Cardiac dysfunction caused by purified human C3a anaphylatoxin.

The purpose of this investigation was to define the cardiac effects of complement-derived C3a anaphylatoxin, in view of the possibility that cardiac dysfunction may occur as a result of complement activation. Purified human C3a was administered by intracoronary bolus injections into isolated guinea pig hearts. As a function of dose, C3a caused tachycardia, impairment of atrioventricular conduction, left ventricular contractile failure, coronary vasoconstriction, and histamine release. These effects were abolished by cleavage of the COOH-terminal arginine by carboxypeptidase B. The magnitude of C3a-induced tachycardia correlated with the amount of endogenous cardiac histamine released into the coronary effluent. Whereas the tachycardia was markedly reduced by the histamine H2 antagonist cimetidine, the contractile failure and the coronary vasoconstriction caused by C3a were antagonized by the leukotriene antagonist FPL 55712 and by the cyclooxygenase inhibitor indomethacin, respectively. This suggests that histamine, leukotrienes, and vasoactive prostanoates may mediate the various cardiac effects of C3a. Our findings indicate that C3a anaphylatoxin has marked cardiac effects at concentrations that are likely to be attained with a degree of C3 activation commonly seen in various disease states. Thus, our data are compatible with the hypothesis that generation of anaphylatoxins may induce cardiac dysfunction in clinical conditions.     

Actions of platelet-activating factor on isolated rat hearts.

The actions of Platelet-Activating Factor (PAF) on isolated rat hearts were investigated. In a dose-dependent manner PAF decreased peak systolic pressure and maximum rate of rise of intraventricular pressure (+dP/dt(max]. PAF dose-dependently decreased coronary flow, prolonged the P-R interval of the EKG, and decreased heart rate. These actions of PAF were only partially blocked by drugs blocking receptors for PAF (CV 3988, WEB 2086), thromboxanes (ONO 3708), or leukotrienes (FPL 55712, L-655,240) or by a blocker of eicosanoid production (ibuprofen). Since depressed contractions will of themselves reduce coronary flow, PAF's action on flow was also investigated in hearts whose contractions were blocked by elevated potassium concentrations plus tetrodotoxin. Such treatment did not prevent PAF reducing coronary flow, indicating that a direct vasoconstriction occurred. The reductions in coronary flow in non-contracting hearts induced by PAF were equal to those induced by the coronary vasoconstrictors vasopressin and ergonovine under the same conditions. In order to isolate direct effects of PAF on myocardial contractile cells from effects mediated via changes in coronary flow, PAF was given to hearts maximally dilated by a concentration of nifedipine (0.03 microM) which had no effect on contractility. This concentration of nifedipine increased flow from 15.5 +/- 1.4 mL/min to 18.1 +/- 2.4 mL/min. In the presence of this nifedipine-induced vasodilation, PAF still exhibited negative inotropic actions, but without reducing coronary flow. Thus the effects of PAF on isolated rat hearts involve direct actions on both myocardial contracting cells and on coronary vessels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of arachidonic acid metabolites in hypoxic contractions of isolated porcine pulmonary artery and vein

Recently it has been proposed that hypoxic pulmonary vasoconstriction (HPV) is mediated by local release of sulfidopeptide leukotriene products of the lipoxygenase pathway of arachidonic acid metabolism. In the present study the response to reduced oxygen supply of isolated porcine lobar pulmonary artery and pulmonary vein spiral strips has been studied. Contractions of the pulmonary artery (mean maximum tension 66.9 +/- 13.0 mg, n = 10) required an increase in baseline tone of the preparation followed by exposure to anoxia (mean bath PO2 O +/- 3 mm Hg), whereas contractions of the pulmonary vein (mean maximum tension 75.2 +/- 13.3 mg, n = 10) could be elicited in response to hypoxia alone (mean bath PO2 40 +/- 4 mm Hg). Indomethacin (5.6 microM), a cyclooxygenase inhibitor, attenuated the arterial contraction, but the mechanism may have been independent of the cyclooxygenase pathway since phenidone, an inhibitor of both cyclooxygenase and lipoxygenase pathways, had no effect. Inhibition by FPL 55712, a leukotriene end-organ antagonist, was achieved only at a high concentration (20 microM). In the case of the pulmonary vein, both indomethacin and phenidone inhibited the contractile response, whereas FPL 55712 had no effect. Contractile responses to reduced oxygen supply can be induced in isolated porcine pulmonary artery and vein strips, but probably are not mediated by leukotrienes.     

