The purpose of this study was to evaluate the hypoglycemic effect of the extract from the leaves of Lagerstroemia speciosa L. in normal and streptozotocin (STZ)-induced diabetic rats. Diabetes mellitus (DM) was induced in rats by intraperitoneal injection of streptozotocin at a dose of 45 mg/kg. Extract at the doses of 500, 1000 and 2000 mg/kg, glibenclamide (3 mg/kg) and vehicle were administered orally for 12 days. Blood glucose levels were measured on the 5th and 12th days of the experiment and at three days after ceasing the extract administration. A significant (p<0.05) decrease in fasting blood glucose level was observed in diabetic rats that received the extract at the doses of 1000 and 2000 mg/kg on the 5th and 12th days of administration when compared to the control diabetic group. However, in an oral glucose tolerance test study, none of the doses of the extract showed any effects on blood glucose level in either diabetic or normal rats. The histological examination of liver showed some vacuoles in the cytoplasm of hepatocytes of normal rats receiving the extract at a dose of 2000 mg/kg. This result demonstrates that the water extract from leaves of L. speciosa can reduce fasting blood glucose of STZ-induced diabetic rats. Future studies are needed to identify its mechanism for controlling DM and to investigate its toxicity.
