The investigators will assess whether the DPP-inhibitor sitagliptin will ameliorate glucocorticoid-induced impairment of glucose metabolism and beta-cell dysfunction and thus could be used as a prophylaxis for glucocorticoid-induced diabetes. Therefore the investigators will administer in males with the metabolic syndrome 30 mg prednisolone daily for two weeks and give simultaneously sitagliptin 100 mg daily. Subjects will undergo at baseline and after two weeks of treatment several tests to assess changes in glucose metabolism.