thromboxane-a2 and imidazole

In this study, we examined whether PC-09, a new pyridazinone derivative, has antiplatelet activity in vitro and further investigated the possible mechanisms involved. Pretreatment with PC-09 resulted in an inhibition on rabbit platelet aggregation and ATP release induced by arachidonic acid, collagen or thrombin, with the IC(50) values of 5.4 to 76.8 muM. The thromboxane B(2) formation caused by collagen or thrombin was markedly inhibited by PC-09, but there was no alteration in that caused by arachidonic acid. The rise of platelet intracellular calcium level stimulated by aggregation agonists and collagen-induced platelet membrane surface glycoprotein IIb/IIIa expression was also reduced by PC-09. In addition, PC-09 itself significantly increased the cyclic AMP level through inhibiting cyclic AMP phosphodiesterase activity. These findings demonstrate that PC-09 is an inhibitor of platelet aggregation, which may be associated with mechanisms including inhibition of thromboxane A(2) formation, intracellular calcium mobilization and platelet surface GPIIb/IIIa expression accompanied by increasing cyclic AMP level.

Topics: 1-Methyl-3-isobutylxanthine; 3',5'-Cyclic-AMP Phosphodiesterases; Adenosine Triphosphate; Alprostadil; Animals; Arachidonic Acid; Blood Platelets; Calcium; Collagen; Cyclic AMP; Cyclic GMP; Dose-Response Relationship, Drug; Imidazoles; Indomethacin; Naphthalenes; Phosphodiesterase Inhibitors; Platelet Aggregation; Platelet Aggregation Inhibitors; Platelet Glycoprotein GPIIb-IIIa Complex; Pyridazines; Rabbits; Thrombin; Thromboxane A2; Thromboxane-A Synthase

There is substantial evidence of increased platelet reactivity in vivo and in vitro during pregnancy, with the risk of developing pre-eclampsia. In this study, platelet function was studied during 28-40 weeks of gestation in a group of women who remained normotensive and in a group of nonpregnant female controls. Platelet aggregation stimulated by thrombin and adenosine diphosphate was markedly enhanced in washed platelets from pregnant subjects. Thrombin (0.04 U/ml)-evoked increases in intracellular Ca+2 mobilization of Fura 2-AM-loaded platelets were also enhanced in pregnant subjects. The binding of fluorescein isothiocyanate (FITC)-triflavin (2 microg/ml) to the glycoprotein IIb/IIIa complex in thrombin-activated platelets did not differ significantly between the nonpregnant and pregnant groups. Thromboxane A2 (TXA2) formation in both resting and thrombin-activated platelets from pregnant subjects was significantly greater than from nonpregnant subjects. Levels of cyclic adenosine monophosphate (cAMP) in both resting and prostaglandin E1-treated platelets (10 micromol/l) from pregnant subjects were significantly lower than those from nonpregnant subjects. There were no significant differences between nonpregnant and pregnant subjects in platelet cAMP levels in the presence of imidazole (600 micromol/l) and indomethacin (500 micromol/l). Intracellular pH values in platelets were measured spectrofluorometrically using the fluorescent probe, BCECF-AM. The increase in intracellular pH stimulated by thrombin (0.04 U/ml) in pregnant subjects was markedly greater than that in observed nonpregnant subjects. We conclude that the agonist-induced hyperaggregability of platelets in normal pregnancy may be due, at least partly, to stimulation of the Na+/H+ exchanger and subsequently to elevated intracellular Ca+2 mobilization, and then to increased TXA2 formation and a lowered level of cAMP, which leads to further increases in intracellular Ca+2 mobilization, and finally to enhanced platelet aggregation.

Topics: Adult; Alprostadil; Calcium Signaling; Cyclic AMP; Disease Susceptibility; Female; Humans; Hydrogen-Ion Concentration; Imidazoles; Indomethacin; Intracellular Fluid; Peptides; Platelet Aggregation; Pre-Eclampsia; Pregnancy; Pregnancy Complications, Hematologic; Second Messenger Systems; Sodium-Hydrogen Exchangers; Thrombin; Thrombophilia; Thromboxane A2

Topics: Aspirin; Blood Platelets; Cyclooxygenase Inhibitors; Humans; Imidazoles; In Vitro Techniques; Lasers; Platelet Aggregation; Platelet Count; Prostaglandin-Endoperoxide Synthases; Thromboxane A2; Thromboxane-A Synthase

YC-1 [3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole] inhibited the aggregation of and ATP release from washed rabbit platelets induced by arachidonic acid (AA), collagen, U46619, platelet-activating factor (PAF), and thrombin in a concentration-dependent manner. YC-1 also disaggregated the clumped platelets caused by these inducers. The thromboxane B2 formation caused by collagen, PAF, and thrombin was inhibited by concentrations of YC-1 that did not affect formation of thromboxane B2 and prostaglandin D2 caused by AA. YC-1 suppressed the increase of intracellular Ca2+ concentration and generation of inositol 1,4,5-trisphosphate caused by these five aggregation inducers. Both the cAMP and cGMP contents of platelets were increased by YC-1 in a concentration- and time-dependent manner. Like sodium nitroprusside, YC-1 potentiated formation of cAMP caused by prostaglandin E1 but not that by 3-isobutyl-1-methylxanthine. Adenylate cyclase and cAMP phosphodiesterase activities were not altered by YC-1. Activity of cGMP phosphodiesterase was unaffected by YC-1. Activities of guanylate cyclase in platelet homogenate and cytosolic fraction were activated by YC-1, whereas particulate guanylate cyclase activity was unaffected. The antiplatelet effect of sodium nitroprusside but not that of YC-1 was blocked by hemoglobin and potentiated by superoxide dismutase. After intraperitoneal administration for 30 minutes, YC-1 prolonged the tail bleeding time of conscious mice. These data indicate that YC-1 is a direct soluble guanylate cyclase activator in rabbit platelets. It may also possess antithrombotic potential in vivo.

