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Modulation of choroidal autoregulation in the rabbit
1Department of Ophthalmology, University of Texas Health Science Center, San Antonio, Texas 78299-3900, USA.
Experimental Eye Research
|October 3, 1999
Summary
Choroidal blood flow autoregulation involves a complex interplay. Neural and local factors, including nitric oxide and endothelin, influence vascular tone, with endothelial nitric oxide playing a predominant role.
Area of Science:
- Ophthalmology
- Neuroscience
- Physiology
Background:
- The choroid maintains blood flow despite pressure changes, suggesting autoregulation.
- Autoregulation may involve neural mechanisms due to rich autonomic innervation.
Purpose of the Study:
- To evaluate the neural contribution to choroidal blood flow autoregulation.
- To identify potential neural vasodilators and vasoconstrictors involved.
Main Methods:
- Measuring choroidal blood flow using laser Doppler flowmetry in anesthetized rabbits.
- Administering ganglionic blockade, cholinergic blockade (atropine), nitric oxide synthase inhibition (L-NAME), and other antagonists.
Main Results:
- Ganglionic blockade caused a downward shift in the pressure-flow curve, contrary to expectations.
- Nitric oxide synthase inhibition (L-NAME) induced a greater downward shift, indicating predominant endothelial nitric oxide.
- Endothelin and an unknown neural dilator appear to compete with local nitric oxide and an unknown vasoconstrictor.
Conclusions:
- Choroidal vascular tone is modulated by competing influences of neural dilators, local nitric oxide, and endothelin.
- Endothelial nitric oxide plays a primary role in choroidal autoregulation.
- Extrinsic neurohumoral factors have a lesser influence in anesthetized rabbits.