Alpha1-adrenergic blockers selectively antagonize the contractions induced by 6-nitrodopamine in the human vas deferens

6-Nitrodopamine potentiates catecholamine-induced contractions of human isolated vas deferens

6-Nitrodopamine (6-ND) is the main catecholamine released from human isolated vas deferens and the adrenergic nervous system is known to play a major role in the contractions of the epididymal portion of the vas deferens. Here it was investigated the interactions of 6-ND on the contractions of the human isolated vas deferens induced by either classical catecholamines or electric-field stimulation (EFS). The vas deferens obtained from 106 patients who underwent vasectomy surgery were mounted in a 10-mL glass chamber filled with warmed (37°C) and oxygenated Krebs-Henseleit's solution. The strips were pretreated (30 min) with 6-ND (0.1-100 nM) and exposed to increasing concentrations of noradrenaline (0.01-300 M), dopamine (0.00001-10 mM), or adrenaline (0.01-300 M). The strips were also submitted to EFS in tissues pre-incubated or not with 6-ND (1-100 nM), noradrenaline (100 nM), adrenaline (100 nM), or dopamine (100 nM). Catecholamine basal release was evaluated by LC-MS/MS and expression of tyrosine hydroxylase by both immunohistochemistry (IC) and fluorescence in-situ hybridization (FISH). Pre-incubation of the vas deferens with 6-ND caused marked potentiation of the contractions induced by noradrenaline, adrenaline, and dopamine, as characterized by significant increases in Emax, without changes in pEC50 values. 6-nitrodopamine also caused significant increases in the EFS-induced contractions. The basal release of 6-ND was not affected by pre-treatment of the tissues with tetrodotoxin. Tyrosine hydroxylase was detected in epithelial cells of human vas deferens samples by both IC and FISH. The results clearly demonstrate that epithelium-derived 6-ND is a major modulator of human vas deferens contractility.

The pivotal role of neuronal nitric oxide synthase in the release of 6-nitrodopamine from mouse isolated vas deferens

6-Nitrodopamine (6-ND) is released from rat and human vas deferens and is considered a major mediator of both tissues contractility. The contractions induced by 6-ND are selectively blocked by both tricyclic antidepressants and α1-adrenoceptor antagonists. Endothelial nitric oxide synthase (eNOS) is the major isoform responsible for 6-ND release in mouse isolated heart, however the origin of 6-ND in the vas deferens is unknown. Here it was investigated by LC-MS/MS the basal release of 6-ND from isolated vas deferens obtained from control, eNOS-/-, nNOS-/-, and iNOS-/- mice. In addition, it was evaluated in vitro vas deferens contractility following electric field stimulation (EFS). Basal release of 6-ND was significantly reduced in nNOS-/- mice compared to control mice, but not decreased when the vas deferens were obtained from either eNOS-/- or iNOS-/- mice. Pre-incubation of the vas deferens with tetrodotoxin (1 μM) significantly reduced the basal release of 6-ND from control, eNOS-/-, and iNOS-/- mice but had no effect on the basal release of 6-ND from nNOS-/- mice. EFS-induced frequency-dependent contractions of the vas deferens, which were significantly reduced when the tissues obtained from control, eNOS-/- and iNOS-/- mice, were pre-incubated with l-NAME, but unaltered when the vas deferens was obtained from nNOS-/- mice. In addition, the EFS-induced contractions were significantly smaller when the vas deferens were obtained from nNOS-/- mice. The results clearly demonstrate that nNOS is the main NO isoform responsible for 6-ND release in mouse vas deferens and reinforces the concept of 6-ND as a major modulator of vas deferens contractility.