Effects of endogenously produced leukotrienes, thromboxane, and prostaglandins on coronary vascular resistance in rabbit myocardial infarction

Arachidonate metabolism in cultured fibroblasts derived from normal and infarcted canine heart

Metabolites of arachidonic acid (eicosanoids) may have an important role in the healing process after myocardial infarction. We examined the ability of cardiac fibroblasts from normal and from healing infarcted ventricle to metabolize arachidonate. We induced myocardial infarction in dogs and then allowed them to recover for 1 week, at which time they were killed, and the heart was removed. Fibroblasts were harvested from normal and from the healing, infarcted areas of the left ventricle. The cells from each source were morphologically indistinguishable. There were 347 +/- 102-fold more fibroblasts cultured from the infarcted area than from the normal area. Interestingly, the infarct-derived cells had a slower doubling time (37.4 +/- 3.7 hours) than the normal cells (22.0 +/- 3.6 hours). The uptake of exogenous arachidonate and its distribution in complex lipids was the same in the cells from each area. When stimulated with the calcium ionophore, free exogenous arachidonate, bradykinin, or histamine the cells produced prostaglandin E2 and prostaglandin I2. In each case the infarct-derived cells produced from twofold to fivefold more prostaglandin than the normal cells. We also found that prostaglandin synthesis was highly dependent on the growth state of the cells with a marked decrease a confluence. Finally, in experiments designed to mimic the early state of infarction, we confirmed that isolated cardiac myocytes release arachidonate and showed that normal fibroblasts can incorporate it. The production of eicosanoids by cardiac fibroblasts may be substantial during the healing of myocardial infarction due to their dramatic proliferation and the increased prostaglandin production per cell.

Cardiac ischemia and endothelial function in the isolated rabbit heart

Truly effective prevention of reperfusion myocardial damage is precluded in part by a lack of understanding of the earliest events which accompany ischemia. The purpose of this study was to assess the coronary endothelial response to two forms of ischemic injury in an isolated crystalloid perfused rabbit heart. Global cardiac ischemia, confirmed by NADH fluorescence photography, was induced either by mechanically reducing coronary flow by 90% (MRCF, N = 11) or by an infusion of N-formyl-methionyl-leucyl-phenylalanine (fMLP, N = 11), a known stimulus for leukotriene synthesis and coronary vasospasm. Compared with control, MRCF resulted in an increase in effluent concentrations of both prostacyclin (152 +/- 22 pg/ml vs 951 +/- 214 pg/ml, P less than 0.05) and plasminogen activator (0.8 +/- .3 IU/ml vs 1.4 +/- 0.5, P less than 0.05) but no detectable increase in effluent thromboxane B2 or leukotriene C4 concentrations. fMLP infusion resulted in an immediate reduction in coronary flow coincident with diffuse myocardial ischemia. In contrast to MRCF, however, fMLP-induced ischemia resulted in a significant but smaller increase in effluent prostacyclin concentration (210 +/- 47 pg/ml vs 606 +/- .55 pg/ml, P = 0.05) and a marked increase in both thromboxane B2 (less than or equal to 33 +/- 4 pg/ml vs 1141 +/- 375 pg/ml, P less than 0.05) and leukotriene C4 (less than 0.25 ng/ml vs 3.3 +/- 1.2 ng/ml, P less than 0.05) concentrations. Additionally, fMLP caused a reduction in effluent plasminogen activator activity (0.5 +/- 0.1 IU/ml vs 0.39 +/- 0.1 IU/ml, N = 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular effects of leukotrienes

Leukotrienes have been shown to significantly influence coronary vascular resistance, infarct size, pulmonary vascular resistance, bronchial tone, and renal vascular resistance either directly or indirectly. There is a notable dearth of data on human pathophysiologic conditions. With the advent of specific inhibitors of the synthesis and action of leukotrienes and, more importantly, of methods on the in-vivo synthesis of these potentially important mediators, these gaps in our understanding will be closed.

Essential fatty acid deficiency inhibits early but not late leukocyte infiltration in rabbit myocardial infarcts

Essential fatty acid (EFA) deficiency, induced by elimination of the dietary (n-6) fatty acids, has been shown to limit inflammatory cell influx and consequent enhanced eicosanoid production in experimental glomerulonephritis and hydronephrosis. To determine whether EFA-deficiency exerts anti-inflammatory effects following left ventricular myocardial infarction (LVMI), male weanling rabbits were fed EFA-deficient diet for 3 months prior to 60 minutes of distal left circumflex coronary artery occlusion followed by reperfusion. One and 4 days later, corresponding to infiltration of cardiac tissue with polymorphonuclear (PMN) and mononuclear leukocytes respectively, infarcted hearts were buffer perfused and stimulated to produce eicosanoids with f-met-leu-phe or bradykinin. One day following LVMI, the hearts of EFA-deficient rabbits demonstrated a marked suppression of PMN infiltration and eicosanoid production relative to controls. Four days following myocardial infarction, no differences were observed in mononuclear cell invasion, collagen deposition, or eicosanoid production between EFA-deficient and normal hearts. Our data show that EFA-deficiency inhibits PMN influx and consequent enhanced eicosanoid production without affecting the later appearance of mononuclear cells, collagen deposition, or eicosanoid production. Recent studies have shown that suppression of PMN invasion limits the extent of tissue damage following LVMI. Selective inhibition of PMN infiltration is possible and may be useful in the management of acute myocardial infarction.

