23 September 2008
One of the major biological effects of the endothelium-derived peptide endothelin-1 (ET-1) is its receptor-mediated constrictive action on vascular smooth muscle. In this study, we have examined the effects on the ET-1 pathway of 18 h exposure at 37°C of cultured rat aortic smooth muscle cells to dexamethasone (DEX) and phosphoramidon. ET-1 synthesis was evaluated by radioimmunoassay, ET-1 binding characteristics were determined with [<sup>125</sup>I]iodo-ET-1, and ET-1-induced intracellular calcium mobilization was measured using fura-2-loaded cells. DEX (100 n M) led to a 2- to 3-fold-increase of ET-1 production, it down-regulated ET-1 receptors and reduced ET-1-stimulated calcium mobilization by 70%. In contrast, phosphoramidon (100 µ M) inhibited ET-1 production by 60%, up-regulated ET-1 receptors and potentiated ET-1-induced calcium mobilization by 75%. These results indicate that the regulatory effects of DEX and phosphoramidon on ET-1 receptors are mediated via ET-1 production by the cells. This suggests an autocrine control of ET-1 receptors by endogenous ET-1 synthesis in vascular smooth muscle cells.