The effects of arachidonic acid, indomethacin and SC-19220 on guinea-pig tracheal muscle tone.

The effects on guinea-pig tracheal muscle of a prostaglandin synthesis inhibitor, indomethacin, antagonist, SC-19220, and precursor, arachidonic acid have been studied in order to investigate the possible role of prostaglandins in the maintenance of respiratory smooth muscle tone. Indomethacin reduced the resting tone of the muscle, and increasing concentrations reduced the response to arachidonic acid without affecting the response to acetylcholine. Prostaglandins E2 and F2alpha caused contractions of indomethacin-relaxed muxcle, and tachyphylaxis was induced by repeated exposure of the muscle to these agonists, but not to arachidonic acid. The prostaglandin antagonist, SC-19220 relaxed the muscle and abolished its response to a standard dose of prostaglandin E2. Increasing concentrations of SC-19220 reduced the responses to both arachidonic acid and large doses of prostaglandin E2. The responses of tracheal muscle to arachidonic acid are concluded to be partly due to prostaglandin synthesis, supporting the hypothesis that this process maintanins tracheal muscle tone.