thromboxane-a2 and sulotroban

Thromboxane A2 (TXA2) and prostacyclin (PGI2) are two labile products formed from arachidonic acid by the way of cyclooxygenase. An overproduction of thromboxane A2 has been detected in a series of diseases whereby this prostanoid is assumed to contribute to the underlying pathomechanisms by its potent stimulation of platelet aggregation and smooth muscle contraction. This increased TXA2 biosynthesis is frequently accompanied by a stimulation of prostacyclin formation which is one of the most potent inhibitors of platelet aggregation and smooth muscle contraction. Therefore, TXA2 / prostaglandin endoperoxide H2 receptor antagonists, thromboxane synthase inhibitors and drugs which combine both activities have been developed with the aim to suppress the formation and/or the action of thromboxane A2. Since prostacyclin has been demonstrated to counterbalance the pathological effects of TXA2, several PGI2 agonists have also been developed. This review will highlight the evolution and some of the latest findings in the field of prostacyclin and thromboxane A2 modulators mainly those which are under clinical evaluation or marketed.

Topics: Enzyme Inhibitors; Epoprostenol; Fibrinolytic Agents; Humans; Imidazoles; Receptors, Thromboxane; Sulfonamides; Thromboxane A2; Thromboxane-A Synthase

Antithromboxane therapy with aspirin reduces acute procedural complications of coronary angioplasty (PTCA) but has not been shown to prevent restenosis. The effect of chronic aspirin therapy on long-term clinical events after PTCA is unknown, and the utility of more specific antithromboxane agents is uncertain. The goal of this study was to assess the effects of aspirin (a nonselective inhibitor of thromboxane A2 synthesis) and sulotroban (a selective blocker of the thromboxane A2 receptor) on late clinical events and restenosis after PTCA.. Patients (n = 752) were randomly assigned to aspirin (325 mg daily), sulotroban (800 mg QID), or placebo, started within 6 hours before PTCA and continued for 6 months. The primary outcome was clinical failure at 6 months after successful PTCA, defined as (1) death, (2) myocardial infarction, or (3) restenosis associated with recurrent angina or need for repeat revascularization. Neither active treatment differed significantly from placebo in the rate of angiographic restenosis: 39% (73 of 188) in the aspirin-assigned group, 53% (100 of 189) in the sulotroban group, and 43% (85 of 196) in the placebo group. In contrast, aspirin therapy significantly improved clinical outcome in comparison to placebo (P = .046) and sulotroban (P = .006). Clinical failure occurred in 30% (49 of 162) of the aspirin group, 44% (73 of 166) of the sulotroban group, and 41% (71 of 175) of the placebo group. Myocardial infarction was significantly reduced by antithromboxane therapy: 1.2% in the aspirin group, 1.8% in the sulotroban group, and 5.7% in the placebo group (P = .030).. Thromboxane A2 blockade protects against late ischemic events after angioplasty even though angiographic restenosis is not significantly reduced. While both aspirin and sulotroban prevent the occurrence of myocardial infarction, overall clinical outcome appears superior for aspirin compared with sulotroban. Therefore, aspirin should be continued for at least 6 months after coronary angioplasty.

Topics: Angioplasty, Balloon, Coronary; Aspirin; Coronary Angiography; Coronary Disease; Double-Blind Method; Female; Humans; Male; Middle Aged; Platelet Aggregation Inhibitors; Prospective Studies; Recurrence; Sulfonamides; Thromboxane A2; Time Factors; Treatment Outcome

Topics: Acute Disease; Adolescent; Adult; Cold Temperature; Double-Blind Method; Female; Fingers; Humans; Imidazoles; Male; Middle Aged; Prospective Studies; Raynaud Disease; Receptors, Thromboxane; Sulfonamides; Thromboxane A2; Thromboxane-A Synthase; Vasoconstriction

To test the hypothesis that the vasoconstrictor thromboxane A2 may affect renal hemodynamics in lupus nephritis, we examined the short-term effects of a selective thromboxane-receptor antagonist, BM 13,177, and of low-dose aspirin. In a randomized, double-blind, crossover study, 10 patients with biopsy-proved lupus nephritis were given a 48-hour continuous infusion of BM 13,177 or placebo. At base line, seven patients had markedly elevated urinary levels of thromboxane B2, the breakdown product of thromboxane A2. During the infusion of BM 13,177, the inulin clearance rate, which was 68 ml per minute per 1.73 m2 of body-surface area at base line, increased by an average of 24 percent (range, 12 to 47 percent; P less than 0.01). Para-aminohippurate clearance was increased to the same extent, with no change in the filtration fraction. The bleeding time doubled, indicating an occupancy of platelet thromboxane receptors of more than 95 percent. The hemodynamic changes were associated with a significant increase in sodium excretion from 76 to 118 mmol per day (P less than 0.01) but with no change in arterial blood pressure. In another study, 10 additional patients with lupus nephritis were randomly assigned to receive either placebo or 20 mg of aspirin twice daily for four weeks. The aspirin regimen produced a selective, cumulative inhibition of platelet cyclooxygenase activity and a doubling of bleeding time. However, there was no change in the inulin clearance rate and no change in urinary levels of thromboxane B2 or 6-keto-prostaglandin F1 alpha, which are indicators of renal synthesis of thromboxane A2 and prostacyclin, respectively. We conclude that in lupus nephritis, impairment of renal function is at least in part mediated hemodynamically and is reversible with a thromboxane antagonist. Platelets, however, are not a major source of thromboxane A2 synthesis and action within the kidney.

Topics: Adolescent; Adult; Aged; Aspirin; Clinical Trials as Topic; Double-Blind Method; Female; Humans; Kidney; Lupus Nephritis; Male; Middle Aged; Random Allocation; Renal Circulation; Sulfonamides; Thromboxane A2

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

Clinical and experimental evidence has shown that myocardial ischemia activates cardiac spinal afferents that mediate sympathoexcitatory reflex responses. During myocardial ischemia, thromboxane A2 (TxA2) is released in large quantities by activated platelets in the coronary circulation of patients with coronary artery disease. We hypothesized that endogenous TxA2 contributes to sympathoexcitatory reflexes during myocardial ischemia through stimulation of TxA2/prostaglandin endoperoxide (TP) receptors. Regional myocardial ischemia was induced by occlusion of a diagonal branch of left anterior descending coronary artery of anesthetized cats. Hemodynamic parameters and renal sympathetic nerve activity were recorded after sinoaortic denervation and bilateral vagotomy. Regional myocardial ischemia evoked significant increases in mean blood pressure (122+/-10 vs. 139+/-12 mmHg, before vs. ischemia), aortic flow (153+/-18 vs. 167+/-20 ml/min), first derivative of left ventricular pressure at 40-mmHg developed pressure (2,736+/-252 vs. 2,926+/-281 mmHg/s), systemic vascular resistance (0.6+/-0.1 vs. 0.9+/-0.12 peripheral resistance units), and renal sympathetic nerve activity (by 22%). The reflex nature of the excitatory responses was confirmed by observing its disappearance after blockade of cardiac nerve transmission with intrapericardial 2% procaine treatment. Moreover, application of U-46619 (2.5-10 microg), a TxA2 mimetic, on the heart caused graded increases in mean arterial pressure and renal nerve activity, responses that were abolished 3 min after local blockade of cardiac neural transmission with intrapericardial procaine. BM 13,177 (30 mg/kg iv), a selective TP receptor antagonist, eliminated the reflex responses to U-46619 and significantly attenuated the excitatory responses during brief (5 min) regional myocardial ischemia. The sympathoexcitatory reflex responses to U-46619 were unchanged by blockade of histamine H1 receptors with pyrilamine and serotonin 5-HT3 receptors with tropisetron, indicating specificity of this TP receptor agonist. These data indicate that endogenous TxA2 participates in myocardial ischemia-mediated sympathoexcitatory reflex responses through a TP receptor mechanism.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Anesthetics, Local; Animals; Cats; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Heart; Hemodynamics; Histamine H1 Antagonists; Indoles; Kidney; Male; Myocardial Ischemia; Pressoreceptors; Procaine; Pyrilamine; Receptors, Thromboxane; Reflex; Serotonin Antagonists; Sulfonamides; Sympathetic Nervous System; Thromboxane A2; Tropisetron; Vagotomy

We studied the effect of endotoxin on bradykinin-induced inositol 1,4,5-triphosphate (IP3) production and the relationship between IP3 and phospholipase A2 or thromboxane A2. When exposed with 0.1, 1.0, and 10 microg ml(-1) lipopolysaccharide (LPS) for short-term (60 min), 100 nmol L(-1) bradykinin-induced IP3 production was stimulated in a dose-dependent manner from 569.2+/-42.4 in absence of LPS to 714.3+/-52.8, 804.5+/-42.6, and 894.1+/-62.6 pmol mg protein(-1). Treatment of 100 micromol L(-1) ACA (a phospholipase A2 inhibitor) and 10 micromol L(-1) BM13.177 (a thromboxane A2 inhibitor) significantly decreased bradykinin-induced IP3 production and LPS (1.0 microg mL(-1)) modulation of bradykinin-induced IP3 formation from 804.5+/-42.6 to 217.4+/-12.7 and 208.6+/-17.1 pmol mg protein(-1), respectively. LPS modulation of bradykinin-induced IP3 production was significantly blocked by 1 micromol L(-1) TMB-8 (an intracellular Ca2+ antagonist) from 804.5+/-42.6 to 507.8+/-33.4 pmol mg protein(-1). LPS modulation of bradykinin-induced IP3 production was significantly inhibited from 804.5+/-42.6 to 397.4+/-30.3 pmol mg protein(-1) by treatment of 10 micromol L(-1) indomethacin. In conclusion, short-term administration of LPS stimulates bradykinin-induced IP3 formation through activation of phospholipase A2 and thromboxane A2 and the stimulation is associated with an elevation of intracellular Ca2+.