Topics: 1-Methyl-3-isobutylxanthine; Adenosine Triphosphate; Alprostadil; Animals; Bleeding Time; Blood Platelets; Calcium; Colforsin; Collagen; Cyclic AMP; Cyclic GMP; Drug Interactions; Enzyme Activation; Guanylate Cyclase; Imidazoles; Indazoles; Indomethacin; Methemoglobin; Mice; Molecular Structure; Nitroprusside; Phosphoric Diester Hydrolases; Platelet Aggregation Inhibitors; Prostaglandin D2; Rabbits; Superoxide Dismutase; Thromboxane A2

1. Administration of bradykinin caused dose-dependent vasoconstriction in rat isolated perfused mesenteric arteries precontracted with noradrenaline. 2. The vasoconstrictor response was not mediated by BK1-bradykinin receptors. 3. Inhibition of cyclo-oxygenase with indomethacin, aspirin or meclofenamate abolished the vasoconstrictor effect of bradykinin, showing that a member of the arachidonic acid cascade may be involved. 4. Inhibitors of thromboxane synthesis (imidazole and UK 38485) did not affect or only reduced the bradykinin-induced vasoconstriction. 5. The endoperoxide H2/thromboxane A2 receptor antagonist SQ 29548 significantly reduced the vasoconstrictor effect of bradykinin, but did not affect the vasoconstrictor response to noradrenaline, adrenaline, vasopressin, 5-hydroxytryptamine or prostaglandins. 6. The eicosanoid(s) that mediate bradykinin-induced vasoconstriction appear to be synthesized outside the arterial endothelium. 7. The data suggest that the vasoconstrictor effect of bradykinin in the rat isolated mesenteric artery is mediated by vasoconstrictor arachidonic acid metabolites including the cyclic endoperoxides and/or the thromboxanes.

Topics: Animals; Aspirin; Bradykinin; Bridged Bicyclo Compounds, Heterocyclic; Cyclooxygenase Inhibitors; Eicosanoids; Endothelium, Vascular; Fatty Acids, Unsaturated; Hydrazines; Imidazoles; In Vitro Techniques; Indomethacin; Meclofenamic Acid; Mesenteric Arteries; Norepinephrine; Rats; Receptors, Prostaglandin; Receptors, Thromboxane; Thromboxane A2; Thromboxane-A Synthase; Vasoconstriction

Fibronectin is a normal glycoprotein component of plasma, interstitial fluid, and extracellular matrix which has binding sites for collagen, gelatin, actin, glycosaminoglycans, fibrin, Staphylococcus aureus, and some cells. Since it is a dimer, it can crosslink these substances to each other or to extracellular components of basement membrane, thereby affecting many physiological processes. The level of circulating fibronectin is markedly reduced following even moderate blunt or operative trauma, thermal injury, starvation, advanced cancers, hemorrhage, etc. Replacement therapy has been tried with some success in patients who become septic following multiple injuries. The reduction in plasma fibronectin has been attributed to several causes including consumption by binding to cell debris at the site of injury, binding to circulating cell debris and its subsequent removal by elements of the phagocytic system, and degradation by proteolytic cleavage. However, the amount of fibronectin removed from circulation raises some question about this. In this paper, we used indomethacin, ibuprofen, imidazole, and essential fatty acid deprivation to inhibit the synthesis of prostaglandins in young adult rats. Thirty minutes after ip administration of one of the inhibitors, the rats were subjected to a midline laparotomy and mild intestinal manipulation. Blood samples were taken at intervals following closure of the incision and analyzed for fibronectin. In all cases, the normal decline in plasma fibronectin seen in untreated rats was abrogated by inhibiting prostaglandin synthesis. Since imidazole specifically inhibits thromboxane A synthesis, this strongly suggests that thromboxanes directly or indirectly control the trauma-induced reduction in circulating fibronectin. This was confirmed by ip injection of thromboxane into the rats which resulted in a decline in plasma fibronectin levels.

Topics: Animals; Epoprostenol; Fibronectins; Ibuprofen; Imidazoles; Indomethacin; Prostaglandins; Rats; Rats, Inbred Strains; Thromboxane A2

