thromboxane-a2 and beraprost

ONO-1301 [(E)-[5-[2-[1-phenyl-1-(3-pyridyl)methylidene-aminooxy]ethyl]-7,8-dihydronaphthalene-1-yloxy]acetic acid] is a novel prostaglandin (PG) I2 mimetic with inhibitory activity on the thromboxane (TX) A2 synthase. Interestingly, ONO-1301 retains its inhibitory effect on platelet aggregation after repeated administration, while beraprost, a representative agonist for the PGI2 receptor (IP), loses its inhibitory effect after repeated administration. In the present study, we intended to clarify the mechanism by which ONO-1301 escapes desensitization of an antiplatelet effect. In platelets prepared from wild-type mice, ONO-1301 inhibited collagen-induced aggregation and stimulated cAMP production in an IP-dependent manner. In addition, ONO-1301 inhibited arachidonic acid-induced TXA2 production in platelets lacking IP. Despite the decrease in stimulatory action on cAMP production, the antiplatelet effect of ONO-1301 hardly changed after repeated administration for 10 days in wild-type mice. Noteworthy, beraprost could retain its antiplatelet effect after repeated administration in combination with a low dose of ozagrel, a TXA2 synthase inhibitor. Therefore, we hypothesized that chronic IP stimulation by beraprost induces an increase in TXA2 production, leading to reduction in the antiplatelet effect. As expected, repeated administration of beraprost increased the plasma and urinary levels of a TXA2 metabolite, while ONO-1301 did not increase them significantly. In addition, beraprost could retain the ability to inhibit platelet aggregation after repeated administration in mice lacking the TXA2 receptor (TP). These results indicate that TP-mediated signaling participates in platelet desensitization against IP agonists and that simultaneous inhibition of TXA2 production confers resistance against desensitization on IP agonists.

Topics: Administration, Oral; Animals; Blood Pressure; Cyclic AMP; Epoprostenol; Male; Mice; Platelet Aggregation; Platelet Aggregation Inhibitors; Pyridines; Receptors, Thromboxane A2, Prostaglandin H2; Signal Transduction; Thromboxane A2; Thromboxane-A Synthase

Our in vivo assay system developed to search for allergy-preventive substances, assesses the blood flow decrease in tail vein microcirculation of mice subjected to sensitization with hen-egg white lysozyme (HEL). The blood flow decrease appears to be regulated by various factors such as nitric oxide (NO), thromboxane (TX) A(2), prostacyclin (PGI(2)) and endothelin (ET)-1 together with cyclooxygenase (COX)-1, COX-2, inducible nitric oxide synthase (iNOS), and constitutive nitric oxide synthase (cNOS). In this study, we examined in detail the roles of iNOS in this assay system using an iNOS knockout (KO) mouse. We found that the blood flow decrease in the HEL-sensitized iNOS KO mice was slightly weaker than that in their wild type (WT) mice. This blood flow decrease was not affected by a selective COX-1 inhibitor, a selective COX-2 inhibitor and a PGI(2) agonist unlike the case of the WT mice. However, it was inhibited by a nonselective NOS inhibitor, a specific TXA(2) synthase inhibitor and a specific ET-1 receptor blocker as in the case of the WT mice. The present results indicate that the blood flow decrease occurs via two pathways; one is an iNOS-independent response involving TXA(2) and ET-1, and the other is an iNOS-dependent response involving COX-1, COX-2 and PGI(2). cNOS appears to play some roles in the blood flow decrease and iNOS acts as an exacerbation factor. Our method using HEL-sensitized should be useful for searching for agents that can prevent allergy via new mechanisms.

