Studies on the stimulation of human blood platelets by semi-synthetic platelet-activating factor

"Saturated" and "unsaturated" platelet-activating factor (PAF) obtained from ratfish liver oil were proved to exert potent stimulation on human blood platelets. Using 0.025 to 1.0 mumol/1 PAF a dose-dependent platelet aggregation in platelet-rich plasma was observed. During PAF-induced irreversible aggregation a 9 to 40% release of platelet bound serotonin occurred. The specific effect of PAF, however, seems to be limited to induce reversible aggregation since second wave of aggregation and serotonin release were suppressed by a combination of acetylsalicylic acid and an ADP scavenging system. Incubation of PAF for 30 min in plasma resulted in a 90% loss of its platelet aggregating power. Subthreshold concentrations of PAF enhanced the platelet aggregation triggered by suboptimal concentrations of ADP, epinephrine, or collagen. Vice versa non-aggregating concentrations of ADP, epinephrine, collagen, Ca-ionophore A 23,187, or arachidonic acid amplified PAF-induced platelet aggregation. The synergistic effect of PAF and other stimuli of blood platelet activation can be partly interpreted as a stimulating effect of PAF on the metabolization of arachidonic acid.