nitroarginine and Insulin-Resistance

Obesity is related to insulin resistance and hypertension, but the underlying mechanisms are unclear. Insulin exerts both vasodilator and vasoconstrictor effects on muscle resistance arteries, which may be differentially impaired in obesity.. To investigate whether vasodilator and vasoconstrictor effects of insulin are impaired in muscle resistance arteries of obese rats and the roles of Akt and endothelial NO synthase (eNOS).. Effects of insulin were studied in resistance arteries isolated from cremaster muscles of lean and obese Zucker rats. In arteries of lean rats, insulin increased activity of both NO and endothelin (ET-1), resulting in a neutral effect under basal conditions. In arteries of obese rats, insulin induced endothelin-mediated vasoconstriction (-15 +/- 5% at 1 nM, P < 0.05 vs. lean). Insulin induced vasodilatation during endothelin receptor blockade in arteries of lean rats (20 +/- 5% at 1 nM) but not in those of obese rats. Inhibition of NO synthesis increased vascular tone (by 12 +/- 2%) and shifted insulin-mediated vasoreactivity to vasoconstriction (-25 +/- 1% at 1 nM) in lean rats but had no effect in arteries of obese rats, indicating reduced NO activity. Protein analysis of resistance arteries revealed that insulin-mediated activation of Akt was preserved in obese rats, whereas expression of eNOS was markedly decreased.. Vasodilator but not vasoconstrictor effects of insulin are impaired in muscle resistance arteries of obese rats, and this selective impairment is associated with decreased protein levels of eNOS. These findings provide a new mechanism linking obesity to insulin resistance and hypertension.

Topics: Animals; Blotting, Western; Endothelin Receptor Antagonists; Endothelin-1; Enzyme Inhibitors; In Vitro Techniques; Insulin; Insulin Resistance; Muscle, Smooth, Vascular; Nitric Oxide Synthase Type III; Nitroarginine; Obesity; Oligopeptides; Oncogene Protein v-akt; Rats; Rats, Zucker; Receptors, Endothelin; Vasoconstriction; Vasodilation

This study assessed the effect of metformin treatment on insulin, mean arterial pressure (MAP), and endothelial function in insulin-resistant (IR) rats. In addition, we assessed the direct effect of metformin in vitro. Sprague-Dawley rats were randomized to control (n=28) or IR (n=28) groups. Rats were further randomized to receive metformin (300 mg/kg) or placebo for 2 weeks. MAP and insulin were measured. Subsequently, a third-order branch of the superior mesenteric artery was isolated, and endothelial function was assessed. Specifically, dose-response experiments of acetylcholine (ACh) with or without N-nitro-L-arginine (LNNA) were performed. For in vitro experiments, mesenteric arteries were removed from untreated control and IR rats and treated with metformin (100 micromol/L) before ACh+/-LNNA. MAP and insulin levels were improved in IR-metformin compared with IR-placebo rats. Maximal relaxation (E(max)) to ACh was enhanced in IR-metformin (92+/-2%) compared with IR-placebo rats (44+/-4%) (P<0.05). Relaxation in response to ACh+LNNA was greater in IR-metformin (33+/-4%) than in IR-placebo rats (12+/-4%) but remained depressed compared with control rats (E(max)=68+/-5%). The control group was not affected by metformin. In vitro treatment of arteries with metformin in response to ACh produced results similar to those in the experiments with metformin-treated rats. Although metformin improves metabolic abnormality in IR rats, this action does not appear to mediate its effect on vascular function. Both in vivo and in vitro metformin improved ACh-induced relaxation in IR rats to control levels, apparently through nitric oxide-dependent relaxation. These data suggest that metformin improves vascular function through a direct mechanism rather than by improving metabolic abnormalities.

