Relative roles of nitric oxide and cyclo‐oxygenase and lipoxygenase products of arachidonic acid in the contractile responses of rat renal arcuate arteries

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Abstract
1 We have examined the effects of inhibition of nitric oxide synthase, cyclo-oxygenase and lipoxygenase on the responses of renal arcuate arteries of Wistar rats, with and without endothelium, to noradrenaline, potassium chloride, endothelin-1, acetylcholine and sodium nitroprusside. 2 Noradrenaline, potassium chloride and endothelin-1 caused concentration-dependent contraction of the vessels. Indomethacin (14 μm) attenuated the contractile response to noradrenaline and to potassium chloride. The inhibitory effect of indomethacin persisted following endothelial removal. 3 Acetylcholine produced concentration-dependent relaxation of the vessels which was potentiated by indomethacin (14 μm). 4 NG-nitro-l-arginine methyl ester (l-NAME, 100 μm) did not affect the contractile response to either noradrenaline or potassium chloride but abolished relaxation to acetylcholine. In addition, l-NAME abolished the affects of indomethacin on acetylcholine-induced relaxation and noradrenaline- and potassium chloride-induced contraction. 5 BWC755C attenuated noradrenaline and potassium chloride-induced contraction. This effect persisted in the presence of indomethacin. 6 In vessels pretreated with CHAPS, BW755C inhibited both noradrenaline and potassium chloride-induced contraction. In these vessels BW755C had no additional inhibitory effect to indomethacin on noradrenaline- and potassium-induced contraction. 7 Inhibition of nitric oxide synthase with l-NAME (100 μm) attenuated the effect of BW755C on noradrenaline- and potassium-induced contraction. 8 BW755C alone did not affect endothelium-dependent relaxation as assessed by the response to acetylcholine. However, in the presence of indomethacin, BW755C inhibited acetylcholine-induced relaxation. 9 BW755C did not affect endothelium-independent relaxation as assessed by the response to sodium nitroprusside in vessels with or without endothelium. 10 These data support the existence of two vasoconstrictor products of arachidonic acid released during contraction of renal arcuate arteries with noradrenaline and potassium chloride. A cyclo-oxygenase product which appears to be endothelium-independent and the other an endothelium-dependent lipoxygenase product.