ABSTRACT
Nitric oxide (NO) is known to have a strong relaxant effect in various biological organs including blood vessels and corpus cavernosum. The goal of the present study was to investigate the role of NO on penile erection in vivo. In 42 adult (250-350 gm) Sprague Dawley rats, we observed cavernosal and systemic response to cavernous nerve stimulation (1 Hz. 3-5 volt), intracavernosal injection of nitric oxide synthase (NOS) inhibitor , L-arginine hydrochloride and guanylate cyclase inhibitor (methylene blue). Intracavernous injections of L-NOARG (0.000001M to 0.00lM, n=7) and L- NAME (0.000001M to 0.001M n=7) were found to suppress the nerve induced erection in concentration dependent manner. Subsequent intracavernous injection of L- arginine hydrochloride ( 0.0lM n=7) partially stored penile erection suppressed by L-NOARG (0.00lM) or L-NAME (0.00lM). Intracavernous injection of methylene blue (0.000001M to 0.000000lM n=7) suppressed both nerve induced erection and sodium nitroprusside (0.001M)-induced erection in concentration dependent manner. These results indicate that nitric oxide is a strong neurotransmitter that mediates penile erection, and that nitric oxide/cyclic GMP pathway is responsible for penile erection.