Mediation of prostaglandin E2 in the triphasic response to ATP of the isolated tracheal muscle of guinea-pigs

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Abstract
ATP, at a dose higher than 0·1 μg ml−1, showed a biphasic action consisting of an initial increase followed by a gradual decrease of muscle tension in the isolated tracheal strip-chains of guinea-pigs. The pattern of this biphasic response to ATP varied with the level of basal tone of the preparation at the moment of application of ATP. A similar biphasic action was obtained by prostaglandin (PG) E2 among the various active substances studied including acetylcholine, histamine, catecholamines and various types of PG. Indomethacin (0·1 μg ml−1) and aspirin (30 μg ml−1) completely abolished the ATP-induced inhibitory response observed in the presence of histamine (10 μm). Polyphloretin phosphate (100 μg ml−1) also significantly depressed the inhibitory response to ATP or PGE2. It is concluded that the response to ATP of the preparation is mediated by PGE2 released via the stimulation of its biosynthesis.