Cooperative effects of 1-O-alkyl-2-O-acetyl-sn-glycero-3-phosphocholine (PAF-acether) and exogenous arachidonic acid in stimulation of human blood platelets.

Cooperative effects of PAF-acether and arachidonic acid in blood platelet activation were studied in human platelet-rich plasma. Using a combination of low concentrations of PAF-acether and subthreshold amounts of exogenous arachidonic acid an enhancement of aggregation and an increased formation of malondialdehyde are obtained. Both effects are completely suppressed either by acetylsalicylic acid or by use of PAF-acether desensitized platelets, indicating that cyclooxygenase products and intact receptors for PAF-acether are of primary importance in the observed synergism. Stimulating activity of PAF-acether on the formation of cyclooxygenase products is also seen with use of higher concentrations of arachidonic acid during mild stimulation of human platelets. This effect of PAF-acether is dependent on the concentration used and is obviously due to changes in the platelet membrane as derived from experiments with lysed platelets. Enhanced capacity of platelets to synthesize endoperoxides and thromboxane in consequence of an in vivo release of PAF-acether into the circulation might be of pathobiochemical relevance in some circumstances.