Role of peptide leukotrienes and their hepatobiliary elimination in endotoxin action

The lethal action of endotoxin was studied in mice sensitized against the lipopolysaccharide by D-galactosamine. Protection was obtained by FPL 55712, a selective antagonist of sulfidopeptide leukotrienes, by diethylcarbamazine, an inhibitor of leukotriene biosynthesis, by BW 755C, a dual lipoxygenase and cyclooxygenase inhibitor, and by dexamethasone, which inhibits arachidonate release. Indomethacin incompletely antagonized endotoxin lethality; indoprofen did not protect at all. Leukotriene generation induced by endotoxin in vivo could be demonstrated in rats by employing a radioimmunoassay on bile extracts since intravascular sulfidopeptide leukotrienes were rapidly eliminated into bile. Additionally, however, endotoxin affected the hepatobiliary elimination of sulfidopeptide leukotrienes. From intravenously injected tracer [3H]leukotriene D4, 67% appeared only partially metabolized in bile within 30 min in control rats. Endotoxin and lipid A reduced the biliary [3H]leukotriene D4 secretion by up to 80% while enhancing the hepatic [3H]leukotriene D4 content up to twofold. This inhibition of hepatobiliary elimination was stronger than endotoxin-induced reductions of bile flow or of biliary [14C]taurocholate secretion. Endotoxin, as an activator of the arachidonate cascade, thus potentiates its action in vivo by interfering with the rapid hepatobiliary clearance of sulfidopeptide leukotrienes in addition to stimulating leukotriene and prostanoid formation.     

Mechanisms of platelet-activating factor-induced cardiac depression in the isolated perfused rat heart

A potent phospholipid (platelet-activating factor, PAF) has been implicated in a variety of inflammatory and ischemic responses (eg, myocardial ischemia and anaphylactic shock). In isolated rat hearts perfused at constant flow, PAF produced a dose-dependent increase in coronary perfusion pressure (CPP) and a decrease in contractile force (CF). At 20 nM, PAF increased CCP by 21 +/- 1 mm Hg and decreased CF by 31 +/- 3% in nine hearts. At the peak of the PAF response, coronary effluent contained LTC4, LTD4, and LTE4 (0.22 +/- 0.05 pmol/ml) and TxB2 (0.97 +/- 0.16 pmol/ml). Addition of specific PAF receptor antagonists (eg, BN-52021 and CV-3988) inhibited peptide leukotriene and TxB2 production and blocked the coronary vasoconstriction and decrease in contractile force. Cyclooxygenase inhibitors (eg, naproxen) or specific TxA2 receptor antagonists (eg, BM-13,505) failed to prevent the increase in CPP or the decrease in CF. Furthermore, a lipoxygenase inhibitor (ie, propyl gallate) or a specific LTD4 receptor antagonist (ie, LY-171,883) prevented the increase in CPP but did not antagonize the negative inotropic response. These data indicate that the coronary constriction in the isolated perfused rat heart is a result of the PAF-induced release of endogenous peptide leukotrienes but not TxA2 production. However, the negative inotropic response appears to be partly due to a direct negative inotropic action of PAF on cardiac muscle. Thus, PAF produces a variety of direct actions and indirect effects via release of eicosanoid mediators contributing to cardiac impairment in the rat heart.     

