Effects of chronic l-DOPA administration on neurogenic and endothelium-dependent relaxation responses in rabbit corpus cavernosum

Background dopamine is a crucial central neurotransmitter that plays a fundamental role in the autonomic and somatic components of penile reflexes in animals and humans. similar to the erectile responses of dopamine,systemic administration of l-dopa induces yawning and penile erection in some species. the possible effects of l-dopa on nitric oxide (no)-dependent and -independent non-adrenergic non-cholinergic (nanc) relaxation responses mediated by electrical field stimulation (efs) and endothelium-dependent relaxation were investigated in this study. methods thirty-two adult albino male rabbits,in two- and four-week-treatment groups,were divided into three subgroups: control group (saline-injected) (n = 4),3 mg/kg/day (low dose) l-dopa-injected groups (n = 6) and 12 mg/kg/day (high dose) l-dopa-injected groups (n = 6). after the intraperitoneal injection treatments,the corpus cavernosum tissues were placed in organ bath chambers. the efs-mediated responses,and the concentration-response curve to carbachol,sodium nitroprusside (snp),sildenafil were assessed. results the two-week treatment with high-dose l-dopa decreased the no-dependent nanc relaxation responses,while there was no change in the low-dose two- and four-week treatment groups. the no-independent nanc relaxation responses in the two-week groups decreased,and the responses in the four-week groups were unchanged when compared to the controls. the relaxation responses to carbachol showed no differences among all groups except for the high-dose four-week l-dopa group. the relaxation responses of snp and sildenafil were increased in all of the treatment groups when compared to the controls. conclusions the observed increases in snp- and sildenafil-induced responses,along with the decreased efs-mediated responses,suggest increased sensitivity in the no-signalling pathway following l-dopa administration. © 2016 institute of pharmacology,polish academy of sciences.