thromboxane-b2 and pirmagrel

In this study we evaluated the role of thromboxane in causing allergen-induced early and late asthmatic responses and airway hyperresponsiveness in asthmatic subjects. Twelve atopic subjects with stable asthma and documented early and late asthmatic responses to an inhaled allergen were treated with placebo or CGS 13080, a specific thromboxane synthetase inhibitor, given orally (200 mg four times daily) for two days before, the day of, and the day after allergen inhalation. Treatments were administered in a double-blind, placebo-controlled, crossover fashion. The effect of pretreatment with CGS 13080 was examined on serum TxB2 levels and the magnitude of the asthmatic responses after inhaled allergen. Serum TxB2 levels increased significantly from 96 ng.ml-1 (SEM 29) 3 h after diluent to 151 ng.ml-1 (SEM 27) 3 h after allergen (p = 0.008). CGS 13080 pretreatment markedly inhibited the levels of TxB2 at all time points before and after inhaled allergen (p = 0.0001) and had a small but significant effect on the magnitude of the early asthmatic responses after allergen (p = 0.0009). CGS 13080 did not alter either late asthmatic responses, baseline airway responsiveness, or the increase in histamine airway responsiveness after allergen. These results suggest that allergen-induced early asthmatic responses, but not late responses or allergen-induced airway hyperresponsiveness, are partly caused by thromboxane release.

Topics: Adult; Allergens; Asthma; Bronchial Provocation Tests; Bronchoconstriction; Double-Blind Method; Female; Humans; Imidazoles; Male; Pyridines; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes; Time Factors

CGS 13080, a selective thromboxane synthetase inhibitor, was given intravenously (0.6 mg/kg over 6 hours) to eight hypertensive (diastolic 95-115 mm Hg) euvolemic caucasian females on their customary salt intake (24 hour urine Na: 142.9 +/- 14.8 meq). No change occurred in blood pressure or glomerular filtration rate (GFR): 95.2 +/- 7.2, control versus 95.0 +/- 9.0, CGS 13080 (ml/min); or renal plasma flow (RPF): 363.2 +/- 34.2, control, versus 373.2 +/- 31.2, CGS 13080, (ml/min). Prostaglandin production was altered: platelet generation of thromboxane B2 83.3 +/- 10.9, control, versus 5.4 +/- 1.8, CGS 13080 (ng/hr) (P less than .001); urinary prostaglandin E (PGE) 249.0 +/- 56.3, control, versus 443.9 +/- 79.8, CGS 13080 (ng/6 hr) (P = .06); urinary 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) 188.6 +/- 23.4, control, versus 287.9 +/- 21.8, CGS 13080 (ng/6 hr) (P = .01); urinary thromboxane B2 54.8 +/- 12.9, control, versus 58.6 +/- 20.3 CGS 13080 (ng/6 hr) (P = NS). Serum levels of renin, angiotensin II and aldosterone were not altered by CGS 13080. Captopril when dosed to lower diastolic blood pressure 5-7 mm Hg did not significantly affect GFR, RPF or RVR. Nor did it affect platelet generation of thromboxane B2 or urine concentrations of PGE, 6-keto-PGF1 alpha or thromboxane B2. Captopril did increase renin levels 1.2 +/- 0.2, control, versus 2.9 +/- 1.1, captopril (ng/ml/hr) (P = NS), but did not statistically change angiotensin II, or aldosterone levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adult; Aldosterone; Angiotensin-Converting Enzyme Inhibitors; Blood Pressure; Captopril; Clinical Trials as Topic; Female; Hemodynamics; Humans; Hypertension; Imidazoles; Kidney; Middle Aged; Potassium; Prostaglandins; Pyridines; Renin-Angiotensin System; Sodium; Thromboxane B2; Thromboxane-A Synthase

Although thromboxane A2 is a potent platelet agonist and vasoconstrictor in vitro, our knowledge of its pathophysiologic importance in human disease is limited. To facilitate the elucidation of its role in vivo, we sought to define a human syndrome in which pharmacologic interventions designed to inhibit the biosynthesis or biologic actions of thromboxane A2 might be appropriately assessed. Patients with severe peripheral vascular disease were selected on the basis of elevated plasma beta-thromboglobulin and circulating platelet aggregates and compared with healthy, age-matched control subjects. In addition to the platelet indexes, their bleeding time was shorter and excretion of 2,3-dinor-thromboxane B2, a noninvasive index of thromboxane formation in vivo, and 2,3-dinor-6-keto-prostaglandin F 1 alpha, the major urinary metabolite of prostacyclin, was markedly increased. A selective inhibitor of thromboxane synthase, imidazo (1,5-2) pyridine-5-hexanoic acid, was administered to these patients under randomized, double-blind, controlled conditions. Platelet aggregation ex vivo, the circulating platelet aggregate ratio, and the bleeding time were all unaltered, despite almost maximal inhibition of platelet thromboxane formation 1 hr after dosing. By contrast, pronounced inhibition of aggregation was observed when platelet cyclooxygenase was inhibited by aspirin. During long-term dosing with the synthetic inhibitor, inhibition of thromboxane biosynthesis was incomplete, which would permit continued thromboxane-dependent platelet aggregation to occur. However, the failure of enzyme blockade to influence platelet function at the time of maximal drug action, despite efficient inhibition of serum thromboxane B2, suggests that accumulation of proaggregatory endoperoxides is also likely to have contributed to the persistence of platelet activation. We have characterized a human preparation in which platelet activation coexists with increased thromboxane biosynthesis. In this setting, platelet activation persists despite long-term administration of a thromboxane synthase inhibitor in a dosing regimen representative of that employed in clinical trials. Prolongation of drug action and combination with antagonists of the shared endoperoxide/thromboxane A2 receptor may be necessary to assess the potential of selective inhibition of thromboxane synthase as a therapeutic strategy in man.

