title: Urethral circular smooth muscle in young and old women.
abstract: OBJECTIVE
  The purpose of this study was to determine whether thickness, fiber count, and density of urethral circular smooth muscle (CSM) differ in young and old women.
  
  
  METHODS
  Mid urethral hemiaxial sections from female cadavers aged 20-39 years (n = 12) and 70-89 years (n = 16) were stained for smooth muscle alpha actin. The CSM was studied at 0 degrees (pubic bone side) and 180 degrees (vaginal side) and in between at 45, 90, and 135 degrees. CSM layer width was measured; fibers were counted; density was calculated (fiber count/layer width).
  
  
  RESULTS
  Density of urethral CSM was 25%-50% higher in specimens aged 20-39 years, compared with those aged 70-89 years. Differences were observed at 0, 135, and 180 degrees. In the younger group, higher fiber counts were observed at 135 and 180 degrees, and the CSM layer was thinner but not significantly so.
  
  
  CONCLUSIONS
  The density of CSM was lower among older women, which may account for age-related decline in urethral closure pressure.
authors.affiliation: Department of Obstetrics and Gynecology, Women's Hospital, University of Michigan, Ann Arbor, MI 48109, USA.
authors.forename: Amy
authors.initials: A
authors.lastname: Clobes
authors.forename: John O L
authors.initials: JO
authors.lastname: DeLancey
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Morgan
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology; D005260:Female; D006801:Humans; D018485:Muscle Fibers, Skeletal; D009130:Muscle, Smooth / Q000033:anatomy & histology* / Q000503:physiopathology; D010784:Photomicrography; D011312:Pressure; D014521:Urethra / Q000033:anatomy & histology / Q000502:physiology / Q000503:physiopathology; D014549:Urinary Incontinence / Q000503:physiopathology