Increased response of renal perfusion to the antioxidant vitamin C in type 2 diabetes

Abstract

Background. Reactive oxygen species play a major role in the development of endothelial dysfunction. It is as yet unspecified whether increased oxidative stress contributes to endothelial dysfunction of the renal vasculature in patients with type 2 diabetes. Methods. Renal haemodynamics were studied in 20 patients with type 2 diabetes and arterial hypertension (age 62 ± 5 years) and 20 non-diabetic hypertensive patients at baseline and following infusions of the nitric oxide synthase inhibitor, N^G-monomethyl-l-arginine (l-NMMA; 4.25 mg/kg); the substrate of nitric oxide synthase, l-arginine (100 mg/kg); and the antioxidant, vitamin C (3 g, co-infused with l-arginine 100 mg/kg). Results. The response of renal plasma flow (RPF) to l-NMMA (−54 ± 62 and −45 ± 42 ml/min/1.73 m²; P = NS) and l-arginine (+46 ± 36 and +49 ± 25 ml/min/1.73 m²; P = NS) was not different between diabetic and non-diabetic patients. In contrast, vitamin C induced a more pronounced increase in RPF in diabetic than in non-diabetic patients when co-infused with l-arginine (+71±47 and +43±33 ml/min/1.73 m²; PConclusions. The difference in the response of renal perfusion to an antioxidant suggests increased formation of reactive oxygen species and thereby reduced nitric oxide bioavailability in the renal vasculature of patients with type 2 diabetes.