Numerous reports have shown that intravascular lipid infusion may cause pulmonary dysfunction in a variety of species, including humans. To determine the effects of parenteral lipid on neonatal pulmonary hemodynamics, lung fluid filtration, and respiratory gas exchange, we measured pulmonary arterial and left atrial pressures, cardiac output, lung lymph flow, lymph and plasma protein concentrations, and partial pressures of oxygen and carbon dioxide in arterial blood of 11 awake chronically catheterized lambs that received a 2-3 h control infusion of glucose-saline solution followed by Intralipid at a dose of 67.5, 125, or 250 (mg/h)/kg body weight for 6 h. Intralipid caused an acute dose-dependent increase in pulmonary arterial pressure, with no significant change in cardiac output or left atrial pressure. The pulmonary hypertension, which lasted for at least 2 h, was accompanied by a greater than 50% increase in lung lymph flow and a significant decrease in lymph protein concentration relative to plasma protein concentration. Pulmonary artery pressure gradually decreased to control values during the final 2 h of lipid infusion, but lymph flow remained 35% above control and lymph protein concentration remained low. Lipid infusion also was associated with a modest decrease in PaO2. Both arterial and venous administration of lipid gave similar results. In separate studies, lipid infusion caused a significant increase in plasma concentrations of thromboxane B2, the stable metabolite of thromboxane A2, without affecting plasma concentrations of 6-keto prostaglandin F1 alpha, the stable metabolite of prostacyclin. Pretreatment with imidazole, which attenuated the lipid-induced increase in thromboxane B2 concentration, completely blocked the pulmonary hemodynamic response to lipid.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Animals, Newborn; Fat Emulsions, Intravenous; Imidazoles; Lymph; Pulmonary Circulation; Sheep; Thromboxane A2; Thromboxane-A Synthase

Visceral microcirculatory insufficiency has been demonstrated in sepsis despite a hyperdynamic systemic circulation. This study examines the effect of the cyclo-oxygenase inhibitor indomethacin and the thromboxane synthetase inhibitor imidazole on septic hemodynamics and visceral perfusion in a septic rat model of cecal ligation and puncture. Animals received either indomethacin (INDO), imidazole (IMID), or saline intramuscularly at t = 0, 6, and 12 hr of peritonitis. Thermodilution cardiac output, mean arterial pressure, heart rate, hematocrit, effective hepatic blood flow, effective renal plasma flow, and arterial and mixed venous blood gases were determined at 15 hr. Both INDO and IMID improved effective hepatic blood flow in the septic animals to virtually sham, nonseptic levels without significantly altering systemic hemodynamics. This study suggests that the reduction in hepatic perfusion in sepsis may be mediated by thromboxane, the synthesis of which is suppressed by both INDO and IMID.

Topics: Animals; Female; Hemodynamics; Imidazoles; Indomethacin; Liver Circulation; Peritonitis; Rats; Rats, Inbred Strains; Renal Circulation; Thromboxane A2

Glycerol-treated rats exhibited significantly increased urinary thromboxane B2(TXB)2, prostaglandin E2 (PGE2) and 6-ketoprostaglandin F1 alpha (6kPGF1 alpha) excretion and urine volume (UV). These increases were associated with significant decreases in creatinine clearance (CCr), urinary sodium concentration (UNa), urinary sodium excretion (UNaV), and fractional excretion of sodium (FENa%), which is consistent with the development of the prerenal (reversible) phase of acute renal failure (ARF). When glycerol-treated rats were pretreated with a selective inhibitor of thromboxane A2 (TXA2) synthesis (imidazole), urinary PGE2 and 6kPGF1 alpha excretion and UV remained unchanged, whereas CCr, UNa, UNaV decreases were partially prevented. Additionally, FENa% was increased, indicating inhibition of sodium reabsorption. The findings indicate that inhibition of TXA2 synthesis increases UNaV and partially improves CCr in glycerol-treated rats. Further histologic observation and functional follow-up over longer periods of time are needed to clarify the role of TXA2 in the development of ARF.

Topics: Acute Kidney Injury; Animals; Creatinine; Female; Glycerol; Imidazoles; Natriuresis; Prostaglandins; Rats; Thromboxane A2

Thromboxane (Tx) inhibition prevents pulmonary leukostasis after acid aspiration. This observation prompted study of polymorphonuclear leukocyte (PMN) accumulations and products of cyclooxygenase. Experiments were conducted with a skin abrasion preparation. Five groups of six rabbits were pretreated intravenously with: (1) placebo, (2) ibuprofen, (3) imidazole and two other Tx syntase inhibitors, (4) OKY 1555, or (5) OKY 046. Zymosan-activated serum (ZAS) and leukotriene B4 were used as chemotaxins and balanced salt solution as control. After pretreatment with placebo, PMN accumulation in leukotriene B4 sites was 2130 +/- 874 PMN/mm3 (mean +/- SD). Pretreatment with ibuprofen, imidazole, or OKY 046 decreased (p less than 0.05) accumulations to 205 +/- 139 PMN/mm3, 485 +/- 387 PMN/mm3, and 504 +/- 260 PMN/mm3, respectively. In ZAS sites, placebo pretreatment led to 2006 +/- 866 PMN/mm3, while the ibuprofen, imidazole, and OKY 046 groups had decreased (p less than 0.05) responses of 295 +/- 218 PMN/mm3, 444 +/- 477 PMN/mm3, and 386 +/- 151 PMN/mm3, respectively. Pretreatment with OKY 1555 did not produce significant reductions in response. Six animals in each group received intradermal injections of the two chemotaxins or Hank's balanced salt solution. Reduction in PMN accumulations after cyclooxygenase and Tx inhibition were similar to those observed in the skin abrasion preparation. Pretreatment with either ibuprofen, imidazole, or OKY 046 resulted in a decreased concentration of Tx in abrasion fluid exudate in response to leukotriene B4, 275 +/- 164 pg/ml, 460 +/- 144 pg/ml, and 440 +/- 260 pg/ml, respectively, as compared with 1168 +/- 380 pg/ml in the placebo group. The reduced responses were not the result of a decrease in regional perfusion as measured by 133Xe washout. The in vitro chemotactic response of PMN to leukotriene B4 and ZAS was unchanged after incubation in either ibuprofen, imidazole, OKY 1555, or OKY 046. These data show that cyclooxygenase and Tx syntase are integrally associated with PMN accumulations.

