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      Correction of Endothelial Dysfunction in Diabetic Female Rats by Tetrahydrobiopterin and Chronic Insulin

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          Abstract

          Diabetes-induced vascular dysfunction has mainly been studied in males. However, the mechanisms involved may not correspond to those in females. Here we analyzed the effects of tetrahydrobiopterin (BH<sub>4</sub>) and chronic insulin on the physiology of mesenteric arterioles of alloxan-diabetic female rats. The parameters studied were the mesenteric arteriolar reactivity (intravital microscopy), nitric oxide synthase (NOS) activity (conversion of L-arginine to L-citrulline), eNOS gene expression (RT-PCR), NO production (diaminofluorescein), reactive oxygen species (ROS) generation (intravital fluorescence microscopy) and Cu/Zn superoxide dismutase (SOD) activity (spectrophotometry) and gene expression (RT-PCR). The reduced endothelium-dependent vasodilation of diabetic females was corrected by both BH<sub>4</sub> and insulin. NOS activity was decreased by diabetes, but insulin did not correct it. However, NOS expression was not modified by either diabetes or insulin. Arterioles of diabetic rats exhibited lower NO production, which was fully corrected by BH<sub>4</sub> and only partially by insulin. ROS generation was increased in diabetic rats, and both BH<sub>4</sub> and insulin normalized it. Diabetes did not change SOD activity and gene expression. However, insulin increased SOD activity but not its expression. Our data suggest that, similarly to males, endothelial dysfunction in female diabetic rats involves an altered ROS/NO imbalance. In contrast to males, however, insulin does not regulate NOS in the microcirculation of diabetic females.

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          Most cited references 28

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          Detection and imaging of nitric oxide with novel fluorescent indicators: diaminofluoresceins.

          Nitric oxide is a gaseous, free radical which plays a role as an intracellular second messenger and a diffusable intercellular messenger. To obtain direct evidence for NO functions in vivo, we have designed and synthesized diaminofluoresceins (DAFs) as novel fluorescent indicators for NO. The fluorescent chemical transformation of DAFs is based on the reactivity of the aromatic vicinal diamines with NO in the presence of dioxygen. The N-nitrosation of DAFs, yielding the highly green-fluorescent triazole form, offers the advantages of specificity, sensitivity, and a simple protocol for the direct detection of NO (detection limit 5 nM). The fluorescence quantum efficiencies are increased more than 100 times after the transformation of DAFs by NO. Fluorescence detection with visible light excitation and high sensitivity enabled the practical assay of NO production in living cells. Membrane-permeable DAF-2 diacetate (DAF-2 DA) can be used for real-time bioimaging of NO with fine temporal and spatial resolution. The dye was loaded into activated rat aortic smooth muscle cells, where the ester bonds are hydrolyzed by intracellular esterase, generating DAF-2. The fluorescence in the cells increased in a NO concentration-dependent manner.
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            Insulin-mediated skeletal muscle vasodilation is nitric oxide dependent. A novel action of insulin to increase nitric oxide release.

            The purpose of this study was to examine whether insulin's effect to vasodilate skeletal muscle vasculature is mediated by endothelium-derived nitric oxide (EDNO). N-monomethyl-L-arginine (L-NMMA), a specific inhibitor of NO synthase, was administered directly into the femoral artery of normal subjects at a dose of 16 mg/min and leg blood flow (LBF) was measured during an infusion of saline (NS) or during a euglycemic hyperinsulinemic clamp (HIC) designed to approximately double LBF. In response to the intrafemoral artery infusion of L-NMMA, LBF decreased from 0.296 +/- 0.032 to 0.235 +/- 0.022 liters/min during NS and from 0.479 +/- 0.118 to 0.266 +/- 0.052 liters/min during HIC, P < 0.03. The proportion of NO-dependent LBF during NS and HIC was approximately 20% and approximately 40%, respectively, P < 0.003 (NS vs. HIC). To elucidate whether insulin increases EDNO synthesis/release or EDNO action, vasodilative responses to graded intrafemoral artery infusions of the endothelium-dependent vasodilator methacholine chloride (MCh) or the endothelium-independent vasodilator sodium nitroprusside (SNP) were studied in normal subjects during either NS or HIC. LBF increments in response to intrafemoral artery infusions of MCh but not SNP were augmented during HIC versus NS, P < 0.03. In summary, insulin-mediated vasodilation is EDNO dependent. Insulin vasodilation of skeletal muscle vasculature most likely occurs via increasing EDNO synthesis/release. Thus, insulin appears to be a novel modulator of the EDNO system.
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              Tetrahydrobiopterin improves endothelium-dependent vasodilation by increasing nitric oxide activity in patients with Type II diabetes mellitus.

              Tetrahydrobiopterin is an essential cofactor of nitric oxide synthase, and its deficiency decreases nitric oxide bioactivity. Our aim was to find whether supplementation of tetrahydrobiopterin could improve endothelial dysfunction in diabetic patients. Forearm blood flow responses to the endothelium-dependent vasodilator acetylcholine (0.75-3.0 microg x 100 ml(-1) x min(-1)) and to the endothelium-independent vasodilator sodium nitroprusside (0.1-1.0 microg x 100 ml(-1) x min(-1)) before and during concomitant intra-arterial infusion of tetrahydrobiopterin (500 microg/min) were measured by venous occlusion plethysmography in 12 control subjects and 23 patients with Type II (non-insulin-dependent) diabetes mellitus. In control subjects, tetrahydrobiopterin had no effect on the dose-response curves to acetylcholine and sodium nitroprusside. In contrast, in diabetic patients, the attenuated endothelium-dependent vasodilation to acetylcholine was considerably improved by concomitant treatment with tetrahydrobiopterin, whereas the endothelium-independent vasodilation was not affected. This beneficial effect of tetrahydrobiopterin in diabetic patients could be completely blocked by N(G)-monomethyl-L-arginine. These findings suggest the possibility that endothelial dysfunction in Type II diabetes might be related to decreased availability of tetrahydrobiopterin.
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                Author and article information

                Journal
                JVR
                J Vasc Res
                10.1159/issn.1018-1172
                Journal of Vascular Research
                S. Karger AG
                1018-1172
                1423-0135
                2006
                July 2006
                28 July 2006
                : 43
                : 4
                : 309-320
                Affiliations
                Departments of aPharmacology, and bPhysiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil
                Article
                93196 J Vasc Res 2006;43:309–320
                10.1159/000093196
                16682803
                © 2006 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Figures: 7, Tables: 3, References: 39, Pages: 12
                Categories
                Research Paper

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