title: Effect of noradrenaline on retinal blood flow in healthy subjects.
abstract: OBJECTIVE
  To gain insight into the role of circulating catecholamines on retinal blood flow in vivo.
  
  
  METHODS
  Nonrandomized, open, crossover design.
  
  
  METHODS
  In 10 healthy male subjects, tyramine and noradrenaline were administered in stepwise increasing doses. These doses were selected to induce comparable changes in systemic blood pressure.
  
  
  METHODS
  During each infusion step, retinal vessel diameter and retinal venous blood speed were measured with the Zeiss retinal vessel analyzer (Zeiss, Jena, Germany) and laser Doppler velocimetry, respectively.
  
  
  METHODS
  Retinal blood flow through a major temporal vein was calculated.
  
  
  RESULTS
  As expected, tyramine and noradrenaline induced a systemic hypertensive response. Tyramine caused a moderate increase in noradrenaline plasma levels, whereas exogenous noradrenaline increased noradrenaline plasma levels more than 10-fold. Nevertheless, neither tyramine nor noradrenaline induced any effect on retinal hemodynamic parameters.
  
  
  CONCLUSIONS
  These data indicate that even high levels of circulating noradrenaline have little impact on retinal vascular tone and retinal blood flow. Hence, the adrenergic system appears not to play a major role in retinal blood flow regulation.
authors.affiliation: Department of Clinical Pharmacology, University of Vienna, Vienna, Austria.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Jandrasits
authors.forename: Alexandra
authors.initials: A
authors.lastname: Luksch
authors.forename: Gabor
authors.initials: G
authors.lastname: Söregi
authors.forename: Guido T
authors.initials: GT
authors.lastname: Dorner
authors.forename: Kaija
authors.initials: K
authors.lastname: Polak
authors.forename: Leopold
authors.initials: L
authors.lastname: Schmetterer
mesh_terms: D018759:Adrenergic Uptake Inhibitors / Q000008:administration & dosage; D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage* / Q000097:blood; D000328:Adult; D001783:Blood Flow Velocity; D001794:Blood Pressure / Q000187:drug effects; D018592:Cross-Over Studies; D006801:Humans; D007262:Infusions, Intravenous; D007429:Intraocular Pressure / Q000187:drug effects; D017078:Laser-Doppler Flowmetry; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000502:physiology; D009638:Norepinephrine / Q000008:administration & dosage* / Q000097:blood; D011941:Receptors, Adrenergic / Q000502:physiology; D012039:Regional Blood Flow; D012169:Retinal Vein / Q000502:physiology*; D014439:Tyramine / Q000008:administration & dosage; D014662:Vasoconstrictor Agents / Q000008:administration & dosage* / Q000097:blood
chemical_list: D018759:Adrenergic Uptake Inhibitors; D000316:Adrenergic alpha-Agonists; D011941:Receptors, Adrenergic; D014662:Vasoconstrictor Agents; D009638:Norepinephrine; D014439:Tyramine