Pfister S L, Spitzbarth N, Edgemond W, Campbell W B
Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee 53226, USA.
Am J Physiol. 1996 Mar;270(3 Pt 2):H1021-30. doi: 10.1152/ajpheart.1996.270.3.H1021.
Arachidonic acid elicited relaxation responses in normal rabbit aorta precontracted with norepinephrine. The relaxation response was enhanced by the cyclooxygenase inhibitor indomethacin and inhibited by lipoxygenase inhibitors, including nordihydroguaiaretic acid and cinnamyl-3,4-dihydroxy-alpha-cyanocinnamate. The cytochrome P-450 epoxygenase inhibitor metyrapone had no effect on arachidonic acid-induced relaxations. The present study hypothesized that a lipoxygenase metabolite of arachidonic acid mediated the response. Incubation of rabbit aorta with [14C]arachidonic acid resulted in the synthesis of a previously unidentified 14C-labeled metabolite and was called the unknown factor. Production of the unknown factor was not inhibited by indomethacin and decreased by lipoxygenase inhibitors. Production of the unknown factor and arachidonic acid-induced relaxations were dependent on an intact endothelium, indicating that the cellular source of the unknown relaxant factor was the endothelial cell. This was confirmed by demonstrating the ability of cultured rabbit aortic endothelial cells to produce the unknown factor from [14C]arachidonic acid. Feeding rabbits a 2% cholesterol diet for 2 wk induced hypercholesterolemia without causing atherosclerosis. In the cholesterol-fed rabbits, indomethacin enhanced arachidonic acid-induced relaxations in norepinephrine-precontracted aortas (maximal relaxation 49.0 +/- 2.5 vs. 35.5 +/- 1.7%, cholesterol-fed vs. normal) and increased production of the unknown factor compared with normal rabbits. The partially purified unknown factor elicited an approximately 26% inhibition of the vasoconstrictor response to norepinephrine in intact rabbit aorta. Further purification of the unknown factor by reverse-phase high-pressure liquid chromatography system resulted in isolation of a radioactive product that relaxed precontracted rabbit aorta. Therefore these data suggest that in normal and hypercholesterolemic rabbit aorta the endothelium produces an unknown metabolite of arachidonic acid that causes vasorelaxation and may regulate vascular tone.
花生四烯酸可使预先用去甲肾上腺素收缩的正常兔主动脉产生舒张反应。环氧化酶抑制剂吲哚美辛可增强这种舒张反应，而脂氧合酶抑制剂（包括去甲二氢愈创木酸和肉桂酰 - 3,4 - 二羟基 - α - 氰基肉桂酸）则可抑制该反应。细胞色素P - 450环氧化酶抑制剂美替拉酮对花生四烯酸诱导的舒张反应无影响。本研究推测花生四烯酸的一种脂氧合酶代谢产物介导了该反应。用[14C]花生四烯酸孵育兔主动脉可导致合成一种先前未鉴定的14C标记代谢产物，该产物被称为未知因子。未知因子的产生不受吲哚美辛抑制，但可被脂氧合酶抑制剂减少。未知因子的产生以及花生四烯酸诱导的舒张反应依赖于完整的内皮，这表明未知舒张因子的细胞来源是内皮细胞。培养的兔主动脉内皮细胞能够从[14C]花生四烯酸产生未知因子，这证实了上述结论。给兔子喂食2%胆固醇饮食2周可诱导高胆固醇血症，但不会导致动脉粥样硬化。在喂食胆固醇的兔子中，吲哚美辛增强了花生四烯酸对去甲肾上腺素预收缩主动脉的舒张作用（最大舒张率：喂食胆固醇组为49.0±2.5%，正常组为35.5±1.7%），并且与正常兔子相比，未知因子的产生增加。部分纯化的未知因子可使完整兔主动脉对去甲肾上腺素的血管收缩反应产生约26%的抑制。通过反相高压液相色谱系统对未知因子进一步纯化，得到了一种可使预收缩兔主动脉舒张的放射性产物。因此，这些数据表明，在正常和高胆固醇血症兔主动脉中，内皮可产生一种花生四烯酸的未知代谢产物，该产物可引起血管舒张并可能调节血管张力。
