vapiprost and dazoxiben

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

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

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

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

We previously demonstrated that the bradykinin-induced contraction of human isolated small bronchi is inhibited by indomethacin, capsaicin (N-methyl-N-6-nonenamide) and ruthenium red but not by tachykinin receptor antagonists. The thromboxane A2 receptor (TP receptor) antagonist GR32191 ((1R-(1 alpha(Z),2 beta,3 beta,5 alpha))-(+)-7-(5-(((1,1'-biphenyl)-4-yl)- methoxy)-3-hydroxy-2-(1-piperidinyl)cyclopentyl)-4-heptenoic acid, hydrochloride) (10(-10) to 10(-8) M) dose dependently inhibited the effect of bradykinin, suggesting the mediation of the TP receptor in the action of bradykinin. With higher concentrations of GR32191 (10(-7) and 10(-6) M) bradykinin induced a relaxation which was inhibited by indomethacin and by the bradykinin B2 receptor antagonist Hoe 140 (D-Arg0[Hyp3,Thi-5,D-Tic7,Oic8]bradykinin). The thromboxane A2 synthase inhibitor dazoxiben (4-(-2-(1H-imidazol-1-yl)ethoxy) benzoic acid hydrochloride) 10(-6) M inhibited the bradykinin-induced contraction, suggesting that thromboxane A2 was involved in TP receptor stimulation. The thromboxane A2 mimetic U-46619 (9,11-dideoxy-11 alpha,9 alpha-epoxy-methano-prostaglandin F2 alpha)-induced contraction of human distal bronchi was not inhibited by capsaicin and ruthenium red. Our data suggest that bradykinin contracts human isolated small bronchi through thromboxane A2 release. The inhibitory effect of ruthenium red and capsaicin on the bradykinin response may be due to inhibition of thromboxane A2 release or arachidonic mobilisation.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adult; Aged; Biphenyl Compounds; Bradykinin; Bronchi; Capsaicin; Dose-Response Relationship, Drug; Heptanoic Acids; Humans; Imidazoles; Indomethacin; Male; Middle Aged; Muscle Contraction; Muscle Relaxation; Muscle, Smooth; Prostaglandin Endoperoxides, Synthetic; Receptors, Thromboxane; Ruthenium Red; Thromboxane A2; Thromboxane-A Synthase; Vasoconstrictor Agents

1. The present study has compared the relative anti-aggregatory effect of various compounds which interfere with thromboxane (Tx) A2-dependent aggregation of human platelets in whole blood in vitro. These included the cyclo-oxygenase inhibitor aspirin, the TxA2 synthase inhibitor dazoxiben, the TxA2 (TP-) receptor blocking drug GR32191 and two compounds, R.68070 ((E)-5-[[[(3-pyridinyl) [3-(trifluoromethyl)phenyl]-methylen] amino]oxy] pentanoic acid) and CV-4151 [E)-7-phenyl-7-(3-pyridyl)-6-heptenoic acid), which possess both TP-receptor blocking and TxA2 synthase inhibitory activities in the same molecule. 2. GR32191, R.68070 and CV-4151 all antagonized aggregation to the TxA2 mimetic U-46619, with pA2 values of approximately 8.2, 5.4 and 4.8 respectively. This effect was specific, platelet aggregation induced by adenosine 5'-diphosphate (ADP) being unaffected by concentrations up to 10, 1000 and 300 microM respectively. In contrast, neither aspirin nor dazoxiben exhibited any measurable TP-receptor blocking activity. 3. The rank order of potency (pIC50) for inhibition of TxA2 formation in serum was R.68070 (7.4) greater than CV-4151 (6.9) greater than dazoxiben (5.7) greater than aspirin (5.3). In addition, all four drugs abolished collagen-induced platelet TxA2 formation. In contrast, GR32191 produced no consistent inhibition of TxA2 formation in either system up to concentrations of 10-30 microM. 4. The specificity of R.68070, CV-4151 and dazoxiben for TxA2 synthase was indicated by their ability to increase serum levels of prostaglandin E2 (PGE2) and PGD2 in parallel with decreases in TxA2 formation. This profile was not observed with aspirin or GR32191. However, high concentrations of R.68070 (100,microM) and CV-4151 (1000 microM) necessary for maximum TP-receptor blocking activity, produced substantially smaller increases in PGE2 and PGD2, consistent with an aspirin-like effect of these compounds upon cyclo-oxygenase. With dazoxiben (1000 microM), PGE2 and PGD2 levels remained elevated. 5. Aspirin inhibited collagen-induced platelet aggregation, the effect correlating with inhibition of TxA2 formation. Dazoxiben, whilst also achieving maximal inhibition of TxA2 formation, produced significantly less inhibition of aggregation than aspirin. In contrast, GR32191 (0.1-1O microM), at concentrations specific for TP-receptor blockade, produced a significantly greater antagonism of collagen-induced platelet aggregation than aspirin. This additional effect o

