Purpose: L-Arginine, a non-toxic amino acid, is converted to nitric oxide (NO) by NO synthase. Recent findings have demonstrated that NO serves as an ocular hypotensive agent. The objectives of the present study were to clarify the effect of L-arginine on intraocular pressure (IOP), pupil size, refraction and accommodative amplitude in human eyes, and to examine whether L-arginine is converted to NO in vivo.
Methods: Fourteen volunteers received an intravenous drip-infusion of 100 ml of L-arginine (10.0 g) solution. IOP levels were measured before, during and after infusion using Goldmann applanation tonometry. Pupillary diameter, refraction and accommodative amplitude were also measured in human subjects. In rabbits, the nitrite levels in the aqueous humor were measured during L- or D-arginine infusion.
Results: The mean IOP of the L-arginine group was significantly decreased during infusion, but recovered rapidly after infusion. The mean IOP of the control group increased during infusion. The changes in pupillary diameter, refraction, and accommodative amplitude before and after infusion of L-arginine were not significant. L-Arginine significantly elevated the level of nitrite in the aqueous humor compared with the controls.
Conclusions: These findings demonstrated that L-arginine lowers IOP mainly through the formation of NO.