Metabolic fate of platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) and lyso-PAF (1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine) in FRTL5 cells.

The metabolism of platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) and lyso-PAF (1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine) was investigated in FRTL5 cells, a normal rat thyroid cell line. FRTL5 cells incorporated [3H]PAF and deacetylated this compound to the corresponding [3H]lyso-PAF which was not accumulated or secreted but converted mainly to alkyl-acyl-phosphocholine indicating that this acylation process was particularly active in these cells. Among metabolic products of both [3H]PAF and [3H]lyso-PAF were alkylglycerol as well as its mono- and diacyl derivatives. [3H]alkylglycerol could be the intermediate compound for the production of [3H]alkyl- and [3H]alkenyl-phosphoethanolamine (plasmalogen) which were also metabolic products. FRTL5 cells were able to convert lyso-PAF to PAF especially when they were stimulated by ionophore A23187 in the presence of [3H]Iyso-PAF and phenylmethylsulfonyl fluoride. The amount of PAF increased for the first 30 min and declined thereafter. PAF resting levels were found low in the same cells. Furthermore, PAF-acetylhydrolase activity was determined in cell homogenates. The presence of metabolic products such as alkyl-phosphatidylcholine, alkyl- and alkenyl-phosphatidylethanolamine and alkyl-glycerol, as well as, its mono- and diacyl derivatives, indicates that FRTL5 cells and probably other thyroid cells, are very active in metabolizing PAF and lyso-PAF and suggests the co-operation of the corresponding metabolic pathways in these cells.