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Related Concept Videos

Autoregulation of Blood Flow01:17

Autoregulation of Blood Flow

Autoregulation mechanisms are characterized by their inherent capacity for self-regulation without necessitating specific nervous stimulation or endocrine control. These mechanisms facilitate the adjustment of blood flow and, therefore, perfusion specific to each tissue region. This self-regulation encompasses chemical signals and myogenic controls.
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Glaucoma is an eye condition characterized by increased intraocular pressure that damages the retina and optic nerve, leading to irreversible blindness if left untreated. The human eye has various components, including the cornea, iris, pupil, lens, and optic nerve. Aqueous humor is secreted by the epithelium of the ciliary body in the posterior chamber and flows through the trabecular meshwork and canal of Schlemm, maintaining normal intraocular pressure. The trabecular meshwork and the canal...
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Role of NO in the control of choroidal blood flow during a decrease in ocular perfusion pressure.

Christian Simader1, Solveig Lung, Günther Weigert

  • 1Department of Clinical Pharmacology, Division of Ophthalmo-Pharmacology, Medical University of Vienna, Vienna, Austria.

Investigative Ophthalmology & Visual Science
|January 7, 2009
PubMed
Summary

The L-arginine/nitric oxide system helps maintain choroidal blood flow (ChBF) at rest. However, it does not appear to be involved in regulating ChBF when intraocular pressure (IOP) increases.

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Area of Science:

  • Ophthalmology
  • Physiology
  • Vascular Biology

Background:

  • Choroidal blood flow (ChBF) is crucial for retinal health.
  • Regulation of ChBF is complex and influenced by various physiological factors.
  • The role of the L-arginine/nitric oxide system in ChBF regulation under altered ocular perfusion pressure (OPP) requires further investigation.

Purpose of the Study:

  • To investigate the involvement of the L-arginine/nitric oxide system in choroidal blood flow (ChBF) regulation.
  • To determine the effect of decreased ocular perfusion pressure (OPP) on ChBF.
  • To assess the impact of N(G)-monomethyl-L-arginine (L-NMMA) and phenylephrine on ChBF and OPP.

Main Methods:

  • A randomized, double-masked, placebo-controlled, three-way crossover study.
  • Intravenous infusions of N(G)-monomethyl-L-arginine (L-NMMA), phenylephrine, or placebo were administered.
  • Ocular perfusion pressure (OPP) was manipulated by stepwise increments in intraocular pressure (IOP) using a suction cup.

Main Results:

  • L-NMMA and phenylephrine increased resting ocular perfusion pressure (OPP).
  • L-NMMA significantly reduced resting choroidal blood flow (ChBF).
  • Decreased OPP, induced by increased IOP, led to a significant decrease in ChBF, but the choroid demonstrated some regulatory capacity.

Conclusions:

  • The L-arginine/nitric oxide system plays a role in maintaining basal vascular tone in the choroid.
  • The choroid exhibits regulatory capacity in response to reduced ocular perfusion pressure (OPP).
  • The L-arginine/nitric oxide system does not appear to be involved in the choroidal vasodilator response during elevated intraocular pressure (IOP).