augmented pressure (14 ± 4.9 vs 11 ± 4.1 mmHg, P < .008), AIx (32 ± 6.6 vs 27 ± 6.6%, P < .003), LVEw (30 ± 12 vs 21 ± 10 dyne-s/cm(2) × 10(2), P < .02) and reduced pulse pressure amplification (1.20 ± .07 vs 1.26 ± .10, P < .008) and pressure wave travel time (133 ± 7.3 vs 138 ± 6.9 milliseconds, P < .04).

CONCLUSIONS

Among symptomatic women without obstructive CAD, CFR was inversely related to aortic systolic pressure and indices of aortic stiffness. These changes in arterial properties increase left ventricular afterload requiring the ventricle to generate additional, but wasted, energy that increases indices of myocardial oxygen demand, reduces CFR and increases vulnerability to ischemia.

Effect of Aspiration Thrombectomy on Microvascular Dysfunction in ST-Segment Elevation Myocardial Infarction With an Elevated Neutrophil Count

Background and Objectives

Aspiration thrombectomy (AT) during primary percutaneous coronary intervention (PCI) is an effective adjunctive therapy for ST-segment elevation myocardial infarction (STEMI). An elevated neutrophil count in STEMI is associated with microvascular dysfunction and adverse outcomes. We evaluated whether AT can improve microvascular dysfunction in patients with STEMI and an elevated neutrophil count.

Subjects and Methods

Seventy patients with STEMI undergoing primary PCI from August 2007 to February 2009 in our institution were classified by tertiles of neutrophil count on admission (<5,300/mm³, 5,300-7,600/mm³, and >7,600/mm³). The angiographic outcome was post-procedural thrombolysis in myocardial infarction (TIMI) flow grade. Microvascular dysfunction was assessed by TIMI myocardial perfusion (TMP) grade and ST-segment resolution on electrocardiography 90 minutes after PCI. The clinical outcome was major adverse cardiac event (MACE), defined as cardiac death, re-infarction, and target lesion revascularization at 9 months.

Results

There were no significant differences in the clinical characteristics and pre- and post-procedural TIMI flow grades between the neutrophil tertiles. As the neutrophil count increased, a lower tendency toward TMP grade 3 (83% vs. 52% vs. 54%, p=0.06) and more persistent residual ST-segment elevation (>4 mm: 13% vs. 26% vs. 58%, p=0.005) was observed. The 9-month MACE rate was similar between the groups. On subgroup analysis of AT patients (n=52) classified by neutrophil tertiles, the same tendency toward less frequent TMP grade 3 (77% vs. 56% vs. 47%, p=0.06) and persistent residual ST-segment elevation (>4 mm: 12% vs. 28% vs. 53%, p=0.05) was observed as neutrophil count increased.

Conclusion

A higher neutrophil count at presentation in STEMI is associated with more severe microvascular dysfunction after primary PCI, which is not improved with AT.

Coronary vasoregulation in health and disease

The present article reviews pertinent contributions from the Coronary Physiology Research Group at the Quebec Heart Institute to the understanding of coronary physiology in health and disease. Mechanisms that contribute to regulation of coronary blood flow and its distribution across the ventricular wall are discussed. Data from animal studies of ischemia-reperfusion injury are also presented and discussed in the context of current concepts regarding postischemic myocardial protection strategies. Future research directions regarding the cardiac nervous system and its importance in the regulation of coronary blood flow, cardiac function and myocyte injury during acute myocardial infarction are also discussed.

Relationship of admission neutrophil count to microvascular injury, left ventricular dilation, and long-term outcome in patients treated with primary angioplasty for acute myocardial infarction

BACKGROUND

The relationship of admission neutrophil count to the degree of microvascular injury, left ventricular (LV) volume, and long-term outcome after acute myocardial infarction (AMI) was examined in the present study.

METHODS AND RESULTS

The study group comprised 228 consecutive patients with a first anterior wall AMI who underwent primary angioplasty within 12 h of onset. The degree of microvascular injury was evaluated by Doppler guidewire. Adverse cardiac events were recorded during an average follow-up of 52+/-28 months. Using a receiver-operating characteristic analysis, a neutrophil count >or=7,260 cells/mm(3) was the best predictor of future cardiac events. By regression analysis, the neutrophil count significantly correlated with diastolic deceleration time (r=-0.40, p<0.0001), coronary flow reserve (r=-0.43, p<0.0001), and LV end-diastolic volume at 4 weeks (r=0.32, p<0.0001). Kaplan-Meier survival analysis showed a higher incidence of adverse cardiac events in patients with a high neutrophil count (p=0.002). By multivariate analysis, a neutrophil count >or=7,260 cells/mm(3) was an independent predictor of long-term adverse cardiac events (odds ratio 3.8, p=0.002).

CONCLUSION

Neutrophilia on admission is associated with impaired microvascular perfusion, LV dilation, and long-term adverse cardiac events in patients treated with primary angioplasty for AMI.

Relation between neutrophil counts on admission, microvascular injury, and left ventricular functional recovery in patients with an anterior wall first acute myocardial infarction treated with primary coronary angioplasty

Increased neutrophil counts have been associated with an increased risk of adverse clinical events after acute myocardial infarction (AMI). We examined the association of neutrophil counts on admission with degree of microvascular injury and left ventricular functional recovery after primary coronary angioplasty in AMI. We studied 116 patients with a first anterior wall AMI who underwent primary coronary angioplasty within 12 hours of onset. Patients were categorized into 3 groups based on initial neutrophil count: low (<5,000/mm(3)), intermediate (5,000 to 10,000/mm(3)), and high (>10,000/mm(3)). Coronary flow velocity parameters were assessed immediately after reperfusion using a Doppler guidewire. We defined severe microvascular injury as the presence of systolic flow reversal and a diastolic deceleration time <600 ms. Echocardiographic wall motion was analyzed before revascularization and 4 weeks after revascularization. In patients with a high neutrophil count, systolic flow reversal was more frequently observed, diastolic deceleration time was shorter, and coronary flow reserve was lower. By regression analysis, neutrophil count significantly correlated with diastolic deceleration time (r = -0.38, p <0.0001), coronary flow reserve (r = -0.33, p = 0.0004), and score for change in wall motion (r = -0.36, p = 0.0004). Multivariate analysis showed that neutrophil count on admission was an independent predictor of severe microvascular injury (odds ratio 2.94, p = 0.02). In conclusion, neutrophilia on admission is associated with impaired microvascular reperfusion and poor functional recovery after primary coronary angioplasty.

Vasoconstrictor prostanoids may be involved in reduced coronary reactive hyperemia after ischemia-reperfusion in anesthetized goats

To examine coronary vasodilator reserve after ischemia-reperfusion, reactive hyperemia was determined during reperfusion after partial and total, brief and prolonged ischemia. To this, left circumflex coronary artery flow was electromagnetically measured, and partial (60 min) or total (15 and 60 min) occlusions of this artery were induced, followed in each case by 60-min reperfusion in anesthetized goats untreated and treated with N(W)-nitro-l-arginine methyl ester (l-NAME) or meclofenamate. In untreated and treated animals, coronary flow was decreased during reperfusion after the three types of ischemia. In hyperemic responses to 5- and 10-s coronary occlusions, repayment of debt decreased during reperfusion after the three types of ischemia in untreated animals, and this decrease was not affected by l-NAME. This decrease during reperfusion after partial and total, 60-min ischemia, but not after total, 15-min ischemia, reversed with meclofenamate. Peak hyperemic flow/control flow ratio decreased only during reperfusion after total 60-min occlusion in untreated animals and it was normalized by meclofenamate. These results show that ischemia-reperfusion reduces hyperemic response (vasodilator reserve); this diminution being dependent on duration and severity of ischemia. The hyperemic responses reduction during reperfusion after prolonged ischemia, but not after brief ischemia may be related at least in part to increased production of vasoconstrictor prostanoids.

