We investigated the role of epithelial modulation of contraction caused by endothelin-1 in airway smooth muscle in guinea pigs in situ. Airway responses were assessed isometrically as tracheal force and simultaneously as change in lung resistance. Intravenous administration of 10(-8) mol/kg endothelin-1 caused a biphasic response in tracheal active tension: initial relaxation (-0.82 +/- 0.22 g/cm after 30 s, p less than 0.05 versus baseline) followed by contraction (1.65 +/- 0.28 g/cm after 7 min, p less than 0.05 versus baseline). Endothelin-1 also elicited immediate bronchoconstriction; lung resistance increased from 0.148 +/- 0.030 to 0.992 +/- 0.274 cm H2O/L/s (p less than 0.005) after 10(-8) mol/kg endothelin-1 given intravenously. Active tension elicited by 10(-8) mol/kg endothelin-1 after removal of the epithelium from the tracheal segment (0.59 +/- 0.16 g/cm) was less than in segments with an intact epithelium (1.65 +/- 0.28 g/cm, p less than 0.01). Both tracheal contraction and bronchoconstriction were attenuated by pretreatment with indomethacin orally, BW 755C intravenously, or substitution of endothelin-C-terminal hexapeptide for endothelin-1. However, the initial tracheal relaxation response was similar after each intervention. These data suggest actions of endothelin-1 that have not been demonstrated previously: (1) endothelin-1 elicits a biphasic response in tracheal smooth muscle (an initial relaxation response elicited by the carboxy-terminal residues and a later contractile response that requires synthesis of a cyclooxygenase mediator) and (2) epithelium adjacent to the airway smooth muscle modulates contraction elicited by endothelin-1.