Production of platelet-activating factor in slugs.

The land slug, Incilaria bilineata, was shown to contain a large amount of 1-O-alkyl-2-acyl (long chain)-sn-glycero-3-phosphocholine, which accounts for as much as 47% of the choline glycerophospholipid fraction. Since this unique either phospholipid has been regarded as a stored precursor form of platelet-activating factor (PAF) in mammalian inflammatory cells, we examined the possibility of the presence of PAF in this animal. We obtained the evidence for the occurrence of significant amounts of PAF in two species of slugs, Incilaria bilineta and Incilaria fruhstorferi. Gas chromatography-mass spectrometry analysis revealed that the alkyl fatty chain of PAF principally consists of 16:0. We confirmed the presence of both enzyme activities catalyzing the formation of PAF, one for the remodeling pathway and the other for the de novo pathway. We also found the occurrence of other enzyme activities involved in PAF metabolism: acetylhydrolase activity which inactivates PAF and phospholipase A2 activity toward alkylacylglycerophosphocholine. However, we failed to detect cofactor-independent transacylation activity in this animal. The amounts of PAF in slugs were markedly increased when slugs were administered several treatments which are considered to induce shock, such as the injection of dimethyl sulfoxide or injuries. These results suggest that PAF is produced and may have certain physiological and pathological roles in the land slug, as in the case of mammals.