Steroids and cardioplegia: effects of glucocorticoids upon vascular resistance during cardioplegic perfusion

The effects are assessed of methyl prednisolone sodium succinate (MPSS) upon coronary flow rate (CFR) during a 20 minute anoxic, cold (20 degrees C) cardioplegic perfusion with a potassium-enriched (K+ 20 mmol/l) commercially obtained Ringer solution and 15 min of subsequent normothermic aerobic reperfusion without steroid, based on measurements made on the isolated rat heart. Myocardial release of creatine kinase (CK) was obtained during reperfusion and at the end of the experiments the hearts were freezeclamped and analyzed for high energy phosphate compounds and tissue calcium. In the absence of filtering and MPSS the coronary flow rate gradually declined to 32% +/- 4 after 20 min. MPSS presented a bell-shaped concentration response curve with respect to improvement of CFR. An optimal effect (only reduction to 64% +/- 11) was obtained with MPSS 100 mg/l, while no improvement was obtained with 1000 mg/l (reduction to 28% +/- 3). After 15 min of reperfusion with normal medium at 37 degrees the hearts perfused with MPSS 100 mg/l presented with higher values for energy charge and ATP and lower tissue calcium content than the hearts perfused with MPSS 1000 mg/l. Using filtration (0.8 micron) of the cardioplegic solution the CFR was reduced to 45% +/- 4. We therefore conclude that MPSS in an optimal concentration (100 mg/l) may afford effective coronary vasodilation and overcome particle induced vasospasm, and that in higher concentrations (1000 mg/l) the improvement in CFR is lost. This high concentration may also have unfavorable effects upon the myocardium.     

Calcium paradox-evoked release of prostacyclin and immunoreactive leukotriene C4 from rat and guinea-pig hearts. Evidence that endogenous prostaglandins inhibit leukotriene biosynthesis

The purpose of this study was to assess the influence of the calcium paradox (5 min calcium-free perfusion followed by 15 min calcium repletion) on the release of immunoreactive leukotriene C4 and 6 Keto-prostaglandin F1 alpha from rat and guinea-pig hearts. Under control conditions or during the 5 min calcium-free perfusion period no immunoreactive leukotriene C4 was detectable in the coronary effluent. Following reperfusion with calcium-containing medium a large release of leukotriene C4 was observed although the amount was significantly greater in the rat heart. 6 keto-prostaglandin F1 alpha was detected during normal and calcium-free perfusion and the release was significantly stimulated during calcium repletion. Treatment with ibuprofen, a cyclo-oxygenase inhibitor, prevented the release of 6 keto-prostaglandin F1 alpha but increased the efflux of immunoreactive LTC4 during calcium repletion. Arachidonic acid, the substrate for prostaglandin and leukotriene synthesis increased the efflux of 6 keto-prostaglandin F1 alpha but decreased the release of leukotriene C4. The latter effect was reversed by perfusion with ibuprofen, and mimicked by prostacyclin, the primary cardiac prostaglandin. This study shows that the calcium paradox is a potent stimulus for eicosanoid release from rat and guinea-pig hearts, a phenomenon likely due to the activation of calcium-dependent enzymes. The study also suggests that endogenous prostaglandins inhibit leukotriene synthesis in cardiac tissue.     

Sensitivity of mechanical and metabolic functions to changes in coronary perfusion: A metabolic basis of perfusion-contraction coupling

