Differential effects of ouabain on the vasodilator actions of nitric oxide and S-nitrosothiols in vivo: Relevance to the identity of EDRF/EDHF

This study examined the role of Na +/K +-ATPase in the vasodilator actions of nitric oxide (NO), S-nitrosothiols and the endothelium-dependent agonist, acetylcholine. The vasodilator responses elicited by intravenous injections of (i) the NO-donors, sodium nitroprusside and MAHMA NONOate, (ii) the S-nitrosothiols, l- S-nitrosocysteine and S-nitrosocoenzyme A, and (iii) acetylcholine, in urethane-anesthetized rats. The NO-donors, S-nitrosothiols and acetylcholine elicited dose-dependent depressor responses and reductions in hindquarter (HQR) and mesenteric (MR) vascular resistances. The depressor responses and associated reductions in HQR elicited by NO-donors were markedly attenuated after injection of ouabain. In contrast, the depressor responses and reductions in HQR elicited by the S-nitrosothiols and acetylcholine were not affected. The reductions in MR elicited by all vasodilator agents were exaggerated after injection of ouabain. Finally, the decomposition of sodium nitroprusside, MAHMA NONOate, l- S-nitrosocysteine and S-nitrosocoenzyme A to NO upon addition to rat blood or vascular preparations was not affected by ouabain. This study demonstrates that ouabain has opposing effects on NO-mediated vasodilation in resistance arteries in the hindquarter and mesenteric beds of the rat. The similarity of effects of ouabain on the vasodilator actions of acetylcholine, l- S-nitrosocysteine and S-nitrosocoenzyme A as opposed to the NO-donors supports the possibility that endothelium-derived relaxing factor released by acetylcholine in resistance arteries is an S-nitrosothiol.