Association of peripheral neutrophilia with adverse angiographic outcomes in ST-elevation myocardial infarction

We hypothesized that absolute and relative neutrophilia would be associated with adverse angiographic outcomes in the 394 patient Limitation of Myocardial Infarction Following Thrombolysis in Acute Myocardial Infarction (LIMIT) Acute Myocardial Infarction (AMI) trial of fibrinolysis in ST-elevation myocardial infarction. The mean neutrophil count was 7.9 x 10(9)/L, with a mean neutrophil percentage of 72%. Patients with time from symptom onset to fibrinolytic treatment more than the median (2.7 hours) had a higher neutrophil count and percentage of neutrophils than patients with shorter time to treatment. Patients with a closed infarct-related artery at 90 minutes (Thrombolysis In Myocardial Infarction [TIMI] grade 0/1 flow) had higher neutrophil counts (8.8 +/- 3.8 vs 7.6 +/- 3.0, p = 0.02) but no difference in the percentage of neutrophils than patients with an open artery. Higher neutrophil counts were also mildly correlated with longer corrected TIMI frame counts (CTFC) in the infarct-related artery (r = 0.14, p = 0.02). Patients with impaired myocardial perfusion by TIMI myocardial perfusion grade (TMPG) had a greater percentage of neutrophils (73.2 +/- 10.7% for TMPG 0/1 vs 69.9 +/- 12.6% for TMPG 2/3, p = 0.047) but no detectable difference in neutrophil counts (8.2 +/- 3.3 vs 7.7 +/- 2.9, p = 0.24). There were no significant associations between other indexes in the cell differential and angiographic or clinical outcomes. Higher neutrophil counts remained independently associated with both closed arteries and CTFC in multivariable models controlling for age, left anterior descending artery infarct location, time to treatment, and pulse and blood pressure on admission. A greater percentage of neutrophils remained independently associated with impaired microvascular perfusion in a similar multivariable model. In patients with ST-elevation myocardial infarction, absolute and relative neutrophilia were associated with impaired epicardial and microvascular perfusion.

Flow heterogeneity following global no-flow ischemia in isolated rabbit heart

The purpose of this study was to evaluate flow heterogeneity and impaired reflow during reperfusion after 60-min global no-flow ischemia in the isolated rabbit heart. Radiolabeled microspheres were used to measure relative flow in small left ventricular (LV) segments in five ischemia + reperfused hearts and in five nonischemic controls. Relative flow heterogeneity was expressed as relative dispersion (RD) and computed as standard deviation/mean. In postischemic vs. preischemic hearts, RD was increased for the whole LV (0.92 +/- 0.41 vs. 0.37 +/- 0.07, P < 0.05) as well as the subendocardium (Endo) and subepicardium considered separately (1.28 +/- 0.74 vs. 0.30 +/- 0.09 and 0.69 +/- 0.22 vs. 0.38 +/- 0.08; P < 0.05 for both comparisons, respectively) during early reperfusion. During late reperfusion, the increased RD for the whole LV and Endo remained significant (0.70 +/- 0.22 vs. 0.37 +/- 0.07 and 1.06 +/- 0.55 vs. 0.30 +/- 0.09; P < 0.05 for both comparisons, respectively). In addition to the increase in postischemic flow heterogeneity, there were some regions demonstrating severely impaired reflow, indicating that regional ischemia can persist despite restoration of normal global flow. Also, the relationship between regional and global flow was altered by the increased postischemic flow heterogeneity, substantially reducing the significance of measured global LV reflow. These observations emphasize the need to quantify regional flow during reperfusion after sustained no-flow ischemia in the isolated rabbit heart.

Na(+)/H(+) exchange inhibition prevents endothelial dysfunction after I/R injury

Whereas inhibition of the Na(+)/H(+) exchanger (NHE) has been demonstrated to reduce myocardial infarct size in response to ischemia-reperfusion injury, the ability of NHE inhibition to preserve endothelial cell function has not been examined. This study examined whether NHE inhibition could preserve endothelial cell function after 90 min of regional ischemia and 180 min of reperfusion and compared this inhibition with ischemic preconditioning (IPC). In a canine model either IPC, produced by one 5-min coronary artery occlusion (1 x 5'), or the specific NHE-1 inhibitor eniporide (EMD-96785, 3.0 mg/kg) was administered 15 min before a 90-min coronary artery occlusion followed by 3 h of reperfusion. Infarct size (IS) was determined by 2,3,5-triphenyl tetrazolium chloride staining and expressed as a percentage of the area-at-risk (IS/AAR). Endothelial cell function was assessed by measurement of coronary blood flow in response to intracoronary acetylcholine infusion at the end of reperfusion. Whereas neither control nor IPC-treated animals exhibited a significant reduction in IS/AAR or preservation of endothelial cell function, animals treated with the NHE inhibitor eniporide showed a marked reduction in IS/AAR and a significantly preserved endothelial cell function (P < 0.05). Thus NHE-1 inhibition is more efficacious than IPC at reducing IS/AAR and at preserving endothelial cell function in dogs.

Platelet GPIIb/IIIa receptor blockade reduces infarct size in a canine model of ischemia-reperfusion

OBJECTIVES

We studied the effects of N-acetyl-cys-asn-(5,5-dimethyl-4-thiazolidine-carbonyl)-4-amino-methyl-phe-gly-asp-cys, monoacetate (MK-0852) (platelet GPIIb/IIIa receptor blocker) on peak reactive hyperemia, distribution of blood flow, regional contractile function and infarct size in a canine model of acute ischemia-reperfusion injury.

BACKGROUND

Platelet activation and formation of platelet microaggregates in coronary vessels could contribute to ischemia-induced myocyte injury. Inhibition of platelet aggregation could reduce ischemia-reperfusion injury.

METHODS

Three groups of dogs (n = 10/group) were studied; group 1--heparin (HEP) (100 U/kg/h intravenously), group 2--MK-0852 (300 microg/kg intravenous bolus followed by 3 microg/kg/min for 3 h) and group 3--MK-0852 plus HEP. Infarct size after 60 min regional ischemia and 3 h reperfusion was evaluated by tetrazolium staining and normalized to risk area (Monastral blue dye).

RESULTS

Infarct size in HEP-treated controls was 32.4+/-2.8%; in MK-0852 without or with HEP groups, infarct size was 17.4+/-1.9% (p = 0.001) and 23.4+/-3.0% (p = 0.04), respectively. Cardiac hemodynamics and rate-pressure product were comparable between groups. Multivariate analysis using collateral blood flow as the independent variable confirmed the cytoprotective actions of MK-0852. Postischemic peak reactive hyperemia in the infarct-related artery was depressed in all groups; during reperfusion, transmural distribution of myocardial blood flow returned to near control levels, but severe regional hypokinesia persisted.

CONCLUSIONS

Diminished infarct size with MK-0852 treatment suggests an additional mechanism of benefit for GPIIb/IIIa blockers beyond stabilization of a "culprit" acute coronary lesion. This cytoprotective effect was unrelated to preservation of coronary vasoreactivity (assessed by reactive hyperemia), restoration of blood flow across the myocardium or acute improvement in contractility.

Ischemic preconditioning attenuates postischemic coronary artery endothelial dysfunction in a model of minimally invasive direct coronary artery bypass grafting

OBJECTIVE

Unmodified reperfusion without cardioplegia in minimally invasive direct coronary artery bypass grafting procedures causes endothelial dysfunction that may predispose to polymorphonuclear neutrophil-mediated myocardial injury. This study tested the hypothesis that ischemic preconditioning in a minimally invasive direct coronary artery bypass grafting model attenuates postischemic endothelial dysfunction in coronary vessels.

METHODS

In anesthetized dogs, the left anterior descending coronary artery was occluded for 30 minutes and reperfused for 3 hours without ischemic preconditioning (no-ischemic preconditioning; n = 7); in 7 dogs, the left anterior descending occlusion was preceded by 5 minutes occlusion followed by 5 minutes of reperfusion. Relaxation responses to stimulators of nitric oxide synthase were used to evaluate endothelial function in arteries from the ischemic-reperfused (left anterior descending) and nonischemic (left circumflex coronary artery) zones.

RESULTS

Stimulated endothelial-dependent relaxation of epicardial left anterior descending artery to incremental concentrations of acetylcholine in the no-ischemic preconditioning animals was shifted to the right, and maximal relaxation was attenuated compared with the nonischemic left circumflex coronary artery (117% +/- 4% vs 138% +/- 5%). In contrast, acetylcholine-induced maximal relaxation was comparable in the left anterior descending artery versus left circumflex coronary artery in the ischemic preconditioning group (130% +/- 6% vs 135% +/- 5%). In 150- to 200- microm left anterior descending microvessels, 50% relaxation occurred with a lower concentration (log[M]) of acetylcholine in ischemic preconditioning versus no-ischemic preconditioning (-8.0 +/- 0.4 vs -7.0 +/- 0.1) with no group differences in smooth muscle relaxation to sodium nitroprusside, suggesting endothelial-specific damage. Adherence of fluorescent labeled polymorphonuclear neutrophils to epicardial coronary artery endothelium, used as an index of basal (unstimulated) anti-polymorphonuclear neutrophil function, was significantly attenuated by ischemic preconditioning versus no-ischemic preconditioning (293 +/- 25 polymorphonuclear neutrophils/mm2 vs 528 +/- 29 polymorphonuclear neutrophils/mm2).

