New hope for preventing major problems of ...( ists decrease IOP; D2 agents have oppos...)

ists decrease IOP; D2 agents have opposite effects. Dopamine also has an important role in sensory processing. As a neurotransmitter, it is involved in regulating the rod pathway. However, dopamine actions are not restricted to the transmission of nerve impulses. It is also used as a neuromodulator distributed diffusely in the outer retina during light adaptation. The modulatory functions include horizontal cell and photoreceptor coupling to change the receptive field organization. A direct connection exists between sensory input and retinal blood flow. Diffuse luminance flicker stimuli increase retinal vessel diameter in humans. However, the how this pathway works is still elusive.

A New Study
A new study examines the effect of dopamine on retinal vessel diameters and its modulatory effect on flicker-induced vasodilatation, or widening of the vessel's tubes. Local retinal vascular effects were studied in healthy human subjects after intravenous administration of dopamine. The authors of the study, "Effects of Dopamine on Human Retinal Vessel Diameter and its Modulation During Flicker Stimulation," are Karl-Heinz Huemer, Gerhard Garhfer, Claudia Zawinka, Elisabeth Golestani, Brigitte Litschauer, Leopold Schmetterer, and Guido T. Dorner, all from the University of Vienna Medical School, Vienna, Austria. Their findings appear in the January 2003 edition of the American Journal of Physiology--Heart and Circulatory Physiology.

Methodology
The research entailed a randomized, subject-blinded, placebo and time- controlled, two-way crossover study in 12 healthy male subjects. Placebo or dopamine was administered on two separate study days. After saline infusion, dopamine hydrochloride was infused in three consecutive doses. Plasma levels of dopamine were determined at each perfusion step. Arterial and venous retinal vessel diameters were measured with the use of a Zeiss retinal vessel analyzer. Diffuse luminance fl
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Contact: Donna Krupa
djkrupa1@aol.com
703-527-7357
American Physiological Society
12-Feb-2003

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