Topics: Animals; Epoprostenol; Female; Hypersensitivity; Methacrylates; Mice; Mice, Inbred C57BL; Muramidase; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase Type II; Nitrobenzenes; Peptides, Cyclic; Regional Blood Flow; Sulfonamides; Thromboxane A2; Veins

Acute hemodynamic effects of beraprost sodium were tested in a canine vasoconstrictive pulmonary hypertension model induced by the continuous infusion of U-46619, a thromboxane A(2)mimetic. The effects of beraprost were compared with those of prostaglandin E(1), nitroglycerin and nifedipine. Beraprost and nitroglycerin decreased pulmonary arterial pressure. On the other hand, prostaglandin E(1)and nifedipine increased pulmonary arterial pressure. All drugs except nitroglycerin increased cardiac output and decreased pulmonary vascular resistance. Beraprost was selective to pulmonary circulation, while nitroglycerin, prostaglandin E(1), and nifedipine showed poor selectivity for the pulmonary vasculature. These results suggest that the vasodilative effect of beraprost is the most selective for the pulmonary circulation among these four vasodilators.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Alprostadil; Animals; Antihypertensive Agents; Disease Models, Animal; Dogs; Dose-Response Relationship, Drug; Epoprostenol; Humans; Hypertension, Pulmonary; Male; Nifedipine; Nitroglycerin; Oxygen; Thromboxane A2; Vasoconstrictor Agents; Vasodilator Agents

Abnormal biosynthesis of thromboxane and prostacyclin has been implicated in patients with primary pulmonary hypertension and secondary pulmonary hypertension associated with congenital heart disease, and could be involved in the pathogenesis of pulmonary vascular disease. The chronic effects of an oral prostacyclin analogue, beraprost sodium, on thromboxane and prostacyclin biosynthesis and on pulmonary circulation were investigated in 15 children with pulmonary hypertension. The plasma concentrations of thromboxane B2 and 6-keto-prostaglandin F1 alpha were measured, as was the urinary excretion of 11-dehydro-thromboxane B2 and 2,3-dinor-6-keto-prostaglandin F1 alpha, which are stable metabolites of thromboxane A2 and prostacyclin, respectively. In patients with pulmonary hypertension, the plasma concentration of thromboxane B2 and the ratio of thromboxane B2 to 6-keto-prostaglandin F1 alpha were greater than in healthy controls: 210 +/- 49 versus 28 +/- 4 pg/mL (P < 0.05) and 32.6 +/- 8.9 versus 5.7 +/- 1.8 (P < 0.01), respectively. After 3 months of administration of beraprost, the plasma concentration of thromboxane B2 and the ratio of thromboxane B2 to 6-keto-prostaglandin F1 alpha were reduced significantly: 210 +/- 49 to 98 +/- 26 pg/mL (P < 0.01) and 32.6 +/- 8.9 to 18.0 +/- 6.7 (P < 0.05), respectively. In contrast, the plasma concentrations of 6-keto-prostaglandin F1 alpha in patients were slightly but not significantly higher than in controls, and did not change significantly after administration of beraprost. The concentrations of 11-dehydro-thromboxane B2 and 2,3-dinor-6-keto-prostaglandin F1 alpha in urine correlated significantly with thromboxane B2 and 6-keto-prostaglandin F1 alpha, respectively, in plasma. Beraprost improved the imbalance of thromboxane and prostacyclin biosynthesis and has a potential efficacy for preventing the progressive development of pathological changes in pulmonary vasculature.

Topics: Child; Child, Preschool; Epoprostenol; Heart Defects, Congenital; Hemodynamics; Humans; Hypertension, Pulmonary; Infant; Platelet Aggregation Inhibitors; Prostaglandins F; Thromboxane A2; Thromboxane B2; Vasodilator Agents

The pathogenesis of intestinal damage caused by bolus intravenous injection of endotoxin (ETX; 3 mg/kg) was investigated. Administration of ETX to rats induced reddish discoloration suggestive of bleeding, increased hemoglobin amounts, and leakage of plasma protein in the intestine. However, light microscopic examination of the intestine demonstrated blood congestion of the microvessels. Plasma accumulation was partially inhibited by combined pretreatment with a histamine H1 antagonist and a serotonin (5-HT) antagonist. Neither a 5-lipoxygenase inhibitor, a soybean trypsin inhibitor, nor atropine was observed to inhibit plasma accumulation. Both the intestinal leakage of plasma and the accumulation of hemoglobin were completely inhibited by indomethacin, a selective thromboxane A synthetase inhibitor (OKY 1581), and a stable PGI2 analogue (beraprost). Intravital microscopic observation of the microvessels of the small intestinal villi demonstrated microthrombus formation within several minutes after the injection of ETX, and pretreatment with OKY 1581 attenuated the formation of microthrombus. Platelet counts decreased significantly 10 min after ETX administration, and the decrease was not inhibited by pretreatment with either OKY 1581 or beraprost. Prothrombin time (PT) and activated partial thromboplastin time (APTT) were not prolonged. These observations thus suggest that microcirculatory disturbances by platelet thrombus, which are mediated by thromboxane A2 at least in part, play an important role in ETX-induced intestinal damage.

