Effect of inhaled norepinephrine on the nitroglycerin-induced bronchodilatation in asthmatics

Previous studies on the bronchodilating effect of nitrates yielded conflicting results. We hypothesized that the concomitant bronchial vasodilatation induced by nitrates may limit the increase of airway patency due to bronchial smooth muscle relaxation. To test this hypothesis, we evaluated the bronchodilating effect of nebulized nitroglycerine (NTG), 0.2 mg, in 12 patients with reversible airway obstruction (FEV1 64.3 +/- 8.2% predicted, > 15% increase after salbutamol 200 micrograms by metered-dose inhaler), pretreated with aerosolized norepinephrine (NE) (0.04 mg) or placebo (PL), in a randomized double-blind crossover design, in two separate days. Baseline FEV1 values of the two test days and FEV1 after NE or PL inhalations were not significantly different. After NTG inhalation, FEV1 was 73.8 +/- 7.9% predicted, with NE pretreatment, and 70 +/- 8.2% predicted with PL pretreatment (p < 0.01). The maximal percent increases of FEV1 above baseline were 14.9 +/- 4.8% and 9.2 +/- 2.4%, respectively, after NE and PL pretreatment (p < 0.01). In conclusion, NTG produces a better bronchodilatation when the concomitant vasodilatation is attenuated by a vasocostrictive agent.