CONCLUSION

In this minimally invasive direct coronary artery bypass grafting model, both agonist-stimulated and basal postischemic endothelial dysfunction were attenuated by ischemic preconditioning.

Human and rat neutrophils constitutively express neural nitric oxide synthase mRNA

Freshly isolated rat circulating neutrophils (PMN) constitutively expressed neural nitric oxide synthase (nNOS) mRNA and nNOS protein and exhibited spontaneous basal release of low concentrations of nitrate and nitrite anion (RNI). In contrast, rat peripheral monocytes and macrophages were devoid of nNOS mRNA and protein and did not exhibit basal or spontaneous release of RNI. Constitutive neural NOS mRNA was also found in human PMN. However, nNOS protein was not expressed and spontaneous generation of RNI was absent in the human PMN. Spontaneous release of RNI from rat PMN was inhibited by 7-nitroindazole but not by L-N-iminoethyllysine, which further supported the nNOS origin of the spontaneously produced RNI. Intravenous administration of Escherichia coli endotoxin (0.6 mg/kg) did not acutely affect the content of nNOS mRNA or protein but inhibited nNOS-derived production of RNI in PMN and up-regulated iNOS mRNA and iNOS protein in PMN, macrophages, and monocytes. This communication demonstrates the existence of nNOS mRNA in rat and human PMN and nNOS protein in rat PMN. Moreover, the data also show that the nNOS system in rat PMN is functional and is inhibitable by the nNOS inhibitor 7-nitroindazole. These findings offer an explanation for the spontaneous formation of the PMN-derived relaxing factor resembling nitric oxide (NO). Moreover, since basal production of NO can affect expression of adhesion molecules and cell-cell binding, the nNOS system within the rat may play an important role in PMN function in normal and disease states. Finally and speculatively, if constitutively expressed nNOS mRNA is subject to activation and translation into nNOS protein, nNOS may also play a role in the function of human PMN.

Relaxin counteracts myocardial damage induced by ischemia-reperfusion in isolated guinea pig hearts: evidence for an involvement of nitric oxide

Relaxin was previously shown to cause coronary vasodilation and to inhibit mast cell activation through a stimulation of endogenous nitric oxide production. This suggests that relaxin may have beneficial effects on ischemia-reperfusion-induced myocardial injury, which is triggered by endothelial damage and impaired nitric oxide generation. In this study, we tested the effect of relaxin on isolated and perfused guinea pig hearts subjected to ischemia and reperfusion. Ischemia was induced by ligature of the left anterior descending coronary artery; removal of the ligature induced reperfusion. Relaxin, at the concentration of 30 ng/ml of perfusion fluid, causes: a significant increase in coronary flow and in nitric oxide generation; a significant decrease in malonyldialdehyde production and in calcium overload, both markers of myocardial injury; an inhibition of mast cell granule exocytosis and histamine release, which are known to contribute to myocardial damage; a reduction of ultrastructural abnormalities of myocardial cells; an improvement of heart contractility. The beneficial effects of relaxin were blunted by the NO synthase inhibitor L-NMMA. The current study provides first experimental evidence that relaxin has a powerful protective effect on the heart undergoing ischemia and reperfusion acting through a nitric oxide-driven mechanism.

The leukocyte cell adhesion cascade and its role in myocardial ischemia-reperfusion injury

Cell-cell and cell-matrix interactions are known to be mediated by specific cell adhesion receptors expressed on the cell surface. The characterization of these cell adhesion molecules has allowed researchers to examine their roles in a variety of physiologic and pathophysiologic conditions. Numerous studies have demonstrated that myocardial ischemia-reperfusion injury is an acute inflammatory process in which leukocytes are intimately involved. In this review, we summarize the current data on the leukocyte cell adhesion cascade, focus upon studies which have demonstrated specific cell adhesion molecule interactions which mediate the leukocyte involvement in myocardial ischemia-reperfusion injury and suggest future avenues of exploration and possible clinical implications of the studies reviewed.

Protection of rat myocardium by mitogenic and non-mitogenic fibroblast growth factor during post-ischemic reperfusion

The effects of acidic fibroblast growth factor (FGF-1) and basic fibroblast growth factor (FGF-2) and a non mitogenic form of FGF1 on myocardial ischemia and reperfusion were assessed. Rats underwent 10 minutes of coronary artery occlusion followed by 24 hours of reperfusion. Creatinine kinase content of the affected myocardium showed that both fibroblast growth factors 1 and 2 effectively protected against ischemia reperfusion injury (p < 0.01), and that the vasoactive but nonmitogenic form of the FGF1 was equally protective (p < 0.01 versus control + vehicle). The results were confirmed by light and electron-microscopy histological studies. Histological evaluations after treatment with the non-mitogenic fibroblast growth factor 1 showed that it did not generate the severe hyperplasia and connective tissue disorganization observed with the native mitogenic proteins. The possibility of using a non-mitogenic form of fibroblast growth factor for cardio-protection circumvents many of the potentially undesirable effects that may derive from systemically introducing broad spectrum acting fibroblast growth factors in vivo. This myocardial protection observed 24 hours after the treatment with fibroblast growth factors, and the efficacy of the non-mitogenic form of the protein, also suggest that the protective effect of fibroblast growth factors may be due to the increased blood flow rather than to angiogenesis.

Impact of left ventricular unloading after late reperfusion of canine anterior myocardial infarction on remodeling and function using isosorbide-5-mononitrate

BACKGROUND

Late reperfusion during acute myocardial infarction results in delayed recovery of ventricular function and less remodeling, whereas ventricular unloading with nitrates improves function and attenuates remodeling. Whether late reperfusion combined with prolonged unloading with isosorbide-5-mononitrate (ISMN) might produce greater functional recovery and less remodeling than late reperfusion alone is not known.

METHODS AND RESULTS

In vivo left ventricular function and topography (echocardiograms), postmortem topography (planimetry), and collagen (hydroxyproline) were measured in dogs that were randomized to reperfusion 2 hours after left anterior descending coronary artery ligation, and ISMN (n = 12) or placebo (n = 12) was given as 25 mg IV over 4 hours followed by 50 mg PO QID for 6 weeks. Compared with placebo, the ISMN group had similar heart rate but lower left atrial pressure, mean arterial pressure, and rate-pressure products. Although in vivo baseline remodeling and functional parameters were similar in the two groups, by 6 weeks the ISMN group had smaller (P < or = .05) infarct and noninfarct segment lengths, ventricular volumes, and mass; less (P < .001) asynergy; and greater (P < .001) ejection fraction. More important, by 2 days, ejection fraction was 18% greater (P < .025) and asynergy 26% less (P < .05) with ISMN. At 6 weeks, ISMN showed less (P < or = .05) scar size, scar collagen, cavity dilation, noninfarct wall thickness, and apical bulging than placebo. In another 4 dogs, acute ISMN produced less improvement in function and remodeling than prolonged ISMN.

CONCLUSIONS

Late reperfusion of acute anterior myocardial infarction combined with prolonged ISMN unloading results in greater and earlier recovery of ventricular function and less remodeling than late reperfusion alone.

