Prominent Expression of Phosphodiesterase 5 in Striated Muscle of the Rat Urethra and Levator Ani

Purpose: We investigated phosphodiesterase 5 distribution and activity in the urethra. Materials and Methods: Rat tissues were examined for phosphodiesterase 5 and alpha-smooth muscle actin expression. Urethral phosphodiesterase 5 activity was examined by tissue bath in the presence of sildenafil (Pfizer, New York, New York). Results: Anti-alpha-smooth muscle actin antibody (Abeam (R)) stained all known smooth muscles in all tested tissues and revealed a few smooth muscle fibers in the levator ani muscle. Anti-phosphodiesterase 5 antibody (Abeam) stained smooth muscle in the penis and bladder but not striated leg muscle. However, it stained predominantly striated muscle in the urethra and the levator ani muscle. In the urethra the amount of phosphodiesterase 5 in striated muscle was 6 times that in smooth muscle. In urethral striated muscle phosphodiesterase 5 expression was localized to Z-band striations. Smooth and striated muscle intermingling was clearly visible on the inner and outer rims of the circularly arranged striated muscle layer. Relaxation of precontracted urethral tissues by sodium nitroprusside (Sigma-Aldrich (R)) was enhanced by sildenafil, indicating phosphodiesterase 5 activity, which was primarily located in the striated muscle according to phosphodiesterase 5 staining. Conclusions: Despite its presumed smooth muscle specificity phosphodiesterase 5 was predominantly expressed in the striated muscle of the urethra and in the levator ani muscle. Results are consistent with earlier studies in which these striated muscles were developmentally related to smooth muscle. They also suggest that these striated muscles are possibly regulated by phosphodiesterase 5.