After fasting 18 hours, the rats were injected intravenously through tail vein with a single dose of 40mg/kg STZ (Sigma, St. Louis, Mo, USA), freshly dissolved in citrate buffer (pH 4.5). After injection, the rats had free access to food and water and were given 5% glucose solution to drink overnight to counter hypoglycaemic shock. Diabetes in rats were observed by moderate polydipsia and marked polyuria.