Effects of peptides and amines on isolated guinea pig tracheae as influenced by inhibitors of the metabolism of arachidonic acid.

Stimulants (histamine, acetylcholine and substance P) and relaxants (isoprenaline and bradykinin) of the guinea pig trachea were tested in the absence and presence of mepacrine, eicosatetraynoic acid, BW 755C and indomethacin in order to evaluate the involvement of prostaglandins and congeners in the effects of amines and peptides. While histamine appeared to stimulate tracheal smooth muscle directly, acetylcholine acted in part by promoting the release of contractile leukotrienes. Substance P was unable to express its full stimulating effect because of a likely release of an inhibitory prostaglandin. Isoprenaline inhibited tracheal smooth muscles by a direct action, while the relaxation of the trachea in response to bradykinin appeared to depend on the release of prostaglandins, since it was reduced in the presence of inhibitors of cyclo- and lipooxygenase. It is concluded that enzymes involved in the metabolism of arachidonic acid are present in the guinea pig trachea and are activated both by relaxant and stimulant agents.