title: Cyclooxygenase- and lipoxygenase-dependent relaxation to arachidonic acid in rabbit small mesenteric arteries.
abstract: We recently reported that the lipoxygenase product 11,12,15-trihydroxyeicosatrienoic acid (THETA) mediates arachidonic acid (AA)-induced relaxation in the rabbit aorta. This study was designed to determine whether this lipoxygenase metabolite is involved in relaxation responses to AA in rabbit small mesenteric arteries. AA (10(-9)-10(-4) M) produced potent relaxations in isolated phenylephrine-preconstricted arteries, with a maximal relaxation of 99 +/- 0.5% and EC(50) of 50 nM. The cyclooxygenase (COX) inhibitors indomethacin (10 microM), NS-398 (10 microM, selective for COX-2), and SC-560 (100 nM, selective for COX-1) caused a marked rightward shift of concentration responses to AA. With the use of immunohistochemical analysis, both COX-1 and COX-2 were detected in endothelium and smooth muscle of small mesenteric arteries. Indomethacin-resistant relaxations were further reduced by the lipoxygenase inhibitors cinnamyl-3,4-dihydroxy-cyanocinnamate (CDC; 1 muM), nordihydroguaiaretic acid (NDGA; 1 microM), and ebselen (1 microM). HPLC analysis showed that [(14)C]AA was metabolized by mesenteric arteries to PGI(2), PGE(2), THETAs, hydroxyepoxyeicosatrienoic acids (HEETAs), and 15-hydroxyeicosatetraenoic acid (15-HETE). The production of PGI(2) and PGE(2) was blocked by indomethacin, and the production of THETAs, HEETAs, and 15-HETE was inhibited by CDC and NDGA. Column fractions corresponding to THETAs were further purified, analyzed by gas chromatography/mass spectrometry, and identified as 11,12,15- and 11,14,15-THETA. PGI(2), PGE(2), and purified THETA fractions relaxed mesenteric arteries precontracted with phenylephrine. The AA- and THETA-induced relaxations were blocked by high K(+) (60 mM). These findings provide functional and biochemical evidence that AA-induced relaxation in rabbit small mesenteric arteries is mediated through both COX and lipoxygenase pathways.
authors.affiliation: Department of Pharmacology and Toxicology, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53226, USA.
authors.forename: David X
authors.initials: DX
authors.lastname: Zhang
authors.forename: Kathryn M
authors.initials: KM
authors.lastname: Gauthier
authors.forename: Yuttana
authors.initials: Y
authors.lastname: Chawengsub
authors.forename: Blythe B
authors.initials: BB
authors.lastname: Holmes
authors.forename: William B
authors.initials: WB
authors.lastname: Campbell
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism / Q000494:pharmacology*; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D066298:In Vitro Techniques; D008084:Lipoxygenase / Q000502:physiology*; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects / Q000201:enzymology / Q000502:physiology*; D011451:Prostaglandin-Endoperoxide Synthases / Q000502:physiology*; D011817:Rabbits; D014664:Vasodilation / Q000187:drug effects* / Q000502:physiology*
chemical_list: D016718:Arachidonic Acid; D008084:Lipoxygenase; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases