Arachidonic acid metabolites and glucocorticoid regulatory mechanism in cultured porcine tracheal smooth muscle cells

Abstract

To elucidate the signal transduction system in the production of prostaglandin E2 (PGE2) by porcine tracheal smooth muscle cells in culture (PTSMC), we examined the pattern of arachidonic acid metabolites released from PTSMC and the relationship between bradykinin-stimulated rises in intracellular calcium concentration ([Ca2+]i) and PGE2 production by PTSMC. We next examined the effect of dexamethasone on these parameters. Bradykinin induced a dose-dependent increase in both the rise in [Ca2+]i and PGE2 production by PTSMC. The increase in [Ca2+]i paralleled an increase in PGE2 production. High-performance liquid chromatography (HPLC) revealed that dexamethasone-treated PTSMC were suppressed to release arachidonic acid metabolites such as PGE2 and prostaglandin F2 alpha (PGF2 alpha). Incubation of PTSMC with 10(-6)M dexamethasone for 24 h significantly suppressed both the rise in [Ca2+]i and PGE2 production by PTSMC in response to bradykinin, and also significantly suppressed bradykinin-stimulated release of radioactivity from PTSMC prelabeled with 3H-labeled arachidonic acid (3H-AA). When PTSMC pretreated with dexamethasone were incubated with 170 nM prostaglandin H2 (PGH2) or 20 microM arachidonic acid; PTSMC synthesized less PGE2 than control PTSMC. Results suggest that bradykinin stimulates PTSMC to produce PGE2 via the signal transduction system including Ca2+, and dexamethasone appeared to suppress PGE2 production by reducing the activity of cytosolic phospholipase A2 (cPLA2) and PGE2 synthase. However, we failed to demonstrate the suppression of the activity of cyclooxygenase in PTSMC by dexamethasone. Since the elevation of [Ca2+]i is necessary for the contraction of airway smooth muscles, dexamethasone seems to reduce the contraction of airway smooth muscles by suppressing the rise in [Ca2+]i and the release of arachidonic acid metabolites. Reduced production of arachidonic acid metabolites may also contribute to improvement in the bronchial inflammation.

Glucocorticoids shift arachidonic acid metabolism toward endocannabinoid synthesis: A non-genomic anti-inflammatory switch

“…Bradykinin stimulates a rise in intracellular calcium concentration leading to PGE 2 production in cultured porcine tracheal smooth muscle cells, an effect that is suppressed by dexamethasone pretreatment for 24 h. Dexamethasone also suppressed bradykinin-stimulated release of radioactivity from cells that had been prelabeled with 3 H-arachidonic acid. These findings suggest that dexamethasone suppressed PGE 2 production by reducing the activity of cytosolic PLA 2 and PGE 2 synthase (Tanaka et al, 1995).…”

Cytosolic phospholipase A2α mediates Pseudomonas aeruginosa LPS-induced airway constriction of CFTR -/- mice

“…Recent studies reported that accumulation and/or hypertrophy of airway SMCs contribute to airway narrowing and airway constriction in CF patients [32,33]. A previous study showed that bradykinin-induced contraction of airway SMC occurs, in part, via a process involving a rise of [Ca 2+ ] and enhanced release of AA [34]. More recently, it has been shown that the AA metabolite 20-HETE induces sustained contraction of isolated guinea pig airway SMC [35].…”

Airway Remodeling: Effect of Current and Future Asthma Therapies

“…Glucocorticoids have been reported to reduce airway constriction to various stimuli, including histamine, bradykinin and acetylcholine [58][59][60][61]. The mechanisms by which glucocorticoids reduce constriction have been investigated and include altered inositol phosphate formation and cyclic AMP levels, through receptor uncoupling or downregulation, as well as altered calcium mobilization or Na + /K + ATPase potentiation.…”