Fifty diabetic and hypertensive patients will be randomized at first visit, submitted to endothelial function testing by the Endo-PAT 2000 device, and divided into 2 groups: group 1 will receive vildagliptin (100 mg/day, divided in 2 times) added-on to metformin (500 to 2550 mg/day, according to glycemic control) and group 2 will receive glibenclamide (5 to 20 mg/day, according to glycemic control) added-on to metformin. Blood samples will be collected after 12-hour overnight fast at screening visit and 12 weeks after treatment with vildagliptin (group 1) and glibenclamide (group 2).