LIPID INHIBITORS OF PLATELET-ACTIVATING-FACTOR (PAF) IN NORMAL HUMAN PLASMA

Endogenous, human plasma-derived lipids that inhibit the platelet stim ulating activity of platelet-activating factor (PAF) have been identif ied. Chromatographic fractionation of neutral lipid PAF inhibitors rev ealed a majority of PAF inhibitory activity comigrating with cholester ol and a second peak localized with free fatty acids. Plasma phospholi pids demonstrated three distinct PAF inhibitory fractions in TLC regio ns corresponding to those of sphingomyelin, phosphatidylcholine and ph osphatidylethanolamine. Three fractions (one neutral lipid and two pho spholipid) specifically inhibited PAF-induced platelet activation. Thu s, there are both specific and non-specific lipid inhibitors of PAF in normal human plasma. These plasma lipids may be important in the spec ific regulation of the diverse, potent biological activities of PAF in various physiological states.