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Objective: Experimental studies have shown that glucose releases endothelial nitric oxide (NO) and that NO contributes to renal hyperperfusion in models of diabetes. To examine whether this translates into the human condition, we studied the relationship between glycemic control and renal NO activity in patients with type 2 diabetes., Research Design and Methods: A total of 113 patients with type 2 diabetes and a wide range of HbA1c concentrations were included. Renal plasma flow (RPF) and glomerular filtration rate (GFR) were determined by constant infusion input clearance. Functional NO activity in the renal circulation was determined as change of RPF to infusion of the NO synthase (NOS) inhibitor N(G)-monomethyl-L-arginine (L-NMMA) (4.25 mg/kg). As additional markers, we measured urinary excretion of NO (UNOx) and L-arginine-to-asymmetrical dimethylarginine (ADMA) ratio in plasma., Results: Subjects within the highest tertile of HbA1c concentration had increased RPF (low, medium, and high tertiles 576 ± 17 vs. 585 ± 22 vs. 627 ± 33 mL/min/m(2), P = 0.05 by one-way ANOVA), while GFR was similar across tertiles. The response of RPF to NOS blockade was augmented in subjects with higher HbA1c levels (-55 ± 7 vs. -64 ± 8 vs. -86 ± 8 mL/min, P = 0.04 by one-way ANOVA). Further, L-arginine-to-ADMA ratio and UNOx were increased in subjects with higher HbA1c levels., Conclusions: In line with experimental evidence, we could demonstrate in humans that poor glycemic control is related to higher NO activity and hyperperfusion of the kidney. The renal NO system may thus be a novel therapeutic target for improving renal hemodynamics in patients with diabetes.

Background: Changes of renal nitric oxide (NO) production have been associated with glomerular hyperfiltration, vascular permeability, albuminuria, glomerulosclerosis and tubulointerstitial fibrosis. Several studies demonstrated an up- as well as downregulated expression of NO-synthases (NOS) in experimental diabetic nephropathy. It is still not yet specified whether the regulation and activity of NOS is changed in human diabetic nephropathy., Methods: Renal biopsies and clinical data of 45 patients with diabetic nephropathy and of 10 control subjects were investigated. Glomerular and cortical endothelial NOS (eNOS) and inducible NOS (iNOS) expression were assessed by immunohistochemical staining and related to clinical data such as the duration of diabetes, insulin therapy and arterial hypertension, albuminuria/proteinuria, eGFR according to the formula modification of diet in renal disease (MDRD), presence of vascular complications or diabetic retinopathy., Results: The mean age of patients at biopsy was 60.3 years and the mean duration of diabetes 12.9 years. Expression of cortical and glomerular eNOS was increased in type 2 diabetes (P < 0.05). Increased expression of glomerular and cortical eNOS correlated with more severe vascular complications (r = 0.44; P < 0.05). Glomerular eNOS was strongly increased among different degrees of proteinuria (P < 0.01). In contrast to expression levels of eNOS, the glomerular expression pattern of iNOS changed from an endothelial pattern in glomeruli with preserved morphology towards expression predominantly by inflammatory cells., Conclusions: Thus, increased eNOS expression by the renal endothelium could be demonstrated in type 2 diabetic nephropathy, whereas iNOS was unchanged but spatially differentially expressed. The eNOS expression was related to vascular lesions and the degree of proteinuria.