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.