Localization and role of nitric oxide synthase and endogenous nitric oxide synthase inhibitors in the rabbit lower urinary tract

Purpose: We investigated the possible role of endogenous methylarginine derivatives, such as N-G-monomethyl-L-arginine (L-NMMA), asymmetrical N-G, N-G-dimethyl-L-arginine (ADMA) and symmetrical N-G, N-'G-dimethyl-L-arginine (SDMA), for regulating nitric oxide synthase in the rabbit lower urinary tract. Materials and Methods: Strips of detrusor, trigone and proximal urethra were processed for the determination of endogenous methylarginines and L-arginine by automated high performance liquid chromatography. We also compared nitric oxide synthase activity and nitric oxide mediated functional responses to electrical field stimulation in the 3 regions. Nitric oxide synthase activity was measured by determining the conversion of [H-3] L-arginine to [H-3]L-citrulline. Results: L-NMMA, ADMA and SDMA were detectable by high performance liquid chromatography in the detrusor, trigone and proximal urethra. Electrical field stimulation induced nitric oxide mediated prominent relaxation in the trigone and proximal urethra, while no relaxation response was observed in the detrusor. Exogenously applied 1 to 100 muM. L-NMMA and 1 to 100 muM. ADMA but not 100 muM. SDMA dependently inhibited Ca2+ dependent nitric oxide synthase activity in all regions, and electrical field stimulation induced relaxation in the trigone and proximal urethra. Inhibition with L-NMM.A and ADMA was blocked in the presence of 3 mM. L-arginine but not by 3 mM. D-arginine. Conclusions: Three methylarginines and nitric oxide synthase are localized throughout the rabbit lower urinary tract. Endogenous L-NMMA and ADMA may be involved in regulating nitric oxide biosynthesis of the micturition reflex in the normal or disease state.