Endotoxin increases pulmonary vascular protein permeability in the dog

Endotoxin increases pulmonary vascular permeability consistently in some species but fails to reliably cause injury in the dog. We wondered whether this phenomenon depended on the method of injury assessment, as others have relied on edema measurement; we quantified injury by monitoring the rate of extravascular protein accumulation. 113mIn-labeled protein and 99mTc-labeled erythrocytes were injected into anesthetized dogs and monitored by an externally placed lung probe. A protein leak index, the rate of extravascular protein accumulation, was derived from the rate of increase in lung protein counts corrected for changes in intravascular protein activity. After administration of Salmonella enteriditis endotoxin (4 micrograms/kg), the protein leak index was elevated 2.5-fold (41.1 +/- 4.6 X 10(-4) min-1) compared with control (16.0 +/- 2.8 X 10(-4) min-1). In contrast, wet-to-dry weight ratios failed to increase after endotoxin (4.6 +/- 0.8 vs. control values of 4.2 +/- 0.5 g/g dry bloodless lung). However, we observed that endotoxin increased lung dry weight (per unit body weight), which may have attenuated the change in wet-to-dry weight ratios. To determine whether low microvascular pressures following endotoxin attenuated edema formation, we increased pulmonary arterial wedge pressures in five dogs by saline infusion, which caused an increase in wet-to-dry weight ratios following endotoxin but no change in the five controls. We conclude that low dose endotoxin causes pulmonary vascular protein leak in the dog while edema formation is minimal or absent.     

TLR4 inactivation and rBPI(21) block burn-induced myocardial contractile dysfunction

Both large burns and severe gram-negative sepsis are associated with acute myocardial contractile dysfunction. Because others have reported that burn injury may be followed by transient endotoxemia, we hypothesized that bacterial endotoxin induces contractile impairment after burn trauma. We tested this hypothesis in two rodent models. In each model, postburn myocardial contractility was assessed using Langendorff preparations of excised hearts. In the first model, mice expressing either a mutant form of or no Toll-like receptor 4 (TLR4), a critical element of the mammalian endotoxin receptor, were resistant to postburn myocardial contractile dysfunction. In the second model, starting 30 min or 4 h after burn injury, rats were infused with recombinant bactericidal/permeability-increasing protein (rBPI(21)), a protein that binds and neutralizes endotoxin. Hearts from rBPI(21)-treated animals were completely protected from postburn contractile impairment. Because burn-induced contractile dysfunction can be prevented either by blocking signaling through the endotoxin receptor or by neutralizing circulating LPS, bacterial endotoxin may contribute to impaired myocardial contractility after burn injury.     

Intracoronary boluses of adenosine and sodium nitroprusside in combination reverses slow/no-reflow during angioplasty: a clinical scenario of ischemic preconditioning

No or slow reflow following percutaneous coronary intervention (PCI), despite the presence of a patent epicardial vessel, is a serious complication resulting in increased morbidity and mortality. In the present study, we have evaluated the combination therapy of adenosine and sodium nitroprusside administered as sequential intracoronary (IC) boluses on no-reflow during PCI. Seventy-five high risk acute coronary syndrome patients who underwent PCI with evidence of initial less than TIMI (thrombolysis in myocardial infarction) III flow or developed deterioration in TIMI flow during the procedure were randomized to prophylactic administration of multiple boluses of IC saline solution, adenosine (12 microg/bolus) or the combination of adenosine (12 microg/bolus) and sodium nitroprusside (50 microg/bolus), sequentially. Assessment of TIMI and the TMP (tissue myocardial perfusion) grade was done and major adverse cardiac events (MACE) were assessed at the end of 6 months. Slow or no-reflow was persistent in 70% patients receiving saline solution, 31% patients receiving adenosine, and 4% patient receiving the combination. IC injection with saline solution did not produce improvement in TIMI flow or TMP grade. IC injection with combination resulted in greater improvement of TIMI flow and TMP grade. The crossover of patients with no-reflow in saline solution group or adenosine with combination treatment was associated with reestablishment of TIMI II in 4 and TIMI III in 20 patients. Our data suggest that combination therapy of adenosine and nitroprusside is safe and provides better improvement in coronary flow and MACE as compared with IC adenosine alone in cases of impaired flow during coronary interventions.     

