title: 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.
abstract: OBJECTIVE
  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.
authors.affiliation: New England College of Optometry, Boston, Massachusetts 02115, USA. nicklad@ne-optometry.edu
authors.forename: Debora L
authors.initials: DL
authors.lastname: Nickla
authors.forename: Christine F
authors.initials: CF
authors.lastname: Wildsoet
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects*; D000818:Animals; D000831:Animals, Newborn; D002645:Chickens; D002829:Choroid / Q000000981:diagnostic imaging / Q000503:physiopathology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005403:Fixation, Ocular; D009216:Myopia / Q000000981:diagnostic imaging / Q000503:physiopathology*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors*; D014463:Ultrasonography
chemical_list: D004791:Enzyme Inhibitors; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester