Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase and is metabolised by dimethylarginine dimethylaminohydrolase (DDAH). Elevated levels of circulating ADMA correlate with various cardiovascular pathologies less is known about the cellular effects of altered DDAH activity. We modified DDAH activity in cells and measured the changes in ADMA levels, morphological phenotypes on Matrigel, and expression of vascular endothelial growth factor (VEGF). DDAH overexpressing ECV304 cells secreted less ADMA and when grown on Matrigel had enhanced tube formation compared to untransfected cells. VEGF mRNA levels were 2.1-fold higher in both ECV304 and murine endothelial cells (sEnd.1) over-expressing DDAH. In addition the DDAH inhibitor, S-2-amino-4(3-methylguanidino)butanoic acid (4124W 1 mM), markedly reduced human umbilical vein endothelial cell tube formation in vitro. We have found that upregulating DDAH activity lowers ADMA levels, increases the levels of VEGF mRNA in endothelial cells, and enhances tube formation in an in vitro model, whilst blockade of DDAH reduces tube formation. (C) 2003 Elsevier Inc. All rights reserved.