Topics: Animals; Chemotaxis, Leukocyte; Cyclooxygenase Inhibitors; Ibuprofen; Imidazoles; Male; Methacrylates; Neutrophils; Premedication; Prostaglandin-Endoperoxide Synthases; Rabbits; Skin; Skin Tests; Thromboxane A2; Thromboxane-A Synthase

Acute renal failure (ARF) was induced in 35 week-old conscious female Wistar rats, by intramuscular (IM) injection of glycerol. Intraperitoneal (IP) injection of imidazole, an inhibitor of thromboxane (TXA2) synthesis, partially protected the animals against ARF. This protection was accompanied by a significant decrease in renal TXB2 (the stable chemical metabolite of TXA2) and a significant increase in renal 6-keto-PGF1 alpha (the stable chemical metabolite of PGI2) synthesis. Intraperitoneal injection of captopril (SQ 14225) an angiotensin-converting-enzyme inhibitor, did not protect the animals against ARF. This lack of protection was accompanied by a significant increase in renal TXB2 and a significant decrease in renal 6-keto-PGF1 alpha synthesis. The results suggest that: (a) the renin-angiotensin (R-A) system does not play a role, or has only a secondary one in the development of ARF; (b) thromboxane A2 (the most potent vasoconstrictor and platelet aggregator agent known) is the preponderant agent responsible for the development of this pathological syndrome.

Topics: 6-Ketoprostaglandin F1 alpha; Acute Kidney Injury; Angiotensin II; Animals; Captopril; Dinoprostone; Female; Glycerol; Imidazoles; Prostaglandins; Prostaglandins E; Rats; Thromboxane A2; Thromboxane B2; Thromboxanes

Inhibitors of thromboxane synthetase (imidazole), cyclooxygenase (indomethacin), phospholipase A2 (Mepacrine) were used in the experiments on rabbits with experimental hypoparathyroidism to study the role of aggregation factors in the changes of ADP- and collagen-induced platelet aggregation. The enhancement of arachidonic acid metabolism and the release of platelet aggregation factor are discussed.

Topics: Adenosine Diphosphate; Animals; Collagen; Hypoparathyroidism; Imidazoles; Indomethacin; Platelet Aggregation; Rabbits; Thromboxane A2

Recently, addition of gamma linolenic acid (GLA) which is a precursor of prostaglandin E1 (PGE1) to cell cultures, has been shown to inhibit growth of various carcinoma cells (1,2,3,4). These findings are consistent with Horrobin's proposal that some of the metabolic abnormalities of malignant cells may be due to deficiencies of certain prostanoids. To determine whether the observed effects of GLA are in fact mediated by increasing levels of its metabolites, this study investigated the influence of various inhibitors and stimulants of prostaglandin (PG) synthesis on the effects of GLA on carcinoma cells in vitro. Most of the agents used (aspirin, imidazole, lithium carbonate and ascorbic acid) produced results consistent with the idea that elevation of levels of thromboxane A2 (TxA2) and/or PGE1 may be important as regards the actions of GLA. In sharp contrast was the result obtained with indomethacin. This drug, which could be expected to block conversion of GLA to PGE1 and therefore protect cells against the effects of GLA, actually exaggerated the effects of this fatty acid, thereby causing cell death and desquamation.

Topics: Alprostadil; Aspirin; Cell Division; Cell Line; Cell Survival; gamma-Linolenic Acid; Humans; Imidazoles; Indomethacin; Linolenic Acids; Neoplasms; Prostaglandins; Prostaglandins E; Thromboxane A2; Thromboxanes

The excretion rates of renal thromboxane B2 (TXB2) and 6-ketoPGF1 alpha, the stable chemical metabolites of thromboxane A2 (TXA2) and prostaglandin I2 (PGI2) respectively, PGE2 and sodium were determined in normal and saline-loaded rats treated with the thromboxane synthetase inhibitor imidazole. In normal rats the administration of imidazole in doses which did not affect renal 6-keto-PGF1 alpha and PGE2 excretion but selectively inhibited renal TXB2 excretion, significantly increased the sodium excretion rate. Volume expansion with saline increased renal PGE2 and 6-ketoPGF1 alpha excretion but did not alter renal TXB2 excretion. The increase in renal prostaglandin excretion was accompanied by an increased sodium excretion rate. The administration of imidazole to saline-loaded animals also decreased renal TXB2 excretion but did not alter the increased excretion of renal PGE2 and 6-ketoPGF1 alpha. This reduction in renal thromboxane biosynthesis by imidazole further increased the sodium excretion rate. We suggest that TXA2 is a potent antinatriuretic factor as well as the most potent vasoconstrictor agent known.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Dinoprostone; Epoprostenol; Imidazoles; Kidney; Male; Prostaglandins E; Rats; Rats, Inbred Strains; Sodium; Sodium Chloride; Thromboxane A2; Thromboxane B2; Thromboxanes

