Interaction between aspirin and prostaglandins in the isolated guinea-pig tracheal muscle.

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Abstract
The effects of PG[prostaglandin]E2 and PGF2.alpha. on the tonus of isolated guinea pig tracheal chain were studied and compared with those of histamine and acetylcholine. PGE2 reduced tonus in normal resting state, but elevated tracheal tonus reduced by aspirin. Such PGE2-induced contractions did not exceed the initial resting tonus, and the magnitude and duration of the contractions progressively diminished with increased PGE2 concentrations. Aspirin did not produce relaxation or contraction in the presence of a low dose of PGE2. PGF2.alpha. produced a dose-related contraction in the normal tracheal chain, and the contractile response to PGF2.alpha. was potentiated by aspirin. In the presence of PGF2.alpha., aspirin caused a dose-related tracheal contraction. The contractile effect of histamine, but not of acetylcholine, was potentiated by aspirin, but there was a slight difference between PGF2.alpha. and histamine in that the potentiation of action of PGF2.alpha. by aspirin was more easily diminished by PGE2. PGE2 may be important in the maintenance of the resting tonus of the isolated guinea-pig tracheal chain, and in large doses it may act as a tracheal relaxant and attenuate the tracheal responses to PGF2.alpha. and histamine.