15-hydroxy-11-alpha-9-alpha-(epoxymethano)prosta-5-13-dienoic-acid and Coronary-Disease

Multiple factors are involved in thrombus formation and require complex and highly therapeutic strategies. Platelet activation plays a critical role in the genesis of acute coronary syndromes involving not only platelets but also endothelial cells, leucocytes and erythrocytes. Angiotensin II (Ang II) is a vasoconstrictor that could participate in the thrombotic process. Platelets also express Ang II AT1 type receptors on their surface. Losartan is a non-peptidic inhibitor of AT1 receptors. It has been demonstrated that losartan reduced platelet aggregation induced by the thromboxane A2 (TXA2) analogue U46619. This effect was not observed with the losartan metabolite EXP 3174. The effect of losartan was assessed in binding studies in which losartan competitively inhibited the binding of [3H]U46619 to platelets in a dose-dependent manner. Irbesartan also inhibits the TXA2 receptor in platelets, an effect that was not obtained with the active form of candesartan, CV11974, and with valsartan. These results suggest that the structural requirements necessary to antagonize the TXA2/PGH2 platelet receptor may be different from those involved in AT1 receptor antagonism. The in vivo relevance of the in vitro findings has been confirmed by the fact that in vivo administration of losartan decreases P-selectin expression in platelets obtained from stroke-prone spontaneously hypertensive rats.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Angiotensin Receptor Antagonists; Animals; Antihypertensive Agents; Benzimidazoles; Biphenyl Compounds; Coronary Disease; Coronary Thrombosis; Humans; Losartan; P-Selectin; Platelet Activation; Platelet Aggregation; Rats; Rats, Inbred SHR; Receptor, Angiotensin, Type 1; Receptor, Angiotensin, Type 2; Receptors, Thromboxane; Tetrazoles; Thrombosis; Thromboxane A2; Valine; Valsartan

We investigated the contractile response of human coronary microvasculature to thromboxane A-2 (TXA-2), with and without the blockade of TXA-2 receptors or the inhibition of phospholipase-C (PLC) or of protein kinase C-α (PKC-α) in the human coronary microvasculature before and after cardioplegia, followed by reperfusion (CP/Rep). Protein/gene expression and localization of TXA-2 receptors, TXA-2 synthase, PLC, and other TXA-2-related proteins was also examined.. Right atrial tissue was harvested before and after cold blood cardioplegia, followed by about 10 minutes of reperfusion, from 28 patients undergoing cardiac operations. Coronary arterioles (90 to 170 μm in diameter) were dissected from the harvested tissue.. The post-CP/Rep contractile response of coronary arterioles to TXA-2 analog U-46619 was significantly impaired vs pre-CP/Rep (p<0.05). The TXA-2 receptor antagonist SQ-29548 (10(-6) M) prevented the contractile response to U-46619 (p<0.05). Pretreatment with the PLC inhibitor U73122 (10(-6) M) significantly inhibited the U-46619-induced contractile response (p<0.05). Administration of the PKC-α inhibitor safingol failed to affect U-46619-induced contraction. Total protein levels and gene expression of TXA-2 receptors, TXA-2 synthase, PLC-β3, phospho-PLC-β3, PLC-γ1, and phospho-PLC-γ1 were not altered after CP/Rep. Confocal microscopy showed no significant differences in the expression of TXA-2 receptors or PLC-β3 in the microcirculation. TXA-2 receptors and PLC-β3 were both present in smooth muscle and endothelium.. Cardioplegia/Rep decreases the contractile response of human coronary arterioles to TXA-2 soon after cardiac operations. The contractile response to the TXA-2 analog U-46619 is through activation of TXA-2 receptors and PLC.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Aged; Arterioles; Coronary Circulation; Coronary Disease; Coronary Vessels; Female; Gene Expression; Heart Arrest, Induced; Humans; Immunoblotting; Male; Microarray Analysis; Microscopy, Confocal; Receptors, Thromboxane A2, Prostaglandin H2; RNA; Thromboxane A2; Thromboxane-A Synthase; Type C Phospholipases; Vasoconstriction

Patients with ischemic heart disease have platelets that are resistant to the anti-aggregatory effects of nitric oxide (NO) donors. This NO resistance is associated with increased whole blood superoxide radical (O2-) content. Angiotensin II (Ang II) has been shown to augment O2- formation. Recent studies have demonstrated that angiotensin-(1-7) [Ang-(1-7)] has opposite actions to those of Ang II in the vasculature. This study compares the effects of Ang-(1-7) and Ang II on platelet aggregation and platelet responsiveness to the NO donor sodium nitroprusside (SNP). Platelet aggregation was induced by the thromboxane A2 mimetic U46619 (1-5 micromol/L), and the inhibitory effects of SNP (10 micromol/L) on the rate and extent of aggregation were quantified. Ang II did not induce aggregation, but 10-100 nmol/L Ang II potentiated U46619-induced aggregation by 21+/-6% in the absence and by 26+/-9% in the presence of SNP (P<0.01 for both), in blood samples from 8 normal subjects. By contrast, Ang-(1-7) alone did not affect platelet aggregation, but 10-100 nmol/L Ang-(1-7) potentiated the anti-aggregatory effects of SNP in blood samples from both normal subjects (n=17) and patients with acute coronary syndromes (n=17). This effect of Ang-(1-7) was bimodal, and at higher concentrations of Ang-(1-7), potentiation was abolished. The maximum incremental effects of Ang-(1-7) on inhibition of aggregation were 25+/-4% and 28+/-5%, for rate and extent of aggregation respectively (P<0.01 for both), corresponding to a 2.3-fold potentiation of the anti-aggregatory effect of SNP. Platelets from patients were resistant to the anti-aggregatory effect of SNP, but potentiation of SNP effects by Ang-(1-7) was similar for patients and normal subjects. Thus, Ang-(1-7) potentiates the anti-aggregatory effects of NO donor, and may therefore counteract platelet NO resistance that accompanies cardiovascular disease.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adult; Aged; Angiotensin I; Angiotensin II; Antihypertensive Agents; Coronary Disease; Drug Synergism; Female; Humans; Male; Myocardial Infarction; Nitric Oxide Donors; Nitroprusside; Peptide Fragments; Platelet Aggregation; Platelet Aggregation Inhibitors; Vasoconstrictor Agents

