prostaglandin-h2 and sulotroban

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

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

1. Canine jugular and femoral veins were studied to determine the possible importance of thromboxane (TXA2) and prostaglandin endoperoxides (prostaglandin H2, PGH2) in mediating bradykinin(BK)-induced contraction. 2. Isolated vein rings incubated in modified Krebs solution contracted to TXA2/PGH2 analogs SQ26655 and U44069 with potency of contraction exceeding that for BK. The potency ranking for both veins was SQ26655 greater than U44069 greater than BK greater than PGF2 alpha greater than TXB2 much greater than PGD2. 3. The cyclo-oxygenase inhibitors indomethacin (3 x 10(-7) M) and flufenamic acid (10(-5) M) reduced BK contractions without affecting those induced by noradrenaline (NA). 4. TXA2/PGH2 receptor antagonists SQ29548 (10(-8) M) and BM13177 (10(-6) M) strongly inhibited BK-induced tension. The action of antagonists was reversible with negligible influence on NA-elicited contraction. Selective removal of endothelium had no effect on BK-induced contraction or the action of the antagonists. 5. The thromboxane synthase inhibitors dazoxiben (10(-4) M) and CGS 12970 (10(-5) M) had no significant inhibitory effect on BK-induced tension. 6. These results suggest that in canine jugular and femoral vein, the action of BK is largely dependent upon stimulation of the cyclo-oxygenase pathway to produce PGH2 and possibly TXA2, which can activate a smooth muscle TXA2/PGH2 receptor to elicit vasoconstriction.

Topics: Animals; Bradykinin; Bridged Bicyclo Compounds, Heterocyclic; Dogs; Endothelium, Vascular; Fatty Acids, Unsaturated; Female; Hydrazines; Imidazoles; In Vitro Techniques; Muscle Contraction; Muscle, Smooth, Vascular; Prostaglandin Endoperoxides; Prostaglandin Endoperoxides, Synthetic; Prostaglandin H2; Prostaglandin-Endoperoxide Synthases; Prostaglandins H; Pyridines; Receptors, Prostaglandin; Sulfonamides; Thromboxane-A Synthase; Thromboxanes; Veins

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

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

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

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

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

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