Active bronchial anaphylaxis in the rat: inhibition by tiaramide.

Intravenous administration of the benzothiazoline derivative tiaramide hydrochloride, to rats actively sensitized to ovalbumin, inhibited immunologic lung reactions in a dose-related manner. Methysergide also inhibited anaphylactic lung reactions. Serotonin, but not other chemical mediators, produced changes in pulmonary mechanics qualitatively similar to those produced by the sensitizing antigen. The bronchoconstrictive action of serotonin was blocked by methysergide and tiaramide. The latter drug also inhibited bronchoconstriction induced by methacholine. The results implicate serotonin as the primary mediator of the respiratory component of systemic anaphylaxis in the rat: however, the mechanism by which tiaramide inhibits anaphylactic bronchoconstriction remains to be elucidated.