Intravenous administration of L-arginine increases retinal and choroidal blood flow

PURPOSE: Nitric oxide (NO) is among the most important regulators of ocular perfusion. L-arginine, an amino acid, is the precursor of NO synthesis. The aim of the present study was to determine whether administration of L-arginine affects ocular blood flow. DESIGN: L-arginine (1 g/min) or placebo was administered intravenously for 30 minutes in 12 healthy volunteers in a randomized, double-masked, two-way cross-over design. METHODS: Ocular hemodynamics were measured before, in the last 10 minutes of the infusion period, as well as 30 minutes after cessation of the administration. Retinal vessel diameters were measured with a retinal vessel analyzer, red blood cell velocities with bidirectional laser Doppler velocimetry, and pulsatile choroidal blood flow was measured using laser interferometry. RESULTS: L-arginine significantly decreased mean arterial pressure by -8 ± 5% and -6 ± 7% at the two time points (P < .01), respectively. Intravenous administration of L-arginine increased choroidal blood flow by +10 ± 6% and +12 ± 7%, respectively. Retinal venous diameters decreased by -2.5 ± 2.1% and -1.4 ± 2.7%, respectively, whereas red blood cell velocity significantly increased after administration of L-arginine by +22 ± 23% and +20 ± 19% at the two time points. Thus, calculated blood flow in retinal veins, increased by +21 ± 18% and +21 ± 19% before and after the end of L-arginine infusion. CONCLUSIONS: Intravenous administration of L-arginine increases retinal and choroidal blood flow in healthy volunteers. Whether this effect is related to an increased NO-production or an unidentified mechanism remains to be clarified. However, administration of L-arginine might be an interesting new approach to therapeutically increase ocular blood flow in ocular vascular disease.