fMet-Leu-Phe receptor expression by an interstitial cell in rabbit right atrium following left ventricular myocardial infarction

Previous studies have shown that rabbit hearts subjected to in vivo left ventricular myocardial infarction and subsequent ex vivo perfusion respond to N-formylmethionyl-leucyl-phenylalanine (fMLP) with enhanced eicosanoid synthesis. This synthetic response occurs primarily in the right cardiac atrium, a site distant from the injury, and is not the result of increased enzymatic capacity for arachidonate metabolism. To further investigate the mechanism of this enhanced synthetic response, [3H]fMLP binding was characterized and binding sites were localized autoradiographically in intact tissue sections prepared from control hearts and hearts subjected to left ventricular myocardial infarction (1, 2, and 4 days postinfarction). Analysis of binding isotherms revealed a saturable high affinity (KD approximately 1 nM) fMLP binding site in the right cardiac atrium. After myocardial infarction specific binding in right atria (2 day) increased 12-fold (Bmax = 14.8 +/- 2.4 fmol/cm2) compared with normal controls (Bmax = 1.2 +/- 0.1 fmol/cm2). Specific binding of fMLP also increased in the infarcted zone of left ventricle, but Bmax was only 30-50% that of right atria. Light microscopic autoradiography studies revealed that atrial fMLP binding sites were highly concentrated in small morphologically undifferentiated cells located in interstitial and perivascular spaces. These results demonstrate the existence of a formylated peptide receptor on a nonleukocytic cell and illustrate its regulation following left ventricular injury.

Selective antagonism of peptidoleukotriene responses does not reduce myocardial damage or neutrophil accumulation following coronary artery occlusion with reperfusion

This study was designed to assess the effect of a peptidoleukotriene receptor antagonist, SK&F 104353, for limiting myocardial damage and neutrophil accumulation in rats subjected to myocardial reperfusion injury (MI/R). In conscious rats, SK&F 10,4353 (25 mg/kg, i.v.) antagonized LTD4-induced vasopressor responses by 90% and 60% at 1 and 4 hr, respectively, indicating effective blockade of peptido-leukotriene responses. In another group of animals subjected to 30 min of coronary artery occlusion with reperfusion for 24 hr, myocardial injury and neutrophil infiltration were determined by measuring creatine phosphokinase (CPK) specific activity and myeloperoxidase (MPO) activity, respectively, in the left ventricular free wall (LVFW). Myocardial CPK levels were 8.1 +/- 0.2 U/mg protein in Sham-MI/R vehicle-treated animals, and were significantly decreased to 6.4 +/- 0.6 U/mg protein in MI/R-vehicle animals. Myocardial MPO values were 1.5 +/- 0.5 U/g LVFW in Sham-MI/R vehicle-treated animals, and significantly increased to 4.3 +/- 0.6 U/g LVFW in MI/R-vehicle animals. Administration of SK&F 10,4353 (25 mg/kg, i.v.) 1 min prior to coronary occlusion and 3.5 hr post reperfusion had no effect on the loss of myocardial CPK specific activity or the increase in MPO levels (p greater than 0.05, compared to the MI/R-vehicle group). Thus, at a dose that antagonized LTD4-induced vasopressor responses, SK&F 104353 did not attenuate either the extent of myocardial injury or inflammatory cell accumulation associated with myocardial ischemia/reperfusion. These results suggest that peptidoleukotrienes do not contribute to the progression of myocardial ischemic/reperfusion injury.

Reduced myocardial neutrophil accumulation and infarct size following thromboxane synthetase inhibitor or receptor antagonist

Since thromboxane A2 (TXA2) release may relate to the extension of myocardial injury following coronary ligation, the authors examined the effects of pretreatment with a selective TXA2 synthetase inhibitor U-63,557A, or a TXA2 receptor antagonist SQ-29,548, on myocardial infarct size forty-eight hours following left coronary ligation in rats. Myocardial infarct size (as percent of left ventricle, LV) was decreased from 44 +/- 3% in saline-treated control animals to 34 +/- 4% (P less than 0.05) in U-63,557A-treated animals and to 32 +/- 4% (P less than 0.05) in SQ-29,548 treated animals (U-63,557A-treated vs SQ-29,548-treated, P = NS). LV creatine kinase (CK) was 5.08 +/- 0.42 IU/mg protein in noninfarcted untreated rats and 1.79 +/- 0.21 IU/mg protein in saline-treated infarcted rats. LV CK was 2.86 +/- 0.40 IU/mg protein in U-63,557A-treated rats and 3.11 +/- 0.51 IU/mg protein in SQ-29,548-treated infarcted rats (both P less than 0.05 compared with saline-treated rats). The beneficial effects of U-63,557A and of SQ-29,548 were not accompanied by reduction in indices of myocardial oxygen demand (heart rate and arterial pressure). However, neutrophil accumulation in the infarcted myocardium was markedly decreased by U-63,557A and SQ-29,548 pretreatment. Myocardial myeloperoxidase activity, a specific marker of neutrophil infiltration, was also decreased (P less than 0.02) in U-63,557A- and SQ-29,548-treated animals (0.09 +/- 0.03 and 0.07 +/- 0.02 units/100 mg, respectively) compared with saline-treated infarcted rats (0.19 +/- 0.04 units/100 mg). In vitro incubation of U-63,557A and SQ-29,548 caused a significant and similar reduction in f-MLP-induced neutrophil chemotaxis, and U-63,557A increased prostacyclin formation in whole blood. These data suggest that reduction in the extent of myocardial injury by TXA2 synthetase or receptor inhibitors may, in part, relate to a decrease in neutrophil accumulation in the infarcted tissue. In spite of differences in mechanisms of action of U-63,557A and SQ-29,548, both agents exert a similar protective effect on the extent of myocardial injury following coronary ligation. Reduction in neutrophil accumulation in the infarcted zone, as well as in f-MLP-directed chemotaxis in vitro, suggests that TXA2 inhibition may modulate neutrophil migration.

