[Effect of moxisylyte on the lower urinary tracts (1). Effect on the isolated rabbit urethra and bladder]

Effect of moxisylyte on the lower urinary tracts was studied in comparison with those of prazosin and bunazosin in the isolated rabbit bladder and urethra. Moxisylyte dose-dependently inhibited the urethral contraction induced by phenylephrine. The IC50 value of moxisylyte was 1.01 x 10(-6) M. Prazosin and bunazosin inhibited the urethral contraction as well as moxisylyte. The IC50 values of prazosin and bunazosin were 2.88 x 10(-7) M and 1.44 x 10(-7) M, respectively. Moreover, moxisylyte and bunazosin inhibited the urethral contraction induced by KCl. The IC50 values of moxisylyte and bunazosin were 1.17 x 10(-5) M and 1.35 x 10(-4) M, respectively. The KCl/phenylephrine ratios of moxisylyte, bunazosin and prazosin were as follows: 17, 938 and 9201, respectively. Moxisylyte has a relaxant action on the urethra that is probably ascribable to its alpha 1-adrenoceptor antagonist and Ca++ antagonist actions. In the isolated bladder, moxisylyte inhibited the bladder contraction induced by KCl, with an IC50 value of 4.46 x 10(-5) M. However, moxisylyte did not affect the contractile response to acetylcholine. These results suggest that the relaxant effect of moxisylyte on the urethra is due to alpha 1-adrenoceptor antagonist and Ca++ antagonist actions. Therefore, moxisylyte is useful for the therapeutic treatment of micturitional disorder.