Effect of noradrenaline on retinal blood flow in healthy subjects.
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.
Jandrasits
Kerstin
K
Department of Clinical Pharmacology, University of Vienna, Vienna, Austria.
Luksch
Alexandra
A
Söregi
Gabor
G
Dorner
Guido T
GT
Polak
Kaija
K
Schmetterer
Leopold
L
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
D018759:Adrenergic Uptake Inhibitors; D000316:Adrenergic alpha-Agonists; D011941:Receptors, Adrenergic; D014662:Vasoconstrictor Agents; D009638:Norepinephrine; D014439:Tyramine