Whereas numerous studies have investigated the role of prostacyclin and thromboxane A2 in the maintenance of coronary blood flow, most of these have focused on normal vessels. In the present investigation, we examined the prostaglandin- and thromboxane-synthesizing capacity of isolated coronary artery segments obtained from the site of a critical coronary artery stenosis. Cyclic flow variations were produced by placing a hard cylindrical constrictor on the proximal left anterior descending coronary artery in open-chest, anesthetized dogs. Cyclic flow variations are characterized by progressive declines in coronary blood flow, interrupted by sudden spontaneous restorations of flow. After cyclic flow variations had been induced, the hearts were removed, and the left anterior descending and circumflex coronary arteries were dissected. The vessels were cut into segments and incubated in the presence of increasing concentrations of arachidonic acid (10(-4)-10(-6) M). The synthesis of prostaglandin E2, thromboxane B2, and 6-keto prostaglandin F1 alpha by the coronary segments was measured by radioimmunoassay. When incubated in the presence of 10(-5) M arachidonic acid, coronary artery segments obtained from the left anterior descending coronary artery undergoing cyclic flow variations produced substantially more thromboxane B2 (142 +/- 27 vs. 29 +/- 3 pg/mg P less than 0.01) and less 6-keto prostaglandin F1alpha (125 +/- 12 vs. 350 +/- 30 pg/mg, P less than 0.01) than control circumflex coronary artery segments. Circumflex coronary vessels in which the endothelium was removed ex vivo produced 6-keto prostaglandin F1alpha levels comparable to those found in the left anterior descending coronary artery (147 +/- 17 pg/mg), but did not synthesize thromboxane B2 (23 +/- 2.6 pg/mg).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Aortic Valve Stenosis; Arachidonic Acid; Arachidonic Acids; Chromatography, High Pressure Liquid; Coronary Circulation; Coronary Vessels; Dinoprost; Dinoprostone; Dogs; Epoprostenol; Imidazoles; Male; Platelet Aggregation; Prostaglandins E; Prostaglandins F; Regional Blood Flow; Thromboxane A2; Thromboxane B2; Thromboxanes

Within 24 hours after a full-thickness burn injury, predictable alterations occur in the dermal vasculature. At the immediate site of injury, vessels lose patency. In the periphery, vasodilation and increased permeability become widespread. A variety of interventions were employed to prevent these vascular sequelae. While systemic treatment, immediately after burn trauma, with hydrocortisone or the non-steroidal anti-inflammatory compound indomethacin, was ineffective in preventing vascular alteration, treatments with other NSAI agents such as ibuprofen and imidazole were effective in preventing microvascular occlusion. In addition, utilizing standard radioimmunoassay techniques, the concentrations of the metabolites of two potent eicosanoids, thromboxane and prostacyclin, were measured from fluid collected in the implanted wound chambers. Following full-thickness burns, the synthesis and release of thromboxane were inhibited by indomethacin, imidazole, and ibuprofen. Furthermore, indomethacin and ibuprofen, but not imidazole, blocked the synthesis and release of prostacyclin into wound fluid. Significantly, ibuprofen was effective in preserving the dermal vasculature, even when administration was delayed as long as 6 hours after burn trauma. Pharmacologic actions not associated with the production of thromboxane or prostacyclin appear responsible for the protective effects of ibuprofen during burn injury. Such findings do not support an important role for either thromboxane or prostacyclin in the development of vascular alterations following burn injury.

Topics: Animals; Anti-Inflammatory Agents; Blood Coagulation; Burns; Epoprostenol; Hydrocortisone; Ibuprofen; Imidazoles; Ischemia; Male; Rats; Rats, Inbred Strains; Skin; Thromboxane A2; Time Factors; Vasodilation

Topics: Animals; Gastric Acid; Gastric Mucosa; Humans; Imidazoles; Immersion; Indomethacin; Ischemia; Male; Rats; Regional Blood Flow; Stomach Ulcer; Stress, Psychological; Thromboxane A2; Thromboxanes

Prostaglandin E1 and thromboxane A2 (PGE1 and TXA2) have been proposed to bind to DNA, regulate gene action and prevent mutagenesis. Benzo (a) pyrene (BP) is a known mutagen and tumor promotor. BP-induced damage to the bone marrow cells of mice was prevented and/or reversed by PGE1 and by colchicine, an agent which may enhance PGE1 synthesis and TXA2 synthesis or action. PGF2 alpha did not have any action. Imidazole, a selective TXA2 synthesis inhibitor, enhanced the mutagenic action of benzo (a) pyrene. These results lend support to the concept that an altered PG system may have a role in the pathogenesis of mutagenesis and carcinogenesis.

Topics: Alprostadil; Animals; Benzo(a)pyrene; Bone Marrow; Colchicine; Dinoprost; Imidazoles; Male; Mice; Mutation; Prostaglandins E; Prostaglandins F; Thromboxane A2

Contractile responses to prostacyclin (PGI2) as well as the generation of PGI2 "like-material" in isolated aorta from rabbits and rats, were studied. PGI2 produced a biphasic response on thoracic aorta isolated from rabbits and rats, i.e. vasodilatation at low concentrations and distinct contraction at higher ones. The rabbit aortic arch responded with relaxation in the presence of a wide range PGI2 concentration. Inhibitors of prostaglandins and thromboxane A2 (TXA2) biosynthesis such as corticosterone, indomethacin, acetylsalicyclic acid, imidazole and L-8027, abolished the stimulatory effect of PGI2 in the thoracic aorta from rats and rabbits, while alpha adrenoreceptor blockers failed to modify the vasoconstricting influence. The basal generation of PGI2 "like-material" by thoracic aorta was significantly higher in rats than in rabbits. Thoracic aortic strips from rabbits diminished the antiaggregatory capacity of 5 ng/ml of PGI2 during 40 sec and the effect disappears within 2 min. The foregoing results suggest that in thoracic aorta from rats and rabbits the vasoconstrictor effect of PGI2 could be evoked by the production of an unstable constricting prostanoid with aggregatory capacity, presumably TXA2.