Experimental evidence indicates a metabolic basis of contraction-perfusion coupling during an increase in cardiac work load. This study aims to characterize adjustment of myocardial energy metabolism in response to acute low flow ischemia (LFI), and to determine its involvement in perfusion-contraction coupling. Intracellular parameters were measured in isolated rat hearts by NMR spectroscopy and biochemical methods during 30 min of graded LFI and reperfusion as compared to continuous perfusion (control). Oxygen pressure was set to reach maximal oxygen extraction at 70% coronary flow rate (CFR), therefore oxygen limitation was proportional to coronary underperfusion. At 69, 38 and 10% CFR left ventricular pressures decreased to 71, 43 and 25% of pre-ischemic values respectively (P<0.005 v 97% in control) without an increase in diastolic tone, and recovered to 92+/-3% after 30 min of reperfusion. Despite hydrolysis of high energy phosphates and cellular acidification, ADP concentrations were stable in underperfused hearts. At 69, 38 and 10% CFR, cytosolic phosphorylation potentials (PP) decreased from 74+/-10 m M(-1)during pre-ischemia to 40+/-6, 25+/-4 and 14+/-4 m M(-1)respectively (P<0.05 v 63+/-9 m M(-1)in control), and lactate efflux increased to 256+/-18, 386+/-22 and 490+/-43 micromol /gdw respectively (P<0.005 v 186+/-22 micromol/gdw in control). Glycogen contents decreased (P<0.005 v control) and accounted for 27-30% of lactate efflux. These results indicate: (a) proportionate depression of contraction force and glycogen contents, and increased glucose uptake and anaerobic energy production in the underperfused myocardium. Coordinated modulation of these parameters attributes cytosolic PP a regulatory function; (b) resetting of cytosolic PP to lower levels mediates perfusion-contraction coupling during graded LFI. The data are consistent with the concept that glycolytic energy production improves myocardial tolerance to ischemia.     

Naloxone blocks transferred preconditioning in isolated rabbit hearts

We have shown that the cardioprotective benefits of ischemic preconditioning (PC) can be transferred from PC to virgin acceptor hearts via coronary effluent transfusion, implicating the presence of hormonal preconditioning factor(s). Using isolated buffer-perfused rabbit hearts, our aims were to: (1) determine whether the protective factor(s) could be concentrated and recovered by reverse phase chromatography and (2) whether opioid receptor activation contributes to this transferred cardioprotection. Material released into the coronary effluent during PC ischemia/reperfusion or normoxic perfusion was concentrated by reverse phase chromatography. In phase one, hearts received no intervention (controls), PC ischemia, concentrate generated from normoxic hearts (normoxic acceptors) or concentrate from PC hearts (PC acceptors). All hearts underwent 40 min of global ischemia, and area of necrosis (AN) was delineated by tetrazolium staining. In phase two, three additional groups of hearts (control, PC and PC acceptors) received the opioid antagonist naloxone (2 microM) throughout the intervention phase. Treatment with normoxic concentrate had no effect on infarct size: (AN: normoxic acceptors 39+/-8%; control 42+/-8%). In contrast, treatment with PC concentrate evoked cardioprotection equivalent to that afforded by conventional PC (AN 19+/-5% and 21+/-6% respectively P<0.05 v control). Naloxone had no effect on infarct size in controls, and did not inhibit preconditioning. However, naloxone abrogated the protection achieved by transfer of PC concentrate (AN: 44+/-7%). These results indicate that PC concentrate evokes a cardioprotective effect via a mechanism requiring an intact opioid receptor system.     

Altered coronary vascular responsiveness to leukotrienes in alloxan-diabetic rats

Altered responsiveness to and metabolism of various eicosanoids in diabetic animals and patients has been reported by several investigators. The purpose of this investigation was to examine the coronary vascular responsiveness of alloxan-diabetic rats to the leukotrienes. Hearts from 12- to 16-week-old alloxan-diabetic rats and weight-matched controls were perfused at constant flow by the Langendorff method. Coronary vasoactivity to leukotrienes B4, C4, D4 and E4 was assessed by measuring the change in coronary perfusion pressure upon infusion of these eicosanoids. Hearts from diabetic rats showed increased responsiveness to leukotrienes C4 (4-40 nM) and D4 (10-100 nM). Both control and diabetic rat hearts were only slightly responsive to leukotriene E4, and no difference between the two groups existed in the reactivity to this leukotriene. Neither group was responsive to the chemotactic leukotriene, B4. Perfusion of the hearts with the cyclooxygenase inhibitor, ibuprofen, failed to alter the coronary vascular responses to the leukotrienes. The coronary constrictor effects of the leukotrienes are the primary effect of these agents on the rat heart, since heart rate does not change significantly, and changes in contractile force are secondary to the coronary vascular constriction. These alterations in responsiveness to leukotrienes may play a role in the cardiovascular complications associated with diabetes.     