Hyperhomocysteinemia is an independent risk factor of coronary artery disease. Clinical studies have indicated that moderate red wine consumption is associated with a reduction of incidence of coronary artery disease. In this study, we determined the effect of red wine on homocysteine- induced endothelial dysfunction in porcine coronary arteries.. Porcine coronary arteries were dissected from 6 pig hearts and cut into 5-mm ring segments, which were assigned into 4 groups (9 rings/group): blank control, homocysteine treated (50 muM), red wine treated (0.08% alcohol), and homocysteine plus red wine treated. The rings were cultured in cell culture medium with or without treatment for 24 h. Myograph analysis was performed with U46619 (10(-7) M) for contraction and cumulative bradykinin (10(-9) to 10(-5) M) for endothelium-dependent relaxation. The endothelial nitric oxide synthase (eNOS) levels were analyzed by RT-PCR, Western blot, and immunohistochemistry.. In response to 10(-5) M bradykinin, porcine coronary artery rings treated with homocysteine (50 muM) showed a significant reduction of endothelium-dependent vasorelaxation by 43% as compared to controls (P < 0.05). However, rings treated with red wine (0.08% alcohol) plus homocysteine showed no significant difference as compared to controls. Endothelium-dependent vasorelaxation was not different between control and red wine treated groups. Furthermore, eNOS mRNA density levels were significantly reduced by 36% in homocysteine treated group as compared to controls (P < 0.05). eNOS protein levels were also substantially reduced in the homocysteine-treated group. However, red wine treatment reversed the effect of homocysteine-induced eNOS downregulation.. Homocysteine significantly impaired endothelial functions including endothelium-dependent vasorelaxation and eNOS mRNA and protein levels in porcine coronary arteries; and red wine effectively prevented homocysteine-induced endothelial dysfunction. This study suggests that protecting coronary endothelial cells from homocysteine damage may be an important mechanism of red wine for preventing coronary artery disease.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Blotting, Western; Bradykinin; Coronary Disease; Coronary Vessels; Culture Media; Culture Techniques; Endothelium, Vascular; Gene Expression; Homocysteine; Immunohistochemistry; Muscle Contraction; Muscle Relaxation; Muscle, Smooth, Vascular; Nitric Oxide Donors; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroprusside; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Swine; Wine

The adenosine triphosphate (ATP)-sensitive potassium channels (K(+)-ATP channels) are activated by decreases in intracellular ATP and help to match blood flow to tissue needs. Such metabolism-flow coupling occurs predominantly in the smallest arterioles measuring 50 microm or less in diameter. Previous studies demonstrated that isoflurane may activate the K(+)-ATP channels in larger arteries. We examined whether isoflurane also activates the channels in the smallest arterioles of approximately 50 microm. Microvessels of approximately 50 microm were dissected from right atrial appendages from patients undergoing coronary artery bypass surgery and were monitored in vitro for diameter changes by videomicroscopy. With or without preconstriction with the thromboxane analog U46619 1 microM, vessels were exposed to isoflurane 0%-3% either in the presence or absence of the K(+)-ATP channel blocker glibenclamide 1 microM. Without preconstriction, isoflurane neither dilated nor constricted the vessels significantly. After preconstriction, isoflurane had a concentration-dependent dilation of the small arterioles (39 +/- 13% [mean +/- SD] dilation at 3% isoflurane) (P < 0.001), and this effect was significantly attenuated by glibenclamide (18 +/- 5% dilation at 3% isoflurane) (P < 0.01). In comparison, nitroprusside 10(-4) M produced 79 +/- 6% dilation, and adenosine diphosphate 10(-4) M produced 29 +/- 7% dilation. We conclude that isoflurane-mediated dilation of the smallest resistance arterioles may be in part based on activation of the K(+)-ATP channels when the arterioles are relatively constricted.. Vasodilation of very small coronary arterioles by isoflurane depends on preexisting tone and may in part be mediated by the K(+)-ATP channels.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine Diphosphate; Adenosine Triphosphate; Anesthetics, Inhalation; Arterioles; Atrial Appendage; Coronary Disease; Coronary Vessels; Humans; In Vitro Techniques; Isoflurane; Middle Aged; Nitroprusside; Potassium Channels; Vasoconstriction; Vasoconstrictor Agents; Vasodilation; Vasodilator Agents