Myocardial neutrophil infiltration, lipid peroxidation, and antioxidant activity after coronary artery thrombosis and thrombolysis

Neutrophil accumulation and free radical release are implicated in the genesis of reperfusion injury. However, little is known about the changes in myocardial lipid peroxidation and antioxidant activity in relation to coronary artery thrombosis and thrombolysis. To investigate this issue, 18 dogs with electrically induced occlusive thrombus in the left anterior descending (LAD) coronary artery were given tissue-type plasminogen activator (TPA). Sustained reflow (lasting > 120 min) occurred in 4 dogs, reocclusion after initial thrombolysis (transient reflow, duration of reflow 5 to 25 min) occurred in 7 dogs, and no reperfusion was evident in 7 dogs. Myocardial neutrophil infiltration was determined by measuring myeloperoxidase (MPO) activity, lipid peroxidation by malondialdehyde (MDA) levels and antioxidant activity by superoxide dismutase (SOD) activity in the myocardial regions supplied by the nonischemic left circumflex (Cx) and the ischemic LAD coronary arteries. In dogs with ischemia alone (no reperfusion), MPO activity and MDA levels in the LAD-supplied myocardium were modestly higher and SOD activity modestly lower than in the corresponding Cx-supplied myocardium. In dogs with sustained reperfusion there was a marked increase in MPO and MDA and a marked reduction in SOD activity in the reperfused myocardium. The MPO and MDA values in the myocardium of dogs with transient reperfusion, although much higher than the corresponding normal myocardial values, were less marked than in the myocardium of dogs with sustained reperfusion, and the SOD activity was preserved in the transiently reperfused regions. Myocardial shortening fraction in the LAD region was worse in dogs with sustained reperfusion than in those with sustained ischemia or transient reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of neutrophil activity by nitric oxide during acute myocardial ischaemia and reperfusion

Nitric oxide (NO) exerts an inhibitory effect on polymorphonuclear neutrophil (PMN) function, via a cyclic GMP-mediated mechanism, while PMNs are known to play an important role in myocardial ischaemia-reperfusion injury (MI-R). Since the major source of NO, vascular endothelium, becomes functionally impaired during MI-R, it is attractive to hypothesize that it is this loss of endothelial nitric oxide production that allows PMN adherence and activation. The studies reviewed here add substance to this hypothesis. Authentic NO, administered during MI-R both reduces myocardial necrosis and PMN accumulation, while basal NO release, as estimated by coronary artery ring responses to L-NAME, an NO synthase inhibitor, declines during reperfusion with a time-course mirrored by PMN adherence in the same preparation. Reduction in infarct size and decreased PMN accumulation can also be demonstrated with L-arginine and NO donors. Since endothelial dysfunction leads to PMN adherence and PMNs have been shown to contribute to endothelial dysfunction, it seems probable that a positive feedback loop is generated during MI-R, leading to the amplification of PMN activity and subsequent myocardial damage.

Attenuation of coronary flow reserve and myocardial function after temporary subtotal coronary artery occlusion and increased myocardial oxygen demand in dogs

OBJECTIVES

We examined whether subtotal coronary artery occlusion and reperfusion alter coronary flow reserve and regional myocardial function.

BACKGROUND

Total coronary artery occlusion followed by reperfusion results in decreased coronary flow reserve and regional myocardial dysfunction.

METHODS

Thirteen anesthetized dogs were subjected to subtotal occlusion of the left anterior descending coronary artery for 1 h, followed by reperfusion for 1 h. During subtotal left anterior descending occlusion, heart rate was increased by atrial pacing. After reperfusion, coronary flow reserve, indicated by reactive hyperemia, as well as coronary flow responses to acetylcholine and nitroglycerin, regional myocardial function and myocardial leukocyte accumulation were measured.

RESULTS

After reperfusion, coronary flow reserve was decreased in the ischemic left anterior descending but not the nonischemic circumflex coronary artery region. Myocardial function was also depressed in the left anterior descending coronary region and did not improve on reperfusion. Histologic study showed no leukocyte infiltration in the ischemic left anterior descending coronary region. Myeloperoxidase, an index of myocardial leukocyte accumulation, was similar in the left anterior descending and circumflex coronary regions. Sensitivity of epicardial left anterior descending coronary artery rings to the thromboxane A2 analog U46,619 was enhanced, and relaxation of these rings in response to endothelium-dependent relaxants was decreased.

CONCLUSIONS

Coronary flow reserve is reduced and regional myocardial function depressed after subtotal coronary artery occlusion and increased heart rate. A decreased synthesis or increased breakdown of endothelium-derived relaxing factor may be related to a decrease in coronary flow reserve. However, the reduction in coronary flow reserve appears to be unrelated to leukocyte accumulation in the reperfused region.

Regional vasodilating properties of isoflurane in stunned swine myocardium

Studies about the coronary vasodilating properties of isoflurane indicate that this drug induces coronary vasodilation. No work has examined isoflurane-induced vasodilation in known stunned myocardium. This study was conducted to determine isoflurane's coronary vasodilation potency in stunned myocardium and to compare the results obtained with normal myocardium. We determined the vasodilating properties of isoflurane in regionally perfused swine myocardium. Six domestic swine were anesthetized with pentobarbital and fentanyl. The left anterior descending artery (LAD) was cannulated and perfused with blood drawn from the carotid artery and passed thorough a membrane oxygenator. LAD arterial flow was controlled by a calibrated roller pump with continuous digital readout, and LAD arterial pressure was measured directly. The anterior interventricular vein was cannulated and dimension crystals placed in the LAD-perfused myocardium. Myocardial stunning was induced by reduction of coronary blood flow (CBF) to 30% of control flow for 20 minutes. One hour after reperfusion, the vasodilatory response to 0%, 1%, and 2% isoflurane administered via the membrane oxygenator was determined and compared to maximum vasodilatation produced by regional intracoronary administration of adenosine. Systemic blood pressure and heart rate remained constant throughout the experiment. At 2% isoflurane, systolic shortening and regional myocardial oxygen consumption decreased 53% and 17%, respectively. The same concentration increased CBF by 33% and reduced coronary vascular resistance (CVR) by 25%. One percent isoflurane affected neither CBF nor CVR. Regional coronary administration of adenosine produced much greater changes in CBF (+509) and CVR (-89.5%).(ABSTRACT TRUNCATED AT 250 WORDS)

Responses of blood flow, oxygen consumption, and contractile function to inotropic stimulation in stunned canine myocardium

To examine the effects of inotropic stimulation on regional myocardial blood flow (MBF), oxidative metabolism, and contractile function in stunned myocardium, nine closed-chest dogs were studied 2 hours postreperfusion after a 25 minute occlusion of the left anterior descending coronary artery (LAD). MBF was determined with microspheres, and regional myocardial oxygen consumption (MVO2) was estimated from the rate constant k1 of the rapid clearance phase of [1-11C] acetate time activity curves, recorded with dynamic positron emission tomography. Myocardium at risk was determined from [13N] ammonia images obtained during occlusion. Wall motion, assessed by two-dimensional echocardiography, was impaired in postischemic myocardium in all dogs 2 hours after reperfusion. Dobutamine infusion increased the rate pressure product by 70% +/- 31% and significantly improved contractile function in the postischemic region in all dogs. In remote myocardium, MVO2 increased from 5.7 +/- 1.2 to 8.6 +/- 1.6 mumol/gm/min, and blood flow from 0.87 +/- 0.16 to 1.52 +/- 0.42 ml/gm/min in response to dobutamine. In reperfused myocardium, MVO2 increased from 3.1 +/- 0.7 to 7.4 +/- 1.5 mumol/gm/min, and blood flow from 0.51 +/- 0.12 to 1.2 +/- 0.4 ml/gm/min. Oxygen extraction increased significantly in reperfused myocardium relative to remote myocardium consistent with a flow-limited response to dobutamine stimulation. The improvement in contractile function failed to correlate significantly with relative increases in MBF or MVO2, suggesting that mechanical function is not as tightly coupled as MBF and MVO2 in postischemic myocardium during inotropic stimulation.

Hemodynamic vascular forces contribute to impaired endothelium-dependent vasodilation in reperfused canine epicardial coronary arteries

OBJECTIVES

We studied canine coronary arterial vasoreactivity after occlusion and reperfusion to examine whether reduced flow or pressure contributed to the abnormalities observed.

BACKGROUND

Ischemia and reperfusion alter endothelial and myocardial function. Causative factors may include altered flow, complement activation or free radical production by endothelial or white blood cells after reoxygenation and neutrophil activation.

METHODS

The coronary arteries of anesthetized, open chest dogs were subjected to 90-min occlusion +/- 2 h of reperfusion. The effect of reperfusion on arterial responses to intracoronary acetylcholine, nitroprusside and phenylephrine was studied using in vivo ultrasound. Arterial segments were also harvested, perfused ex vivo with cell-free buffer and exposed to potassium chloride, nitroprusside, acetylcholine and bradykinin. The effect of ex vivo flow cessation with or without maintained intralumen pressure was also studied.

