thromboxane-b2 and dazoxiben

Topics: Animals; Arachidonic Acid; Arachidonic Acids; Fibrinolytic Agents; Humans; Imidazoles; Microsomes; Platelet Aggregation; Sheep; Swine; Thromboxane B2; Thromboxanes

The immersion of a limb in a mixture of water and ice induces in normal humans an initial vasoconstriction mediated mainly by catecholamine release. In some studies the cold pressor test was associated with an increase in vasoconstrictor thromboxane A2 and in vasodilating prostacyclin. Dazoxiben hydrochloride, a thromboxane synthase inhibitor, has been reported to suppress cold-induced vasoconstriction. We compared in a double-blind, crossover, placebo-controlled study the effects of indomethacin (a cyclooxygenase inhibitor), dazoxiben hydrochloride, and BM13.177 (a novel thromboxane receptor antagonist) on the changes in cutaneous vascular resistance and arterial blood pressure induced by cold in 12 healthy volunteers. Cold challenge produced an increase in blood pressure and an initial decrease in finger blood flow, reflecting an increase in cutaneous vascular resistance. Neither effective suppression of thromboxane A2 generation or of the effects of thromboxane A2 on platelets by the three active treatments nor increase in prostacyclin generation after ingestion of dazoxiben hydrochloride modified the hemodynamic response to cold. In conclusion, thromboxane A2 and prostacyclin do not play a significant role in the modulation of the systemic hemodynamic response to cold. In addition, thromboxane receptor antagonism in normal humans does not influence basal blood pressure.

Topics: 6-Ketoprostaglandin F1 alpha; Adult; beta-Thromboglobulin; Blood Pressure; Cold Temperature; Double-Blind Method; Epoprostenol; Fingers; Humans; Imidazoles; Indomethacin; Male; Platelet Aggregation; Regional Blood Flow; Sulfonamides; Thromboxane A2; Thromboxane B2; Vascular Resistance; Vasoconstriction

Levels of thromboxane B2 (TxB2), the stable metabolite of thromboxane A2, are elevated in human and experimental septic shock. The thromboxane synthetase inhibitor dazoxiben has improved survival and decreased pulmonary hypertension in experimental endotoxemia. A randomized prospective study of 10 patients with the clinical diagnosis of sepsis and early adult respiratory distress syndrome (hypoxemia, radiologic evidence of the syndrome, and intrapulmonary shunt greater than 20%) was performed to test the efficacy of dazoxiben in ameliorating the effects of human sepsis. Five subjects received dazoxiben and five received placebo. Dazoxiben, 100 mg, or placebo was injected intravenously every 4 hours for a maximum of 72 hours. Plasma immunoreactive TxB2 (iTxB2) levels were determined by radioimmunoassay. Before dazoxiben, the plasma iTxB2 level was 752 +/- 261 pg/ml (n = 5) and was reduced within 1 hour to 333 +/- 137 pg/ml. The plasma levels of iTxB2 remained significantly decreased with subsequent doses of dazoxiben and it was 201 +/- 67 pg/ml (n = 4) 60 hours after dosing. In contrast, placebo had no significant effect on plasma iTxB2 levels (n = 5) throughout the entire period of observation. Dazoxiben did not induce any significant changes in pulmonary or systemic vascular resistance, intrapulmonary shunting, clotting studies, or extravascular lung water. One of the five subjects in the placebo group died and two of the five subjects in the dazoxiben group died. We conclude that dazoxiben was safe and effectively lowered plasma iTxB2 levels in patients with sepsis and incipient adult respiratory distress symptom, but did not significantly alter the hemodynamic and pulmonary sequelae of established sepsis.

Topics: Adult; Aged; Blood Pressure; Cardiac Output; Drug Evaluation; Female; Humans; Imidazoles; Infusions, Parenteral; Male; Middle Aged; Prospective Studies; Pulmonary Wedge Pressure; Radioimmunoassay; Random Allocation; Respiratory Distress Syndrome; Shock, Septic; Thromboxane B2; Vascular Resistance

1 We have assessed the thromboxane synthetase inhibitor, dazoxiben (UK 37248), during dialysis in a double-blind, placebo-controlled crossover study. 2 Thromboxane generation was markedly inhibited, and there was an increase in serum 6-keto prostaglandin F1 alpha levels during active treatment studies. 3 We were unable to demonstrate any reduction of platelet activation, or dialyser fibrin deposition, nor were heparin requirements altered by the drug. 4 Dazoxiben had no adverse effects.

Topics: 6-Ketoprostaglandin F1 alpha; Blood Coagulation; Clinical Trials as Topic; Double-Blind Method; Humans; Imidazoles; Oxidoreductases; Platelet Count; Renal Dialysis; Thromboxane B2; Thromboxane-A Synthase

The consequences of inhibiting the metabolism of prostaglandin G2 to thromboxane A2 in man were studied by using an inhibitor of thromboxane synthase, 4-[2-(IH-imidazol-1-yl)ethoxy] benzoic acid hydrochloride (dazoxiben). Single doses of 25, 50, 100, and 200 mg of dazoxiben were administered to healthy volunteers at 2-wk intervals in a randomized, placebo-controlled, double-blind manner. Serum thromboxane B2 and aggregation studies in whole blood and platelet-rich plasma were measured before dosing and at 1, 4, 6, 8, and 24 h after dosing. Both serum thromboxane B2 and the platelet aggregation response to arachidonic acid (1.33 mM) were reversibly inhibited in a dose-dependent manner. Aggregation induced by 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (0.4 and 4.0 microM) in platelet-rich plasma as well as both aggregation and nucleotide release induced by collagen (95 micrograms/ml) in platelet-rich plasma and whole blood were unaltered by dazoxiben. Additional evidence for a platelet-inhibitory effect of the compound was a significant prolongation of the bleeding time at 1 h after administration of the highest dose (200 mg) of dazoxiben. Endogenous prostacyclin biosynthesis was assessed by measurement of the major urinary metabolite of prostacyclin, 2,3-dinor-6-keto-PGF1 alpha (PGI-M). PGI-M excretion was increased by dazoxiben; it rose a mean 2.4-fold from predosing control values at 0-6 h after administration of the highest dose studied (200 mg).

Topics: Adult; Bleeding Time; Depression, Chemical; Dose-Response Relationship, Drug; Epoprostenol; Humans; Imidazoles; Male; Oxidoreductases; Platelet Aggregation; Prostaglandins F, Synthetic; Thromboxane B2; Thromboxane-A Synthase

1 We have performed a double-blind, randomized, 7-d cross-over study of the thromboxane synthetase inhibitor dazoxiben (UK 37248) in 20 patients with stable coronary heart disease. 2 All patients had a history of exertional angina of greater than two years duration and no patient had suffered a myocardial infarction in the preceding twelve months. 3 All patients had a positive exercise stress test for myocardial ischaemia and 15 had undergone coronary angiography. All these patients had a 50% narrowing in at least one vessel. 4 All patients were on conventional anti-anginal medication and the doses of their various therapies remained unchanged in the three months prior to and during the study period. 5 Therapy with dazoxiben 200 mg four times daily produced no alteration in the subjective or objective features of angina in these patients. There was no alteration in angina attack rate, glyceryl trinitrate consumption or duration of treadmill exercise. 6 Dazoxiben produced a highly significant reduction in both the resting and the post-exercise levels of serum thromboxane B2 levels, although there was no significant difference between the pre-exercise and post-exercise values. 7 Dazoxiben is an effective inhibitor of the synthesis of thromboxane but it has no effect on the subjective or objective features of stable coronary disease. This would suggest that the production of thromboxane and the development of circulating platelet aggregates play no part in the mechanism of angina in patients with stable coronary heart disease.

Topics: Angina Pectoris; Coronary Disease; Double-Blind Method; Humans; Imidazoles; Nitroglycerin; Oxidoreductases; Physical Exertion; Platelet Aggregation; Thrombelastography; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

Twenty-four men received either placebo, 0.1 g of the thromboxane synthetase inhibitor dazoxiben, 0.25 or 1.0 g of acetylsalicylic acid (ASA). Dazoxiben reduced the maximal rate of collagen-induced platelet aggregation, but less than did ASA. ASA abolished secondary, ADP-induced aggregation, dazoxiben not. Both drugs prolonged the bleeding-time. Plasma thromboxane B2 (TxB2) levels did not change significantly after dazoxiben, whereas the prostacyclin metabolite 6-keto-PGF1 alpha rose. The larger dose of ASA reduced both TxB2 and 6-keto-PGF1 alpha in plasma. Whole blood was allowed to clot in order to estimate prostaglandin metabolism. Both drugs prevented thromboxane production effectively. Formation of 6-keto-PGF1 alpha decreased by 95 per cent after ASA but was more than doubled after dazoxiben. Dazoxiben is a selective and effective thromboxane synthetase inhibitor, but has a weaker effect on platelet reactivity than ASA, possibly because endoperoxide formation is not prevented.

Topics: 6-Ketoprostaglandin F1 alpha; Adult; Aged; Aspirin; Blood Platelets; Humans; Imidazoles; Male; Middle Aged; Oxidoreductases; Platelet Adhesiveness; Platelet Aggregation; Prostaglandins; Thromboxane B2; Thromboxane-A Synthase

The imidazole derivative UK-37 248, a thromboxane synthetase inhibitor, reduces the in-vitro formation of thromboxane B2 and hydroxyheptadecatrienoic acid by washed platelets, and this is compensated for by an increased production of prostaglandins E2 and F2 alpha; arachidonic acid challenged platelets pretreated with UK-37 248 also stimulate the production of prostacyclin by aspirin pretreated cultured endothelial cells. In a double-blind placebo controlled study to examine the in vivo properties of UK-37 248, human volunteers ingested 200 mg of the compound. Their serum thromboxane B2 levels dropped and their plasma 6-keto-prostaglandin F1 alpha values rose. Arachidonic acid induced platelet aggregation was completely inhibited whereas that elicited by adenosine-5'-diphosphate was unaffected. By reducing formation of pro-aggregatory tromboxane A2 and increasing production of anti-aggregatory prostacyclin, thromboxane synthetase inhibitors may be better than aspirin as antithrombotic agents.

Topics: 6-Ketoprostaglandin F1 alpha; Adult; Blood Platelets; Clinical Trials as Topic; Double-Blind Method; Fibrinolytic Agents; Humans; Imidazoles; Male; Oxidoreductases; Platelet Aggregation; Prostaglandins E; Prostaglandins F; Thromboxane A2; Thromboxane B2; Thromboxane-A Synthase

Microsomal prostaglandin E synthase (mPGES)-1 is one of several prostaglandin E synthases involved in prostaglandin H2 (PGH2) metabolism. In the present report, we characterize the contribution of mPGES-1 to cellular PGH2 metabolism in murine macrophages by studying the synthesis of eicosanoids and expression of eicosanoid metabolism enzymes in wild type and mPGES-1-deficient macrophages. Thioglycollate-elicited macrophages isolated from mPGES-1-/- animals and genetically matched wild type controls were stimulated with diverse pro-inflammatory stimuli. Prostaglandins were released in the following order of decreasing abundance from wild type macrophages stimulated with lipopolysaccharide: prostaglandin E2 (PGE2)>thromboxane B2 (TxB2)>6-keto prostaglandin F1alpha (PGF1alpha), prostaglandin F(2alpha) (PGF2alpha), and prostaglandin D2 (PGD2). In contrast, we detected in mPGES-1-/- macrophages a >95% reduction in PGE2 production resulting in the following altered prostaglandin profile: TxB2>6-keto PGF1alpha and PGF2alpha>PGE2, despite the comparable release of total prostaglandins. No significant change in expression pattern of key prostaglandin-synthesizing enzymes was detected between the genotypes. We then further profiled genotype-related differences in the eicosanoid profile using macrophages pre-stimulated with lipopolysaccharide followed by a 10-min incubation with 10 microm [3H]arachidonic acid. Eicosanoid products were subsequently identified by reverse phase high pressure liquid chromatography. The dramatic reduction in [3H]PGE2 formation from mPGES-1-/- macrophages compared with controls resulted in TxB2 and 6-keto PGF1alpha becoming the two most abundant prostaglandins in these samples. Our results also suggest a 5-fold increase in 12-[3H]hydroxyheptadecatrienoic acid release in mPGES-1-/- samples. Our data support the hypothesis that mPGES-1 induction in response to an inflammatory stimulus is essential for PGE2 synthesis. The redirection of prostaglandin production in mPGES-1-/- cells provides novel insights into how a cell processes the unstable endoperoxide PGH2 during the inactivation of a major metabolic outlet.

Topics: Animals; Arachidonic Acid; Blotting, Western; Chromatography, High Pressure Liquid; Dose-Response Relationship, Drug; Eicosanoids; Fatty Acids, Unsaturated; Genotype; Imidazoles; Inflammation; Intramolecular Oxidoreductases; Kinetics; Lipopolysaccharides; Macrophages; Mice; Mice, Transgenic; Microsomes; Prostaglandin-E Synthases; Prostaglandins; Thioglycolates; Thromboxane B2; Time Factors

The aim of this study was to compare the effects of a new thromboxane synthase inhibitor, camonagrel, on platelet aggregation and platelet-subendothelium interaction under flow conditions, in comparison with a standard thromboxane synthase inhibitor (dazoxiben) and a cyclooxygenase inhibitor (acetylsalicylic acid). With respect to platelet aggregation in whole blood, the 50% inhibitory concentrations (IC(50)) of camonagrel were between 318 and 797 micromol/l after induction with collagen and adenosine 5'-diphosphate, respectively. For inhibition of thromboxane B(2) synthesis, the IC(50) values were 868 +/- 68 micromol/l; prostaglandin E(2) was inhibited only by acetylsalicylic acid (IC(50) for camonagrel >2,000 micromol/l), and the leukocyte 6-keto-PGF(1alpha) level was increased by camonagrel. The greatest reduction in percentage subendothelial surface occupied by platelets (mainly in the thrombi) after blood perfusion was seen after incubation with camonagrel in the range of concentrations that inhibited collagen-induced platelet aggregation. In conclusion, camonagrel reduced platelet-subendothelium interaction under flow conditions, showing this effect in a range of concentrations lower than in inhibition of platelet aggregation.

Topics: Adolescent; Adult; Animals; Aspirin; Blood Platelets; Dose-Response Relationship, Drug; Humans; Imidazoles; Indans; Male; Middle Aged; Platelet Aggregation; Prostaglandins; Prostaglandins E; Rabbits; Thrombosis; Thromboxane B2; Thromboxane-A Synthase; Tunica Intima

1. Drugs that inhibit TxA(2) synthesis are used to reduce platelet aggregation. The aim of this study was to compare the effects of a cyclo-oxygenase (COX) inhibitor (acetylsalicylic acid, ASA), a thromboxane synthetase (TxS) inhibitor (dazoxiben) and a dual TxS inhibitor and TxA(2) receptor blocker (DT-TX 30) on platelet aggregation and the platelet-subendothelium interaction in flow conditions. 2. The techniques used in this in vitro study were platelet aggregometry in whole blood, and measurement of platelet thromboxane B(2) and prostaglandin E(2) production and leucocyte production of 6-keto-PGF(1alpha). The platelet-subendothelium interaction was evaluated in rabbit aorta subendothelium preparations exposed to flowing blood at a shear stress of 800 s(-1). Morphometric methods were used to calculate the percentage of subendothelium occupied by platelets. 3. The 50% inhibitory concentration (IC(50)) of DT-TX 30 in whole blood was in the range of 10(-7) micro M (induced with collagen or arachidonic acid) to 10(-5) micro M (induced with thrombin) or 10(-4) (induced with ADP). IC(50) values under all experimental conditions were lower with DT-TX 30 than with ASA. For thromboxane B(2) the IC(50) were: ASA 0.84+/-0.05 micro M, dazoxiben 765+/-54 micro M, DT-TX 30 8.54+/-0.60 micro M. Prostaglandin E(2) was inhibited only by ASA (IC(50) 1.21+/-0.08 micro M). Leucocyte 6-keto-PGF(1alpha) was inhibited by ASA (IC(50) 6.58+/-0.76 micro M) and increased by dazoxiben and DT-TX 30. The greatest reduction in percentage subendothelial surface occupied by platelets after blood perfusion was seen after treatment with DT-TX 30 in the range of concentrations that inhibited collagen-induced platelet aggregation (control group: 31.20+/-3.8%, DT-TX 30 at 0.1 micro M: 10.71+/-0.55%, at 1.0 micro M: 6.53+/-0.44%, at 5.0 micro M; 1.48+/-0.07%). All three drugs reduced thrombus formation, although ASA (unlike dazoxiben or DT-TX 30) increased the percentage surface occupied by adhesions. 4. In conclusion, the effect of specific blockage of TxS together with blockage of membrane receptors for TxA(2) can surpass the effect of ASA in inhibiting the platelet-subendothelium interaction in flow conditions.

