Renal nitric oxide production during the early phase of experimental diabetes mellitus

Background. Diabetic nephropathy (DN) is characterized by hyperfiltration a nd hypertrophy in experimental models of diabetes mellitus (DM). Several st udies have demonstrated that the pathophysiologic and morphologic changes i n DN are mediated by either an increase or decrease in renal nitric oxide ( NO) production and/or activity. The goal of the present study was to determ ine the effects that the early diabetic state has on NO production in the k idney of rats with streptozotocin-induced DM. Methods. Experimental DM was induced in rats with streptozotocin. Urinary N O production was measured, and levels and activity of the different NOS iso forms were determined by a combination of techniques, including immunoblott ing, immunohistochemistry, diaphorase staining, and reverse transcription-p olymerase chain reaction. Results. During the first week of DM, urinary NO metabolites (uNO(2) + NO3) were reduced as compared with controls, which were unrelated to changes in serum levels of NO. Total NO synthase (NOS) activity was reduced in the re nal cortex beginning at 30 hours after the induction of DM. NADPH diaphoras e staining of renal cortical slices showed reduced NOS activity in the macu la densa in diabetic animals. By immunohistochemical staining with antibodi es to the different isoforms of NOS, it was found that protein levels of th e neuroneal NOS (nNOS) isoform was diminished in the macula densa. No chang es were found in the levels of endothelial NOS (eNOS) activity and protein in the renal cortex in the early diabetic state. Conclusions. This study provides strong evidence that renal production of N O is reduced in early DM and that this reduction is associated with decreas ed levels of nNOS activity and protein in the macula densa.