We have previously shown that superoxide anion (O2-) stimulates the release of vasoconstrictor prostanoids and induces a prolonged rise in coronary perfusion pressure (CPP) that persists even after removal of O2-. In this study, we tested the hypothesis that the increased CPP is mediated by activation of TxA2/ PGH2 (TP) receptors and protein kinase C (PKC)-dependent mechanisms. In Langendorff perfused rat hearts, O2- was applied for 15 min and then washed out over a period of 20 min. Application of O2- increased the release of vasoconstrictive (TxA2 and PGF2alpha) and decreased vasodilating (PGI2 and PGE2) prostanoids. Although indomethacin (10 microM), a cyclooxygenase inhibitor, attenuated the rise in CPP during O2- perfusion, the increase was not completely blocked. OKY 046Na (10 microM), a thromboxane synthase inhibitor, had no effect on O2--induced increases in CPP, whereas ONO 3708 (10 microM), a TP receptor antagonist, suppressed this effect. PKC activity was also elevated by more than 50% by O2- perfusion. CPP typically increased throughout the O2- wash-out. This post-O2- vasoconstriction was not inhibited by indomethacin, nitroglycerin or nitrendipine. In contrast, ONO 3708 (10 microM) and two PKC inhibitors, staurosporine (10 nM) and calphostin C (100 nM), completely blocked the rise in CPP, and even elicited vasodilation. PDBu enhanced the post-O2- vasoconstriction. We conclude that O2--induced coronary vasoconstriction is initially mediated by TP receptors, but activation of PKC sustains the response.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Calcium Channel Blockers; Cardiovascular Agents; Coronary Disease; Dinoprost; Enzyme Inhibitors; In Vitro Techniques; Indomethacin; Male; Methacrylates; Naphthalenes; Perfusion; Prostaglandins; Protein Kinase C; Rats; Rats, Sprague-Dawley; Receptors, Prostaglandin; Receptors, Thromboxane; Receptors, Thromboxane A2, Prostaglandin H2; Staurosporine; Superoxides; Thromboxane A2; Thromboxane-A Synthase; Vasoconstrictor Agents

The membrane complex alpha(IIb)beta(3) is the major receptor for fibrinogen and is involved in platelet adhesion and aggregation. Evidence has been presented that the Pl(A2) allele of the beta(3) Pl(A1/A2) gene polymorphism might be an independent risk factor for coronary thrombosis, but the matter is still controversial. We investigated the relationship between this polymorphism and possible alterations of platelet functions in vitro. The platelet adhesion to fibrinogen-coated microplate wells and the aggregation induced by several different agonists were tested in 63 healthy volunteers, among them, 49 subjects with Pl(A1/A1) polymorphism, 12 subjects with Pl(A1/A2) polymorphism and two subjects with (PlA2/A2) polymorphism. Subjects with PlA1/A2 polymorphism or with Pl(A2/A2) polymorphism showed significantly lower platelet responses as compared with Pl(A1/A1) subjects when either arachidonic acid or the thromboxane A(2) analogue, U46619, were used as agonists. In resting condition and after thrombin or ADP stimulation, platelet function was normal in all the subjects. An increased sensitivity to the anti-aggregatory effect of acetylsalicylic acid was observed in platelets from subjects with the Pl(A2) allele. Finally, using a flow-cytometric evaluation and determining the beta-thromboglobulin plasma levels, we did not find any evidence of a Pl(A2) platelet hyper-reactivity ex vivo. Our findings are not consistent with the hypothesis that the purported increase of cardiovascular risk in these subjects may be as a result of platelet hyperactivation. On the contrary, the Pl(A2) allele is associated with a platelet functional deficiency, specifically linked to the activation of the fibrinogen receptor by thromboxane A(2).

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine Diphosphate; Adult; Arachidonic Acid; Aspirin; beta-Thromboglobulin; Blood Platelets; Coronary Disease; Female; Flow Cytometry; Genotype; Humans; Male; Middle Aged; Platelet Adhesiveness; Platelet Aggregation; Platelet Aggregation Inhibitors; Platelet Function Tests; Platelet Glycoprotein GPIIb-IIIa Complex; Polymorphism, Genetic; Risk Factors; Statistics, Nonparametric; Thrombin; Thromboxane A2

Changes in the vascular response of isolated, perfused rat hearts to endothelin-1 (ET-1) and binding of [125I]ET-1 to cardiac membranes were examined following ischemia (30 min, zero flow) and reperfusion (15 min). Infusion of ET-1 (0, 2.5, 5, 7.5, and 10 x 10(-10) M) increased the control heart perfusion pressure (61, 73, 88, 102, and 117 mm Hg, respectively). Ischemic and reperfused hearts were more sensitive to ET-1 infusion (p less than 0.05 at all concentrations). Nisoldipine (NIS, 1 nM) prevented the rise in sensitivity to ET-1 following ischemia and reperfusion. Two binding sites for [125I]ET-1 were identified in cardiac membranes. High-affinity (Kd = 0.04 nM, Bmax = 0.46 pmol/mg of protein) and low-affinity (Kd = 13.8 nM, Bmax = 5.4 pmol/mg of protein) sites were unchanged by ischemia and reperfusion, and NIS did not change binding constants in control or ischemic and reperfused hearts. Increased ET-1 sensitivity after ischemia may be due to other factors. Endothelium-dependent vasodilation and endothelium-independent vasodilation were significantly reduced following 30 min of ischemia. Inhibition of dilator responses may account for increased ET-1 responses following transient ischemia.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Acetylcholine; Animals; Coronary Disease; Endothelins; Heart; In Vitro Techniques; Myocardial Reperfusion; Myocardium; Nisoldipine; Nitroglycerin; Prostaglandin Endoperoxides, Synthetic; Rats; Rats, Inbred Strains; Vasoconstriction

