The role of mast cells in citric acid-induced airway constriction and cough.

Inhalation of citric acid (CA) causes airway constriction and coughing. To investigate the role of mast cells in CA-induced airway constriction and cough, three experiments using guinea pigs were carried out. In the first experiment, we used compound 48/80 to deplete mast cells, cromolyn sodium to stabilize mast cells, MK-886 to inhibit synthesis of leukotrienes, pyrilamine to antagonize histamine H1 receptor, methysergide to antagonize serotonin receptor, and indomethacin to inhibit cyclooxygenase. In the second experiment, compound 48/80-pretreated animals were divided into 2 parts; the first one was used to test the role of exogenous leukotriene (LT) C4, while the second one to test the role of exogenous histamine. Decreases in respiratory compliance (Crs) and forced expiratory volume in 0.1 sec (FEV0.1) were used as indicators for airway constriction in anesthetized guinea pigs. CA-induced cough was recorded for 12 min using a barometric body plethysmograph in conscious animals. In the third experiment, the activation of mast cells upon CA inhalation was investigated by determining lung tissue or arterial plasma histamine concentration in animals. Exposure to CA induced marked airway constriction and increase in cough number. Compound 48/80, cromolyn sodium, MK-886 and pyrilamine, but not indomethacin or methysergide, significantly attenuated CA-induced airway constriction and cough. Injection of LTC4 or histamine caused a significant increase in CA-induced airway constriction and cough in compound 48/80-pretreated animals. In addition, CA inhalation caused significant increase in lung tissue and plasma histamine concentrations, which were blocked by compound 48/80 pretreatment. These results suggest that mast cells play an important role in CA aerosol inhalation-induced airway constriction and cough via perhaps mediators including LTs and histamine.