title: Role of NO in choroidal blood flow regulation during isometric exercise in healthy humans.
abstract: OBJECTIVE
  Nitric oxide (NO) is an important regulator of basal choroidal blood flow. Animal experiments indicate that NO is also involved in choroidal blood flow regulation during changes in ocular perfusion pressure and inhibition of NO synthase (NOS) has been reported to shift choroidal pressure-flow curves to the right. The hypothesis for the study was that inhibition of NOS may influence choroidal blood flow during isometric exercise.
  
  
  METHODS
  To test this hypothesis, a randomized, double-masked, placebo-controlled, three-way crossover study was performed in 12 healthy male volunteers. Subjects received on different study days intravenous infusions of N(G)-monomethyl-L-arginine (L-NMMA), phenylephrine, or placebo. During these infusion periods, subjects were asked to squat for 6 minutes. Choroidal blood flow was assessed with laser Doppler flowmetry, and ocular perfusion pressure (OPP) was calculated from mean arterial pressure and intraocular pressure.
  
  
  RESULTS
  L-NMMA and phenylephrine increased resting OPP by 10% and 13%, respectively, but only L-NMMA reduced resting choroidal blood flow (-17%, P < 0.001). The relative increase in OPP during isometric exercise was comparable with all drugs administered. Isometric exercise increased choroidal blood flow during administration of placebo and phenylephrine, but not during administration of L-NMMA (P < 0.001 vs. placebo).
  
  
  CONCLUSIONS
  These data indicate that NO plays an important role in the regulation of choroidal blood flow during isometric exercise.
authors.affiliation: Department of Clinical Pharmacology, University of Vienna, Vienna, Austria.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Luksch
authors.forename: Elzbieta
authors.initials: E
authors.lastname: Polska
authors.forename: Andrea
authors.initials: A
authors.lastname: Imhof
authors.forename: Joanne
authors.initials: J
authors.lastname: Schering
authors.forename: Gabriele
authors.initials: G
authors.lastname: Fuchsjäger-Mayrl
authors.forename: Michael
authors.initials: M
authors.lastname: Wolzt
authors.forename: Leopold
authors.initials: L
authors.lastname: Schmetterer
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure; D002829:Choroid / Q000098:blood supply*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007429:Intraocular Pressure; D017078:Laser-Doppler Flowmetry; D008297:Male; D009569:Nitric Oxide / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000502:physiology; D052247:Nitric Oxide Synthase Type II; D010656:Phenylephrine / Q000494:pharmacology; D012039:Regional Blood Flow / Q000502:physiology; D014065:Tonometry, Ocular; D019323:omega-N-Methylarginine / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D010656:Phenylephrine; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; C496319:NOS2 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II