Neutrophil function in ischemic heart disease

Neutrophils contribute to the healing of and scar formation in myocardium after ischemic injury. Many recent studies indicate that neutrophils may be involved in the genesis and propagation of myocardial ischemia. To characterize neutrophil function in ischemic heart disease, neutrophil chemotaxis, leukotriene B4 (LTB4) generation, and elastase release in plasma were measured in 20 patients with stable angina, 17 patients with unstable angina or acute myocardial infarction (AMI), and 20 age-matched control subjects. Neutrophils from patients with stable angina exhibited markedly increased chemotactic activity and LTB4 generation as compared with the age-matched control subjects (p less than 0.01). Neutrophils of nine of 17 patients with unstable angina or AMI clumped spontaneously ex vivo and exhibited marked pseudopod formation and granule extrusion on electron microscopy. Subsequent chemotactic activity and LTB4 generation by neutrophils from these patients was less than in patients with stable angina, suggesting previous in vivo activation. Plasma levels of peptide B beta, a product of fibrin degradation by human neutrophil elastase, were approximately 15-fold higher (p less than 0.001) in patients with unstable angina or AMI (588 +/- 171 pmol/l, mean +/- SEM) compared with those in patients with stable angina (37 +/- 25 pmol/l) or control subjects (40 +/- 22 pmol/l), confirming intense in vivo neutrophil activation. Our study shows enhanced neutrophil function in patients with ischemic heart disease. The increased neutrophil chemotactic activity and LTB4 generation may be markers of stable angina pectoris. Intense neutrophil activation in unstable angina or AMI, as manifested by morphologic changes in neutrophils and elastase release, may relate to ongoing in vivo cellular activation.

Tissue plasminogen activator and plasmin independently decrease human neutrophil activation

Tissue-plasminogen activator (t-PA) and plasmin both decrease platelet aggregation, which may contribute to thrombolysis and tissue salvage. Since neutrophils may contribute to reperfusion injury, we examined the effects of t-PA and plasmin on human neutrophil function. t-PA (1 to 100 micrograms/ml) decreased f-MLP-induced chemotaxis and ionophore A23187-induced superoxide and LTB4 release in isolated neutrophils, and these effects were not blocked by the plasmin-inhibitor epsilon-aminocaproic acid (epsilon-ACA). On the other hand, plasmin (0.05 to 0.5 units/ml) also decreased these neutrophil functions but its effects were blocked in the presence of epsilon-ACA. Thus, while both t-PA and plasmin decrease neutrophil functions, effects of t-PA are independent of plasmin generation. Cumulative effects of t-PA and plasmin on neutrophil functions may relate to the overall efficacy of t-PA in thrombotic disorders.

Role of invading leukocytes in enhanced atrial eicosanoid production following rabbit left ventricular myocardial infarction

The isolated perfused hearts of rabbits previously subjected to in vivo left ventricular myocardial infarction (LVMI) show a 5-10-fold increase in f-Met-Leu-Phe (FMLP) and bradykinin (BK)-stimulated eicosanoid metabolite production relative to noninfarcted hearts. This exaggerated arachidonate metabolism has been shown to occur primarily in the cardiac atria, a site remote from the zone of injury and to be associated with a 10-15-fold increase in atrial FMLP receptor number in the absence of atrial inflammation. All of these changes were temporally related to leukocyte infiltration into the infarct zone. To determine whether invading leukocytes mediate these responses, acute inflammatory cell influx was suppressed either by inducing leukopenia with nitrogen mustard or by administration of BW-755C, a mixed cyclooxygenase-lipoxygenase inhibitor. Both pharmacological manipulations resulted in a decrease in inflammatory cells in the infarct zone and a marked suppression (50-70%) of ex vivo agonist-stimulated eicosanoid metabolite production from perfused hearts and isolated atria. These manipulations also resulted in reversal of ex vivo FMLP-induced coronary vasoconstriction as well as augmentation of BK-induced coronary vasodilation. Further studies in nitrogen mustard-treated animals revealed a suppression of the LVMI-stimulated increase in atrial FMLP receptor number. These data show that suppression of leukocyte invasion after LVMI attenuates enhanced cardiac and atrial eicosanoid metabolite production, and results in marked changes in coronary vascular reactivity. An additional finding was that basal and stimulated LTB4 production was markedly increased in infarcted hearts. In vivo suppression of the increase in LTB4 production by BW-755C was associated with inhibition of inflammatory cell influx into the infarct zone. It therefore appears that LTB4 may be an important proinflammatory mediator of leukocyte invasion after LVMI.

