title: Myoendometrial versus placental uterine arteries: structural, mechanical, and functional differences in late-pregnant rabbits.
abstract: OBJECTIVE
  This study compared late-pregnant radial uterine arteries that supplied the placenta versus the myoendometrium to evaluate differences in active and passive mechanical properties.
  
  
  METHODS
  Pressurized segments of placental versus myoendometrial radial uterine arteries from late-pregnant (day 28 to 30) New Zealand White rabbits (n = 12) were compared in vitro for differences in luminal diameter, wall thickness, distensibility, and intrinsic tone as a function of transmural pressure.
  
  
  RESULTS
  Both types of arteries responded to increased transmural pressure with active vasoconstriction; however, the amount of tone present in myoendometrial arteries was significantly greater than in placental arteries (percent tone at 75 mm Hg = 39% +/- 3% for myoendometrial versus 31% +/- 2% for placental arteries, p < 0.01). Measurements of unpressurized, fully relaxed arteries revealed that placental arteries were 38% larger in diameter and had thicker walls than myoendometrial arteries did. However, myoendometrial arteries were significantly more distensible at transmural pressures >5 mm Hg.
  
  
  CONCLUSIONS
  The increased size and diminished tone of placental compared with adjacent myoendometrial arteries would favor increased blood flow to the placenta; differences in size and passive mechanical properties suggest that a localized factor(s) originating from the fetus or placenta contributes to the gestational enlargement of those arteries that perfuse the placenta.
authors.affiliation: Department of Surgery, Oregon Health Sciences University, Portland 97201, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Cipolla
authors.forename: N D
authors.initials: ND
authors.lastname: Binder
authors.forename: G
authors.initials: G
authors.lastname: Osol
mesh_terms: D000818:Animals; D001158:Arteries / Q000033:anatomy & histology / Q000502:physiology; D005260:Female; D008954:Models, Biological; D009215:Myometrium / Q000098:blood supply* / Q000502:physiology; D010920:Placenta / Q000098:blood supply* / Q000502:physiology; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D011817:Rabbits; D012039:Regional Blood Flow; D014599:Uterus / Q000098:blood supply* / Q000502:physiology*; D014655:Vascular Resistance / Q000502:physiology; D014661:Vasoconstriction / Q000502:physiology