12-Lipoxygenase in porcine coronary microcirculation: implications for coronary vasoregulation

Noncyclooxygenase metabolites of arachidonic acid (AA) have been proposed t o mediate endothelium-dependent vasodilation in the coronary microcirculati on. Therefore, we examined the formation and bioactivity of AA metabolites in porcine coronary (PC) microvascular endothelial cells and microvessels, respectively. The major noncyclooxygenase metabolite produced by microvascu lar endothelial cells was 12(S)-hydroxyeicosatetraenoic acid (HETE), a lipo xygenase product. 12(S)-HETE release was markedly increased by pretreatment with 13(S)-hydroperoxyoctadecadienoic acid but not by the reduced congener 13(S)-hydroxyoctadecadienoic acid, suggesting oxidative upregulation of 12 (S)-HETE output. 12(S)-HETE produced potent relaxation and hyperpolarizatio n of PC microvessels (EC50, expressed as -log[M] = 13.5 +/- 0.5). Moreover, 12(S)-HETE potently activated large-conductance Ca2+-activated K+ currents in PC microvascular smooth muscle cells. In contrast, 12(S)-HETE was not a major product of conduit PC endothelial AA metabolism and did not exhibit potent bioactivity in conduit PC arteries. We suggest that, in the coronary microcirculation, 12(S)HETE can function as a potent hyperpolarizing vasod ilator that may contribute to endothelium-dependent relaxation, particularl y in the setting of oxidative stress.