ARACHIDONIC-ACID METABOLITES AND GLUCOCORTICOID REGULATORY MECHANISM IN CULTURED PORCINE TRACHEAL SMOOTH-MUSCLE CELLS

To elucidate the signal transduction system in the production of prost aglandin E(2) (PGE(2)) by porcine tracheal smooth muscle cells in cult ure (PTSMC), we examined the pattern of arachidonic acid metabolites r eleased from PTSMC and the relationship between bradykinin-stimulated rises in intracellular calcium concentration ([Ca2+](i)) and PGE(2) pr oduction by PTSMC. We next examined the effect of dexamethasone on the se parameters. Bradykinin induced a dose-dependent increase in both th e rise in [Ca2+](i) and PGE(2) production by PTSMC. The increase in [C a2+](i) paralleled an increase in PGE(2) production. High-performance liquid chromatography (HPLC) revealed that dexamethasone-treated PTSMC were suppressed to release arachidonic acid metabolites such as PGE(2 ) and prostaglandin F-2 alpha (PGF(2 alpha)). Incubation of PTSMC with 10(-6)M dexamethasone for 24 h significantly suppressed both the rise in [Ca2+](i) and PGE(2) production by PTSMC in response to bradykinin , and also significantly suppressed bradykinin-stimulated release of r adioactivity from PTSMC prelabeled with H-3-labeled arachidonic acid ( H-3-AA). When PTSMC pretreated with dexamethasone were incubated with 170 nM prostaglandin H-2 (PGH(2)) or 20 mu M arachidonic acid; PTSMC s ynthesized less PGE(2) than control PTSMC. Results suggest that bradyk inin stimulates PTSMC to produce PGE(2) via the signal transduction sy stem including Ca2+, and dexamethasone appeared to suppress PGE(2) pro duction by reducing the activity of cytosolic phospholipase A(2) (cPLA (2)) and PGE(2) synthase. However, we failed to demonstrate the suppre ssion of the activity of cyclooxygenase in PTSMC by dexamethasone. Sin ce the elevation of [Ca2+](i) is necessary for the contraction of airw ay smooth muscles, dexamethasone seems to reduce the contraction of ai rway smooth muscles by suppressing the rise in [Ca2+](i) and the relea se of arachidonic acid metabolites. Reduced production of arachidonic acid metabolites may also contribute to improvement in the bronchial i nflammation.