title: Two isoforms of cyclooxygenase contribute to augmented endothelium-dependent contractions in femoral arteries of 1-year-old rats.
abstract: OBJECTIVE
  The present experiments were designed to study the changes in endothelium-dependent contractions with aging.
  
  
  METHODS
  The rat femoral arteries of 20-week and 1-year-old rats with and without endothelium were suspended in organ chambers to record isometric tension. The production of oxygen-derived free radicals in the endothelium was measured with 2,7o-dichlorodihydrofluorescein diacetate (DCF) using confocal microscopy. Protein presences were determined by Western blotting.
  
  
  RESULTS
  In the arteries from the 1-year-old rats, endothelium-dependent relaxations to A23187 were reduced, but the endothelium-dependent contractions to A23187 (in the presence of Nomega-nitro-L-arginine methyl ester hydrochloride [L-NAME; an inhibitor of nitric oxide synthase]) were augmented, demonstrating endothelial dysfunction with aging. Indomethacin normalized the responses, suggesting that a cyclooxygenase (COX)-dependent contraction is prominent in aging. The endothelium-dependent contractions were also prevented by terutroban (a blocker of thromboxane-prostanoid receptors), confirming the activation of thromboxane-prostanoid receptors on vascular smooth muscle. Valeryl salicylate and NS-398 (preferential inhibitors of COX-1 and COX-2, respectively) partially reduced the response, indicating that both COX-1 and COX-2 are involved. Western blotting confirmed the upregulation of both isoforms in the arteries of the 1-year-old rats. In the presence of L-NAME, A23187 increased the DCF fluorescence in the endothelium, demonstrating that the production of oxygen-derived free radicals contributes to endothelium-dependent contractions. The activity of catalase was reduced in the arteries with endothelium of 1-year-old rats, indicating that hydrogen peroxide is the likely mediator of increased oxidative stress in the aging endothelium.
  
  
  CONCLUSIONS
  Endothelium-dependent contractions are augmented with aging. Oxidative stress potentiates the response, and both COX-1 and COX-2 are involved.
authors.affiliation: Department of Pharmacology, The University of Hong Kong, Hong Kong, China. yi.shi@access.uzh.ch
authors.forename: Yi
authors.initials: Y
authors.lastname: Shi
authors.forename: Ricky Y K
authors.initials: RY
authors.lastname: Man
authors.forename: Paul M
authors.initials: PM
authors.lastname: Vanhoutte
mesh_terms: D000818:Animals; D002374:Catalase / Q000378:metabolism; D051545:Cyclooxygenase 1 / Q000502:physiology*; D051546:Cyclooxygenase 2 / Q000502:physiology*; D004730:Endothelium, Vascular / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005263:Femoral Artery / Q000502:physiology; D005978:Glutathione / Q000378:metabolism; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D052250:Nitric Oxide Synthase Type III / Q000037:antagonists & inhibitors; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D017382:Reactive Oxygen Species; D002374:Catalase; D052250:Nitric Oxide Synthase Type III; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D005978:Glutathione; D019331:NG-Nitroarginine Methyl Ester