1 Antioxidants attenuate noncholinergic airway constriction. To further investigate the relationship between tachykinin-mediated airway constriction and oxygen radicals, we explored citric acidinduced bronchial constriction in 48 young Hartley strain guinea-pigs, divided into six groups: control; citric acid; hexa(sulphobutyl)fullerenes+citric acid; hexa(sulphobutyl)fullerenes+phosphor-amidon+citric acid; dimethylthiourea (DMTU)+citric acid; and DMTU+phosphoramidon+citric acid. Hexa(sulphobutyl)fullerenes and DMTU are scavengers of oxygen radicals while phosphoramidon is an inhibitor of the major degradation enzyme for tachykinins. 2 Animals were anaesthetized, paralyzed, and arti®cially ventilated. Each animal was given 50 breaths of 4 ml saline or citric acid aerosol. We measured dynamic respiratory compliance (Crs), forced expiratory volume in 0.1 (FEV 0.1 ), and maximal expiratory¯ow at 30% total lung capacity (V . max30 ) to evaluate the degree of airway constriction. 3 Citric acid, but not saline, aerosol inhalation caused marked decreases in Crs, FEV 0.1 and V . max30 , indicating marked airway constriction. This constriction was signi®cantly attenuated by either hexa(sulphobutyl)fullerenes or by DMTU. In addition, phosphoramidon signi®cantly reversed the attenuating action of hexa(sulphobutyl)fullerenes, but not that of DMTU. 4 Citric acid aerosol inhalation caused increases in both lucigenin-and t-butyl hydroperoxideinitiated chemiluminescence counts, indicating citric acid-induced increase in oxygen radicals and decrease in antioxidants in bronchoalveolar lavage¯uid. These alterations were signi®cantly suppressed by either hexa(sulphobutyl)fullerenes or DMTU. 5 An elastase inhibitor eglin-c also signi®cantly attenuated citric acid-induced airway constriction, indicating the contributing role of elastase in this type of constriction. 6 We conclude that both oxygen radicals and elastase play an important role in tachykininmediated, citric acid-induced airway constriction.

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