Metabolism of arachidonic acid by canine polymorphonuclear leukocytes synthesis of lipoxygenase and omega-oxidized metabolites

Both polymorphonuclear (PMN) leukocytes and metabolites of arachidonic acid, especially lipoxygenase products, have been reported to contribute to myocardial damage after coronary artery occlusion and reperfusion. While canine models of myocardial ischemia were used in many of these studies, very little is known about arachidonic acid metabolism by canine PMNs. Moreover, it is unclear whether arachidonic acid metabolites released by canine PMNs affect vascular tone. Therefore, we characterized arachidonic acid metabolism by canine PMNs; and determined the effect of these metabolites an vascular tone of isolated canine coronary arteries. Suspensions of canine PMNs were incubated with [¹⁴C]arachidonic acid and the calcium ionophore A23187. The incubation media was extracted, and the metabolites resolved by HPLC. 20-Hydroxy-leukotriene B₄ (LTB₄), 12,20-dihydroxyeicosatetraenoic acid (diHETE), LTB₄, 12-hydroxyheptadeclatrienoic acid (HHT), and 12(S)-hydroxyeicosatetraenoic acid (HETE) were isolated, and their structures confirmed by gas chromatography/mass spectrometry. There was also evidence for the formation of 20-HETE, thromboxane B₂ (TXB₂), 5-HETE, and several isomers of LTB₄. None of the arachidonic acid metabolites that were isolated from incubates of canine PMNs augmented vascular tone, but material migrating with 12,20-diHETE relaxed canine coronary arteries. Authentic 12(S),20-diHETE also produced a concentration-relate relaxation of canine coronary artery. 12(R), 20-diHETE was inactive. 20-HETE inhibited A23187-induced PMN aggregation, Thus, arachidonic acid is metabolized in canine PMNs through the cyclooxygenase, lipoxygenases and cytochrome P-450 pathways. Whether these metabolites contribute to myocardial injury remains to be determined.