RESPONSE OF HUMAN ISOLATED BRONCHIAL AND LUNG PARENCHYMAL STRIPS TO SRS‐A AND OTHER MEDIATORS OF ASTHMATIC BRONCHOSPASM

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Abstract
1 The responses of human isolated bronchial and lung parenchymal strips to cumulative doses of slow reacting substance of anaphylaxis (SRS-A), histamine, prostaglandin F2 alpha (PGF2 alpha) and acetylcholine have been examined, after storing the tissues overnight in Krebs solution at 4 degrees C. 2 Both tissues contracted to all four agonists. The order of potency (as determined by height of maximal contraction) was: bronchial strip: acetylcholine greater than histamine = PGF2 alpha greater than SRS-A, and parenchymal strip: PGF2 alpha much greater than histamine = SRS-A greater than acetylcholine. 3 Maximal contractions to SRS-A of both the human bronchial and parenchymal strips were approx. 30% of the maximal contractions produced by the most potent agonist on each tissue (PGF2 alpha on the parenchymal strip and acetylcholine on the bronchial strip). SRS-A, therefore, does not have a powerful direct contractile effect on either parenchymal or bronchial strip of human lung, and is approximately equipotent on both tissues. A part of the broncho-constrictor activity of SRS-A in vivo may be mediated via indirect pathways. 4 The selective SRS-A antagonist, FPL 55712, was approximately equipotent in antagonizing contractions induced by SRS-A on both human bronchial and parenchymal strips.