Background: Different mechanisms may underlie bronchial hyperresponsiveness (BHR) in different diseases. The aim of this study was to investigate the bronchial responsiveness profile produced by three different challenge tests, methacholine, a direct stimulus, and two indirect stimuli, adenosine 5'-monophosphate (AMP) and cold air, in subjects with asthma and patients with Sjögren's syndrome.
Methods: The study population comprised 40 adult patients with asthma, 18 subjects with Sjögren's syndrome, and 20 controls. Blood samples were collected before each challenge for measurements of serum eosinophil peroxidase (S-EPO) and eosinophil cationic protein (S-ECP). The investigated subjects recorded peak expiratory flow and kept a symptom diary.
Results: Atopic subjects with asthma were significantly more hyperresponsive to AMP than nonatopic subjects with asthma (P=0.01) and subjects with Sjögren's syndrome (P=0.02). No difference was seen between atopic and nonatopic subjects with asthma in the case of challenges with methacholine or cold air. In atopic subjects with asthma, a significant correlation was found between challenges with methacholine and AMP (r=0.91, P=0.0001) and methacholine and cold air (r=0.83, P=0.004), but, in nonatopic subjects with asthma, no significant correlation was seen between methacholine and AMP or cold air challenges. In atopic subjects with asthma, the dose-response slope for AMP was correlated to S-EPO (r= -0.56; P = 0.01) and S-ECP (r= -0.51, P = 0.02), while no correlation between BHR and inflammation markers was found in the two other patient groups.
Conclusions: The results of this study suggest that patients with asthma and subjects with Sjögren's syndrome display different bronchial responsiveness profiles for different challenge agents. Atopic subjects with asthma are more hyperresponsive to AMP than nonatopic subjects and patients with Sjögren's syndrome. More than one challenge may be required to detect different aspects of bronchial responsiveness.