nitroarginine and Coronary-Disease

We previously reported that combined blockade of adenosine receptors and ATP-sensitive K+ channels (K+(ATP) channels) blunted but did not abolish the response of coronary blood flow to exercise. This study tested the hypothesis that the residual increase in coronary flow in response to exercise after adenosine receptor and K+(ATP) channel blockade is dependent on endogenous NO. Dogs were studied at rest and during a four-stage treadmill exercise protocol under control conditions, during K+(ATP) channel blockade with glibenclamide (50 microg x kg(-1) x min(-1) i.c.) in the presence of adenosine receptor blockade with 8-phenyltheophylline (8-PT, 5 mg/kg i.v.), and after the addition of the NO synthase inhibitor N(G)-nitro-L-arginine (LNNA, 1.5 mg/kg i.c.). During control conditions, coronary blood flow was 49 +/- 3 mL/min at rest and increased to 92 +/- 8 mL/min at peak exercise. LNNA alone or in combination with 8-PT did not alter resting coronary flow and did not impair the normal increase in flow during exercise, indicating that when K+(ATP) channels are intact, neither NO nor adenosine-dependent mechanisms are obligatory for maintaining coronary blood flow. Combined K+(ATP) channel and adenosine blockade decreased resting coronary flow to 27 +/- 3 mL/min (P<.05), but exercise still increased flow to 45 +/- 5 mL/min (P<.05). The subsequent addition of LNNA further decreased resting coronary flow to 20 +/- 2 mL/min and markedly blunted exercise-induced coronary vasodilation (coronary vascular conductance, 0.20 +/- 0.03 mL x min(-1) x mm Hg(-1) at rest versus 0.24 +/- 0.04 mL x min(-1) x mm Hg(-1) during the heaviest level of exercise; P=.22), so that coronary flow both at rest and during exercise was below the control resting level. The findings suggest that K+(ATP) channels are critical for maintaining coronary vasodilation at rest and during exercise but that when K+(ATP) channels are blocked, both adenosine and NO act to increase coronary blood flow during exercise. In the presence of combined K+(ATP) channel blockade and adenosine receptor blockade, NO was able to produce approximately one quarter of the coronary vasodilation that occurred in response to exercise when all vasodilator systems were intact.

Topics: Adenosine; Adenosine Triphosphate; Animals; Coronary Disease; Coronary Vessels; Dogs; Enzyme Inhibitors; Glyburide; Hemodynamics; Hyperemia; Nitric Oxide; Nitroarginine; Physical Exertion; Potassium Channels; Purinergic P1 Receptor Antagonists; Theophylline; Vasodilation

1. The overall aim of this study was to determine if adrenomedullin (AM) protects against myocardial ischaemia (MI)-induced arrhythmias via nitric oxide (NO) and peroxynitrite. 2. In sham-operated rats, the effects of in vivo administration of a bolus dose of AM (1 nmol kg-1) was assessed on arterial blood pressure (BP), ex vivo leukocyte reactive oxygen species generation and nitrotyrosine deposition (a marker for peroxynitrite formation) in the coronary endothelium. 3. In pentobarbitone-anaesthetized rats subjected to ligation of the left main coronary artery for 30 min, the effects of a bolus dose of AM (1 nmol kg-1, i.v.; n=19) or saline (n=18) given 5 min pre-occlusion were assessed on the number and incidence of cardiac arrhythmias. In a further series of experiments, some animals received infusions of the NO synthase inhibitor N(G)-nitro-L-arginine (LNNA) (0.5 mg kg-1 min-1) or the peroxynitrite scavenger N-mercaptopropionyl-glycine (MPG) (20 mg kg-1 h-1) before AM. 4. AM treatment significantly reduced mean arterial blood pressure (MABP) and increased ex vivo chemiluminescence (CL) generation from leukocytes in sham-operated animals. AM also enhanced the staining for nitrotyrosine in the endothelium of coronary arteries. 5. AM significantly reduced the number of total ventricular ectopic beats that occurred during ischaemia (from 1185+/-101 to 520+/-74; P<0.05) and the incidences of ventricular fibrillation (from 61 to 26%; P<0.05). AM also induced a significant fall in MABP prior to occlusion. AM-induced cardioprotection was abrogated in animals treated with the NO synthase inhibitor LNNA and the peroxynitrite scavenger MPG. 6. This study has shown that AM exhibits an antiarrhythmic effect through a mechanism that may involve generation of NO and peroxynitrite.

