Background: In addition to their proliferative and differentiating effects, several growth factors are capable of inducing a sustained airway smooth muscle (ASM) contraction. These contractile effects were previously found to be dependent on Rho-kinase and have also been associated with the production of eicosanoids. However, the precise mechanisms underlying growth factor-induced contraction are still unknown. In this study we investigated the role of contractile prostaglandins and Rho-kinase in growth factor-induced ASM contraction.
Methods: Growth factor-induced contractions of guinea pig open-ring tracheal preparations were studied by isometric tension measurements. The contribution of Rho-kinase, mitogen-activated protein kinase (MAPK) and cyclooxygenase (COX) to these reponses was established, using the inhibitors Y-27632 (1 microM), U-0126 (3 microM) and indomethacin (3 microM), respectively. The Rho-kinase dependency of contractions induced by exogenously applied prostaglandin F2alpha (PGF2alpha) and prostaglandin E2 (PGE2) was also studied. In addition, the effects of the selective FP-receptor antagonist AL-8810 (10 microM) and the selective EP1-antagonist AH-6809 (10 microM) on growth factor-induced contractions were investigated, both in intact and epithelium-denuded preparations. Growth factor-induced PGF2alpha-and PGE2-release in the absence and presence of Y-27632, U-0126 and indomethacin, was assessed by an ELISA-assay.
Results: Epidermal growth factor (EGF)-and platelet-derived growth factor (PDGF)-induced contractions of guinea pig tracheal smooth muscle preparations were dependent on Rho-kinase, MAPK and COX. Interestingly, growth factor-induced PGF2alpha-and PGE2-release from tracheal rings was significantly reduced by U-0126 and indomethacin, but not by Y-27632. Also, PGF2alpha-and PGE2-induced ASM contractions were largely dependent on Rho-kinase, in contrast to other contractile agonists like histamine. The FP-receptor antagonist AL-8810 (10 microM) significantly reduced (approximately 50 %) and the EP1-antagonist AH-6809 (10 microM) abrogated growth factor-induced contractions, similarly in intact and epithelium-denuded preparations.
Conclusion: The results indicate that growth factors induce ASM contraction through contractile prostaglandins - not derived from the epithelium - which in turn rely on Rho-kinase for their contractile effects.