The effect of the nonspecific nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester on the choroidal compensatory response to myopic defocus in chickens

Optom Vis Sci. 2004 Feb;81(2):111-8. doi: 10.1097/00006324-200402000-00009.

Abstract

Purpose: Chick eyes show rapid compensation to retinal defocus. One component of this mechanism involves changes in the thickness of the choroid: when the retina is exposed to myopic defocus, the choroid thickens, pushing the retina forward; conversely, when the eye is exposed to hyperopic defocus, the choroid thins. The underlying mechanism(s) for these changes are unknown. We tested the hypothesis that nitric oxide might play a role.

Methods: We examined the effect of the nonspecific nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) on the compensatory choroidal thickening in response to myopic defocus using two visual paradigms: first, in previously form-deprived "recovering" eyes and, second, in eyes wearing +15 D spectacle lenses. L-NAME was injected intravitreally after removal of the diffuser or immediately before putting on the lenses. In addition, we looked at the effect of L-NAME on experimentally thickened choroids (induced by 1 week of recovery from deprivation myopia or 1 week of +15 D lens wear) and on choroids of normal eyes. Eyes were measured using A-scan ultrasonography before the injections and at subsequent intervals for several days. As a control for the injection procedure, eyes with the same visual conditions were injected with saline. Fellow eyes were untreated and uninjected.

Results: L-NAME inhibited choroidal thickening in both previously form-deprived eyes (2 vs. 117 microm; p < 0.001) and eyes wearing +15 D lenses (3 vs. 137 microm; p < 0.02). The effect was rapid, transient, and dose dependent (ED50, 0.26 micromoles). L-NAME produced thinning in experimentally thickened choroids (recovering: -116 microm; lenses: -219 microm) and in normal choroids (-47 microm) within 7 hours.

Conclusions: Nitric oxide may play a role in modulating choroidal thickness. The mechanism is as yet unknown.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adaptation, Physiological / drug effects*
  • Animals
  • Animals, Newborn
  • Chickens
  • Choroid / diagnostic imaging
  • Choroid / physiopathology*
  • Enzyme Inhibitors / pharmacology*
  • Fixation, Ocular*
  • Myopia / diagnostic imaging
  • Myopia / physiopathology*
  • NG-Nitroarginine Methyl Ester / pharmacology*
  • Nitric Oxide Synthase / antagonists & inhibitors*
  • Ultrasonography

Substances

  • Enzyme Inhibitors
  • Nitric Oxide Synthase
  • NG-Nitroarginine Methyl Ester