TANNIN STIMULATES ARACHIDONIC-ACID RELEASE FROM BOVINE TRACHEAL EPITHELIAL-CELLS

Condensed tannin, isolated from cotton bracts extract (CBE), increases arachidonic acid (AA) release from rabbit alveolar macrophages and in hibits its subsequent reacylation. We determined whether tannin from C BE had any effect upon AA release in bovine tracheal epithelial cells (BTE). [C-14]AA release was measured at timed intervals after addition of various concentrations of tannin to BTE cells grown to confluence in the presence of [C-14]AA. Tannin caused a time- and dose-dependent release of AA from airway cells, with a maximum release occurring at 1 min in the presence of 100 mu g/ml of tannin, and was confirmed by hi gh-pressure liquid chromatography. The pattern of release was similar to that observed with bradykinin (2 x 10(-6) M). AA release by tannin was partially inhibited by indomethacin (10(-5) M) but not by 5,8,11,1 4-eicosatetraynoic acid (ETYA; 10(-5) M). Both of these drugs were eff ective in inhibiting bradykinin-induced AA release. In addition, AA re lease was not inhibited by cycloheximide. Endotoxin at 100 pg/ml and h igher also caused a time-dependent release of AA that was not inhibita ble by indomethacin or ETYA. Tannin-induced AA release was inhibited b y pretreatment with pertussis toxin but not by neomycin, an inhibitor of phospholipase C (PLC). Neither pertussis toxin nor neomycin had any effect upon endotoxin-induced AA release. In other experiments, neith er tannin nor endotoxin had any effect on [C-14]AA uptake by BTE. Thes e data demonstrate that tannin at low concentrations and endotoxin at high concentrations increase AA release by BTE cells. The AA released by tannin is partially metabolized by the cyclooxygenase pathway We hy pothesize that tannin-induced AA release is not mediated by PLC but ma y be mediated by other phospholipases, including PLA(2).