Evidence that the histamine sensitivity and responsiveness of guinea‐pig isolated trachea are modulated by epithelial prostaglandin E2 production

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Abstract
1 Guinea-pig isolated tracheal preparations in which the epithelium had been removed exhibited a greater contractile response to histamine (intact: 1.91 ± 0.12g; n = 6 and rubbed: 2.76 ± 0.15g; n = 11; P < 0.001). The histamine sensitivity (pD2 value) of these preparations was also significantly greater (intact: 4.80 ± 0.04 and rubbed: 5.40 ± 0.08; P < 0.01). 2 Indomethacin suppressed the basal tone of both intact and rubbed preparations but was more effective in the former tissues (intact: −0.70 ± 0.14g; n = 22 and rubbed: −0.17 ± 0.05g; n = 12; P < 0.02). 3 Arachidonic acid (AA; 10 μM) suppressed the basal tone of intact tissues but contracted such preparations following indomethacin treatment (1.7 μM; 30 min). However, in rubbed tissues AA (10 μM) induced a contraction which was attenuated following indomethacin treatment. 4 Prostaglandin E2 (PGE2; 0.01 and 0.1 μM) suppressed the basal tone of intact preparations and always evoked contraction of rubbed tissues. Following indomethacin treatment PGE2 (0.01 and 0.1 μM) generally evoked spasm of intact and rubbed tissues while at higher concentrations (1 μM) relaxant effects were observed. 5 Removal of the epithelium did not alter the relaxant effect of PGE2 (pD2 value) on histamine (50 μM)-contracted tissues (intact: 6.86 ± 0.08 and rubbed: 7.10 ± 0.3; n = 4; P > 0.1). 6 In rubbed preparations treated with indomethacin, PGE2 (0.01 and 0.1 μM) evoked spasm. However, when added to preparations contracted with 5 μM histamine, PGE2 always caused relaxation. 7 The release of immunoreactive PGE2 by rubbed preparations during histamine and/or AA stimulation was significantly less than that produced by intact stimulated tissues. 8 Exogenous PGE2 (0.01-1 μM) decreased the maximal response and sensitivity of rubbed tracheal preparations to histamine. 9 These results suggest that release of an epithelial derived cyclo-oxygenase product, namely PGE2, may regulate basal tone, histamine response and sensitivity of the guinea-pig isolated trachea.