The aim was to test the hypothesis that thromboxane A2 can cause vasoconstriction of coronary resistance vessels during exercise in hypoperfused regions of myocardium distal to an arterial stenosis.. Eight adult mongrel dogs were studied. Chronically instrumented animals with a left circumflex coronary artery Doppler flow meter, hydraulic occluder, and indwelling catheter underwent treadmill exercise at heart rates of 190-200 beats.min-1. Myocardial blood flow was measured with microspheres during unimpeded arterial inflow and in the presence of a coronary stenosis which decreased distal pressure to 42-45 mm Hg. Measurements were repeated during infusion of the thromboxane A2 analogue, U46619.. When the occluder was partially inflated to produce a stenosis, blood flow in the region perfused by the stenotic artery was 58 (SEM 6)% of flow in the normally perfused region (p less than 0.01). U46619 (0.01 microgram.kg-1.min-1) caused a further 21 (7)% decrease in blood flow in the region perfused by the stenotic artery (p less than 0.05). The vasoconstriction produced by U46619 was uniform across the left ventricular wall from epicardium to endocardium. U46619 did not significantly decrease myocardial blood flow in the absence of a coronary stenosis.. Even during hypoperfusion produced by a flow limiting arterial stenosis, the coronary resistance vessels remain responsive to the vasoconstrictor effect of thromboxane A2. Liberation of thromboxane A2 during platelet activation at the site of a proximal coronary stenosis may worsen myocardial hypoperfusion by causing vasoconstriction of the distal resistance vessels.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Blood Pressure; Coronary Circulation; Coronary Disease; Dogs; Heart Rate; Microspheres; Physical Exertion; Prostaglandin Endoperoxides, Synthetic; Regional Blood Flow; Thromboxane A2

We tested the direct effects of thromboxane A2/prostaglandin endoperoxide (TP) receptor agonists and antagonists on ischemic rat hearts to determine if any significant actions of TP may be occurring in a buffer-perfused system (without blood). Buffer-perfused rat hearts were treated with the TP antagonist SQ 30,741 (0.5-1.0 microM) during 15 min of ischemia and 30 min reperfusion. SQ 30,741 had no effect on severity of ischemia. In the same model, the TP receptor agonists U-46619 (0.01-1.0 microM) and SQ 26,655 (0.1 microM) reduced coronary flow and cardiac function both before and after ischemia. The decrease in contractile function appeared to be secondary to flow decrement. Despite the flow effects, U-46619 reduced ischemia-induced lactate dehydrogenase (LDH) release and contracture, indicating some beneficial effects. Measurement of prostacyclin release during reperfusion with and without U-46619 treatment showed that U-46619 significantly increased prostacyclin production. Meclofenamate (5.0 microM) did not reverse the vasoconstrictor and cardiodepressant effects of U-46619 but completely reversed its beneficial effect on LDH release. TP receptor blockade with 1.0 microM SQ 30,741 completely reversed the flow and cardiodepressant effects of SQ 26,655 but did not reverse the beneficial effects of this compound on LDH release. Receptor binding studies using [3H]-SQ 29,548 and [3H]-U-46619 indicated that few if any TP receptors exist in myocytes. In conclusion, TP antagonists are not cardioprotective in this model, but exogenous TP receptor agonists have complex actions in buffer-perfused hearts, some of which are mediated by vascular TP receptors and others which are not.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Coronary Circulation; Coronary Disease; Cyclooxygenase Inhibitors; Epoprostenol; Fatty Acids, Monounsaturated; Heart; In Vitro Techniques; L-Lactate Dehydrogenase; Male; Meclofenamic Acid; Myocardium; Platelet Aggregation Inhibitors; Prostaglandin Endoperoxides, Synthetic; Prostaglandin H2; Prostaglandins H; Rats; Rats, Inbred Strains; Thromboxane A2

Defibrotide is known to enhance prostacyclin (PGI2) release from the vascular endothelium. We investigated the vasoactive effects of defibrotide in isolated rat hearts perfused at constant flow subjected to ischaemia and reperfusion. Defibrotide at 10 or 100 micrograms/ml did not exert any direct vasoactive effect on normal rats hearts. However, ischaemia and reperfusion resulted in an impaired vasodilation to acetylcholine, an endothelium-dependent vasodilator. In contrast, the vasodilator response to the endothelium-independent dilator, nitroglycerin, was unaffected. Defibrotide, at 10 or 100 micrograms/ml, markedly restored the vasodilation to acetylcholine 10 nmol/l to 1 mumol/l (P less than 0.01) without influencing the vasodilator response to nitroglycerin (2 to 200 micrograms/l). Haemoglobin (150 nmol/l) inhibited the dilation to acetylcholine in response to defibrotide. However, no evidence of PGI2 release was observed with acetylcholine-induced vasodilation in the presence or absence of defibrotide. Additionally, 10-100 micrograms/ml of defibrotide did not significantly decrease superoxide radicals generated by a xanthine-xanthine oxidase synthetic system under conditions in which superoxide dismutase was effective. Thus, defibrotide appears to exert an endothelium-protective effect preserving endothelium-derived relaxing factor (EDRF) without directly scavenging free signals.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; 6-Ketoprostaglandin F1 alpha; Acetylcholine; Animals; Coronary Disease; Coronary Vessels; Endothelium, Vascular; Epoprostenol; Fibrinolytic Agents; In Vitro Techniques; Male; Myocardial Reperfusion; Nitric Oxide; Nitroglycerin; Polydeoxyribonucleotides; Prostaglandin Endoperoxides, Synthetic; Rats; Rats, Inbred Strains; Superoxide Dismutase; Superoxides