Intracoronary C5a induces myocardial ischemia by mechanisms independent of the neutrophil: leukocyte filters desensitize the myocardium to C5a.

Activation of the complement cascade with the generation of anaphylatoxins accompanies the inflammatory response elicited by acute myocardial ischemia and reperfusion. Although complement is activated in the interstitium during acute myocardial ischemia, we have studied mechanisms whereby complement might exacerbate ischemia by using a model employing intracoronary injection of C5a in nonischemic hearts. Intracoronary injection of complement component C5a induces transient myocardial ischemia, mediated through the production of the coronary vasoconstrictors thromboxane A2 and peptidoleukotrienes (LTC4, LTD4), and causes sequestration of polymorphonuclear leukocytes (PMN) in the coronary vascular bed. To further investigate the role of the PMN in the C5a-induced vasoconstriction, the left anterior descending coronary artery (LAD) in pigs was perfused at constant pressure and measurements of coronary blood flow, myocardial contractile function (sonomicrometry), arterial/coronary venous blood PMN count, and thromboxane B2 (TxB2) levels were performed. The myocardial response to intracoronary C5a (500 ng) was determined before, during, and after perfusion with blood depleted of PMNs using leukocyte filters (Sepacell R-500, Pall PL-100). In additional animals, the myocardial response to the PMN chemotactic agent, LTB4, and the effects of intracoronary C5a during constant flow perfusion were measured. Control intracoronary injection of C5a decreased flow (41% of baseline) and contractile function (39% of baseline), PMNs were trapped (5.1 x 10(3) cells/microliters), and TxB2 concentration increased in coronary venous blood. The response to C5a during coronary perfusion with arterial blood depleted of PMNs with Sepacell or Pall filters (less than 0.1 x 10(3) cells/microliters) was greatly blunted, with flow and contractile function falling by less than 14 and 8%, respectively, from baseline, and release of TxB2 was greatly attenuated. However, the myocardial ischemia and TxB2 release remained depressed in response to C5a after removal of the filters and perfusion with either arterial blood containing normal levels of PMNs or stored arterial blood never exposed to filters. In contrast, the repeat C5a challenge resulted in equivalent myocardial extraction of PMNs, thus indicating a dissociation of PMN sequestration from the acute ischemic response and release of TxB2. In separate experiments, the intracoronary injection of LTB4 also resulted in a pronounced myocardial extraction of PMNs (8.6 x 10(3) cells/microliters) greater than during C5a, but did not depress coronary flow or function. Perfusion at constant flow greatly diminished the ischemic response to C5a, indicating that vasoconstriction and resultant ischemia is the main cause of the contractile dysfunction. These data indicate that leukocyte filters inhibit the myocardial ischemia and release of TxB2 induced by C5a via mechanisms not related to PMN depletion.(ABSTRACT TRUNCATED AT 400 WORDS)     

Increased superoxide production causes coronary endothelial dysfunction and depressed oxygen consumption in the failing heart

This study examined whether increased superoxide (O(2)(-).) production contributes to coronary endothelial dysfunction and decreased coronary blood flow (CBF) in congestive heart failure (CHF). To test this hypothesis, the effects of the low-molecular-weight SOD mimetic M40401 on CBF and myocardial oxygen consumption (MVo(2)) were examined in dogs during normal conditions and after CHF was produced by 4 wk of rapid ventricular pacing. The development of CHF was associated with decreases of left ventricular (LV) systolic pressure, maximum first derivative of LV pressure, MVo(2), and CBF at rest and during treadmill exercise as well as endothelial dysfunction with impaired vasodilation in response to intracoronary acetylcholine. M40401 increased CBF (18 +/- 5%, P < 0.01) and MVo(2) (14 +/- 6%, P < 0.01) in CHF dogs and almost totally reversed the impaired CBF response to acetylcholine. M40401 had no effect on acetylcholine-induced coronary vasodilation, CBF, or MVo(2) in normal dogs. Western blot analysis demonstrated that extracellular SOD (EC-SOD) was significantly decreased in CHF hearts, whereas mitochondrial Mn-containing SOD was increased. Cytosolic Cu/Zn-containing SOD was unchanged. Both increased O(2)(-). production and decreased vascular O(2)(-). scavenging ability by EC-SOD could have contributed to endothelial dysfunction in the failing hearts.     