The cell biology of fibroblast cyclooxygenase

We have prepared polyclonal antisera against sheep seminal vesicles cyclooxygenase (COX) which cross-reacted with human COX. We employed this antisera in studies with human dermal fibroblast cultures to immunoprecipitate selectively the COX enzyme. Labeling of the cells with [35S]-methionine, solubilization of cellular COX followed by its immunoprecipitation, SDS-PAGE electrophoresis and fluorography enabled us to determine directly the synthetic rate of COX protein and its modulation by the monokine interleukin-1 (IL-1). The immunoprecipitated [35S]-labeled COX, as judged from SDS-PAGE electrophoresis, has a molecular size of approximately 73,000 daltons, similar to that of native sheep COX and [3H]-acetyl COX. IL-1 stimulation of enhanced COX synthesis was time and dose dependent; as little as 0.03 units/ml of IL-1 produced significant stimulation of [35S]-labeled COX synthesis. Maximum stimulation was 3-10-fold after preincubation of the cells with IL-1 for 12-16 hours. IL-1 treatment of cells in serum-free media yielded parallel dose response curves for stimulation of PGE2 formation, cellular solubilized COX activity and synthesis of newly formed COX, suggesting that this IL-1 effect is mediated solely via induction of new COX protein synthesis. In contrast, IL-1 effect on cells incubated in the presence of fetal calf serum is more complex. Serum synergistically augments the IL-1 effect on PGE2 synthesis in intact cells but concurrently blunts IL-1 induction of COX synthesis, thus suggesting that a factor (or factors) in serum may stimulate PGE2 production by activating cellular phospholipase(s).

Method for quantification of myocardial infarction and inflammatory cell infiltration in rat cardiac tissue

A method to quantitate both creatine phosphokinase (CPK) and myeloperoxidase (MPO) activity from the same cardiac tissue homogenate preparation is described. Depletion of CPK specific activity is used to quantitate myocardial infarct size, while MPO activity is utilized as a marker for polymorphonuclear leukocyte and monocyte infiltration into inflammatory sites. However, the standard assay systems are not compatible, necessitating the use of different groups of animals for these two parameters. This leads to an increase in cost, effort, and variability. The described method utilized a standard CPK methodology. It was found that interference in the MPO assay was likely caused by 2-mercaptoethanol present in the homogenate buffer (IC50 = 90 microM). Washing of the 30 K X g pellet followed by rehomogenization restored the MPO activity. Negligible MPO activity was found in the original supernatant or washes. Through the use of this technique, MPO activity was measured in the hearts of myocardial infarcted animals. The results indicated that MPO activity generated from CPK homogenate pellets compared favorably to the activity seen using standard methodology homogenates. The procedure described thus allowed the simultaneous determination of myocardial CPK specific activity and MPO activity, resulting in decreased animal usage and potentially less variability.

Invited comment: lipids and the development of immune dysfunction and infection

Excessive W-6 PUFA metabolism due to high levels of dietary fat intake can encourage infection via prolonged inflammation, enhanced Gram negative survival, reticuloendothelial blockage, immunosuppression, and monokine depression. Lipids can influence host immunity by altering eicosanoid metabolism and membrane structure and function. Further investigations are essential to answer questions regarding the levels and properties of various essential fatty acids in TPN lipid emulsions. Combining the features of LCT in the form of W-3 PUFA (fish oil) and MCT in the form of medium-chain triglyceride in a "structured lipid" may decrease infection and may improve survival rates by producing fewer inflammatory eicosanoids of the two- and four-series, and serving as a more "efficient fuel." The introduction of W-3 polyunsaturated fatty acids into the TPN emulsions as well as into normal diets may provide an important therapeutic advance in the pathogenesis of disease. Such unique antiinflammatory properties of W-3 PUFA require intensive research.

Neutrophils as potential participants in acute myocardial ischemia: relevance to reperfusion

An interaction among leukocytes, platelets and endothelial cells is important in atherogenesis and in maintenance of blood flow and vascular tone. These complex cell-cell interactions are mediated by release of such metabolic substances as arachidonic acid metabolites, growth factors, oxygen free radicals and endothelium-derived relaxing factor. These substances participate in the regulation of blood flow in health and disease, and perturbation in the delicate equilibrium among various cellular elements may lead to evolution and propagation of myocardial ischemia. During reperfusion of ischemic myocardium, neutrophils together with platelets cause capillary plugging in the coronary microcirculation and exert detrimental effects on endothelial function resulting in the "no reflow" phenomenon, ventricular arrythmias, loss of coronary vascular reserve and, perhaps, extension of cellular injury. This review addresses the mechanisms of cell-cell interactions with special reference to myocardial ischemia and the potential for development of improved therapy to protect and preserve ischemic myocardium.