Topics: 6-Ketoprostaglandin F1 alpha; Aged; Arteriosclerosis; beta-Thromboglobulin; Epoprostenol; Female; Humans; Imidazoles; Male; Middle Aged; Platelet Aggregation; Platelet Factor 4; Pyridines; Thromboxane B2; Thromboxane-A Synthase

Oral administration of CGS-13080 [imidazo (1, 5-alpha) pyridine-5-hexanoic acid], a thromboxane synthetase inhibitor, has been reported to cause a marked reduction in serum thromboxane B2 concentration in humans and animals. Since thromboxane metabolites play an important role in ocular inflammation, the effect of oral CGS-13080 in the development of experimental autoimmune uveoretinitis in Lewis rats has been investigated. Females were immunized with bovine S-antigen (S-Ag). Treatment was started on day 0 of immunization. Animals were divided into three groups. The control group was fed a standard pellet diet, while the treated groups were fed the standard diet supplemented with either a low dose (0.8 g per 10 kg pellet) or a high dose (1.6 g per 10 kg pellet) of CGS 13080. From day 10 after immunization, the eyes of these rats were examined daily for clinical evidence of experimental autoimmune uveoretinitis. On day 14, the eyes were collected for histologic study. The cellular immune responses were evaluated on the draining inguinal lymph nodes. Blood samples were also collected for the measurement of anti-S-Ag antibody production, thromboxane B2 and prostaglandin A2 levels. Clinical disease developed in 73.3% of the control rat group, 30.0% of the low-dose treated group and 17.6% of the high-dose group. The average histologic grade was 1.9 in the control group, 0.65 in low-dose group and 0.32 in high-dose group. Lymphocyte proliferation to S-Ag paralleled the clinical disease scores. Average stimulation indices were 10.9 in the controls, 7.5 in the low-dose group and 2.2 in the high-dose group.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Antigens; Arrestin; Autoantigens; Autoimmune Diseases; Chorioretinitis; Choroid; Dinoprostone; Eye Proteins; Female; Imidazoles; Immunoglobulin G; Lymphocyte Activation; Pyridines; Rats; Rats, Inbred Lew; Retina; Thromboxane B2; Thromboxane-A Synthase

The effects of a 48-hour 0.5 mg/kg/hr infusion of the thromboxane synthase inhibitor pirmagrel were studied in 10 renal allograft recipients with cyclosporine nephrotoxicity. Plasma concentrations reached a mean steady-state plasma level of 1798 +/- 481 ng/ml. Biphasic, rapid elimination of pirmagrel was observed with a distribution half-life of 6.7 minutes and a terminal half-life of 73 minutes. Plasma clearance and the volume of distribution of the drug were 300 +/- 87 ml/hr/kg and 497 +/- 232 ml/kg, respectively. The pharmacodynamic effects of pirmagrel were marked by a mean 96% suppression of serum thromboxane B2 (TXB2), which coincided with a suppression of urinary excretion of TXB2, 2,3-dinor-TXB2, and 11-dehydro-TXB2 of 85% +/- 8%, 91% +/- 5%, and 89% +/- 9%, respectively. Urinary excretion of all thromboxane metabolites measured at the end of 1 week after termination of infusion was returned to the baseline. In conclusion, pirmagrel caused effective and sustained suppression of all thromboxane derived metabolites in plasma and urine during continuous infusion in kidney transplant patients receiving cyclosporine.

Topics: Adult; Half-Life; Humans; Imidazoles; Infusions, Intravenous; Kidney Transplantation; Pyridines; Radioimmunoassay; Thromboxane B2; Thromboxane-A Synthase; Transplantation, Homologous

Neutralization of heparin anticoagulation by protamine produces catastrophic hemodynamic reactions in some patients. Using a canine model, we tested effects of thromboxane synthetase inhibition (CGS-13080) and glucocorticoid pretreatment on the cardiorespiratory effects of protamine. In control dogs, protamine decreased mean arterial pressure and cardiac output and increased mean pulmonary artery pressure, systemic and pulmonary vascular resistances (SVR, PVR), and airway pressure. Both CGS-13080 and methylprednisolone ameliorated some effects of protamine. CGS-13080 infusion decreased mean pulmonary artery pressure, SVR, and airway pressure after protamine injection relative to controls. Cardiac output and PVR were unaffected by the drug, whereas the decrease in mean arterial pressure was prolonged. Plasma thromboxane A2 metabolite (TXB2) concentrations were lower and prostacyclin metabolite (6-keto PGF1 alpha) concentrations were higher compared with that of controls. These experiments support a role for TXA2 in the response to protamine. Methylprednisolone pretreatment produced larger cardiac output and lower airway pressure after protamine injection compared with controls. Mean arterial pressure was improved, but not significantly. Mean pulmonary artery pressure, SVR, and PVR were not different from that of controls; TXB2 and 6-keto PGF1 alpha were unaffected. The effects of methylprednisolone appear unrelated to arachidonic acid metabolism, as TXB2 and 6-keto PGF1 alpha levels were unaffected.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Dogs; Drug Interactions; Hemodynamics; Imidazoles; Methylprednisolone; Protamines; Pyridines; Thromboxane B2; Thromboxane-A Synthase