Topics: 6-Ketoprostaglandin F1 alpha; Adult; Animals; Aspirin; Blood Platelets; Chlorobenzenes; Cyclooxygenase Inhibitors; Dinoprost; Dose-Response Relationship, Drug; Endothelium, Vascular; Humans; Imidazoles; Male; Middle Aged; Platelet Aggregation; Platelet Aggregation Inhibitors; Pyridines; Rabbits; Receptors, Thromboxane; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

Arachidonic acid (AA) is a potent inducer of platelet aggregation in vitro; this activity is due to its conversion to biologically active metabolites, prostaglandin (PG) endoperoxides and thromboxane A2 (TxA2). PG endoperoxides and TxA, are thought to act on the same receptor; however, at least two isoforms of this receptor have been identified. The aim of our work was to clarify whether endoperoxides and TxA2 activate the same or different receptor subtypes to induce aggregation and calcium movements in human platelets. AA-induced aggregation and calcium rises were still detectable in platelets preincubated with thromboxane synthase inhibitors, which suppress TxA2 formation and induce PGH2 accumulation, suggesting that PG endoperoxides can activate platelets. Exogenously added PGH2 was able to induce aggregation and calcium rises. Pretreatment of platelets with GR32191B or platelet activating factor, which desensitize one of the two receptor subtypes identified in platelets, did not prevent calcium rises induced by endogenously generated or by exogenouly added PGH2, indicating that TxA2 and PG endoperoxides share the same receptor subtype(s) to activate platelets. HEK-293 cells overexpressing either of the two thromboxane receptor isoforms cloned to date (TPalpha and TPbeta) and identified in human platelets, stimulated with PGH2, or with the stable endoperoxide analog U46619, formed inositol phosphates. These data show that endoperoxides and TXA2 mediate their effects on platelets acting on both, and the same, receptor isoform(s).

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Aspirin; Biphenyl Compounds; Blood Platelets; Bridged Bicyclo Compounds, Heterocyclic; Calcium Signaling; Cells, Cultured; Enzyme Inhibitors; Fatty Acids, Unsaturated; Heptanoic Acids; Humans; Hydrazines; Imidazoles; Inositol Phosphates; Kidney; Methacrylates; Phenylacetates; Platelet Activating Factor; Platelet Activation; Prostaglandin H2; Prostaglandins H; Protein Isoforms; Receptors, Thromboxane; Recombinant Fusion Proteins; Sulfonamides; Thromboxane A2; Thromboxane B2; Thromboxane-A Synthase

Combined thromboxane synthase inhibitors and thromboxane receptors antagonists have been shown to have a beneficial effect on different models of thrombosis in vivo. We studied the action of one of these compounds (DT-TX 30) compared with dazoxiben (a thromboxane synthase inhibitor) on retinal vascularity in streptozotocin-diabetic rats. Ten nondiabetic animals were treated with isotonic saline, 30 (10 animals per group) were given 0.4, 4, and 8 mg kg(-1) per day of DT-TX 30 (p.o.) and 30 (10 animals per group) were given 10, 50, and 100 mg kg(-1) per day of dazoxiben (p.o.) over a 90-day study period. DT-TX 30 caused a dose-dependent decrease of platelet aggregation and thromboxane B2 synthesis. There was an increase of 9, 65, and 166% in the synthesis of prostacyclin after treatment with 0.4, 4, and 8 mg kg(-1) per day, respectively. Retinal vascularity increased in 51, 72, and 182% of animals in response to the three doses used. Synthesis of prostacyclin and the degree of retinal vascularity showed a linear correlation (r2=0.6528,p<0.00001). Dazoxiben, at doses that inhibited thromboxane synthesis as much as DT-TX 30, increased prostacyclin production and retinal vascularity with less potency than DT-TX 30. In conclusion, the antagonism of thromboxane receptors may be an important additional effect to the inhibition of thromboxane synthase in the prevention of ischemic retinal lesions in experimental diabetes.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Blood Glucose; Chlorobenzenes; Collagen; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Enzyme Inhibitors; Imidazoles; Male; Platelet Aggregation; Pyridines; Rats; Rats, Wistar; Receptors, Thromboxane; Retinal Vessels; Thromboxane B2; Thromboxane-A Synthase

This study investigated, in isolated human internal mammary artery, the involvement of the cyclooxygenase and the lipoxygenase pathways of arachidonic acid metabolism in the contraction induced by angiotensin II.. Rings of human internal mammary arteries were suspended in organ baths for recording of isometric tension. In addition, the release of eicosanoids in response to angiotensin II (0.3 microM) was measured by enzyme immunoassay.. In human arterial rings without endothelial dependent relaxation in response to substance P or acetylcholine, the angiotensin II-induced contractions were significantly (P<0.05) reduced by 27% in the presence of GR32191 0.3 microM (thromboxane A(2) (TXA(2)) receptor antagonist) but remained unchanged in the presence of dazoxiben 100 microM (thromboxane synthase inhibitor). In addition, angiotensin II failed to modify TXB(2) and 6-keto-PGF(1alpha) production. These results suggest the contribution of a TXA(2)/PGH(2) agonist other than TXA(2) in angiotensin II-induced contractions. However, indomethacin increased (P<0.05) angiotensin II-mediated contractile response and cysteinyl leukotriene production, suggesting a redirection of arachidonic acid metabolism from the cyclooxygenase pathway to the lipoxygenase pathway. Indeed, the contractions induced by angiotensin II were inhibited (P<0.05) by phenidone 100 microM (cyclooxygenase and lipoxygenase inhibitor), baicalein 100 microM (5-, 12- and 15-lipoxygenases inhibitor), AA861 10 microM (5-lipoxygenase inhibitor) and MK571 1 microM (CysLT(1) receptor antagonist). Cysteinyl leukotrienes were released in response to angiotensin II (pg/mg dry weight tissue: 32+/-9 (basal, n=6) vs. 49+/-9 (angiotensin II 0.3 microM, n=6), P<0.05). LTD(4), and at a lesser degree LTC(4), induced contractions of internal mammary artery and MK571 1 microM abolished the contraction to LTD(4).. This study suggests that the in vitro vasoconstrictor effects of angiotensin II in human internal mammary artery are enhanced at least in part by eicosanoids produced by the cyclooxygenase pathway, probably PGH(2), acting on TXA(2)/PGH(2) receptors, and by lipoxygenase-derived products, particularly cysteinyl leukotrienes acting on CysLT(1) receptors.

Topics: 6-Ketoprostaglandin F1 alpha; Acetylcholine; Angiotensin II; Benzoquinones; Biphenyl Compounds; Cyclooxygenase Inhibitors; Depression, Chemical; Dose-Response Relationship, Drug; Enzyme Inhibitors; Flavanones; Flavonoids; Heptanoic Acids; Humans; Imidazoles; In Vitro Techniques; Indomethacin; Leukotrienes; Lipoxygenase Inhibitors; Mammary Arteries; Propionates; Pyrazoles; Quinolines; Receptors, Thromboxane; Substance P; Thromboxane B2; Thromboxane-A Synthase; Vasoconstriction

The capacity of glial tumor cells to migrate and diffusely infiltrate normal brain compromises surgical eradication of the disease. Identification of genes associated with invasion may offer novel strategies for anti-invasive therapies. The gene for TXsyn, an enzyme of the arachidonic acid pathway, has been identified by differential mRNA display as being overexpressed in a glioma cell line selected for migration. In this study TXsyn mRNA expression was found in a large panel of glioma cell lines but not in a strain of human astrocytes. Immunohistochemistry demonstrated TXsyn in the parenchyma of glial tumors and in reactive astrocytes, whereas it could not be detected in quiescent astrocytes and oligodendroglia of normal brain. Glioma cell lines showed a wide range of thromboxane B2 formation, the relative expression of which correlated with migration rates of these cells. Migration was effectively blocked by specific inhibitors of TXsyn, such as furegrelate and dazmegrel. Other TXsyn inhibitors and cyclooxygenase inhibitors were less effective. Treatment with specific inhibitors also resulted in a decrease of intercellular adhesion in glioma cells. These data indicate that TXsyn plays a crucial role in the signal transduction of migration in glial tumors and may offer a novel strategy for anti-invasive therapies.

Topics: Arachidonic Acids; Aspirin; Astrocytes; Benzofurans; Brain Neoplasms; Cell Adhesion; Cell Movement; Enzyme Induction; Enzyme Inhibitors; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Glioma; GTP-Binding Proteins; Humans; Imidazoles; Indomethacin; Lysine; Models, Biological; Neoplasm Proteins; Neoplastic Stem Cells; Oligodendroglia; Pentanoic Acids; Phenotype; Pyridines; RNA, Messenger; RNA, Neoplasm; Signal Transduction; Thromboxane B2; Thromboxane-A Synthase; Tumor Cells, Cultured

Platelet hyperactivity accompanied by an increased synthesis of thromboxane and/or a decreased prostacyclin production are important factors in ischemic diabetic retinopathy. We studied the effect of camonagrel and dazoxiben, two thromboxane synthase inhibitors, on retinal vascularization in a model of streptozotocin-induced diabetes in rats. Ten nondiabetic rats, 10 diabetic animals treated with saline (i.e., not treated), and 60 diabetic animals treated with dazoxiben or camonagrel (10, 50 or 100 mg kg(-1) day(-1) p.o.) were studied. All treatments lasted for 90 days. Dazoxiben and camonagrel produced a dose-dependent reduction in platelet aggregation and thromboxane synthesis. Dazoxiben increased prostacylin synthesis by 78% at 100 mg kg(-1) day(-1), and camonagrel by 154%. Dazoxiben increased retinal vascularity by 74%, and by 183% after camonagrel treatment. Prostacyclin synthesis showed a direct linear correlation with the degree of retinal vascularization (r2=0.6733, P < 0.00001). We conclude that an increased prostacyclin synthesis may have a greater influence than the inhibition of thromboxane synthesis in preventing ischemic diabetic retinopathy in experimental diabetes. Camonagrel may be an alternative treatment in the prevention of these lesions.

Topics: Animals; Blood Cell Count; Blood Glucose; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Enzyme Inhibitors; Fibrinolysis; Imidazoles; Indans; Male; Platelet Aggregation; Platelet Aggregation Inhibitors; Rats; Rats, Wistar; Retinal Neovascularization; Streptozocin; Thromboxane B2; Thromboxane-A Synthase

The effect of IL-6 on in vitro platelet function was investigated. Platelet-rich plasma (PRP) incubated with IL-6 showed a dose dependent enhancement of agonist induced maximum aggregation (AIMA) and secretion of thromboxane B2 (TXB2) as measured by RIA, in short term incubations. Dazoxiben (0.2 to 160 microM) pretreated PRP incubated with IL-6 and aggregated with ionophore A23187, showed a dose dependent inhibition of TXB2 secretion concomitant with a dose dependent abrogation of IL-6's enhancement of AIMA. A similar abrogation of AIMA was observed when these experiments were repeated using indomethacin. Further, PRP incubated with IL-6 showed a dose dependent increase in TXB2 and BTG secretion as measured by RIA and an increased incorporation of actin binding protein, talin, and myosin into the cytoskeletal core (triton insoluble residue) as shown by SDS-PAGE. The integrin glycoprotein IIIa (GPIIIa) was also observed to be retained into the cytoskeleton by immunoblot. These results suggest that IL-6 activates platelets in vitro and enhances AIMA via a mechanism involving arachidonic acid metabolism.

Topics: Adenosine Diphosphate; Arachidonic Acid; beta-Thromboglobulin; Blood Platelets; Calcimycin; Cytoskeleton; Drug Synergism; Humans; Imidazoles; Indomethacin; Interleukin-6; Platelet Activation; Prostaglandin-Endoperoxide Synthases; Recombinant Proteins; Thromboxane B2

1-(1,2,3,4-tetrahydro-1-naphthylenyl)-1H-imidazole, nitric acid salt (LY150310), was examined for bronchodilator activity in the guinea pig. In guinea pig tracheal preparations, LY150310 competitively antagonized the contractile effects of exogenous histamine and blocked the histamine-mediated component of contractions produced by ovalbumin challenge. LY150310 had little effect on the nonhistamine component of ovalbumin-induced contractions of lung parenchymal strips, but it enhanced the production of prostaglandin (PG) E2 and PGF2 alpha although it partially inhibited thromboxane B2 formation. In other studies, in which postmortem pulmonary gas trapping was used as an index of in vivo airway obstruction, i.v. LY150310 dose-dependently inhibited the bronchospasm produced by aerosols of the divalent cationic ionophore A23187, histamine, 5-hydroxytryptamine, leukotriene D4, methacholine, ovalbumin or platelet activating factor. LY150310 was equal to or more potent than aminophylline in all test systems. Also, orally administered LY150310 inhibited the airway obstruction produced by selected challenge aerosols. In ex vivo studies, LY150310 elevated PGE2 and tended to decrease thromboxane B2 in sodium arachidonate-stimulated whole blood. However, PGE2 and other cyclooxygenase products did not appear to account for in vivo bronchodilation, because combining LY150310 and piroxicam did not alter inhibition of A23187-induced airway obstruction. Our results demonstrate that LY150310 reduces airway obstruction caused by a variety of bronchoconstrictive agents, including A23187 and ovalbumin. Although this substituted imidazole appears to have activity as a histamine H1-receptor antagonist and can alter prostanoid concentrations in vitro and in vivo, its mode of bronchodilation is unclear.

