Effects of platelet activating factor (PAF) on human citrated whole blood

Effects of PAF on citrated whole blood (C-WB) from 38 healthy donors have been studied by impedance aggregometry and by morphologic examination of blood cells using scanning and transmission electron microscopy. In the aggregometer, the C-WB samples showed distinct differences in PAF sensitivity. C-WB specimens from high responders (= 15 donors) displayed a dose-related response to PAF stimulation but those from low responders (= 23 donors) did not indicate an impedance alteration even after the addition of high PAF doses (greater than or equal to 10(-6) mol/l). Morphologic studies revealed shape-changed platelets and primary aggregates in all C-WB samples, whereas secondary aggregates occurred only in C-WB specimens from high responders. Monocytes and neutrophil PMNs showed typical morphologic alterations which were observed in PAF-stimulated C-WB samples from all donors. Both cell types appeared polarized in shape and exhibited large vacuoles in the cytoplasm after PAF activation. In addition, monocytes came into close contact with shape-changed platelets as well as primary and secondary aggregates, whereas PMNs had no special relationship to single or aggregated platelets. In summary, our study indicates that PAF acts on different cell types in C-WB including platelets, monocytes and PMNs. The sensitivity of platelets against PAF stimulation appears to vary between different donors and in certain cases seems to be limited to the formation of primary aggregates.