To test the hypothesis that prostanoids contribute to angiotensin II-induced vascular contraction, we compared the effect of angiotensin II on isometric tension development by rings of descending thoracic aorta bathed in Krebs' bicarbonate buffer with and without indomethacin (10 microM) to inhibit cyclooxygenase, CGS13080 (10 microM) to inhibit thromboxane A2 synthesis, or SQ29548 (1 microM) to block thromboxane A2/prostaglandin endoperoxide receptors. The comparisons were made in rings of aorta taken from normotensive rats and from rats with aortic coarctation-induced hypertension at 12 days and 90-113 days after coarctation. These rings released thromboxane B2, which was found to be endothelium dependent, increased in hypertensive rats, and stimulated by angiotensin II (10(-6) M) in normotensive rats and in hypertensive rats at 12 days after coarctation. The angiotensin II (10(-6) to 10(-5)M)-induced contraction of aortic rings was increased by about 30% at 12 days after coarctation and decreased at 90-113 days after coarctation. Removal of the endothelium increased the contractile effect of angiotensin II (10(-6) M) in aortic rings of normotensive rats and hypertensive rats at 90-113 days after coarctation but decreased the effect in aortic rings of hypertensive rats at 12 days after coarctation. In rats at 12 days after coarctation, the angiotensin II (10(-6) M)-induced contraction of aortic rings with endothelium was attenuated by indomethacin and SQ29548 but not by CGS13080. These data suggest that a prostanoid-mediated and endothelium-dependent mechanism of vasoconstriction contributes to the constrictor effect of angiotensin II in aortic rings of rats in the early phase of aortic coarctation-induced hypertension.

Topics: Acetylcholine; Analysis of Variance; Angiotensin II; Animals; Aorta; Aortic Coarctation; Bridged Bicyclo Compounds, Heterocyclic; Dose-Response Relationship, Drug; Endothelins; Endothelium; Fatty Acids, Unsaturated; Hydrazines; Hypertension; Imidazoles; In Vitro Techniques; Indomethacin; Isometric Contraction; Male; Phenylephrine; Prostaglandin Endoperoxides, Synthetic; Pyridines; Rats; Rats, Inbred Strains; Thromboxane A2; Thromboxane B2; Thromboxane-A Synthase; Vasoconstriction

Pulmonary hypertension occurs after the intravascular activation of complement. However, it is unclear which activated complement fragments are responsible for the pulmonary vascular constriction. We investigated the 21-carboxy-terminal peptide of C3a (C3a57-77) to see if it would cause pulmonary vascular constriction when infused into isolated buffer-perfused rat lungs. Injection of C3a57-77 (225 to 450 micrograms) caused mean pulmonary arterial pressure (Ppa) to rapidly increase. However, the response was transient, with Ppa returning to baseline within 10 min of its administration. C3a57-77 also resulted in an increase in lung effluent thromboxane B2 (TXB2), concomitant with the peak increase in Ppa. C3a57-77 did not affect the amount of 6-keto-PGF1 alpha in the same effluent samples. Indomethacin inhibited the C3a57-77-induced pulmonary artery pressor response and the associated TXB2 production. Indomethacin also decreased lung effluent 6-keto-PGF1 alpha. The thromboxane synthetase inhibitors CGS 13080 and U63,357 inhibited the C3a57-77-induced pulmonary artery pressor response and TXB2 production without affecting 6-keto-PGF1 alpha. These inhibitors did not inhibit pulmonary artery pressor responses to angiotensin II. Tachyphylaxis to C3a57-77 occurred because a second dose of C3a57-77 administered to the same lung failed to cause a pulmonary artery pressor response or TXB2 production. The loss of the pressor response was not due to a C3a57-77-induced decrease in pulmonary vascular responsiveness because pressor responses elicited by angiotensin II were not altered by lung contact with C3a57-77. Thus, C3a57-77 caused thromboxane-dependent pulmonary vascular constriction in isolated buffer perfused rat lungs.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Benzofurans; Blood Pressure; Complement C3a; Cyclooxygenase Inhibitors; Imidazoles; In Vitro Techniques; Indomethacin; Lung; Male; Peptide Fragments; Perfusion; Pyridines; Rats; Thromboxane B2; Thromboxane-A Synthase; Vasoconstriction

The effects of the thromboxane synthase inhibitor CGS13080 on the in vivo synthesis of thromboxane and prostacyclin were determined in six healthy volunteers. Two different doses (0.08 and 0.25 mg/kg x h) were infused for six hours under strictly controlled conditions and 2,3-dinor-TxB2 and 2,3-dinor-6-keto-PGF1 alpha were measured in urine using gaschromatography--mass spectrometry. The in vivo synthesis of thromboxane was inhibited by 80-75% while there was no effect on the in vivo prostacyclin synthesis.

