Arachidonic acid metabolites and airway epithelium-dependent relaxant

Exogenous arachidonic acid (1 O to 1 0 M) contracted epithe-hum-free guinea pig tracheal strips. Intact tracheal strips were contracted slightly by low concentrations of arachidonic acid (1 O to 1 O- M), but higher concentrations relaxed them. In contrast, when tracheal strips were precontracted with histamine or carbachol, exogenous arachidonic acid had no effect on epithelium-free preparations but induced concentration-depend-ent (1 0-8 to 1 0- M) relaxation of intact tracheal strips. The effects of arachidonic acid both in epithelium-free and epithelium-contning trachea were blocked by either indomethacin (1 0 M) or aspirin (1 0 M). Studies on the effects of exogenous arachidonic acid, performed with a “sandwich protocol, ” dem-onstrated that the postulated airway epithelium-dependent relax-ant factor released by an intact tracheal strip relaxes an adjacent epithelium-free strip in the same organ bath. This relaxation i