Effect of intravenous administration of L–Arginine on retinal vessel diameters and choroidal blood flow

Abstract

Abstract: : 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 elucidate whether the administration of L–Arginine affects retinal vessel diameters and choroidal blood flow in healthy volunteers. Methods: 12 healthy male volunteers were included in the study. L–arginine (1g/min) or placebo (NaCl) was administered intravenously for 30 minutes in a randomized, double masked, two way cross over design. Retinal vessel diameters and choroidal blood flow was measured before administration, in the last 10 minutes of the infusion as well as 20 minutes after cessation of the administration. Retinal vessel diameter were assessed with a Retinal Vessel Analyzer and pulsatile choroidal blood flow was measured using laser interferometry. Intraocular pressure was determined at the beginning and at the end of the experiment. Blood pressure and pulse rate was monitored throughout the whole experiment. Results: Intravenous administration of L–arginine increased pulsatile choroidal blood flow by +10.1±6.3% and +12.4±7.9%, at the two time points, respectively (ANOVA, p<0.05 versus placebo). However, administration of L–arginine did not affect retinal vessel diameters or intraocular pressure. L–arginine significantly decreased mean arterial pressure by –8±5% and –6±7%. (ANOVA, p<0.05 versus placebo) Neither retinal vessel diameters nor pulsatile choroidal blood flow was influenced by administration of placebo. Conclusion: Intravenous administration of L–arginine increases pulsatile choroidal blood flow in healthy volunteers, whereas retinal vessel diameters remained unchanged. Whether this effect is related to an increased NO–production or to an hitherto unidentified mechanism remains to be clarified.

Keywords: nitric oxide • drug toxicity/drug effects • retina