title: Evidence for endothelium-derived relaxing factor/nitric oxide in equine digital arteries.
abstract: OBJECTIVE
  To test the hypothesis that endothelium-derived nitric oxide modulates vasomotor reactivity in equine digital arteries.
  
  
  METHODS
  Digital arteries were isolated from adult horses, and their vasodilator properties were examined in an in vitro controlled environment.
  
  
  METHODS
  Five adult horses (1 gelding, 4 mares) without evidence of hoof or vascular disease were studied.
  
  
  METHODS
  Arterial rings with or without endothelium were exposed to endothelium-dependent vasodilator drugs in the presence or absence of a pharmacologic inhibitor of the enzyme nitric oxide synthase.
  
  
  RESULTS
  Vasodilator effects of 3 endothelium-dependent vasorelaxant agents were significantly greater in endothelium-intact vessels than in endothelium-denuded vessels. Moreover, a nitric oxide synthase inhibitor reduced vasodilator responses to endothelium-dependent vasodilators in endothelium-intact arteries, but had no discernable effects in endothelium-denuded arteries.
  
  
  CONCLUSIONS
  These findings indicate the presence of endothelium-derived relaxing factor/nitric oxide in blood vessels of horses, and identify vascular endothelium as an endogenous modulator of vasomotor tone in the digital arteries of this species.
authors.affiliation: Department of Veterinary Biomedical Sciences, College of Veterinary Medicine, University of Missouri, Columbia 65211, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Cogswell
authors.forename: P J
authors.initials: PJ
authors.lastname: Johnson
authors.forename: H R
authors.initials: HR
authors.lastname: Adams
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D001158:Arteries / Q000737:chemistry / Q000502:physiology; D001920:Bradykinin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000737:chemistry* / Q000502:physiology; D005260:Female; D006724:Hoof and Claw / Q000098:blood supply*; D006736:Horses / Q000502:physiology*; D008297:Male; D019331:NG-Nitroarginine Methyl Ester; D009569:Nitric Oxide / Q000032:analysis* / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D009638:Norepinephrine / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D014665:Vasodilator Agents; D009569:Nitric Oxide; D000244:Adenosine Diphosphate; D001120:Arginine; D019001:Nitric Oxide Synthase; D000109:Acetylcholine; D001920:Bradykinin; D019331:NG-Nitroarginine Methyl Ester; D009638:Norepinephrine