phosphoramidon and Myocardial-Ischemia

Endothelin-1 and norepinephrine are involved in myocardial ischemia/reperfusion injury. The aim of this study was to investigate the role of endogenously generated endothelin-1 in ischemia/reperfusion-induced norepinephrine overflow and cardiac dysfunction using a nonselective prototype of endothelin-converting enzyme (ECE) inhibitor, phosphoramidon, and a selective ECE inhibitor, SM-19712 (4-chloro-N-[[(4-cyano-3-methyl-1-phenyl-1H-pyrazol-5-yl)amino]carbonyl]benzenesulfonamide, monosodium salt). According to the Langendorff technique, isolated Sprague-Dawley rat hearts were subjected to 40-min global ischemia followed by 30-min reperfusion. Phosphoramidon and SM-19712 were perfused 30 min before ischemia and during reperfusion. Endothelin-1 level in left ventricle was increased by ischemia/reperfusion. This increase in left ventricular endothelin-1 level was suppressed by treatment with SM-19712. SM-19712 significantly improved ischemia/reperfusion-induced cardiac dysfunction such as decreased left ventricular developed pressure and dP/dt(max) and increased left ventricular end diastolic pressure. In addition, this agent suppressed excessive norepinephrine overflow in the coronary effluent from the post-ischemic heart. In contrast, treatment with phosphoramidon further enhanced left ventricular endothelin-1 level and norepinephrine overflow, and significantly worsened cardiac dysfunction after ischemia/reperfusion. These responses such as exaggerated norepinephrine overflow and the cardiac dysfunction observed after ischemia/reperfusion were markedly suppressed in the presence of a selective endothelin ET(A) receptor antagonist, ABT-627 [2R-(4-methoxyphenyl)-4S-(1,3-benzodioxol-5-yl)-1-(N,N-di(n-butyl)aminocarbonyl-methyl)-pyrrolidine-3R-carboxylic acid]. These findings indicate that cardiac endothelin-1 production is enhanced by ischemia/reperfusion, and this endogenously increased endothelin-1 is involved in post-ischemic norepinephrine overflow and cardiac dysfunction via the activation of endothelin ET(A) receptors.

Topics: Animals; Aspartic Acid Endopeptidases; Atrasentan; Endothelin-1; Endothelin-Converting Enzymes; Enzyme Inhibitors; Glycopeptides; Male; Metalloendopeptidases; Myocardial Ischemia; Myocardial Reperfusion Injury; Norepinephrine; Pyrrolidines; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A; Sulfonamides; Sulfonylurea Compounds

Transient ischemia has been shown to impair endothelium-dependent, but not endothelium-independent, coronary vasodilation, indicating selective endothelial dysfunction. Here a hypothesis was tested that agonist mediated activation of protein kinase C (PKC) and the related overproduction of the oxidative species contribute to the mechanism of the endothelial dysfunction. Perfused guinea-pig hearts were subjected either to 30 min global ischemia/30 min reperfusion or to 30 min aerobic perfusion with a PKC activator, phorbol ester (1 n M, PMA). Coronary flow responses to a bolus of acetylcholine (ACh) and sodium nitroprusside (SNP) were used as measures of endothelium-dependent and endothelium-independent vascular function, respectively. Salicylate hydroxylation was used as the assay for the myocardial hydroxyl radical (.OH) formation. Both ischemia/reperfusion and PMA impaired the ACh response and augmented the myocardial.OH production. The effect of ischemia/reperfusion on the ACh response: (i) was fully prevented by a PKC inhibitor, chelerythrine (2microM) and a mixed endothelin blocker, bosentan (20microM); (ii) was partially prevented by an endothelin converting-enzyme inhibitor, phosphoramidon (40microM), and superoxide dismutase (150-500 U/ml, SOD) and (iii) was affected neither by catalase (600 U/ml) nor by losartan (20microM) and captopril (250microM), nor by prazosin (10microM). SOD, but not bosentan, partially prevented the effect of PMA on the ACh response. None of the interventions studied affected the SNP response. The reperfusion-induced.OH release was attenuated by chelerythrine and bosentan, was not affected by prazosin and was increased by SOD. These results implicate the following sequence of events in the mechanism of the post-ischemic endothelial dysfunction: ischemia/reperfusion, endothelin-induced PKC activation, increased production of superoxide and/or some of its toxic metabolite, damage to the endothelium and endothelial dysfunction. The results argue against the contribution of angiotensin II, adrenergicalpha(1)-receptors and kinins in the mechanism of the post-ischemic endothelial dysfunction in guinea-pig hearts.

