Abstract

The effects of the peptidoleukotrienes C4 (LTC4), D4 (LTD4), E4 (LTE4) and a series agonists and antagonists on arachidonic acid metabolism were characterized in minced guinea pig lung. In response to LTD4, guinea pig lung utilized and converted the endogenous arachidonic acid into a variety of cyclooxygenase metabolites [prostaglandins (PGs) E2, F2 alpha, 6-keto-F1 alpha and thromboxane (Tx) B2] and lipoxygenase metabolites (5,12-dihydroxy-6,8,11,14-eicosatetraneoic acid and 5,15-dihydroxy-5,9,11,13-eicosatetraneoic acid). Using radioimmunoassays, the stable, pharmacologically important metabolites of the cyclooxygenase pathway, 6-keto-PGF1 alpha and TxB2, were quantitated. LTD4, LTE4 and several synthetic agonists induced dose-dependent synthesis and release of TxB2 and 6-keto-PGF1 alpha. Agonist-induced synthesis and release of 6-keto-PGF1 alpha and TxB2 was time-dependent and was maximal after 10 to 12 min of incubation. The slow-reacting substance of anaphylaxis antagonist, FPL 55712, and the newly reported dithioacetal LTD4 receptor antagonists (SKF 102922 and SKF 102081) did not induce synthesis and release of TxB2 and 6-keto-PGF1 alpha in concentrations that blocked the agonist-induced smooth muscle contraction. Preincubation with these antagonists inhibited the synthesis and release of prostanoids induced by LTD4 in the guinea pig lung. Islet activating protein, which inactivates the inhibitory guanine nucleotide binding protein (Gi protein), partially inhibited the agonist-induced synthesis and release of prostanoids. Furthermore, the receptor binding affinities and/or the myotonic activities of the LTD4 agonists correlated linearly with the agonist-induced prostanoid synthesis and release effect.(ABSTRACT TRUNCATED AT 250 WORDS)