[Experimental studies on effect on nitric oxide on the internal urethral relaxation in anesthetized rats]

Effects of L-arginine and the inhibitors of nitric oxide/cyclic GMP pathway on the internal urethral relaxation were examined in anesthetized rats. The bladder pressure and internal urethral pressure were continuously recorded during the rhythmic bladder contractions before and after intraarterial administration of the following drugs. Used drugs were L-arginine from which nitric oxide is synthesized, NG-monomethyl-L-arginine (L-NMMA), NG-nitro-L-arginine methyl ester (L-NAME) which inhibit the synthesis of nitric oxide from L-arginine, and methylene blue which inhibits the activation of soluble guanylyl cyclase. In anesthetized rats, rhythmic bladder contractions with concomitant urethral relaxations were occurred. Administration of L-arginine (30 mg/kg, i.a.) produced a decrease in the internal urethral pressure. Administration of L-NMMA (3-30 mg/kg, i.a.), L-NAME (3-10 mg/kg, i.a.), and methylene blue (3-30 mg/kg, i.a.) produced an inhibition of the relaxations of the internal urethral sphincter during rhythmic bladder contractions. Present study suggests that nitric oxide/cyclic GMP pathway takes an important role for the relaxation of the internal urethral sphincter during rhythmic bladder contractions.