Topics: Adrenomedullin; Anesthesia; Animals; Anti-Arrhythmia Agents; Arrhythmias, Cardiac; Coronary Disease; Coronary Vessels; Glycine; Male; Myocardial Ischemia; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Peroxynitrous Acid; Placebos; Rats; Rats, Sprague-Dawley; Sulfhydryl Compounds

We examined whether nitric oxide (NO) inhibition during moderate reduction in coronary blood flow (CBF) would affect perfusion-contraction matching. Coronary stenosis (CS) was induced in conscious pigs, which resulted in a stable 39 +/- 1% reduction in CBF for 1.5 h. Ischemic zone wall thickening (IZWT) decreased by an average of 56 +/- 2% during CS from 2.7 +/- 0.2 mm. After reperfusion, myocardial stunning was observed, but this recovered without evidence of necrosis. After recovery and subsequent administration of systemic NO synthase inhibition (N(omega)-nitro-L-arginine, 25 mg. kg(-1). day(-1) x 3 days), CS for 1.5 h reduced CBF similarly but decreased IZWT significantly more, P < 0.05, by 89 +/- 5%. Myocardial stunning, i.e., the decrease in IZWT at 12 h post-CS, was more severe (-65 +/- 5% vs. -21 +/- 3%), P < 0.05. Furthermore, CS during NO synthase inhibition resulted in multifocal subendocardial areas of necrosis in the area at risk. These data suggest that in the intact, conscious pig, NO inhibition prevents perfusion-contraction matching, resulting in intensification of post-ischemic stunning and development of subendocardial necrosis.

Topics: Animals; Coronary Circulation; Coronary Disease; Hemodynamics; Myocardial Contraction; Myocardial Ischemia; Myocardial Reperfusion; Myocardial Stunning; Necrosis; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Swine

The goal of the current study was to determine the effects of cAMP-mediated coronary reactivity in conscious pigs with stunned myocardium induced by 1.5 h coronary stenosis (CS) and 12 h coronary artery reperfusion (CAR). Domestic swine (n = 5) were chronically instrumented with a coronary artery blood flow (CBF) probe, hydraulic occluder, left ventricular pressure gauge, wall-thickening crystals in the ischemic and nonischemic zones, and a coronary sinus catheter. The hydraulic occluder was inflated to induce a CS with a stable 38 +/- 1% reduction in CBF for 1.5 h. Before flow reduction and during CAR, cAMP-induced coronary vasodilation was investigated by forskolin (20 nmol. kg(-1). min(-1)). Enhanced CBF responses [+62 +/- 9%, P < 0.05, compared with pre-CS (+37 +/- 3%)] were observed for forskolin at 12 h after CAR as well as for bradykinin and reactive hyperemia. With the use of a similar protocol during systemic nitric oxide (NO) synthase inhibition with N(omega)-nitro-L-arginine (30 mg. kg(-1). day(-1) for 3 days), the enhanced CBF responses to forskolin, bradykinin, and reactive hyperemia were not observed after CS. Isolated microvessel preparations from pigs (n = 8) also demonstrated enhanced NO production to direct stimulation of adenylyl cyclase with forskolin (+71 +/- 12%) or NKH-477 (+60 +/- 10%) and administration of 8-bromo-cAMP (+74 +/- 13%), which were abolished by protein kinase A or NO synthase inhibition. These data indicate that cAMP stimulation elicits direct coronary vasodilation and that this action is amplified in the presence of sustained myocardial stunning after recovery from CS. This enhanced cAMP coronary vasodilation is mediated by an NO mechanism that may be involved in myocardial protection from ischemic injury.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Adenylyl Cyclase Inhibitors; Adenylyl Cyclases; Animals; Colforsin; Consciousness; Coronary Circulation; Coronary Disease; Cyclic AMP; Enzyme Inhibitors; Microcirculation; Myocardial Stunning; Myocardium; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Oxygen Consumption; Swine; Thionucleotides; Vasodilation; Vasodilator Agents; Ventricular Pressure

Clinical studies have shown that low doses of aspirin (<300 mg/day) inhibit thromboxane A2 production and platelet aggregation but preserve prostacyclin synthesis. In contrast, high doses of aspirin (>1,000 mg/day) suppress the synthesis of both eicosanoids. Because the consequences of aspirin administration have never been investigated on coronary vasomotor tone in vivo, we investigated the effects of low and high doses of aspirin on systemic and coronary hemodynamics under basal conditions and after myocardial reactive hyperemia in conscious dogs. Dogs were instrumented with a Doppler flow probe and a hydraulic occluder. Coronary blood flow was measured in the conscious state at baseline and during myocardial reactive hyperemia after 10, 20, and 30 s of coronary occlusion. Thromboxane B2 serum concentrations, an index of platelet aggregation, decreased by >90% after long-term i.v. administration of aspirin, 100 mg/day for 7 days (low dose). Neither systemic and coronary hemodynamics nor reactive hyperemia were affected by the drug. After combined administration of this low dose of aspirin and of the nitric oxide synthase (NOS) inhibitor, N(omega)-nitro-L-arginine (L-NNA, 30 mg/kg/day/7 days), reactive hyperemia decreased to the same extent as when L-NNA was administered alone. After administration of a unique high-dose aspirin (1,000 mg, i.v.), myocardial reactive hyperemia was markedly reduced, and this effect was still observed after previous blockade of NOS and cyclooxygenase by L-NNA and diclofenac, respectively. Thus long-term treatment with a low antiaggregant dose of aspirin does not alter the ability of coronary vessels to dilate during myocardial reactive hyperemia in conscious dogs. In contrast, short-term administration of a high antiinflammatory dose of aspirin severely blunts myocardial reactive hyperemia through a mechanism that is independent of both cyclooxygenase and nitric oxide metabolic pathways.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Aspirin; Bradykinin; Coronary Disease; Coronary Vessels; Cyclooxygenase Inhibitors; Diclofenac; Dogs; Dose-Response Relationship, Drug; Hyperemia; Male; Myocardium; Nitric Oxide Synthase; Nitroarginine; Salicylic Acid; Thromboxane B2; Time Factors

