To determine whether normalizing the disorder of DDAH/ADMA/NO pathway is involved in the mechanism underlying PDTC protection against diabetes-induced impaired vasodilation, the serum ADMA concentration and its key metabolic enzyme DDAH activity, protein expression of DDAH and NOS as well as contents of NO metabolites nitrite/nitrate in aortic tissue were measured in the present study. This evidence concerns the gene DDAH1 and diabetes mellitus.