Evaluation of plasma concentration changes of nitric oxide metabolites during glucose tolerance test in type II diabetic rats

Introduction: Repeated hyperglycemia play an important role in development of atherosclerosis in diabetic patients. Endothelium is the first-line defense against atherosclerosis and nitric oxide has a major role in this task. In this study, changes in plasma concentration of nitric oxide metabolites (NOx) during glucose tolerance test were evaluated in type II diabetic rats. Methods: Male neonatal Wistar rats were divided into control and diabetic groups. Type II diabetes was induced by administration of Streptozotocin (100 mg/kg, i.p.) to neonatal rats on day 2. Plasma glucose and NOx concentration were measured on days 7, 30, 45, 60, and 75. Intravenous glucose tolerance test was done in adult rats and blood samples were collected 0, 5, 10, 30, and 60 min after glucose infusion for determining plasma glucose, insulin, and NOx. Two-way mixed (between-within) ANOVA was used for comparing data. Results: Plasma glucose was returned to basal values 60 min after glucose injection in the control group, while in diabetic rats it was higher than basal levels (P < 0.001). After glucose injection, plasma insulin concentration was increased to 4.5 and 1.9 folds in control and diabetic groups, respectively. Basal NOx concentration was higher in diabetic rats (50.4 ± 6.4 vs. 28.8 ± 3.8 μmol/l, P < 0.05). During glucose tolerance test there was 35 and 62 % fall in plasma NOx concentration in control and diabetic groups, respectively. This reduction returned to basal values after 30 min in the control group, while in diabetic rats it was 17% less than basal levels 60 min after glucose injection. Conclusion: Decreased nitric oxide production or increased degradation may be the cause of endothelial dysfunction and atherosclerosis in type II diabetes.