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

BACKGROUND
Diabetic nephropathy (DN) is characterized by hyperfiltration and hypertrophy in experimental models of diabetes mellitus (DM). Several studies have demonstrated that the pathophysiologic and morphologic changes in 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 determine the effects that the early diabetic state has on NO production in the kidney of rats with streptozotocin-induced DM.


METHODS
Experimental DM was induced in rats with streptozotocin. Urinary NO production was measured, and levels and activity of the different NOS isoforms were determined by a combination of techniques, including immunoblotting, immunohistochemistry, diaphorase staining, and reverse transcription-polymerase chain reaction.


RESULTS
During the first week of DM, urinary NO metabolites (uNO2 + 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 renal cortex beginning at 30 hours after the induction of DM. NADPH diaphorase staining of renal cortical slices showed reduced NOS activity in the macula densa in diabetic animals. By immunohistochemical staining with antibodies to the different isoforms of NOS, it was found that protein levels of the neuroneal NOS (nNOS) isoform was diminished in the macula densa. No changes 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 NO is reduced in early DM and that this reduction is associated with decreased levels of nNOS activity and protein in the macula densa.