title: Functional and biochemical characterization of immunologically derived equine platelet-activating factor.
abstract: Antigen-specific challenge of equine leukocytes induced the non-lytic release of a platelet-activating factor in vitro. The equine platelet-activating factor stimulated the release of serotonin from equine platelets in a dose-responsive manner, independent of the presence of cyclo-oxygenase pathway inhibitors such as indomethacin. Rabbit platelets were also responsive to equine platelet-activating factor. The release of equine platelet-activating factor was a rapid reaction with near maximal secretion taking place in 30 seconds. Addition of equine platelet-activating factor to washed equine platelets stimulated platelet aggregation which could not be inhibited by the presence of aspirin or indomethacin. Platelets pre-incubated with equine platelet-activating factor became specifically desensitized to equine platelet-activating factor while remaining responsive to other platelet stimuli such as collagen and epinephrine. The following biochemical properties of equine platelet-activating factor are identical to those properties of 1-0-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine (AGEPC): stability upon exposure to air and acid; loss of functional activity after base-catalyzed methanolysis with subsequent acylation that returned all functional activity; and identical relative mobilities on silica gel G plates developed with chloroform:methanol:water (65:35:6, volume/volume). The combined functional and biochemical characteristics of equine platelet-activating factor strongly suggest identity between this naturally occurring, immunologically derived equine factor and AGEPC.
mesh_terms: D000818:Animals; D000947:Antigens, Helminth / Q000276:immunology; D001200:Ascaris / Q000276:immunology; D001241:Aspirin / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism; D002855:Chromatography, Thin Layer; D004305:Dose-Response Relationship, Drug; D005260:Female; D006736:Horses / Q000502:physiology*; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D007962:Leukocytes / Q000276:immunology / Q000378:metabolism; D008297:Male; D010972:Platelet Activating Factor / Q000032:analysis / Q000494:pharmacology / Q000502:physiology*; D010974:Platelet Aggregation; D012701:Serotonin / Q000378:metabolism
chemical_list: D000947:Antigens, Helminth; D010972:Platelet Activating Factor; D012701:Serotonin; D007770:L-Lactate Dehydrogenase; D001241:Aspirin; D007213:Indomethacin