Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New Hope For Preventing Major Problems Of The Retina

13.02.2003


Study findings may offer prevention for avoiding those annoying spots caused by macular degeneration



The primary function of the retina is to capture light and initiate neural signals. The retina contains the photoreceptors, which are the site of sensory transduction in the visual pathway. Major landmarks in the retina are the fovea and macula, where light has a direct pathway to the receptors. An interruption of the blood supply to these landmarks can lead to age-related macular degeneration and diabetes, the cause of severe visual problems.

Dopamine is an intermediate in tyrosine metabolism and precursor of norepinephrine and epinephrine; it accounts for 90 percent of the catecholamines; its presence in the central nervous system and localization in the basal ganglia (caudate and lentiform nuclei) suggest that dopamine may have other functions. Now a new research study reveals that the body’s dopaminergic system plays a role in the regulation of retinal blood flow in the body. In addition, their data presents evidence for an the diminishing effect of dopamine on the pathways coupling sensory input to vascular response.


Dopaminergic functions in the eye are complex and affect several ocular tissues. These include transmitter effects and impacts on intraocular (within the eyeball) pressure (IOP) and ocular blood flow. It is known from several tissues that vascular effects of dopamine are not only mediated via specific dopamine receptors but also by influencing other effector pathways like catecholamine receptors, a major responder to stress.

Vascular dopaminergic effects in the eye in past studies have revealed that dopamine antagonists (domperidone and haloperidol) increase ocular blood flow in rabbits. Other dopamine antagonists had similar effects, whereas dopamine agonists did not affect beating ocular blood flow. Dopamine has been investigated extensively in glaucoma research. One previous effort found that D1 agonists (when combined with receptors initiate drug action) increase pressure within the eye, where D1 antagonists 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 Garhöfer, 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 flicker stimuli of eight Hz were applied for 60 seconds. Blood pressure and pulse rate were monitored.

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 because vessels are already predilated via the dopamine pathway. In conclusion, their data indicate a dopaminergic contribution to retinal vascular tone in the human retina.

Dopamine appears to play a role in flicker-induced vasodilatation. This could implicate possible roles of dopaminergic agents in alleviating the reduction of blood to the retina, thereby saving thousands of Americans from future vision problems.


Source: January 2003 edition of the American Journal of Physiology—Heart and Circulatory Physiology.

The American Physiological Society (APS) was founded in 1887 to foster basic and applied science, much of it relating to human health. The Bethesda, MD-based Society has more than 10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals every year.

Contact: Donna Krupa: 703.527.7357
Cell: 703.967.2751 or
djkrupa1@aol.com

Donna Krupa | The American Physiological Socie

More articles from Health and Medicine:

nachricht Finding new clues to brain cancer treatment
21.02.2020 | Case Western Reserve University

nachricht UIC researchers find unique organ-specific signature profiles for blood vessel cells
18.02.2020 | University of Illinois at Chicago

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A step towards controlling spin-dependent petahertz electronics by material defects

The operational speed of semiconductors in various electronic and optoelectronic devices is limited to several gigahertz (a billion oscillations per second). This constrains the upper limit of the operational speed of computing. Now researchers from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, Germany, and the Indian Institute of Technology in Bombay have explained how these processes can be sped up through the use of light waves and defected solid materials.

Light waves perform several hundred trillion oscillations per second. Hence, it is natural to envision employing light oscillations to drive the electronic...

Im Focus: Freiburg researcher investigate the origins of surface texture

Most natural and artificial surfaces are rough: metals and even glasses that appear smooth to the naked eye can look like jagged mountain ranges under the microscope. There is currently no uniform theory about the origin of this roughness despite it being observed on all scales, from the atomic to the tectonic. Scientists suspect that the rough surface is formed by irreversible plastic deformation that occurs in many processes of mechanical machining of components such as milling.

Prof. Dr. Lars Pastewka from the Simulation group at the Department of Microsystems Engineering at the University of Freiburg and his team have simulated such...

Im Focus: Skyrmions like it hot: Spin structures are controllable even at high temperatures

Investigation of the temperature dependence of the skyrmion Hall effect reveals further insights into possible new data storage devices

The joint research project of Johannes Gutenberg University Mainz (JGU) and the Massachusetts Institute of Technology (MIT) that had previously demonstrated...

Im Focus: Making the internet more energy efficient through systemic optimization

Researchers at Chalmers University of Technology, Sweden, recently completed a 5-year research project looking at how to make fibre optic communications systems more energy efficient. Among their proposals are smart, error-correcting data chip circuits, which they refined to be 10 times less energy consumptive. The project has yielded several scientific articles, in publications including Nature Communications.

Streaming films and music, scrolling through social media, and using cloud-based storage services are everyday activities now.

Im Focus: New synthesis methods enhance 3D chemical space for drug discovery

After helping develop a new approach for organic synthesis -- carbon-hydrogen functionalization -- scientists at Emory University are now showing how this approach may apply to drug discovery. Nature Catalysis published their most recent work -- a streamlined process for making a three-dimensional scaffold of keen interest to the pharmaceutical industry.

"Our tools open up whole new chemical space for potential drug targets," says Huw Davies, Emory professor of organic chemistry and senior author of the paper.

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

70th Lindau Nobel Laureate Meeting: Around 70 Laureates set to meet with young scientists from approx. 100 countries

12.02.2020 | Event News

11th Advanced Battery Power Conference, March 24-25, 2020 in Münster/Germany

16.01.2020 | Event News

Laser Colloquium Hydrogen LKH2: fast and reliable fuel cell manufacturing

15.01.2020 | Event News

 
Latest News

Active droplets

21.02.2020 | Medical Engineering

Finding new clues to brain cancer treatment

21.02.2020 | Health and Medicine

Beyond the brim, Sombrero Galaxy's halo suggests turbulent past

21.02.2020 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>