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A Luksch, EA Polska, G Fuchsjager-Mayrl, M Wolzt, L Schmetterer; Role of NO in Choroidal Blood Flow Regulation During Isometric Exercise in Healthy Humans . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3308.
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Purpose: Nitric oxide (NO) is an important regulator of basal choroidal blood flow. Animal experiments indicate that NO is also involved in choroidal autoregulation and NO synthase (NOS) inhibition and has been reported to shift choroidal pressure/flow curves to the right. We hypothesized that NOS inhibition may influence choroidal blood flow during isometric exercise. Methods: To test this hypothesis we performed a randomized, double-masked, placebo-controlled, three way cross over study in 12 healthy male volunteers. Subjects received on different study days intravenous infusions of NG-monomethyl-L-arginine (L-NMMA), phenylephrine or placebo. During these infusion periods subjects performed squatting 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 administered drugs. Isometric exercise increased choroidal blood flow during placebo and phenylephrine administration, but not during administration of L-NMMA (p < 0.001 versus placebo). Conclusion: These data indicate that NO plays an important role in the regulation of choroidal blood flow during isometric exercise.
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