title: 1-O-alkyl-2-acyl-sn-glycero-3-phosphorylcholine is the precursor of platelet-activating factor in stimulated rabbit platelets. Evidence for an alkylacetyl-glycerophosphorylcholine cycle.
abstract: The metabolism of [3H]PAF-acether ([1',2'-3H]alkyl-2-acetyl-sn-glycero-3-phosphorylcholine ([3H]alkylacetyl-GPC)) by rabbit platelets was investigated using thin-layer chromatography and high-performance liquid chromatography followed by radioactivity detection. After 2 h of incubation at 37 degrees C, 90 +/- 5.3% of [3H]PAF-acether taken up by the platelets were converted into a product identified as sn-2 long-chain acyl analogue ([3H]alkylacyl-GPC) which was incorporated in the membranes. This conversion was independent from extracellular calcium and was completely inhibited by platelet pre-exposure to 2 mM phenylmethylsulfonyl fluoride, a serine hydrolase inhibitor, which failed to inhibit the uptake of [3H]PAF-acether by the cells. The 2-deacetylated derivative, lyso-[3H]PAF-acether was found to be an intermediate of the conversion of [3H]PAF-acether into [3H]alkylacyl-GPC in platelet homogenates. Platelet stimulation with 2.5 U/ml of thrombin induced a reduction (16.5 +/- 2.2%) of its content of [3H]alkylacyl-GPC, accompanied by the release of [3H]PAF-acether and lyso-[3H]PAF-acether to the medium. These effects were suppressed by the phospholipase A2 inhibitor, p-bromophenacyl bromide. Our results demonstrate that intact platelets convert exogenous PAF-acether into alkylacyl-GPC, which can serve as the precursor of PAF-acether released during stimulation. The existence of a metabolic cycle for the uptake, the release and the inactivation of PAF-acether by platelets is suggested.
mesh_terms: D000215:Acylation; D000478:Alkylation; D000818:Animals; D055598:Chemical Phenomena; D002621:Chemistry; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D010664:Phenylmethylsulfonyl Fluoride / Q000494:pharmacology; D010972:Platelet Activating Factor / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects*; D011498:Protein Precursors / Q000378:metabolism*; D011817:Rabbits; D013917:Thrombin / Q000494:pharmacology
chemical_list: D010972:Platelet Activating Factor; D011498:Protein Precursors; D010664:Phenylmethylsulfonyl Fluoride; D013917:Thrombin