yielding normal results and did not have hypoglycemia unawareness , and they had no major macrocomplications or microcomplications of diabetes . all subjects were nonsmokers and had normal blood cell counts , plasma lipids , plasma electrolytes , and liver and renal function , and they were normotensive . no subject was using medications known to affect neuroendocrine responses to hypoglycemia or that were anti - inflammatory . studies were approved by the ethical committees of the authors ' institutions , and all participants gave written informed consent . baseline characteristics of the two groups of type 1 diabetic patients all study patients were asked to avoid any exercise and to consume their usual weight - maintaining diet for 3 days before each experiment . all people were asked to perform intensive home blood glucose monitoring and to avoid hypoglycemia for at least 5 days before a study . on the day before a study , intermediate or long - acting insulin was discontinued and replaced by injections of regular insulin before breakfast and lunch . each subject was admitted to the research center the evening before an experiment . at that time , all subjects received an evening meal and a continuous low - dose infusion of insulin to normalize plasma glucose . the insulin infusion was adjusted overnight to maintain blood glucose between 4.4 and 7.2 mmol / l . two different experiments were planned for each subject in randomized order , a period of 2 h of hypoglycemia with or without glp-1 infusion . each subject underwent each experiment within at least 2-week interval , but within 4 weeks . at time zero , a primed constant ( 9.0 pmolkgmin ) infusion of insulin ( actrapid ; novonordisk , copenhagen , denmark ) was started and continued for 120 min . the rate of decline of glucose was controlled ( 0.08 mmol / min ) and the glucose nadir ( 2.9 mmol / l ) was achieved using a modification of the glucose clamp technique . during the clamp period , plasma glucose was measured every 5 min and a 20% dextrose infusion was adjusted so that plasma glucose levels were held constant at 2.9  0.1 mmol / l ( 19 ) . potassium chloride ( 20 mmol / l ) was infused during the clamp to reduce insulin - induced hypokalemia . the experiment was repeated with glp-1 infusion at the rate of 0.4 pmolkgmin , according to nauck et al . two different experiments were planned for each subject in randomized order , a period of 2 h of hyperglycemic clamp at the level of hyperglycemia of 15 mmol / l ( 21 ) with or without glp-1 ( 0.4 pmolkgmin ) ( 20 ) infusion . each subject underwent each experiment within at least 2-week interval , but within 4 weeks . at baseline and after 1 and 2 h , blood samples were withdrawn for biochemical assays to measure glycemia , plasma nitrotyrosine , and plasma 8-iso prostaglandin f2alpha ( 8-iso - pgf2a ) , which are markers of oxidative stress , and to measure soluble intercellular adhesion molecule-1 ( sicam-1 ) and interleukin-6 ( il-6 ) , which are markers of inflammation , whereas endothelial function was measured by flow - mediated dilation ( fmd ) . cholesterol , triglycerides , hdl cholesterol , ldl cholesterol , and plasma nitrotyrosine were measured as previously described ( 22 ) . plasma glucose was measured by the glucose - oxidase method , hba1c was measured by high - performance liquid chromatography , insulin was measured by microparticle enzyme immunoassay ( abbott laboratories , wiesbaden , germany ) . plasma 8-iso - pgf2a ( cayman chemical , ann arbor , mi ) , sicam-1 ( british bio - technology , abington , oxon , uk ) , and il-6 ( r&d systems , minneapolis , mn ) were determined with commercially available kits . endothelial function was evaluated measuring the fmd of the brachial artery ( 15 ) . at the end of each test , the subjects laid quietly for 15 min . then , sublingual nitroglycerin ( 0.3 mg ) was administered , and 3 min later the last measurements were performed . the kolmogorov - smirnov algorithm was used to determine whether each variable had a normal distribution . comparisons of baseline data among the groups were performed using unpaired student t test or mann - whitney u test , when indicated . the changes in variables during the tests were assessed by two - way anova with repeated measures or kolmogorov - smirnov test , when indicated . if differences reached statistical significance , then post hoc analyses with two - tailed paired t test or wilcoxon signed rank test for paired comparisons were used to assess differences at individual time periods in the study . correlations between fmd changes and plasma levels of nitrotyrosine , 8-iso - pgf2a , sicam-1 , and il-6 during each experiment were examined using linear regression analysis . two different experiments were planned for each subject in randomized