Evaluation of thyrotropin releasing hormone as a therapeutic intervention for endotoxemia

Thyrotropin releasing hormone (TRH) has been reported to reduce endotoxin-induced hypotension and mortality rate in conscious rats. Limited data are available to explain these effects. We evaluated hemodynamic parameters, metabolic function, tissue injury, and survival rate in three groups of instrumented conscious rats following intravenous endotoxin (20 mg/kg, LD/90-24 h) challenge. Pretreatment with TRH (2.0 mg/kg, i.v.) was administered 10 min before endotoxin (n = 10) and control (n = 10) animals were given an equivalent volume of saline. The post-treated group (n = 7) was given TRH at the nadir of the hypotensive response following endotoxin to duplicate published protocols. 5 min after endotoxin blood pressure and cardiac output were significantly higher in the post and pre-treatment groups, respectively, compared to the untreated group. There were no differences at other times. Systemic vascular resistance was not affected by either treatment mode at any time. TRH treatment following endotoxin resulted in transient increases in heart and respiration rates and decreased central venous pressure during the first 30 min. Metabolic function indicated by measurements of glucose, lactate, hematocrit, pH, PO2, and PCO2 at 60 and 240 min after endotoxin was not modified by TRH. The hemorrhagic small intestine characteristic of this model was not improved by either treatment mode. Mortality rates at 4 h after endotoxin were 20% for the untreated, 40% for the pre-treated, and 43% for the post-treated. These results suggest TRH exerts early transient effects on cardiovascular responses evoked by endotoxin in the conscious rat but no lasting beneficial effects were found to support the use of TRH as a mono-therapy for endotoxemia.     

Tracheal venous blood and lymph collection: a model to study airway injury in sheep

Airway injury is a frequent result of the inhalation or aspiration of toxic material. Although upper airway damage can be identified endoscopically, pathophysiological changes are difficult to evaluate. This paper describes an animal model in which changes in tracheal blood and lymph flow rates, wet-to-dry weight ratios, and lymph-to-plasma protein ratios can be evaluated after injury. In this model, 12 cm of the cervical trachea were isolated using a double-cuffed endotracheal tube and injured with cotton smoke at near room temperature. Injury to the trachea was evaluated in twenty-five anesthetized sheep 4 (n = 3), 8 (n = 3), 24 (n = 3), 48 (n = 3), 96 (n = 3), and 192 (n = 2) h after smoke exposure and compared with sham control animals (n = 8). A significant increase in tracheal venous blood flow from 1.3 +/- 0.4 (SD) ml.min-1.cm-1 for the noninjured trachea to 2.8 +/- 1.2 was noted 24 h after injury (P less than 0.01). Lymph flow significantly increased from 1.3 +/- 0.4 microliters.min-1.cm-1 for the noninjured trachea to 9.8 +/- 3.3 24 h after injury while wet-to-dry weight ratios were elevated from 3.0 +/- 0.2 for noninjured trachea to 4.6 +/- 0.9 from 4 to 24 h after injury (P less than 0.01) and decreased to 3.7 +/- 0.5 by 96 h. Cast material consisting of airway exudate, cellular debris, and intact ciliated epithelial cells was both expectorated and found in the trachea when the animals were killed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pressure-dependent vasoactive effects of histamine in the coronary circulation

Twenty-one isolated, perfused, spontaneously rhythmic guinea pig hearts (Langendorff preparation) were used to investigate the effects of coronary perfusion pressure (CPP) on the coronary vasoactive response to a continuous infusion of histamine. Heart rate (HR), coronary perfusate flow (CPF), left ventricular pressure, dp/dtmax, oxygen extraction, and myocardial oxygen consumption (MVO2) were measured at constant CPP of 40 (n = 9), 53 (n = 6), and 65 cm H2O (n = 6) in the absence and presence of continuous intracoronary infusion of histamine [0.9 +/- 0.2 microgram/(min X g)]. At 40 cm H2O histamine caused significant coronary vasodilation. At 65 cm H2O histamine caused significant coronary vasoconstriction. At an intermediate pressure of 53 cm H2O histamine had no effect on CPF. At all three pressures HR, left ventricular pressure, dp/dtmax, and oxygen extraction increased significantly in response to histamine. MVO2 was unchanged by histamine at 65 cm H2O (flow was reduced but extraction increased. MVO2 increased modestly but significantly at 53 cm H2O (12% increase; flow unchanged but extraction increased), and increased prominently at 40 cm H2O (50% increase; flow and extraction increased). We conclude that the coronary vascular effects of continuously infused histamine are dependent on the preexisting, steady-state level of CPP in the isolated perfused guinea pig heart.     

