Effects of nonsteroid antiinflammatory drugs on the specific binding of platelet activating factor to membrane preparations of rabbit platelets

Abstract

The inhibitory effects of several antiinflammatory agents on the specific binding of tritiated 1-O-alkyl-2-O-acetyl-sn-glycero-3-phosphorylcholine, (platelet activating factor, PAF), with its receptor on isolated rabbit platelet plasma membranes were investigated. Several potent cyclooxygenase inhibitors do not inhibit 3H-PAF binding to its receptor sites. Yet, three others, indomethacin, phenylbutazone and sulfinpyrazone, as well as three non-cyclooxygenase inhibitors, the 3′,4′-dimethoxy analog of indomethacin, the prodrug sulindac and its sulfone metabolite, are moderately active at relatively high concentrations (50 - 100 μM). Parallel inhibitions of 3H-PAF binding and PAF-induced platelet aggregation by derivatives of these antiinflammatory agents suggest that these inhibitors are probably interacting with the functional binding sites of PAF. The results clearly indicate that the configuration of PAF binding site is very different from the inhibitory site of cyclooxygenase. A preference for oxygenated substituents in these hydrophobic molecules to inhibit the PAF-receptor binding is noted. Some binding characteristics of the receptor are briefly discussed.