CONTRACTILE AND RELAXANT ACTIONS OF PROSTAGLANDINS ON GUINEA‐PIG ISOLATED TRACHEA

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Abstract
The effects of 12 prostaglandins on guinea‐pig isolated trachea have been examined in the presence of indomethacin. Two series of experiments were carried out, the first on preparations without tone (‘zero tone’), and the second on preparations with tone induced with acetylcholine (‘high tone’). The compounds tested fell into two groups. The first, comprising prostaglandins F1α, F2α F2α acetal, I2 and Wy 17186, contracted both zero and high tone preparations. The second, comprising prostaglandins A1, A2, B1, B2, E1 E2 and F2β, contracted zero, but relaxed high tone preparations. Responses to the second group of compounds are probably the resultant of their contractile and relaxant actions. The order of potency for contracting zero tone preparations was prostaglandin E (PGE) > F = I = Wy 17186 > B > A, 2‐series compounds being 5 to 18 times more potent than 1‐series compounds. The order of potency for relaxing high tone preparations was PGE > Fβ > B > A > Wy 17186 > Fα = I = 0. There was little difference between the potency of 1‐ and 2‐series compounds. The possible relevance of these results to the interpretation of the effects of prostaglandins on human airways is discussed.