Reversal of myocardial dysfunction in endotoxin shock with insulin.

Recent data reported from this laboratory have documented myocardial functional depression in endotoxin shock. The purpose of the present study was to determine the effects of insulin on the dysfunctioning canine myocardium subjected to lethal endotoxin shock. Experiments were conducted on isolated working left ventricular preparations in which LD90-100 endotoxin was administered prior to, or following, isolation of the heart. Determinations of myocardial performance were conducted under the conditions of controlled mean aortic pressure and cardiac output. Myocardial dysfunction occurred between 2 and 6 h postendotoxin, as evidenced by significantly increased left ventricular end-diastolic pressure, decreased power, and depressed negative dP/dt, although blood glucose concentrations were maintained at control values. Intraatrial infusions of insulin at rates of 6 U/min reversed all signs of myocardial dysfunction. During insulin infusion, heart rates decreased (p less than 0.02) and myocardial lactate uptake increased (p less than 0.02), while oxygen uptake and coronary blood flow were insignificantly altered.     

Coronary smooth muscle reactivity to muscarinic stimulation after ischemia-reperfusion in porcine myocardial infarction.

This study tested whether ischemia-reperfusion alters coronary smooth muscle reactivity to vasoconstrictor stimuli such as those elicited by an adventitial stimulation with methacholine. In vitro studies were performed to assess the reactivity of endothelium-denuded infarct-related coronary arteries to methacholine (n = 18). In addition, the vasoconstrictor effects of adventitial application of methacholine to left anterior descending (LAD) coronary artery was assessed in vivo in pigs submitted to 2 h of LAD occlusion followed by reperfusion (n = 12), LAD deendothelization (n = 11), or a sham operation (n = 6). Endothelial-dependent vasodilator capacity of infarct-related LAD was assessed by intracoronary injection of bradykinin (n = 13). In vitro, smooth muscle reactivity to methacholine was unaffected by ischemia-reperfusion. In vivo, baseline methacholine administration induced a transient and reversible drop in coronary blood flow (9.6 +/- 4.6 to 1.9 +/- 2.6 ml/min, P < 0.01), accompanied by severe left ventricular dysfunction. After ischemia-reperfusion, methacholine induced a prolonged and severe coronary blood flow drop (9.7 +/- 7.0 to 3.4 +/- 3.9 ml/min), with a significant delay in recovery (P < 0.001). Endothelial denudation mimics in part the effects of methacholine after ischemia-reperfusion, and intracoronary bradykinin confirmed the existence of endothelial dysfunction. Infarct-related epicardial coronary artery shows a delayed recovery after vasoconstrictor stimuli, because of appropriate smooth muscle reactivity and impairment of endothelial-dependent vasodilator capacity.     

Induction of endotoxin tolerance improves lung function after warm ischemia in dogs

In shock models, induction of endotoxin tolerance (ET) is known to have a protective effect. The present study was designed to explore if ET is effective in protecting lungs from reperfusion injury. Twelve foxhounds were used as experimental animals. After a left thoracotomy, the left hilum was clamped for 3 h, followed by 8 h of reperfusion. In the treatment group (ET, n = 6), dogs were pretreated with incremental daily endotoxin doses of up to 60 microg/kg on day 6. The ischemia and reperfusion experiment was carried out on day 9. Control group animals (n = 6) were not subjected to endotoxin. After 8 h of observation, functional parameters of the reperfused lung of the ET and the control group were statistically different (P < 0.05) with respect to Po(2) [ET vs. control: 172.7 +/- 12.9 vs. 66.1 +/- 7.2 (SE) mmHg], compliance (16.0 +/- 1.2 vs. 8.3 +/- 1.0 ml/0.1 kPa), and the wet-to-dry ratio (9.4 +/- 0.8 vs. 16.7 +/- 1.2). After 3 h of warm ischemia and 8 h of reperfusion, pulmonary function and lung water content improved in the endotoxin-tolerant group.     