RESULTS

Results are expressed as mean value +/- SEM. In vivo arterial cross-sectional area increased during infusion with acetylcholine (10(-5) mol/liter [18.5 +/- 9%]) and nitroprusside (10(-5) mol/liter [22.5 +/- 10%]) and decreased with phenylephrine (10(-5) mol/liter [7.6 +/- 7%]). After reperfusion, acetylcholine caused 13.5 +/- 9% vasoconstriction. Nitroprusside and phenylephrine responses were unchanged. Reperfused arterial segments also showed impaired vasodilation in response to 10(-6) mol/liter of acetylcholine (10.6 +/- 5.1% vs. 47.1 +/- 4.9% in control vessels) and 10(-8) mol/liter of bradykinin (4.4 +/- 6.7% vs. 27.9 +/- 8% in control vessels). Ex vivo flow cessation impaired acetylcholine-mediated vasodilation, but this abnormality was prevented when high intralumen pressure was maintained during the no-flow period.

CONCLUSIONS

Reduction in flow and intralumen pressure contribute to the impaired acetylcholine-mediated vasodilation seen after coronary occlusion. This is prevented by maintaining high intralumen pressure during the no-flow period, suggesting that hemodynamic forces may change endothelial function independent of circulating complement or blood cell elements.

Myocardial ischaemia: what happens to the coronary arteries?

Study of the effects of myocardial ischaemia and reperfusion has largely been confined to the impairment of cardiac contractility. However, emerging recognition of the importance of endothelium-derived vasoactive factors in blood flow regulation has stimulated interest in the effect of pathological states such as ischaemia on coronary vascular function and is discussed in this review by Christopher Sobey and Owen Woodman. Neutrophils may play a key role in impaired reperfusion and endothelial damage, and pharmacological intervention to preserve endothelial function could significantly improve coronary blood flow and cardiac function after an ischaemic attack.

Antineutrophil and myocardial protecting actions of a novel nitric oxide donor after acute myocardial ischemia and reperfusion of dogs

BACKGROUND

It has recently been demonstrated that myocardial ischemia and reperfusion results in a marked decrease in the release of nitric oxide (NO) by the coronary endothelium. NO may possess cardioprotective properties, possibly related to inhibition of neutrophil-related activities. We tested the hypothesis that a cysteine-containing nitric oxide donor compound, SPM-5185, would reduce infarct size and inhibit neutrophil-related activities (adherence to coronary vascular endothelium, accumulation).

METHODS AND RESULTS

The effects of intracoronary infusion of SPM-5185 were investigated in a 5.5-hour model of myocardial ischemia (1 hour) and reperfusion (4.5 hours) (MI-R) in anesthetized, open-chest dogs. SPM-5185 (500 nmol/L) or saline vehicle was infused for 4.5 hours into the left anterior descending coronary artery (LAD) at the time of reperfusion after 1 hour of LAD occlusion. MI-R in dogs receiving saline vehicle resulted in severe myocardial injury characterized by dyskinesis, a profound elevation of plasma creatine kinase, marked myocardial necrosis, and high cardiac myeloperoxidase (MPO) activity in the ischemic and necrotic zones. In contrast, treatment with SPM-5185 resulted in a modest restoration of regional function, a reduction of myocardial necrosis expressed as a percentage of the area at risk (12.5 +/- 3.2% versus 41.7 +/- 5.4%, P < .001), and significant reductions of MPO activity in the ischemic zone (0.8 +/- 0.1 versus 2.5 +/- 0.7 U/100 mg tissue, P < .05) and the necrotic zone (1.6 +/- 0.2 versus 3.3 +/- 0.6 U/100 mg tissue, P < .05). In additional studies, SPM-5185 (500 nmol/L) significantly (P < .001) attenuated the adherence of LTB4-stimulated canine neutrophils to autologous segments of coronary artery and attenuated the neutrophil-induced contraction of isolated coronary arterial rings.

CONCLUSIONS

SPM-5185 reduces myocardial necrosis and neutrophil accumulation in an acute model of canine myocardial ischemia and reperfusion. This reduction in myocardial cell injury may be partially related to the inhibitory actions of this novel NO donor on neutrophil adherence to the coronary endothelium.

Platelets protect against myocardial dysfunction and injury induced by ischemia and reperfusion in isolated rat hearts

Platelets are a source of vasoactive mediators that regulate vascular tone. Platelets also play a role in intravascular thrombus formation and dynamic coronary constriction that result in myocardial ischemia. However, effects of platelets on myocardial function after ischemia and reperfusion are unknown. In this study, we examined the effects of platelets on myocardial dysfunction caused by ischemia/reperfusion. Buffer-perfused isolated rat hearts, after global ischemia (15 minutes) and reperfusion (10 minutes), developed marked myocardial dysfunction, indicated by a 65 +/- 4% decrease in the force of cardiac contraction (FCC) and a 26 +/- 7% increase in coronary perfusion pressure (CPP). Ischemia/reperfusion was also associated with release of creatine kinase (CK) and ATP metabolites in the coronary effluents. Perfusion of hearts with buffer containing washed rat platelets (3-8 x 10(7) cells/ml) protected hearts against dysfunction from ischemia/reperfusion, indicated by minimal changes in CPP (-1 +/- 1%) and FCC (-1 +/- 3%). Release of CK in the coronary effluent was also reduced, as was the release of ATP metabolites in the platelet-perfused hearts. Perfusion of hearts with serotonin receptor antagonist LY53,857 (10(-6) M), thromboxane A2 receptor antagonist SQ29,548 (10(-6) M), adenine nucleotide scavenger apyrase (0.4 units/ml), or nitric oxide synthetase inhibitor NG-monomethyl-L-arginine (2 x 10(-4) M) attenuated (p < 0.05) the platelet-mediated cardioprotective effects. Perfusion of the hearts with L-arginine (2 x 10(-4) M) instead of platelets also showed modest protective effects on FCC (-4.3 +/- 13%), CPP (+18 +/- 7%), and CK release. Prolongation of the ischemic period to 30 minutes and reperfusion to 20 minutes also demonstrated marked cardiac dysfunction (FCC, -58 +/- 10%; CPP, +36 +/- 8%) in buffer-perfused hearts. Perfusion of hearts with platelets in this setting of prolonged ischemia/reperfusion also exhibited protective effects on FCC (-24 +/- 10%), CPP (+12 +/- 6%), and CK release. Thus, platelets protect myocardium from ischemia/reperfusion-induced injury, and these protective effects of platelets are evident regardless of the duration of ischemia/reperfusion. Furthermore, these cardioprotective effects of platelets seem to be related to the release of serotonin, thromboxane A2, and adenine nucleotides. These substances most likely elicit release of endothelium-derived relaxing factor, with its attendant tissue-protective effects, from the microvascular endothelium of hearts.

Decreased endothelium-dependent vascular relaxation following subtotal coronary artery occlusion in dogs

Total coronary artery occlusion followed by reperfusion leads to neutrophil accumulation in the reperfused myocardium and a reduction in endothelium-dependent coronary artery relaxation. Attenuated coronary artery relaxation in the affected regions is thought to be related to breakdown of endothelium-derived relaxing factor (EDRF) by free oxygen radicals released during reperfusion. To determine if temporary subtotal coronary artery narrowing leads to similar alteration in vascular reactivity, eight open-chest dogs were subjected to 1 h of left anterior descending (LAD) coronary artery narrowing (70% reduction in basal flow) and pacing-induced increase in heart rate (30% above baseline) followed by reperfusion for 1 h. Thereafter reactivity of ischemic-reperfused LAD and nonischemic circumflex (Cx) coronary artery rings to the thromboxane A2 analog U46,619 and EDRF-dependent vasorelaxants acetylcholine (ACh), thrombin, and adenosine diphosphate (ADP), as well as to EDRF-independent vasorelaxant nitroglycerin (NTG), was examined. Unlike in the setting of total coronary artery occlusion, reperfused myocardium or LAD did not reveal neutrophil infiltration. However, contraction in response to U46,619 was markedly (P < .001) increased in the LAD rings compared to that in the Cx rings. ACh-induced relaxation was only modestly decreased (P < .05) in the LAD coronary artery rings, but the relaxation in response to both thrombin and ADP was markedly diminished (P < .01) as compared to that in the Cx rings. Coronary artery ring relaxation in response to NTG was preserved in the LAD rings. Pretreatment of coronary artery rings with indomethacin did not alter the enhanced contraction or diminished endothelium-dependent relaxation of LAD coronary artery rings.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary pressure-flow regulation in the stunned myocardium

In this study, we used a swine model to study coronary autoregulation in the stunned myocardium. In 18 domestic swine, the left anterior descending coronary artery was cannulated and flow to this artery controlled via an extracorporeal perfusion circuit. Stunning was induced by reducing pump flow to approximately 25% of the baseline value for 15 minutes followed by 1 hour of reperfusion. This ischemia/reperfusion protocol reduced systolic shortening to approximately 50% of control, at 1 hour of reperfusion. Neither the slope of the coronary pressure-flow relation (0.41 +/- 0.19 vs 0.48 +/- 0.26 mL/100 g per min per mmHg) nor an autoregulation index (0.43 +/- 0.16 vs 0.30 +/- 0.32) was significantly changed at 1 hour reperfusion (p > 0.05) compared to baseline. These findings argue against the hypothesis that the mechanical dysfunction of the stunned myocardium is due to suboptimal perfusion caused by poor coronary autoregulation.

