L-DOPA suppresses bladder smooth muscle contraction induced by carbachol in rats

L-3,4-Dihydroxyphenylalanine (L-DOPA) has been recognized as a precursor of dopamine. Recently, L-DOPA has been proposed as a neurotransmitter and is reported to sensitize vasomotor response to sympathetic tone through activation of L-DOPA receptor GPR143. In this study, to clarify roles of L-DOPA/GPR143 signaling in regulation of parasympathetic tone, we examined effects of L-DOPA on muscarinic receptor-mediated bladder contraction in wild-type (WT) and Gpr143 gene-deficient (Gpr143-/y) rats. Bladder strips were prepared from nine-week-old male rats, and effects of pretreatment with L-DOPA (10-8, 10-7 and 10-6 M) on carbachol (CCh, 10-8 to 3×10-4 M)-induced bladder strips contraction were investigated by organ bath study. In bladder strips from WT rats, L-DOPA alone showed no contraction or relaxation, while pretreated L-DOPA dose-dependently suppressed CCh-induced contraction. The L-DOPA-induced suppression was also observed in bladder strips from Gpr143-/y rats. These results suggest that L-DOPA induces suppression of the muscarinic receptor-mediated rat bladder contraction independently of GPR143 signal transduction.