Antidiabetic activity of methanol extract and fractions of Costus speciosus leaves in normal and alloxan induced diabetic rats

Abstract

Introduction: Costus speciosus is a common plant used for the treatment of diabetes mellitus and various other ailments in traditional medicine in Sri Lanka. The present study was conducted to investigate the hypoglycemic effect of the leaves of C. speciosus in both normal and alloxan induced male Wistar diabetic rat models. Methods: A methanolic extract of the leaves was produced and used for the preliminary phytochemicals screening. Methanol extract was further partitioned with different solvents (n-hexane, chloroform, ethyl acetate and n-butanol) according to their polarity. Male Wistar rats weighing 150-220 g were randomly divided during the test. In vivo antidiabetic activity of partitioned fractions of C. speciosus leaves was performed in normal rats and alloxan induced NIDDM rats. Standard t-test was used to determine statistical significance. Results: A glucose tolerance test with normal rats indicated that peak levels of blood glucose were reached in 90 minutes after the glucose load. It is noteworthy that the test group recorded a significantly (p < 0.05) lower blood glucose level at 90 minutes, indicating that the 80 % methanol extract exerted an overall hypoglycemic effect with normal rats at 90 minutes, despite being challenged with glucose load. The same dose showed an improvement in the glucose tolerance of alloxan-induced diabetic rats, reducing the blood glucose at 90 minutes by 60 % compared with control. These effects were found to be comparable with the effect of the synthetic drug glipizide at a dose of 20 mg/kg. In alloxan-induced diabetic rats, long term administration of the 80% methanolic extract of C. speciosus leaves daily for 6 weeks resulted in a significant lowering of fasting and postprandial serum glucose when compared to diabetic control rats. Conclusion: Diabetic rats group treated with C. speciosus extract displayed significantly (p<0.05) decreased blood glucose level compared to the control group.
 Keywords: Alloxan, Costus speciosus, diabetes mellitus, hypoglycemia, anti-hyperglycemia