Nagase, Takahide, Tomoko Aoki, Teruaki Oka, Yoshinosuke Fukuchi, and Yasuyoshi Ouchi. ET-1-induced bronchoconstriction is mediated via ET_B receptor in mice.J. Appl. Physiol. 83(1): 46–51, 1997.—Endothelin (ET)-1 is one of the most potent agonists of airway smooth muscle and can act via two different ET receptor subtypes, i.e., ET_A and ET_B. To determine the effects of ET-1 on in vivo pulmonary function and which ET receptors are involved in murine lungs, we investigated 1) the effects of ET and sarafotoxin S6c (S6c), a selective ET_B agonist, on pulmonary function and 2) the effects of BQ-123 and BQ-788, specific ET_A- and ET_B-receptor antagonists, on ET-1-induced bronchoconstriction. ICR mice were anesthetized and mechanically ventilated (frequency = 2.5 Hz, tidal volume = 8 ml/kg, positive end-expiratory pressure = 3 cmH₂O). Intravenous ET-1, ET-2, and ET-3 increased lung resistance similarly and equipotently, whereas S6c elicited a greater degree of bronchoconstriction. Mice were then pretreated with saline (Sal), BQ-123 (0.2, 1, and 5 mg/kg), or BQ-788 (0.2, 1, and 5 mg/kg) before administration of ET-1 (10⁻⁷ mol/kg iv). No dose of BQ-123 blocked ET-1-induced constriction, whereas pretreatment with each dose of BQ-788 significantly inhibited ET-1-induced responses. There were significant differences in morphometrically assessed airway constriction between Sal and BQ-788 and between BQ-123 and BQ-788, whereas no significant difference was observed between Sal and BQ-123. There were no significant morphometric differences in the airway wall area among the three groups. These observations suggest that the ET_B- but not ET_A-receptor subtype may mediate the changes in murine pulmonary function in response to ET-1. In addition, the ET_B-receptor antagonist reduces ET-1-induced airway narrowing by affecting airway smooth muscle contraction in mice.