Topics: Adenosine Diphosphate; Animals; Aorta, Thoracic; Aspirin; Corticosterone; Epoprostenol; Imidazoles; In Vitro Techniques; Indomethacin; Male; Prostaglandins; Rabbits; Rats; Species Specificity; Thromboxane A2; Thromboxanes; Vasoconstriction

The larval stage of the tapeworm, Taenia taeniaeformis, was incubated in different concentrations of arachidonic acid. At various times after incubation, aliquots were removed for bioassay on either 38 microM aspirin or non-aspirin-treated equine platelets and by radioimmunoassay for the thromboxane A2 breakdown product, thromboxane B2 (TXB2). Platelet agonist activity was detected as early as 30 sec after addition of the arachidonic acid. In aspirin-treated platelets, this agonist activity peaked at 1 to 4 min and thereafter decayed rapidly with a time course that was both worm and arachidonic acid dependent. When assayed on non-aspirin-treated platelets the agonist activity was again detectable as early as 30 sec after addition of arachidonic acid, peaked at 1 to 3 min and then decayed very slowly over a 30-min period of incubation. It was found that levels of TXB2 were detected which increased over time concomitant with the decay of the platelet agonist activity. The most consistent detection of TXB2 generation was at 30 min with a mean of 49.6 pg and a range of 22.1 to 84.8 pg for four experiments. This report presents the first evidence for arachidonic acid utilization by a cestode or trematode and could in part provide an explanation for the marked cellular inflammation noted around dead or dying parasites.

Topics: Animals; Arachidonic Acid; Arachidonic Acids; Aspirin; Horses; Imidazoles; Indomethacin; Kinetics; Larva; Platelet Aggregation; Rats; Taeniasis; Thromboxane A2; Thromboxane B2; Thromboxanes

Human arterial and venous segments from patients under-going operations when incubated in Tris buffer both alone and with arachidonic acid were able to produce thromboxane B2 (assessed by radioimmunoassay). Thromboxane B2 (TxB2) production was progressive in time (till 40 min.) and was enhanced by the addition of 1mM norepinephrine. Contamination of tissues by platelet was checked and platelets did not contribute to thromboxane formation. The investigation of the conversion of 1-14C arachidonic acid by vascular tissue indicated that human vascular tissues produce the metabolites of the cyclooxygenase dependent pathway and that prostacyclin is the main metabolite with a PGI2/TxA2 ratio of 4:1. The arterial wall was found to possess an active lipoxygenase dependent pathway. Thromboxane production by intimal cells was negligible and the main source of thromboxane was the media. The production of thromboxane did not change in relation to age, but arterial segments from men produced significantly larger amounts of thromboxane than those from women.

Topics: Adult; Aged; Arachidonic Acid; Arachidonic Acids; Arteries; Biotransformation; Blood Platelets; Chromatography, High Pressure Liquid; Female; Humans; Imidazoles; In Vitro Techniques; Indomethacin; Male; Middle Aged; Norepinephrine; Radioimmunoassay; Thromboxane A2; Thromboxanes; Time Factors; Veins

The effects of dipyridamole on thromboxane A2 formation by horse platelet microsomes were studied in comparison with those of imidazole, a prototype inhibitor of TXA2 synthetase and nifedipine, a calcium antagonistic vasodilator. Thromboxane A2 was synthesized by incubating PGH2 with horse platelet microsomes and was assayed on the superfused rabbit aorta. Dipyridamole induced as strong an inhibition of TXA2 synthesis as imidazole, while nifedipine was without effects. The possible beneficial clinical outcomes of this effect of dipyridamole are discussed.

Topics: Animals; Blood Platelets; Dipyridamole; Horses; Imidazoles; In Vitro Techniques; Microsomes; Muscle Contraction; Muscle, Smooth, Vascular; Nifedipine; Thromboxane A2; Thromboxanes; Vasodilator Agents

Prostaglandin E2, colchicine and imidazole, known to enhance and inhibit thromboxane A2 (TxA2) synthesis respectively and chloroquine, a PGE1 synthesis enhancer and PGE2 antagonist can alter the leukocyte alkaline phosphatase (LAP) enzyme activity. Thromboxane A2 and other related prostaglandins (PGs) are known to bind to DNA and thus possibly regulate DNA action. It is proposed here that prostaglandins are able to modify LAP activity by their action on the DNA and thus the Gene that codes for LAP. This hypothesis envisages that normally there are specific receptors on the genes for PGs. Taking LAP enzyme system as the model, it is proposed that the affinity of TxA1, TxA2, PGE2 and PGE1 to the operator is more than to that of the repressor. But when the levels of TxA2, PGE2 and PGE1 are in excess, all the receptors on the operator are not only completely occupied but they are also able to bind to repressor in sufficient amounts to transiently switch off the LAP synthesis by the structural gene. It is further envisaged that the affinity of the PG receptors on the operator and repressor systems of the operon is greatest for TxA1 and least for PGE2 (TxA1 greater than TxA2 greater than PGE1 greater than PGE2). This hypothesis though simply in its model explains all the variables obtained in our studies on the effect of PGs on the LAP activity. This concept by itself or a suitable modification, may explain the role of PGs in the pathogenesis of cancer. It will be interesting to study, in the light of this hypothesis, the role of the PG system on DNA repair mechanism, m-RNA and t-RNA synthesis and gene action in several systems.