A novel sheep model to study the effect of high rate intracoronary perfusion on cardiac electrophysiology

An increase in coronary flow is known to enhance myocardial metabolism and contractility (the Gregg effect) but the effect on cardiac electrophysiology is unclear. In 5 pentobarbital-anesthetised open-chest sheep, left circumflex coronary artery was perfused with fresh arterial blood at 6 and 10 ml/min respectively in the presence of normal coronary flow. The perfusion was repeated in these animals after treatment with nitro-L-arginine, a nitric oxide synthase inhibitor. The high rate intracoronary perfusion caused a flow-dependent T wave inversion on body surface ECG in all animals (p < 0.01). Pre-treatment with nitro-L-arginine abolished T wave inversion during 6 ml/min perfusion, and diminished the T inversion during 10 ml/min perfusion. Conclusion: An increase in coronary flow alters ventricular repolarisation through nitric oxide release from coronary endothelium.     

Acute ischemic cardiac dysfunction is attenuated via gene transfer of a peptide inhibitor of the beta-adrenergic receptor kinase (betaARK1)

Acute myocardial ischemia is a critical adverse effect potentially occurring during cardiac procedures. A peptide inhibitor of the beta-adrenergic receptor kinase (betaARK1), betaARKct, has been successful in rescuing chronic myocardial ischemia. The present study focused on the effects of adenoviral-mediated betaARKct (Adv-betaARKct) delivery on left ventricle (LV) dysfunction induced by acute coronary occlusion. Rabbits received intracoronary delivery of phosphate-buffered saline (PBS) (n=9) or 5x10(11) viral particles of betaARKct (n=8). A loose prolene 5-0 Potz-loop suture was placed around the circumflex coronary artery (LCx) with both ends buried under the skin. Four days later, the suture was retrieved and pulled to occlude the LCx. Ischemia was confirmed by immediate ECG changes. LV function was continuously recorded for 45 min. Contractility (LVdP/dtmax), relaxation (LVdP/dtmin) and end diastolic pressure (EDP) were less impaired in the betaARKct group as compared to PBS (P<0.05, two-way ANOVA). betaAR density was higher in the ischemic area of the LV in the betaARKct group (betaARKct: 71.9+/-4.6 fmol/mg protein, PBS: 54.5+/-4.0 fmol/mg protein, P<0.05). Adenylyl cyclase activity was also improved basally and in response to betaAR stimulation. betaARK1 activation was less in the betaARKct group (P<0.05). Therefore, inhibition of myocardial betaARK1 may represent a new strategy to prevent LV dysfunction induced by acute coronary ischemia.     

Effect of angiotensin inhibition on the coronary artery lower pressure limit in anesthetized dogs

The renin-angiotensin system plays a critical role in regulating vasoconstriction and vasodilatation that can influence myocardial blood flow and its transmural distribution. We tested the hypothesis that angiotensin inhibition can induce a leftward shift of the coronary autoregulatory pressure-flow relation and preserve distribution of myocardial blood flow at lower coronary perfusion pressures. We established circumflex artery pressure-flow relations under baseline conditions and after intracoronary enalaprilat or losartan potassium. Thereafter, transmural myocardial blood flow was measured at baseline and at the lower coronary pressure limit (LPL). With enalaprilat, the LPL was shifted leftward from 48 +/- 6 mmHg at baseline to 43 +/- 3 mmHg (P = 0.026); with losartan, the LPL was shifted leftward from 48 +/- 10 mmHg at baseline to 41 +/- 5 mmHg (P = 0.027). The leftward shift occurred while cardiac hemodynamics and MVO2 were maintained at control levels. These results indicate that angiotensin inhibition extends the range of coronary autoregulation to lower LPL while preserving myocardial blood flow distribution, a physiologic effect that might explain the lower incidence of coronary events in treated patients.     