Identification and characterization of leukotriene C4 receptors in isolated rat renal glomeruli

The immediate reduction of renal blood flow and glomerular filtration rate in response to intravenous infusion of leukotriene C4 in the rat prompted an analysis of isolated rat renal glomeruli for the presence of specific receptors for leukotriene C4. Specific binding of [3H]leukotriene C4 to glomeruli increased in a time-dependent manner, reached equilibrium after 60 minutes of incubation at 4 degrees C, and was 80% reversible upon addition of excess unlabeled leukotriene C4 at equilibrium. Specific binding of [3H]leukotriene C4 to glomeruli increased in a dose-dependent manner, approaching saturation at concentrations of 40-60 nM. Inhibition of binding of [3H]leukotriene C4 with increasing concentrations of unlabeled leukotriene C4 was dose dependent. The equilibrium dissociation constant for [3H]leukotriene C4 binding to glomeruli, calculated from saturation and competitive binding-inhibition studies, was 25 +/- 7 nM and 35 +/- 16 nM (mean +/- SEM), respectively, and glomerular leukotriene C4 receptor density was 8.5 +/- 1.5 and 9.0 +/- 3.0 pmol/mg protein, respectively. The other natural vasoactive sulfidopeptide leukotrienes, leukotriene D4 and leukotriene E4, the chemotactic agent, leukotriene B4, and the sulfidopeptide leukotriene antagonist, FPL 55712, competed for the receptor at concentrations 2-3 orders of magnitude higher than the homoligand, leukotriene C4. The binding and specificity characteristics of the glomerular leukotriene C4 receptor are similar to those previously reported for the DDT1 nonvascular smooth muscle cell line derived from hamster vas deferens, for guinea pig ileum smooth muscle, and for a subcellular fraction of rat lung homogenate, and represent the first characterization of such a receptor in a vascular tissue.     

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

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

Renal and systemic hemodynamic responses to intravenous infusion of leukotriene C4 in the rat

We studied the systemic and renal hemodynamic effects of leukotriene C4 (2 micrograms/kg per min for 5 minutes, iv) in the rat. During the period of its infusion, leukotriene C4 produced a significant elevation of mean arterial pressure and reductions in cardiac output and renal blood flow, as measured by electromagnetic flow probes. These effects were abolished by FPL55712 , a putative antagonist of sulfidopeptide leukotrienes, but not by saralasin or indomethacin. Leukotriene C4 also resulted in an average loss of 20% in plasma volume which, during the postinfusion period, perpetuated the low cardiac output state and thus provoked the release of angiotensin II. This vasoactive peptide sustained the elevation in systemic vascular resistance and the reduction in renal blood flow over a 70-minute postinfusion observation period. Consequently, glomerular filtration rate fell by approximately 50%. These angiotensin II-mediated effects were abolished by saralasin. Indomethacin prevented the leukotriene C4-induced loss of plasma volume and, thus, allowed for the significant recovery of cardiac output and renal blood flow during the post-infusion period, thereby preserving glomerular filtration rate. We conclude that leukotriene C4 exerts direct systemic and renal vasoconstrictor, as well as cardiodepressant effects, during the period of its infusion. By virtue of its vasopermeability enhancing effect, leukotriene C4 also results in an immediate loss of plasma volume, an effect which requires the presence of secondarily generated cyclooxygenase products and which perpetuates the hemodynamic abnormalities observed beyond the period of leukotriene C4 infusion.     

Characterization of a leukotriene D4 receptor in guinea pig lung.