Topics: 6-Ketoprostaglandin F1 alpha; Adult; Epoprostenol; Humans; Imidazoles; Male; Pyridines; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

While platelets have been shown to be capable of supplying prostaglandin (PG) H2 to endothelial cells in culture for PGI2 synthesis, endothelial cells have been shown unable to supply PGH2 to platelets for thromboxane (TX) A2 synthesis. We incubated rings of the bovine coronary artery (BCAR) with human platelets treated with aspirin (to inhibit cyclooxygenase) or CGS 13080 (to inhibit TXA2 synthase) in the presence of 20 microM arachidonic acid. BCAR, with damaged endothelium, produced significantly less PGI2 than that with intact endothelium. However, co-incubation with CGS 13080-treated platelets resulted in an increase in PGI2 independent of endothelium, demonstrating a shunt of PGH2 from platelets to BCAR. Co-incubation of BCAR with aspirin-treated platelets resulted in a net increase in TXA2 demonstrating a shunt of PGH2 from BCAR to platelets. Employing [14C]PGH2 as substrate, BCAR with and without intact endothelium produced similar amounts of 6-keto-[14C]PGF1 alpha. Likewise, homogenates (50 micrograms protein) of intimal and subintimal regions of BCAR and BCAR converted similar amounts of PGH2 to 6-keto-PGF1 alpha. These data suggest that vascular production of PGH2 is more dependent on an intact endothelium than is the conversion of PGH2 to PGI2. These data also suggest a potential for a bidirectional exchange of PGH2 between platelets and vascular wall during platelet-vascular wall interactions.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Arachidonic Acid; Arachidonic Acids; Aspirin; Blood Platelets; Cattle; Coronary Vessels; Cyclooxygenase Inhibitors; Cytochrome P-450 Enzyme System; Epoprostenol; Humans; Imidazoles; Intramolecular Oxidoreductases; Isomerases; Prostaglandin Endoperoxides; Prostaglandin Endoperoxides, Synthetic; Prostaglandin H2; Prostaglandins H; Pyridines; Thromboxane B2; Thromboxane-A Synthase

Prostacyclin (PGI2) is an inhibitor of platelet function in vitro. We tested the hypothesis that PGI2 is formed in biologically active concentrations at the platelet-vascular interface in man and can be pharmacologically modulated to enhance its inhibitory properties. This became feasible when we developed a microquantitative technique that permits the measurement of eicosanoids in successive 40-microliters aliquots of whole blood emerging from a bleeding time wound. In 13 healthy volunteers the rate of production of thromboxane B2 (TXB2) gradually increased, reaching a maximum of 421 +/- 90 (mean +/- SEM) fg/microliters per s at 300 +/- 20 s. The hydration product of PGI2, 6-keto-PGF1 alpha, rose earlier and to a lesser degree, reaching a peak (68 +/- 34 fg/microliters per s) at 168 +/- 23 s. The generation of prostaglandins PGE2 and D2 resembled that of PGI2. Whereas the threshold concentration of PGI2 for an effect on platelets in vitro is approximately 30 fg/microliters, only less than 3 fg/microliters circulates under physiological conditions. By contrast, peak concentrations of 6-keto-PGF1 alpha obtained locally after vascular damage averaged 305 fg/microliters. Pharmacological regulation of PG endoperoxide metabolism at the platelet-vascular interface was demonstrated by administration of a TX synthase inhibitor. The rate of production of PGI2, PGE2, and PGD2 increased coincident with inhibition of TXA, as reflected by three indices; the concentration of TXB2 in bleeding time blood and serum, and excretion of the urinary metabolite, 2,3-dinor-TXB2. These studies indicate that PGI2 is formed locally in biologically effective concentrations at the site of vessel injury and provide direct evidence in support of transcellular metabolism of PG endoperoxides in man.

Topics: 6-Ketoprostaglandin F1 alpha; Bleeding Time; Blood Platelets; Blood Vessels; Epoprostenol; Gas Chromatography-Mass Spectrometry; Humans; Imidazoles; Prostaglandin Endoperoxides; Pyridines; Reference Values; Thromboxane A2; Thromboxane B2