Topics: Animals; Animals, Newborn; Bradykinin; Cinnamates; Endotoxins; Gallic Acid; Heart; In Vitro Techniques; Indomethacin; Inositol 1,4,5-Trisphosphate; Kinetics; Lipopolysaccharides; Myocardium; ortho-Aminobenzoates; Rats; Sulfonamides; Thromboxane A2

The present study was undertaken to examine the involvement of platelet-derived serotonin (5-hydroxytryptamine; 5-HT) in thromboxane A2 (TXA2)-induced platelet aggregation. Pharmacological experiments with 5-HT2 and TXA2 inhibitors were conducted on platelet aggregation in platelet-rich plasma from cats. Exogenously added 5-HT, U-46619 (a stable TXA2 analogue) and collagen caused platelet aggregation in a concentration-dependent manner. The combination of low concentrations of 5-HT and U-46619 caused full platelet aggregation, whereas each agent alone, at these concentrations, caused a transient aggregation. 5-HT-induced aggregation was inhibited by ketanserin (0.01-0.3 micromol/l), a 5-HT2 receptor antagonist, in a concentration-dependent manner. Collagen-induced platelet aggregation was also inhibited by ketanserin, whereas the inhibition by indomethacin was modest even at the highest concentration tested (300 micromol/l). U-46619 triggered platelet aggregation in a biphasic manner. Ketanserin inhibited only the second phase of the aggregation. The inhibition of U-46619-induced aggregation by ketanserin occurred at a concentration range similar to that for 5-HT-induced platelet aggregation. Likewise, platelet aggregation induced by the combination of low concentrations of 5-HT and U-46619 was fully inhibited by ketanserin. These data suggest a major involvement of platelet-derived 5-HT in TXA2-dependent aggregation in cat platelets.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Blood Platelets; Cats; Collagen; Cyclooxygenase Inhibitors; Drug Interactions; Female; Indomethacin; Ketanserin; Male; Platelet Aggregation; Platelet Aggregation Inhibitors; Serotonin; Serotonin Antagonists; Sulfonamides; Thromboxane A2

The shape change that occurs when platelets are stimulated with an agonist can be quantitated by monitoring changes in their forward-scatter/side-scatter profile using a flow cytometer. Here we have stimulated platelets in citrated whole blood with several agonists and determined the time-course and extent of the shape change that occurs. In some experiments parallel investigations of shape change and aggregation were performed. Aggregation was measured by monitoring the fall in number of single platelets using a Whole Blood Platelet Counter. Some agents (ADP, PAF, U46619 and 5HT) produced a strong and rapid change in platelet forward-scatter/side-scatter that was maximal within 10 s. Others (A23187 and collagen) produced a strong but slower response. Adrenaline produced only a weak response that was also slow to develop, and PMA did not produce any response. The concentrations of each of ADP, PAF, U46619 and 5HT needed to induce a shape change were lower than those required for aggregation. Selective PAF, TXA2 and 5HT antagonists (WEB 2086, sulotroban and MCI-9042) clearly inhibited both the shape change and the aggregation induced by the appropriate agonist; in each case the effect of the antagonist was to move the dose-response curve to the right. These results are consistent with the shape change and aggregation brought about by each of these agonists being mediated via a single receptor. In contrast, a selective P2T purinoceptor antagonist (ARL 66096) markedly inhibited the aggregation induced by ADP but was found to have little or no effect on shape change. This is consistent with these platelet responses to ADP being mediated by different receptors, with P2T receptors mediating only the aggregation response.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine Diphosphate; Adenosine Triphosphate; Azepines; Blood Platelets; Humans; In Vitro Techniques; Piperazines; Piperidines; Platelet Activating Factor; Platelet Aggregation; Platelet Aggregation Inhibitors; Prostaglandin Endoperoxides, Synthetic; Serotonin; Succinates; Sulfonamides; Thromboxane A2; Triazoles; Vasoconstrictor Agents

This study reports the synthesis, biological evaluation, and application of a new biotinylated derivative 1-[[1S-[1 alpha, 2 alpha (Z),3 alpha, 4 alpha]]-7-[3-[[[[(1-oxocyclohexylpropyl)amino]acetyl]amino] methyl]-7-oxabicyclo [2.2.1]hept-2-yl]-5-heptenoyl]-2-[hexahydro-2'-oxo-1H-thieno[3',4' d] imidazole-4'-pentanoyl]hydrazine (SQB) of the thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor antagonist [1S-[1 alpha,2 alpha(Z),3 alpha,4 alpha]]-7-[3-[[[[(1-oxocyclohexylpropyl)amino]acetyl] amino]methyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid (SQ31,491). SQB was synthesized by reacting SQ31,491 with biotin hydrazide, and the product was purified by flash chromatography. It was found that SQB specifically inhibited platelet aggregation in response to U46619 with an IC50 of 275 nM. On the other hand, SQB did not inhibit adenosine diphosphate or A23187-induced aggregation. Competition binding studies revealed that SQB produced a concentration-dependent inhibition of [3H]-[1S-[1 alpha, 2 beta (5Z),3 beta, 4 alpha]]-7-[3-[[2[(phenylamino) carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid ([3H]SQ29,548) specific binding in 3-[(3-cholamidopropyl)dimethylammonio]-1-propane-sulfonate (CHAPS)-solubilized platelet membranes, with a Ki of 220 nM. The shape of the SQB inhibition binding curve was indistinguishable from that produced by the TXA2/PGH2 receptor antagonist BM13.177. Finally, incubation of gel-filtered platelets or platelet-rich plasma with SQB and fluorescein isothiocyanate (FITC)-avidin demonstrated fluorescent labeling of platelet plasma membrane TXA2/PGH2 receptors. Furthermore, this SQB-FITC fluorescent labeling was reduced significantly by co-incubation of the platelets with the TXA2/PGH2 antagonist SQ29,548. Based on the ability of SQB-FITC-avidin to label intact platelets, it can be concluded: (1) that a pool of platelet TXA2/PGH2 receptors resides in the plasma membrane; and (2) that the binding domains for these receptors are oriented at or near the external membrane surface. Collectively, these data demonstrate that SQB is a highly specific probe for TXA2/PGH2 receptors, which should be of significant value for receptor localization studies in platelets and other tissues.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Biotin; Blood Platelets; Bridged Bicyclo Compounds, Heterocyclic; Cell Membrane; Fatty Acids, Unsaturated; Humans; Hydrazines; Microscopy, Fluorescence; Molecular Probes; Platelet Aggregation Inhibitors; Prostaglandin Endoperoxides, Synthetic; Radioligand Assay; Receptors, Prostaglandin; Receptors, Thromboxane; Receptors, Thromboxane A2, Prostaglandin H2; Spectrometry, Fluorescence; Sulfonamides; Thromboxane A2

It has been postulated that the main proaggregatory effect of thromboxane A2 (TxA2) is mediated by an inhibition of adenylate cyclase/cAMP complex, an effect similar to that of Na+ ion. The possibility of a modulation of the effect of Na+ on in vivo and in vitro platelet function of Dahl salt-sensitive (Dahl-S) and Dahl salt-resistant (Dahl-R) rats was investigated. Sulotroban, a powerful antagonist of prostaglandin peroxides and TxA2 was administered at doses of 1, 3 and 10 micrograms/kg/min. In vivo platelet activity was estimated on the basis of bleeding time and thrombocytopenia produced by i.v. bolus injection of 100 micrograms/kg collagen, and by plasma measurement of the stable prostacyclin and TxA2 analogs. In vitro aggregation was induced by collagen at concentrations of 10, 20, 30 and 40 micrograms/ml. Main blood pressure was measured directly in common carotid artery. The results showed that sulotroban did not produce hypotensive effects but did increase the bleeding time almost 2-fold. Plasma TxA2 levels were significantly increased in both Dahl-S and Dahl-R rats. The inhibition of collagen-induced aggregation and thrombocytopenia by sulotroban was negligible on Dahl-R rats but significant in Dahl-S rats. The results suggested a blocking effect of sulotroban not only on stimulus/receptor TxA2 complex but also on the inhibitory unit of adenylate cyclase complex, confirming this pathway of TxA2-induced aggregation.

