Modulation of the reactivity of the guinea‐pig isolated trachealis by respiratory epithelium: Effects of cooling

1 Examination has been made of the effects of epithelium removal on the reactivity of guinea‐pig trachealis to methacholine at 37°C and 22°C, and on responses to activation of the Na + /K + ‐pump by abrupt temperature increase from 22°C to 37°C. 2 At 37°C, epithelium removal increased the sensitivity of isolated tracheal strips to methacholine without affecting the maximum isometric contractile response. Epithelium removal resulted at 22°C in a decrease in sensitivity to methacholine, i.e. an effect opposite to that seen at 37°C. While the maximum response of intact strips to methacholine was enhanced at 22°C, the maximum response of denuded preparations was decreased. 3 The increase in sensitivity to methacholine at 37°C after epithelium removal was mimicked in intact preparations by indomethacin (1 μ m ). Indomethacin did not mimic the decrease in methacholine sensitivity and maximum response caused by epithelium removal at 22°C. 4 Following incubation at 22°C, abrupt increase in temperature to 37°C elicited relaxation in both epithelium‐containing and epithelium‐denuded tracheal strips. In epithelium‐containing preparations the relaxation was more pronounced and followed by contraction. Ouabain (1 μ m ) converted the relaxation of denuded preparations to contraction, but was ineffective in intact strips. The relaxation of intact strips was, however, inhibited by a greater ouabain concentration (10 μ m ). 5 These findings indicate that the modulatory effect of the epithelium is temperature‐dependent. In cooled preparations, the epithelium enhances reactivity. At 37°C, an epithelium‐derived factor reduces reactivity, and this may partially be due to activation of the electrogenic Na + /K + ‐pump.