Topics: Alkaline Phosphatase; Alprostadil; Animals; Colchicine; DNA; Genes; Humans; Imidazoles; Leukocytes; Prostaglandins; Prostaglandins E; Thromboxane A2

Humoral factors released from platelets during pulmonary embolism may be the cause of several attendant cardiopulmonary abnormalities. This study examines the role of thromboxanes (Tx) after experimental embolism induced with 0.5 g/kg autologous clot in four groups of five dogs: (a) untreated embolized controls; (b) pretreatment with the Tx synthetase inhibitor, imidazole 25 mg/kg . h i.v., starting 30 min before embolization; (c) pretreatment with the cyclooxygenase inhibitor indomethacin, 5 mg/kg, 12 h per os and 1 mg/kg, 1 h i.v. before the experiment; (d) treatment with prostacyclin (PGI(2)) 100 etag/kg . min i.v. for 1 h, 1 h after embolization. Within 30 min, embolization led to increases of 6-keto-PGF(1alpha), the stable hydrolysis product of PGI(2), from 0.11+/-0.08 etag/ml (mean+/-SD) to 0.33+/-0.10 etag/ml (P < 0.005) and TxB(2), the stable product of TxA(2), from 0.10+/-0.04 etag/ml to 0.38+/-0.06 etag/ml (P < 0.001). Increases were observed in total dead space (V(D)/V(T)) from 0.46+/-0.03 to 0.61+/-0.08 (P < 0.025, physiologic shunting (Q(S)/Q(T)) from 16+/-4% to 38+/-9% (P < 0.01), pulmonary vascular resistance (PVR) from 2.27+/-0.59 mm Hg.min/liter to 9.21+/-1.90 mm Hg.min/liter (P < 0.005) and mean pulmonary arterial pressure from 14+/-6 mm Hg to 34+/-1 mm Hg (P < 0.001). Cardiac index (CI) fell from 139+/-11 ml/kg.min to 95+/-17 ml/kg.min in 4 h (P < 0.025). Imidazole pretreatment prevented a rise of TxB(2), but not 6-keto-PGF(1alpha); indomethacin blocked both. Both agents maintained V(D)/V(T) at base line and limited increases in Q(S)/Q(T) and PVR. CI was higher after imidazole pretreatment compared with controls (P < 0.025). Indomethacin led to intermediate levels of CI. PGI(2) lowered TxB(2) (P < 0.025), V(D)/V(T) (P < 0.025), Q(S)/Q(T) (P < 0.025) and PVR (P < 0.05) within 30 min. During PGI(2) infusion, CI was higher than controls. Concentrations of TxB(2) correlated with V(D)/V(T), r = 0.79 and Q(S)/Q(T), r = 0.69 (P < 0.001). Treatment of three dogs with the imidazole derivative ketoconazole, 10 mg/kg IV, 30 min after 0.75 g/kg autologous clot resulted in a lowering of physiologic dead space, but no other improvement of cardiopulmonary function. These results show that a number of cardiopulmonary abnormalities induced by pulmonary embolism are related directly or indirectly to platelet secretions and that V(D)/V(T) is closely allied to TxA(2) levels.

Topics: Animals; Dogs; Epoprostenol; Female; Heart; Imidazoles; Indomethacin; Ketoconazole; Male; Piperazines; Platelet Count; Pulmonary Embolism; Thromboxane A2; Thromboxanes; Time Factors; Vascular Resistance

1 Leukotriene C4 (LTC4), LTD4, slow-reacting substance of anaphylaxis (SRS-A) (from guinea-pig lung), bradykinin (Bk) and arachidonic acid (AA) release thromboxane A2 (TxA2) and prostaglandin-like materials from guinea-pig isolated perfused lungs. 2 Release of TxA2 induced by LTC4 and LTD4 is inhibited by a thromboxane synthetase inhibitor, imidazole (2.9 mM). 3 Mepacrine (200 microM), a phospholipase inhibitor, inhibits release of TxA2 and prostaglandin-like materials caused by SRS-A and Bk but not that due to exogenous AA 4 Leukotrienes B4, C4 and D4 are approximately equipotent in inducing dose-related contractions of guinea-pig parenchymal strips (GPPs). 5 Leukotriene-induced contractions of GPPs are greatly inhibited by imidazole (2.9 mM), carboxyheptylimidazole (24 microM) and mepacrine (400 microM). 6 FPL 55712 (1.9 microM), the SRS-A antagonist, blocks contractions of GPPs induced by LTC4 and LTD4 but not those due to LTB4 or Bk. 7 Tachyphylaxis to LTB4 occurs in GPPs but not to LTC4 or LTD4. 8 These results suggest that in guinea-pig lung in vitro, LTB4, LTC4 and LTD4 activate a phospholipase with subsequent generation of cyclo-oxygenase products of which TxA2 plays an important role.