Daily exercise enhances coronary resistance vessel sensitivity to pharmacological activation

The effect of daily exercise on the coronary resistance vessel sensitivity to intracoronary infusion of several pharmacological agents was assessed in 12 conscious adult mongrel dogs. alpha-Adrenergic receptor agonists (norepinephrine and phenylephrine) significantly decreased coronary blood flow velocity. beta 2-Adrenergic receptor agonists (isoproterenol and zinterol) and a metabolic vasodilator (adenosine) significantly increased coronary blood flow velocity. These responses occurred without altering factors that influence myocardial metabolism. Daily exercise significantly enhanced the coronary vascular sensitivity to each of the pharmacological agents. These results suggest that a nonspecific potentiation to pharmacological activation occurs after daily exercise. After left stellate ganglionectomy, intracoronary infusions of each pharmacological agent had similar effects on coronary blood flow velocity as presented for the intact dogs; however, daily exercise did not enhance the coronary vascular sensitivity to the pharmacological agents. These results demonstrate the need for an intact nervous system for the vascular adaptations associated with daily exercise.     

Endotoxemia decreases matching of regional blood flow and O2 delivery to O2 uptake in the porcine left ventricle

Heterogeneity of regional coronary blood flow is caused in part by heterogeneity in O(2) demand in the normal heart. We investigated whether myocardial O(2) supply/demand mismatching is associated with the myocardial depression of sepsis. Regional blood flow (microspheres) and O(2) uptake ([(13)C]acetate infusion and analysis of resultant NMR spectra) were measured in about nine contiguous tissue samples from the left ventricle (LV) in each heart. Endotoxemic pigs (n = 9) showed hypotension at unchanged cardiac output with a fall in LV stroke work and first derivative of LV pressure relative to controls (n = 4). Global coronary blood flow and O(2) delivery were maintained. Lactate accumulated in arterial blood, but net lactate extraction across the coronary bed was unchanged during endotoxemia. When LV O(2) uptake based on blood gas versus NMR data were compared, the correlation was 0.73 (P = 0.007). While stable over time in controls, regional blood flows were strongly redistributed during endotoxin shock, with overall flow heterogeneity unchanged. A stronger redistribution of blood flow with endotoxin was associated with a larger fall in LV function parameters. Moreover, the correlation of regional O(2) delivery to uptake fell from r = 0.73 (P < 0.001) in control to r = 0.18 (P = 0.25, P = 0.009 vs. control) in endotoxemic hearts. The results suggest a redistribution of LV regional coronary blood flow during endotoxin shock in pigs, with regional O(2) delivery mismatched to O(2) demand. Mismatching may underlie, at least in part, the myocardial depression of sepsis.     

MPG静注减轻清醒狗缺血后心肌顿抑

为了解自由基清除剂２巯基丙酰基甘氨酸（ＭＰＧ）能否减轻缺血后心肌顿抑,本文报告了在清醒狗模型中氧自由基清除剂ＭＰＧ对缺血后心肌顿抑的疗效。３９只清醒狗模型阻闭前降支１５ｍｉｎ后再灌注４８ｈ。治疗组（ｎ＝１７）于阻闭前１５ｍｉｎ始静脉给予ＭＰＧ（１００ｍｇ／ｋｇ·ｈ）,共持续６０ｍｉｎ,对照组（ｎ＝２２）给予生理盐水。结果表明,二组缺血区侧支血流、缺血区大小及血液动力学指标无显著差异,而治疗组室壁收缩增厚指数（一种局部心肌功能指标）于再灌注后２、３、４、５、６ｈ明显大于对照组,当侧支血流低于１０％时,改善更明显。指数回归分析结果显示,治疗组侧支血流越低,收缩功能恢复程度越明显。结论,ＭＰＧ可以促进缺血后心肌顿抑的恢复,这种有益的疗效在低侧支血流时更明显。     

Coronary plaque injury triggers neutrophil activation in patients with coronary artery disease