We studied the effects of a thrombolytic agent (t-PA) and a thromboxane synthetase inhibitor (CGS-13080) in a model of myocardial ischemia and reperfusion. Occlusion of the left anterior descending coronary artery for 2 hours followed by 4 hours of reperfusion in anesthetized cats results in a large washout of creatine kinase into the blood (32 +/- 7 IU/mg protein) and an area of necrotic tissue comprising 52 +/- 5% of the area at risk and 9 +/- 0.6% of the left ventricle. Intravenous administration of t-PA (500 IU/kg.min) for 30 minutes alone at reperfusion or infusion of CGS-13080 (500 micrograms/kg.hr) had no effect on washout of creatine kinase or extent of necrotic tissue development. Administration of the same doses of both t-PA and CGS-13080 together markedly attenuated creatine kinase release to 10 +/- 2 IU/mg protein (p less than 0.01) and reduced the area of necrotic tissue to 9 +/- 2% of the area at risk and only 1.3 +/- 0.3% of the left ventricle (p less than 0.001). No significant sustained effects of these agents were observed on mean arterial blood pressure, heart rate, or the pressure rate index in these experiments. Thus, t-PA and CGS-13080 exert synergistic effects in preserving myocardial integrity in cats subjected to acute myocardial ischemia followed by reperfusion. The mechanism of this beneficial effect does not appear to be via reduced myocardial oxygen demand, increased myocardial oxygen supply, or enhanced inhibition of thromboxane A2 formation. The mechanism of this anti-ischemic effect is not clear but may involve a metabolic or a cytoprotective effect.

Topics: Animals; Cats; Coronary Disease; Creatine Kinase; Drug Synergism; Hemodynamics; Imidazoles; Male; Myocardium; Necrosis; Pyridines; Thromboxane B2; Thromboxane-A Synthase; Tissue Plasminogen Activator

The capacity of the perfused rat liver to produce thromboxane after stimulation by phorbol myristate acetate was examined. A total of 109 +/- 20 and 155 +/- 28 pmol/g liver were found in the perfusate and in the bile, respectively, after 40 min. The amount of thromboxane recovered in the perfusate and in the bile accounted for 12.6% of the production calculated from the same number of Kupffer cells in primary cultures, indicating that a major part of thromboxane was taken up and inactivated by hepatocytes. The effect of endogenously synthesized thromboxane on the liver was assessed by using CGS 13080, a thromboxane synthase inhibitor, or BM 13.177, a thromboxane receptor antagonist. 20 nM CGS 13080 in the perfusate inhibited the synthesis of thromboxane and at the same time the elevation of portal pressure and glycogenolysis following administration of phorbol 12-myristate 13-acetate (PMA). The thromboxane receptor antagonist BM 13.177 did not inhibit the synthesis of thromboxane, but reduced the PMA-related elevation of portal pressure and glycogenolysis to the same extent (greater than 60%) as CGS 13080. Sodium nitroprusside, a vasodilator, inhibited the rise in portal pressure caused by PMA to the same extent as CGS 13080 or BM 13.177 but reduced the increase in glycogenolysis only by 25%. These results indicate that thromboxane released by stimulated Kupffer cells of the liver elevates portal pressure and glycogenolysis in the perfused rat liver, although by different mechanisms.

Topics: Animals; Bile; Female; Imidazoles; Kinetics; Liver; Perfusion; Prostaglandins; Pyridines; Rats; Rats, Inbred Strains; Reference Values; Sulfonamides; Tetradecanoylphorbol Acetate; Thromboxane B2; Thromboxane-A Synthase

Topics: Depression, Chemical; Graft Rejection; Humans; Imidazoles; Immunosuppression Therapy; Immunosuppressive Agents; Kidney Transplantation; Pyridines; Thromboxane B2; Thromboxane-A Synthase

Pulmonary hypertension with an elevated pulmonary vascular resistance was observed during the immediate recovery period in patients who underwent mitral valve surgery. In eight such patients, intravenous infusion of CGS-13080, imidazo(1,5-a)pyridine-5-hexanoic acid (a thromboxane synthetase inhibitor), at a dose range of 0.08-0.1 mg/kg/hr, effectively reduced pulmonary hypertension (from a mean pulmonary arterial pressure of 36 +/- 2 to 31 +/- 2 torr) and pulmonary vascular resistance (from 339 +/- 38 to 238 +/- 37 dynes.sec.cm-5) within 30 minutes and remained reduced for the entire infusion period (48 hours in five patients and 18 hours in three patients). Mean arterial pressure or systemic vascular resistance were not significantly affected by the drug infusion. Serum thromboxane B2 levels (a stable metabolic product of thromboxane A2) were significantly reduced after administration of the compound, with the maximum effect of greater than 90% reduction. All patients tolerated the drug infusion without significant side effects.

Topics: 6-Ketoprostaglandin F1 alpha; Cardiopulmonary Bypass; Heart Valve Prosthesis; Hemodynamics; Humans; Hypertension, Pulmonary; Imidazoles; Mitral Valve; Postoperative Complications; Pulmonary Circulation; Pyridines; Thromboxane B2; Thromboxane-A Synthase; Vascular Resistance