Topics: Aerosols; Animals; Antineoplastic Agents; Bronchoconstriction; Bronchoconstrictor Agents; Dinoprost; Dinoprostone; Drug Interactions; Eicosanoids; Guinea Pigs; Imidazoles; In Vitro Techniques; Lipopolysaccharides; Lung; Male; Piroxicam; Tetrahydronaphthalenes; Thromboxane B2; Trachea

We investigated the relation between the changes of TXA2-PG1 alpha balance and glomerular injury, and the effects of Dazoxiben, Chuan Xiong on in situ immune complex glomerulonephritis (ISICGN) produecd by C-BSA in rats. After two weeks of immunization, the level of renal cortical TXB2 and urine protein was increased, while that of 6-keto-PGF1 alpha was decreased. Four weeks later, the changes as mentioned above were more significant, and platelet aggregation revealed an increase of maximal aggregation. Positive correlation was seen between urine protein and renal cortical TXA2, and negative correlation between urine protein and 6-keto-PGF1 alpha. Histological examination showed morphological changes. Two treated-groups showed significant reduction of urine protein and renal cortical TXB2, but increase of 6-keto-PGF1 alpha. Besides the changes like worm-eaten in electron-dense deposits, foot process fusion disappeared. The thickened GBM and mesangial proliferation were lessened, especially in Dazoxiben group. These results suggests that there is a TXA2-PG1 alpha imbalance in ISICGN, and TXA2 plays an important pathogenetic role in the onset and progression of glomerulonephritis. Dazoxiben and Chuan Xiong might improve TXA2-PG1 alpha imbalance and attenuate glomerular injury to some extent in ISICGN.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Antigen-Antibody Complex; Drugs, Chinese Herbal; Glomerulonephritis; Imidazoles; Kidney Cortex; Male; Rats; Rats, Sprague-Dawley; Serum Albumin, Bovine; Thromboxane B2; Thromboxane-A Synthase

Advanced cirrhosis is known to be associated with extrahepatic organ dysfunction, but the mechanism for this cirrhosis complication is largely unknown. We measured tissue albumin leakage in rats with biliary cirrhosis or acute cholestasis and tested the hypothesis that arachidonic acid metabolites contribute to the vascular permeability change. Six weeks after bile duct ligation, rats with biliary cirrhosis exhibited increased extravascular leakage of 125I-albumin in lung (p < 0.001) and kidney (p < 0.01) but not in heart or brain. In contrast, in cholestatic rats 10 days after bile duct ligation, only the kidney albumin leak was significantly increased (p < 0.01). Tissue thromboxane B2 levels, measured with an enzyme immunoassay, were increased in lung, kidney and liver of cirrhotic and cholestatic rats. To determine whether thromboxane A2 contributes to the vascular permeability defects in cirrhosis, we pretreated cirrhotic rats with the thromboxane synthase inhibitor dazoxiben (10 mg/kg intraperitoneally every 8 hr) for 20 hr before assessment of vascular permeability. Dazoxiben blocked the increase in thromboxane B2 level in lung but not in kidney and lowered the lung but not the kidney albumin leak index. In cholestatic rats given a higher dose of dazoxiben (40 mg/kg intraperitoneally every 8 hr) for 20 hr, the kidney thromboxane B2 level but not albumin leak was significantly lowered. We conclude that chronic biliary obstruction in rats leads to increased vascular permeability in selected extrahepatic organs and that thromboxane A2 contributes to the vascular permeability increase in the lung. Whether thromboxane A2 plays a role in renal albumin leakage will require further study.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Arachidonic Acid; Bile Ducts; Capillary Permeability; Cholestasis; Eicosanoids; Imidazoles; Kidney; Ligation; Liver Cirrhosis, Biliary; Lung; Male; Rats; Rats, Sprague-Dawley; Serum Albumin, Radio-Iodinated; Thromboxane A2; Thromboxane B2

Rats with liver cirrhosis exhibit arterial hypoxemia and loss of hypoxic pulmonary vasoconstriction similar to some patients with end-stage liver disease. We hypothesized that the pulmonary circulatory dysfunction in cirrhosis results from vascular endothelial cell injury and interstitial lung edema. To investigate this hypothesis, we compared the extravascular lung albumin leak, lung ultrastructural changes, and tissue eicosanoid levels in control and cirrhotic rats. In comparison to sham-operated controls, rats with biliary cirrhosis, 6 wk after ligation of the common bile duct, had increased lung albumin leak index (1.46 +/- 0.12 vs. 0.80 +/- 0.04, P < 0.001) and bloodless lung wet-to-dry weight ratio (4.94 +/- 0.05 vs. 4.78 +/- 0.03, P < 0.05). Electron-microscopic sections of lungs from cirrhotic rats demonstrated infiltration with intravascular macrophage-like cells, endothelial cell injury, and interstitial edema. In addition, lung tissue thromboxane B2 was significantly increased in cirrhotic rats, and pretreatment with a thromboxane synthase inhibitor, dazoxiben, reduced lung thromboxane B2 level and attenuated extravascular lung albumin leak (control 1.03 +/- 0.07, cirrhotic 2.29 +/- 0.06, cirrhotic plus dazoxiben, 1.57 +/- 0.17). In contrast, WEB 2086, a platelet-activating factor antagonist, had no effect on lung albumin leak. We conclude that pulmonary vascular permeability is increased in rats with biliary cirrhosis and that thromboxane A2 contributes to the pulmonary circulatory abnormalities in cirrhosis.

Topics: Albumins; Animals; Capillary Permeability; Eicosanoids; Imidazoles; Liver; Liver Cirrhosis, Biliary; Lung; Macrophages; Male; Microscopy, Electron; Models, Biological; Rats; Rats, Sprague-Dawley; Thromboxane A2; Thromboxane B2; Thromboxane-A Synthase; Vasoconstriction

Exposing rabbits for 1 h to 100% O2 at 4 atm barometric pressure markedly increases the concentration of thromboxane B2 in alveolar lavage fluid [1,809 +/- 92 vs. 99 +/- 24 (SE) pg/ml, P less than 0.001], pulmonary arterial pressure (110 +/- 17 vs. 10 +/- 1 mmHg, P less than 0.001), lung weight gain (14.6 +/- 3.7 vs. 0.6 +/- 0.4 g/20 min, P less than 0.01), and transfer rates for aerosolized 99mTc-labeled diethylenetriamine pentaacetate (500 mol wt; 40 +/- 14 vs. 3 +/- 1 x 10(-3)/min, P less than 0.01) and fluorescein isothiocyanate-labeled dextran (7,000 mol wt; 10 +/- 3 vs. 1 +/- 1 x 10(-4)/min, P less than 0.01). Pretreatment with the antioxidant butylated hydroxyanisole (BHA) entirely prevents the pulmonary hypertension and lung injury. In addition, BHA blocks the increase in alveolar thromboxane B2 caused by hyperbaric O2 (10 and 45 pg/ml lavage fluid, n = 2). Combined therapy with polyethylene glycol- (PEG) conjugated superoxide dismutase (SOD) and PEG-catalase also completely eliminates the pulmonary hypertension, pulmonary edema, and increase in transfer rate for the aerosolized compounds. In contrast, combined treatment with unconjugated SOD and catalase does not reduce the pulmonary damage. Because of the striking increase in pulmonary arterial pressure to greater than 100 mmHg, we tested the hypothesis that thromboxane causes the hypertension and thus contributes to the lung injury. Indomethacin and UK 37,248-01 (4-[2-(1H-imidazol-1-yl)-ethoxy]benzoic acid hydrochloride, an inhibitor of thromboxane synthase, completely eliminate the pulmonary hypertension and edema.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Bronchoalveolar Lavage Fluid; Butylated Hydroxyanisole; Hyperbaric Oxygenation; Hypertension, Pulmonary; Imidazoles; In Vitro Techniques; Indomethacin; Lung; Lung Injury; Male; Pulmonary Edema; Rabbits; Superoxide Dismutase; Thromboxane B2; Thromboxane-A Synthase

When injected i.v. to guinea pigs, the granulocyte secretagog N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) induces bronchoconstriction (BC), lung platelet sequestration and increased transendothelial albumin exchanges in lungs. We evaluated BC and the variations of the lung contents in radiolabeled platelets, erythrocytes and extravascular albumin, as measurements of platelet lung entrapment, reduction of lung blood volume and increase of transendothelial albumin exchanges, respectively. Trimetoquinol, a thromboxane A2 (TXA2)-endoperoxide receptor antagonist, inhibited BC and platelet entrapment by lungs induced by fMLP, but protection was nonspecific because it also suppressed BC by histamine. The specific TXA2 synthetase inhibitor/endoperoxide receptor antagonist ridogrel suppressed BC and reduced lung platelet entrapment, but failed to prevent the increase of extravascular albumin and the decrease of erythrocyte lung contents due to fMLP. Consequently, the fMLP-induced increase of vascular albumin exchanges and reduction of lung blood volume are TXA2-independent. Aspirin prevented BC, but failed to suppress lung platelet entrapment by fMLP, indicating that in vivo platelet activation is not TXA2-dependent, even though the levels of circulating TXB2, the stable metabolite of TXA2, were increased after fMLP concomitantly with that of 6-keto-prostaglandin (PG)F1 alpha, the stable metabolite of PGI2. The ridogrel-treated animals showed reduced blood level of TXB2 and increased levels of 6-keto-PGF1 alpha after fMLP challenge. Blocking the cyclooxygenase pathway with aspirin prevented ridogrel-induced protection against lung platelet sequestration after fMLP, supporting the concept that rechanneling of arachidonate metabolism toward protective prostaglandins accounts for protection by ridogrel.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; 6-Ketoprostaglandin F1 alpha; Animals; Arachidonic Acid; Blood Platelets; Bronchoconstriction; Guinea Pigs; Imidazoles; Lung; N-Formylmethionine Leucyl-Phenylalanine; Pentanoic Acids; Platelet Aggregation; Prostaglandin Endoperoxides, Synthetic; Pyridines; Radioimmunoassay; Serum Albumin; Suprofen; Thrombocytopenia; Thromboxane A2; Thromboxane B2; Thromboxane-A Synthase; Tretoquinol

The in vitro properties of CS-518 (RS-5186; sodium 2-(1-imidazolylmethyl)- 4,5-dihydrobenzo[b]thiophene-6-carboxylate, CAS 113817-57-5), a new thromboxane (TX) synthetase inhibitor, as an antiplatelet agent were investigated. Incubation of clotting whole blood from man, rabbits, and dogs with CS-518 resulted in a concentration-dependent reduction of TXB2 production and an increase in 6-keto-PGF1 alpha. Similar properties were also observed for ozagrel and isbogrel, but both agents were less effective on TXB2 production. CS-518 inhibited arachidonic acid (AA)- or collagen-induced platelet aggregation in platelet rich plasma (PRP) from man, rabbits and dogs. In addition, antiaggregatory effects of CS-518 were confirmed in whole blood by two methods: impedance method and free platelet count method. TXA2 formation in washed canine platelets in response to AA (0.1 mmol/l) was dose-dependently inhibited by incubation with CS-518. This inhibition by CS-518 was gradually attenuated after platelets were subsequently washed with drug-free buffer, but a dose-dependent inhibition was still observed with platelets that had been washed three times. Ozagrel also inhibited TXB2 formation when incubated with platelets, whereas this inhibition disappeared with platelets only washed once. In contrast, platelets treated with acetylsalicylic acid, an irreversible inhibitor of cyclooxygenase showed a comparable inhibition before and after they were washed three times. These results indicate that CS-518 exerts antiplatelet effects in vitro via potent, selective, and long-lasting but reversible inhibition on TX synthetase.

Topics: 6-Ketoprostaglandin F1 alpha; Adult; Animals; Aspirin; Dogs; Humans; Imidazoles; In Vitro Techniques; Male; Methacrylates; Platelet Aggregation; Platelet Aggregation Inhibitors; Rabbits; Thiophenes; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

To clarify whether activated platelets play an important role in the occurrence and exacerbation of disseminated intravascular coagulation (DIC), we investigated the effects of 4 anti-platelet drugs, a PGI2 analog (CS-570), a thromboxane synthetase inhibitor (dazoxiben), a thromboxane receptor antagonist (BM-13177), and ticlopidine, in an experimental DIC model in rats. Experimental DIC was induced by a continuous infusion of lipopolysaccharide (LPS derived from E. coli, 055 B5, 25 mg/kg/hr) for 4 hrs. In the time-course determination of the coagulation parameters and prostanoids, an abrupt increase in TxB2 (a stable metabolite of TxA2) and 6-keto-PGF1 alpha (a stable metabolite of PGI2) was followed by a decrease in platelet count, a prolongation of blood coagulation time, and an increase in fibrinogen/fibrin degradation products (FDP). Four hours after the start of LPS infusion, the rats were considered to be in the state of DIC. The effects of the anti-platelet drugs were investigated 4 hrs after the start of LPS infusion. CS-570 and ticlopidine ameliorated DIC in a dose-dependent manner. CS-570 (10 micrograms/kg/min) improved DIC in the platelet count, prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen (Fbg), and FDP, without affecting TxB2 and 6-keto-PGF1 alpha formation. Ticlopidine (200 mg/kg, i.p.) prevented the exacerbation of DIC in such item parameters as platelet count, APTT, and FDP. Both dazoxiben and BM-13177 (30 mg/kg, i.p.) ameliorated DIC in following parameters as platelet count, APTT and FDP. Dazoxiben, but not BM-13177, significantly inhibited the increase in TxB2 concentration at 4 hr. These observations suggest that drugs which inhibit platelet activation by a TxA2-dependent route are effective in improving DIC induced by LPS, and that drugs which inhibit multiple platelet-activating routes improve DIC in more item parameters than drugs which inhibit only the TxA2-dependent activating route. Consequently, it is concluded that activated platelets might play an important role in the occurrence and exacerbation of DIC induced by LPS, and that one of the roles of TxA2 in DIC is to activate platelets.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Blood Coagulation; Disseminated Intravascular Coagulation; Endotoxins; Epoprostenol; Fibrin; Humans; Imidazoles; Kidney Glomerulus; Male; Platelet Activation; Platelet Aggregation Inhibitors; Platelet Count; Prostaglandins, Synthetic; Rats; Rats, Inbred Strains; Sulfonamides; Thromboxane B2; Thromboxane-A Synthase; Ticlopidine

Dazoxiben, a selective TXA2 synthetase inhibitor, was studied in the incubating sections of porcine basilar arteries with arachidonic acid (AA) 50 mumols/L and calcimycin (calcium inophore A-23187) 50 mumol/L. TXB2 and 6-keto-PGF1 alpha were determined by radioimmunoassay. Leukotrienes (LT) were extracted and purified with SEP-PAK column, identified by HPLC and determined by bioassay with ileum of guinea pig. The results showed that the production of TXB2 was unaltered whether or not the incubation of arteries were induced by AA or calcimycin. Dazoxiben and indomethacin 0.05-50 mumols/L had no effects on the production of TXB2. However, dazoxiben 0.5, 5 and 50 mumols/L increased the production of 6-keto-PGF1 alpha by 16.3%, 19.0% and 30.7%, respectively. Indomethacin 0.5, 5 and 50 mumols/L decreased the production of 6-keto-PGF1 alpha by 22.3%, 24.9% and 24.0%, respectively. Meanwhile dazoxiben 1, 10 and 100 mumols/L decreased the production of LT by 33.4%, 45.6% and 66.4%, respectively. These results suggest that the protective effect of dazoxiben on the damages which resulted from brain ischemia may be related to the change of TAX2/PGI2 balance in the brain tissue as well as the inhibition of production of LT.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Arachidonic Acid; Arachidonic Acids; Basilar Artery; Biological Assay; Imidazoles; In Vitro Techniques; Indomethacin; Leukotrienes; Radioimmunoassay; Swine; Thromboxane B2; Thromboxane-A Synthase

An approach to the design of potential combined antithrombotic-antihypertensive agents is described. A series of 1,4-dihydropyridines bearing a 1H-imidazol-1-yl or pyrid-3-yl substituted side chain in the 2-position were synthesized and tested for antihypertensive activity in spontaneously hypertensive rats and for inhibition of TXA2 synthetase in rabbit platelets, in vitro. 1,4-Dihydro-2-(1H-imidazol-1-ylmethyl)-6-methyl- 4-(3-nitrophenyl)pyridine-3,5-dicarboxylic acid 3-ethyl 5-methyl diester (1) was shown to be similar in potency to nitrendipine as an antihypertensive agent. Compound 1 inhibited TXA2 synthetase in rabbit and human platelets in vitro and reduced plasma TXB2 levels in rats at antihypertensive dose levels. The reductions in thromboxane production observed in vivo and in vitro were accompanied by enhanced levels of 6-KPGF1 alpha, reflecting diversion of the arachidonic acid cascade toward prostacyclin synthesis.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Antihypertensive Agents; Chemical Phenomena; Chemistry; Dihydropyridines; Drug Design; Fibrinolytic Agents; Humans; Hypertension; Imidazoles; Nitrendipine; Rats; Rats, Inbred SHR; Structure-Activity Relationship; Thromboxane B2; Thromboxane-A Synthase

