Influence of epithelium on the responsiveness of guinea-pig isolated trachea to adenosine.

1. The influence of epithelium removal on the effects of adenosine on airway contractility was investigated on the guinea-pig isolated trachea. 2. In preparations under resting tone or precontracted with histamine 10(-5) M, removal of the tracheal epithelium resulted in similar shifts to the left of the adenosine concentration-response curves (0.61 +/- 0.18 (P less than 0.05) and 0.80 +/- 0.09 (P less than 0.001) log units; n = 5), corresponding to 4.07 and 6.31 fold potentiations of the relaxant effect of adenosine. 3. In the presence of dipyridamole 10(-5) M the relaxant effects of adenosine were potentiated 85.1 fold on tracheae with epithelium; removal of the epithelium did not produce a significant additional shift to the left of the adenosine concentration-response curves (0.07 +/- 0.03 log units; n = 5; NS). 4. In the absence of dipyridamole, the theophylline-adenosine antagonism was not of the competitive type, irrespective of whether the tracheae were with or without epithelium. 5. In the presence of dipyridamole, this antagonism was likely to be of the competitive type and its characteristics were the same when the epithelium was present or absent. Regression slope and pA2 values were 0.84 and 5.07, respectively, in the presence of epithelium and 0.76 and 4.89, respectively, in its absence. 6. It is suggested that, at least in the guinea-pig isolated trachea model, the airway epithelium seems to be involved only in the uptake and metabolism of adenosine.