Enhancement of isolated airway responses to bronchoconstrictive agonists by the slow-reacting substance of anaphylaxis antagonist FPL 55712.

The activity of the SRS-A antagonist FPL 55712 against histamine, carbachol and ion-induced contraction of isolated airway smooth muscle was evaluated. FPL 55712 enhanced responses of guinea-pig trachea and parenchymal lung strips to histamine and carbachol. Enhancement was not obviously related to concentration. It is suggested that this effect may be the result of cyclo-oxygenase inhibition by FPL 55712. These observations may account for some of the anomalous findings regarding the antagonism of leukotrienes by FPL 55712 previously reported.