The effect of a specific inhibitor of thromboxane (Tx) A2 synthesis, CGS-13080, a new angiotensin converting enzyme inhibitor, CGS-16617, and a combination of both drugs was studied in hemorrhagic shock in rats. Treatment with CGS-16617 (1 microgram/kg) or CGS-13080 (200 micrograms/kg) alone did not alter significantly postoligemic hypotension or the increase in plasma cathepsin D activity in shocked rats, compared with hemorrhaged rats receiving only their vehicle. Combined treatment with both drugs maintained postreinfusion mean arterial blood pressure and attenuated the increase in plasma cathepsin D activity in hemorrhaged rats. Treatment of shocked rats with each drug alone attenuated the accumulation of a myocardial depressant factor activity in the plasma, but the lowest myocardial depressant factor activities were observed in rats treated with the drug combination. Additionally, animals treated with the drug combination exhibited significantly longer postreinfusion survival times than rats receiving either the vehicle (P less than .01), CGS-16617 (P less than .05) or CGS-13080 (P less than .02). CGS-16617 (1 microgram/kg) attenuated significantly the pressor response to angiotensin I throughout the shock period. CGS-13080 attenuated the increase in TxB2 plasma concentrations in shock when compared with hemorrhaged rats receiving the vehicle (P less than .05). Greater attenuation of TxB2 was found after treatment with the drug combination (P less than .01 from vehicle, P less than .05 from CGS-13080 alone). CGS-16617, but not CGS-13080, was also found to have a direct antiproteolytic action in pancreatic homogenates. However, the drug combination (CGS-16617 and CGS-13080) decreased proteolytic activity even further (P less than .001) from CGS-16617 alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Angiotensin I; Angiotensin-Converting Enzyme Inhibitors; Animals; Benzazepines; Blood Pressure; Cathepsin D; Drug Synergism; Drug Therapy, Combination; Imidazoles; Male; Myocardial Depressant Factor; Pyridines; Rats; Rats, Inbred Strains; Shock, Hemorrhagic; Thromboxane B2; Thromboxane-A Synthase

Thromboxane synthetase inhibitors have been shown to reduce thromboxane, a potent vasoconstrictor, and increase prostacyclin, a potent vasodilator, in normal subjects. We evaluated the acute and chronic (three months) effects of the thromboxane synthetase inhibitor CGS13080 administered 200 mg every six hours on the resting hemodynamics in ten patients with primary pulmonary hypertension (PPH), and on their response to 20 mg of nifedipine given sublingually before and after the thromboxane synthetase inhibitor treatment. It was concluded that one can modulate the levels of endogenous thromboxane and prostacyclin in patients with primary pulmonary hypertension using a thromboxane synthetase inhibitor. Although the thromboxane synthetase inhibitor alone produced only modest hemodynamic changes over time, the addition of nifedipine was able to produce a further lowering of pulmonary artery pressure and pulmonary vascular resistance.

Topics: Adult; Epoprostenol; Female; Humans; Hypertension, Pulmonary; Imidazoles; Male; Middle Aged; Nifedipine; Pyridines; Thromboxane B2; Thromboxane-A Synthase

Pretreatment with the thromboxane synthase inhibitor OKY-046 but not the cyclo-oxygenase inhibitor ibuprofen protects against ischemia-induced acute tubular necrosis. However, ibuprofen together with the vasodilating agent prostaglandin E1 is protective. This suggests that a high prostaglandin to thromboxane ratio is the major factor operative in preventing tubular necrosis, the subject of this study. Rats that had unilateral nephrectomy (n = 60) with the exception of rats that had sham operations (n = 8) underwent 45 minutes of left renal pedicle clamping. Thirty minutes before the operation, the rats received either a saline solution or a thromboxane synthase inhibitor that was given intravenously. The inhibitors OKY-046 (2 milligrams per kilogram, n = 10), UK38485 (1 milligram per kilogram, n = 9) and U63357A (10 milligrams per kilogram, n = 10) were given as a single bolus while the inhibitor CGS13080 (0.1 milligram per kilogram, n = 9, and 1.0 milligram per kilogram, n = 7) was given by constant infusion and continued for 60 minutes after reperfusion. With saline solution therapy, five minutes after reperfusion, thromboxane B2 increased from 154 to 2,537 picograms per milliliter (p less than 0.00001) and 6-keto-prostaglandin F1 alpha increased from 51 to 266 picograms per milliliter (p less than 0.004). At 24 hours, the creatinine level increased from 0.5 to 2.8 milligrams per deciliter (p less than 0.00001). Only OKY-046 yielded a creatinine level at 24 hours of 1.2 milligrams per deciliter, a value lower than that for those in the saline solution control group (p less than 0.002). Furthermore, OKY-046 led to the highest prostaglandin to thromboxane ratio (p less than 0.035). The five other ratios which occurred after drug therapy were inversely related to the decrease in the creatinine value (r = -0.93, p less than 0.02). Histologically, OKY-046 was the only thromboxane synthase inhibitor to prevent acute tubular necrosis (p less than 0.05). Results show that a high prostaglandin to thromboxane ratio protects against acute tubular necrosis.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Benzofurans; Creatinine; Evaluation Studies as Topic; Ibuprofen; Imidazoles; Ischemia; Kidney; Kidney Tubular Necrosis, Acute; Male; Methacrylates; Pyridines; Rats; Thromboxane B2; Thromboxane-A Synthase

