Basal nitric oxide (NO) activity plays a pivotal role in the regulation of glomerular hemodynamics, and in animal experiments its alteration has been associated with morphological changes characteristic of diabetic nephropathy. The investigators aimed to assess in a prospective study: 1. basal NO activity of renal vasculature and 2. renal hemodynamics to examine whether impairment of basal NO activity of the renal vasculature is related to development and progression of diabetic nephropathy and other cardiovascular endpoints.