[3H]Leukotriene D4 was found to bind, in a saturable manner and with exceedingly high affinity, to a membrane preparation from guinea pig lung. Measurement of saturation at equilibrium yielded Kd values of 5.46 +/- 0.31 X 10(-11) M at 20 degrees C and 2.12 +/- 0.37 X 10(-10) M at 0 degree C while the numbers of binding sites (Bmax) were 384 +/- 34 and 302 +/- 44 fmol/mg of protein at 20 and at 0 degree C, respectively. The time courses of both association and dissociation were slow but the rate of dissociation was accelerated by either NaCl or GTP. Binding was enhanced by Ca2+, Mg2+, and Mn2+ and inhibited by Na+ but not by Li+ or K+, suggesting that the binding of leukotriene D4 may be regulated by ions. Leukotriene E4, but not leukotriene C4, had a high affinity for the putative receptor, consistent with the pharmacological evidence that the actions of leukotrienes D4 and E4 are mediated by a receptor distinct from that for leukotriene C4. Affinities of stereoisomers and related compounds for the leukotriene D4 binding sites closely paralleled their contractile activities in guinea pig lung parenchymal strips. In addition, the antagonist of slow-reacting substance of anaphylaxis, FPL 55712, inhibited the binding of [3H]leukotriene D4 with a Ki value of 1 X 10(-7) M, which is in agreement with reported Kb values obtained in pharmacological studies.     

The role of cyclooxygenase and lipoxygenase mediators in oxidant-induced lung injury

Infusion of the oxidant lipid peroxide tert-butyl hydroperoxide (t-bu-OOH) causes pulmonary vasoconstriction and increases vascular permeability in isolated perfused rabbit lungs. We have previously shown that t-bu-OOH stimulates arachidonic acid metabolism, increasing the synthesis of the cyclooxygenase products. The current experiments were designed to determine the role that cyclooxygenase- and lipoxygenase-derived mediators play in the lung injury caused by t-bu-OOH. In the present experiments, we found that t-bu-OOH not only increased the synthesis of the cyclooxygenase-derived products thromboxane and prostacyclin but also increased the synthesis of the lipoxygenase-derived products leukotrienes B4, C4, D4, and E4. To determine the role that these arachidonic acid metabolites play in the increase in pressure and vascular permeability caused by t-bu-OOH, we studied the effect that inhibitors of arachidonic acid metabolism or a leukotriene receptor blocker had on the pulmonary edema. We compared an uninjured control group with 4 groups of lungs given t-bu-OOH: a t-bu-OOH control group; a group pretreated with the cyclooxygenase inhibitor indomethacin (14 microM); a group pretreated with an analogue of arachidonic acid, 5-, 8-, 11-, 14-eicosatetraynoic acid (ETYA) (100 microM), that inhibits both the cyclooxygenase and lipoxygenase pathways; and a group pretreated with the leukotriene receptor antagonist FPL 55712 (38 microM). To produce lung injury, t-bu-OOH (300 microM) was infused throughout the first minute of 4 successive 10-min periods.(ABSTRACT TRUNCATED AT 250 WORDS)     

Coronary constriction by leukotriene C4, D4, and E4 in the intact pig heart

Leukotrienes are naturally occurring vasoactive metabolites of arachidonic acid that increase during inflammatory reactions and anaphylaxis. Coronary constriction and reduced myocardial contractility after leukotriene C₄ and D₄ administration were demonstrated in the isolated guinea pig heart. To explore the effects of leukotrienes in the in situ, blood-perfused heart, we administered leukotrienes C₄, D₄, and E₄ into the coronary artery of the domestic pig.Increasing doses (0.1, 0.3, 1.0, and 3.0 μg) of leukotrienes C₄, D₄, and E₄ were injected into the left anterior descending coronary artery of 8 openchest domestic pigs. Significant dose-related reduction in coronary blood flow was observed after each leukotriene administration. Three micrograms of each leukotriene produced the following maximal decreases (mean ± standard error): C₄ = 80 ± 9%, p < 0.001; D₄ = 81 ± 3%, p < 0.001; E₄ = 64 ± 12%, p < 0.005. In several instances, surface electrograms recorded from the myocardial region exposed to leukotrienes showed signs of focal myocardial ischemia, sometimes accompanied by ventricular arrhythmia. Significant elevation of left ventricular end-diastolic pressure was observed after large doses (1 or 3 μg) of leukotrienes C₄ and D₄. Minimal (5 to 10%) decreases in mean arterial pressure and no change in heart rate were observed after leukotriene injection.We conclude that leukotrienes C₄, D₄, and E₄ are extremely potent coronary constrictors in the in situ heart. The intensity of response and associated electrocardiographic signs of ischemia suggest that constriction is mainly due to a primary effect on vascular smooth muscle. However, coronary flow reduction may also reflect consequences of a primary negative inotropic action. Leukotrienes may play a significant role in the pathogenesis of a variety of cardiac disorders, particularly those associated with extensive inflammatory charges.     