The effects of intravenously administered collagen on the circulatory platelet count, TxB2, 6-keto PGF1 alpha and 51Cr-labelled platelet accumulation in the thorax have been evaluated in the guinea-pig. Administration of collagen induced a dose-related peripheral thrombocytopenia and a concomitant increase in 51Cr-labelled platelets in the thorax. There was also a transient dose-related increase in plasma TxB2 but no change in plasma 6-keto PGF1 alpha levels. The thromboxane synthetase inhibitors tested, reduced the platelet accumulation, but only CGS 13080 significantly inhibited TxB2 production. In contrast all the cyclooxygenase inhibitors tested impaired the elevation of plasma TxB2 after collagen, but only diclofenac inhibited the 51Cr-labelled platelet accumulation. The greater effect of thromboxane synthetase inhibitors compared to cyclooxygenase inhibitors on platelet accumulation in this system cannot be completely explained by the changes measured in the circulating prostanoids.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Blood Platelets; Chromium Radioisotopes; Collagen; Cyclooxygenase Inhibitors; Diclofenac; Dose-Response Relationship, Drug; Guinea Pigs; Imidazoles; Injections, Intravenous; Platelet Aggregation; Platelet Count; Prostaglandins; Pyridines; Thorax; Thromboxane B2; Thromboxanes

The antithrombotic potential of the thromboxane (TX) synthetase inhibitor CGS 13080 (CGS) was studied in an anesthetized open-chest canine model of coronary artery intimal wall injury induced by the local application of a low amperage electrical current (100 microA for 6 hr). CGS was administered by i.v. infusion (1 mg/kg/min) beginning 30 min before applying the direct current to the intimal wall of the vessel. CGS did not alter basal values for heart rate, blood pressure or coronary blood flow. After 6 hr of current application to the vessel, 1 of 10 CGS-treated dogs exhibited complete thrombotic occlusion of the circumflex coronary artery compared to 8 of 10 nontreated control dogs (P less than .01). Thrombus masses within the injured left circumflex coronary artery were: Control, 25.9 +/- 4.5 mg (n = 10) and CGS, 11.0 +/- 2.8 mg (n = 10); P less than .01. The concentration of TXB2 determined ex vivo in serum from thrombin-activated whole blood was decreased by CGS administration: Control, 43.15 +/- 16.08 ng/ml (n = 9) vs. CGS, 1.72 +/- .69 ng/ml (n = 10); P less than .001. Ex vivo platelet aggregometry demonstrated that arachidonic acid (0.65 mM)-induced aggregation was reduced from a control value of 82.3 +/- 7.8% (n = 10) to 45.0 +/- 11.3% (n = 10) (P less than .05), whereas aggregation in response to ADP (5 micrograms/ml) or collagen (156 and 312 micrograms/ml) was unaffected. CGS was compared with two other TX synthetase inhibitors, U63557A and OKY1581, for the ability to divert cyclic endoperoxide metabolism to the synthesis of prostaglandin (PG) E2 and prostacyclin in response to stimulation of whole blood in vitro with collagen (25 micrograms/ml). CGS, U63557A and OKY 1581 were found to be equally effective with respect to PGE2 and 6-keto PGF1 alpha production in vitro. The data demonstrate that CGS is an effective antithrombotic agent in vivo and that it selectively inhibits arachidonic acid-induced platelet aggregation ex vivo and the formation of TXA2 in thrombin-activated whole blood.

Topics: Animals; Blood Pressure; Collagen; Coronary Circulation; Coronary Disease; Dogs; Heart Rate; Imidazoles; Male; Platelet Aggregation; Pyridines; Thromboxane B2; Thromboxane-A Synthase

The hematological and pharmacological effects of a new thromboxane synthetase inhibitor, CGS-13080 (imidazo[1,5-alpha]pyridine-5-hexanoic acid), were investigated during cardiopulmonary bypass in a blinded, randomized manner in dogs. Compared with placebo, CGS-13080 suppressed thrombin-stimulated platelet thromboxane B2 production by 90% during cardiopulmonary bypass (p less than .001), an effect that persisted for two hours after stopping the infusion. In the CGS-13080-treated group, plasma 6-keto-prostaglandin F1 alpha levels significantly increased over time (p less than .03) and were somewhat higher when compared with those in the placebo-treated group. This observation suggests that an "endoperoxide shunt" may have occurred. In the control group, an inverse correlation between platelet count and level of thromboxane B2 per platelet following in vitro thrombin stimulation (r = .5, p less than .001) was apparent, but there was no correlation between these two variables (r = .18, p less than .10) in the CGS-13080-treated group. No adverse hemodynamic or other effects attributable to CGS-13080 occurred during or immediately following cardiopulmonary bypass. These results suggest that CGS-13080 is an effective inhibitor of thromboxane B2 production during cardiopulmonary bypass in dogs and has no adverse physiological effects.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Blood; Cardiopulmonary Bypass; Dogs; Double-Blind Method; Drug Evaluation, Preclinical; Female; Hemodynamics; Imidazoles; Male; Platelet Count; Pyridines; Random Allocation; Thromboxane B2; Thromboxane-A Synthase; Time Factors

Release of thromboxane (TXA2) during acute myocardial infarction may be an important contributing factor in the genesis of ventricular fibrillation (VF). We assessed the effect of selective TXA2 inhibition on vulnerability to VF after total occlusion of the anterior descending coronary artery in chloralose-anesthetized cats. Animals were pretreated with vehicle or with CGS-13080, a TXA2 synthetase inhibitor, 3.0 or 9.0 mg/kg intravenously. There was an apparent dose-dependent protective effect following CGS-13080 administration, in which the decrease in VF threshold following coronary occlusion was attenuated. Also, the incidence of spontaneous ventricular arrhythmia in the first 30 minutes after occlusion was reduced by two thirds in the 9.0 mg/kg CGS-13080 group compared to the vehicle-treated animals. This protective effect does not appear to be due to a change in hemodynamics, effective refractory periods, or extent of ischemia. TXA2 released during coronary occlusion appears to be arrhythmogenic, and inhibiting its synthesis may be protective.

