Investigation of effects of l-DOPA administration on the non-adrenergic non-cholinergic relaxant responses in rabbit corpus cavernosum

In this study, the possible effects of intraperitoneal administration of low dose (3mg/kg/day) and high dose (12mg/kg/day) L-DOPA in 2weeks and 4weeks on NO-dependent and ?independent NANC relaxation responses mediated by electrical field stimulation (EFS), postsynaptic NO/guanylate cyclase/cGMP pathway and endothelium-dependent relaxation was investigated. Isolated rabbit corpus cavernosum tissues were obtained from thirty-two adult albino male rabbits weighing 2-3kg, were placed in Krebs solution containing organ bath chambers to record isometric contractions via a force displacement transducers. In the presence of guanethidine and atropine, EFS induced NANC responses were inhibited by ?-conotoxin GVIA. This finding suggests that EFS mediated NANC responses depend on synaptic transmission. High-dose administration in 2-week-group caused that NO-dependent NANC relaxation responses were decreased, the responses in low-dose administration in 2-week-group and in 4-week-groups were unchanged. NO-independent NANC relaxation responses in 2-week-groups decreased, the responses in 4-week-groups were unchanged. These results suggest that may have formed on dopaminergic pathways at central nerve system or postganglionic nerve terminations via desensitization or downregulation. These changes in 4-week-groups may have disappeared in timely manner. Relaxation responses to carbachol had no difference among all groups except high-dose administration of 4-week-group. It was interpreted that endothelial NO-mediated signaling pathway is not affected by L-DOPA administration. However, the response in high-dose administration of 4-week-group increased. Relaxation responses to SNP and sildenafil increased in all treated groups compared to controls. These responses were interpreted that sensitivity of NO/guanylate cyclase/cGMP pathway in tissues increased and/or inhibition of PDE activity within the application of L-DOPA.