Wy 27569 (1,4 dihydro-2-[imidazol-1-yl-methyl]-6-methyl-4- [3-nitrophenyl] pyridine-3,5, dicarboxylic acid 3-ethyl 5-methyl diester) is a combined calcium channel blocker and thromboxane synthetase inhibitor. This article reports the in vivo and in vitro pharmacological studies demonstrating these properties. Wy 27569 evoked rightward shifts and depressed the maximum of calcium dose response curves in potassium depolarised rat aortas [concentration required to inhibit the response by 50% (IC50) = 7.3 nM]. The calcium channel blocker nitrendipine exhibited a similar profile to, although more potent than, Wy 27569 (IC50 = 0.28 nM). Comparison of the data obtained in aortas with the effects of these compounds in electrically stimulated isolated ventricle strips (IC50 for Wy 27569 = 8.3 microM, IC50 for nitrendipine = 0.41 microM) suggests that Wy 27569, like nitrendipine, is a vascular selective calcium channel blocker. Wy 27569 and the thromboxane synthetase inhibitor dazoxiben inhibited the collagen-stimulated production of thromboxane B2 (TXB2, IC50 = 3.9 and 2.8 microM, respectively) and, over the same concentration range, enhanced the production of immunoreactive 6 keto prostaglandin F1 alpha (6 keto-PGF1 alpha) by human platelet rich plasma. Single doses of Wy 27569 (0.3-10 mg kg-1 p.o.) or dazoxiben (3-10 mg kg-1 p.o.) evoked a dose-related reduction of TXB2 and enhancement of immunoreactive 6 keto PGF1 alpha levels in rat plasma and serum. Nitrendipine (0.3-10 mg kg-1 p.o.) had no significant effect on either eicosanoid.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Blood Pressure; Calcium Channel Blockers; Dihydropyridines; Dose-Response Relationship, Drug; Female; Humans; Imidazoles; In Vitro Techniques; Male; Nitrendipine; Prostaglandins F; Rats; Rats, Inbred SHR; Thromboxane B2; Thromboxane-A Synthase

The effects of dazoxiben, a TXA2 synthetase inhibitor, and indomethacin were compared on cerebrovascular resistance (CVR) and levels of serum TXB2, 6-keto-PGF1 alpha (the stable metabolites of TXA2 and PGI2, respectively) and on protection from acute brain ischaemia caused by ia arachidonic acid (AA) in rabbits. The flow represented the cerebral blood flow (CBF) in two internal jugular arteries were measured with electromagnetic flow meter after occlusion of bilateral vertebral arteries and external jugular arteries. CVR was represented as blood pressure/(CBF.100 g brain). Serum TXB2 and 6-keto-PGF1 alpha levels were determined by radioimmunoassay. The results showed that CVR and BP, EEG, ECG were not affected by treatment with iv dazoxiben 2 or 10 mg/kg. The CVR was enhanced by 35.5 and 49.8% at 30 and 40 min, respectively after iv indomethacin 10 mg/kg. The serum TXB2 level (872 +/- 85) was inhibited to 511 +/- 169 pg/ml (n = 5, P less than 0.05) and 6-keto-PGF1 alpha increased from 668 +/- 309 to 890 +/- 357 pg/ml (n = 5, P less than 0.05) at 30 min after iv 2 mg/kg dazoxiben. However, both TXB2 and 6-keto-PGF1 alpha decreased by 26.4 and 32.7%, respectively at 40 min after iv indomethacin 10 mg/kg. In a model of cerebral ischaemia caused by ia AA in rabbits, the EEG change and enhancement of CVR were antagonized by iv dazoxiben 10 mg/kg completely, but only partly antagonized by indomethacin 10 mg/kg. The results suggest that PGI2 and TXA2 may play a minor role in the regulation of CVR in the physiological condition.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Cerebrovascular Circulation; Imidazoles; Male; Rabbits; Thromboxane B2; Thromboxane-A Synthase; Vascular Resistance

We investigated the effect of IL-2 in the isolated guinea pig lung perfused with phosphate-buffered Ringer's solution (containing 0.5 g/100 ml albumin and 5.5 mM dextrose) to determine the mechanism of IL-2-induced pulmonary edema. IL-2 (0 to 10,000 U/ml) was added to the perfusate following a 10 min baseline steady-state period. Pulmonary arterial pressure (Ppa), pulmonary capillary pressure (Ppc), and change in lung weight (as a measure of developing pulmonary edema) were recorded at 0, 10, 30, 40, and 60 min. The capillary filtration coefficient (Kf.c), an index of vascular permeability to water, was measured at 30 and 60 min. Infusion of IL-2 increased Ppc (from 3.9 +/- 0.1 cm H2O at baseline to 8.8 +/- 1.1 cm H2O at 60 min for IL-2 at 2000 U/ml, p less than 0.01; and from 3.8 +/- 0.1 cm H2O at baseline to 8.9 +/- 0.6 cm H2O at 60 min for IL-2 at 10,000 U/ml, p less than 0.01. The lung weight also increased (32% at IL-2 concentration of 2000 U/ml, and 26% at IL-2 concentration of 10,000 U/ml) The capillary filtration coefficient did not change with IL-2 infusion. The IL-2 response was prevented using the pulmonary vasodilator, papaverine. The infusion of IL-2 was associated with the generation of thromboxane A2(TxA2) in the effluent perfusate. Inhibition of TxA2 synthetase using Dazoxiben prevented the pulmonary vasoconstriction and edema response to IL-2. In addition, IL-2 had no effect on the transendothelial clearance of 125I-albumin. The results indicate that IL-2 causes pulmonary edema secondary to an increase in Ppc. The response is mediated by IL-2 stimulation of TxA2 generation from the lung.

Topics: Animals; Capillary Permeability; Endothelium, Vascular; Female; Guinea Pigs; Imidazoles; In Vitro Techniques; Interleukin-2; Killer Cells, Natural; Lymphocyte Activation; Male; Organ Size; Papaverine; Prostaglandins F; Pulmonary Edema; Pulmonary Wedge Pressure; Serum Albumin, Radio-Iodinated; Thromboxane B2; Vasoconstriction

(1) When platelets form TXA2 from endogeneous AA, PGH2 reaches concentrations very similar to those of TXA2 and high enough to produce strong platelet activation. Therefore, platelet activation by TXA2 appears to go along with an activation by PGH2. (2) PGH2 is a more potent stimulus of platelet shape change and aggregation than U 46619. (3) The agonism of PGH2 is limited by the formation of inhibitory prostaglandins, especially PGD2 at higher concentrations. That is why thromboxane synthase inhibitors in PRP and at a physiological HSA concentration do not augment platelet activation. (4) HSA promotes the formation of inhibitory PGD2 at the expense of agonistic PGH2.

Topics: Blood Platelets; Humans; Imidazoles; In Vitro Techniques; Methylmercury Compounds; Platelet Aggregation; Prostaglandin Endoperoxides; Prostaglandin Endoperoxides, Synthetic; Prostaglandin H2; Prostaglandins H; Thrombin; Thromboxane A2; Thromboxane B2; Thromboxane-A Synthase

Goats were divided into three groups and given infusions of live Escherichia coli bacteria. Group I received no treatment, group II was treated with indomethacin (a cyclooxygenase inhibitor), and group III with dazoxiben (a thromboxane synthase inhibitor). Double indicator-dilution extravascular lung water (EVLW) in group I was significantly different from the treated groups. There was an early increase in EVLW in group I and group III but not in group II animals. At 6 h EVLW's in group I, group II, and group III were 100, 45, and 30% above base line, respectively. Lymph flow (QL) and lymph-to-plasma protein ratio (L/P) was not statistically different between groups. Estimated total fluid filtration [QL + d(EVLW)/dt] in group I and III was markedly elevated between 0 and 1.5-2 h after E. coli infusion. Cardiac output (QT) decreased to 40% of base line in group I, and it decreased slightly in group II because of the indomethacin but did not decrease after E. coli. QT decreased in group III but recovered more rapidly than group I. Mean pulmonary arterial pressure increased more rapidly in group I and reached a higher peak than either treated group. At 6 h these groups had similar pulmonary arterial and pulmonary arterial wedge pressures. We conclude that 1) indomethacin but not dazoxiben blocks the early increase in total fluid filtration after bacterial infusion, 2) dazoxiben does not prevent the increased endothelial permeability resulting from infusion of live bacteria, and 3) indomethacin may somewhat ameliorate the endothelial permeability change.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Blood Pressure; Body Water; Cardiac Output; Escherichia coli Infections; Imidazoles; Indomethacin; Lung; Lymph; Pulmonary Circulation; Reference Values; Thromboxane B2; Thromboxane-A Synthase

The possible role of thromboxane A2 (TXA2) in acute necrotizing pancreatitis (ANP) was investigated in rats. After ANP was induced by injecting sodium taurocholate (5% w/v) into the pancreatic duct, the thromboxane B2 (TXB2) levels in plasma increased significantly. The effects of indomethacin, a general blocker of prostaglandin synthesis, on survival time and on plasma TXB2 levels were compared with those of dazoxiben, a more specific blocker of TXA2 synthesis, and Flunarizine, a calcium entry blocker known to inhibit the effects of TXA2. In a test group without any treatment, all animals died within 30 h of ANP induction. Although TXB2 levels were lowered by the administration of indomethacin, dazoxiben, and Flunarizine, survival times were not significantly altered. Indomethacin pretreatment had no beneficial effect, whereas 30% and 40% of the animals survived for 36 h after treatment with Flunarizine and dazoxiben, respectively. The results of the present study indicate that inhibition of TXA2 synthesis alone does not dramatically alter survival time. However, a potential role for other arachidonate metabolites in ANP cannot be ruled out by this study.

Topics: Acute Disease; Animals; Flunarizine; Imidazoles; Indomethacin; Male; Necrosis; Pancreatitis; Rats; Rats, Inbred Strains; Thromboxane A2; Thromboxane B2

CGS 15435A, a novel thromboxane (Tx) synthetase inhibitor (5-chloro-1-methyl-2-(3-pyridyl)-3-indolhexanoic acid HCl), had a selectivity for Tx synthetase 100,000-fold greater than that for cyclooxygenase, PGI2 synthetase and lipoxygenase enzymes. In conscious beagles, 1 h following a single 3 mg/kg p.o. dose, serum TxB2 was inhibited 95% by CGS 15435 and 82% by dazoxiben (DAZ). Unlike the short acting Tx synthetase inhibitor DAZ, CGS 15435A significantly inhibited TxB2 formation 4, 6, 12 and 24 h after dosing. Serum levels of 6-keto PGF1 alpha and PGE2 were significantly increased following the administration of either drug. CGS 15435A and DAZ were further examined in a model with known Tx involvement. Thrombotic sudden death, produced in anesthetized rabbits by injection of 0.75 mg/kg arachidonic acid (AA) i.v. resulted in a 45% fall in the platelet count and 0% survival. Pretreatment with DAZ (8.6 mumol/kg i.v.) at 0.25 or 2 h pre-AA resulted in 3 and 42% thrombocytopenia and 100 and 0% survival respectively. CGS 15435A (8.6 mumol/kg i.v.) prevented the increases in plasma TxB2 levels, thrombocytopenia and sudden death with pretreatment at 0.25 h (0% thrombocytopenia and 100% survival) or 24 h (11% thrombocytopenia and 83% survival) before AA. These data indicate that CGS 15435A is a potent and selective Tx synthetase inhibitor with a long duration of action, and suggest that the compound could be useful in chronic, non-symptomatic indications of Tx involvement.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Cyclooxygenase Inhibitors; Cytochrome P-450 Enzyme System; Death, Sudden; Dinoprostone; Dogs; Epoprostenol; Imidazoles; In Vitro Techniques; Indoles; Intramolecular Oxidoreductases; Lipoxygenase Inhibitors; Platelet Count; Prostaglandins E; Rabbits; Thromboxane B2; Thromboxane-A Synthase

In rabbits receiving a normal laboratory diet the platelet half-life was 40.4 +/- 2.5h (mean +/- S.D., n = 35). In animals fed the cholesterol-enriched diet for 12 weeks the platelet half-life was reduced to 31.6 +/- 3.6h (mean +/- S.D., n = 35). Treatment of cholesterol-fed animals with a single daily dose of CGS 12970 (a long acting inhibitor of thromboxane synthase) normalised the platelet half-life. Single daily doses of the relatively shorter acting thromboxane synthase inhibitors (CGS 13080 and dazoxiben) failed to correct the reduced platelet survival. However, twice daily dosing with dazoxiben was effective. The cyclooxygenase inhibitors, aspirin and sulphinpyrazone, failed to correct the reduced platelet survival.

Topics: Animals; Aspirin; Blood Platelets; Cell Survival; Cholesterol, Dietary; Cyclooxygenase Inhibitors; Hypercholesterolemia; Imidazoles; Pyridines; Rabbits; Sulfinpyrazone; Thromboxane B2; Thromboxane-A Synthase

The influence of different vasoactive substances on the evolution of HgCl2-induced acute renal failure (ARF) was evaluated in the dog. HgCl2 alone caused a progressive fall in both glomerular filtration (GFR) and renal blood flow (RBF) during the first 3 h of the mercury administration (delta after 3 h: -44% and -39%) and provoked a concomitant stimulation of the renin-angiotensin (RAS) and thromboxane systems. The administration of the thromboxane inhibitor dazoxiben (2 mg/kg i.v. every 2 h) adequately inhibited the activation of the thromboxane system after HgCl2, but could not prevent the fall in GFR and RBF. The continuous intrarenal administration of the Ca2+ entry blocker verapamil (0.005 mg/kg per min) into the left kidney resulted in the prevention of the postmercurial fall in GFR and RBF at the perfusion site. This beneficial effect was immediately lost when the verapamil administration was stopped. Finally, the administration of the converting enzyme inhibitor captopril (300 micrograms/kg every 2 h) resulted in an effective inhibition of the renin-angiotensin system, the prevention of the postmercurial fall in RBF, and the partial attenuation of the fall in GFR. This beneficial effect was immediately lost after the intravenous administration of indomethacin (2 mg/kg). These results indicate that the fall in GFR after HgCl2 can be prevented by vasoactive agents such as captopril and verapamil and point at least in part to a pathophysiological role of the renin-angiotensin system or of an alteration in the equilibrium between renin-angiotensin and prostaglandins. The thromboxane system is seemingly of no major importance.

Topics: Acute Kidney Injury; Animals; Captopril; Dogs; Glomerular Filtration Rate; Imidazoles; Mercuric Chloride; Prostaglandins; Renal Circulation; Renin-Angiotensin System; Thromboxane B2; Time Factors; Verapamil

Using our in vivo model for studying drugs which prevent deposition of thrombi or dissipate thrombi formed in extra-corporeal circulation over a collagen strip superfused with arterial blood of anaesthetized and heparinized cats, we have found that dazoxiben--a thromboxane synthetase inhibitor--possesses not only antithrombotic but also thrombolytic potency in vivo (ED50 = 3.8 mg/kg i.v.). The thrombolytic potency of dazoxiben was antagonized by aspirin at a dose of 50 mg/kg i.v. Moreover, dazoxiben stimulated the generation of prostacyclin in isolated rat aortic slices incubated in platelet rich plasma, but not in platelet poor plasma. It is suggested that the thrombolytic potency of thromboxane synthetase inhibitors after their systemic administration is associated with the release of prostacyclin and/or prostacyclin-stable metabolites by the vascular endothelium owing to feeding of prostacyclin synthetase with prostaglandin endoperoxides accumulated in platelets following the inhibition of thromboxane synthetase.