The effects of coronary artery disease (CAD) on human coronary microvascular responses to vascular endothelial growth factor (VEGF) and the alterations of the myocardial expressions of VEGF and its flk-1 and flt-1 receptors were examined in 48 patients. Microvascular studies were performed in vitro with video microscopy. The expressions of VEGF and its receptors were examined using Northern analysis of total mRNA, and the expressions of constitutive nitric oxide synthase (cNOS) and inducible nitric oxide synthase (iNOS) were examined by RT-PCR. VEGF and hepatocyte growth factor (HGF) caused potent relaxations of microvessels. These responses were reduced in the presence of NG-nitro-L-arginine and the tyrosine kinase inhibitor genistein or in microvessels from patients with CAD. Relaxations to substance P and sodium nitroprusside were similar in both groups. The substance P response was abolished in the presence of NG-nitro-L-arginine. The expression of VEGF and its receptors and the expression of cNOS and iNOS were not altered in patients with CAD. In conclusion, VEGF and HGF elicit the release of nitric oxide through activation of tyrosine kinase receptors. CAD is associated with reduced vascular responses to both VEGF and HGF; this is not likely due to a reduced expression of VEGF or flt-1 or flk-1 receptors and not due to a generalized endothelium dysfunction despite the presence of mild hypercholesterolemia in these patients with CAD. These findings may have important implications regarding the efficacy of endogenous and exogenous VEGF in patients with risk factor for CAD.

Topics: Adenosine Diphosphate; Cell Division; Coronary Artery Bypass; Coronary Disease; Endothelial Growth Factors; Endothelium, Vascular; Female; Gene Expression Regulation; Genistein; Heart Atria; Hepatocyte Growth Factor; Humans; In Vitro Techniques; Kinetics; Lymphokines; Male; Microcirculation; Microscopy, Video; Middle Aged; Muscle Relaxation; Muscle, Smooth, Vascular; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Nitroarginine; Proto-Oncogene Proteins; Receptor Protein-Tyrosine Kinases; Receptors, Growth Factor; Receptors, Mitogen; Receptors, Vascular Endothelial Growth Factor; RNA, Messenger; Transcription, Genetic; Vascular Endothelial Growth Factor A; Vascular Endothelial Growth Factor Receptor-1; Vascular Endothelial Growth Factors; Vasodilation

Vascular responses were studied in both large and small arteries of rats following 8 weeks of heart failure produced by coronary ligation. Responses to noradrenaline, acetylcholine and sodium nitroprusside were studied in isolated thoracic aorta and mesenteric arteries. In the aorta, concentration-response curves for noradrenaline were similar between heart failure and sham animals and unaffected by the nitric oxide synthase inhibitor, NG-nitro-L-arginine (L-NOARG). Relaxation by acetylcholine was impaired in heart failure rats (EC50-6.79 log M heart failure vs. -7.15 log M sham). In the presence of L-NOARG, relaxation by acetylcholine was completely abolished in rings from sham rats, whereas constriction was observed in rings from heart failure rats. Relaxation by sodium nitroprusside was not different between sham and heart failure rats. In mesenteric arteries, responses to noradrenaline, acetylcholine and sodium nitroprusside were not different between heart failure and sham rats. L-NOARG reduced the maximum response to acetylcholine in both heart failure (82% to 50%) and shams (89% to 49%) by a similar magnitude, with no effect on relaxation to sodium nitroprusside. These data suggest that acetylcholine-induced relaxation is impaired in the aorta, but not mesenteric arteries in rats with heart failure. The mechanism is not solely due to impaired nitric oxide release and may be due to acetylcholine-induced contraction.

