title: Contractile properties of the proximal urethra and bladder in female pig: morphology and function.
abstract: OBJECTIVE
  To compare the contractile properties of proximal urethral and bladder muscle of the female pig.
  
  
  METHODS
  In two proximal segments (I and II) of the urethra, small muscle bundles were excised to measure the force-length (maximum force) and the force-velocity (unloaded shortening velocity) relation using the stop-test. The rate of force development was calculated using phase plots. Contractile properties of urethral and bladder segments were statistically compared using the Mann-Whitney U-test. Immunohistochemical staining of whole circumference urethral cross sections was used to identify the location of smooth and striated muscle fibres.
  
  
  RESULTS
  On isometric force development, the urethral muscle bundles revealed a fast ( approximately 0.5 sec) and a slow ( approximately 2.1 sec) time constant, whereas in bladder only a slow ( approximately 2.3 sec) component was measured. On average, isometric force was highest in bladder. The length range over which force was produced was smallest in urethral segment II, followed by urethral segment I and finally bladder. The unloaded shortening velocity was 0.15, 0.25 and 0.35 1/sec, respectively. Histological preparations showed that smooth as well as striated muscle was present in proximal urethra. In urethral muscle bundles, spontaneous contractions were measured with a frequency of 0.4 Hz.
  
  
  CONCLUSIONS
  Differences in contractility found between urethra and bladder may be ascribed to the presence of striated muscle in the proximal urethra. The regulation of tone and spontaneous contractions may be part of the continence mechanism in the female pig urinary tract.
authors.affiliation: Department of Urology, Sector Furore, Erasmus MC, Rotterdam, The Netherlands. j.pel@erasmusmc.nl
authors.forename: J J M
authors.initials: JJ
authors.lastname: Pel
authors.forename: E
authors.initials: E
authors.lastname: van Asselt
authors.forename: R
authors.initials: R
authors.lastname: van Mastrigt
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D004396:Coloring Agents; D003627:Data Interpretation, Statistical; D003893:Desmin / Q000378:metabolism; D004558:Electric Stimulation; D005260:Female; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D009130:Muscle, Smooth / Q000502:physiology; D013552:Swine; D014521:Urethra / Q000033:anatomy & histology* / Q000502:physiology*; D001743:Urinary Bladder / Q000033:anatomy & histology* / Q000502:physiology*
chemical_list: D000199:Actins; D004396:Coloring Agents; D003893:Desmin