order , a period of 2 h of hypoglycemia with or without glp-1 infusion . each subject underwent each experiment within at least 2-week interval , but within 4 weeks . at time zero , a primed constant ( 9.0 pmolkgmin ) infusion of insulin ( actrapid ; novonordisk , copenhagen , denmark ) was started and continued for 120 min . the rate of decline of glucose was controlled ( 0.08 mmol / min ) and the glucose nadir ( 2.9 mmol / l ) was achieved using a modification of the glucose clamp technique . during the clamp period , plasma glucose was measured every 5 min and a 20% dextrose infusion was adjusted so that plasma glucose levels were held constant at 2.9  0.1 mmol / l ( 19 ) . mmol / l ) was infused during the clamp to reduce insulin - induced hypokalemia . the experiment was repeated with glp-1 infusion at the rate of 0.4 pmolkgmin , according to nauck et al . two different experiments were planned for each subject in randomized order , a period of 2 h of hyperglycemic clamp at the level of hyperglycemia of 15 mmol / l ( 21 ) with or without glp-1 ( 0.4 pmolkgmin ) ( 20 ) infusion . each subject underwent each experiment within at least 2-week interval , but within 4 weeks . at baseline and after 1 and 2 h , blood samples were withdrawn for biochemical assays to measure glycemia , plasma nitrotyrosine , and plasma 8-iso prostaglandin f2alpha ( 8-iso - pgf2a ) , which are markers of oxidative stress , and to measure soluble intercellular adhesion molecule-1 ( sicam-1 ) and interleukin-6 ( il-6 ) , which are markers of inflammation , whereas endothelial function was measured by flow - mediated dilation ( fmd ) . cholesterol , triglycerides , hdl cholesterol , ldl cholesterol , and plasma nitrotyrosine were measured as previously described ( 22 ) . plasma glucose was measured by the glucose - oxidase method , hba1c was measured by high - performance liquid chromatography , insulin was measured by microparticle enzyme immunoassay ( abbott laboratories , wiesbaden , germany ) . plasma 8-iso - pgf2a ( cayman chemical , ann arbor , mi ) , sicam-1 ( british bio - technology , abington , oxon , uk ) , and il-6 ( r&d systems , minneapolis , mn ) were determined with commercially available kits . endothelial function was evaluated measuring the fmd of the brachial artery ( 15 ) . at the end of each test , the subjects laid quietly for 15 min . then , sublingual nitroglycerin ( 0.3 mg ) was administered , and 3 min later the last measurements were performed . the kolmogorov - smirnov algorithm was used to determine whether each variable had a normal distribution . comparisons of baseline data among the groups were performed using unpaired student t test or mann - whitney u test , when indicated . the changes in variables during the tests were assessed by two - way anova with repeated measures or kolmogorov - smirnov test , when indicated . if differences reached statistical significance , then post hoc analyses with two - tailed paired t test or wilcoxon signed rank test for paired comparisons were used to assess differences at individual time periods in the study . correlations between fmd changes and plasma levels of nitrotyrosine , 8-iso - pgf2a , sicam-1 , and il-6 during each experiment were examined using linear regression analysis . similar to previous studies ( 4,5 ) , after 2 h of hypoglycemia fmd significantly decreased , whereas sicam-1 , 8-iso - pgf2a , nitrotyrosine , and il-6 significantly increased compared with basal values ( fig . when hypoglycemia was accompanied by the simultaneous infusion of glp-1 , all these phenomena were significantly attenuated ; fmd decreased less , and sicam-1 , 8-iso - pgf2a , nitrotyrosine , and il-6 were not as increased ( fig . 1 ) . similar results were obtained in the hyperglycemic clamp experiments . according to previous studies ( 23 ) , after 2 h of hyperglycemia fmd significantly decreased and sicam-1 , 8-iso - pgf2a , nitrotyrosine , and il-6 significantly increased compared with basal values ( fig . 2 ) . when hyperglycemia was accompanied by the simultaneous infusion of glp-1 , all these phenomena were significantly attenuated ( fig . glycemia , fmd , sicam-1 , nitrotyrosine , il-6 , and 8-iso - pgf2a in type 1 diabetes during hypoglycemia experiments . open triangles (  ) indicate hypoglycemia and filled triangles (  ) indicate hypoglycemia plus glp-1 . glycemia , fmd , sicam-1 , nitrotyrosine , il-6 , and 8-iso - pgf2a in type 1 diabetes during hyperglycemia experiments . open circles (  ) indicate hyperglycemia and filled circles (  ) indicate hyperglycemia plus glp-1 . * p < 0.01 vs. basal . # p < 0.01 vs. hyperglycemia plus glp-1 .  