Ca(2+)-dependent and Ca(2+)-independent exhaled nitric oxide, presence in germ-free animals, and inhibition by arginine analogues

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 NG,NG-dimethyl-L-arginine-dihydrochloride = L-NG-mono-methyl -arginine = L-N5- (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 Ca(2+)-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.