Topics: Animals; Blood Pressure; Cats; Coronary Disease; Female; Heart Rate; Imidazoles; Male; Pyridines; Thromboxane B2; Thromboxane-A Synthase; Ventricular Fibrillation

Increase in thromboxane A2 (TXA2) generation has been proposed as a mechanism of dynamic vaso-occlusion and in vivo platelet thrombus formation. We have examined the effects of CGS-13080, an imidazole derivative, on rabbit and human TXA2-prostacyclin (PGI2) "balance." In rabbits given CGS-13080, serum levels of TXB2 (stable metabolite of TXA2) were inhibited 81% at 2 hours and 56% at 24 hours (both P less than or equal to 0.01). Collagen-induced platelet aggregation was inhibited at 2 hours after CGS-13080 administration. In contrast, serum levels of 6-keto-PGF1 alpha (stable hydrolysis product of PGI2) increased 587% compared with control values at 2 hours (P less than or equal to 0.01). Platelet and white blood cell counts were not significantly altered. In human blood incubated in vitro with CGS-13080, serum TXB2 was completely inhibited, whereas PGI2 generation was stimulated (both P less than or equal to 0.001). In other experiments, we demonstrated uptake of platelet-generated cyclic endoperoxides by leukocytes and generation of PGI2 in the presence of CGS-13080 but not indomethacin. Thus, CGS-13080 inhibits TXA2 and stimulates PGI2 production in rabbit and human blood. Increase in PGI2 generation with TXA2 inhibition may be of potential benefit in conditions characterized by platelet hyperactivity.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Blood Platelets; Calcimycin; Calcium Chloride; Collagen; Epoprostenol; Imidazoles; Indomethacin; Leukocytes; Oxidoreductases; Platelet Aggregation; Pyridines; Rabbits; Thromboxane A2; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

Thromboxane A2, the predominant cyclooxygenase product of arachidonic acid in the platelet, is a potent vasoconstrictor and stimulus of platelet aggregation. Prostacyclin, the principal cyclooxygenase metabolite formed in the vascular endothelium, inhibits platelet aggregation and dilates blood vessels. A therapeutic objective in the treatment of human vascular occlusive disease has been the inhibition of thromboxane formation without coincident reduction in prostacyclin biosynthesis. We compared the biochemical selectivity and platelet inhibitory actions of single doses of aspirin, a cyclooxygenase inhibitor, with imidazo(1,5-2)pyridine-5-hexanoic acid (CGS 13080), an inhibitor of thromboxane synthase. Aspirin, 325 mg, prolonged the bleeding time markedly, inhibited aggregation and nucleotide release in whole blood and platelet-rich plasma, and maximally inhibited thromboxane generation in serum. The effects of aspirin, 20 mg, were considerably less marked but, as with the higher dose, persisted throughout the study period (24 hr after dosing). CGS 13080 also prolonged bleeding time and inhibited thromboxane formation. In contrast to aspirin, these effects were reversible and inhibition of aggregation was less marked. Endogenous prostacyclin biosynthesis was measured by excretion of the major urinary metabolite 2,3-dinor-6-keto-PGF1 alpha (PGI-M). Whereas aspirin, 325 mg, reduced PGI-M excretion a mean 29%, excretion increased 48% and 100% after CGS 13080, 100 mg and 200 mg. Aspirin, 20 mg, did not alter prostacyclin biosynthesis. Inhibition of thromboxane synthase permits selective inhibition of thromboxane formation in man. Although drugs of greater potency and longer duration of action are desirable, enhanced prostacyclin synthesis may be an important component of the platelet inhibitory actions of thromboxane synthase inhibitors in man.

Topics: Aspirin; Blood Platelets; Collagen; Epoprostenol; Humans; Imidazoles; Male; Pyridines; Random Allocation; Thromboxane A2; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

CGS 13080 inhibited cell-free thromboxane synthetase with an IC50 of 3 nM. It was at least five orders of magnitude less potent toward other key enzymes involved in arachidonic acid metabolism. Submicromolar concentrations inhibited calcium ionophore-induced formation of thromboxane B2 by intact human platelets with concomitant accumulation of prostaglandin E2. Oral doses lower than 1 mg/kg in rats suppressed the elevations of plasma thromboxane B2 induced by calcium ionophore. This was attended by shunting of endoperoxide substrate to 6-keto-prostaglandin F1 alpha and prostaglandin E2. CGS 13080 is one of the most potent and selective thromboxane synthetase inhibitors yet identified.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Blood Platelets; Humans; Imidazoles; In Vitro Techniques; Male; Oxidoreductases; Prostaglandins E; Pyridines; Rats; Rats, Inbred Strains; Thromboxane B2; Thromboxane-A Synthase

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