Synthesis of platelet-activating factor from human polymorphonuclear leukocytes: regulation and pharmacological approaches.

Human polymorphonuclears release a platelet-activating factor (PAF-acether) when challenged with various stimuli. PAF-acether is a mediator that is synthesized during cell activation in a process in which a phospholipase A2 and an acetyltransferase take part. These enzymes are finely regulated and accordingly PAF-acether release may be modulated. The authors have studied some of the transductory mechanisms which are triggered during cell stimulation and the effect of their pharmacological modulation on PAF-acether release. Theophylline, methylisobutylxanthine and dipyridamole, which block phosphodiesterase of cyclic nucleotides, induce a dose-dependent inhibition of PAF-acether release without affecting phagocytic uptake. Polyamines (dansylcadaverine, rimantadine and amantadine) reduced PAF-acether release and the phagocytic process in an order of potency similar to their ability to inhibit phospholipid methylation and the cholinephosphotransferase pathway. The calmodulin antagonist trifluoperazine induced a dose-dependent inhibition of PAF-acether release and acetyltransferase at concentrations from 10(-4) to 10(-5) M. Hence it appears that modulation of PAF-acether release can be obtained by different pharmacological blockades: phosphodiesterase of cyclic nucleotides, phospholipid metabolism and calcium-calmodulin.