Role of NO in choroidal blood flow regulation during isometric exercise in healthy humans.
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.
Luksch
Alexandra
A
Department of Clinical Pharmacology, University of Vienna, Vienna, Austria.
Polska
Elzbieta
E
Imhof
Andrea
A
Schering
Joanne
J
Fuchsjäger-Mayrl
Gabriele
G
Wolzt
Michael
M
Schmetterer
Leopold
L
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
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