The effects of lipoxygenase inhibitor and peptidoleukotriene antagonist on myocardial injury in a canine coronary occlusion-reperfusion model

We studied effects of lipoxygenase inhibitor (AA-861) and peptidoleukotriene antagonist (ONO-1078) on infarct size, polymorphonuclear leukocyte (PMNs) infiltration, gross myocardial hemorrhage and ventricular arrhythmias in canine coronary occlusion (2 hr)-reperfusion (5 hr) model. Infarct size (IS) and risk area (RA) were determined by dual staining technique. Thirty minutes before coronary occlusion dogs were randomly assigned to one of the following three groups: lipoxygenase inhibitor group (n = 11) receiving AA-861 3 mg/kg i.v., peptidoleukotriene antagonist group (n = 11) receiving continuous intravenous infusion of ONO-1078 1 micrograms/kg/min and vehicle control group (n = 15). Both AA-861 and ONO-1078 reduced infarct size [AA-861: 21.8 +/- 1.3% of RA (mean +/- SEM), ONO-1078: 22.5 +/- 4.4% vs

CONTROL

54.0 +/- 6.4%, p less than 0.01 and p less than 0.01, respectively] and area of gross myocardial hemorrhage (AA-861: 5.1 +/- 2.4% of IS, ONO-1078: 5.2 +/- 2.5% vs

CONTROL

22.3 +/- 3.9%, p less than 0.01 and p less than 0.01, respectively). Both drugs also decreased frequency of ventricular premature contractions both during occlusion and during reperfusion, and that of ventricular tachycardia during reperfusion. AA-861 inhibited PMNs recruitment into infarcted area. However, ONO-1078 had no significant influence on degree of PMNs infiltration. These results suggest that lipoxygenase products, especially peptidoleukotrienes (LTC4, D4 and E4) may play important roles in the pathogenesis of myocardial ischemic and reperfusion injuries.

Activated neutrophils release mediators that may contribute to myocardial injury and dysfunction associated with ischemia and reperfusion

Neutrophils accumulate in the ischemic myocardium and exacerbate postischemic cardiac dysfunction and injury. The formation of lipoxygenase metabolites of AA, derived either directly from the neutrophils or by interactions with other blood elements or cells, may promote neutrophil-mediated injury. Recognition of the roles played by neutrophils and AA metabolites in reperfusion injury may lead to the development of new therapies that can be used in conjunction with thrombolytic drugs to reduce the complications associated with restoring blood flow to the ischemic heart.

Reduction in myocardial neutrophil accumulation and infarct size following administration of thromboxane inhibitor U-63,557A

We examined the effects of a new selective thromboxane A2 (TXA2) synthetase inhibitor, U-63,557A, on myocardial infarct size 48 hours following left coronary ligation in rats. With a single 8 mg/kg dose of U-63,557A (furegrelate) administered prior to coronary ligation, platelet aggregation and serum TXA2 formation declined significantly (p less than 0.02) for up to 48 hours. Myocardial infarct size, as measured by planimetry of serial left ventricular sections, was decreased from 44 +/- 3% (saline-treated control rats) to 34 +/- 4% (p less than 0.05). Left ventricular creatine kinase (CK) following coronary ligation was also preserved in U-63,557A vs saline-treated control animals (p less than 0.05). These beneficial effects of U-63,557A were not accompanied by reduction in the indices of myocardial oxygen demand (heart rate and arterial pressure). Furthermore, neutrophil accumulation in the infarcted myocardium was significantly decreased by U-63,557A (26 +/- 6 vs 96 +/- 3/high-power field [p less than 0.01]). These data suggest that administration of a single dose of selective TXA2 synthetase inhibitor prior to coronary ligation modulates platelet function for up to 48 hours and reduces the extent of myocardial injury, which may, in part, relate to decrease in neutrophil accumulation.

Inhibition of human platelet and neutrophil function by piriprost (U-60,257)

Platelets and neutrophils are important in determining the extent of myocardial injury following coronary occlusion. The detrimental effects of these blood elements are mediated in part via release of arachidonate metabolites and oxidative species. A new selective inhibitor of leukotriene formation, piriprost (U-60,257), has been observed to decrease both neutrophil accumulation in the myocardium and infarct size following coronary ligation in experimental animals. Since piriprost may have clinical use, we examined its effects on human platelet and neutrophil functions. This compound was found to exert potent inhibitory effects on epinephrine-induced human platelet aggregation and TXA2 biosynthesis (IC50 0.04 microM). Piriprost also inhibited human neutrophil chemotaxis, oxidative species release, aggregation, and LTB4 synthesis with IC50 of 0.1, 0.04, 10 and 14 microM, respectively. Thus, piriprost inhibits a variety of human platelet and neutrophil functions. Because of its suppressive effects on human platelet and neutrophil functions and protective effects in experimental myocardial infarction, this agent may have clinical applications.

Effect of endogenously produced leukotrienes and thromboxane on renal vascular resistance in rabbit hydronephrosis

Ureteral obstruction in rabbits is characterized by mononuclear cell invasion of the renal cortex and proliferative fibrosis that is associated with exaggerated prostaglandin synthesis in response to vasoactive and inflammatory cell agonists. In this investigation, we studied the effects of the chemotactic peptide N-formylmethionyl-leucyl-phenylalanine (fMLP) and bradykinin (BK) on eicosanoid synthesis and renal vascular resistance in the ex vivo perfused hydronephrotic kidney (HNK). Administration of fMLP resulted in the dose-dependent synthesis of leukotrienes, thromboxane A2 (TXA2), prostaglandin E2 (PGE2), and prostacyclin (PGI2). Peptidoleukotriene synthesis was monitored by specific radioimmunoassay and by guinea pig ileum bioassay and it was then validated by inhibition of the ileal contractile activity with the peptidoleukotriene receptor antagonist FPL-55712. The leukotrienes produced were identified as LTB4, LTC4, LTD4, and LTE4 by comigration with authentic standards on reverse phase high-performance liquid chromatography (RP-HPLC) and by ultraviolet spectroscopy. BK administration stimulated the synthesis of TXA2, PGE2, and PGI2 but not the synthesis of leukotrienes, in contrast to the results with fMLP, suggesting the involvement of different cell types. Administration of fMLP to the HNK also resulted in a renal vasoconstriction that was partially inhibited by FPL-55712 and that was completely inhibited by the thromboxane synthase inhibitor OKY-1581. Consistent with this result, exogenous administration of LTC4 resulted in the synthesis of TXA2 and in a renal vasoconstriction that was inhibited by either FPL-55712 or OKY-1581.(ABSTRACT TRUNCATED AT 250 WORDS)

Antagonism of vasoconstriction induced by platelet-activating factor in guinea-pig perfused hearts by selective platelet-activating factor receptor antagonists

Platelet-activating factor (Paf) is a potent coronary vasoconstrictor in rat, guinea-pig, dog and pig. The present study investigated the mechanism and duration of Paf in guinea-pig isolated, Krebs-perfused hearts. Dose-related and sustained decreases in cardiac contractility and increases in coronary perfusion pressure were elicited by bolus doses of Paf (0.3-100 pmol). Platelet-activating factor (30 pmol) induced increases in the production of immunoreactive thromboxane B2 (TXB2), leukotriene B4 (LTB4) and LTC4, but not 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha). In addition, the release of leukotriene-like material following Paf was observed using on-line superfusion bioassay. The coronary vasoconstrictor actions of Paf were partially antagonized by the leukotriene receptor antagonist, FPL 55712 (1.9 microM), or by indomethacin (2.8 microM). The combined use of these compounds did not result in further significant inhibition. The Paf receptor antagonists, BN 52021 (30 microM) and L 652, 731 (10 microM), antagonized both the increase in coronary perfusion pressure and the decrease in cardiac contractility induced by Paf (10-100 pmol) in a surmountable and relatively selective manner. The effects of a bolus dose of 100 pmol Paf were sustained in excess of 18 min. Exogenous Paf underwent little metabolism on passing through the coronary circulation with only 2% being converted to lyso-Paf and approximately 4% being retained by the heart after 18 min of perfusion. These results suggest that the coronary vasoconstrictor actions of Paf are partially dependent on the release of vasoactive arachidonic acid metabolites. The extraordinary potency and the long-lasting action of Paf indicate a potential role for this pro-inflammatory mediator in disorders of the coronary circulation.

sn-1,2-Diacylglycerols and phorbol diesters stimulate thromboxane synthesis by de novo synthesis of prostaglandin H synthase in human promyelocytic leukemia cells

We studied the regulation of thromboxane (TX) synthesis in promyelocytic leukemia cells during macrophage differentiation. Cells treated with 12-O-tetradecanoylphorbol-13-acetate (TPA) showed rates of TXB2 synthesis from exogenous arachidonic acid that exceeded that of control cells by a factor of up to 81. Cells treated with sn-1,2-dioctanoylglycerol (diC8) showed similarly high TXB2 synthesis rates when diC8 was added concomitantly with a subthreshold concentration of TPA or when given in multiple doses. These activities depended on de novo synthesis of prostaglandin H (PGH) synthase because: microsomal PGH synthase activity showed large increases in Vmax values, and mass measurements of PGH synthase revealed the presence of PGH synthase in differentiating cells whereas the enzyme was undetectable in control cells. These results indicate that macrophage differentiation is associated with stimulation of TXB2 synthesis that requires both activation of protein kinase C and de novo synthesis of PGH synthase.

Release of leukotrienes and histamine by the isolated anaphylactic heart

The purpose of this study was to demonstrate the ability of heart tissue to release the mediators of anaphylaxis after antigenic challenges. Guinea pigs were sensitized with ovalbumin. Hearts were excised, perfused in a langendorff apparatus, and challenged with a bolus injection of ovalbumin. Analysis of the perfusates demonstrated the presence of histamine as determined by radioenzymatic assay. Histamine release was observed to be maximum after 2 min (8 +/- 1 nmol) of perfusion, then decreased to baseline level. The heart also released LTB4, LTC4, LTD4, and LTE4 as determined by high performance liquid chromatography and bioassays. The release of LTC4 occurred rapidly, reaching maximum after 2 min (4.2 +/- 1 pmol) and then returned to baseline level. Although the release of LTD4 paralleled the release of LTC4, it reached a maximum after 5 min (7.7 +/- 2 pmol). LTE4 was detected after 10 min and was undetectable after 15 min. Maximum release of LTB4 was observed after 5-10 min (15 +/- 3 pmol) and was no longer detectable after 15 min. These results indicate that the isolated sensitized heart undergoing antigenic challenge releases leukotrienes and histamine suggesting the cardiac anaphylaxis might occur by the locally released mediators.

