Purpose: New treatments are currently under investigation for intrinsic sphincter insufficiency. However, animal models in which to study the resting urethral tone generated by the striated urethral sphincter are still lacking. We describe the striated urethral sphincter in the pig. We investigated its participation in resting urethral tone with the aim of developing new tools for evaluating therapies for sphincter insufficiency.
Materials and methods: A total of 15 female pigs were used in this study. Anatomy of the striated urethral sphincter was described via transpubic and endoscopic approaches. Participation of the striated urethral sphincter in resting urethral tone was assessed by analysis of urethral pressure profilometry (maximum urethral closure pressure, functional urethral length and area under the curve) before and after curare injection or by destruction of the striated urethral sphincter by endoscopic electrocautery. Serial urethral cross sections were immunostained for slow/fast myosin and digitalized for 3-dimensional reconstructions to determine striated urethral sphincter volume.
Results: The striated urethral sphincter was Omega-shaped and it encircled the distal third of the urethra. A mean peak intraurethral pressure +/- SEM of 58.9 +/- 13.4 cm H(2)O was noted in front of the striated urethral sphincter. Curare injection and endoscopic injury decreased maximum urethral closure pressure by 48.4% and 51.1%, functional urethral length by 10.3% and 15.3%, and area under the curve by 47% and 64%, respectively. The striated urethral sphincter consisted of 52% slow and 48% fast myofibers. Its mean volume was 0.87 cm.
Conclusions: The striated urethral sphincter of the female pig shows the morphological and functional features of a tonic muscle. Methods of measuring resting urethral tone generated by the striated urethral sphincter represent original tools for evaluating therapies for intrinsic sphincter insufficiency.