PAF-induced synthesis of tetraenoic and pentaenoic leukotrienes in the isolated rabbit lung

In an isolated rabbit lung model, we tested the hypothesis that platelet-ac tivating factor (PAF)induced leukotriene (LT) synthesis is critically depen dent on the free precursor fatty acid supply and the possible substitution of arachidonic acid (AA) by eicosapentaenoic acid (EPA). To augment the int ravascular polymorphonuclear neutrophils (PMNs) in the isolated lung, human PMNs were infused into the pulmonary artery. LTs and hydroxyeicosatetra(pe nta)enoic acids were quantified with HPLC techniques, Application of PAF (5 mu M) or AA(10 mu M) provoked the generation of limited quantities of 4-se ries LTs and 5-hydroxyeicosatetraenoic acid (total sum of 5-lipoxygenase pr oducts approximate to 7 and approximate to 27 pmol/ml in lungs both with an d without infused PMNs, respectively). Combined administration amplified 5- lipoxygenase product formation, with a predominance of cysteinyl-LT synthes is in lungs both without (total sum approximate to 67 pmol/ml) and, much mo re strikingly, with (total sum approximate to 308 pmol/ml) an infusion of n eutrophils. EPA(10 mu M) elicited exclusive generation of 5-series Lm and 5 -hydroxyeicosapentaenoic acid (total sum approximate to 82 pmol/ml). Dual s timulation with PAF and EPA provoked amplification of EPA-derived 5-lipoxyg enase product formation, again. with predominance of cysteinyl-LTs in lungs without (total sum approximate to 224 pmol/ml) and, in particular, with (t otal sum approximate to 545 pmol/ml) preceding microvascular PMN entrapment . Combined application of PAF, AA, and EPA resulted in the synthesis of LTs derived from both fatty acids, with a predominance of 5-series products. W e conclude that the PAF-evoked 5-lipoxygenase product formation in the neut rophil-harboring lung capillary bed is critically dependent on intravascula r precursor fatty acid supply, with EPA representing the preferred substrat e compared with AA. PMN-related transcellular eicosanoid synthesis is sugge sted to underlie the predominant generation of cysteinyl-LTs. The supply of n-3 versus n-6 precursor fatty acid may thus have a major impact on inflam matory mediator generation.