Accumulating evidence shows that aldosterone plays an important role in the pathogenesis of renal fibrosis but its mechanism has not been completely defined. Recently, exogenous administration of aldosterone significantly alleviated ischemic states in a model of femoral artery ligated rats, accompanied by an obvious enhancement of VEGF upregulation. We hypothesized that aldosterone may also regulate the expression of VEGF in the kidney. To confirm this, cultured cortical collecting duct epithelial cells (M-1 cell line) were incubated with aldosterone and control media, respectively. The pathway by which aldosterone regulates VEGF expression was tested by the administration of spironolactone, a specific mineralocorticoid receptor (MR) antagonist. VEGF expression was detected by immunofluorescence staining, ELISA, Western blot and RT-PCR. Aldosterone induced an elevation of VEGF excretion in a time- and dose-dependent manner. Western blotting showed a 1.4-fold elevation in cytosolic VEGF expression following aldosterone (10(-8) M) incubation for 48 h (p<0.01). After aldosterone (10(-7) M) incubation for 48 h, the mRNA level of VEGF164 and VEGF120 showed 1.8- and 1.7-fold increases, respectively (p<0.01). This upregulation was almost completely blocked by spironolactone as shown both by mRNA levels and cytosolic protein levels. In addition, the mRNA of aldosterone receptor was detected in M-1 cells. We demonstrated for the first time that aldosterone induced VEGF expression in M-1 cells, an effect mediated by classic mineralocorticoid receptor. This finding provides experimental evidence for the local non-hemodynamic action of aldosterone.