L-ARGININE INCREASES EXHALED NITRIC-OXIDE IN NORMAL HUMAN-SUBJECTS

1. Endogenous nitric oxide plays an important physiological role and i s synthesized by several isoforms of nitric oxide synthase from the se miessential amino acid L-arginine. Nitric oxide is detectable in the e xhaled air of normal individuals and may be used to monitor the format ion of nitric oxide in the respiratory tract. 2. We have investigated the effect of orally administered L-arginine (0.05, 0.1, 0.2g/kg) comp ared with matched placebo on the concentration of nitric oxide in the exhaled air in 23 normal individuals. 3. L-Arginine caused significant increases in the concentration of nitric oxide in exhaled air at dose s of 0.1 and 0.2mg/kg, which was maximal 2h after administration. This was associated with an increase in the concentration of L-arginine an d nitrate in plasma, There were no significant changes in heart rate, blood pressure or forced expiratory volume in 1 s. 4. These results su ggest that an increase in the amount of substrate for nitric oxide syn thase can increase the formation of endogenous nitric oxide, This may have therapeutic relevance in diseases in which there is defective pro duction of nitric oxide.