Further studies on the SRS-A antagonist FPL 55712.

FPL 55712, previously reported to be a selective antagonist of SRS-A on the guinea-pig ileum, has now been shown to be similarly selective, though less potent, in its antagonism of contractions induced by SRS-A on in vitro preparations of respiratory smooth muscle (human bronchial strips and guinea-pig tracheal tubes). In vivo, bronchoconstriction induced in guinea-pigs by the endogenous release of SRS-A was partially inhibited by relatively large intravenous doses of FPL 55712 and by inhalation of aerosol compound. FPL 55712 was very rapidly cleared following intravenous administration.