Bay U 3405 is a novel thromboxane receptor blocker. The present investigations describe its effects on experimental canine and porcine cardiac damage. In anesthetized dogs, a coronary artery was occluded for 6 hours and reperfused for 30 minutes. Bay U 3405 was administered intravenously 15 minutes after occlusion (1 mg/kg) followed by infusion of 10 mg/kg/hr from 30 minutes after ligature. In a second study, the effects of Bay U 3405 on endoperoxide analogue U-46619-induced coronary constriction were studied in anesthetized, open-chest pigs. Bay U 3405 reduced myocardial infarct expansion by 65% (p less than 0.01) assessed with biochemical staining. Hemodynamics and collateral blood flow were unaffected. However, reperfusion arrhythmias were suppressed. In porcine experiments, 1 mg/kg Bay U 3405, given intravenously or intraduodenally, antagonized U-46619-induced coronary vasoconstriction over 5 hours. The studies demonstrate anti-ischemic and antivasoconstrictor properties of Bay U 3405 probably due to binding to platelet and smooth muscle thromboxane receptors. This may have clinical relevance in angina pectoris and myocardial infarction.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Carbazoles; Coronary Disease; Coronary Vessels; Disease Models, Animal; Dogs; Hemodynamics; Myocardial Infarction; Prostaglandin Endoperoxides, Synthetic; Sulfonamides; Swine; Thromboxanes; Vasoconstriction

1. The effects of calcitonin gene-related peptide (CGRP) and neuropeptide Y (NPY) were examined on sheep circumflex (2-2.5 mm o.d.) coronary artery rings, with and without endothelium, under oxygenated, hypoxic and simulated ischaemic conditions. The interaction between the vasoconstrictor effects of NPY and the thromboxane mimetic, U46619, was also studied. 2. Ischaemia was simulated by modification of the composition of the physiological salt solution by increasing potassium and H+, including lactate and reducing glucose and PO2. 3. Hypoxia alone and simulated ischaemia increased the maximum vasodilatation produced by CGRP. CGRP (30 nM) abolished and markedly reduced the contraction that was induced by hypoxia and simulated ischaemia respectively. 4. Hypoxia increased and simulated ischaemia reduced the contractile response to NPY in endothelium intact rings. When the endothelium was removed, NPY caused a contraction under ischaemic conditions only. The hypoxic and ischaemic-induced contractions were augmented by NPY (30 nM). 5. In the rings containing endothelium, NPY enhanced the contraction caused by U46619 during hypoxia only. In endothelium-denuded preparations, NPY increased or partially restored the contraction caused by U46619. 6. These results show that the responsiveness of coronary artery rings isolated from sheep to either CGRP or NPY is modified by hypoxia or simulated myocardial ischaemia.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Calcitonin Gene-Related Peptide; Coronary Disease; Coronary Vessels; Endothelium, Vascular; Hypoxia; In Vitro Techniques; Muscle, Smooth, Vascular; Neuropeptide Y; Potassium Chloride; Prostaglandin Endoperoxides, Synthetic; Sheep

The effects of simulated myocardial ischaemia on tone and on the responsiveness to contractile and relaxant agents were examined on sheep circumflex coronary artery rings. Introduction of ischaemia caused a transient relaxation followed by sustained contraction which was inhibited by adenosine or by the removal of the endothelium. Under ischaemic conditions, the contractile effects of 5-hydroxytryptamine and acetylcholine were markedly depressed while those of potassium and U46619 (a stable thromboxane analogue) were not modified. In contrast, the vasodilating effects of adenosine, noradrenaline and iloprost (a prostacyclin mimetic) were significantly potentiated. Addition of adenosine to the ischaemic Krebs solution abolished the contractile effects of 5-hydroxytryptamine and U46619 but did not modify the vasorelaxant effects of noradrenaline and iloprost. These results indicate that the ischaemic-induced contraction is endothelium-dependent and the responsiveness of the coronary artery to both constrictors and vasodilators changed under conditions of simulated myocardial ischaemia.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine; Animals; Coronary Disease; Coronary Vessels; Epoprostenol; Glucose; Guinea Pigs; Hydrogen-Ion Concentration; Iloprost; In Vitro Techniques; Muscle Relaxation; Muscle, Smooth, Vascular; Norepinephrine; Oxygen; Potassium; Prostaglandin Endoperoxides, Synthetic; Serotonin; Sheep