Activation of leukocytes, in particular polymorphonuclear neutrophils (PMN), is considered an early event in unstable coronary disease. Upon activation PMN liberate myeloperoxidase (MPO), an enzyme which binds to the vessel wall and depletes vascular NO bioavailability. Using coronary balloon angioplasty as a trigger to provoke coronary plaque injury, we assessed the time course of neutrophil activation, local and peripheral levels of myeloperoxidase, and systemic vascular NO bioavailability in patients with stable coronary artery disease. Twenty-four patients with stable CAD were enrolled prior to undergoing percutaneous interventions (PCI, n=14) and diagnostic coronary angiography (n=10), respectively. Following angioplasty arterial MPO plasma levels increased (231.5+/-67.6 to 273.8+/-80.4 pg/mg protein; P<0.01) whereas MPO levels in the coronary sinus decreased (240.8+/-74.4 vs 205.4+/-60.1 pg/mg protein; P<0.01) in the absence of elevated serum markers for myocardial necrosis. Following PCI, patients revealed impaired vascular NO bioavailability as reflected by reduced brachial flow-mediated dilation (FMD; 6.25+/-3.03 to 4.90+/-2.70%; P<0.01), whereas FMD increased in the angiography group. Coronary plaque injury provokes rapid activation of PMN in the absence of myocardial necrosis; the coronary circulation emerges as a primary site for deposition of MPO following injury of the coronary vessel wall. Activation of PMN with release of MPO is not only restricted to the target site, but can be assessed systemically and may represent a critical mechanistic link for impaired systemic vascular NO bioavailability in patients suffering unstable coronary disease.     

Reactive oxygen species modulate coronary wall shear stress and endothelial function during hyperglycemia

Hyperglycemia is associated with generation of reactive oxygen species (ROS), and this action may contribute to accelerated atherogenesis. We tested the hypothesis that hyperglycemia produces alterations in left anterior descending coronary artery (LAD) wall shear stress concomitant with endothelial dysfunction and ROS production in dogs (n = 12) instrumented for measurement of LAD blood flow, velocity, and diameter. Dogs were randomly assigned to receive vehicle (0.9% saline) or the superoxide dismutase mimetic 4- hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (tempol) and were administered intravenous infusions of d-glucose to achieve target blood glucose concentrations of 350 and 600 mg/dl (moderate and severe hyperglycemia, respectively). Endothelial function and ROS generation were assessed by coronary blood flow responses to acetylcholine (10, 30, and 100 ng/kg) and dihydroethidium fluorescence of myocardial biopsies, respectively. Indexes of wall shear stress were calculated with conventional fluid dynamics theory. Hyperglycemia produced dose-related endothelial dysfunction, increases in ROS production, and reductions in oscillatory shear stress that were normalized by tempol. The results suggest a direct association between hyperglycemia-induced ROS production, endothelial dysfunction, and decreases in oscillatory shear stress in vivo.     

TGF-beta 1 attenuates myocardial ischemia-reperfusion injury via inhibition of upregulation of MMP-1

Ischemia-reperfusion (I/R) is thought to upregulate the expression and activity of matrix metalloproteinases (MMPs), which regulate myocardial and vascular remodeling. Previous studies have shown that transforming growth factor-beta(1) (TGF-beta(1)) can attenuate myocardial injury induced by I/R. TGF-beta(1) is also reported to suppress the release of MMPs. To study the modulation of MMP-1 by TGF-beta(1) in I/R myocardium, Sprague-Dawley rats were given saline and subjected to 1 h of myocardial ischemia [total left coronary artery (LCA) ligation] followed by 1 h of reperfusion (n = 9). Parallel groups of rats were pretreated with recombinant TGF-beta(1) (rTGF-beta(1), 1 mg/rat, n = 9) before reperfusion or exposure to sham I/R (control group). I/R caused myocardial necrosis and dysfunction, indicated by decreased first derivative of left ventricular pressure, mean arterial blood pressure, and heart rate (all P < 0.01 vs. sham-operated control group). Simultaneously, I/R upregulated MMP-1 (P < 0.01). Treatment of rats with rTGF-beta(1) reduced the extent of myocardial necrosis and dysfunction despite I/R (all P < 0.01). rTGF-beta(1) treatment also inhibited the upregulation of MMP-1 in the I/R myocardium (P < 0.05). To determine the direct effect of MMP-1 on the myocardium, isolated adult rat myocytes were treated with active MMP-1, which caused injury and death of cultured myocytes, measured as lactate dehydrogenase release and trypan blue staining, in a dose- and time-dependent manner (P < 0.05). Pretreatment with PD-166793, a specific MMP inhibitor, attenuated myocardial injury and death induced by active MMP-1. The present study for the first time shows that MMP-1 can directly cause myocyte injury or death and that attenuation of myocardial I/R injury by TGF-beta(1) may, at least partly, be mediated by the inhibition of upregulation of MMP-1.