[Bronchial hyperresponsiveness to histamine induced by intravenous administration of thromboxane A2 (TXA2) in guinea-pigs].

Thromboxane A2 (TXA2) has been suggested to play an important role in the pathogenesis of bronchial asthma. In this study the effects of intravenous administration of TXA2 on bronchial smooth muscle in guinea-pigs were investigated by measuring dynamic compliance and dynamic respiratory resistance, using a formula to exclude the effects of differences in airway wall thickness. Using this formula, the ratio of bronchial smooth muscle constriction by histamine can be estimated as an index of bronchial hyperresponsiveness. Administration of TXA2 did not induce airway wall edema. The ratio of bronchial smooth muscle constriction by histamine was significantly (p less than 0.01) enhanced by the administration of TXA2. Moreover, TXA2 antagonists, ONO-NT-126 and ONO-8809, inhibited the effect of TXA2 administration. These results suggest that TXA2 is an important mediator affecting bronchial hyperresponsiveness.