Topics: Acetylcholine; Animals; Blood Pressure; Diabetes Mellitus, Type 2; Diabetic Angiopathies; Endothelium, Vascular; Humans; Hypoglycemic Agents; In Vitro Techniques; Insulin; Insulin Resistance; Male; Metformin; Nitric Oxide; Nitroarginine; Rats; Rats, Sprague-Dawley; Triglycerides; Vasodilation

Mechanical responses to superoxide anion scavengers and nitric oxide (NO) synthase inhibitors in aortic endothelial cells were compared in normal chow-fed rats and those made insulin-resistant by feeding of fructose. Cu(2+), Zn(2+)-superoxide dismutase-induced vascular relaxation and superoxide production, measured by the lucigenin-enhanced chemiluminescence method, were greater in aortas from fructose-fed rats than in those from normal chow-fed rats. N(G)-nitro-L-arginine-induced contractions due to suppression of NO synthase activity were smaller in aortas from fructose-fed rats. Vascular mechanical responses may reflect the generation of superoxide and NO by the endothelium. Thus, isometric tension studies may be a useful tool for evaluating the production of these radicals in blood vessels.

Topics: Animals; Aorta, Thoracic; Blood Pressure; Endothelium, Vascular; Enzyme Inhibitors; Free Radicals; Hypoglycemic Agents; In Vitro Techniques; Insulin; Insulin Resistance; Isometric Contraction; Male; Muscle Contraction; Muscle Relaxation; Muscle, Smooth, Vascular; Nitric Oxide; Nitroarginine; Rats; Rats, Sprague-Dawley; Superoxide Dismutase; Superoxides

The JCR:LA-corpulent rat is a unique animal model of human vascular disease that exhibits a profound insulin resistance, vasculopathy, and cardiovascular dysfunction. We tested the hypothesis that the defects affect endothelial and smooth muscle function of the coronary microvasculature as well as cardiac contractility. Coronary, myocardial and aortic function were assessed in obese (homozygous for the cp gene, cp/cp) and lean (heterozygous or homozygous normal, +/?) littermates aged 7 and 18 weeks.. Coronary endothelial relaxation was examined in isolated perfused hearts by determining the effect of bradykinin (0. 1-1000 nmol l(-1)) on coronary perfusion pressure (CPP), myocardial mechanical function was evaluated in terms of left-ventricular developed pressure (LVDevP), and aortic relaxation with the endothelium-dependent agonist, A 23187 (1-1000 nmol l(-1)).. In rats aged 7 weeks, bradykinin reduced CPP from 133+/-1 mmHg to 43+/-1 mmHg (-67%) in lean rats, but only to 64+/-3 mmHg (-52%) in corpulent rats (n=6, P<0.05). Similar differences were found in rats aged 18 weeks (n=8). Inhibition of NO synthase with N(G)-nitro-L-arginine (L-NNA; 0.2 mmol l(-1)) impaired, and tetrahydrobiopterin (0.1 mmol l(-1)), a NO synthase cofactor, restored relaxation in cp/cp rats. Spermine/NO equally reduced CPP in both groups (-58%). Mechanical function was similar in lean and corpulent rats, aortic endothelial relaxation was attenuated by approximately 30% and aortic smooth muscle function was normal (7 weeks) or improved (18 weeks) in the cp/cp genotype.. These results suggest that (i) there is a specific impairment of NO-mediated relaxation of the coronary resistance vessels in the JCR:LA-corpulent rat that is not associated with impaired baseline myocardial contractility, and (ii) exogenous tetrahydrobiopterin reversed the relaxation defects that are part of the vascular complications typical for the insulin resistance syndrome.

Topics: Animals; Antioxidants; Aorta, Thoracic; Biopterins; Bradykinin; Calcimycin; Dose-Response Relationship, Drug; Endothelium, Vascular; Enzyme Inhibitors; In Vitro Techniques; Insulin Resistance; Ionophores; Male; Microcirculation; Myocardial Contraction; Nitric Oxide Synthase; Nitroarginine; Obesity; Perfusion; Rats; Rats, Inbred Strains