Incorporation of arachidonic acid into lipids of the isolated perfused rat lung

This study has attempted to identify the cells and phosphoglyceride molecular species associated with the rapid turnover of arachidonic acid (AA) in the isolated rat lung. In initial studies, AA complexed to trace amounts of albumin was added to the perfusate of rat lungs for 15 min and the incorporation of [³H]AA into various cells and phosphoglyceride molecular species was determined. Autoradiographic analysis revealed that the AA had labeled endothelial cells but also had already escaped from the intravascular space and labeled epithelial cells including alveolar type II cells. In addition, [³H]AA was found to be incorporated into various phosphoglycerides: phosphatidylcholine (PC) > phosphatidylethanolamine (PE) > phosphatidylinositol (PI). The majority of this [³H]AA was incorporated into 1-acyl-2-arachidonoyl-sn-glycero-3-PC, -PE, and -PI during the 15-min labeling period. In subsequent experiments, AA remodeling in the lung was examined by pulse labeling with [³H]AA for 15 min, washing unbound AA with albumin, and perfusing for an additional 120 min. In these lungs, some of the [³H]AA was remodeled into 1-alk-1-enyl-acyl-sn-glycero-3-PE. Gas chromatography-mass spectrometry analysis revealed that the largest pools of endogenous AA in the lung are found in PE associated with 1-alk-1-enyl-linked molecular species. On ionophore stimulation of lungs labeled for 15 min, labeled leukotriene (LT) B₄, leukotriene C₄, and 6-ketoprostaglandin F(1α) (6-keto-PGF(1α)) were produced. LTC₄ had a profoundly different radiospecific activity compared with LTB₄ and 6-keto-PGF(1α), suggesting a different source of AA as contributing to the production of this eicosanoid. In conclusion, these results suggest that there is rapid uptake of arachidonate from the perfusate into vascular and alveolar cells and incorporation into phosphoglyceride molecular species of the lung cells. Moreover, different eicosanoids are derived from selective sources of arachidonate within the lung.