Activated polymorphonuclear leukocytes (PMNs) contribute to myocardial injury during ischemia and reperfusion. There is evidence that activation of the complement pathway may be one of the mechanisms of PMN activation during ischemia. Intracoronary infusion of complement C5a during normal perfusion pressure is associated with decreased coronary flow, contractile dysfunction, and PMN accumulation. The mechanisms responsible for these changes have not been identified. Thromboxane A2 (TXA2) is a potential mediator of this myocardial ischemic response. Activated PMNs produce TXA2, a known coronary vasoconstrictor, and TXA2 was shown to be a mediator of the pulmonary hypertensive response to activated complement. The goal of the present study was to determine if an enhanced TXA2 production is associated with the myocardial response to C5a and whether cyclooxygenase blockade would reduce the myocardial ischemia. In open-chest pigs, intracoronary C5a (500 ng) caused reversible reductions in blood flow (50.0% of control), regional contractile function (25.8% of control), leukocyte trapping (1.0 x 10(6) cells/g myocardium or a peak artery-coronary venous difference of 5.3 x 10(3) cells/microliters blood), and increased coronary venous TXB2 (the TXA2 breakdown product) from 1.6 pmol/ml to a peak of 6.9 pmol/ml. Cyclooxygenase blockade with aspirin or indomethacin, which prevented TXB2 production, did not alter the response in flow, function, or PMN trapping. Ibuprofen, a known direct inhibitor of PMNs in addition to its cyclooxygenase blockade effect, reduced the response slightly. The pig coronary vascular bed was responsive to the TXA2 agonist U46619, which reduced flow and function without PMN trapping. Mechanical reductions in coronary flow to levels equivalent to those during the C5a infusions did not increase coronary venous TXB2 nor cause PMN trapping but did cause equivalent contractile dysfunction. Incubation of whole blood with C5a at concentrations equivalent to those achieved in vivo did not cause TXB2 production. We conclude that 1) TXA2 is produced in response to intracoronary C5a and 2) cyclooxygenase blockade does not prevent the C5a-induced myocardial ischemia, contractile dysfunction, and PMN trapping. The TXA2 production likely involves a vascular site or a blood cell-vascular interaction. This model system indicates the potential for persistently activated PMNs to cause continued ischemia during myocardial reperfusion.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Aspirin; Complement C5a; Coronary Disease; Coronary Vessels; Cyclooxygenase Inhibitors; Female; Indomethacin; Injections, Intra-Arterial; Leukocyte Count; Leukocytes; Male; Myocardium; Prostaglandin Endoperoxides, Synthetic; Swine; Thromboxane B2; Thromboxanes

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Coronary Disease; Male; Myocardial Infarction; Myocardial Reperfusion Injury; Neutrophils; Phenylacetates; Prostaglandin Endoperoxides, Synthetic; Rats; Rats, Inbred Strains; Receptors, Prostaglandin; Receptors, Thromboxane; Sulfonamides

The effect of the thromboxane A2 (TXA2) receptor antagonist SQ 30,741 on infarct size and myocardial blood flow during coronary occlusion and reperfusion was determined. In anesthetized dogs, the left circumflex coronary artery (LCX) was occluded and after 10 min a continuous infusion of SQ 30,741 (1 mg/kg + 1 mg/kg/h, i.v.) or saline was begun. After 90 min of LCX occlusion, the LCX was reperfused for 5 h and infarct size was then determined. Myocardial blood flows before, during, and after occlusion were determined using radioactive microspheres. SQ 30,741 resulted in a significant decrease in infarct size (34% +/- 6% of left ventricular area at risk) compared to controls (60% +/- 9%). Cardioprotection was also found with SQ 30,741 when infarct size was normalized for both area at risk and predrug collateral flow. The protective effect of SQ 30,741 occurred without an increase in collateral flow. At 1 h postreperfusion, subendocardial flow was significantly higher in SQ 30,741-treated animals (109 +/- 15 ml/min/100 g) compared to controls (71 +/- 16 ml/min/100 g). SQ 30,741, in the dose resulting in infarct size reduction, produced a 95% inhibition of platelet TXA2 receptors throughout the experiment as measured by dose-dependent inhibition of the ex vivo platelet shape change response to U-46,619, a TXA2 mimetic. Thus, a dose of SQ 30,741 that results in TXA2 blockade also results in myocardial salvage without changes in collateral flow.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Blood Platelets; Coronary Circulation; Coronary Disease; Dogs; Female; Hemodynamics; Male; Myocardial Infarction; Myocardial Reperfusion; Oxygen Consumption; Prostaglandin Endoperoxides; Prostaglandin Endoperoxides, Synthetic; Receptors, Prostaglandin; Thromboxane A2

