A practical guide for induction of type-2 diabetes in rat: Incorporating a high-fat diet and streptozotocin.
Reduction in nitric oxide (NO) production and bioavailability contribute to the pathogenesis of type 2 diabetes. Administration of nitrate has strong NO-like outcomes in both animals and humans. In this study, we examined the effects of dietary nitrate on glucose tolerance and lipid profile in type 2 diabetic rats. Type 2 diabetes was induced by injection of streptozotocin and nicotinamide. Thirty-two male Wistar rats were divided into 4 groups: controls (C), control+nitrate (CN), diabetes (D), and diabetes+nitrate (DN). For 8 weeks, the CN and DN groups consumed sodium nitrate (100 mg/L in drinking water) while the C and D groups consumed tap water. Serum nitrate+nitrite (NOx), glucose, lipid profile, total antioxidant capacity (TAC), and catalase (CAT) activity were measured before and at the end of the study. Systolic blood pressure (SBP) was measured every 10 days. Intravenous glucose tolerance test (IVGTT) was performed at the end of the study. Serum NOx decreased in diabetic rats and dietary nitrate restored it to normal values. Increases in serum glucose levels was significantly lower in the DN group compared to the D group (24.1% vs. 90.2%; p < 0.05). Nitrate therapy in diabetic rats significantly improved lipid profile, glucose tolerance (AUC: 20264 ± 659 vs. 17923 ± 523; p < 0.05 for D and DN groups respectively) and restored elevated SBP to normal values. Diabetic rats had lower TAC and CAT activity and dietary nitrate restored these to normal status. In conclusion, dietary nitrate prevented increase in SBP and serum glucose, improved glucose tolerance and restored dyslipidemia in an animal model of hyperglycemia.