L-Arginine-derived Nitric Oxide: A Major Determinant of Uveal Blood Flow

Abstract

The effect of inhibition of the l-arginine-nitric oxide pathway on regional ocular blood flow was studied in anaesthetized Beagle dogs. Under control conditions (mean arterial blood pressure 105 ± 6 mmHg) trapping of 11 and 15-μm-diameter tracer microspheres revealed the following regional blood flows (ml min -1 g -1): retina 0·065 ± 0·016, choroid 5·72 ± 0·32, ciliary body 0·77 ± 0·11, iris 0·18 ± 0·04. After i.v. infusion of nitro- l-arginine methylester (20 mg kg -1), a potent inhibitor of nitric oxide production from l-arginine, mean arterial blood pressure increased from 105 ± 6 mmHg by 19% to a new steady-state level of 125 ± 7 mmHg. This increase of arterial blood pressure extended over 3 hr and was reversible after i.v. infusion of l -arginine (100 mg kg -1 over 10 min). Despite the increase in blood pressure following infusion of nitro- l-arginine methylester blood flow of choroid, ciliary body, and iris were significantly decreased by 40, 40 and 48%, respectively. Retinal blood flow did not change significantly (-12%). These results suggest that the l-arginine-nitric oxide pathway is of major importance for the adjustment of uveal blood flow under resting physiological conditions.