Allopurinol and amlodipine improve coronary vasodilatation after myocardial ischaemia and reperfusion in anaesthetized dogs

1. We have assessed the effect of allopurinol, amlodipine and propranolol pretreatment on both endothelium-dependent and endothelium-independent coronary vasodilatation in vivo, by comparing pre-ischaemic responses with those measured after 60 min of coronary artery occlusion and 30 min of reperfusion in anaesthetized dogs. 2. In 15 untreated dogs ischaemia and reperfusion attenuated the increases in coronary blood flow produced by either acetylcholine (0.01-0.05 micrograms kg-1, i.a.) or glyceryl trinitrate (0.05-0.2 micrograms kg-1, i.a.), to an average of 39 +/- 4% and 42 +/- 5% of the pre-ischaemic control response, respectively (both P < 0.05). 3. In 5 dogs treated with allopurinol (25 mg kg-1, orally, 24 h previously, plus 50 mg kg-1, i.v., 5 min before occlusion), the increases in coronary blood flow after ischaemia and reperfusion (acetylcholine: 78 +/- 12%, glyceryl trinitrate: 60 +/- 3% of pre-ischaemic response) were significantly larger than post-ischaemic responses in untreated dogs (both P < 0.05). 4. Similarly, amlodipine treatment (3 micrograms kg-1 min-1, i.v., starting 90 min before occlusion) in 5 dogs improved post-ischaemic increases in blood flow (acetylcholine: 58.5%, glyceryl trinitrate: 66 +/- 6% of pre-ischaemic response, significantly greater than post-ischaemic responses in untreated dogs, P < 0.05). 5. In contrast, in a further 6 dogs pretreated with propranolol (1 mg kg-1, i.v., 30 min before occlusion,plus 0.5 mg kg-1 h-1, i.v.), blood flow responses after ischaemia and reperfusion were not different from post-ischaemic responses in untreated dogs (acetylcholine: 46 +/- 6%, glyceryl trinitrate: 46 +/-6% of pre-ischaemic response).6. These results suggest that allopurinol and amlodipine protect against the post-ischaemic impairment of endothelium-dependent and endothelium-independent coronary vasodilatation in vivo by mechanisms additional to endothelial protection.

Leukocyte depletion in a neonatal model of cardiac surgery

Neonatal cardiac surgical procedures continue to be associated with a considerable incidence of severe post-operative ventricular dysfunction. The role of neutrophils in mediating such injury has recently been proposed but remains controversial. The present study was undertaken to examine the potential benefits of leukocyte depletion for myocardial preservation using an in situ, in vivo porcine model of neonatal cardiac surgery. Sixteen 3- to 5-day-old piglets, 8 controls and 8 leukocyte-depleted animals (LD group), underwent 90 minutes of hypothermic ischemia. Mechanical leukocyte filtration during cardiopulmonary bypass reduced the granulocyte count in the initial reperfusate to 0.7% of controls. This was associated with a reduction in leukocyte sequestration in the coronary vascular bed (p < 0.005), a decrease in myocardial creatine kinase release (p < 0.02), and a reduction in coronary vascular resistance (p < 0.03). These changes in physiological response to ischemia were associated with improved postischemic recovery of left ventricular systolic function in LD animals (p < 0.05), although there was no significant improvement in diastolic function. Application of this technique in neonatal cardiac operations may improve myocardial protection and reduce the associated morbidity and mortality.

Ibuprofen abolishes the increase in leucocyte chemiluminescence observed during ischemic myocardial failure, but fails to improve hemodynamic function

The aim of the study was to evaluate 1) whether the ability of leucocytes to produce oxygen radicals was increased by ischemia and 2) if ibuprofen pretreatment could influence leucocyte oxygen radical production, hemodynamic function, and myocardial oxygen consumption during acute ischemic myocardial failure. We studied two groups of anesthetized dogs (control and ibuprofen-treated), both subjected to coronary embolization with polystyrene microspheres (diameter 50 microns). The embolization procedure was ended when left-ventricular end-diastolic pressure in both groups exceeded 20 mm Hg. Before and after induction of ischemia leucocytes were isolated and stimulated with opsonized zymosan, and oxygen radical production was measured using the luminol-dependent chemiluminescence technique. Significant increase occurred in oxygen radical production (from 10.9 +/- 2.2 to 16.3 +/- 2.3 x 10(5) counts x 10(6) cells-1 x 60 min-1) 90 min after failure in the control group, whereas in ibuprofen-pretreated dogs oxygen radical production was unchanged. Hemodynamic registrations and myocardial oxygen consumption 90 min after failure were, however, not significantly different in control dogs and dogs pretreated with ibuprofen. Thus, in the present study, within the first 90 min of acute ischemic failure, a decrease in the ability of leucocytes to produce oxygen radicals was not related to significant changes in myocardial function.

Increased urinary leukotriene excretion in patients with cardiac ischemia. In vivo evidence for 5-lipoxygenase activation

BACKGROUND

Experimental cardiac ischemia in some animal models results in the activation of the enzyme 5-lipoxygenase and the subsequent production of leukotrienes, potent proinflammatory lipid mediators, by the affected myocardium. Furthermore, prototype antileukotriene drugs can show some beneficial effects on infarct size and cardiac function in these models. Accordingly, urinary excretion of leukotriene E4 (LTE4), the major urinary metabolite of peptide leukotrienes in humans, was measured in patients admitted to the hospital with evidence of acute myocardial ischemia to assess in vivo release of 5-lipoxygenase products during and after the ischemic episode.

METHODS AND RESULTS

Urinary leukotriene excretion was measured by reversed-phase high-performance liquid chromatography and specific radioimmunoassay on admission with acute chest pain and again on day 3 in the following patient groups: acute myocardial infarction (AMI), AMI and clinical evidence of early reperfusion after treatment with recombinant tissue-type plasminogen activator (rt-PA), diagnosis of unstable angina (UA) based on clinical history and coronary arteriography, controls with nonischemic chest pain who underwent coronary arteriography, and age-matched controls and normal hospital employees. In 16 patients with diagnosis of AMI, LTE4 excretion on admission (331 +/- 99 pg/mg creatinine sulfate; mean +/- SEM) was considerably higher than that measured on day 3 (195 +/- 59 pg/mg creatinine sulfate). In a subgroup of seven subjects treated with rt-PA resulting in early reperfusion, day 1 excretion was similar (215 +/- 50 pg/mg) but had significantly declined by day 3 (65 +/- 16 pg/mg; p less than 0.01). Urinary LTE4 excretion at admission for chest pain was also elevated in 14 patients having unstable angina (UA; 370 +/- 125 pg LTE4/mg creatinine sulfate). This had declined significantly (p less than 0.05) by day 3 (at which time chest pain had resolved) to 94 +/- 31 pg/mg creatinine sulfate, an excretion rate comparable with that measured in eight similarly aged subjects (64 +/- 12 pg/mg creatinine).

CONCLUSIONS

This study suggests that peptide leukotrienes are released during episodes of myocardial ischemia and provides clinical evidence for involvement of their biosynthetic enzyme, 5-lipoxygenase, during and after acute myocardial infarction and unstable angina attacks. Thus, potent and specific orally active leukotriene biosynthesis inhibitors may have therapeutic potential in limiting myocardial damage and functional abnormalities after acute ischemia.

