thromboxane-b2 and 4-bromophenacyl-bromide

1. The effect of the NSAIDs indomethacin, indoprofen, diclofenac and acetylsalicylic acid on the increase in guanosine 3':5'-cyclic monophosphate (cyclic GMP) induced by nitric oxide-donor agents was tested in human whole platelets and in platelet crude homogenate. 2. In whole platelets, indomethacin reduced the increase in cyclic GMP induced by the nitric oxide-donors (NO-donors) sodium nitroprusside (NaNP) and S-nitroso-N-acetylpenicillamine (SNAP) in a dose-dependent way, its IC50 being 13.7 microM and 15.8 microM, respectively. 3. Of the other cyclooxygenase inhibitors tested, only indoprofen reduced the increase in cyclic GMP induced by both NO-donors in a dose-dependent way (IC50=32.7 microM, NaNP and 25.0 microM, SNAP), while acetylsalicylic acid (up to 1000 microM) and diclofenac (up to 100 microM) were ineffective. 4. However, in platelet crude homogenate neither indomethacin nor indoprofen reduced the cyclic GMP production. 5. Indomethacin (10 microM), indoprofen (30 microM), diclofenac (100 microM) and acetylsalicylic acid (1000 microM) showed a comparable efficacy in inhibiting platelet thromboxane B2 (TXB2) production, suggesting that the inhibitory effect of indomethacin and indoprofen on the increase in cyclic GMP induced by both NO-donors was not mediated by inhibition of cyclooxygenase. 6. In vitro, the NSAIDs analysed did not interfere with nitrite production of SNAP. 7. The unhomogeneous behaviour of NSAIDs on the increase in cyclic GMP induced by NO-donors in whole platelets may contribute to the different pharmacological and toxicological characteristics of the drugs, providing new knowledge on the effect of indomethacin and indoprofen.

Topics: Acetophenones; Aspirin; Blood Platelets; Cyclic GMP; Cyclooxygenase Inhibitors; Diclofenac; Humans; Indomethacin; Indoprofen; Nitric Oxide; Nitroprusside; Penicillamine; Phospholipases A; Thromboxane B2

In isolated perfused rat liver, adenosine infusion (50 microM) led to increases in glucose output and portal pressure and a net K+ release of 3.7 +/- 0.21 mumol/g, which was followed by an equivalent net K+ uptake after cessation of the nucleoside infusion. These effects were accompanied by a transient stimulation of hepatic prostaglandin D2 and thromboxane B2 release. The Ca2+ release observed upon adenosine infusion (50 microM) was 23.5 +/- 5.2 nmol/g, i.e. 10-20% of the Ca2+ release observed with extracellular ATP (50 microM). Indomethacin (10 microM) prevented the adenosine-induced stimulation of glucose output and the increase in portal pressure by 79 and 63% respectively, and completely abolished the stimulation of prostaglandin D2 release. The thromboxane A2 receptor antagonist BM 13.177 (20 microM), the phospholipase A2 inhibitor 4-bromophenacyl bromide (20 microM) and the cyclo-oxygenase inhibitor ibuprofen (50 microM) also decreased the glycogenolytic and vasoconstrictive responses of the perfused rat liver upon adenosine infusion by 50-80%. When the indomethacin inhibition of adenosine-induced prostaglandin D2 release was titrated, a close correlation between prostaglandin D2 release and the metabolic and vascular responses to adenosine was observed. These findings suggest an important role for eicosanoids in mediating the nucleoside responses in the perfused rat liver. Since eicosanoids are known to be formed by non-parenchymal cells in rat liver [Decker (1985) Semin. Liver Dis. 5, 175-190], the present study gives further evidence for an important role of eicosanoids as signal molecules between the different liver cell populations.

Topics: Acetophenones; Adenosine; Animals; Blood Pressure; Glucose; Ibuprofen; Indomethacin; Liver; Male; Portal System; Prostaglandin D2; Rats; Rats, Inbred Strains; Secretory Rate; Sulfonamides; Thromboxane B2

4-Bromophenacyl bromide at a concentration of 50 microM does not inhibit phospholipase A2 activity in liver macrophages. Rather, this compound increases the amount of radioactivity released from [3H]arachidonate-prelabeled Kupffer cells and leads to the formation of small amounts of thromboxane, prostaglandin D2 and prostaglandin E2. Also the zymosan-induced formation of thromboxane and prostaglandin E2 from endogenous sources which is thought to involve phospholipase A2 remains unaffected in the presence of this compound. The generation of superoxide and the formation of prostaglandin D2 from arachidonate and after stimulation of the cells with zymosan, however, are blocked by 4-bromophenacyl bromide. Furthermore, this compound suppresses the incorporation of externally added arachidonate into membrane lipids of the cells. 4-Bromophenacyl bromide seems, therefore, not to be a useful tool to demonstrate the involvement of phospholipase A2 in complex biological systems.

Topics: Acetophenones; Animals; Arachidonic Acids; Cells, Cultured; Chromatography, High Pressure Liquid; Kupffer Cells; Membrane Lipids; Phospholipases; Phospholipases A; Phospholipases A2; Phospholipids; Prostaglandin D2; Prostaglandins E; Radioimmunoassay; Rats; Thromboxane B2; Zymosan