Neuronal nitric oxide synthase is the main isoform responsible for 6-nitrodopamine release from mouse isolated vas deferens

Rat and human vas deferens (VD) present basal release 6-nitrodopamine (6-ND), which is significantly reduced when the VD is pre-incubated with the nitric oxide (NO) synthase inhibitor L-NAME, or in the case of the rat, when the VD was obtained from rats chronically treated with L-NAME. 6-Nitrodopamine is considered a major mediator of both rat and human VD contractility. Since the origin of 6-ND is not clear in the VD, here it was investigated the basal release of 6-ND from control, eNOS−/−, nNOS−/− and iNOS−/− mice VD to ascertain which NOS isoform(s) play(s) an essential role in 6-ND biosynthesis in the mouse VD. Euthanasia was performed by isoflurane overdose and both VD were removed and immediately placed in Krebs-Henseleit solution (KHS). The release of 6-ND was measured by LC-MS/MS. To evaluate contractility, the mice VD strips were submitted to EFS (60 V for 20 sec, at 2-16 Hz in square-wave pulses, 0.3 ms pulse width, and 0.1 ms delay), using a Grass S88 stimulator (Astro-Medical, Industrial Park, RI, USA). The tissues were allowed to equilibrate under a resting tension of 10 mN, and the isometric tension was registered using a PowerLab system. Isolated VD from control, nNOS−/−), eNOS−/−, and iNOS−/− mice present basal release of both 6-ND and dopamine, as detected by LC-MS/MS. The basal release of 6-ND from isolated VD of nNOS−/− mice was significantly reduced when compared to that obtained from control mice VD, whereas that of dopamine was significantly increased. The basal release of both 6-ND and dopamine from eNOS−/− mice VD was not different compared to that obtained from control mice VD. The basal release of 6-ND from iNOS−/− mice was significantly increased compared to that observed in control mice VD. Electric-field stimulation (EFS) caused frequency-dependent (2Hz - 32Hz) contractions of the mouse isolated VD. The contractions induced by EFS were significantly decreased in nNOS−/− mouse isolated VD, but unaltered in isolated VD obtained from either eNOS−/− or iNOS−/− mice. The results clearly demonstrate that neuronal nitric oxide synthase is the main isoform responsible for 6-ND synthesis/release from mouse isolated VD. The results obtained with the contractions induced by EFS in the mouse VD further support the concept that 6-ND is a major modulator of VD contractility, since the contractions of the VD was only reduced in tissue obtained from nNOS−/− mice. The reduction in the EFS-induced contractions observed in the vas deferens obtained from nNOS−/− mice could be attributed to the reduction observed in the basal release of 6-ND. This research is supported by the São Paulo Research Foundation (FAPESP). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.