Topics: Animals; Bleeding Time; Blood Pressure; Collagen; Platelet Aggregation; Platelet Aggregation Inhibitors; Platelet Count; Prostaglandin H2; Prostaglandins H; Rats; Rats, Inbred Strains; Sodium; Sulfonamides; Thromboxane A2

Fura-2-loaded human platelets were used to study Ca2+ release from intracellular compartments, as well as Ca2+ influx from the extracellular space. We investigated the response towards the endoperoxide/thromboxane-receptor agonist. U46619, and the inhibitor of the endoplasmic-reticulum Ca(2+)-ATPase, thapsigargin. U46619 dose-dependently depleted intracellular Ca2+ stores, followed by active sequestration of released Ca2+. Ca2+ influx induced by U46619 largely relies on receptor occupancy. Removing the thromboxane analogue from its receptor by using the endoperoxide/thromboxane-receptor antagonist BM 13177 largely blunted U46619-mediated Ca2+ influx. The Ca(2+)-ATPase inhibitor thapsigargin evoked a gradual rise in intracellular Ca2+, which was potentiated by a preceding activation of platelets with the receptor agonist U46619. This agonist-sensitizing effect also depends on receptor occupancy. Removing U46619 from its receptor by addition of the endoperoxide/thromboxane-receptor antagonist BM13177 suppressed the sensitizing effect completely. Furthermore, interrupting downstream receptor signalling events by raising intracellular levels of cyclic nucleotides (cyclic AMP, cyclic GMP) again suppressed the U46619-sensitizing effect on thapsigargin-induced Ca2+ release. This study indicates that the process of Ca2+ release followed by resequestration in response to a platelet agonist by its own is not sufficient to produce the sensitizing effect. Rather, a continuously occupied receptor triggering sustained downstream signalling events seems to be required for sensitization. The presence of a receptor agonist may induce an increased cycling of Ca2+ between the agonist-responsive and the thapsigargin-dischargeable compartment, leading to faster and more intense accumulation of Ca2+ in the cytosolic compartment after inhibition of the Ca(2+) ATPase. Suggestively, receptor occupancy increases the Ca(2+)-releasing potency of thapsigargin by coupling the thapsigargin-sensitive Ca(2+)-storing compartments with an agonist-responsive compartment that exhibits a high leakage rate in stimulated platelets.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Blood Platelets; Calcium; Cyclic AMP; Cyclic GMP; Cytosol; Epoprostenol; Humans; Intracellular Fluid; Nitroprusside; Platelet Activation; Prostaglandin Endoperoxides, Synthetic; Receptors, Thromboxane; Signal Transduction; Sulfonamides; Terpenes; Thapsigargin; Thromboxane A2

We examined acute and chronic effects of thromboxane (TX) A2 inhibition on the renal hemodynamics at early and late stage of untreated streptozotocin (STZ)-induced diabetic rats. Two weeks and 28 weeks after the induction of diabetes, renal blood flow (RBF) under anesthesia was measured with an electromagnetic flowmeter before and after TXA2 inhibition. In two-week-old diabetic rats, a specific TXA2 synthetase inhibitor, OKY-046, or a specific TXA2 receptor antagonist, Sulotroban, increased renal vascular resistance (RVR) and ameliorated the hyperperfusion. The renal vasoconstrictive effect of OKY-046 was blunted by an angiotensin converting enzyme (ACE) inhibitor, MK422, or an angiotensin II receptor antagonist, Saralasin. On the contrary, OKY-046 ameliorated the renal hypoperfusion by decreasing RVR in 28-week-old diabetic rats. Chronic oral administration of OKY-046 ameliorated not only the renal hyperperfusion but increased urinary albumin excretion (UAE) at two weeks, but also the renal hypoperfusion, filtration fraction and UAE at 24 weeks. It is suggested that TXA2 might, at least in part, play important roles in the hyperperfusion by modulating activity of the renin-angiotensin system at an early stage of untreated diabetic rats and in the hypoperfusion at the late stage of untreated diabetic rats, and that TXA2 is also involved in the increase of UAE. These results support roles for TXA2 in the progression of renal injury in STZ-induced diabetic rats.

Topics: Angiotensin-Converting Enzyme Inhibitors; Animals; Diabetes Mellitus, Experimental; Hemodynamics; Kidney; Male; Methacrylates; Rats; Rats, Sprague-Dawley; Receptors, Thromboxane; Renal Circulation; Streptozocin; Sulfonamides; Thromboxane A2; Thromboxane-A Synthase; Vascular Resistance; Vasoconstriction

Topics: Animals; Dibenzoxepins; Drug Design; Guinea Pigs; Histamine H1 Antagonists; In Vitro Techniques; Receptors, Prostaglandin; Receptors, Thromboxane; Receptors, Thromboxane A2, Prostaglandin H2; Structure-Activity Relationship; Sulfonamides; Thromboxane A2

The involvement of prostaglandins in thromboembolic processes, as induced by wall puncture, was studied in rabbit mesenteric arterioles and venules using intravital videomicroscopy. Inhibition of prostaglandin formation with aspirin (100 mg/kg, i.v.) significantly increased in arterioles duration of embolization (from 91 to 200 s) and number of emboli produced (from 4 to 8.5 per vessel), while rate of embolus production was not influenced. In venules, aspirin only influenced embolization rate (a significant decrease from one embolus/14 s to one/23 s). Specific blockade of TXA2-receptors by sulotroban (30 mg/kg, i.v.) only influenced the arteriolar reaction: it significantly decreased embolization duration (from 560 to 218 s) and number of emboli produced (from 23 to 10 emboli per vessel), without affecting embolization rate. These findings indicate that both platelet activating and inhibiting prostaglandins play a more important role in thromboembolism in arterioles than in venules; this suggests a difference in prostaglandin synthetic capacity between arteriolar and venular endothelium.

Topics: 12-Hydroxy-5,8,10,14-eicosatetraenoic Acid; Animals; Arterioles; Aspirin; Epoprostenol; Female; Hydroxyeicosatetraenoic Acids; Leukocytes; Male; Mesentery; Platelet Activation; Prostaglandins; Rabbits; Receptors, Thromboxane; Regional Blood Flow; Sulfonamides; Thromboembolism; Thromboxane A2; Venules; Videotape Recording

The i.v. bolus application of 1 nmol/kg endothelin-1 (ET-1) in anaesthetized and ventilated guinea-pigs caused an increase in mean arterial blood pressure (BP) and a bronchoconstriction. Both have been reduced or abolished by COX inhibition (ASA) or substances specifically reducing the thromboxane A2 (TXA2) generation (HOE 944) or receptor binding (BM 13177). The significant increase in TXB2 concentrations in plasma and bronchoalveolar lavage (BAL) after ET-1 challenge (15-fold and 4-fold, respectively) have been reduced or abolished by ASA as well as HOE 944 and not altered by BM 13177.

Topics: Animals; Aspirin; Blood Pressure; Bronchoalveolar Lavage Fluid; Bronchoconstriction; Endothelins; Guinea Pigs; Imidazoles; Male; Naphthalenes; Prostaglandin-Endoperoxide Synthases; Receptors, Thromboxane; Sulfonamides; Thromboxane A2; Thromboxane B2; Thromboxane-A Synthase; Vasopressins

The platelet-activating factor (PAF) induced a marked increase of the thromboxane (TX) B2-formation in the incubation medium of isolated myocardium and tissue from other organs. The content of the 6-oxo-prostaglandin (PG)F1 alpha, the inactive metabolite of PGI2, remained uninfluenced or showed a small decrease. PAF, given in a concentration of 2.10(-9) mol/l or a single dose of 100 ng, significantly reduced the contraction force and the coronary flow of isolated guinea-pig hearts. This effect was connected with a high efflux of TXA2. The PAF-antagonist, WEB 2086, nearly abolished the cardiac effects of PAF, and iloprost or a pretreatment with indomethacin markedly reduced the PAF-influence on the heart. The TXA2-antagonist BM 13177 was ineffective. The results indicate a close interaction between the myocardial PAF-effect and the TXA2-formation of the heart tissue, but gave no suggestion for a mediation of the PAF-effect by TXA2. The PAF-antagonistic action of WEB 2086, iloprost and indomethacin could be of some interest in the therapy of cardiovasculatory diseases.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Azepines; Guinea Pigs; Heart; Iloprost; In Vitro Techniques; Indomethacin; Myocardial Contraction; Perfusion; Platelet Activating Factor; Prostaglandins; Sulfonamides; Thromboxane A2; Thromboxane B2; Triazoles

The effects of thromboxane B2 (TxB2) and of two thromboxane mimetics, dl-(9,11), (11,12)-dimethano-TxA2 (ONO 11006) and 9,11-dideoxy-11,9-epoxymethano prostaglandin F2 alpha (U46619) on the cardiac response to adrenergic nerve stimulation in isolated guinea-pig atria were evaluated. All the agonists dose dependently reduced the positive inotropic effect induced by field stimulation, U46619 being the most active. The inhibitory effect of U46619 was reduced by the thromboxane receptor antagonists, sulotroban and AH 23848B. U46619 did not significantly reduce the positive inotropic effect induced by exogenous noradrenaline. However U46619 was unable to modify the tritium overflow induced by field stimulation in preparations preloaded with [3H]noradrenaline. In addition to this influence on adrenergic neurotransmission, U46619 also had a direct positive inotropic effect on cardiac contractility, which was antagonized by AH 23848B. These results indicate that U46619 reduces the cardiac response to sympathetic nerve stimulation and that is also has a direct stimulatory effect on cardiac muscle.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Biphenyl Compounds; Dose-Response Relationship, Drug; Electric Stimulation; Guinea Pigs; Heart Atria; In Vitro Techniques; Male; Norepinephrine; Prostaglandin Endoperoxides, Synthetic; Receptors, Prostaglandin; Receptors, Thromboxane; Sulfonamides; Sympathetic Nervous System; Synaptic Transmission; Thromboxane A2; Thromboxane B2

The influence of a transient asphyxia on cochlear potentials, i.e. endolymphatic potential (EP), summating potential (SP) and cochlear microphonics (CM) was investigated in guinea pigs when pretreating the animals with various substances interacting with the arachidonic acid (AA) cascade at the level of thromboxane. The controls showed the well-known decline of the EP, CM and the SP increase. When infusing a thromboxane synthetase inhibitor (dazoxiben) or two different thromboxane receptor blockers (daltroban or sulotraban) before the 3-minutes' period of asphyxia was started, the electrophysiological responses of the inner ear (cochlea) could significantly be influenced. The results indicate that a shift of the thromboxane (TXA2)/prostacyclin (PGI2)-balance in favour of the last improve the metabolic conditions for a survival of the cochlea when it is challenged.

