Basal release of 6-cyanodopamine in human vas deferens, a new endogenous catecholamine that enhances smooth muscle contractility.

6-Cyanodopamine (6-CYD) is a novel endogenous catecholamine that is released from rat isolated vas deferens epithelium and regulates smooth muscle contractility. Here it was investigated whether 6-CYD is released from human epididymal vas deferens (HEVD) and its interaction with the classical catecholamines dopamine, noradrenaline, and adrenaline. Basal release of 6-CYD was quantified by liquid chromatography coupled to tandem mass spectrometry in the absence and presence of either the voltage-gated sodium channel blocker tetrodotoxin or the dual NADPH oxidase NOX1,4 inhibitor GKT137831. Concentration-response curves to dopamine, noradrenaline, and adrenaline were performed in the presence and absence of 6-CYD. Frequency-dependent electric-field stimulation (EFS) was conducted with and without pre-incubation with 6-CYD. The basal release of 6-CYD was decreased with pre-incubation with GKT137831 and unaffected by tetrodotoxin. Although 6-CYD itself (up to 100 μM) did not induce HEVD contractions, at 10 nM it remarkably potentiated the contractions induced by dopamine, noradrenaline, and EFS. At 100 nM, 6-CYD also potentiated the adrenaline-induced HEVD contractions. The potentiation of noradrenaline-induced contractions by 6-CYD was not observed in HEVD pre-treated with tetrodotoxin (1 μM). In separate experiments, HEVD strips also released 6-nitrodopamine (6-ND) that was significantly reduced by GKT137831 (1 μM). Co-incubation (30 min) with 6-CYD (100 pM) and 6-ND (100 pM) caused a significant leftward shift in the concentration-response curve to noradrenaline. The results indicate that epithelium 6-CYD is an endogenous mediator of HEVD contractility. Whether NADPH oxidases are involved in 6-CYD biosynthesis remains to be further investigated.