Topics: Animals; Aorta; Blood Platelets; Cats; Epoprostenol; Female; Fibrinolytic Agents; Imidazoles; In Vitro Techniques; Male; Thromboxane B2; Thromboxane-A Synthase

We examined the direct effects of thrombin on pulmonary vasomotor tone in isolated guinea pig lungs perfused with Ringer albumin (0.5% g/100 ml). The injection of alpha-thrombin (the native enzyme) resulted in rapid dose-dependent increases in pulmonary arterial pressure (Ppa) and pulmonary capillary pressure (Ppc), which were associated with an increase in the lung effluent thromboxane B2 concentration. The Ppa and Ppc responses decreased with time but then increased again within 40 min after thrombin injection. The increases in Ppc were primarily the result of postcapillary vasoconstriction. Pulmonary edema as evidenced by marked increases (60% from base line) in lung weight occurred within 90 min after thrombin injection. Injection of modified thrombins (i.e., gamma-thrombin lacking the fibrinogen recognition site or i-Pr2P-alpha-thrombin lacking the serine proteolytic site) was not associated with pulmonary hemodynamic or weight changes nor did they block the effects of alpha-thrombin. Indomethacin (a cyclooxygenase inhibitor), dazoxiben (a thromboxane synthase inhibitor), or hirudin (a thrombin antagonist) inhibited the thrombin-induced pulmonary vasoconstriction, as well as the pulmonary edema. We conclude that thrombin-induced pulmonary vasoconstriction is primarily the result of constriction of postcapillary vessels, and the response is mediated by generation of cyclooxygenase-derived metabolites. The edema formation is also dependent on activation of the cyclooxygenase pathway. The proteolytic site of alpha-thrombin is required for the pulmonary vasoconstrictor and edemogenic responses.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Female; Guinea Pigs; Hirudins; Imidazoles; Indomethacin; Lung; Male; Organ Size; Pulmonary Artery; Pulmonary Wedge Pressure; Thrombin; Thromboxane B2; Thromboxane-A Synthase; Vasoconstriction

We have previously demonstrated that arachidonic acid (AA) and the stable cyclic endoperoxide analogue (U46619) desensitize human platelets at a common site, which is sensitive to endoperoxides/thromboxane receptor antagonists. We now report on the influence of agents which evaluate intracellular levels of platelet adenosine 3',5'-cyclic monophosphate (cAMP) on AA- and U46619-induced platelet desensitization. Prostaglandin E1, prostacyclin, carbacyclin, forskolin or dibutyryl cAMP prevented platelet activation by and desensitization to AA and to U46619 under conditions where the formation of thromboxane B2 was not significantly modified. Inhibition of platelet activation (aggregation and secretion) required a lower increase of the cAMP content than was needed to inhibit desensitization, confirming previous findings that desensitization to and by AA or U46619 are independent from the platelet release reaction. Together, these results indicate that AA-induced desensitization can be modulated by the adenylate cyclase/cAMP system acting at a site distinct from the known mechanisms of Ca2+ sequestration. This site is shared by the AA metabolite responsible for desensitization and by U46619 and is related to their common platelet membrane receptor.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenylyl Cyclases; Arachidonic Acid; Arachidonic Acids; Blood Platelets; Bucladesine; Cyclic AMP; Humans; Imidazoles; In Vitro Techniques; Prostaglandin Endoperoxides, Synthetic; Thromboxane B2

1-(3-Benzyloxy-1[E]octenyl)imidazole (CBS-645) is a specific inhibitor of thromboxane synthetase. It inhibits the platelet enzyme in human and rabbit at micromolar concentrations. At a dose of 12.5 mg kg-1 in rabbits, CBS-645 displays a prolonged inhibitory effect on the formation of thromboxane (Tx) B2 induced by blood coagulation in vitro. In human volunteers, an oral dose of 50 mg leads to an average 70% inhibition of TxB2 formation. CBS-645 administered at a dose of 25 mg kg-1 p.o. in the rat, significantly increases bleeding time. In another test in which platelet interaction with the vessel wall is involved, i.e. in vivo platelet deposition onto desendothelialized aorta in the rabbit, the drug shows antithrombotic activity after a single oral administration of 5 mg kg-1. CBS-645 could be of interest in the treatment of the various diseases in which the pathological role of thromboxane A2 is suspected.

Topics: Adult; Animals; Arachidonic Acid; Arachidonic Acids; Bleeding Time; Blood Platelets; Dinoprostone; Humans; Imidazoles; In Vitro Techniques; Male; Middle Aged; Prostaglandins E; Rabbits; Rats; Rats, Inbred Strains; Thrombosis; Thromboxane B2; Thromboxane-A Synthase

The purpose of this study was to compare the effects of dazoxiben (DAZ), UK 38,485 (UK) and aspirin (ASA) in the prevention of thrombotic sudden death in rabbits. In anesthetized male rabbits, sudden death was produced by intravenous administration of 0.75 mg/kg arachidonic acid (AA). AA increased plasma TxB2 levels from 0.20 +/- 0.10 ng/ml to 8.75 +/- 1.79 ng/ml and produced a 42% reduction in the number of circulating platelets. Death occurred in all animals within 5 minutes. Administration of DAZ (8.6 mumole/kg) 15 min before AA prevented the increase in plasma TxB2, the thrombocytopenia and sudden death while pretreatment with DAZ 2 hr before AA did not. The administration of UK (8.6 mumole/kg) 15 min. 4 hrs or 8 hrs before AA resulted in 100%, 67% and 33% survival, respectively. ASA (110 mumole/kg) administered 2 or 24 hrs before AA inhibited the increase in plasma TxB2 and prevented the fall in platelet counts. All animals pretreated with ASA survived. These data demonstrate that DAZ and UK have only a short to moderate duration of action in preventing AA-induced increases in plasma Tx levels and thrombocytopenia.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Arachidonic Acid; Arachidonic Acids; Aspirin; Imidazoles; Male; Rabbits; Thrombocytopenia; Thrombosis; Thromboxane B2; Time Factors

Twenty-four hours of complete unilateral ureteral obstruction (UUO) produces intense renal vasconstriction in the rat even after release of obstruction. In the ex vivo perfused hydronephrotic rabbit kidney, bradykinin stimulates increased production of the vasoconstrictor autocoid thromboxane. In the present study, we measured basal and bradykinin-stimulated thromboxane and prostaglandin E2 production by UUO and contralateral rat kidneys perfused ex vivo. Furthermore, we evaluated thromboxane synthetase inhibition by imidazole and by two of its substituted derivatives, UK 37248 and UK 38485, in vitro. We compared these in vitro findings with in vivo measurements of renal hemodynamics and excretory function before and after the intrarenal artery administration of thromboxane synthetase inhibitors. Both basal and bradykinin-stimulated thromboxane and prostaglandin E2 production were significantly increased in hydronephrotic kidneys. Imidazole and its substituted congeners were effective inhibitors of bradykinin-stimulated thromboxane B2 production in vitro. However, the substituted imidazoles were more potent, more efficacious, and more selective for thromboxane synthetase inhibition than the parent compound. In vivo, administration of imidazole into the renal artery of the UUO kidney improved function slightly, whereas administration of UK 37248 or UK 38485 doubled renal blood flow and excretory function but did not restore them to normal. We conclude that the hydronephrotic rat kidney produces increased amounts of the vasoconstrictor eicosanoid thromboxane and that thromboxane is an important mediator of vasoconstriction in this model of disease.

Topics: Animals; Dinoprostone; Dose-Response Relationship, Drug; Hydronephrosis; Imidazoles; Methacrylates; Prostaglandins E; Rats; Rats, Inbred Strains; Thromboxane B2; Thromboxane-A Synthase; Ureteral Obstruction

Aggregating human platelets contract isolated rings of canine coronary artery without endothelium, but relax rings with intact endothelium. We performed experiments to identify the substances released from platelets responsible for these effects. The contraction in rings without endothelium was reduced by treating the platelets with thromboxane synthetase inhibitor, dazoxiben, or treating the vessels with the thromboxane-receptor antagonist, SQ 29548. The serotonergic antagonist, methiothepin, also reduced the platelet-induced contraction. The combination of methiothepin plus dazoxiben or SQ 29548 caused a further inhibition. The endothelium-dependent relaxation to platelets during contractions evoked by prostaglandin F2 alpha was nearly abolished by the ADP- and ATP-scavenger, apyrase. It was not inhibited by methiothepin, which antagonizes endothelium-dependent relaxations to serotonin. Thus, both serotonin and thromboxane A2 contribute to the direct activation of coronary smooth muscle by aggregating human platelets, whereas adenine nucleotides are the principal mediators of the endothelium-dependent relaxation.

Topics: Adenine Nucleotides; Animals; Coronary Vessels; Dogs; Endothelium; Female; Humans; Imidazoles; In Vitro Techniques; Male; Methiothepin; Muscle Contraction; Muscle Relaxation; Muscle, Smooth, Vascular; Platelet Aggregation; Serotonin; Thromboxane A2; Thromboxane B2

Administration of dazoxiben (5 mg/kg, i.v.), which effectively suppressed plasma thromboxane concentrations, decreased the number of dogs that deteriorated into shock following a temporary (3-hr) splanchnic artery occlusion (SAO). Dazoxiben pretreatment also moderated the rise of plasma prostacyclin, but it augmented circulating prostaglandin E2 following the release of SAO. These alterations in arachidonic acid metabolism were accompanied by a moderation in the rise of plasma beta-glucuronidase activity, suggesting a moderation of tissue damage in the ischemic splanchnic region, and mitigation of the progressive hemodynamic deterioration caused by the SAO. The possible existence of causal relationships between the plasma eicosanoid concentrations, extent of damage in the ischemic splanchnic region, hemodynamic deterioration, and ultimate production of circulatory failure in dogs subjected to SAO are discussed.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Blood Pressure; Cardiac Output; Dogs; Female; Glucuronidase; Heart Rate; Imidazoles; Indomethacin; Ischemia; Kinetics; Male; Shock; Splanchnic Circulation; Thromboxane B2; Thromboxane-A Synthase; Vascular Resistance

During infusion of thrombin in rats pulmonary arterial pressure rose from 15 +/- 2 to 35 +/- 3 mmHg and mean arterial pressure fell from 120 +/- 6 to 49 +/- 27 mmHg. Plasma thromboxane B2 (TxB2) increased from 0.3 +/- 0.04 to 3.6 +/- 0.5 ng/ml. Ninety minutes later the lung weight and albumin concentration in the lung were increased (2.21 +/- 0.13 g and 22.7 +/- 4.7 mg/g) compared with controls (1.12 +/- 0.14 g and 8.5 +/- 0.9 mg/g). An inhibitor of thromboxane synthetase, Dazoxiben R, reduced the elevated pulmonary arterial pressure and the elevated plasma TxB2 concentration following infusion of thrombin. Ninety minutes after infusion of thrombin, the in vitro synthesis of TxB2 in lung tissue was increased. Dazoxiben and antineutrophil serum reduced this synthesis of TxB2 in vitro. The lung weight (2.18 +/- 0.20 g) and lung albumin concentration (21.4 +/- 3.4 mg/g) was not affected by Dazoxiben. The results indicate that TxA2 is an important mediator of the pressure changes in the early phase after infusion of thrombin and that neutrophils are associated with thromboxane formation in the lung tissue.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Blood Pressure; Cattle; Fibrinogen; Fibrinolysis; Imidazoles; Indomethacin; Lung; Lung Diseases; Male; Organ Size; Platelet Count; Rats; Rats, Inbred Strains; Serum Albumin; Thrombin; Thromboxane B2; Thromboxane-A Synthase

Collagen (10-40 micrograms kg-1), thrombin (1-10 units kg-1), adenosine diphosphate (ADP; 3-300 micrograms kg-1), 1-0-hexadecyl Paf-acether and 1-0-octadecyl Paf-acether (1-300 ng kg-1) administered by bolus intravenous injection each caused dose-dependent thrombocytopoenia accompanied by marked hypotension in anaesthetized rabbits. Responses to ADP and the Paf-acether derivatives were transient in nature (3-8 min) whereas those induced by collagen and thrombin were always of longer duration (5-20 min) and frequently fatal at high doses. Responses to collagen, thrombin, and the Paf-acether derivatives were invariably accompanied by substantial, dose-related increases in plasma levels of thromboxane B2 in samples obtained 30 s after agonist administration, whereas following ADP, no change in plasma thromboxane B2 was detected at any dose level. Indomethacin (3.0 mg kg-1 by infusion) had no effect on responses to thrombin or Paf-acether, partially inhibited collagen-induced thrombocytopenia, and potentiated responses to ADP. In contrast, dazoxiben (10 mg kg-1 by infusion) partially but significantly inhibited responses to thrombin, whereas those induced by collagen, Paf-acether or ADP were unchanged. These results indicate that in this model of intravascular aggregation, whilst platelet responses to collagen and thrombin appear partially dependent on intact cyclic endoperoxide and thromboxane A2 synthetic capacity respectively, responses to ADP and Paf-acether are independent of arachidonate metabolism via cyclo-oxygenase despite measurably increased TXB2 formation in the latter case.

Topics: Adenosine Diphosphate; Animals; Collagen; Dose-Response Relationship, Drug; Imidazoles; Indomethacin; Male; Platelet Activating Factor; Platelet Aggregation; Rabbits; Thrombin; Thromboxane B2

We examined the pulmonary vascular response to an intravenous leukotriene D4 (LTD4) injection of (1 microgram X kg-1 X min-1 for 2 min) immediately followed by infusion of 0.133 microgram X kg-1 X min-1 for 15 min in awake sheep prepared with lung lymph fistulas. LTD4 resulted in rapid generation of thromboxane A2 as measured by an increase in plasma thromboxane B2 concentration. The thromboxane B2 generation was associated with increases in pulmonary arterial and pulmonary arterial wedge pressures while left atrial pressure did not change significantly. Pulmonary lymph flow (Qlym) increased (P less than 0.05) transiently from base line 6.87 +/- 1.88 (SE) ml/h to maximum value of 9.77 +/- 1.27 at 15 min following the LTD4 infusion. The maximum increase in Qlym was associated with an increase in the estimated pulmonary capillary pressure. The increase in Qlym was not associated with a change in the lymph-to-plasma protein concentration (L/P) ratio. Thromboxane synthetase inhibition with dazoxiben (an imidazole derivative) prevented thromboxane B2 generation after LTD4 and also prevented the increases in pulmonary vascular pressures and Qlym. We conclude that LTD4 in awake sheep increases resistance of large pulmonary veins. The small transient increase in Qlym can be explained by the increase in pulmonary capillary pressure. Thromboxane appears to mediate both the pulmonary hemodynamic and lymph responses to LTD4 in sheep.

Topics: Animals; Hemodynamics; Imidazoles; Lung; Lymph; Pulmonary Circulation; Sheep; SRS-A; Thromboxane B2; Wakefulness

Human platelets pre-exposed to arachidonic acid (AA) (0.1-1 mM) or to the endoperoxide analogue U46619 (1-3 microM) and then washed and resuspended, failed to respond with aggregation or secretion to a second challenge by either agonist. The response to thrombin at low (0.04-0.1 u ml-1) but not at high (2.5 u ml-1) concentrations was also inhibited by pre-exposure to AA and U46619. The ability of platelets to synthesize thromboxane (Tx) B2 from AA or upon challenge with thrombin persisted despite platelet desensitization. In the presence of the reversible cyclo-oxygenase (CO) inhibitors methyl salicylate (MS) or L8027, pre-exposure to AA had no effect on subsequent challenge by the same agonist or by U46619, whereas platelet desensitization by pre-exposure to U46619 persisted. However, platelet activation by, and desensitization to AA and U46619, was prevented by trimetoquinol and compound L636499, two thromboxane/endoperoxide receptor antagonists. In contrast to the CO inhibitors, the thromboxane synthetase inhibitor dazoxiben, which in 3 'responders' out of 5 subjects suppressed aggregation, secretion, and Tx formation induced by AA, failed to prevent AA-induced desensitization. Compared to quiescent cells the distances between platelets desensitized after re-exposure to AA were reduced in electron microscopy, but the tight connections associated with aggregated cells were not observed. Degranulation was also not observed and cell morphology resembled that of normal quiescent platelets. In conclusion, (a) AA and U46619 desensitize human platelets at a similar site sensitive to prostaglandin/thromboxane receptor antagonists, and show cross-desensitization; (b) desensitization by AA appears to be mediated by a CO-dependent metabolite, as CO inhibitors prevent desensitization by AA but not to U46619; (c) the failure of dazoxiben to prevent desensitization by AA suggests that a metabolite other than TxA2, possibly the endoperoxides, mediates the phenomenon; (d) desensitization does not involve inactivation of CO or thromboxane synthetase enzymes.

