Effect of platelet-activating factor (PAF) on human platelets.

The effect of pure synthetic PAF (1-0-alkyl-2-acetyl-sn-glycero-3-phosphorylcholine) was studied in human platelets. PAF (0.2--2.0 micrograms/ml) produced a dose-dependent aggregation in human platelet-rich plasma (PRP) or platelet suspension obtained by gel-filtration (GFP). In addition, PAF (0.8 microgram/ml) induced secretion of 14C-serotonin (45% +/- 10%; mean +/- SD, n = 9) and platelet factor 4 (PF4) (12.89 +/- 3.81 micrograms/10(9) platelets; n = 9) in PRP. Similar results were obtained in GFP. Aggregation and release of 14C-serotonin and PF4 were inhibited by the metabolic inhibitors 2-deoxyglucose (16.7 mM) and antimycin-A (8.3 micrograms/ml), by the membrane-active drugs mepacrine (10 microM) and chlorpromazine (0.025 mM), by PGI2 (5.34 nM), which elevates intracellular c-AMP, by indomethacin (10 microM) or aspirin (100 microM). The ADP scavengers, creatine phosphate and creatine phosphokinase (CP/CPK), inhibited the second wave of aggregation but not secretion. These data suggest that the major effect of PAF on human platelets is mediated through the cyclo-oxygenase pathway and not through a third pathway.