Measurement by fluorescence of interstitial adenosine levels in normoxic, hypoxic, and ischemic perfused rat hearts

An improved assay was used to investigate the effects of hypoxia or ischemia on interstitial fluid and coronary venous effluent levels of adenosine in isolated perfused nonworking rat hearts. The adenosine in 5- to 10-microliter samples of left ventricular epicardial surface transudates and coronary effluents was reacted with chloroacetaldehyde, and the fluorescent derivative (1,N6-ethenoadenosine) was quantitated using high pressure liquid chromatography and fluorescence detection. Hearts responding to hypoxia could be separated into two groups. In one group of hearts, the control (normoxic) transudate and effluent adenosine concentrations were 94 +/- 24 and 41 +/- 6 pmol/ml, respectively. These values increased by 118 and 96%, respectively, with 5 minutes of hypoxia (30% O2), and returned to control levels 5 minutes after resumption of normoxia. In a second group of hearts, the normoxic control levels of adenosine in the transudates (42 +/- 7 pmol/ml) and coronary effluents (62 +/- 17 pmol/ml) were increased with hypoxia by 174 and 1,178%, respectively. However, the transudate levels continued to rise for 5 minutes after resumption of normoxic perfusion while effluent levels fell. In another series of hearts, global ischemia for 30 seconds elicited an elevation of transudate adenosine levels by 362 to 641% above control (58 +/- 15 pmol/ml) as determined 30 seconds after resumption of perfusion flow.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relation between stress-induced myocardial perfusion defects on cardiovascular magnetic resonance and coronary microvascular dysfunction in patients with cardiac syndrome X.

OBJECTIVES: The purpose of this study was to investigate whether a direct relation can be demonstrated between myocardial perfusion defects detected during dobutamine stress test (DST) by cardiovascular magnetic resonance (CMR) and impairment of coronary microvascular dilatory function in patients with cardiac syndrome X (CSX). BACKGROUND: Despite the fact that coronary microvascular dysfunction has been shown in most patients with CSX, the ischemic origin of CSX remains debated. No previous study assessed whether a strict relation exists between abnormalities in myocardial perfusion and coronary microvascular dysfunction in CSX patients. METHODS: Eighteen CSX patients (mean age 58 +/- 7 years, 7 men) and 10 healthy control subjects (mean age 54 +/- 8 years, 4 men) underwent myocardial perfusion study by gadolinium-enhanced CMR at rest and at peak DST (maximal dose 40 microg/kg/min). Coronary flow response (CFR) to adenosine (140 microg/kg/min in 90 s) in the left anterior descending (LAD) coronary artery was assessed by high-resolution transthoracic echo-Doppler and expressed as the ratio between coronary flow velocity at peak adenosine and at rest. RESULTS: At peak DST, reversible perfusion defects on CMR were found in 10 CSX patients (56%) but in none of the control subjects (p = 0.004). The CFR to adenosine in the LAD coronary artery was lower in CSX patients than in control subjects (2.03 +/- 0.63 vs. 3.29 +/- 1.0, p = 0.0004). The CSX patients with DST-induced myocardial perfusion defects in the LAD territory on CMR had a lower CFR to adenosine compared with those without perfusion defects in the LAD territory (1.69 +/- 0.5 vs. 2.31 +/- 0.6, p = 0.01). A significant correlation was found in CSX patients between CFR to adenosine and a DST perfusion defect score on CMR in the LAD territory (r = -0.45, p = 0.019). CONCLUSIONS: Our data concurrently show DST-induced myocardial perfusion defects on CMR and reduced CFR in the LAD coronary artery territory in CSX patients, thus giving strong evidence that a dysfunction of coronary microcirculation resulting in myocardial perfusion abnormalities is present in these patients.     