Topics: Acetylcholine; Adrenergic alpha-Antagonists; Alkaloids; Angiotensin-Converting Enzyme Inhibitors; Animals; Anti-Arrhythmia Agents; Aspartic Acid Endopeptidases; Benzophenanthridines; Bosentan; Captopril; Catalase; Coronary Vessels; Endothelin-Converting Enzymes; Endothelins; Endothelium, Vascular; Enzyme Activation; Enzyme Inhibitors; Female; Free Radicals; Glycopeptides; Guinea Pigs; Heart; Losartan; Male; Metalloendopeptidases; Muscle Proteins; Myocardial Ischemia; Myocardial Reperfusion; Myocardium; Nitroprusside; Oxidative Stress; Phenanthridines; Prazosin; Protein Kinase C; Reactive Oxygen Species; Sulfonamides; Superoxide Dismutase; Tetradecanoylphorbol Acetate; Vasodilator Agents

The effects of diltiazem and phosphoramidon on sudden death induced by endothelin (ET)-1 and by big ET-1 were compared in rodents. Diltiazem (2 mg/kg, i.v.) remarkably diminished the lethal toxicity of ET-1 with a reduction in the extent of the rise in plasma immunoreactive ET-1-like activity (IR-ET-1), tissue IR-ET-1 accumulation in the heart and the rise in plasma potassium concentration. In big ET-1-induced lethality, diltiazem only slightly prolonged the latency and did not reduce the mortality. Although diltiazem moderately inhibited the rise in plasma IR-ET-1 and potassium concentration in these mice, it did not affect the accumulation of IR-ET-1 in the heart, lung or kidney. Phosphoramidon (2 mg/kg, i.v.) decreased the lethality of big ET-1 with the decrement in elevation of IR-ET-1 in the heart, lung and plasma as well as with the decrease in plasma potassium concentration, but it failed to improve any parameters in ET-1-induced lethality. In anesthetized rats, ET-1 (5 nmol/kg, i.v.) elevated ST-segment of electromyocardiograms, and diltiazem (2 mg/kg, i.v.) significantly reversed this change. Big ET-1 (25 nmol/kg, i.v.) also induced the ST-segment elevation, which was significantly inhibited by phosphoramidon but not by diltiazem. These findings suggest that accumulation of ET-1 in the heart, which may lead to lethal cardiac ischemia, is an important factor in the lethality of ET-1, while additional factors (such as hemoconcentration and bronchoconstriction) may be involved in big ET-1-induced lethality.

Topics: Anesthesia; Animals; Death, Sudden, Cardiac; Diltiazem; Electrocardiography; Endothelin-1; Endothelins; Glycopeptides; Kidney; Lung; Male; Mice; Mice, Inbred ICR; Myocardial Ischemia; Myocardium; Potassium; Protease Inhibitors; Protein Precursors

The role of cardiac endothelin-1 (ET-1) was studied by determining endogenous tissue and coronary ET-1 levels in isolated rat hearts. Hearts were perfused in an upside-down position with a colloid-free buffer and immunoreactive ET-1 was determined in timed collections of coronary effluent (E) and interstitial fluid (transudate, T) produced by the ventricles and appearing on their surface. Basal ET-1 concentrations were 0.2 +/- 0.01 pg/ml (T) and 0.03 +/- 0.002 pg/ml (E), i.e., the T:E concentration ratio was 7. Angiotensin II (0.1 mumol/L) or thrombin (5 U/ml) increased coronary perfusion pressure and ET-1 secretion but had no effect on the T:E ET-1 concentration ratio (5 and 9). In two different protocols of ischemia/reperfusion, T and E concentrations increased up to two- and fivefold, respectively. The T:E ratios were approximately 2, and the highest concentrations in either fluid were < 1 pg/ml. No change in coronary perfusion pressure was observed. In the presence of the ET-1-converting enzyme inhibitor phosphoramidon (1.7 mumol/L), ischemia-induced increases of ET-1 concentrations were attenuated in parallel with a time-dependent rise in coronary perfusion pressure. Therefore, under normoxic conditions and in ischemia/reperfusion, ET-1 is an endogenous vasodilator in the rat heart.

Topics: Animals; Endothelins; Glycopeptides; Myocardial Ischemia; Myocardium; Rats

The effect of endothelin-1 (ET-1) and big ET-1 on coronary flow and contractile function was determined in isolated nonischemic and ischemic rat hearts. Both ET-1 (IC50 = 12 pMol) and big ET-1 (IC50 = 2 nMol) reduced coronary flow in a concentration-dependent manner, although ET-1 was > 100-fold more potent. Both compounds decreased contractility, an effect which was lost when coronary flow was held constant, indicating that ET-1 and big ET-1 decrease contractility secondary to reducing coronary flow. Mechanical reduction in coronary flow to levels equivalent to those seen for ET-1 or big ET-1 caused similar reductions in contractility. Both 30 pMol ET-1 and 10 nMol big ET-1 pretreatment significantly reduced the time to contracture in globally ischemic rat hearts, suggesting a proischemic effect. Phosphoramidon (100 microM, endothelin-converting enzyme inhibitor) and BQ-123 (0.3 microM, ETA receptor antagonist) abolished the preischemic increase in coronary perfusion pressure induced by big ET-1 as well as its proischemic effect, whereas only BQ-123 abolished the cardiac effect of ET-1. Neither phosphoramidon nor BQ-123 had an effect on severity of ischemia when given alone. Phosphoramidon was also given i.v. to rats subjected to coronary occlusion and reperfusion and was found to significantly reduce infarct size 24 hr postischemia. Thus, in isolated rat hearts, big ET-1 appears to be converted to ET-1 and is a potent coronary constrictor.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Coronary Circulation; Coronary Vessels; Dose-Response Relationship, Drug; Endothelin-1; Endothelins; Glycopeptides; In Vitro Techniques; Male; Myocardial Contraction; Myocardial Ischemia; Peptides, Cyclic; Protein Precursors; Rats; Rats, Sprague-Dawley