Topics: Analysis of Variance; Animals; Arachidonic Acid; Cochlear Diseases; Epoprostenol; Female; Guinea Pigs; Imidazoles; Male; Phenylacetates; Receptors, Prostaglandin; Receptors, Thromboxane; Sulfonamides; Thromboxane A2; Thromboxane-A Synthase; Time Factors

Topics: Animals; Cell Division; Iloprost; Indomethacin; Rats; Receptors, Prostaglandin; Receptors, Thromboxane; Sulfonamides; Thromboxane A2; Tumor Cells, Cultured

Angiotensin II (A II) when given through the renal artery of the rabbit isolated perfused kidney elicited a concentration-dependent increase in perfusion pressure (PP) and urine flow (UF). Noradrenaline (NA) produced similar effect in PP but slightly not significantly increased UF. Addition of UK 38,485, a thromboxane A2 (TXA2)-synthetase inhibitor, to the bathing medium at the concentration of 10(-7) M caused a significant decrease in the pressor effect of A II but significantly enhanced UF. BM 13,177, a TXA2-receptor blocker, in the bathing medium (10(-6) M) produced identical effect in both PP and UF. The responses to NA were not significantly altered by both compounds. A II-induced enhancement of UF in presence of BM 13,177 was significantly lower than that obtained in presence of UK 38,485. These results were taken as an evidence that A II may increase the production of TXA2 in kidney probably originated from vascular bed or tubuli and part of the pressor effect of the peptide is due to this metabolite of arachidonic acid. Enhancement of UF following UK 38,485 is probably due to the shift of the synthesis toward E series of PGs. In addition this effect seems to be specific for A II since no such effect was seen with NA.

Topics: Angiotensin II; Animals; Female; Imidazoles; In Vitro Techniques; Kidney; Male; Norepinephrine; Perfusion; Rabbits; Sulfonamides; Thromboxane A2; Thromboxane-A Synthase; Urine

The effects of KW-3635 (sodium (E)-11-[2-(5,6-dimethyl-1-benzimidazolyl)- ethylidene]-6,11-dihydrodibenz[b,e]oxepine-2-carboxylate monohydrate, CAS 127166-41-0) on smooth muscle preparations were examined. In isolated guinea-pig aorta, KW-3635 competitively inhibited the U-46619 (a thromboxane mimetic) induced contractions (pA2 = 7.74), the effect being more potent than those of sulotroban and daltroban. In canine saphenous vein, KW-3635 also antagonized the U-46619-induced contraction (pA2 = 8.11). In this preparation, solutroban and daltroban, but not KW-3635, exhibited intrinsic agonistic action. KW-3635, even at a high concentration of 10(-5) mol/l did not affect the norepinephrine- or KCl-induced contractions of guinea-pig or rat aorta, prostaglandin (PG)E2- or PGF2 alpha-induced contractions of guinea-pig ileum nor the PGE2-induced contraction of rat fundus. KW-3635 at concentrations higher than its thromboxane A2- (TxA2-)antagonistic one, non-competitively inhibited the PGF2 alpha-induced contractions of guinea-pig aorta (pD2' = 6.23), as was the case with daltroban. The inhibitory effect of KW-3635 (3 x 10(-6) mol/l) on U-46619-induced contractions of guinea-pig aorta persisted for longer than 2 h following washout of the tissue, whereas that of daltroban (10(-5) mol/l completely disappeared at 1 h after the washout. In anesthetized guinea-pigs, KW-3635 at doses of 10 to 1000 micrograms/kg (i.v.) inhibited U-46619 (1 microgram/kg i.v.)-induced pressor responses in a dose-dependent manner. The effect of KW-3635 (0.1 to 1 mg/kg i.v.) persisted for longer than 3 h. These results demonstrate that KW-3635 is a potent and specific TxA2 antagonist without agonistic action in vascular smooth muscles. KW-3635 is considered to be a promising candidate for the treatment of patients with disorders mediated via TxA2.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Benzimidazoles; Benzoxepins; Blood Pressure; Cats; Dogs; Female; Guinea Pigs; In Vitro Techniques; Male; Muscle Contraction; Muscle, Smooth; Muscle, Smooth, Vascular; Phenylacetates; Platelet Aggregation Inhibitors; Prostaglandin Endoperoxides, Synthetic; Rabbits; Rats; Rats, Inbred Strains; Species Specificity; Sulfonamides; Thromboxane A2

Injection of U-46619 (9,11-dideoxy-9 alpha, 11 alpha-epoxymethano- prostaglandinF2 alpha; 130 micrograms/kg i.v.) produced sudden death in anesthetized guinea-pigs and rats within 10-15 min. This sudden death is typified by a precipitous drop in mean arterial blood pressure (MABP) and a dramatic decrease in the circulating platelet counts. In guinea-pigs, KW-3635 (sodium(E)-11-[2-(5,6-dimethyl-1-benzimidazolyl)ethylidene]-6,11- dihydrodibenz[b,e]oxepine-2-carboxylate monohydrate, CAS 127166-41-0) at doses of 0.1 mg/kg or greater dramatically protected animals against sudden death induced by injection of U-46619. Pretreatment with KW-3635 (0.3, 1.0 mg/kg i.v.) inhibited the decrease in circulating platelet counts and the decline in blood pressure associated with the i.v. injection of U-46619. Oral administration of KW-3635 (10, 30 mg/kg) also protected the animals from the U-46619-induced sudden death. The effect of KW-3635 was almost the same as that of daltroban, and was more potent than that of sulotroban. In rats, intravenous administration of KW-3635 at doses of 0.3 mg/kg or greater protected against sudden death. In contrast, acetylsalicylic acid a cyclooxygenase inhibitor, did not protect against sudden death induced by U-46619, indicating that the formation of endogenous thromboxane does not play a major role in the lethal effect of U-46619, and that the blockade of the lethal effects of U-46619 is specific for thromboxane receptor antagonists. Our data show that KW-3635 protects guinea-pigs and rats against U-46619-induced sudden death. Therefore, KW-3635 may be useful for the investigation of diseases where thromboxane is involved.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Aspirin; Benzimidazoles; Benzoxepins; Blood Pressure; Death, Sudden; Dose-Response Relationship, Drug; Guinea Pigs; Male; Phenylacetates; Platelet Aggregation Inhibitors; Platelet Count; Prostaglandin Endoperoxides, Synthetic; Rats; Rats, Inbred Strains; Sulfonamides; Thromboxane A2; Thromboxanes; Ticlopidine

In open-chest dogs, cyclic flow reductions (CFRs, 5.1-6.6/hr in controls; n = 24) caused by platelet deposition/dislodgment at sites of endothelial cell injury in critically stenosed left anterior descending coronary arteries (59% flow reduction) were attenuated to the same extent either by single thromboxane A2 (TXA2) synthase inhibition (0.31 mg/kg i.v. ridogrel; CFR, 0.16 +/- 0.16/hr; n = 6; p less than 0.05) or by a comparatively modest degree of TXA2/prostaglandin endoperoxide receptor antagonism on top of TXA2 synthase inhibition (5 mg/kg i.v. ridogrel; CFR, 0.22 +/- 0.1/hr; n = 10; p less than 0.05). By contrast, occlusive thrombosis on deep vascular damage elicited by intraluminal stimulation (150-microA anodal constant current) in nonpreconstricted canine coronary arteries (time to occlusion, 237.1 +/- 13.9 minutes; n = 7; incidence of occlusion within 300 minutes, six of seven experiments) was not affected by platelet cyclooxygenase inhibition (5 mg/kg i.v. acetylsalicylic acid; n = 7), single TXA2 synthase inhibition (1.25 mg/kg i.v. ridogrel; n = 7), or single TXA2/prostaglandin endoperoxide receptor antagonism (10 mg/kg + 10 mg/kg/hr i.v. sulotroban for 300 minutes; n = 5). However, such an occlusive thrombus formation was significantly reduced by combined TXA2 synthase/prostaglandin endoperoxide receptor inhibition (5 mg/kg i.v. ridogrel; time to occlusion greater than 300 minutes, n = 7; incidence of occlusion within 300 minutes, one of seven experiments; p less than 0.05). This study reveals 1) a differential efficacy of TXA2 synthase inhibition, singly or combined with TXA2/prostaglandin endoperoxide receptor antagonism, depending on the extent of the vessel wall lesion triggering thrombosis and the size of the thrombus required to obstruct the vascular lumen and 2) a significant synergism in preventing occlusive thrombosis of extensively damaged coronary arteries between strong TXA2 synthase inhibition and comparatively modest TXA2/prostaglandin endoperoxide receptor antagonism with ridogrel.