Topics: Acetylcholine; Animals; Aorta, Thoracic; Coronary Disease; Endothelium, Vascular; Enzyme Inhibitors; Male; Mesenteric Arteries; Nitric Oxide Synthase; Nitroarginine; Nitroprusside; Norepinephrine; Rats; Rats, Sprague-Dawley

The metabolites that mediate coronary reactive hyperemia have not been definitely identified. Although adenosine and endothelium derived substances seem to be involved, their relative contributions have not been defined yet. In the canine coronary circulation, we studied the relative participation of adenosine, nitric oxide and prostacyclin in reactive hyperemia, by measuring the changes produced by interfering with the synthesis or action of these metabolites. The dose-response curve for flow changes vs intracoronary administration of adenosine was displaced to the right after the inhibition of nitric oxide synthesis with N-omega-nitro-L-arginine, revealing that nitric oxide release partly mediates the vasodilator action of adenosine. The inhibition of PGI-2 synthesis with indomethacin did not modify reactive hyperemia. Interference with adenosine action, by administration of adenosine deaminase plus theophylline, decreased reactive hyperemia by 31.0 +/- 4.0% (p < 0.001). Inhibition of nitric oxide synthesis decreased reactive hyperemia by a larger (p < 0.005) magnitude, 41.0 +/- 3.9% (p < 0.001), revealing the existence of other stimuli for nitric oxide release in reactive hyperemia besides adenosine. Simultaneous inhibition of nitric oxide and PGI-2 syntheses and of adenosine action reduced reactive hyperemia, but the effect was not additive, reaching 49.5 +/- 4.5% of control. Since nitric oxide and adenosine are the most important mediators in reactive hyperemia so far described, our results suggest that other metabolites, acting directly or through mediators other than adenosine or nitric oxide, are responsible for about 50% of coronary reactive hyperemia.

Topics: Adenosine; Animals; Coronary Disease; Dogs; Endothelium, Vascular; Enzyme Inhibitors; Epoprostenol; Hyperemia; Neurotransmitter Agents; Nitric Oxide; Nitroarginine; Platelet Aggregation Inhibitors

To determine the role of an endothelium-derived relaxing factor (nitric oxide) in controlling basal coronary tone and coronary vasomotion after brief coronary occlusion (reactive hyperemia).. In 10 chronically instrumented conscious dogs, we studied the diameter changes of the large epicardial coronary artery and coronary blood flow in response to intracoronary administration of acetylcholine (0.1 and 1 microgram) and brief coronary occlusion for 5 and 20 s before and after intracoronary infusion of N-nitro-L-arginine (LNNA).. Intracoronary infusion of LNNA (1, 3, and 10 mg) decreased the diameter of the large epicardial coronary artery and coronary blood flow in a dose-dependent manner without altering arterial pressure and heart rate. LNNA (10 mg) significantly attenuated the increase in artery diameter and coronary blood flow by acetylcholine. The ratio of artery dilation to the blood flow response after acetylcholine was not affected by LNNA. LNNA (10 mg) significantly decreased the ratio of repayment to debt flow volume of reactive hyperemia, but did not affect the ratio of peak to resting flow; it also significantly attenuated the reactive dilation of the large epicardial coronary artery after reactive hyperemia. The ratio of artery dilation to repayment flow volume (micron/ml) during reactive hyperemia was attenuated significantly by LNNA.. These findings suggest that endothelium-derived nitric oxide may contribute to basal coronary tone and that reactive dilation of the large epicardial coronary artery during reactive hyperemia was caused by flow-mediated nitric oxide release, whereas coronary artery dilation after acetylcholine was caused largely by the direct receptor-mediated release of nitric oxide.

Topics: Acetylcholine; Animals; Arginine; Blood Flow Velocity; Consciousness; Coronary Circulation; Coronary Disease; Coronary Vessels; Dogs; Dose-Response Relationship, Drug; Endothelium, Vascular; Hyperemia; Nitric Oxide; Nitroarginine; Vasodilation

Nitric oxide (NO) and prostacyclin (PGI2) release was determined in effluents of Langendorff-perfused rabbit hearts under control conditions and during reperfusion subsequent to 2 h of global, low-flow ischemia. PGI2 release (6-oxo-PGF1 alpha) was significantly enhanced during early reperfusion and remained enhanced during a total time of 70 min of reperfusion. NO formation was reduced during ischemia but was substantially enhanced during reperfusion. Inhibition of endogenous PGI2 production by indomethacin resulted in severe disturbance of myocardial function and NO release. Inhibition of NO generation by L-N-nitroarginine did not affect myocardial contractility. These data suggest a cardioprotective and endothelium-protective role of PGI2 in myocardial ischemia which also involves protection of NO generation.

Topics: Animals; Arginine; Blood Pressure; Coronary Circulation; Coronary Disease; Creatine Kinase; Epoprostenol; Heart; Heart Function Tests; In Vitro Techniques; Indomethacin; Myocardial Contraction; Myocardial Reperfusion; Myocardium; Nitric Oxide; Nitroarginine; Rabbits