Role of leukocytes in coronary vascular endothelial injury due to ischemia and reperfusion

A possible cause of the coronary endothelial injury that occurs with ischemia and reperfusion is the local accumulation of leukocytes during these events. To investigate the role of leukocytes in coronary endothelial injury, we tested the effect of leukocyte removal by filtering on coronary endothelial function in a canine model of regional myocardial ischemia and reperfusion. Blood was supplied to the left anterior descending and circumflex arteries of anesthetized dogs via an extracorporeal circulation. A 60-minute left anterior descending occlusion was followed by 120 minutes of reperfusion either with (n = 6) or without (n = 6) leukocyte filters in the extracorporeal circuit. Regional myocardial blood flow was measured with radiolabeled microspheres. Radiolabeled autologous transferrin (113mIn) and erythrocytes (99mTc) were given intravenously during reperfusion for assessment of microvascular permeability. Left anterior descending and circumflex coronary artery rings were assessed in vitro for endothelium-dependent dilation to acetylcholine, ADP, and thrombin. In unfiltered dogs, ischemia and reperfusion increased the protein leak index of ischemic myocardium 2.3-fold compared with that of nonischemic myocardium (2.3 +/- 0.5 to 5.2 +/- 1.6, p less than 0.05). In filtered dogs, there was no difference in the protein leak index of nonischemic versus ischemic myocardium (1.5 +/- 0.4 versus 1.9 +/- 0.5, p = NS). There was impaired left anterior descending coronary artery relaxation (versus circumflex) in response to endothelium-dependent vasodilators in vitro. However, relaxation was not consistently improved by leukocyte filtering. We conclude that leukocytes are responsible for the endothelial injury secondary to ischemia and reperfusion in the coronary microvasculature but have little or no effect on the endothelial injury in epicardial coronary arteries.

Mechanism of coronary vasodilation produced by bradykinin

BACKGROUND

Bradykinin has been demonstrated to be an endothelium-dependent vasodilator in the cerebral circulation of the mouse, but the actions of bradykinin on regional tissue perfusion in the canine coronary circulation have not been studied.

METHODS AND RESULTS

The mechanism of coronary vasodilation by bradykinin was studied in open-chest, anesthetized dogs. The role of cyclooxygenase stimulation, bradykinin B2 receptor activation, and endothelium-derived relaxing factor in bradykinin-mediated vasodilation was studied in separate groups of dogs. Bradykinin was infused intracoronarily so as to avoid changes in systemic hemodynamics capable of altering the regional distribution of coronary blood flow (radioactive microspheres). Bradykinin produced a preferential increase in subendocardial blood flow. Pretreatment with indomethacin had no effect on bradykinin-mediated increases in total left ventricular flow or the transmural distribution of coronary blood flow. Blockade of bradykinin B2 receptors with the competitive antagonist [Thi5,8, D-Phe7]-bradykinin attenuated both the increase in total flow and redistribution of perfusion to the subendocardium produced by bradykinin. Inhibition of endothelium-derived relaxing factor with quinacrine, occlusion/reperfusion, or NG-monomethyl L-arginine attenuated the total increase in left ventricular flow and blocked the redistribution of flow to the subendocardium produced by bradykinin.

CONCLUSIONS

The present results demonstrate that intracoronary infusion of bradykinin produces a preferential increase in blood flow to the subendocardium via stimulation of B2 receptors and the release of an endothelium-dependent relaxing factor that may be nitric oxide.

Effects of brief coronary occlusion and reperfusion on porcine coronary artery reactivity

The loss of coronary vasodilator reserve after ischemia-reperfusion may be due to endothelial injury, and this vascular dysfunction may contribute to functional alterations observed after ischemia. To determine whether endothelial dysfunction occurs after relatively brief periods of moderate low-flow ischemia in vivo, open-chest swine were subjected to 15 minutes of critical, subtotal left anterior descending coronary artery occlusion (80%) followed by 60 minutes of reperfusion. Serial measurements of regional coronary flow were made with the radiolabeled microsphere technique. After 60 minutes of reperfusion, the left anterior descending coronary artery was excised together with a section of the normally perfused left circumflex coronary artery to examine in vitro the relaxations to the endothelium-dependent dilators ADP and bradykinin and to the endothelial-independent dilators sodium nitroprusside and adenosine. Contractions to serotonin in quiescent rings were also examined. Endocardial and transmural blood flows recovered to preocclusion levels within 60 minutes of reperfusion, as did the epicardial-to-endocardial ratio. Vascular responses in isolated, reperfused left anterior descending coronary artery rings were significantly different from responses in control left circumflex coronary artery rings. Endothelium-dependent relaxations to adenosine diphosphate and bradykinin were significantly depressed in the left anterior descending coronary artery rings compared with left circumflex coronary artery rings (p less than 0.05). Serotonin-induced contractions were significantly greater in occluded-reperfused left anterior descending than in left circumflex coronary arteries (p less than 0.05). Relaxations to adenosine and sodium nitroprusside were not significantly different between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Alteration of endothelium-dependent distribution of myocardial blood flow after coronary occlusion and reperfusion

We have previously demonstrated that intracoronary infusion of the endothelium-dependent vasodilators acetylcholine, ATP, or arachidonic acid produces a preferential increase in subendocardial blood flow in anesthetized dogs. This study was performed to assess the effects of coronary artery occlusion and reperfusion on the distribution of myocardial blood flow produced by endothelium-dependent and endothelium-independent vasodilators. The endothelium was damaged by occlusion of the left anterior descending coronary artery for 45 minutes followed by 60 minutes of reperfusion in pentobarbital-anesthetized dogs. Intracoronary infusions of the endothelium-dependent vasodilators acetylcholine, bradykinin and thiazolylethylamine or the endothelium-independent vasodilator sodium nitroprusside were performed, and regional myocardial blood flow (by radioactive microspheres) was measured before and after occlusion and reperfusion. There were no changes in systemic hemodynamics during intracoronary infusion of vasodilators before or after coronary occlusion and reperfusion. All vasodilators produced similar increases in transmural blood flow before occlusion; however, only the endothelium-dependent vasodilators produced a significant increase in the subendocardial-to-subepicardial blood flow ratio. Increases in transmural flow as well as the preferential increase in subendocardial blood flow produced by acetylcholine, bradykinin, and thiazolylethylamine were attenuated after coronary occlusion and reperfusion. In contrast, increases in transmural blood flow produced by sodium nitroprusside were unchanged. These results suggest that the preferential increase in subendocardial perfusion produced by acetylcholine, bradykinin, and thiazolylethylamine is endothelium-dependent and may be selectively modified by ischemic insult.

Endothelium and myocardial protecting actions of taprostene, a stable prostacyclin analogue, after acute myocardial ischemia and reperfusion in cats

The effects of taprostene, a synthetic prostacyclin analogue, were investigated in a 6-hour model of myocardial ischemia (MI) with reperfusion in anesthetized cats. Taprostene (100 ng/kg/min) was infused intravenously starting 30 minutes postocclusion of the left anterior descending coronary artery followed by reperfusion 1 hour later, and the cats were observed for an additional 4.5 hours. Taprostene infusion resulted in significantly lower plasma creatine phosphokinase activities at every time from 3 to 6 hours for the MI + taprostene group compared with the MI + vehicle group and were not significantly different when compared with sham MI controls. The areas at risk, expressed as a percentage of the total left ventricular weights, were not significantly different between the MI groups. However, the necrotic area expressed as a percentage of the myocardial area at risk was significantly lower in the taprostene-treated cats compared with the untreated MI group (p less than 0.01). Cardiac myeloperoxidase activities indicated that significantly fewer neutrophils were attracted to the area at risk and to the ischemic zone of the MI + taprostene cats when compared with the MI cats given only the vehicle. Data from isolated left anterior descending coronary artery ring preparations removed from hearts after 6 hours of ischemia indicated that the endothelium was damaged by ischemia-reperfusion injury in the untreated cats. However, endothelial dysfunction was not observed in circumflex coronary arteries of ischemic cats or in coronary rings isolated from MI + taprostene cats. Thus, taprostene exerted a significant cardioprotection in cats subjected to ischemia and reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary endothelium-protective effects of defibrotide in ischaemia and reperfusion

Defibrotide is known to enhance prostacyclin (PGI2) release from the vascular endothelium. We investigated the vasoactive effects of defibrotide in isolated rat hearts perfused at constant flow subjected to ischaemia and reperfusion. Defibrotide at 10 or 100 micrograms/ml did not exert any direct vasoactive effect on normal rats hearts. However, ischaemia and reperfusion resulted in an impaired vasodilation to acetylcholine, an endothelium-dependent vasodilator. In contrast, the vasodilator response to the endothelium-independent dilator, nitroglycerin, was unaffected. Defibrotide, at 10 or 100 micrograms/ml, markedly restored the vasodilation to acetylcholine 10 nmol/l to 1 mumol/l (P less than 0.01) without influencing the vasodilator response to nitroglycerin (2 to 200 micrograms/l). Haemoglobin (150 nmol/l) inhibited the dilation to acetylcholine in response to defibrotide. However, no evidence of PGI2 release was observed with acetylcholine-induced vasodilation in the presence or absence of defibrotide. Additionally, 10-100 micrograms/ml of defibrotide did not significantly decrease superoxide radicals generated by a xanthine-xanthine oxidase synthetic system under conditions in which superoxide dismutase was effective. Thus, defibrotide appears to exert an endothelium-protective effect preserving endothelium-derived relaxing factor (EDRF) without directly scavenging free signals.