Topics: Adenosine Triphosphate; Arachidonic Acid; Arachidonic Acids; Blood Platelets; Cyclooxygenase Inhibitors; Humans; Imidazoles; Indoles; Microscopy, Electron; Platelet Aggregation; Prostaglandin Endoperoxides, Synthetic; Receptors, Cell Surface; Receptors, Prostaglandin; Receptors, Thromboxane; Salicylates; Thrombin; Thromboxane B2

The effects of indomethacin, dazoxiben and EPO45 on collagen-induced platelet aggregation in vivo were studied in guinea-pigs and rats to determine the involvement of the prostaglandin endoperoxide/thromboxane A2 pathway in the aggregatory response. Indomethacin and EPO45 (a thromboxane receptor antagonist) partially inhibited platelet aggregation in rats. It was concluded that only one third of the aggregatory response to collagen was mediated by the products of cyclo-oxygenase conversion of arachidonic acid. In rats, dazoxiben was inactive although the conversion of the prostaglandin endoperoxides to thromboxane A2 was inhibited (measured as thromboxane B2). 6-keto PGF1 alpha was detected in plasma after collagen was injected into dazoxiben-treated rats. In this species therefore, the endoperoxides have significant aggregatory activity whilst the apparent increase in the level of prostacyclin was not sufficient to have any anti-aggregatory effect. All three drugs were active in the guinea-pig. About 60% of the aggregatory response to collagen was due to the products of the cyclo-oxygenase pathway, the main mediator being thromboxane A2. In guinea-pigs, dazoxiben also elevated 6-keto PGF1 alpha in the plasma after an injection of collagen. However, this apparent increase in prostacyclin production did not contribute to the anti-aggregatory effect.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Collagen; Female; Guinea Pigs; Imidazoles; In Vitro Techniques; Indomethacin; Male; Platelet Aggregation; Prostaglandin Endoperoxides; Prostaglandin Endoperoxides, Synthetic; Prostaglandin H2; Prostaglandins H; Prostaglandins, Synthetic; Rats; Rats, Inbred Strains; Receptors, Prostaglandin; Receptors, Thromboxane; Species Specificity; Thromboxane A2; Thromboxane B2; Thromboxanes

The effect of a selective inhibitor of thromboxane synthesis (dazoxiben) was evaluated in different acute models for thrombosis and hemostasis. Dazoxiben significantly reduced the thrombogenicity of the modified human umbilical vein (Dardik Biograft) inserted in the carotid artery position in sheep. The effect was evident concerning patency, thrombus weight and platelet accumulation at the distal anastomosis. This paralleled a decreased production of thromboxane in both anastomoses and the midgraft region. Dazoxiben did not reduce either the frequency of jugular vein thrombosis (induced by a combination of endothelial damage and flow restriction) or arteriolar microembolism after laser injury in rabbits. Neither did it influence initial hemostasis as evaluated by measuring the hemostatic plug formation in the rabbit mesenteric microcirculation. It is concluded that thromboxane synthesis inhibition may be of value when attempting to improve the performance of small diameter vascular prostheses, the data obtained indicating a low risk for hemorrhagic complications.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Blood Platelets; Carotid Arteries; Female; Hemostasis; Humans; Imidazoles; Jugular Veins; Male; Oxidoreductases; Rabbits; Sheep; Thrombosis; Thromboxane B2; Thromboxane-A Synthase; Umbilical Veins

Selective pharmacological blockade of thromboxane-synthase in human platelets by dazoxiben resulted in the reorientation of cyclic-endoperoxides towards PGE2, PGD2 and PGF2 alpha. At concentrations which can be reached when thromboxane-synthase is inhibited, PGE2 (100-500 nM) exerted a marked, concentration-dependent pro-aggregatory effect. This required the formation of endogenous or the addition of exogenous endoperoxides and was prevented by PGD2 or 13-aza-prostanoic acid, a selective antagonist of PGH2/TxA2 receptors. The anti-aggregating effect of PGD2 was evident at concentrations lower than those obtained in dazoxiben-treated platelets. It is proposed that in the absence of TxA2 generation, a combination of endoperoxides and PGE2 may result in normal aggregation. The latter may be inhibited by PGD2. No interference of PGF2 alpha on platelet function could be shown.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine Diphosphate; Arachidonic Acid; Arachidonic Acids; Aspirin; Blood Platelets; Dinoprost; Dinoprostone; Drug Synergism; Humans; Imidazoles; Oxidoreductases; Platelet Aggregation; Prostaglandin D2; Prostaglandin Endoperoxides; Prostaglandin Endoperoxides, Synthetic; Prostaglandins; Prostaglandins D; Prostaglandins E; Prostaglandins F; Prostanoic Acids; Thromboxane B2; Thromboxane-A Synthase

The effect of the thromboxane (TX) synthase inhibitors dazoxiben and imidazole on platelet activation by endogenous and exogenous arachidonic acid (AA) was tested with human washed platelets. Dazoxiben (1-20 microM) inhibited the formation of TXB2 and markedly enhanced the shape change, aggregation, and (3H)serotonin release induced by added AA or when prostaglandin synthesis from endogenous AA was triggered by collagen, hydrogen peroxide or methyl mercury chloride (methyl-Hg). Platelet activation by hydrogen peroxide (20-1200 microM) or methyl-Hg (1-5 microM) was entirely dependent on endogenous prostaglandin (PG) synthesis since acetylsalicylic acid (ASA), indomethacin or the cyclic endoperoxide/TXA2-antagonist BM 13.177 counteracted these stimulants with and without dazoxiben. Apparently, the potentiation is due to accumulating cyclic endoperoxides which during TX synthase inhibition reach greater platelet-activating potency than TXA2. Albumin or human platelet-poor plasma inhibited the platelet activation by hydrogen peroxide and methyl-Hg and suppressed the potentiation by dazoxiben. The latter effect of albumin may result from its PGD isomerase activity which redirects the cyclic endoperoxide metabolism to the platelet-inhibitory PGD2. The results show that non-platelet factors such as albumin are necessary to prevent a potentiating effect of TX synthase inhibitors on platelet activation.

Topics: Arachidonic Acid; Arachidonic Acids; Blood Platelets; Collagen; Drug Interactions; Humans; Hydrogen Peroxide; Imidazoles; In Vitro Techniques; Indomethacin; Methylmercury Compounds; Oxidoreductases; Platelet Aggregation; Serotonin; Serum Albumin; Sulfonamides; Thromboxane B2; Thromboxane-A Synthase

Radioimmunoassay and bioassay techniques have been used to investigate the ability of leukotriene (LT)F4 to release products of arachidonic acid metabolism from guinea pig isolated lungs perfused via the pulmonary artery. Also, the abilities of LTC4, LTD4, LTE4 and LTF4 to contract guinea pig ileal smooth muscle (GPISM) was studied. Each of the LT's contracted GPISM. The rank order of potency was LTD4 greater than LTC4 greater than LTE4 much greater than LTF4 in a ratio of 1:7:170:280 respectively. Bioassay of pulmonary effluents indicated the passage of LTF4 through the lungs caused a contraction of rabbit aorta as well as an FPL-55712 sensitive contraction of GPISM. The contractions of rabbit aorta were inhibited by pretreatment of the lungs with Indomethacin but not with the thromboxane synthetase inhibitor Dazoxiben. Radioimmunoassay of the lung effluents indicated LTF4 to cause a 70-fold increase in thromboxane B2 (TXB2), 4-fold increase in prostaglandin (PG)E2 and a 16-fold increase in 6-keto PGF1 alpha levels. The LTF4-induced increments of these immunoreactive metabolites was inhibited by pretreatment of the lungs with Indomethacin. Pretreatment of lungs with Dazoxiben inhibited the LTF4-induced increment in TXB2 and enhanced the effluent levels of PGE2 24-fold (compared with untreated lungs). There were no detectable differences in either immunoreactive LTC4 or immunoreactive LTB4 levels. It is concluded LTF4 is a relatively weak agonist on GPISM and can induce the release of cyclooxygenase products of arachidonic acid metabolism from guinea pig perfused lung.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Arachidonic Acid; Arachidonic Acids; Biological Assay; Dinoprostone; Female; Guinea Pigs; Imidazoles; In Vitro Techniques; Indomethacin; Lung; Male; Prostaglandin-Endoperoxide Synthases; Prostaglandins E; SRS-A; Thromboxane B2

The TxA2 synthetase inhibitor, dazoxiben, and the TxA2 antagonist, +/- SQ 29,548, were examined for effects on release and vasoactivity of TxA2 and prostacyclin. Isolated perfused guinea pig lungs were used as the enzyme source from which TxA2 and prostacyclin were released in response to injections of arachidonic acid or bradykinin. Both dazoxiben and +/- SQ 29, 548 inhibited contraction of the superfused rat aorta and bovine coronary artery after arachidonic acid injection through the lung. +/- SQ 29,548 abolished contractions of the rat aorta, but significant aorta contracting activity persisted during dazoxiben treatment. Dazoxiben significantly inhibited arachidonate-induced release of TxA2 (immunoreactive TxB2) into the superfusate, but TxA2 release was significantly potentiated by +/- SQ 29,548. Thus, in the presence of enhanced TxA2 concentrations, +/- SQ 29,548 effectively antagonized the vasospastic effect of TxA2. Dazoxiben diverted a significantly greater amount of arachidonic acid into prostacyclin synthesis (immunoreactive 6-keto-PGF1 alpha), changing original coronary vasoconstriction into relaxation. +/- SQ 29,548 did not significantly modify lung prostacyclin synthesis. Moreover, with +/- SQ 29,548, the absence of TxA2-mediated coronary contraction unmasked active relaxation of the superfused bovine coronary artery, coincident with thromboxane and prostacyclin release. Dazoxiben consistently inhibited TxA2 synthesis and enhanced prostacyclin synthesis. +/- SQ 29,548 augmented TxB2 release in response to arachidonate, but not bradykinin, and did not significantly alter 6-keto-PGF1 alpha release in response to either arachidonate or bradykinin. In terms of vasoactivity measured in vitro, +/- SQ 29,548 and dazoxiben produced similar anti-vasospastic effects, although this was accomplished by completely different mechanisms.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Arachidonic Acid; Arachidonic Acids; Bradykinin; Bridged Bicyclo Compounds, Heterocyclic; Cattle; Epoprostenol; Fatty Acids, Unsaturated; Guinea Pigs; Hydrazines; Imidazoles; Male; Muscle Contraction; Muscle, Smooth, Vascular; Oxidoreductases; Rats; Thromboxane A2; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

Bovine aortic endothelial cells in culture were incubated with endotoxin. The amount of thromboxane A2 synthesized was then determined by a specific radioimmunoassay for thromboxane B2. After a lag of several hours the cells changed their shape and parallel to the change in cell shape release of thromboxane B2 occurred. At 24 h the amount of thromboxane B2 generated in response to endotoxin was 200-fold above baseline. Thromboxane B2 generation could be blocked by aspirin and the specific thromboxane synthetase inhibitor UK 37248. The endotoxin effect was dependent on protein and RNA synthesis as evidenced by the inhibitory action of cycloheximide (1.5 microM) and actinomycin D (2 micron).

Topics: Animals; Aorta; Aspirin; Cattle; Cells, Cultured; Clone Cells; Cycloheximide; Dactinomycin; Endothelium; Endotoxins; Imidazoles; Thromboxane B2; Thromboxanes; Time Factors

14 patients with effort induced angina pectoris were treated with a specific TxB2 inhibitor Dazoxiben or verapamil for two weeks with a wash-out period of 14 days between the two regimens. A sub-maximal bicycle test was performed before treatment and at the end of each treatment period. The bicycle test induced a significant increase in serum TxB2 in patients without treatment and during verapamil therapy. This increase was significantly inhibited by Dazoxiben treatment. No alterations in plasma TxB2 or 6-keto-PGF1 alpha were observed on either regimen. Dazoxiben had no clinical effect, while verapamil caused a highly significant prolongation of exercise time.

Topics: Aged; Angina Pectoris; Exercise Test; Female; Humans; Imidazoles; Male; Middle Aged; Oxidoreductases; Prostaglandins; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes; Verapamil

The effects of two thromboxane synthetase inhibitors ( dazoxiben and UK 38485) were investigated on the cardiovascular and metabolic effects of Escherichia coli endotoxin infusion in the conscious, unrestrained rat. Infusion of E. coli endotoxin (41.7 ng kg-1 min-1) for 4 h produced a fall in mean arterial pressure, an increase in heart rate, a transient hyperglycaemia (at 1 h) followed by hypoglycaemia (evident at 6 h), an elevation in plasma lactate and a profound thrombocytopenia. The above changes were accompanied by a marked elevation in plasma thromboxane B2 concentrations (e.g. endotoxin-treated 935 +/- 150 pg ml-1 at 1 h compared with pre-endotoxin values of 125 +/- 30 pg ml-1). The administration of either dazoxiben (30 mg kg-1 i.v., given 30 min before starting the endotoxin infusion) or UK 38485 (15 mg kg-1 given 30 min before, and again 4 h after, starting the endotoxin infusion) prevented the rise in plasma thromboxane B2 concentrations. Neither dazoxiben nor UK 38485 prevented the metabolic, cardiovascular or thrombocytopenic effects of endotoxin and did not modify mortality. These results suggest that, although large amounts of thromboxane are generated in response to endotoxin, they do not play an important role in the major pathophysiological consequences of acute endotoxaemia.

Topics: Animals; Blood Glucose; Blood Pressure; Escherichia coli; Heart Rate; Imidazoles; Lactates; Lactic Acid; Male; Platelet Count; Rats; Rats, Inbred Strains; Shock, Septic; Thromboxane B2; Thromboxanes

The amounts of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) and thromboxane B2 (TxB2) produced by the endothelial surfaces of paired samples of human pulmonary arteries and veins, obtained from patients undergoing thoracic surgery, were measured. The amounts of 6-keto-PGF1 alpha and TxB2 produced by arteries compared with veins were not different. However, both arteries and veins produced more 6-keto-PGF1 alpha than TxB2, the ratio being approximately 7.5:1 for both. 6-keto-PGF1 alpha synthesis by arteries was significantly correlated with that produced by veins but the relative amounts of TxB2 were not correlated. 6-keto-PGF1 alpha synthesis was correlated with TxB2 synthesis for veins but not for arteries. 8 of the 12 arterial samples exhibited some degree of intimal fibrosis. Incubation with the thromboxane synthase inhibitor, dazoxiben , caused a significant inhibition of vascular TxB2 synthesis and a significant increase in 6-keto-PGF1 alpha synthesis. In 3 of the 5 cases the increase in 6-keto-PGF1 alpha was too large to be explained by the fall in TxB2.

