title: In vitro responses of equine colonic arterial and venous rings to adenosine triphosphate.
abstract: OBJECTIVE
  To evaluate the in vitro effects of adenosine tryphosphate (ATP) on vasomotor tone of equine colonic vasculature.
  
  
  METHODS
  Arteries and veins from the left ventral colon of 14 mixed-breed horses euthanatized for reasons unrelated to cardiovascular or gastrointestinal tract disease.
  
  
  METHODS
  Endothelium-intact and -denuded arterial and venous rings were precontracted with 10(-7) and 1.8 x 10(-8) M endothelin-1, respectively. In 1 trial, endothelium-intact rings were also incubated with 10(-4) M N omega-nitro-L-arginine methyl ester (L-NAME) to inhibit nitric oxide (NO) production. Adenosine triphosphate (10(-8) to 10(-3) M) was added in a noncumulative manner, and relaxation percentage versus time curves were generated. Areas under the curves (ie, percentage of relaxation time) were calculated.
  
  
  RESULTS
  Relaxation response of arterial and venous rings to ATP was dose-dependent. Percentage of relaxation time in response to 10(-4) and 10(-3) MATP was significantly greater, compared with that for rings not treated with ATP Removal of endothelium attenuated but did not eliminate the relaxation response. Addition of L-NAME did not attenuate the relaxation response in arteries. At higher concentrations, the vascular response to ATP was biphasic.
  
  
  CONCLUSIONS
  ATP applied to equine colonic arterial and venous rings with and without intact endothelium induced a biphasic response characterized by transient contraction followed by slow, substantial, and sustained relaxation. This ATP-induced response is possibly mediated by a mechanism other than NO. Adenosine triphosphate may be a useful treatment to modulate colonic vasomotor tone in horses with strangulating volvulus of the ascending colon.
authors.affiliation: Department of Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge 70803-8410, USA.
authors.forename: J
authors.initials: J
authors.lastname: Tetens
authors.forename: C S
authors.initials: CS
authors.lastname: Venugopal
authors.forename: E P
authors.initials: EP
authors.lastname: Holmes
authors.forename: C E
authors.initials: CE
authors.lastname: Koch
authors.forename: G
authors.initials: G
authors.lastname: Hosgood
authors.forename: R M
authors.initials: RM
authors.lastname: Moore
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D019540:Area Under Curve; D003106:Colon / Q000098:blood supply*; D004730:Endothelium, Vascular / Q000187:drug effects / Q000502:physiology; D006651:Histocytochemistry / Q000662:veterinary; D006736:Horses / Q000502:physiology*; D066298:In Vitro Techniques; D016014:Linear Models; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000098:blood supply* / Q000187:drug effects; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000032:analysis / Q000096:biosynthesis
chemical_list: D009569:Nitric Oxide; D000255:Adenosine Triphosphate; D019331:NG-Nitroarginine Methyl Ester