Topics: Animals; Coronary Thrombosis; Coronary Vessels; Dogs; Endothelium, Vascular; Female; Hemodynamics; In Vitro Techniques; Male; Pentanoic Acids; Pyridines; Receptors, Prostaglandin; Receptors, Thromboxane; Sulfonamides; Thromboxane A2; Thromboxane-A Synthase

Activation of human platelets by diverse receptor-transduced signals is followed by an intracellular calcium increase. Calcium liberation from an inositol 1,4,5-trisphosphate-sensitive compartment is recognized to be one of the prime events, followed by further mechanisms to amplify the signal. Among these, the formation of prostaglandin endoperoxides and thromboxane A2 are part of the self-amplificating activation system. Two inhibitors of intracellular Ca(2+)-ATPases, thapsigargin and 2,5-di-(tert-butyl)-1,4-benzohydroquinone have been reported to deplete the intracellular inositol 1,4,5-trisphosphate-responsive stores. In human platelets with EGTA present, we found that these inhibitors of the microsomal Ca2+ sequestration generate quite different Ca2+ transients due to an inherent cyclooxygenase inhibition by the benzohydroquinone derivative compared to thapsigargin, and, therefore, only one-half of the fura-2 signal is generated. For a maximal calcium release, Ca(2+)-ATPase inhibitors depend on the self-amplification system involving thromboxane formation. Following the thapsigargin-induced [Ca2+]i transient, thrombin was unable to raise [Ca2+]i, indicating that thapsigargin mobilizes calcium from the thrombin-responsive store, as long as the self-amplifying system of platelets is intact. With the thromboxane receptor blocked, thapsigargin releases only one-half of the calcium, and, hence, thrombin was able to release additional calcium. Interestingly, in the converse experiment, thrombin did not prevent a raise of [Ca2+]i by thapsigargin at all, although applying thrombin a second time was without any effect. Therefore, we propose two calcium pools in human platelets: receptor activation transiently releases calcium from an inositol-sensitive pool including the thapsigargin-sensitive compartment, followed by reuptake within minutes. Sequestration occurs into the thapsigargin-sensitive compartment from where it can be released even when the endoperoxide/thromboxane receptor is blocked. Calcium release from both compartments allows the formation of thromboxane B2, but not if only the Ca(2+)-ATPase inhibitor-sensitive pool is emptied. In the presence of a protonophor, a calcium accumulation in the Ca(2+)-ATPase-sensitive pool could be observed.

Topics: Antioxidants; Blood Platelets; Calcium; Calcium-Transporting ATPases; Fibrinolytic Agents; Humans; Hydroquinones; Nigericin; Platelet Activation; Prostaglandin-Endoperoxide Synthases; Sulfonamides; Terpenes; Thapsigargin; Thrombin; Thromboxane A2; Thromboxane B2

The effects of KW-3635 (sodium (E)-11-[2-(5,6-dimethyl-1-benzimidazolyl)- ethylidene]-6,11-dihydrodibenz[b,e] oxepine-2-carboxylate monohydrate, CAS 127166-41-0) on platelet aggregation were examined. In human washed platelets, KW-3635 shifted the concentration-aggregation curves for U-46619, a thromboxane A2 (TxA2) mimetic, to the right. The pA2 value for KW-3635 was 8.8 +/- 0.10, while those for sulotroban and daltroban were 6.31 +/- 0.18 and 7.75 +/- 0.07, respectively. In human platelet rich plasma (PRP), KW-3635 at 10(-8) mol/l to 10(-6) mol/l inhibited the aggregations induced by U-46619 (1 mumol/l) or collagen (1.5 micrograms/ml). However, KW-3635 at up to 10(-5) mol/l did not affect the primary phase of platelet aggregation induced by adenosine diphosphate or epinephrine. KW-3635 at 10(-5) mol/l did not affect the antiaggregatory effects of the prostaglandins PGI2, PGE1 and PGD2. These results indicate that KW-3635 is a potent and selective TxA2 receptor antagonist. The TxA2 antagonistic effects of KW-3635 were compared with that of daltroban in PRP from various animals species. The effects of KW-3635 on platelet aggregation were species-dependent and KW-3635 exhibited the most prominent activity in human platelets. The activities of KW-3635 in mouse and rabbit PRP were much less potent. In PRP from guinea-pigs, dogs, cats and rats, KW-3635 exhibited moderate anti-aggregatory effects. In the guinea-pig PRP, KW-3635 at 10(-7) mol/l to 3 x 10(-6) mol/l inhibited both the platelet aggregation and the concomitant adenosine triphosphate secretion in a concentration-dependent manner, the effect being more potent than those of sulotroban and daltroban. In the experiments on the platelet aggregation ex vivo in guinea-pigs, KW-3635 at oral doses of 3 and 10 mg/kg inhibited the aggregations induced by U-46619 (1, 3 mumol/l), collagen (3, 6, 9 micrograms/ml) and arachidonate (50, 100 mumol/l). The effects lasted for longer than 7 h following oral administration. These results indicate that KW-3635 is a specific and orally active TxA2 receptor antagonist. KW-3635 is expected to be a drug useful for the treatment of patients with thrombotic disorders.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine Triphosphate; Adult; Animals; Benzimidazoles; Benzoxepins; Cats; Dogs; Drug Interactions; Epinephrine; Guinea Pigs; Humans; In Vitro Techniques; Mice; Middle Aged; Phenylacetates; Platelet Aggregation; Platelet Aggregation Inhibitors; Prostaglandin Endoperoxides, Synthetic; Prostaglandins; Rabbits; Rats; Receptors, Prostaglandin; Receptors, Thromboxane; Sulfonamides; Thromboxane A2

1. In anaesthetized, pump-ventilated guinea-pigs, bolus intravenous injection of prostaglandin D2 (PGD2 5-160 micrograms kg-1) caused a dose-dependent rise in both heart rate and systemic mean arterial blood pressure with only a small monophasic rise in pulmonary inflation pressure (PIP). 2. In contrast, inhaled PGD2 (0.1-1 mg ml-1, 30s) provoked a substantial concentration-dependent biphasic rise in PIP. The bronchoconstrictor action of inhaled PGD2 was accompanied by minimal cardiovascular effects. 3. The 3-benzyl substituted hydantoin BW A868C (0.1-1 mg kg-1 i.v.) a novel prostanoid DP-receptor antagonist, had no significant effect on the cardiovascular or bronchoconstrictor effects of intravenously administered or inhaled PGD2. 4. However, BW A868C (0.1-1 mg kg-1 i.v.) did inhibit the hypotensive actions of the DP-receptor agonist, BW 245C (1-3 micrograms kg-1 i.v.). 5. The prostanoid TP-receptor antagonist BM 13.177 (2.5 mg kg-1 i.v.) strongly inhibited the bronchoconstrictor effect of inhaled PGD2, abolishing the first phase of this response and reducing the peak increase in PIP provoked by PGD2 (0.1 or 1 mg ml-1 for 30 s), by 67 +/- 16% and 44 +/- 5% respectively. 6. A combination of BW A868C (0.1 or 1 mg kg-1 i.v.) with BM 13.177 (2.5 mg kg-1 i.v.) produced no greater inhibition of the bronchoconstrictor effect of inhaled PGD2 than that seen with BM 13.177 (2.5 mg kg-1 i.v.) alone. 7. Neither bilateral vagotomy, nor selective inhibition of arachidonate cyclo-oxygenase with indomethacin or 5-lipoxygenase with the novel acetohydroxamic acid BW A4C, significantly reduced the bronchoconstrictor effect of inhaled PGD2. 8. These findings indicate that the bronchoconstrictor effect of inhaled PGD2 in guinea-pigs in vivo is mediated primarily through direct TP-receptor activation and not through actions on DP-receptors.

Topics: Administration, Inhalation; Anesthesia; Animals; Benzeneacetamides; Bronchi; Cyclooxygenase Inhibitors; Guinea Pigs; Hydantoins; Hydroxamic Acids; Indomethacin; Lipoxygenase Inhibitors; Male; Platelet Aggregation Inhibitors; Prostaglandin D2; Prostaglandins D; Receptors, Prostaglandin; Respiratory Function Tests; Sulfonamides; Thromboxane A2; Vagotomy

Conformational analyses on thromboxane A2 (TxA2), its receptor agonist, U-46619, and its receptor antagonist, sulotroban, were carried out by molecular mechanics (MMFF) or molecular orbital (MNDO) methods. Two kinds of putative active conformations of TxA2 and the agonist were proposed on the basis of these results by referring to the hairpin conformation hypothesis. From the superposition of stable conformers of sulotroban on those conformers, the molecular structural requirements for potent TxA2 receptor antagonism were elucidated. S-145 in which these requirements are satisfied was a very potent TxA2 antagonist.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Bridged Bicyclo Compounds; Bridged-Ring Compounds; Computer Simulation; Fatty Acids, Monounsaturated; Models, Molecular; Molecular Conformation; Prostaglandin Endoperoxides, Synthetic; Receptors, Prostaglandin; Receptors, Thromboxane; Stereoisomerism; Structure-Activity Relationship; Sulfonamides; Thromboxane A2

The possible role of thromboxane (TX) A2 in mediating the bronchopulmonary effect of endothelin (ET) was studied in isolated guinea pig airways (trachea, upper bronchi and parenchyma). ET (1-100 nM) evoked a concentration-dependent contraction of all three tissues. The contractile response was significantly attenuated by pretreatment of the tissues with the specific thromboxane receptor blockers, BM 13177 (10-50 microM) and BM 13505 (1-5 microM). Furthermore, ET caused a dose-dependent TXB2 release from trachea and parenchyma. These findings suggest that the bronchopulmonary action of ET is mediated, in part, by the release of TXA2.