Topics: 6-Ketoprostaglandin F1 alpha; Endothelium; Epoprostenol; Humans; Imidazoles; Oxidoreductases; Pulmonary Artery; Pulmonary Veins; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

The mode of action of BM 13.177 (4-[2-(benzenesulfonamido)-ethyl] phenoxyacetic acid), a new anti-aggregating and anti-thrombotic agent, was studied in human washed platelets and citrated PRP. With ASA-treated platelets, BM 13.177 (0.1 - 100 microM) did not inhibit the shape change and the aggregation induced by ADP, serotonin, adrenaline, thrombin, or collagen. Therefore, BM 13.177 is neither an antagonist of ADP, serotonin, adrenaline, thrombin, or collagen nor a common pathway inhibitor like PGE1, or an inhibitor of the platelet interactions during aggregation. However, BM 13.177 (greater than or equal to 0.1 microM) produced a dose-dependent reduction of shape change, aggregation and release of [3H]serotonin induced by the stable PGH2 analogues U 46619 and U 44069 in ASA-treated platelets or ASA-treated citrated PRP. In untreated platelets, BM 13.177 inhibited platelet activation by U 46619 or U 44069 and by exogenous arachidonic acid or by endogenous arachidonic acid mobilized by hydrogen peroxide. Consequently, the ADP- and adrenaline-induced secondary aggregation and [3H]serotonin release in citrated PRP and the major effects of collagen were also inhibited. In washed platelets treated with 10 microM arachidonic acid or 100 microM hydrogen peroxide, the formation of TXB2 was not inhibited by 10 microM BM 13.177. However, the TXB2 formation after stimulation with 1,200 microM hydrogen peroxide was partially reduced by BM 13.177 to the same extent as by PGE1. This reduction may be due to the absence of a secondary release of arachidonic acid from phospholipids if the platelets were prevented from activation by BM 13.177 or PGE1. Arachidonic acid and hydrogen peroxide also induced the shape change, aggregation and release of washed platelets when thromboxane formation was inhibited by dazoxiben. Under these conditions, BM 13.177 was able to abolish the platelet response which was due to accumulating prostaglandin endoperoxides. These results show that BM 13.177 acts as a selective antagonist of TXA2 and prostaglandin endoperoxides. Its inhibitory effect on platelet function does not depend on an inhibition of either the primary release of arachidonic acid or the activities of cyclooxygenase or thromboxane synthetase.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Arachidonic Acid; Arachidonic Acids; Blood Platelets; Collagen; Dose-Response Relationship, Drug; Epinephrine; Humans; Hydrogen Peroxide; Imidazoles; Indomethacin; Platelet Aggregation; Prostaglandin Endoperoxides, Synthetic; Prostaglandins E; Serotonin; Sulfonamides; Thromboxane A2; Thromboxane B2; Thromboxanes

Dazoxiben, a specific thromboxane synthetase inhibitor, was evaluated in 21 patients with Raynaud's phenomenon in a double-blind, placebo-controlled crossover experiment. Total fingertip blood flows were measured by plethysmography and capillary blood flows were measured by 133Xe disappearance rate. Subjects were studied in both a warm (28 degrees) and a cold (20 degrees) room. Arteriovenous (AV) shunt flow was estimated by subtraction of capillary flow from total flow. Ex vivo production of thromboxane B2 (TXB2) and 6-keto PGF1 alpha was determined by specific radioimmunoassay in serum from venous blood incubated for 1 hr (37 degrees). Plasma concentrations of TXB2 and 6-keto PGF1 alpha were also monitored. Dazoxiben (100 mg 4 times a day for 14 days) inhibited ex vivo TXB2 production (from 463.1 +/- 69.9 to 101.8 +/- 13.4 ng/ml/hr; (means +/- SE], enhanced ex vivo 6-keto PGF1 alpha production (from 1.38 +/- 0.05 to 3.76 +/- 0.18 ng/ml/hr), reduced plasma TXB2 concentration (from 88.1 +/- 13.9 to 38.8 +/- 5.9 pg/ml). There were no changes in plasma concentration of 6-keto PGF1 alpha. Dazoxiben did not improve total digital blood flow, capillary flow, AV shunt flow, or forearm blood flow at 28 degrees or 20 degrees. There was no subjective improvement in frequency or severity of Raynaud's attacks (assessed by patient diaries). It is concluded that dazoxiben is a potent and specific thromboxane synthetase inhibitor capable of altering arachidonic acid metabolism, but is of little or no benefit in the treatment of Raynaud's phenomenon.

Topics: 6-Ketoprostaglandin F1 alpha; Adult; Aged; Arachidonic Acid; Arachidonic Acids; Double-Blind Method; Drug Evaluation; Female; Forearm; Humans; Imidazoles; Male; Middle Aged; Plethysmography; Radioimmunoassay; Raynaud Disease; Thromboxane B2

Radioimmunoassay (RIA) and high-resolution gas chromatography-mass spectrometry (HRGC-MS) were compared for the determination of serum 6-keto-PGF-1 alpha and TXB2 in a situation of drug-altered arachidonate metabolism. Results were comparable for TXB2 in both conditions. 6-keto-PGF1 alpha RIA determinations (with two different antisera) revealed increased levels in dazoxiben-treated samples, which were not confirmed by HRGC-MS. The assay were repeatedly checked in controlled conditions to investigate these discrepancies. Interference was found with both antisera, due to the drug-induced change in metabolism.

Topics: 6-Ketoprostaglandin F1 alpha; Arachidonic Acid; Arachidonic Acids; Gas Chromatography-Mass Spectrometry; Humans; Imidazoles; In Vitro Techniques; Oxidoreductases; Radioimmunoassay; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

The leukotriene-dependent component of C5adesArg-induced contractile activity on guinea pig lung parenchymal strips is inhibited by cyclooxygenase inhibitors. Indomethacin simultaneously increased leukotriene release while inhibiting both cyclooxygenase-dependent mediator release and the contractile force generated. Tissue responses to LTC4 and LTD4 are also inhibited by cyclooxygenase blockade, while contractions induced by the thromboxane A2 analog, U-46619, histamine or acetylcholine are not affected. These data indicate a functional role for cyclooxygenase metabolites in leukotriene-induced contractile responses in lung.

Topics: Animals; Anti-Inflammatory Agents, Non-Steroidal; Aspirin; Complement C5; Complement C5a, des-Arginine; Cyclooxygenase Inhibitors; Dinoprost; Dinoprostone; Dose-Response Relationship, Drug; Guinea Pigs; Imidazoles; Indomethacin; Lung; Muscle Contraction; Piroxicam; Prostaglandins E; Prostaglandins F; SRS-A; Thiazines; Thromboxane B2

Pharmacologic inhibition of thromboxane (TX) synthase can result in redirection of prostaglandin (PG) endoperoxide metabolism, possibly affecting platelet, vascular and renal function. This study explores the in vitro, ex vivo and in vivo effects of dazoxiben, an orally active TX-synthase inhibitor, on platelet and renal TXB2 production and associated changes in PG-endoperoxide metabolism. Dazoxiben inhibits TXB2 production in clotting human whole blood with an IC50 of 0.3 micrograms/ml and causes parallel enhancement of PGE2 greater than PGF2 alpha greater than 6-keto-PGF1 alpha production. Similar redirection of PG-endoperoxide metabolism is observed ex vivo, after the oral administration of 1.5 and 3.0 mg/kg to six healthy volunteers. Plasma 6-keto-PGF1 alpha ranges between less than 4 and 8 pg/ml during the first 3 h. Urinary TXB2 excretion, a reflection of renal TXA2 production, is significantly reduced by 30% with no evidence of redirection of renal PG-endoperoxide metabolism. In vitro inhibition of TXB2 production in rat kidney glomeruli requires significantly higher dazoxiben concentration (IC50 = 1.60 micrograms/ml) than in rat whole blood (IC50 = 0.32 micrograms/ml) and is not associated with changes in PGE2, PGF2 alpha and 6-keto-PGF1 alpha production. These results demonstrate quantitatively and qualitatively diverse effects of dazoxiben in different TXA2-producing cells and suggest the possibility of developing tissue-selective TX-synthase inhibitors.

Topics: Adult; Animals; Blood Platelets; Dose-Response Relationship, Drug; Female; Humans; Imidazoles; Kidney; Male; Oxidoreductases; Prostaglandin Endoperoxides; Rats; Thromboxane B2; Thromboxane-A Synthase; Time Factors

The effects of a cyclooxygenase inhibitor (indomethacin), a thromboxane synthetase inhibitor (dazoxiben), and a thromboxane antagonist (EPO45) on rabbit platelet aggregation induced by collagen were studied and compared with effects on platelet uptake both by damaged rabbit aorta and by collagen-coated glass. Platelet aggregation and associated release of serotonin were inhibited to a similar extent both by indomethacin and EPO45. Dazoxiben had a minimal inhibitory effect on aggregation but reduced the release of serotonin by about 40% compared with control. Platelet uptake onto collagen-coated glass was markedly reduced both by indomethacin and EPO45 but not by dazoxiben. In contrast, EPO45 and dazoxiben were equally effective in reducing platelet adhesion to damaged rabbit aorta. At the concentrations used for adhesion studies the formation of thromboxane B2 was reduced both by dazoxiben and by indomethacin (both greater than 95% inhibition compared with control) and to a lesser extent by EPO45 (less than 40% inhibition). The results indicate that thromboxane A2 (and cyclic endoperoxide) released by adherent platelets may enhance thromboxane synthesis and promote platelet uptake both onto collagen-coated glass and onto damaged rabbit aorta. In the presence of vascular tissue, cyclic endoperoxides are readily metabolized and thereby removed. The potential antithrombotic activity of TXA2 synthetase inhibitors could be impaired in situations in which endoperoxide clearance is limited (e.g., accompanying platelet uptake onto artificial surfaces) but not at the damaged vessel wall. Thus, both inhibitors and antagonists are likely to have similar potency as antithrombotic agents in vivo.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Collagen; Imidazoles; In Vitro Techniques; Indomethacin; Male; Muscle, Smooth, Vascular; Platelet Adhesiveness; Platelet Aggregation; Prostaglandins, Synthetic; Rabbits; Serotonin; Thromboxane B2

Topics: 6-Ketoprostaglandin F1 alpha; Chemical Phenomena; Chemistry, Physical; Gas Chromatography-Mass Spectrometry; Humans; Imidazoles; Immunoassay; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

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

Urinary excretion of the vasoconstrictor metabolite thromboxane B2 is increased in some patients with the hepatorenal syndrome. To define the role of thromboxanes in this syndrome and to evaluate a potential treatment for the renal impairment, we administered the thromboxane synthetase inhibitor dazoxiben to 5 patients with alcoholic hepatitis and rapidly progressive renal failure. Dazoxiben 200 mg/day followed by 400 mg/day reduced urinary thromboxane B2 by approximately 50% without altering prostaglandin E2 or 6-keto prostaglandin F1 alpha and without improving creatinine clearance (6 +/- 2 to 6 +/- 3 ml/min). In 3 additional patients, a higher dose of dazoxiben of 600 mg/day reduced thromboxane B2 by approximately 75% without consistent improvement in renal function. Thus, as judged by selective thromboxane inhibition with dazoxiben, thromboxanes are unlikely to be the key renal vasoconstrictor factor in the hepatorenal syndrome.

Topics: 6-Ketoprostaglandin F1 alpha; Acute Kidney Injury; Adult; Creatinine; Dinoprostone; Drug Evaluation; Hepatitis, Alcoholic; Humans; Imidazoles; Middle Aged; Oxidoreductases; Prostaglandins E; Syndrome; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Endotoxins; Epoprostenol; Fibrin; Imidazoles; Indomethacin; Jaundice; Kidney; Male; Rats; Rats, Inbred Strains; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

1 The effects of a selective thromboxane synthetase inhibitor, dazoxiben (UK 37248), on haemodynamics, eicosanoid levels, and lung vascular permeability were assessed in three unanesthetized goats with chronic lung lymph fistulae following infusions of E. coli endotoxin (1 microgram/kg). Each animal received an infusion of endotoxin in both a control and treatment trial. In the control trial endotoxin alone was infused. In the treatment trial endotoxin administration was preceded by a bolus intravenous infusion of dazoxiben 25 mg/kg followed by a maintenance infusion of 10 mg/kg/h. 2 In animals receiving endotoxin alone the peak elevation in pulmonary artery and wedge pressures, the initial increase in lymph flow, and the fall in cardiac output correlated with the peak elevation in plasma thromboxane B2 (TXB2) concentration at 30 min after endotoxin. Although TXB2 levels had returned to baseline by 3 h, lung lymph flow remained elevated for at least 6 h after endotoxin. The lymph/plasma protein ratio (L/P) did not fall. 3 In dazoxiben-treated animals the rise in plasma concentrations of TXB2 after endotoxin was prevented and, in concert, the increase in pulmonary artery and wedge pressures, the fall in cardiac output, and the initial increase in lymph flow were greatly attenuated. The increase in lymph flow at 2-6 h after endotoxin, however, was not prevented in dazoxiben-treated animals, and again L/P did not change. 4 Plasma 6-keto-prostaglandin F1 alpha concentrations were not significantly altered by dazoxiben treatment except for an earlier peak. 5 We conclude that selective total inhibition of thromboxane synthesis can be achieved by dazoxiben. The inhibition ameliorates many of the adverse haemodynamic consequences of experimental endotoxaemia and reduces, but does not prevent pulmonary oedema formation. This seems to be due to an increase in lung microvascular permeability which is not mediated by TXA2.

Topics: Animals; Endotoxins; Escherichia coli; Goats; Hemodynamics; Imidazoles; Lung; Lymphatic System; Oxidoreductases; Pulmonary Circulation; Thromboxane B2; Thromboxane-A Synthase; Time Factors

1 The effects of acute pretreatment with the thromboxane synthetase inhibitor dazoxiben 5 mg/kg intravenously (UK 37248-01) were examined on the acute pulmonary responses of pentobarbitone-anaesthetized cats to E. coli endotoxin 2 mg/kg intravenously. 2 E. coli endotoxin in control, untreated, cats resulted in a marked pulmonary hypertension, an increase in intra-tracheal pressure (at a constant pulmonary inflation volume), an increase in both pulmonary arterial and aortic concentrations of thromboxane B2 (TXB2) and a reduction in systematic arterial PO2. 3 Dazoxiben prevented, or markedly reduced, the endotoxin-induced pulmonary release of TXB2, the decrease in systematic arterial PO2 and the pulmonary arterial hypertension, but did not modify the increase in intratracheal pressure. 4 These results may suggest that TXA2 is responsible for the endotoxin-induced pulmonary arterial hypertension but that some other arachidonic acid derivative (prostaglandin F2 alpha) is responsible for the reduced lung compliance that follows the acute administration of E. coli endotoxin.

Topics: Anesthesia; Animals; Cats; Endotoxins; Escherichia coli; Female; Hydrogen-Ion Concentration; Imidazoles; Lung; Male; Oxidoreductases; Thromboxane B2; Thromboxane-A Synthase; Time Factors

Platelet adhesion to rabbit aortic subendothelium or collagen-coated glass was quantitated in a rotating probe device by uptake of radio-labelled platelets. Under conditions in which aspirin had no effect, dazoxiben, a selective inhibitor of thromboxane synthetase, reduced platelet adhesion to aortic subendothelium by about 40% but did not affect adhesion to collagen-coated glass. Pre-treatment of aortic segments with 15-HPETE, a selective inhibitor of PGI2-synthetase, abolished the inhibitory effect of dazoxiben on adhesion. Concentrations of 6-oxo-PGF1 alpha in the perfusate were raised in the presence of dazoxiben alone, and following addition of thrombin (10 units/ml) there was a 2--3 fold increase in concentration. Perfusion of damaged aorta with platelets labelled with (14C)-arachidonic acid in the presence of thrombin and dazoxiben resulted in the appearance of (14C)-labelled-6-oxo-PGF1 alpha. Inhibition of thromboxane synthetase limits platelet adhesion probably by promoting vascular synthesis of PGI2 from endoperoxides liberated from adherent platelets, which subsequently promotes detachment of cells from the surface.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Aorta; Epoprostenol; Imidazoles; Male; Oxidoreductases; Platelet Adhesiveness; Rabbits; Thrombin; Thromboxane B2; Thromboxane-A Synthase

Five rabbits treated with the thromboxane synthetase inhibitor Dazoxiben and five control rabbits received pig renal xenografts. Plasma albumin, complement factor C3, TXB2, 6-keto-PGF1 alpha, and serum TXB2 and 6-keto-PGF1 alpha were determined before and 1/2 hour after transplantation. The xenograft survival was significantly decreased in the Dazoxiben treated animals compared to the placebo treated animals determined as time to total cyanosis of the graft, total urine production, and time to stop of urine production. Lack of TXB2 production during blood coagulation confirmed inhibition of platelet thromboxane synthesis. The other determined variables showed no significant differences between the treated and the placebo animals.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Blood Platelets; Drug Evaluation, Preclinical; Graft Survival; Imidazoles; Kidney Transplantation; Rabbits; Swine; Thromboxane B2; Thromboxane-A Synthase; Transplantation, Heterologous

1 The effects of the thromboxane synthetase inhibitor dazoxiben (UK 37248) on arachidonic acid and collagen-induced platelet aggregation and arachidonate acid metabolism were studied both in vitro and ex vivo in the presence and absence of sources of prostaglandin I2 synthetase. 2 In platelets activated by exogenous arachidonic acid, the anti-aggregatory activity of dazoxiben was weak compared with indomethacin, despite comparable inhibition of TXB2 production. This was due to the accumulation of pro-aggregatory metabolites, principally endoperoxides. 3 The anti-aggregatory activity of dazoxiben, both in vitro and ex vivo, was higher and more consistent when platelets were stimulated by collagen, threshold levels of which resulted in an endoperoxide accumulation only 2-3% of that achieved with exogenous arachidonic acid. 4 The anti-aggregatory activity of dazoxiben is enhanced if drug equilibration is facilitated by prolonging the preincubation time from 2 to 15 minutes. 5 Incubation of platelets with pig aortic microsomes, which act both as aggregant and a source of PGI2 synthetase, facilitates the conversion to PGI2 of some endoperoxides accumulated after dazoxiben, resulting in augmented anti-aggregatory activity. 6 Leukocytes as well as blood vessels have the capacity to generate PGI2 from platelet derived endoperoxides. This was demonstrated by the increases in 6-keto-PGF1 alpha accompanying decreased TXB2 production in clotted whole blood from volunteers treated with dazoxiben. 7 It was concluded that a closer approach to in vivo conditions allowing a fuller expression of the mechanism of action of dazoxiben could be achieved in vitro by stimulating platelets with a pathophysiological activator such as collagen in the presence of a source of PGI2 synthetase.

