Objectives: The neuronal isoform of nitric oxide synthase (nNOS) has been localized in neurons innervating the penis and is believed to be an important mediator of erection. Using the selective inhibitor 7-nitroindazole (7-NI), we evaluated the possible role of nNOS in penile erection using a rat animal model.
Methods: Eighteen Sprague-Dawley rats were divided into three study groups. A sham group (n = 6) received the vehicle arachis oil, a low-dose group received 5 mg/kg (n = 6), and a high-dose group received 50 mg/kg (n = 6) of 7-NI prior to measurement of blood pressure and cavernous nerve stimulation-induced rise in intracavernous pressure.
Results: A dose-dependent inhibition of erection by 7-NI was seen. Control animals had an intracavernous pressure rise of 55.5 +/- 4.0 cm H2O, whereas the low-dose group had 26.5 +/- 2.8 cm H2O and the high-dose group had 6.2 +/- 2.1 cm H2O. A partial recovery of erection was seen in the low- and high-dose groups after 3 hours. Blood pressure was unaffected by 7-NI administration.
Conclusions: 7-NI induced a reversible, dose-dependent inhibition of erection without affecting blood pressure. This in vivo study provides further evidence of the role played by nNOS in erection.