p < 0.01 vs. hyperglycemia plus glp-1 . endothelial - independent vasodilatation was not affected in any of the experiments . no correlation was found between fmd changes and plasma levels of nitrotyrosine , 8-iso - pgf2a , sicam-1 , and il-6 during each experiment . this study confirms that both hyperglycemia and hypoglycemia induce endothelial dysfunction , oxidative stress , and inflammation in people with type 1 diabetes . however , this study , for the first time , shows that glp-1 administration during hyperglycemia or hypoglycemia can counterbalance the deleterious effects . evidence suggests that both hyperglycemia and hypoglycemia can induce endothelial dysfunction and inflammation , producing oxidative stress ( 3,4,7 ) . furthermore , studies are accumulating showing that glp-1 and its analogs used in clinical practice have antioxidant activity ( 10,15,16 ) . therefore , it is reasonable that glp-1 should , by reducing oxidative stress generation , improve endothelial dysfunction and inflammation generated by both hyperglycemia and hypoglycemia . it is of interest that our study confirms that both hyperglycemia and hypoglycemia can be considered equivalent as proatherosclerotic risk factors , and that they seem to work through the same pathways and mainly by generating oxidative stress ( 1,7 ) . the possibility that glp-1 might directly affect the level of glycemia can not be completely excluded . however , in our opinion , this possibility has been largely minimized by continuously clamping the level of glycemia in both hyperglycemia and hypoglycemia . correlations have not been found in the various parameters during the experiments , particularly between oxidative stress and inflammation and endothelial dysfunction . this can be easily explained . insulin , which has been used during the clamping , has antioxidant activity , although weak ( 24 ) , and it already has been shown that when insulin is introduced in the experiments any kind of association between oxidative stress and another parameter is lost ( 24 ) . in our opinion , this report has important practical implications . the risk of cardiovascular disease in type 1 diabetes , although somewhat neglected , is very high ( 25 ) . the role of hyperglycemia favoring cardiovascular disease in type 1 diabetes seems to be relevant ; however , many other classical and less classical risk factors also seem to be involved ( 7 ) . however , the role of the oxidative stress , in particular , seems relevant in the pathogenesis of these complications in type 1 diabetes . it is well - known that hyperglycemia generates oxidative stress ( 7 ) ; however , data support the hypothesis that the haptoglobin genotype influences cardiovascular risk in type 1 diabetes , favoring the generation of the oxidative stress ( 26 ) . consistent with this hypothesis , the evidence that high -tocopherol levels among patients with renal disease and among those using vitamin supplements was associated with lower cardiovascular risk in type 1 diabetes ( 27 ) . finally , recent findings suggest that hypoglycemia , a frequent event in type 1 diabetes that is emerging as a cardiovascular risk factor , also can produce oxidative stress ( 28 ) . it is currently suggested that glp-1 analogs could be helpful in the management of type 1 diabetes , mainly because they contribute to improving metabolic control and to reducing insulin requirements ( 12 ) . our data suggest that another potential reason to use glp-1 analogs in the management of type 1 diabetes might be their potential to reduce oxidative stress , which is generated during both hyperglycemia and hypoglycemia . in conclusion , this study shows that glp-1 can counterbalance the deleterious effect of both hyperglycemia and hypoglycemia on oxidative stress generation , inflammation , and endothelial function , and it supports the usefulness of glp-1 and its analogs in the management of type 1 diabetes .
objectivehyperglycemia and hypoglycemia currently are considered risk factors for cardiovascular disease in type 1diabetes . 
 both acute hyperglycemia and hypoglycemia induce endothelial dysfunction and inflammation , raising the oxidative stress . 
 glucagon - like peptide 1 ( glp-1 ) has antioxidant properties , and evidence suggests that it protects endothelial function.research design and methodsthe effect of both acute hyperglycemia and acute hypoglycemia in type 1 diabetes , with or without the simultaneous infusion of glp-1 , on oxidative stress ( plasma nitrotyrosine and plasma 8-iso prostaglandin f2alpha ) , inflammation ( soluble intercellular adhesion molecule-1 and interleukin-6 ) , and endothelial dysfunction has been evaluated.resultsboth hyperglycemia and hypoglycemia acutely induced oxidative stress , inflammation , and endothelial dysfunction . 
 glp-1 significantly counterbalanced these effects.conclusionsthese results suggest a protective effect of glp-1 during both hypoglycemia and hyperglycemia in type 1 diabetes .