Platelet-activating factor and endotoxin increase the enzyme activity and gene expression of type II phospholipase A₂ in the rat intestine: Role of polymorphonuclear leukocytes

Type II phospholipase A₂ (PLA₂-II) may regulate eicosanoid synthesis; is involved in various inflammatory processes, septic shock, and inflammatory bowel disease; and is up-regulated by LPS and inflammatory cytokines in vitro. We have previously shown that the platelet-activating factor (PAF)-induced intestinal injury is attenuated by peptido-leukotriene antagonists, suggesting a role of PLA₂. The purpose of this study is to examine the regulation of intestinal PLA₂-II by PAF and LPS. Using synthesized competitor RNA as competitor, we quantified PLA₂-II transcripts by competitive reverse transcription-PCR. We found that PLA₂-II gene is constitutively expressed in the rat ileum. PAF at a dose (1.5 μg/kg) below that causing intestinal injury rapidly up-regulated intestinal PLA₂-II at both transcriptional and post-transcriptional levels, almost tripling its transcripts and significantly increasing enzyme activity in 30 min. LPS (5 mg/kg) also up-regulated PLA₂-II. This effect could not be blocked by PAF antagonist. Depletion of circulating polymorphonuclear leukocytes (PMNs) abolished the effect of PAF on PLA₂-II gene expression and enzyme activation. In contrast, PMN depletion prevented LPS-induced PLA₂-II enzyme activity but enhanced the gene expression. We conclude that: 1) both PAF and LPS induce gene transcription and enzyme activation of PLA₂-II in the small intestine; 2) PAF up-regulates PLA₂-II via PMN activation; 3) LPS effect is independent of endogenous PAF formation; and 4) different pathways exist for PAF and LPS in the regulation of intestinal PLA₂-II gene expression in vivo.