Relaxation effect of phosphodiesterase-5 inhibitor on the animal bladder and prostatic urethra: In vitro and in vivo study

Aim: To assess the relaxation effect of the phosphodiesterase-5 inhibitor udenafil on the bladder and prostatic urethra and its therapeutic potentials for benign prostatic hyperplasia (BPH)/lower urinary tract symptoms (LUTS). Methods: For the in vitro study, muscle strips from urinary bladder and urethra were prepared from male New Zealand rabbits. The strips were mounted in organ baths and connected to force transducers. After stabilization, maximal tissue contractions were obtained by the addition of phenylepinephrine for urethra strips and carbachol for bladder strips. When the contraction was stabilized, a dose-response curve of udenafil was constructed. For the in vivo study using adult male Sprague-Dawley rats, changes of intravesical pressure and urethral perfusion pressure after intraarterial administration of udenafil were monitored. Results: Udenafil significantly relaxed the bladder and urethra strips in a dose-dependent manner. At 10^-3 M, udenafil induced a significant relaxation of the bladder strips by 37.3% and of the urethra strips by 44.0%. In the in vivo study, the intercontraction interval was significantly prolonged (p < 0.01) and the duration of urethral relaxation with high-frequency oscillations was significantly prolonged (p < 0.01) after udenafil. Conclusions: Udenafil had relaxant effects on the bladder and prostatic urethral smooth muscle. Clinically, udenafil could be applied as an effective treatment for BPH/LUTS.