Antagonism of Slow Reacting Substance by Polyphloretin Phosphate on Isolated Human Bronchi

Purified slow reacting substance (SRS) induced a marked and long lasting constriction of isolated human bronchi. No signs of tachyphylaxis in the response to SRS were observed. Blockade of adrenergic, cholinergic, histaminergic and 5–hydroxytryptaminergir receptors did not effect the bronchoconstricting action of SRS. Adrenaline, theophylline and dibutyryl cyclic AMP counteracted the bronchoconstriction induced by SRS. Polyphloretin phosphate (PPP) antagonized the action of SRS, both on isolated human bronchi and on isolated guinea‐pig ileum. Antagonism by PPP could be surmounted by higher doses of agonist, and there was a parallel shift of the dose response curves of the agonist indicating a cormpetitive antagonism. PPP did not modify the bronchoconstriction induced by acetylcholine and histamine.