Topics: Animals; Arachidonic Acid; Arachidonic Acids; Guinea Pigs; Imidazoles; In Vitro Techniques; Leukotriene B4; Lung; Quinacrine; Rabbits; Rats; Rats, Inbred Strains; Species Specificity; SRS-A; Thromboxane A2; Thromboxanes

Acute respiratory failure (ARF) with permeability edema and increased physiologic shunting (QS/QT) occurs after complement activation. Leukocytes aggregate, become entrapped in the lungs, and release vasotoxic agents. This study of 31 sheep infused with zymosan-activated plasma (ZAP) tests the hypothesis tha thromboxane (Tx) A2, a proaggregator and bronchoconstrictor, is an intermediate in complement-induced ARF. Group I animals (n = 11) were untreated controls. An imidazole infusion, 25 mg/kg . hr was started 1 hour before a ZAP infusion in group II (n = 10). Prostacyclin (PGi2) was given to group III sheep (n = 10) in a dose of 100 ng/kg . min 3- minutes before the ZAP infusion. Within 5 minutes ZAP led to a decrease in the leukocyte count to 2900/mm3 (P less than 0.001), a rise in plasma TxB2 concentration (the stable degradation product of TxA2) from 14 to 246 pg/ml (P less than 0.001), a rise in lymph TxB2 from 24 to 609 pg/ml (P less than 0.001), a rise in QS/QT from 13% to 31% (P less than 0.01), and a rise in mean pulmonary arterial pressure from 17 to 43 mm Hg. Both imidazole and PGI2 prevented the increase in TxB2 and QS/QT and limited the increases in MPAP to 25 and 30 mm Hg, respectively--values below those of untreated controls (P less than 0.05). Imidazole, but not PGI2, prevented the increase in lymph flow, which in controls increased from 2.8 +/- 8.5 ml/30 min (P less than 0.01), and lymph albumin clearance, which increased from 2.2 to 6.0 ml/30 min (P less than 0.01). The high lymph concentrations of TxA2 suggest a pulmonary site of production, and its bronchoconstrictive action may account for the increase in QS/QT. However, TxA2 is only partially responsible for the pulmonary hypertension and is apparently unrelated to changes in permeability. The protective action of infused imidazole against increased permeability appears to be independent of its inhibition of Tx synthetase.

Topics: Animals; Blood Platelets; Complement Activation; Epoprostenol; Imidazoles; Leukocyte Count; Lung; Lymph; Platelet Aggregation; Pulmonary Edema; Respiratory Insufficiency; Thromboxane A2; Zymosan

Cyclooxygenase inhibitors prevent the pulmonary vasomotor changes in response to low-dose endotoxin. We, therefore, explored the role of two highly vasoactive prostanoids, thromboxane A(2), a vasoconstrictor, and prostacyclin, a vasodilator, in the transient pulmonary vasoconstriction and subsequent loss of alveolar hypoxis vasoconstriction (AHPV) that follows endotoxin. AHPV was tested in the dog with a double-lumened endotracheal tube allowing ventilation of one lung with nitrogen as a hypoxic challenge while the other lung was ventilated with oxygen to maintain systemic oxygenation. Relative distribution of perfusion to the two lungs was assessed with intravenous (133)Xe and external scintillation detectors. The stable metabolites of thromboxane and prostacyclin, i.e., thromboxane B(2) and 6-keto-prostaglandin F(1alpha) were measured in plasma with radioimmunoassay. 15 mug/kg i.v. of endotoxin induced no rise in pulmonary vascular resistance (PVR), but prevented AHPV so that the initial 33% (+/-2 SEM) decrease in perfusion to the hypoxic lung became only a 2% (+/-1) decrease. Circulating levels of thromboxane and prostacyclin concurrently rose (P < 0.01) from nondetectable levels to 380 pg/ml (+/-40) and 360 pg/ml (+/-130). 150 mug/kg of endotoxin induced a transient rise in PVR from 4.09 to 9.00 mm Hg/liter per min in association (r = 0.89, P < 0.01) with a sharp rise in thromboxane levels to 4,460 pg/ml (+/-1,350) whereas prostacyclin levels were elevated less markedly to 550 pg/ml (+/-400). Prostaglandin F(2alpha), another vasoconstrictor, was not elevated. 30 min after endotoxin when PVR was again base line and AHPV lost, thromboxane fell significantly (P < 0.01) to 2,200 pg/ml (+/-1,100) whereas prostacyclin remained elevated at 360 pg/ml (+/-135), a level similar to that seen when 15 mug/kg of endotoxin induced loss of AHPV. Indomethacin prevented the rise in thromboxane and prostacyclin after endotoxin as well as the changes in pulmonary vasomotor tone. Thus, a complex interaction between thromboxane and prostacyclin is involved in the pulmonary vasomotor response to low-dose endotoxin.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Dogs; Endotoxins; Epoprostenol; Escherichia coli; Hemodynamics; Imidazoles; Prostaglandins; Prostaglandins F; Pulmonary Circulation; Thromboxane A2; Thromboxane B2; Thromboxanes

The effects of imidazole, 1-methyl-imidazole and benzimidazole on bone metabolism in vitro were investigated. The relative potencies of these compounds with respect to the inhibition of bone resorption was found to be comparable to their relative effectiveness as inhibitors of platelet microsome thromboxane synthetase activity. Since studies by others have shown that thromboxanes are produced by resorbing bone in vitro, these results suggest that the inhibition of bone resorption by imidazole is related to the inhibition of thromboxane A2 formation. This could imply that thromboxane A2 is an additional arachidonic acid oxidation product that is of importance in the regulation of bone metabolism.

Topics: Animals; Benzimidazoles; Bone and Bones; Bone Resorption; Calcium; Cells, Cultured; Imidazoles; Parathyroid Hormone; Rats; Thromboxane A2; Thromboxanes