Background:Diabetes mellitus, for a long time, has been treated with plant derived medicines in Sri Lanka.Aim:The aim of this study is to determine the efficacy and dose response of oral antihyperglycaemic activity of eight Sri Lankan medicinal plant extracts, which are used to treat diabetes in traditional medicine in diabetic rats.Materials and Methods:Medicinal plants selected for the study on the basis of documented effectiveness and wide use among traditional Ayurveda physicians in the Southern region of Sri Lanka for the treatment of diabetes mellitus. The effect of different doses of aqueous stem bark extracts of Spondias pinnata (Anacardiaceae), Kokoona zeylanica (Celastraceae), Syzygium caryophyllatum (Myrtaceae), Gmelina arborea (Verbenaceae), aerial part extracts of Scoparia dulcis (Scrophulariaceae), Sida alnifolia (Malvaceae), leaf extract of Coccinia grandis (Cucurbitaceae) and root extract of Languas galanga (Zingiberaceae) on oral glucose tolerance test was evaluated. A single dose of 0.25, 0.50, 0.75, 1.00, 1.25, 2.00 g/kg of plant extract was administered orally to alloxan induced (150 mg/kg, ip) diabetic Wistar rats (n = 6). Glibenclamide (0.50 mg/kg) was used as the standard drug. The acute effect was evaluated over a 4 h period using area under the oral glucose tolerance curve.Statistical Analysis:The results were evaluated by analysis of variance followed by Dunnett's test.Results:The eight plant extracts showed statistically significant dose dependent improvement on glucose tolerance (P < 0.05). The optimum effective dose on glucose tolerance for six extracts was found to be 1.00 g/kg in diabetic rats with the exception of C. grandis: 0.75 g/kg and L. galanga: 1.25 g/kg.Conclusion:The aqueous extract of G. arborea, S. pinnata, K. zeylanica, S. caryophyllatum, S. dulcis, S. alnifolia, L. galanga and C. grandis possess potent acute antihyperglycaemic activity in alloxan induced diabetic rats.
Gmelina arborea Roxb. (common name: Et-demata, Family: Verbenaceae) has been used traditionally in Sri Lanka as a remedy against diabetes mellitus. The objective of the present study was to evaluate antidiabetic mechanisms of the aqueous bark extract of G. arborea in streptozotocin induced (STZ) diabetic male Wistar rats. Aqueous bark extract of G. arborea (1.00 g/kg) and glibenclamide as the standard drug (0.50 mg/kg) were administered orally using a gavage to STZ diabetic rats (65 mg/kg, ip) for 30 days. The antidiabetic mechanisms of aqueous extract of G. arborea (1.00 g/kg) were determined at the end of the experiment. The fasting blood glucose concentration was significantly lowered and the serum insulin and C-peptide concentrations were increased by 57% and 39% in plant extract treated rats on day 30, respectively (p < 0.05). The histopathology and immunohistochemistry results of the plant extract treated group showed a regenerative effect on β-cells of the pancreas in diabetic rats. In addition, serum lipid parameters were improved in G. arborea extract treated diabetic rats. The results revealed that the aqueous stem bark extract of G. arborea (1.00 g/kg) showed beneficial effects against diabetes mellitus through upregulating the β-cell regeneration and biosynthesis of insulin in diabetic rats.
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