Addition of the
calcium inophore,
A 23187, and
cysteine to isolated mononuclear cells from rat peritoneal washings causes a marked increase in the formation of
thromboxane B2 (TxB2) along with the formation of
leukotrienes C and D (LT's). The formation of LT's in this system was inhibited by 6,9-deepoxy-6,9-(phenylimino)-delta 6,8-prostaglandin I1,
U-60,257, or its methyl
ester, U-56,467, (ID50 4.6 and 0.31 microM, respectively). There was no inhibition of TxB2 formation. By contrast, two structurally-related compounds, PGI2 and its stable analog, 6-beta-PGI1, did not affect the formation of either LT's or TxB2. The inhibition of LT formation by
U-60,257 was rapidly reversed after removal of this compound from the cells.
U-60,257 did not inhibit the
cyclooxygenase of human polymorphonuclear leukocytes. Nor did it inhibit formation of 12-L-hydroxy-5,8,10,14-eicosatetraenoic
acid (12-HETE) in human platelets. On the other hand,
U-60,257 inhibited
glutathione S-transferase activity of rat basophil
leukemia cells (ID50, 37 microM), suggesting that this compound may inhibit the last step in LTC biosynthesis. In addition to inhibiting LT synthesis,
U-60,257 also appears to be a competitive inhibitor of the action of LT on the guinea pig ileum, although this inhibition requires a higher
drug concentration than those ordinarily encountered during assay for LT's in U-60,257-treated incubations.