To test the hypothesis that endogenous prostacyclin is required to maintain reduced arteriolar tone distal to a severe coronary arterial stenosis under basal conditions and during challenge with a vasoconstrictor eicosanoid such as thromboxane A2 10 closed chest, domestic swine were prepared with an artificial stenosis, which reduced the luminal diameter of the left anterior descending coronary artery by 80%. Haemodynamic variables, regional myocardial blood flow (microsphere method), and lactate metabolism were measured at control (1); after infusion of U46619 (thromboxane A2 mimetic) distal to the stenosis at 1 microgram.min-1 for 10 min and 5 micrograms.min-1 for 10 min; at control (2); after indomethacin infusion distal to the stenosis; and after repeat infusion of U46619. At the end of the study the animal hearts were removed and their coronary vessels harvested for in vitro determination of prostacyclin (PGI2) production. Regional myocardial blood flow in all layers of the heart distal to the stenosis did not change compared with control during the initial 1 microgram.min-1 dose of U46619 but was reduced significantly after the 5 micrograms.min-1 dose (approximately 20% vs control). Distal zone flow (all layers) returned to baseline at control (2) and remained unchanged after indomethacin infusion. Although distal zone flows were reduced significantly in response to the second 5 micrograms.min-1 dose, the reduction in each layer after indomethacin was comparable to that observed with the 5 micrograms.min-1 dose before indomethacin infusion. Finally, the in vitro production of PGI2 by coronary vessels was considerably impaired by indomethacin infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Coronary Circulation; Coronary Disease; Epoprostenol; Hemodynamics; Lactates; Myocardium; Prostaglandin Endoperoxides, Synthetic; Regional Blood Flow; Swine; Vascular Resistance

Thromboxane A2 and cysteinyl leukotrienes are highly effective microvessel constrictors in normally perfused myocardium. Their release during acute coronary thrombosis might augment myocardial underperfusion. The constrictor action of these substances could be modified substantially, however, by concomitant myocardial ischemia. We compared the effects of the two eicosanoid constrictors in normally perfused and ischemic myocardium of 24 open-chest, pentobarbital-anesthetized pigs. Left anterior descending coronary flow was measured after intracoronary bolus injections of the stable thromboxane A2 analog U46619 (1-10 micrograms) or leukotriene D4 (LTD4, 1-10 micrograms). Each dose was given before and during myocardial ischemia induced by a snare adjusted to produce 63 +/- 2% decrease in coronary flow for 10 min. Marked dose-independent inhibition of eicosanoid-induced coronary flow decrease occurred during ischemia. With 10 micrograms U46619, coronary flow decrease in the unoccluded state (25 +/- 2 from 55 +/- 4 ml/min pretreatment baseline) was virtually eliminated during snare occlusion (1 +/- 1 from 21 +/- 3 ml/min pretreatment baseline, P less than 0.001). Similar results occurred with LTD4. Distal coronary pressure during ischemia indicated a lack of microvessel responsiveness to the eicosanoids rather than a buffering of resistance change by the snare. U46619 and LTD4 did induce transient, small reductions in regional shortening fraction during ischemia. Our data suggest that eicosanoid-induced constriction of myocardial resistance vessels is not a likely complication of acute coronary thrombosis. However, eicosanoids could depress residual contractility in moderately ischemic regions.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Coronary Circulation; Coronary Disease; Eicosanoic Acids; Female; Male; Prostaglandin Endoperoxides, Synthetic; SRS-A; Swine; Thromboxane A2; Vasoconstriction

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine Diphosphate; Adult; Angina Pectoris; Coronary Disease; Humans; Middle Aged; Platelet Adhesiveness; Platelet Aggregation; Prostaglandin Endoperoxides, Synthetic; Thromboxane A2

We tested the hypothesis that thromboxane A2 and thromboxane A2/PGH2 receptor occupation are important in mediating cyclical reductions in coronary blood flow (CFVs) in concentrically narrowed canine coronary arteries. Two potent and selective thromboxane A2/PGH2 receptor antagonists, SQ29,548 and SQ28,668 eliminated CFVs and restored a normal pattern of blood flow through the severely narrowed vessels in 77 and 75% of the dogs, respectively. CFVs were eliminated within several minutes of an intravenous bolus injection of SQ29,548 or SQ28,688. A continuous infusion of SQ29,548 (0.2 mg/kg X min) prevented the recurrence of CFVs throughout the duration of its infusion. Left atrial infusion of the thromboxane A2 mimetic, U46619, restored CFVs in 5 of 8 SQ29,548-treated and in 5 of 7 SQ28,668-treated dogs. Circulating concentrations of the stable metabolites of TxA2 and PGI2, TxB2 and 6-keto-PGF1 alpha, respectively, were unaffected by administration of SQ29,548. However, stenosed vascular segments of the left anterior descending coronary artery (LAD) of SQ29,548-treated dogs produced significantly less thromboxane A2 than comparable segments from untreated dogs. Morphologic studies showed that stenosed coronary arteries in which CFVs had been abolished by either SQ29,548 or SQ28,668 had relatively few adherent platelets, whereas comparable coronary segments removed from untreated animals had relatively large, platelet-rich mural thrombi. SQ29,548 did not alter the synthesis of TxB2 by platelets. 6-keto-PGF1 alpha concentrations in the stenosed LAD and nonstenosed circumflex coronary arteries were not altered by SQ29,548 administration. These data suggest that the thromboxane A2/PGH2 receptor antagonists, SQ29,548 and SQ28,688, inhibit cyclic reductions in coronary blood flow in this model by preventing the accumulation of platelets at the site of a critical coronary arterial stenosis. The data also suggest that TxA2 is important in mediating the interaction between platelets and the constricted coronary artery that is responsible for the development and maintenance of CFVs in this experimental model.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Coronary Circulation; Coronary Disease; Coronary Vessels; Dogs; Epoprostenol; Hemodynamics; Male; Microscopy, Electron, Scanning; Prostaglandin Endoperoxides, Synthetic; Prostaglandins H; Receptors, Prostaglandin; Receptors, Thromboxane A2, Prostaglandin H2; Thromboxane A2; Thromboxanes

