title: Lack of effect of nitroglycerin on the diameter response of larger retinal arterioles in normal persons during hypoxia.
abstract: OBJECTIVE
  Retinal hypoxia with consequent changes in blood flow play a role in a number of vision-threatening diseases, such as diabetic retinopathy. Previous studies have shown that the inhibition of nitric oxide synthase (NOS) and cyclooxygenase (COX) products are involved in the diameter regulation of the retinal vessels during hypoxia. Therefore, the aim of the present study was to examine the effects of an NO donor combined with COX inhibition on the diameter regulation of retinal vessels during hypoxia in normal persons.
  
  
  METHODS
  Twenty normal persons aged 21-47 years were examined. The Dynamic Vessel Analyzer (DVA) was used to measure retinal vessel diameters at rest, during isometric exercise, and during flicker stimulation. The measurements were performed during normoxia and hypoxia before and after sublingual administration of the NO donor nitroglycerin, and were repeated on a second study day after topical administration of the COX-inhibitor diclofenac.
  
  
  RESULTS
  The resting diameter of arterioles and venules increased significantly during hypoxia (p < 0.0001). Hypoxia also significantly reduced the arteriolar constriction during isometric exercise, and the dilatation of the arterioles and venules during flicker stimulation (p < 0.0001). Diclofenac further reduced the arteriolar constriction induced by isometric exercise during hypoxia (p = 0.005). However, the NO-donor nitroglycerin had no effect on vascular diameters.
  
  
  CONCLUSIONS
  Diameter regulation of retinal vessels during hypoxia in normal persons can be influenced by the inhibition of COX products, but not by increasing the NO concentration. The findings suggest that the vasoactive effects of NO on retinal arterioles during hypoxia are saturated in normal persons.
authors.affiliation: Department of Ophthalmology, Aarhus University Hospital, DK-8000, Aarhus C, Denmark. musa.yasin.kaya@post.au.dk.
authors.forename: Musa Yasin
authors.initials: MY
authors.lastname: Kaya
authors.affiliation: Department of Ophthalmology, Aarhus University Hospital, DK-8000, Aarhus C, Denmark.
authors.forename: Line
authors.initials: L
authors.lastname: Petersen
authors.affiliation: Department of Ophthalmology, Aarhus University Hospital, DK-8000, Aarhus C, Denmark.
authors.forename: Toke
authors.initials: T
authors.lastname: Bek
mesh_terms: D000287:Administration, Topical; D000328:Adult; D001160:Arterioles / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004008:Diclofenac / Q000494:pharmacology; D015444:Exercise; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D005996:Nitroglycerin / Q000494:pharmacology*; D010775:Photic Stimulation; D012161:Retinal Artery / Q000502:physiology*; D014664:Vasodilation / Q000187:drug effects; D014665:Vasodilator Agents / Q000494:pharmacology*; D055815:Young Adult
chemical_list: D016861:Cyclooxygenase Inhibitors; D014665:Vasodilator Agents; D004008:Diclofenac; D005996:Nitroglycerin
keywords: Dynamic vessel analyzer; Hypoxia; Nitric oxide; Prostaglandins; Retinal autoregulation