Topics: Animals; Anti-Arrhythmia Agents; Bronchi; Dose-Response Relationship, Drug; Endothelins; Epoprostenol; Guinea Pigs; Lung; Male; Muscle Contraction; Muscle, Smooth; Phenylacetates; Receptors, Prostaglandin; Receptors, Thromboxane; Sulfonamides; Thromboxane A2; Thromboxane B2; Thromboxanes; Trachea

The effects of the PAF receptor antagonists WEB 2086, WEB 2170, BN 50739 and BN 52021 on AA-induced platelet aggregation (PA) and TXA2 formation were investigated in comparison with the TXA2 synthetase inhibitor HOE 944 and the TXA2 receptor antagonist BM 13.177. All PAF antagonists tested were weak inhibitors of AA-induced PA and TXA2 formation (IC50 values between 80 and 2,737 mumol/l). HOE 944 was effective in concentrations 2-3 orders of magnitude lower than PAF antagonists in inhibiting TXA2 generation. These results imply that the inhibition of TXA2 formation is of minor relevance for the actions of the investigated PAF antagonists in AA-induced PA.

Topics: Animals; Arachidonic Acid; Arachidonic Acids; Azepines; Blood Platelets; Diterpenes; Ginkgolides; Imidazoles; In Vitro Techniques; Lactones; Naphthalenes; Platelet Activating Factor; Platelet Aggregation; Platelet Aggregation Inhibitors; Rabbits; Receptors, Prostaglandin; Receptors, Thromboxane; Sulfonamides; Thromboxane A2; Thromboxane-A Synthase; Triazoles

Topics: Animals; Bronchi; Endothelins; Guinea Pigs; In Vitro Techniques; Male; Muscle Contraction; Peptides; Sulfonamides; Thromboxane A2; Thromboxanes; Trachea

Differential effects on human platelet function of thromboxane A2 (TXA2) synthetase inhibition singly and of TXA2 synthetase inhibition combined with TXA2/prostaglandin endoperoxide receptor antagonism were revealed, using ridogrel as a probe. Ridogrel combines selective TXA2 synthetase inhibition with TXA2/prostaglandin receptor antagonism in one molecule: in washed human platelets, the compound reduces the production of TXB2 (IC50 = 1.3 X 10(-8) M) and increases that of PGF2 alpha, PGE2, PGD2 from [14C]arachidonic acid. Additionally, at higher concentrations (Ki = 0.52 X 10(-6) M), it selectively antagonizes the breakdown of inositol phospholipids, subsequent to stimulation of TXA2/prostaglandin endoperoxide receptors with U 46619. The latter happens in a competitive way with fast receptor association-dissociation characteristics. At low concentrations (1 X 10(-9)-1 X 10(-7) M) producing single TXA2 synthetase inhibition, ridogrel reduces the collagen-induced formation of TXB2 by washed platelets, but enhances [32P]phosphatidic acid (PA) accumulation and [3H]5-hydroxytryptamine (5-HT) release. At higher concentrations (1 X 10(-6)-1 X 10(-5) M) which additionally block U 46619-induced [32P]PA accumulation, ridogrel inhibits the [32P]PA accumulation and release of [3H]5-HT by human platelets stimulated with collagen. These observations, corroborated by results obtained with OKY 1581, sulotroban, indomethacin and human serum albumin, suggest a causal role for prostaglandin endoperoxides in the stimulation by TXA2 synthetase inhibition of platelet reactions to collagen. They reinforce the concept that TXA2 synthetase inhibition-induced reorientation of cyclic endoperoxide metabolism, away from TXA2 into inhibitory prostanoids, requires additional TXA2/prostaglandin endoperoxide receptor antagonism to achieve optimal anti-platelet effects.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Blood Platelets; Collagen; Humans; In Vitro Techniques; Indomethacin; Inositol Phosphates; Methacrylates; Platelet Activating Factor; Prostaglandin Endoperoxides; Prostaglandin Endoperoxides, Synthetic; Serotonin; Sulfonamides; Thromboxane A2; Thromboxane-A Synthase

1. Administration of arachidonic acid caused dose-dependent vasoconstriction in the isolated rat kidney perfused in situ with Krebs-Henseleit solution. 2. Inhibition of cyclo-oxygenase with indomethacin or meclofenamate reduced the renal vasoconstrictor effect of arachidonic acid. 3. The renal vasoconstrictor effect of arachidonic acid was unaffected by CGS-13080 at concentrations that effectively reduced thromboxane A2 (TxA2) synthesis by platelets and the kidney. 4. The endoperoxide/TxA2 receptor antagonist, SQ 29,548, abolished the renal vasoconstrictor effect of arachidonic acid and of U46619, an endoperoxide analogue. In contrast, SQ 29,548 did not affect the renal vasoconstrictor response to angiotensin II, prostaglandin E2 or F2 alpha. 5. These data suggest that the vasoconstrictor effect of arachidonic acid in the isolated kidney of the rat is mediated by its metabolites, including the prostaglandin endoperoxides.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Anti-Arrhythmia Agents; Arachidonic Acids; Bridged Bicyclo Compounds, Heterocyclic; Fatty Acids, Unsaturated; Hydrazines; In Vitro Techniques; Kidney; Male; Prostaglandin Endoperoxides; Prostaglandin Endoperoxides, Synthetic; Prostaglandin H2; Prostaglandin-Endoperoxide Synthases; Prostaglandins G; Prostaglandins H; Rats; Rats, Inbred Strains; Receptors, Prostaglandin; Receptors, Thromboxane; Sulfonamides; Thromboxane A2; Thromboxane-A Synthase; Thromboxanes; Vasoconstriction

We examined the ability of the prostaglandin endoperoxide/thromboxane A2 antagonist, sulotroban (BM 13.177; SK&F 95587) to enhance the thrombolytic efficacy of a minimally effective thrombolytic dose of streptokinase. A critical stenosis sufficient to just abolish the hyperemic response to a 20-sec total occlusion was placed on the left circumflex coronary artery of anesthetized open chest dogs using an adjustable screw occluder clamp. Thrombi were formed by applying a 150 microA anodal current to a wire placed within the lumen of the left circumflex just proximal to the screw occluder clamp. After thrombus formation, animals were given either streptokinase (20,000 I.U. bolus + 2,000 I.U./min x 180 min, N = 10), streptokinase + sulotroban (5 mg/kg bolus + 5 mg/kg/hr, N = 10), streptokinase + heparin (300 I.U./kg bolus + 100 I.U./kg/hr, N = 9) or streptokinase + heparin + sulotroban (N = 9). Plasma thromboxane A2 level (as measured by the metabolite, thromboxane B2) was not significantly reduced by any treatment, whereas the dose of sulotroban used completely abolished U46619-induced ex vivo platelet aggregation. Of 10 animals receiving streptokinase alone, only 1 reperfused at 55 min after the start of the streptokinase infusion. Conversely, 9 of 10 animals receiving streptokinase + sulotroban reperfused at 79.4 +/- 10.5 min poststreptokinase (P less than .05). When animals were treated with heparin before streptokinase administration, 8 of 9 animals receiving the streptokinase + heparin combination reperfused in an average of 66.8 +/- 8.6 min after the start of streptokinase infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Dogs; Drug Synergism; Fibrinolytic Agents; Hemodynamics; Heparin; In Vitro Techniques; Platelet Aggregation; Platelet Aggregation Inhibitors; Platelet Count; Receptors, Prostaglandin; Receptors, Thromboxane; Regional Blood Flow; Streptokinase; Sulfonamides; Thromboxane A2; Thromboxane B2

Topics: Blood Platelets; Humans; In Vitro Techniques; Kinetics; Polylysine; Prostaglandin Endoperoxides, Synthetic; Prostaglandin H2; Prostaglandins H; Receptors, Prostaglandin; Receptors, Thromboxane; Sulfonamides; Thromboxane A2

The thrombolytic efficacy of recombinant tissue-type plasminogen activator (tPA) in the presence and absence of the selective endoperoxide/thromboxane A2 (TXA2) receptor antagonist, sulotroban (BM 13.177, SK&F 95587) was studied in a model of femoral artery thrombosis in the anesthetized rabbit. The thrombus was formed by injection of thrombin, CaCl2 and whole blood into an isolated segment of the femoral artery. After 30 min of stable thrombotic occlusion of the femoral artery, tPA was infused IV for 90 min at doses of 5.0, 7.5 and 10.0 micrograms/kg/min. In other experiments, sulotroban was administered as a bolus dose of 1 mg/kg/IV, followed by a constant infusion of 1 mg/kg/hr concurrent with tPA infusion. Sulotroban had no effect on the incidence of tPA-induced reperfusion at any dose studied or on residual clot weight. However, at a tPA dose of 10 micrograms/kg/min, IV lysis time was reduced in sulotroban treated animals from 65 min to 29 min (P less than 0.05), and the magnitude of femoral artery blood flow achieved as a result of tPA-induced reperfusion was greater in sulotroban-treated animals. These data suggest that adjunctive therapy with a selective endoperoxide/TXA2 antagonist improves the response to tPA when tPA is administered at a maximal or near maximally effective pharmacological dose.

