In vivo airway eosinophil accumulation induced by polymyxin-B reduces bronchial responsiveness in guinea pigs

Background Chronic desquamative eosinophilic bronchitis and bronchial hyper responsiveness have been considered essential for bronchial asthma. However , it has not been studied whether airway eosinophils enhance or inhibit bro nchial responsiveness in vivo. Objective This study was conducted to elucidate the influence of airway eos inophil accumulation on bronchial responsiveness in vivo. Materials and methods Guinea pigs were transnasally treated with 75 mug/kg of polymyxin-B or vehicle twice a week for a total of 3 weeks. Guinea pigs were surgically cannulated and artificially ventilated 24 h after the last administration of polymyxin-B or vehicle. Ten minutes after the installatio n of artificial ventilation, ascending doses of methacholine, acetylcholine or histamine were inhaled for 20 s at intervals of 5 min. Subsequent study was conducted 20 min after treatment of 60 mg/kg of indomethacin in the sa me manner. Final study was conducted in naive guinea pigs after single inha lation of 75 mug/mL of polymyxin B. Results The proportion of eosinophils in bronchoalveolar lavage fluid signi ficantly increased in guinea pigs treated with polymyxin-B compared with ve hicle. Bronchial responsiveness to inhaled methacholine, acetylcholine and histamine was significantly decreased by the polymyxin-B treatment. This pr otective effect induced by polymyxin B was abolished by pretreatment of ind omethacin. A significant increase in bronchial responsiveness was observed after a single inhalation of polymyxin B. Conclusion These results suggest that in vivo airway eosinophils may reduce non-specific bronchial responsiveness through inhibitory or bronchoprotect ive prostanoids.