Effect of aging on myocardial adenosine production, adenosine uptake and adenosine kinase activity in rats

Adenosine levels present in the interstitial fluid and coronary effluent of the aged heart exceed those of the young adult heart. The present study investigated mechanisms in the Fischer 344 rat heart which may be responsible for the observed differences. (1) Total production of adenosine was determined in isolated perfused hearts by measuring coronary effluent adenosine content while inhibiting adenosine deamination and rephosphorylation with erythrohydroxy-nonyladenosine (EHNA) and iodotubercidin (ITC), respectively. Total adenosine production was similar in both young (3-4 month) and aged (20-21 month) hearts at 31.8 +/- 6.6 and 38.4 +/- 3.3 nmol/min/g dry wt, respectively. However, stimulation with the beta-adrenergic agent, isoproterenol, elicited a significantly greater increase in adenosine production in the young vs. aged heart. (2) Adenosine transport was evaluated in isolated perfused hearts by determining 14C uptake by the myocardium after 20 min of 14C-adenosine perfusion. Adenosine uptake in the agent-free heart was found to be decreased 17 to 25% in aged compared to young adult hearts. (3) Adenosine transport characteristics were determined with nitrobenzylthioinosine saturation-binding studies in ventricular membrane preparations. The Bmax values were significantly lower in aged than young adult hearts (140.2 +/- 1.5 fmol/mg and 191.9 +/- 2.3 fmol/mg in aged and young hearts, respectively) indicating a decreased number of transporter sites in the aged heart. However, the values for Kd were decreased with aging, suggesting an increase in the affinity of the transporter for adenosine in the aged vs. young adult heart. (4) The activities and kinetics of adenosine kinase were determined in homogenates of aged and young adult ventricular myocardium. No statistical difference was found between the two activities. Taken together these results suggest that increased interstitial adenosine levels in the aged heart result from decreased uptake of adenosine by the ventricular myocardium.     

Cysteinyl leukotrienes are involved in angiotensin II-induced contraction of aorta from spontaneously hypertensive rats

OBJECTIVE: Non specific lipoxygenase inhibitors have been reported to reduce the in vitro constrictor response and the in vivo pressor effect of angiotensin II in rats. The aim of this study was to assess the role of cysteinyl leukotrienes, in the vascular response to angiotensin II in spontaneously hypertensive rats (SHR). METHODS: Rings of thoracic aorta from SHR and normotensive Wistar-Kyoto rats (WKY) were compared in terms of contractile responses and release of cysteinyl leukotrienes in response to angiotensin II. RESULTS: Pretreatment with the specific 5-lipoxygenase inhibitor AA861 10 microM reduced the efficacy of angiotensin II in intact and endothelium-denuded aorta from SHR (% inhibition vs. control: 65+/-12.6% with endothelium (n=6), P<0.05; 43+/-7.2% without endothelium (n=6), P<0.05) but not in aorta from WKY. In addition, in aorta from SHR, the CysLT(1) receptor antagonist MK571 1 microM reduced by 55+/-6.1% (n=6, P<0.05) the contractile effects of angiotensin II in rings with endothelium but not in endothelium-denuded rings. Angiotensin II induced a 8.6+/-2.1-fold increase in cysteinyl leukotriene production in aorta rings from SHR with endothelium which was prevented by the AT(1) receptor antagonist losartan 1 microM but not by the AT(2) receptor antagonist PD123319 0.1 microM. In aorta rings from WKY, cysteinyl leukotriene production remained unchanged after exposition to angiotensin II. The cysteinyl leukotrienes (up to 0.1 microM) induced contractions in aorta rings from SHR but not from WKY. CONCLUSIONS: These data suggest that cysteinyl leukotrienes, acting at least in part on endothelial CysLT(1) receptors, are involved in the contractile response to angiotensin II in isolated aorta from SHR but not from WKY.