CONTRIBUTION OF PROSTAGLANDINS AND THROMBOXANES TO THE ADENOSINE AND ATP‐INDUCED CONTRACTION OF GUINEA‐PIG ISOLATED TRACHEA

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Abstract
1 In in vitro experiments adenosine 5′-triphosphate (ATP) and adenosine were found to exert different effects on the guinea-pig isolated trachea depending on whether the trachea had previously been contracted with acetylcholine (ACh) (6.6 × 10−6 m) or was at resting tone. 2 ATP and adenosine (10−5 and 10−3 m) were equipotent in relaxing the precontracted guinea-pig trachea, since concentrations of 1.09 ± 0.35 and 0.39 ± 0.16 mm respectively reduced by 25% the ACh-induced contraction. 3 ATP and adenosine (10−5 and 10−4 m) caused a moderate contraction of the guinea-pig trachea under resting tone. This effect was antagonized by inhibitors of cyclo-oxygenase (indomethacin 10−6m, aspirin 0.3 × 10−3m and 3 × 10−3m) and of thromboxane synthetase (nictindole 10−7m, imidazole 5 × 10−5 m), which suggests an indirect mechanism of action with release of arachidonic acid derivatives.