6-Nitrodopamine Release From Mouse Seminal Vesicles Is Dependent on Endothelial Nitric Oxide Synthase (eNOS) Activation.

Human seminal vesicles present basal release of epithelium-derived 6-nitrodopamine (6-ND) and this catecholamine potentiates noradrenaline-induced contractions. Since nitric oxide synthase (NOS) activation is a determining factor involved in 6-ND biosynthesis, this study aimed to investigate which NOS isoform is responsible for the 6-ND release in mouse isolated seminal vesicles (MISV). Male control, eNOS(-/-), NOS(-/-), iNOS(-/-), and e/n/iNOS(-/-) mice were used. 6-ND release was evaluated by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). MISV contractility was assessed following electric-field stimulation (EFS) or construction of concentration-response curves to catecholamines. MISV from control, eNOS(-/-), nNOS(-/-), iNOS(-/-), and e/n/iNOS(-/-) mice exhibited basal release of 6-ND, but 6-ND release from eNOS(-/-) and e/n/iNOS(-/-) was significantly reduced compared to control and nNOS(-/-) mice. Epithelium removal in MISV from control mice significantly reduced 6-ND levels. EFS (2-32 Hz) induced frequency-dependent MISV contractions in all groups, but the contractions from eNOS(-/-) and e/n/iNOS(-/-) mice were significantly decreased compared to control groups. In vitro l-NAME treatment or epithelium removal significantly reduced EFS-induced contractions. Pre-incubation of MISV with 6-ND (1-100 nM) significantly potentiated both EFS- and noradrenaline-induced contractions, whereas pre-incubation with noradrenaline, adrenaline, and dopamine did not affect the EFS-induced responses. Immunohistochemistry and fluorescence in situ hybridization (FISH) assays revealed positivity for tyrosine hydroxylase and eNOS in the epithelium and endothelium of the seminal vesicles. In conclusion, MISV releases epithelium-derived 6-ND, and its biosynthesis involves eNOS activation. The finding that 6-ND markedly amplified the noradrenaline-induced contractions indicates that epithelium-derived 6-ND acts as a major modulator of MISV contractility.