L-ARGININE-DERIVED NITRIC-OXIDE - A MAJOR DETERMINANT OF UVEAL BLOOD-FLOW

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) trappine 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. © 1993 Academic Press Limited.