Effect of Insulin on Adiponectin and Adiponectin Receptor-1 Expression in Rats with Streptozotocin-induced Type 2 Diabetes

The present study was designed to investigate the effect of insulin on insulin resistance (IR), plasma adiponectin level and expression of adiponectin receptors 1 (AdipoR1) in obese and streptozotocin-induced type 2 diabetic rats. Male Sprague-Dowley rats were randomized to control group and 3 obese experimental groups. Type 2 diabetic mellitus was induced in the 3rd and 4th experimental groups by given 30 mg/kg of a single dose streptozotocin via intraperitoneal injection (i.p.). Fourth group was treated with i.p. 1 IU insulin/kg/day for 6 days before end of the experiment which lasts for 8 weeks while same amount of normal saline was i.p. given to other group. At the end of the study (8 weeks), plasma levels of adiponectin, triglycerides (TG), cholesterol, fasting blood glucose and insulin were measured. Obesity index (OI) and IR were calculated. AdipoR1 mRNA levels in the soleus muscle tissue were semi-quantitated. Hyperlipidemia, hyperinsulinemia and hyperglycemia were observed in both obese and diabetic rats, which were accompanied by hypoadiponectinemia and down regulation of AdipoR1 expression as compared to the control rats. Adiponectin was negatively correlated with all the biochemical parameters assessed. Insulin treatment significantly improved these metabolic abnormalities and effectively restored adiponectin and AdipoR1 to the control level. In conclusion, adiponectin and its receptor-associated cascade may be aberrantly regulated in both obesity and type 2 diabetes and targeting adiponectin and its receptors may offer a novel therapy against obesity and type 2 diabetes.