Bradykinin‐induced bronchospasm in the rat in vivo : a role for nitric oxide modulation

Bradykinin has an important role in asthma pathogenesis, but its site of action is unclear. It was previously reported by the authors that bradykinin causes a dose–dependent reduction in dynamic compliance but little change in total lung resistance. This suggested that bradykinin may have a preferential effect in the distant lung. The purpose of the current investigation was to better characterize the effects of bradykinin on pulmonary resistance in rodents and explore the role of nitric oxide release in modulating the effect of bradykinin. Airway constriction was induced in the rats by aerosol administration of bradykinin with or without treatments with the inhaled bradykinin‐2 receptor antagonist, Hoe 140 or the nitric oxide synthase inhibitors N G ‐nitro‐ l ‐arginine methylester or N G ‐monomethyl‐ l ‐arginine. Total lung resistance was partitioned into tissue and airway resistance by using the alveolar capsule method. Bradykinin induced a significant increase in both resistances. Hoe 140 abolished the response to bradykinin. The nitric oxide synthase inhibitors enhanced the bronchoconstricting response. In conclusion, the bradykinin response in the rats was not only localized to conducting airways but also involved a relatively selective tissue reaction. Bradykinin‐induced bronchospasm in the rat is solely due to activation of bradykinin‐2 receptor. Further, it was shown that nitric oxide significantly modulates the bronchospasm caused by bradykinin, suggesting that nitric oxide is an important modulator of airways responsiveness to bradykinin.