Physiologic significance of epithelial removal on guinea pig tracheal smooth muscle response to acetylcholine and serotonin.

We studied the modulatory effect of airway epithelium on guinea pig tracheal smooth muscle (TSM) contraction. Isometric force was measured in vivo before and after removal of the tracheal epithelium. In parallel studies, TSM contraction was also measured isometrically in epithelium-intact and epithelium-denuded TSM strips in vitro. Epithelial removal in vivo did not alter the contractile response of TSM to acetylcholine (ACh) or serotonin. In nine guinea pigs, active tension (AT) caused by 3 x 10(-7) mol/kg of intravenous ACh was 0.74 +/- 0.14 g force per longitudinal length of the segment (g/cm) in the presence of epithelium versus 0.89 +/- 0.16 g/cm after removal of airway epithelium (confirmed histologically) (p NS). The threshold response to ACh was also unchanged (-8.0 +/- 0.3 log mol/kg control versus -8.3 +/- 0.3 log mol/kg after epithelial removal, p NS). In six guinea pigs, the AT caused by 3 x 10(-8) mol/kg of intravenous serotonin was 1.92 +/- 0.63 g/cm with an intact epithelium versus 2.15 +/- 0.70 g/cm after epithelial removal in vivo (p NS). Epithelial removal in vitro increased the sensitivity of TSM contraction to ACh when the data were expressed as the percentage maximal response to ACh. The concentration of ACh causing 50% of the maximal response (EC50) was -5.74 +/- 0.25 log M in eight epithelium-intact TSM strips versus -6.37 +/- 0.16 log M after epithelial removal in controls (n = 8) (p = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)