LACK OF EFFECT OF NITRIC-OXIDE INHIBITION ON BRONCHIAL TONE AND METHACHOLINE-INDUCED BRONCHOCONSTRICTION IN MAN

The role of nitric oxide (NO) as a bronchodilator has been studied in humans with controversial results. The aim of the present study was to investigate the role of endogenous NO on bronchial tone by studying w hether nitric oxide synthase (NOS) inhibition with N(G)nitro-L-arginin e-methyl-ester (L-NAME) influences basal bronchial tone, or potentiate s methacholine-induced bronchoconstriction. In a preliminary experimen t in five subjects, a significant reduction in exhaled NO was found af ter delivering L-NAME (15 mg in saline) (from 3.9 +/- 1.2 to 2.4 +/- 1 .1 nmol min(-1), P<0.05). In nine healthy non-smokers, specific airway conductance (SGAw), as a measure of airway calibre, was recorded afte r delivering, in a double-blind, controlled vs. placebo fashion, both nebulized L-NAME and saline, at baseline and after methacholine-induce d bronchoconstriction. There was no significant difference between the baseline SGAw values before and after delivering L-NAME (0.264 +/- 0. 04 and 0.267 +/- 0.05 cm H2O-1 s(-1) , respectively). After pre-treatm ent with L-NAME, SGAw values during methacholine-induced bronchoconstr iction were not different in comparison to values obtained after salin e inhalation. It is concluded that decreased endogenous NO does not in fluence bronchial tone in healthy people, nor does it modify methachol ine-induced bronchoconstriction.