Influence of the Pure Synthetic PAF (Platelet Aggrregating Factor) on Clot Retraction and Platelet Aggregation

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Abstract
Pure synthetic platelet aggregating factor (PAF) (1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphorylcholine) induces a dose-dependent platelet aggregation in platelet-rich plasma (PRP) and in gel-filtered [human]platelets. Irreversible platelet aggregation was observed at final concentrations of PAF higher than 2 .times. 10-7 mol/l, while reversible or 2-wave aggregation was obtained with lower final concentrations. The 2nd wave was inhibited by acetylsalicyclic acid, indomethacin, dipyridamole, EDTA, EGTA [ethyleneglycol bis[.beta.-aminoethyl ether]-N,N,N'',N''-tetraacetic acid], theophylline, caffeine, PGE1 and verapamil. PAF does not induce reptilase clot retraction (RCR); however, it does not inhibit RCR induced by ADP or thrombin. Since all substances known to active platelets also induce RCR, the lack of this activity by PAF would support the existence of a 3rd pathway in platelets.