Topics: Aspirin; Biphenyl Compounds; Drug Interactions; Fatty Acids, Monounsaturated; Heptanoic Acids; Humans; Imidazoles; In Vitro Techniques; Male; Pentanoic Acids; Platelet Aggregation; Platelet Aggregation Inhibitors; Pyridines; Receptors, Prostaglandin; Receptors, Thromboxane; Thromboxane-A Synthase

1. The effects of selective thromboxane antagonists and a thromboxane synthase inhibitor on the contraction to 9,11-dideoxy-11 alpha,9 alpha-epoxymethano-prostaglandin F2 alpha (U46619) and oxygen in the human umbilical artery (HUA) were examined. The effect of the antagonists on contractions to both 5-hydroxytryptamine (5-HT) and 5-carboxamidotryptamine (5-CT) were also examined. 2. U46619 (0.3 nM-10 microM) contracted the HUA. This contraction was antagonized by two selective thromboxane receptor antagonists EP092 (10 nM-1 microM) and GR32191B (10 nM-1 microM). The contraction was not affected by the selective thromboxane synthase inhibitor, dazoxiben (10 nM-1 microM). 3. When the oxygen tension was increased from 16 mmHg to 120 mmHg, the HUA transiently contracted. Both thromboxane antagonists inhibited this contraction in a concentration-dependent manner with 1 microM almost completely abolishing the response (the oxygen-induced contraction of the control preparation normally increases with a second exposure to 120 mmHg oxygen). 4. In low (16 mmHg) oxygen, responses to both 5-HT and 5-CT were unaffected by both thromboxane receptor antagonists at concentrations up to 1 microM. In high oxygen (120 mmHg) responses to both 5-HT and 5-CT were biphasic in nature, with an additional initial high sensitivity phase, which was abolished by a cyclo-oxygenase inhibitor. In high oxygen, EP092 and GR32191B blocked this initial phase in a concentration-dependent manner, returning sensitivity to 5-HT and 5-CT to that seen in low oxygen. 5. The thromboxane synthase inhibitor, dazoxiben, at concentrations greater than 10 nm inhibited the contraction to 120 mmHg oxygen and at 1 microM, dazoxiben almost abolished the response. In low oxygen, the response to 5-HT was unaffected by dazoxiben at concentrations up to 10 microM. In high oxygen, the initial phase of the contraction to 5-HT was inhibited by concentrations greater than 10 nm, with no effect on the maximum response. 6. The results show that thromboxane receptor antagonism or blockade of thromboxane synthesis selectively attenuates oxygen-induced contractions and those responses to 5-HT and 5-CT which are dependent on high oxygen for their expression. This suggests that the contractions caused by high oxygen tension, and the enhancement of the contractile effects of low concentrations of 5-HT and 5-CT in the presence of high oxygen tension are mediated by endogenously released thromboxane A2.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Biphenyl Compounds; Female; Heptanoic Acids; Humans; Imidazoles; In Vitro Techniques; Muscle Contraction; Muscle, Smooth, Vascular; Oxygen; Pregnancy; Prostaglandin Endoperoxides, Synthetic; Prostaglandins, Synthetic; Serotonin; Thromboxane-A Synthase; Thromboxanes; Umbilical Arteries