Topics: Animals; Capillary Leak Syndrome; Cyclooxygenase Inhibitors; Endotoxins; Enzyme Inhibitors; Epoprostenol; Escherichia coli; Gastrointestinal Hemorrhage; Indomethacin; Intestine, Small; Male; Methacrylates; Microcirculation; Platelet Activation; Rats; Rats, Sprague-Dawley; Shock, Septic; Specific Pathogen-Free Organisms; Thrombosis; Thromboxane A2; Thromboxane-A Synthase

We wished to determine the action of prostaglandins (PG) and to analyze pharmacologically the mechanisms of their action in isolated human uterine arteries in special reference to mediators liberated from the endothelium and subendothelial tissues. Helical strips of the human uterine artery with and without the endothelium were suspended in the Ringer-Locke solution for isometric tension recording. The relaxant response to PGF2 alpha was reversed to a contraction by cyclooxygenase inhibitors and suppressed by tranylcypromine, a PGI2 synthase inhibitor, but was not influenced by endothelium denudation. Relaxations induced by PGE2 and beraprost, a PGI2 analogue, were augmented by cyclooxygenase inhibitors and tranylcypromine but were not affected by ONO3708, an antagonist of vasoconstrictor prostanoids, and endothelium denudation. The potentiating effect of indomethacin was observed in the strips both with and without the endothelium and was antagonized by treatment with beraprost. The relaxation caused by PGF2 alpha apparently is mediated by PGI2 released from subendothelial tissues, whereas the PGE2-induced relaxation is due to the direct action on smooth muscle; the action may be eliminated by the basal release of PGI2 from subendothelial tissues.

Topics: Adult; Dinoprost; Dinoprostone; Dose-Response Relationship, Drug; Epoprostenol; Female; Humans; In Vitro Techniques; Middle Aged; Phenylephrine; Potassium Chloride; Thromboxane A2; Uterus; Vasodilation

The vascular contractile mechanism of prostacyclin (PGI2) was investigated using beraprost sodium (BPS), a stable PGI2 analog. Ring strips without endothelium isolated from canine femoral veins and arteries were used. BPS induced a dose-dependent contraction without precontraction and after precontraction with norepinephrine (NE) or 60 mM K+ in the veins. In contrast, BPS induced a dose-dependent relaxation after precontraction with U46619, a thromboxane A2 (TXA2) analog, or prostaglandin F2 alpha (PGF2 alpha) in the veins. In the arteries, BPS induced contraction at higher concentrations after precontraction with NE. However, BPS relaxed arteries dose-dependently after precontraction with PGF2 alpha. By pretreatment with 13-azaprostanoic acid (13-APA), a TXA2/endoperoxide receptor antagonist, the dose-response curve of BPS in the veins was shifted to the right. Schild plot analysis resulted in a linear regression with a slope of 0.86 +/- 0.13, which was not significantly different from unity, and the pA2 value for 13-APA against BPS was 7.10 +/- 0.06. By pretreatment with BPS, the dose-response curve of U46619 in the veins was shifted to the right. Kaumann plot analysis resulted in a linear regression with a slope of 0.89 +/- 0.09, which was not significantly different from unity, and the pA2 value for BPS against U46619 was 5.68 +/- 0.04. These findings indicate that BPS is a partial agonist for the TXA2/endoperoxide receptors.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Acetylcholine; Animals; Dinoprost; Dogs; Dose-Response Relationship, Drug; Epoprostenol; Female; Femoral Artery; Femoral Vein; In Vitro Techniques; Male; Norepinephrine; Potassium; Prostaglandin Endoperoxides, Synthetic; Prostanoic Acids; Thromboxane A2; Vasoconstriction; Vasoconstrictor Agents