Dopaminergic modulation of human bronchial tone

Dopamine exerts inhibitory and excitatory effects on different systems. Its effect on human bronchial tone is controversial. It has been reported that dopamine has no acute effect on human airways from normal subjects or those with asthma background. However, inhaled or infused dopamine decreased histamine-induced bronchoconstriction in both normal and asthmatic subjects.

We examined the possible modulating effect of dopamine on bronchial diameter by administering inhaled dopamine and the DA(2) dopaminergic blocker metoclopramide (MTC) to subjects with various degrees of bronchial tone. We examined 50 volunteers. Arterial blood pressure and heart rate were determined in each subject. By means of spirometry, we measured forced vital capacity (FVC), forced expiratory volume in the first second (FEV(1)), maximal forced expiratory flow (FEF(max)), and forced expiratory flow at 50% of vital capacity (FEF(50)), before and after each treatment. By inhalation with a nebulizer, we administered the following: a) dopamine (0.5 microg/kg/min) to 10 healthy subjects, 10 subjects with asthma without acute bronchospasm (AWAB), and nine subjects with acute asthma attack (AAA), and b) intravenous (i.v.) metoclopramide (7 microg/kg/min) was administered to 10 healthy subjects and 11 subjects with AWAB. For ethical reasons, MTC was not used in subjects with acute asthma attack. Non-parametric Wilcoxon test for paired samples, ANOVA test, and Bonferroni multiple comparison test were performed. Inhaled dopamine increased FEV(1) and FVC, FEF(max), and FEF(50) in the AAA group, but there were no modifications in the healthy group or in the AWAB group. Metoclopramide did not induce changes in respiratory parameters in healthy individuals or in those with AWAB.

Inhaled dopamine is able to induce bronchodilatation when the bronchial tone is already increased by acute asthma attack but did not modify the resting bronchial tone in normal subjects or in asthmatics without acute bronchospasm. Additionally, DA(2) blockade with metoclopramide did not modify resting bronchial tone. Dopamine exerts a modulatory effect on the bronchial tone of human airways depending on the degree of preexisting tone.