Effects of bacterial endotoxin and platelet activating factor (PAF) on human platelet aggregation in native whole blood

An investigation into the effects of bacterial lipopolysaccharide on human platelets

The addition of lipopolysaccharide (LPS) from Gram-negative bacteria to whole blood induced a consistent enhancement of platelet impedance aggregation (WB-PIA) and an increase in median platelet volume (MPV). In contrast, the addition of LPS to platelet rich plasma (PRP) resulted in inconsistent changes in turbidometric platelet aggregation (TPA) and no significant change in MPV. The LPS-induced increase of MPV in whole blood was inhibited by verapamil, a calcium channel blocker. We conclude that: (a) LPS consistently activates platelets in whole blood but not in PRP; (b) LPS-induced activation of platelets is probably mediated by products released by leucocytes and/or erythrocytes; (c) the increase in MPV induced by LPS is probably dependent upon calcium influx; and (4) an increase in MPV may be a useful and sensitive model for the study of platelet activation by LPS, in vitro and in vivo.

Platelet factor 4 (PF4) in septicaemia

The plasma concentrations of platelet factor 4 were measured in ten patients with septicaemia. In the acute phase the platelet factor 4 values were elevated (27.1 +/- 20.1 ng/ml; mean +/- SD; normal values 4.7 +/- 1.2 ng/ml), and declined significantly after treatment with antibiotics and surgical therapy, respectively (10.6 +/- 7.3 ng/ml; p less than 0.005). The determination of prothrombin time, fibrinopeptide A, AT III and platelet counts demonstrated a coagulation disorder in the acute phase of septicaemia in all patients; a thrombocytopenia (less than 100,000/mm3) was observed in three cases. We suggest that the measurement of platelet factor 4 concentration could be useful as an in vivo indicator and as a follow-up parameter of increased platelet activation.

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.