Eicosanoids and myocardial ischaemia

The available data clearly suggest large alterations in myocardial eicosanoid generation during myocardial ischaemia and demonstrate important actions of eicosanoids on myocardial function during ischaemic conditions. These actions include direct effects on the injured myocardium as well as influences on other target cells, such as platelets and leukocytes. Selective modifications of eicosanoid generation, for example by providing exogenous PGI2 or by inhibiting oxygen toxicity are most challenging approaches for the design of new and potentially valuable cardioprotective agents. Antagonism of thromboxane formation and/or action might be of some value in ischaemia but appears to be less important for reperfusion injury. Leukotrienes and other noncyclic fatty acid peroxidation products are another group of potentially deleterious agents and there is a definite need for more selective inhibitors of leukotriene formation and/or action to establish their role in ischaemia.

Exaggerated atrial arachidonate metabolism in rabbit left ventricular myocardial infarction

Isolated perfused rabbit hearts that have previously been subjected to in vivo left ventricular myocardial infarction respond to N-formylmethionyl-leucyl-phenylalanine (fMLP) or bradykinin (BK) administration with the synthesis of large quantities of eicosanoids. To anatomically localize these synthetic responses we studied the effects of fMLP and BK on eicosanoid synthesis in isolated atria and isolated perfused ventricles from normal and infarcted (4 d in vivo) rabbit hearts. These studies revealed that enhanced agonist-stimulated eicosanoid synthesis occurs largely in the right atria of infarcted hearts, a site distant from the zone of injury. Studies of exogenous arachidonate metabolism in microsomes prepared from various regions of the heart showed that while prostaglandin synthetic capacity is preferentially localized to the right atrium, right atria from normal and infarcted hearts have similar thromboxane and PGE2 synthetic capacity. These results demonstrate that enhanced agonist-stimulated eicosanoid synthesis following rabbit left ventricular myocardial infarction occurs largely in the right atrium, and that this effect is independent of the activity of prostaglandin synthetic enzymes.

Analysis of 6-keto PGF1 alpha, 5-HETE, and LTC4 in rat lung: comparison of GM/MS, RIA, and EIA

The recent availability of fast and sensitive radioimmunoassay (RIA) and enzyme immunoassay (EIA) procedures to measure icosanoids has led to utilization of these techniques by many investigators. A major concern has been that techniques based on immunoreactivity may lack specificity, in particular if complex biologic fluids or tissue extracts are evaluated. The purpose of this investigation was the comparison of icosanoid measurements obtained either with EIA or RIA with those obtained by gas chromatography/mass spectrometry (GC/MS). Rats were injected with Salmonella enteritidis endotoxin, killed at various times after the injection and the lung extract assayed for 6-keto-PGF1 alpha, 5-HETE and LTC4. By EIA lung tissue was found to contain large quantities of 6-keto-PGF1 alpha after endotoxin stimulation. Comparisons made between EIA and GC/MS analysis showed good correlation between 6-keto-PGF1 alpha amounts in lung as determined by each technique. It was also determined that little purification of lung extract was needed to obtain reliable quantitation of 6-keto-PGF1 alpha, probably due to the specificity of the antibody and the large quantity of this prostaglandin produced. Crudely purified (Sep-Pak) lung extracts gave 5-HETE levels by RIA which were highly correlated with GC/MS values, but RIA values were 70% higher than those obtained by GC/MS. The presence of other components in lung extract which cross react with this 5-HETE antibody was probably responsible for the higher values obtained by RIA. LTC4 was measured by immunoassay in crude lung extracts, as well as after Sep-Pak purification and HPLC purification. LTC4 levels were identical in unpurified lung extract and after Sep-Pak purification, but decreased substantially after HPLC purification. Thus, by validating the icosanoid immunoassays, we have found that they can give accurate and reproducible results in lung tissue, although LTC4 and 5-HETE must be purified prior to analysis.

Monocyte migration explains the changes in macrophage arachidonate metabolism during the immune response

The profile of arachidonic acid metabolites in resident peritoneal macrophages is distinctly different from the profile of macrophages isolated after an acute bacterial infection. The latter produce decreased prostaglandins E2 and I2 and leukotriene C4 while conserving the synthesis of thromboxane A2. We show here that the initial changes in peritoneal macrophage arachidonate metabolism during the immune response appear to be the result of the large influx of blood monocytes, which have a characteristic metabolism distinct from resident macrophages. We demonstrate that the initial decrease in peritoneal macrophage arachidonate metabolism and the increase in macrophage numbers occur simultaneously after infection with Listeria monocytogenes. Also the macrophage arachidonate metabolism seen at the height of the peritoneal cellular influx is the same as that of purified blood monocytes. Both Listeria peritoneal macrophages and blood monocytes produce equal or greater quantities of thromboxane A2 relative to prostaglandins I2 and E2 or leukotriene C4 whereas resident cells produce 1/10 to 1/25 as much thromboxane A2 compared to the other products. Furthermore, the changes in peritoneal macrophage arachidonate metabolism in response to Listeria infection do not occur if the influx of blood monocytes is stopped by irradiating the mice prior to infection implying that the cellular influx is necessary to see the changes in arachidonate metabolism. Finally, activation of peritoneal macrophages, measured as an increase in Ia expression, occurs 36 hr after the influx of monocytes from the blood and the resultant shift in arachidonate metabolism during Listeria infection.

