CA2+-DEPENDENT AND CA2+-INDEPENDENT EXHALED NITRIC-OXIDE, PRESENCE IN GERM-FREE ANIMALS, AND INHIBITION BY ARGININE ANALOGS

Nitric oxide (NO) was detected by chemiluminescence in exhaled air from awake humans, anaesthetized rabbits, guinea pigs, germ-free rats and conventional rats. Rabbits exhibited the highest concentrations, followed by guinea pigs, humans and rats. There was no significant difference between germ-free rats and control rats. The authenticity of NO was confirmed in cold-trap experiments. Intravenous administration of inhibitors of NO synthase (0.01-300 mg kg(-1)) to guinea pigs dose dependently reduced NO concentrations in exhaled air with the following potency order: L-N-omega-nitro-arginine-methylester > asymmetric N-G,N-G-dimethyl-L-arginine-dihydrochloride = L-N-G-mono-methyl -arginine = L-N-5-(1-iminoethyl)-ornithine = aminoguanidine > L-canavanine. The effect of the NO synthase inhibitors was partly or fully reversed by L-arginine (1 g kg(-1) i.v.), and L-arginine per se induced a significant increment of NO in exhaled air. In rats, L-N-omega-nitro-arginine-methylester was considerably less potent than in guinea pigs. The concentration of NO in exhaled air increased 3-fold when changing from in situ blood auto-perfusion of rabbit lungs to in situ perfusion with saline medium. Addition of L-N-omega-nitro-arginine-methylester to the saline perfusion medium evoked a reduction of NO concentrations in the air from the ventilated perfused lungs. Perfusion of lungs with Ca2+-free medium induced significant decrements in NO concentrations in exhaled air, an effect partly reversed upon reintroducing Ca2+ into the medium. In conclusion, NO was detected in exhaled air from humans and animals by chemiluminescence. Nitric oxide in exhaled air originates from the respiratory system and is formed from L-arginine in a Ca2+-dependent manner. Microbial activity is not necessary for formation of NO in the respiratory system.