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The effect of homocysteine (Hcy) on the synthesis of adrenomedullin (ADM) was examined in vascular fibroblasts of rats to explore the possible activity of ADM in cardiovascular diseases. ADM from cultured vascular fibroblasts was measured by Radioimmunoassay (RIA) and was characterized by reverse phase high performance liquid chromatography. ADM mRNA in the fibroblasts was quantitated by competitive RT-PCR. The synthesis of ADM from vascular fibroblasts was increased by Hcy in a concentration dependent manner. ADM content in cultured medium increased by 68%-150% (P < 0.01, as compared to the control) when the fibroblasts were incubated in 50-200 ?mol@L?1 Hcy for 12 h, and the content increased by 55%-98% (P < 0.01) if the incubation lasted for 24 h. Hydrogen peroxide treatment also increased the synthesis of ADM and it promoted ADM synthesis synergetically with Hcy. The changes of ADM content were partially or completely inhibited by the antioxidant N-acetylcysteine (NAC) treatment. Hcy induced the increase of ADM mRNA and the amount of ADM mRNA was increased by 78% as compared with control (P < 0.05). NAC almost completely inhibited the increase of ADM mRNA induced by Hcy. In conclusion, Hcy treatment up-regulated the expression of ADM gene and increased the synthesis of ADM in vascular fibroblasts. Oxidative stress may be involved in the processes of the ADM changes induce by Hcy.