Augmentation of leukotriene C4 and D4 release due to severe stenosis in the canine coronary artery stimulated by the calcium ionophore A23187

In dogs undergoing 24- or 72-hr severe narrowing of the left anterior descending coronary artery (LAD), the in vitro formation of immunoreactive leukotriene C4 (LTC4) by the stenosed LAD was greatly augmented by 1 microM A23187 in a 10-min incubation at 37 degrees. This stimulated LTC4 formation was abolished by 30 microM nordihydroguaiaretic acid (NDGA). The incubation products were identified by high performance liquid chromatography and radioimmunoassay to be largely composed of LTC4 and LTD4 in similar proportion. In contrast to the stenosed LAD, the non-stenotic left circumflex coronary artery, apex of the heart, and renal artery of the same experimental animals failed to respond to the calcium ionophore up to 10 microM. The vascular and cardiac tissues from sham-operated animals also remained quiescent in the presence of A23187. The normal coronary artery showed low levels of leukotriene formation and was resistant to the ionophore. It is proposed that a latent portion of leukotriene synthesis, which can be triggered by the calcium ionophore, may play a significant role in the pathogenesis of coronary artery spasm associated with acute myocardial infarction and angina pectoris in patients with obstructive coronary artery disease.

Immunological and non-immunological release of leukotrienes and histamine by guinea-pig heart

Fragments of sensitized guinea-pig heart (1 g wet weight) were incubated with 5 micrograms/ml of antigen for up to 30 min, and the incubation media were analysed by reversed-phase high-performance liquid chromatography (RP-HPLC) for the presence of leukotrienes LTB4, LTC4, LTD4 and LTE4. Maximum release of LTB4, LTC4 and LTD4 was observed after 15 min (32.8 +/- 4, 8 +/- 2 and 9.5 +/- 2.5 pmol/g tissue wet weight, respectively, mean +/- SEM). At the same time, histamine was also released, reaching a maximum at 5 min (290 +/- 63 pmol/g tissue) as determined by radioenzymatic assay. Similarly, the non-sensitized guinea-pig heart stimulated with the ionophore A23187 (4 microM) released LTB4, LTC4, LTD4 and LTE4, as well as the 5-hydroxy-eicosatetraenoic acid (5-HETE), 12-HETE, and 15-HETE as determined by RP-HPLC. The release of LTB4, LTC4 and LTD4 was at a maximum after 10-15 min of stimulation (63 +/- 8.4, 10.7 +/- 2 and 17.5 +/- 4 pmol/g tissue). The ionophore also stimulated the release of histamine in heart tissue, with a peak maximum after 5 min (325 +/- 77 pmol/g tissue). These data demonstrate that heart as well as pulmonary tissues release significant amounts of leukotrienes and histamine during immunological or non-immunological challenges.

Verapamil depresses the synthesis of lipoxygenase products by hypoxic cardiac rat fibroblasts in culture

Lipoxygenase metabolites of arachidonic acid are potent chemotactic and vasoconstrictive agents and their local production in the myocardium induces the migration of polymorphonuclear cells into ischemic myocardium. These cells have been shown to play a role in the development of ischemic myocardial lesions. In the present study, the synthesis of arachidonic acid lipoxygenase metabolites by rat cardiac cells in culture and the effect of verapamil were investigated under normal and hypoxic conditions. Myocytes and fibroblasts metabolized exogenous arachidonic acid into 12-HETE and an unidentified metabolite (X). Fibroblasts synthesized significantly greater amounts of 12-HETE than myocytes (P less than 0.01). Hypoxia (glucose-free medium and low PO2) and verapamil (10(-7) M) under normal conditions, did not change metabolite synthesis by either type of cells. Under hypoxia, verapamil decreased significantly 12-HETE and X production by fibroblasts (P less than 0.01 and P less than 0.05), whereas the synthesis in myocytes was not changed. It is concluded that the decrease in lipoxygenase product synthesis under hypoxia by verapamil may contribute to its therapeutic effects on the ischemic heart.

Biological actions of leukotrienes. State of the art lecture

Leukotrienes are novel mediators derived from arachidonic acid through the 5-lipoxygenase enzyme system. Leukotriene B4 has potent effects on leukocyte function and in vivo induces leukocyte accumulation and changes in vascular permeability and modulates pain responses. Peptido-lipid leukotrienes are potent smooth muscle--contracting agents. They may have important cardiovascular actions through mechanisms involving either vasoconstriction or indirect vasodilatation. Evidence for leukotriene production has been found in subjects with allergic conditions and psoriasis, indicating a putative role for these substances in human disease.