Possible involvement of 5-lipoxygenase products in the generation of endothelium-derived relaxing factor

Acetylcholine and substance P applied to the donor tissue, dog femoral artery segments with endothelium, produced moderate relaxations of the assay tissue, endothelium-denuded dog coronary artery strips. The relaxation was attenuated markedly by treatment of the assay tissue with hydroquinone and abolished by oxyhemoglobin or methylene blue. In this bioassay system, the effect of AA861 and TMK777, new 5-lipoxygenase inhibitors, was evaluated. When the donor tissue was treated with AA861 or TMK777, the responses to acetylcholine and substance P were attenuated moderately, whereas the relaxation by nitroglycerin was not influenced by AA861. However, the inhibitors when infused just below the donor tissue did not attenuate relaxant responses to acetylcholine and substance P. Application of superoxide dismutase (SOD) to the donor tissue caused a relaxation of the assay tissue, and potentiated the relaxation by acetylcholine and substance P. AA861 and TMK777 suppressed the relaxant responses to acetylcholine and substance P, respectively, in the presence and absence of SOD to a similar extent and abolished the SOD-induced relaxation. Pyrogallol abolished the relaxation by acetylcholine, but did not inhibit the response when the donor tissue was pretreated with SOD. Therefore, it appears that AA861 and TMK777 do not degrade endothelium-derived relaxing factor (EDRF) in the perfusate via generation of superoxide anion or block the action of EDRF on vascular smooth muscle, but interfere with the synthesis and/or release of EDRF. The findings obtained so far support the idea that lipoxygenase products participate in the generation of EDRF.