Topics: Animals; Femoral Artery; Fibrinolytic Agents; In Vitro Techniques; Male; Platelet Aggregation; Prostaglandin Endoperoxides; Rabbits; Receptors, Prostaglandin; Receptors, Thromboxane; Recombinant Proteins; Regional Blood Flow; Sulfonamides; Thrombosis; Thromboxane A2; Tissue Plasminogen Activator

In order to tag the TXA2/PGH2 receptor of human platelets, we synthesized azido-BSP (= 4-[2-(4-azido-benzenesulfonylamino)-ethyl]phenoxyacetic acid), a photolabile derivative of the specific TXA2/PGH2 receptor antagonist sulotroban (= BM 13.177). If protected from UV light, azido-BSP competitively inhibited the shape change of human washed platelets stimulated by the TXA2 mimetic U 46619. Schild analysis revealed a pA2 = 6.7 (apparent KD = 0.2 mumol/l). Irreversible inhibition of the U 46619-induced platelet activation was achieved by irradiating for 5 min with UV light of 254 nm a platelet suspension containing azido-BSP. After subsequent washing, the platelets were stimulated with U 46619, ADP or PAF. Under these conditions azido-BSP inhibited the shape change, aggregation and [3H]serotonin release induced by U 46619 but not the shape change induced by ADP or PAF. The concentrations of azido-BSP which blocked the U 46619-induced [3H]serotonin release and the aggregation were 0.5 mumol/l and 1.0 mumol/l, respectively, whereas even 50.0 mumol/l of azido-BSP only partially inhibited the U 46619-stimulated shape change. Obviously, increasing numbers of thromboxane receptors have to be blocked in order to inhibit the [3H]serotonin release, the aggregation and the shape change. Even at an azido-BSP concentration equal to 250 times the apparent dissociation constant, enough receptor sites remained active to allow U 46619 to induce the shape change. In sulotroban was added prior to irradiation, the blocking effect of azido-BSP decreased with increasing concentrations of sulotroban. These results show that azido-BSP is a specific and high affinity ligand of the TXA2/PGH2 receptor and that it covalently links to the receptor under irradiation. Azido-BSP is a new tool to identify and characterize the TXA2/PGH2 receptor.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Affinity Labels; Azides; Blood Platelets; Fibrinolytic Agents; Humans; Kinetics; Prostaglandin Endoperoxides; Prostaglandin Endoperoxides, Synthetic; Prostaglandin H2; Prostaglandins H; Receptors, Prostaglandin; Receptors, Thromboxane; Sulfonamides; Thromboxane A2

The purpose of this investigation was to examine the potential beneficial effect of the selective endoperoxide/thromboxane A2 (TxA2) receptor antagonist, sulotroban (BM 13.177), on tissue type plasminogen activator (tPA)-induced coronary thrombolysis in the dog. A stenosis that eliminated reactive hyperemic capacity was placed on the circumflex coronary artery and an occlusive thrombus was produced by electrical injury to the intimal surface of the artery. Upon occlusion, sodium heparin was administered (300 U/kg i.v.) followed by 100 U/kg i.v. every hour thereafter. All dogs received i.v. tPA 60 min after the formation of the occlusive thrombus at a dose of 10 micrograms/kg/min for up to 90 min, if necessary, to elicit reperfusion. Thrombolysis was demonstrated in all dogs by restoration of coronary blood flow. Dogs were randomized to one of three groups. Group I consisted of 24 animals that received vehicle infusion along with tPA. Group II consisted of 10 animals that received sulotroban at a bolus dose of 1 mg/kg i.v. followed by 1 mg/kg/hr i.v. administered simultaneously with tPA. Group III consisted of 11 animals that received sulotroban at a bolus of 10 mg/kg i.v. followed by 10 mg/kg/hr i.v. administered simultaneously with tPA. Infusions of either vehicle or sulotroban were continued for 2 hr, post-thrombolysis. tPA was infused for at least 30 min, after which infusion of tPA was terminated upon achieving a reperfusion level of coronary blood flow equivalent to 50% or greater than control blood flow. All animals occluded spontaneously to electrolytic stimulation between 32 and 62 min. tPA-induced thrombolysis occurred in Group I vehicle-infused animals at 32 +/- 5 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Blood Pressure; Coronary Circulation; Coronary Disease; Coronary Thrombosis; Dogs; Drug Therapy, Combination; Female; Fibrinolytic Agents; Male; Platelet Aggregation Inhibitors; Sulfonamides; Thromboxane A2; Tissue Plasminogen Activator

Two-phase thromboxane A2 (TXA2) generation was observed in washed rat platelets stimulated by collagen. One coincided with shape change and the other with aggregation, and both reactions were inhibited by indomethacin. The collagen-induced first phase was not affected by treatment of the platelets with TXA2 receptor antagonist BM13177, while the shape change, the second phase TXA2 generation and aggregation were completely suppressed. U46619, a stable TXA2 mimetic, induced only platelet shape change and not aggregation or endogenous icosanoid mobilization. However, upon addition of U46619 to platelets previously stimulated by collagen in the presence of indomethacin, icosanoids formation was induced together with aggregation. These results suggest that both the collagen-induced initial TXA2 and the occupation of the receptor by collagen might be a trigger for the second-phase TXA2 formation in concert with platelet aggregation.

Topics: Animals; Arachidonic Acid; Arachidonic Acids; Blood Platelets; Collagen; Dose-Response Relationship, Drug; Indomethacin; Kinetics; Phospholipases; Platelet Aggregation; Prostaglandin Endoperoxides, Synthetic; Prostaglandins, Synthetic; Quinacrine; Rats; Receptors, Prostaglandin; Receptors, Thromboxane; Sulfonamides; Thromboxane A2

Topics: Coronary Circulation; Coronary Disease; Fibrinolytic Agents; Humans; Receptors, Prostaglandin; Receptors, Thromboxane; Sulfonamides; Thromboxane A2

Effects of OKY-046, a thromboxane synthetase inhibitor; BM 13.177, a thromboxane A2-receptor antagonist and FPL 55712, a leukotriene antagonist have been studied on gastric lesions induced by necrotizing agents (80% ethanol, 0.6 M HCl, 0.2 M NaOH, 25% NaCl and 100 mM sodium taurocholate), aspirin, indomethacin, reserpine and hypothermic restraint stress in rats. Ro 22-6923, a synthetic trimethyl prostanoid has been used for comparison. OKY-046, FPL 55712 and Ro 22-6923 produced dose dependent inhibition of gastric lesions induced by necrotizing agents and reduced the severity of aspirin, indomethacin, reserpine and hypothermic restraint stress induced lesions. BM 13.177 was not found effective against any of the models used in this study. These observations indicate towards the role of thromboxane A2 and leukotriene C4 in the genesis of gastric lesions induced by different methods. FPL 55712 required considerably lower doses than those of OKY-046 to display its protective effects in these models. Further studies on the levels of thromboxane A2 and leukotriene C4 in the gastric mucosa, are suggested to substantiate these observations.

Topics: Animals; Anti-Ulcer Agents; Chromones; Female; Fibrinolytic Agents; Male; Methacrylates; Prostaglandins E, Synthetic; Rats; Rats, Inbred Strains; SRS-A; Stomach Ulcer; Sulfonamides; Thromboxane A2

The pharmacokinetics and pharmacodynamics of BM 13.177 were investigated in eight healthy men who received a single oral dose of 800 mg on the first day and seven equal doses in 8-hour intervals on the second to fourth days. Pharmacodynamic effects were measured ex vivo by the testing of platelet functions such as shape change, aggregation, and [3H]serotonin release. The maximum serum concentration of 6.6 or 6.7 mg/L was achieved within 1.6 hours after the first dose and within 1.5 hours after multiple doses, respectively. Afterwards, BM 13.177 was eliminated in urine with a terminal elimination t1/2 of 0.84 or 1.0 hours after single and multiple dosing, respectively. The inhibition of platelet function showed the same close correlation with the serum concentrations of BM 13.177 after single and after multiple doses. Apparently, BM 13.177 induces neither refractoriness to BM 13.177 nor desensitization of the platelet thromboxane receptor. Because BM 13.177 was also well tolerated without subjective or objective side effects, this drug appears to be useful in evaluating the clinical benefit of thromboxane receptor blockade.

Topics: Adult; Blood Platelets; Collagen; Humans; Kidney; Kinetics; Male; Platelet Aggregation; Receptors, Cell Surface; Serotonin; Sulfonamides; Thromboxane A2; Time Factors

In order to elucidate the role of endogenous thromboxane A2 in myocardial ischaemia, cats were subjected to 5 h of permanent occlusion of the left anterior descending coronary artery (LAD) and treated with the thromboxane receptor antagonist BM 13.177 (5 mg kg-1 h-1, i.v.). In comparison with vehicle-treated LAD-occluded cats, BM 13.177 significantly attenuated the loss of creatine phosphokinase-specific activity from the ischaemic myocardium and antagonized the ischaemia-induced rise in the ST-segment of the electrocardiogram. BM 13.177 at the dose used did not reduce plasma thromboxane levels or ischaemia-induced platelet aggregate formation but considerably antagonized thromboxane-dependent platelet secretion ex vivo. The study demonstrates some beneficial effects of selective blockade of thromboxane receptors on biochemical and electrophysiological parameters of acute myocardial ischaemia.

Topics: Adenosine Triphosphate; Animals; Blood Platelets; Cats; Coronary Disease; Creatine Kinase; Electrocardiography; Fibrinolytic Agents; Heart Rate; Hemodynamics; Myocardium; Receptors, Cell Surface; Receptors, Prostaglandin; Receptors, Thromboxane; Sulfonamides; Thromboxane A2; Time Factors

We investigated the effect of a thromboxane antagonist, BM 13.177, during endotoxin-induced pulmonary vasoconstriction in sheep. In control animals intravenous E-coli endotoxin (1 microgram/kg) caused a transient increase of pulmonary artery and airway pressure paralleled by large concentration increases of TXB2: in comparison peak plasma concentrations of 6-keto-PGF1 alpha (a prostacyclin metabolite) were small and delayed in time. Pre-treatment with BM 13.177 (bolus 5 mg/kg), followed by 0.75 mg/kg/min intravenously) abolished the rise of pulmonary artery and airway pressure. Plasma concentrations of TXB2 and 6-keto-PGF1 alpha were similar to controls. These and previous investigations imply that BM 13.177 specifically antagonizes TXA2 on the putative receptor in pulmonary vascular and airway smooth muscle.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Endotoxins; Escherichia coli; Female; Hypertension, Pulmonary; Lung; Sheep; Sulfonamides; Thromboxane A2; Thromboxane B2; Vasoconstriction

Thromboxane A2 (TxA2) production increases significantly during acute myocardial ischemia. Since TxA2 induces platelet aggregation, coronary vasoconstriction, and has a direct cytolytic effect, thromboxane receptor antagonism would be expected to be beneficial in acute myocardial ischemia. Thirty minutes after ligation of the left anterior descending coronary artery (LAD) in anesthetized cats, the TxA2 receptor antagonist BM-13,177 or its vehicle was given as a bolus injection at 20 mg/kg, followed by continuous infusion of 20 mg/kg/hr for 4.5 hours. ST segment elevation declined significantly (p less than 0.02) after BM-13,177 treatment, suggesting a reduction in cellular ischemia. The loss in myocardial creatine kinase (CK) activity and in free amino-nitrogen concentration in the ischemic area was also significantly reduced (p less than 0.01). No significant changes in blood pressure or heart rate were seen with BM-13,177 during myocardial ischemia or in nonischemic control cats. Blood levels of BM-13,177 were sufficient to inhibit ex vivo platelet aggregation induced by the prostaglandin endoperoxide analog, U-46,619. Data from isolated cat coronary arteries suggest that BM-13, 177 antagonizes the thromboxane/endoperoxide receptor in coronary vascular smooth muscle. These experiments indicate that TxA2 plays a significant role in propagating the extension of ischemic damage, and that thromboxane receptor antagonism is an effective means of reducing the damage provoked by TxA2 in acute myocardial ischemia.

Topics: Animals; Blood Pressure; Cats; Coronary Disease; Creatine Kinase; Heart Rate; Myocardium; Pancreas; Platelet Aggregation; Proteins; Receptors, Cell Surface; Receptors, Prostaglandin; Receptors, Thromboxane; Sulfonamides; Thromboxane A2

The main cyclooxygenase-dependent arachidonic acid derivatives produced by monocytes and macrophages have been shown to be thromboxane A2 and prostaglandin E2. The immunomodulatory effects of thromboxane A2 were examined using a specific thromboxane synthase inhibitor (dazoxiben), a thromboxane A2 analog (U46619), and a thromboxane A2 receptor blocker (BM13.177). Dazoxiben inhibited lymphocyte proliferation in response to mitogens (PHA and OKT3), but also reoriented cyclic endoperoxide metabolism towards the production of prostaglandin E2. Prostaglandin E2 has been shown previously to inhibit mitogen-induced lymphocyte proliferation. U46619, a stable thromboxane A2 analog, slightly enhanced lymphocyte responses to mitogens in the presence of dazoxiben and in the presence of a cyclooxygenase inhibitor (indomethacin). This occurred at concentrations of U46619 which are probably supraphysiological in view of the short half-life of natural thromboxane A2. Finally, the thromboxane A2 receptor blocker BM13.177 did not have any effect on mitogen-induced lymphocyte proliferation. It is concluded that thromboxane A2 has no or minimal modulatory effects on lymphocyte proliferative responses to mitogens and that the effect of thromboxane A2 synthase inhibition is rather due to reorientation of cyclic endoperoxide metabolism, resulting in increased prostaglandin E2 production.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Antibodies, Monoclonal; Cyclooxygenase Inhibitors; Dinoprostone; Humans; Imidazoles; Indomethacin; Lymphocyte Activation; Lymphocytes; Phytohemagglutinins; Platelet Aggregation; Prostaglandin Endoperoxides, Synthetic; Prostaglandins E; Receptors, Prostaglandin; Receptors, Thromboxane; Sulfonamides; Thromboxane A2; Thromboxane-A Synthase; Thromboxanes

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Aspirin; Blood Platelets; Collagen; Humans; Prostaglandin Endoperoxides; Prostaglandin Endoperoxides, Synthetic; Prostaglandin H2; Prostaglandins H; Serotonin; Sulfonamides; Thrombin; Thromboxane A2; Thromboxanes

In blood-free perfused isolated rabbit lungs increased availability of free arachidonic acid (AA), whether exogenously applied or released from the endogenous membrane phospholipid pool after different stimuli, causes an acute pulmonary artery pressor response and an increase in vascular permeability. Previous experiments suggested that the vasoconstriction is caused primarily by the cyclooxygenase product thromboxane (Tx) A2, whereas an increase in the capillary filtration coefficient must be ascribed to non-cyclooxygenase products of AA. The influence of BM 13.177, a non-prostanoic antagonist of TxA2- and endoperoxide-effects in platelets, on the AA-induced vascular effects in isolated rabbit lungs was investigated. BM 13.177 dose-dependently inhibited the pressor responses evoked by repetitive direct application of AA (IC50 approximately 10(-6) M) or by repetitive stimulation of endogenous AA-release with the calcium-ionophore A 23187 (IC50 approximately 10(-7) M), with maximum reduction of the pressor responses to less than 15%. The generation of TxA2 and of prostaglandin (PG) I2 evoked by these stimuli was, however, not altered. At a concentration of 10(-5) M BM 13.177 did not influence the capillary filtration coefficient, measured during venous pressure challenge, under baseline conditions and after stimulation with AA in presence of indomethacin.. BM 13.177 acts as TxA2/endoperoxide antagonist with dose-dependent inhibition of AA-induced vasoconstriction in the pulmonary vascular bed.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Arachidonic Acid; Arachidonic Acids; Blood Pressure; Calcimycin; Capillary Permeability; Fibrinolytic Agents; In Vitro Techniques; Indomethacin; Kinetics; Pulmonary Circulation; Rabbits; Sulfonamides; Thromboxane A2; Vascular Resistance; Vasoconstriction

BM 13.177 (4-[2-(benzenesulfonamido)-ethyl]-phenoxyacetic acid) is a representative of a new class of sulfonamidophenylcarboxylic acids which possess platelet-inhibitory and anti-thrombotic activity and inhibits the contraction of rabbit aorta stimulated by PG endoperoxides and TXA2. BM 13.177 5 mg/kg body weight p.o. protected rabbits from arachidonate-induced sudden death and greater than or equal to 10 mg/kg dose-dependently reduced the experimental thrombus formation induced in the rabbit aorta by perivascular administration of silver nitrate. In guinea-pigs, the collagen-induced bronchoconstriction was inhibited in a dose- and time-dependent fashion. The formation of TXA2 and the TXA2-induced platelet aggregation and smooth muscle contraction are probably crucial events in these experimental models. The protective effect of BM 13.177 may, therefore, be due to the TXA2-antagonizing effect of BM 13.177, which has been conclusively demonstrated in human platelets (PATSCHEKE and STEGMEIER, Thrombosis Res., 33, 277-288 (1984). The antagonism of TXA2 is supported by the observation that BM 13.177 also specifically inhibits the contraction of isolated arterial strips from rabbits which were stimulated with the thromboxane A2 mimetic U 46619. Schild-plot with a slope close to unity suggests a competitive type of antagonism. BM 13.177 exhibited neither anti-inflammatory nor ulcer-inducing activity of cyclooxygenase inhibitors. Furthermore it did not block the TXB2 formation in spontaneously clotting blood from rabbits and did not inhibit the release of prostacyclin-like activity from rabbit aortas. The lack of toxicological effects in long-term toxicity studies in rat and dog, together with the absence of objective and subjective side effects in the first human studies have encouraged us to initiate clinical trials in order to evaluate the therapeutic benefit of this new approach in humans.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Epoprostenol; Female; Fibrinolytic Agents; Guinea Pigs; Male; Muscle Contraction; Muscle, Smooth, Vascular; Platelet Aggregation; Prostaglandin Endoperoxides, Synthetic; Rabbits; Sulfonamides; Thrombosis; Thromboxane A2; Thromboxane B2; 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