Basal release of 6-cyanodopamine from rabbit isolated aorta and its modulation of vascular reactivity.

6-Cyanodopamine (6-CYD) is a recently identified endogenous catecholamine that exerts positive chronotropic and inotropic actions, but its occurrence in vascular tissue and effects on vascular reactivity are unknown. In endothelium-intact and endothelium-denuded rabbit isolated aortic rings, we investigated the basal release of 6-CYD and its effects on aortic smooth muscle reactivity. 6-Cyanodopamine release was quantified by LC-MS/MS. Isometric tension was recorded to assess concentration-response curves to noradrenaline, adrenaline, and dopamine in aortic rings pre-incubated or not with 6-CYD, whereas vasorelaxation was evaluated in endothelin-1 (ET-1)-pre-contracted rings. Rabbit aorta released significant amounts of 6-CYD, which were largely reduced either by endothelium removal or pre-incubation with the NOX1/4 inhibitor GKT137831 (1 µM), whereas the nitric oxide (NO) synthase inhibitor L-NAME (100 µM) and the voltage-gated sodium channel blocker tetrodotoxin (TTX, 1 µM) had no significant effect. Addition of 6-CYD (0.1 pM to 10 nM) had no contractile activity itself, but it significantly potentiated noradrenaline- and adrenaline-induced aortic contractions, an effect largely reduced by endothelium removal. The dopamine-induced aortic contractions remained unaffected by 6-CYD. In ET-1-pre-contracted rings, 6-CYD (1 nM-10 µM) produced concentration-dependent relaxations that were significantly reduced by endothelium removal and L-NAME (100 µM), as well as by the soluble guanylyl cyclase (sGC) inhibitors ODQ (100 µM) and methylene blue (10 µM). In conclusion, these findings identify vascular endothelium as a source of 6-CYD and indicate this catecholamine as a novel endogenous modulator of vascular tone, acting through a dual mechanism, namely, potentiating vasoconstriction and producing NO/sGC-dependent vasorelaxation.