title: Role of endothelium and nitric oxide in the in vitro response of equine colonic venous rings to vasoconstrictor agents.
abstract: OBJECTIVE
  To determine in vitro contractile responses of equine colonic veins to various vasoconstrictor agents.
  
  
  METHODS
  Colonic veins collected from 8 adult horses.
  
  
  METHODS
  Veins were cut into 4-mm-wide rings, placed in organ baths at 37 C, and attached to a force-transducer interfaced with a polygraph; 2 g of tension was applied, and rings were allowed to equilibrate for 45 minutes. Bath solution was replaced, and tension was reapplied at 15-minute intervals. Cumulative concentration responses (10(-8) to 10(-4) M) were determined for each agent, using separate rings (n = 8). Three vein groups were evaluated: endothelium-intact, endothelium-denuded, and N omega-nitro-L-arginine methyl ester (L-NAME, 10(-5) M)-treated. Maximal responses by each vein to each agent were considered 100%; responses to lower concentrations were calculated as percentage of maximum.
  
  
  RESULTS
  Considering all vein groups, comparison of the doses that caused 50% of the maximal contraction revealed relative sensitivity of colonic veins to be: angiotensin II (ANG) > thromboxane B2 analogue (TXB) > 5-hydoxytryptamine (5HT) > norepinephrine (NE) > histamine (HST) > prostaglandin F2 alpha (PGF) > vasopressin (VP). Compared with ANG, PGF, TXB, and VP, treatment with HST, 5HT, and NE evoked significantly greater responses. Endothelium-denuded and L-NAME-treated colonic veins had significantly greater maximal contractile responses than did endothelium-intact veins.
  
  
  CONCLUSIONS
  Response of colonic veins to vasoconstrictor agents was differential; sensitivity was not altered by endothelium removal or L-NAME treatment; maximal responses of endothelium-intact veins were greater than those of endothelium-denuded and L-NAME-treated veins; and responses of endothelium-denuded and L-NAME-treated veins were not different.
  
  
  CONCLUSIONS
  Alterations in colonic veins that mimic conditions associated with large-colon volvulus may contribute to blood flow alterations, edema formation, and vascular responses to hypovolemic and endotoxic shock.
authors.affiliation: Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge 70803-8410, USA.
authors.forename: R M
authors.initials: RM
authors.lastname: Moore
authors.forename: C S
authors.initials: CS
authors.lastname: Venugopalan
authors.forename: S A
authors.initials: SA
authors.lastname: Sedrish
authors.forename: E P
authors.initials: EP
authors.lastname: Holmes
mesh_terms: D000704:Analysis of Variance; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D003106:Colon / Q000098:blood supply* / Q000187:drug effects; D015237:Dinoprost / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects / Q000502:physiology*; D006632:Histamine / Q000494:pharmacology; D006736:Horses / Q000502:physiology*; D066298:In Vitro Techniques; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology; D012680:Sensitivity and Specificity; D013929:Thromboxane B2 / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology; D014662:Vasoconstrictor Agents / Q000494:pharmacology*; D014667:Vasopressins / Q000494:pharmacology; D014680:Veins / Q000187:drug effects / Q000502:physiology
chemical_list: D014662:Vasoconstrictor Agents; D014667:Vasopressins; D000804:Angiotensin II; D009569:Nitric Oxide; D013929:Thromboxane B2; D006632:Histamine; D015237:Dinoprost; D019331:NG-Nitroarginine Methyl Ester; D009638:Norepinephrine