We studied the effects of the thromboxane analog, U46619, infused into the left anterior descending (LAD) artery of intact dogs before and after producing endothelial denudation of the mid portion of the LAD. Proximal artery cross-sectional area (CSA) decreased by 47% with 0.1 microgram/min infusion of U46619 with intact and denuded endothelium, while resting CSA reduced spontaneously following denudation. Coronary resistance vessels demonstrated a marked constrictor response to U46619 with a rise in resistance and a fall in flow and myocardial O2 consumption. U46619 produces significant narrowing of proximal epicardial coronary arteries as well as resistance coronary vessels. This effect could cause ischemia in patients with moderate coronary atherosclerosis.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Coronary Disease; Coronary Vasospasm; Coronary Vessels; Disease Models, Animal; Dogs; Endothelium; Male; Oxygen Consumption; Prostaglandin Endoperoxides, Synthetic; Regional Blood Flow; Vascular Resistance; Vasoconstriction

Recent studies suggest that platelet activation and subsequent thromboxane (TX) A2 release play important roles in certain coronary syndromes. To further test this possibility, we examined the ability of a selective TXA2-synthetase inhibitor, dazoxiben (UK-37-248), to abolish cyclic flow reductions (CFRs) that occur in experimentally stenosed canine coronary arteries. CFRs, which are characterized by progressive declines in coronary blood flow and interrupted by sudden and usually spontaneous restorations of flow, were produced by placing hard plastic cylindrical constrictors (5 mm long X 4.5 mm outer diameter) on the proximal left anterior descending or circumflex coronary artery in open-chest, anesthetized dogs. Coronary blood flow was measured with pulsed Doppler flow probes placed proximal to the constrictors and regional myocardial blood flow with 15 micron radiolabeled microspheres. CFRs were observed for 1 hr, during which coronary blood flow was monitored continuously. Regional myocardial blood flow was measured before constriction, when coronary blood flow appeared to be at its nadir, and after spontaneous restorations of flow. After 1 hr dazoxiben (2.5 mg/kg iv) or an equal volume of saline was given and coronary blood flow was monitored for another hour. Dazoxiben abolished CFRs completely in 18 of 28 dogs and significantly reduced their frequency in the dogs receiving the drug (10.1 +/- 0.8 vs 3.2 +/- 1.0 per hour [+/- SE]; p less than .001, n = 28). The frequency and magnitude of variations in cyclic blood flow were unchanged after saline (8.8 +/- 0.8 vs 9.0 +/- 1.0 per hour; p = NS, n = 13). The lowest levels of coronary blood flow before and after dazoxiben were 8.6 +/- 2.2% and 48.8 +/- 5.4% of control, respectively (p less than .001, n = 28), whereas this parameter remained unchanged after saline (18.7 +/- 5.7% vs 13.4 +/- 4.1%, respectively; n = 13). The levels of TXB2 and 6-keto-prostaglandin (PG) F1 alpha (stable breakdown products of TXA2 and prostacyclin, respectively) were measured in blood collected from aortic and distal coronary arterial catheters before coronary constriction (control), during CFRs, and after administration of dazoxiben. TXB2 levels measured distal to the stenosis were increased fivefold during CFRs (352 +/- 126 vs 71 +/- 18 pg/ml plasma; p less than .03) and were reduced to preconstriction (control) levels by dazoxiben (57 +/- 12 pg/ml). Aortic TXB2 levels almost doubled with CFRs and also returned to control le

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; 6-Ketoprostaglandin F1 alpha; Animals; Coronary Circulation; Coronary Disease; Coronary Vessels; Dogs; Female; Hemodynamics; Imidazoles; Male; Platelet Aggregation; Prostaglandin Endoperoxides, Synthetic; Thromboxane B2

Platelet prostaglandin generation (malondialdehyde production) and platelet sensitivity to prostacyclin (a vasodilator and platelet aggregation inhibitor) and to epoxymethanodienoic acid (EMA) (a vasoconstrictor and platelet aggregation stimulant endoperoxide analog) were studied in patients with angina pectoris and in control subjects. Platelet malondialdehyde production was higher in patients than in control subjects (mean +/- standard error of the mean 2.50 +/- 0.30 versus 1.70 +/- 0.13 nmol/10(9) platelets, p < 0.02). Platelets from patients were significantly less sensitive to prostacyclin's antiaggregatory effects than were those from control subjects (amount of prostacyclin required for 50 percent platelet aggregation inhibition 1.90 +/- 0.35 versus 0.68 +/- 0.05 ng, p < 0.02). Furthermore, less EMA was required to induce 50 percent platelet aggregation in patients with angina pectoris than in the normal subjects (133 +/- 8 versus 194 +/- 16 ng, p < 0.001). These observations suggest that increased platelet prostaglandin generation and abnormal platelet sensitivity to prostacyclin and endoperoxide analog in certain patients with coronary artery disease are important potential mechanisms in the pathogenesis of myocardial ischemia.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adult; Aged; Angina Pectoris; Blood Platelets; Coronary Disease; Epoprostenol; Humans; Malondialdehyde; Middle Aged; Platelet Function Tests; Prostaglandin Endoperoxides, Synthetic; Prostaglandins