Synergism between superoxide dismutase and sodium nitrite in cardioprotection following ischemia and reperfusion

The effects of acidified sodium nitrite (NaNO2), a releaser of nitric oxide (NO), combined with human superoxide dismutase (hSOD), were investigated in a 6-hour model of myocardial ischemia (MI) with reperfusion in open-chest, anesthetized cats. Acidified NaNO2 (12.5 mmol/kg/hr) was infused intravenously in cats starting 0.5 hour after occlusion of the left anterior descending (LAD) coronary artery, which was reperfused 1.5 hour following occlusion. Significantly lower plasma creatine phosphokinase activities were observed at all times beyond 3 hours for MI cats given NaNO2 + hSOD when compared with the other MI groups. The areas-at-risk expressed as percentages of the total left ventricular weights were not significantly different among any of the MI groups. However, the necrotic area expressed as a percentage of the myocardial area-at-risk was significantly lower in the MI + NaNO2 + hSOD-treated cats compared with all other MI groups. The NaNO2-treated group also produced a significant decrease in the necrotic area relative to the area-at-risk. Cardiac myeloperoxidase (MPO) activities indicated no significant difference in number of neutrophils attracted to the ischemic zone in the NaNO2 + hSOD-treated MI cats when compared with the other MI groups. Acidified NaNO2 + hSOD together exert significant protection on the myocardium subjected to ischemia and reperfusion injury. NaNO2 may act synergistically with hSOD to prolong the action of NO by scavenging free radicals that inactivate NO.

Endothelial control of vascular tone in large and small coronary arteries

The endothelium modulates coronary vascular tone by the release of endothelium-derived relaxing or contracting substances. The endothelium-derived relaxing factor has been identified as nitric oxide synthesized in endothelial cells from L-arginine. The endothelium can release other relaxing substances such as prostacyclin and a hyperpolarizing factor. Endothelin-1 is a potent vasoconstrictor peptide formed by endothelial cells, and is likely to be the physiologic antagonist of endothelium-derived relaxing factor. Other putative contracting factors include superoxide anions and products of arachidonic acid metabolism. Endothelium-derived relaxing factor is released spontaneously and in response to flow, platelet-derived products (that is, serotonin, thrombin and adenosine diphosphate) and certain autacoids (that is, acetylcholine, bradykinin, histamine, substance P, vasopressin, alpha-adrenergic agonists). A considerable heterogeneity of responses exists among vessels of different size from different anatomic origin and different species. Hypercholesterolemia, atherosclerosis, hypertension and myocardial ischemia or reperfusion, or both, impair endothelium-dependent relaxation. Under normal conditions, endothelium-derived relaxing factor appears to dominate the control of vascular tone of large and small coronary vessels, whereas in disease states, endothelium-derived contracting factors are released. Impairments of endothelial function may be important in the development of various forms of cardiovascular disease.

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.

Protection by superoxide dismutase from myocardial dysfunction and attenuation of vasodilator reserve after coronary occlusion and reperfusion in dog

Previous studies indicate impairment of coronary arterial ring relaxation and loss of coronary vasodilator reserve after coronary artery occlusion and reperfusion. These changes are mediated in part through loss of endothelium-derived relaxing factor (EDRF) and/or myocardial neutrophil accumulation. To examine if superoxide dismutase (SOD), a scavenger of superoxide radicals, would modify the diminished coronary vasodilator reserve after temporary coronary occlusion in the intact animal, open-chest mongrel dogs were subjected to 1 hour of circumflex (Cx) coronary artery occlusion followed by 1 hour of reperfusion and treated with saline or SOD. Before Cx occlusion, coronary blood flow increased, and vascular resistance decreased (both p less than 0.01) in response to EDRF-dependent vasodilator acetylcholine as well as EDRF-independent vasodilator nitroglycerin. After Cx reperfusion, resting Cx coronary blood flow and vascular resistance were similar to the preocclusion values. In the saline-treated animals, there was evidence of myocardial dysfunction, which was measured by segmental shortening (-6 +/- 2% vs. 10 +/- 2%). Furthermore, increase in Cx coronary blood flow and reduction in vascular resistance in response to both vasodilators were significantly (p less than 0.01) impaired; these occurrences suggested loss of coronary vasodilator reserve. Myocardial histology showed extensive capillary plugging by neutrophils in the Cx-supplied myocardium. Myocardial myeloperoxidase activity, an index of neutrophil infiltration, was also increased in the Cx compared with the left anterior descending coronary artery region (p less than 0.02). Treatment of dogs with SOD, started at the end of Cx occlusion and continued during reperfusion, exerted significant (p less than 0.01) protective effect against reperfusion-induced attenuation of coronary vasodilator reserve in response to both acetylcholine and nitroglycerin. Loss of myocardial function (segmental shortening 5 +/- 1% vs. 10 +/- 1%) was less than in the saline-treated animals (p less than 0.01). Cx region-myocardial neutrophil accumulation and myeloperoxidase activity were also less (p less than 0.02) in the SOD-treated than in the saline-treated dogs. These observations suggest that coronary reperfusion impairs coronary vasodilator reserve in intact dogs. This impairment can be modified by treatment of animals with SOD before reperfusion. Capillary plugging by neutrophils may contribute to the altered coronary vasodilator reserve observed in the immediate postreperfusion period, and SOD modifies this reperfusion-induced impairment.

Comparison of the effects of isobutylmethylxanthine and milrinone on ischaemia-induced arrhythmias and platelet aggregation in anaesthetized rabbits

1. The aim of this study was to compare the effects of the non-selective phosphodiesterase (PDE) inhibitor, isobutylmethylxanthine (IBMX) and the selective PDE III inhibitor, milrinone, in a rabbit model of acute myocardial ischaemia. 2. Coronary artery occlusion caused changes in the ST-segment of the ECG and ectopic activity in all control rabbits. Ventricular fibrillation occurred in 10 out of 14 (71%) of these animals. Pretreatment with IBMX 100 micrograms kg-1 plus 10 micrograms kg-1 min-1, starting 10 min before coronary artery occlusion, reduced ischaemia-induced ST-segment changes and ventricular fibrillation occurred in only 10% of this group (n = 10). A similar dose of milrinone had no antiarrhythmic activity, whereas with a lower dose of milrinone, 30 micrograms kg-1 plus 3 micrograms kg-1 min-1 (n = 10), only 30% of rabbits fibrillated and ST-segment changes were attenuated. 3. Acute administration of both IBMX and milrinone reduced arterial blood pressure. With the higher dose of milrinone a significant effect was still present after 10 min of drug infusion. A greater hypotensive response to the higher dose of milrinone was observed in the rabbits which subsequently fibrillated during ischaemia. A marked tachycardia was also observed after administration of the higher dose of milrinone. 4. At the end of the experiment platelet aggregation was studied ex vivo. ADP-induced aggregation was reduced by pretreatment of the rabbits with milrinone but not IBMX. Both PDE inhibitors enhanced the ability of isoprenaline to inhibit ADP-induced platelet aggregation but milrinone was more effective, particularly at the higher dose. The results demonstrate that IBMX was antiarrhythmic but that this activity was not directly related to inhibition of platelet aggregation. Adverse haemodynamic effects may explain the failure of milrinone to have similar activity during myocardial ischaemia.