Topics: Animals; Arachidonic Acid; Arachidonic Acids; Blood Platelets; Dinoprostone; Epoprostenol; Humans; Imidazoles; In Vitro Techniques; Indomethacin; Oxidoreductases; Platelet Aggregation; Prostaglandins E; Rabbits; Thromboxane B2; Thromboxane-A Synthase

The effects of the thromboxane synthetase inhibitor dazoxiben on thrombus formation, platelet aggregation and vascular reactivity have been studied in open-chest anesthetized dogs. Dazoxiben at 4 mg/kg prolonged the time required for occlusive thrombi to form at sites of electrical injury to the left circumflex coronary artery by 3-fold and also decreased venous thromboxane B2 concentrations by 45% within 30 min. The progressive decline in flow observed during thrombogenesis was interrupted by rapid and spontaneous reactive hyperemic responses, the frequency and number of which were diminished by dazoxiben. In vitro platelet aggregation responses to ADP and collagen determined during the course of these experiments also were inhibited to a variable extent. The effect of dazoxiben on coronary vascular responsiveness was examined using an in situ constant pressure perfused coronary vascular bed. Although basal left circumflex coronary blood flow was unaffected by the drug, vasodilation induced by arachidonic acid, but not prostacyclin, was potentiated. The data suggest that dazoxiben possesses in vivo antithrombotic activity due to modification of platelet reactivity and that it can enhance coronary vasodilator responses to exogenously administered arachidonic acid.

Topics: Animals; Arachidonic Acid; Arachidonic Acids; Coronary Circulation; Coronary Disease; Coronary Vessels; Dogs; Dose-Response Relationship, Drug; Hyperemia; Imidazoles; Male; Oxidoreductases; Platelet Aggregation; Thromboxane B2; Thromboxane-A Synthase; Time Factors; Vasodilation

We have developed an experimental model for the study of local prostaglandin production by platelets and the vessel wall following stimulation 'in vivo'. A nylon thread was inserted into the external jugular vein of rabbits; its presence did not induce an occluding thrombus. Thromboxane (TXB2) values in the blood, sampled through the facial vein, immediately distal to the stimulus, rose and remained high for at least 4 hr, while 6-keto prostaglandin (PG) F1 alpha levels, after a first increase, gradually returned to normal ('exhaustion' of the endothelial cells?). No changes were observed in the contralateral jugular vein without thread. After infusion via the femoral vein of 10 mg/kg dazoxiben, a thromboxane synthetase inhibitor, local TXB2 production was completely abolished, whereas 6-keto PGF1 alpha formation no longer returned to basal values, but tended to increase. This leads to the conclusion that upon inhibition of TXB2 formation endoperoxide metabolism is reoriented 'in vivo' towards prostacyclin, and this mainly at the site where platelets are activated. Injection of 100 mg/kg lysine acetylsalicylic acid resulted in complete inhibition of TXB2 and 6-keto PGF1 alpha formation, the latter, however, slowly recovering with time. The administration of nafazatrom to the animals did not influence the local TXB2 changes, but partially prevented the decline of 6-keto PGF1 alpha with time. The antithrombotic properties of this drug thus could be related to protection of the endothelial cells from 'exhaustion'.

Topics: Animals; Aspirin; Dinoprost; Drug Interactions; Fibrinolytic Agents; Functional Laterality; Imidazoles; Kinetics; Male; Prostaglandins F; Pyrazoles; Pyrazolones; Rabbits; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

To determine if inhibition of a rabbit aorta contracting substance (RCS) corresponds to inhibition of thromboxane synthetase human washed platelets were stimulated with thrombin. RCS formation was bioassayed on rabbit aorta strips in Tyrode solution containing selective blocking agents and thromboxane (TX)B2 in the same probes by specific radioimmunoassay. Dazoxiben inhibited the formation of TXB2 but not of RCS, whereas indomethacin inhibited both RCS and TX formation. The data indicate that the rabbit aorta cannot be used alone to predict inhibition of TX formation with specific TX synthetase inhibitors.

Topics: Animals; Blood Platelets; Humans; Imidazoles; In Vitro Techniques; Indomethacin; Rabbits; Thromboxane A2; Thromboxane B2; Thromboxanes

1 Thromboxane B2 (TXB2) levels were measured in three sites (coronary sinus, pulmonary artery, and femoral artery) at rest and during atrial pacing in 11 patients with stable angina pectoris. 2 There was a highly significant increase in arterial TXB2 on pacing (by up to 820 pg/ml) but there was no change in the thromboxane levels at the other two sites. 3 Dazoxiben 200 mg orally abolished the increase in arterial TXB2, but had no effect on systemic, pulmonary or coronary haemodynamics, no effect on myocardial metabolism and a variable effect on atrial pacing time to angina.

Topics: Aged; Angina Pectoris; Cardiac Pacing, Artificial; Hemodynamics; Humans; Imidazoles; Male; Middle Aged; Myocardium; Oxidoreductases; Thromboxane B2; Thromboxane-A Synthase; Time Factors

1 Plasma thromboxane levels were obtained from both the coronary sinus and aorta in patients with stable angina pectoris paced to angina, and in unstable angina patients before and after dazoxiben 100 mg. 2 Although there was a wide range of values in the different groups, dazoxiben significantly reduced plasma thromboxane levels in all patients. 3 Dazoxiben had no adverse effect on coronary and systemic haemodynamics, and atrial pacing time to angina was increased from 245 +/- 41 to 308 +/- 48s (P less than 0.01).

Topics: Adult; Aged; Angina Pectoris; Coronary Circulation; Coronary Disease; Hemodynamics; Humans; Imidazoles; Middle Aged; Myocardium; Oxidoreductases; Platelet Aggregation; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

1 Acute thrombosis was induced in the carotid arteries of anaesthetized rabbits by local electrical stimulation (1 mA for 2 min) of the vessel wall. Histological findings confirmed the platelet-rich composition of the thrombus. Platelet accumulation at the stimulus site was quantitated with 111Indium-labelling of autologous platelets. 2 In rabbits injected intravenously with either the thromboxane synthetase inhibitor dazoxiben 2 mg/kg or aspirin 10 mg/kg, accumulation of labelled platelets was considerably reduced. Animals which received vehicle injection only, showed no such reduced thrombus formation. 3 In separate experiments in anaesthetized rabbits, the levels of thromboxane B2 (TXB2) and 6-keto-prostaglandin F1 alpha in clotting blood were measured in blood samples taken from animals which had received the above drug treatments. Aspirin markedly reduced the production of both arachidonate metabolites. In contrast, dazoxiben almost totally inhibited TXB2 production but caused a 3.5-fold increase in the levels of 6-keto PGF1 alpha. 4 These findings demonstrate an antithrombotic effect and confirm the mechanistic selectivity of a thromboxane synthetase inhibitor.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Aspirin; Blood Platelets; Electric Stimulation; Imidazoles; Indium; Male; Oxidoreductases; Rabbits; Radioisotopes; Thrombosis; Thromboxane B2; Thromboxane-A Synthase

Leukotriene D4 (LTD4) administered intravenously to anesthetized, spontaneously breathing guinea pigs elicited decreases in dynamic lung compliance (Cdyn) and airway conductance (GAW) with a maximal response achieved at 0.5 min. Simultaneously, plasma levels of the thromboxane metabolite, TxB2, and the prostacyclin metabolite, 6-keto-PGF1 alpha, increased 10-fold over pre-LTD4 levels. Pretreatment of the guinea pigs with meclofenamic acid delayed the onset of the LTD4-induced bronchoconstriction, antagonized the magnitude of the decreases in Cdyn and GAW, and blocked the increase in plasma TxB2 and 6-keto-PGF1 alpha levels. The thromboxane synthetase inhibitor, UK 37,248, suppressed the LTD4-induced bronchoconstriction, while it completely blocked TxB2 production without significantly affecting 6-keto-PGF1 alpha. The SRS-A end organ antagonist, FPL 55712, blocked both the LTD4-induced bronchoconstriction and the production of the arachidonic acid metabolites. These results suggest that thromboxane A2 plays an important role in mediating part of the bronchoconstriction elicited by intravenously administered LTD4 in the guinea pig.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Bronchi; Chromones; Guinea Pigs; Imidazoles; Meclofenamic Acid; SRS-A; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

N(7-Carboxyheptyl) imidazole, 4-[2-(1H-imidazol-1-yl) ethoxy] benzoic acid (dazoxiben) and imidazo [1,5-alpha] pyridine-5-hexanoic acid (CGS 13080) are potent selective inhibitors of platelet thromboxane synthetase that have little or no effect on the cyclooxygenase activity. Oral doses of the substances given to rats inhibited platelet thromboxane B2 production induced by intra-venous administration of collagen (100 micrograms/kg). Plasma concentrations of immunoreactive 6-keto PGF1 alpha in treated animals were increased above corresponding concentrations in untreated animals. There were small effects on the thrombocytopenia with CGS 13080 and carboxyheptylimidazole but not with dazoxiben. However these results did not always achieve statistical significance. Confirmation that the immunoreactive prostaglandin measured was actually 6-keto PGF1 alpha was obtained by the facts that indomethacin abolished its appearance in plasma and that the other prostaglandins were not present in sufficient quantities to cross-react with the antiserum to 6-keto PGF1 alpha. Two different antisera to 6-keto PGF1 alpha detected the same changes. Administration of thromboxane synthetase inhibitors to rats causes redirection of prostaglandin production from thromboxane to prostacyclin when platelets are stimulated with collagen in vivo.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Blood Platelets; Collagen; Imidazoles; Indoles; Indomethacin; Male; Oxidoreductases; Pyridines; Radioimmunoassay; Rats; Rats, Inbred Strains; Thrombocytopenia; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

The delayed clearance of endotoxins in obstructive jaundice may cause renal impairment by inducing renal vasoconstriction and glomerular fibrin deposition as a consequence of intravascular coagulation. As endotoxins activate arachidonic acid metabolism we have examined the effects of selective inhibitors on mortality, plasma TXB2 and 6-oxo-PGF1 alpha production and renal fibrin deposition in rats with obstructive jaundice following endotoxin administration. Jaundiced rats had a high mortality following endotoxin--58 per cent at 4 h and 83 per cent at 24 h. Pretreatment with indomethacin 3 mg/kg i.p., dazoxiben 3 mg i.p. or prostacyclin 300 ng/kg i.v. produced significant improvements in survival. Endotoxaemia was associated with significant elevations of plasma TXB2 and early inhibition of plasma 6-oxo-PGF1 alpha generation. Renal fibrin deposition, assessed using indirect immunofluorescence and a 125I-labelled fibrinogen uptake ratio, occurred in jaundiced kidneys following endotoxin and could be prevented using indomethacin, dazoxiben and prostacylin. These results suggest that endotoxin-induced TXA2 production can cause renal fibrin deposition in obstructive jaundice, thus contributing in the pathogenesis of the renal impairment.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Cholestasis; Endotoxins; Epoprostenol; Escherichia coli; Fibrin; Imidazoles; Indomethacin; Kidney; Male; Prostaglandins; Rats; Rats, Inbred Strains; Thromboxane B2

Arachidonic acid (0.2-0.8 mM) retracts clots formed in human citrated platelet-rich plasma by batroxobin. Extracellular calcium ions, but not the secretion of ADP by platelets, are required. AA-induced clot-retraction requires cyclo-oxygenase but not thromboxane synthetase activity since the retraction is inhibited by aspirin but not by selective inhibitors of thromboxane synthesis. The data indicate that endogenous cyclic endoperoxides mediate the retraction. Moreover, intact endoperoxide/thromboxane receptors also seem to be necessary because clot retraction is inhibited by thromboxane receptor antagonists.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Alprostadil; Arachidonic Acid; Arachidonic Acids; Aspirin; Blood Platelets; Clot Retraction; Epoprostenol; Fatty Acids, Unsaturated; Fibrin; Humans; Imidazoles; Prostaglandin Endoperoxides; Prostaglandin Endoperoxides, Synthetic; Prostaglandins D; Prostaglandins E; Prostaglandins H; Prostaglandins, Synthetic; Thromboxane B2

Acute thrombosis was induced in the carotid arteries of anaesthetised rabbits by local electrical stimulation (1mA for 2 min) of the vessel wall. Histological findings confirmed the platelet-rich composition of the thrombus. Platelet accumulation at the stimulus site was quantitated with "'Indium-labelling of autologous platelets. In rabbits injected intravenously with either 2 mg/kg dazoxiben or 10 mg/kg aspirin, accumulation of labelled platelets was considerably reduced. Animals which received vehicle injection only, showed no such reduced thrombus formation. In separate experiments in anaesthetised rabbits, the levels of TxB2 and 6KPGF1 alpha in clotting blood were measured in blood samples taken from animals which had received the above drug treatments. Aspirin markedly reduced the production of both arachidonate metabolites. In contrast, dazoxiben almost totally inhibited TxB2 production but caused a 3.5 fold increase in the levels of 6KPGF1 alpha. These findings demonstrate an anti-thrombotic effect and confirm the mechanistic selectivity of a thromboxane synthetase inhibitor.

Topics: 6-Ketoprostaglandin F1 alpha; Acute Disease; Animals; Aspirin; Carotid Artery Thrombosis; Cells, Cultured; Enzyme Inhibitors; Fibrinolytic Agents; Imidazoles; In Vitro Techniques; Oxidoreductases; Platelet Aggregation; Rabbits; Thromboxane B2; Thromboxane-A Synthase

Pairs of healthy male volunteers received single oral doses (5-200 mg) of UK-37,248-01, a selective thromboxane synthetase inhibitor. Measurement of total thromboxane B2 (TXB2) concentrations in serum from venous blood showed that production of TXB2 was inhibited in a dose-related manner, with peak inhibition 1 h after doses of 50 mg and above. After 100 mg and 200 mg doses TXB2 production was inhibited by more than 90% at 1 h and about 50% at 6 h. Plasma drug assays confirmed oral absorption. About one-third of the dose was excreted unchanged in the urine, most within the first 4 h. Small and transient increases in bleeding time (within the normal range, except in one subject) were seen after the 50, 100, and 200 mg doses and corresponded to low levels of TXB2 production; whole blood clotting time was unchanged. There were no clinically relevant changes in heart rate or blood-pressure, other than a transient reduction in standing systolic blood-pressure and heart rate in one subject who received 200 mg. There were no side-effects and routine laboratory tests revealed no important abnormalities.

Topics: Administration, Oral; Adult; Dose-Response Relationship, Drug; Hemodynamics; Humans; Imidazoles; Male; Middle Aged; Oxidoreductases; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

Topics: Animals; Arachidonic Acid; Arachidonic Acids; Blood Pressure; Death, Sudden; Electrocardiography; Heart Rate; Imidazoles; Male; Oxidoreductases; Prostaglandins F; Pulmonary Artery; Rabbits; Serotonin; Thromboxane A2; Thromboxane B2; Thromboxane-A Synthase; Vasoconstrictor Agents