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Results
Flicker stimulation (8 Hz) increased retinal vessel diameters under basal conditions. The response to 8-Hz flicker light was significantly reduced by dopamine administration. In addition, dopamine slightly but significantly increased retinal vessel diameters. Dopamine hydrochloride significantly increased systolic but not diastolic or mean arterial pressure.

For the first time, evidence exists displaying the for dopaminergic effects on retinal vessels in humans. This indicates that the dopaminergic system plays a role in the regulation of retinal blood flow in vivo. In addition, their data present evidence for an attenuating effect of dopamine on the pathways coupling sensory input to vascular response. The results also reveal that dopamine significantly increases vessel diameters of retinal arteries and veins in a dose-dependent manner. Their finding is that dopamine increases retinal vessel diameters in vivo is an indicator that dopamine probably has a local effect on retinal vessels (also supported by data showing a high density of D1 receptor antibodies in rabbit retinal vessels).

Conclusions
This study finds reveals that flicker response in both retinal arteries and veins is diminished by dopamine. Although this indicates a role of dopamine in the regulation of retinal vascular tone, it does not necessarily prove a crucial role of dopamine in the neuronal pathway regulating this neurovascular response. Their data are, however, compatible with results from many studies showing dopamine release during light-to-dark transitions and during photic stimulation.

On the basis of these previous data, the researchers hypothesize that dopamine increases during flicker-stimulation in the present experiments. Consequently, exogenous administration of dopamine blunts flicker-induced vasodilatation beca
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Contact: Donna Krupa
djkrupa1@aol.com
703-527-7357
American Physiological Society
12-Feb-2003