title: Microvascular responses to adenosine help explain functional and pathologic differences between intestinal segments.
abstract: BACKGROUND
  Many physiologic (post-prandial hyperemia), pathologic (inflammatory bowel disease), and clinical (enteral feeding) phenomena involve changes in microvascular blood flow to the intestine. Adenosine (Ado) derived from energy metabolism causes vasodilation and appears to be involved in some of these events. The Ado-mediated control mechanisms appear to vary with the diameter of the microvessels and the function of the tissue. This suggests the possibility that Ado-based microvascular control varies between anatomic intestinal segments and microvascular levels in those intestinal segments.
  
  
  METHODS
  In vivo digital intravital microscopy was used to measure the responses of larger distributing (A1) and smaller premucosal (A3) vessels to Ado in intact neurovascular loops of jejunum and terminal ileum of the rat. Dose-response curves to Ado were determined.
  
  
  RESULTS
  Microvascular dilation and augmented blood flow to Ado were significantly greater in the jejunum than in the terminal ileum. Ado-induced dilation was greater in the smaller A3 than in the larger A1 microvessels.
  
  
  CONCLUSIONS
  These data indicate (1) different vasodilator mechanisms for the jejunum and the terminal ileum, (2) a greater role for Ado-related microvascular control in the jejunum compared with the ileum, and (3) a greater Ado-related control in the premucosal (A3) vessels. These findings suggest that Ado-mediated microvascular effects could explain why some clinical phenomena vary in intensity in selective intestinal segments, and are likely to involve different microvascular control mechanisms in the different segments. Knowledge of these Ado mechanisms could be beneficial in certain clinical scenarios to control blood flow during pathologic conditions.
authors.affiliation: Department of Physiology and Biophysics, University of Louisville, Louisville, KY, USA.
authors.forename: Na
authors.initials: N
authors.lastname: Li
authors.forename: Patrick D
authors.initials: PD
authors.lastname: Harris
authors.forename: El Rasheid
authors.initials: el R
authors.lastname: Zakaria
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Matheson
authors.forename: R Neal
authors.initials: RN
authors.lastname: Garrison
mesh_terms: D000241:Adenosine / Q000494:pharmacology*; D000818:Animals; D001783:Blood Flow Velocity / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D007082:Ileum / Q000098:blood supply* / Q000187:drug effects; D007413:Intestinal Mucosa / Q000187:drug effects / Q000473:pathology; D007583:Jejunum / Q000098:blood supply* / Q000187:drug effects; D008297:Male; D008833:Microcirculation / Q000187:drug effects*; D023421:Models, Animal; D011336:Probability; D051381:Rats; D017207:Rats, Sprague-Dawley; D012680:Sensitivity and Specificity
chemical_list: D000241:Adenosine