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The present study evaluates the antidiabetic and antihyperlipidemic effects of 125 mg/kg, 250 mg/kg and 500 mg/kg of the Morinda lucida aqueous stem bark extract (MLASE) in alloxan-induced diabetic rats for 8 days based on the African traditional use of the water infusion of the stem bark of Morinda lucida (family: Rubiaceae) in the local management of diabetes mellitus and hyperlipidemia by the Yoruba herbal practitioners (Southwest Nigeria). In this study, experimental diabetes was induced in Wistar rats through intraperitoneal injection of 120 mg/kg of alloxan monohydrate dissolved in cold 0.9% normal saline and sustained hyperglycemia was monitored over the successive three days. Diabetic rats [with the fasting blood glucose (FBG) levels greater or equal to 200 mg/dl] randomly divided into Groups II-VI of six rats per group were daily and orally treated with 10 m/kg of distilled water, 5 mg/kg of glibenclamide, 125 mg/kg, 250 mg/kg and 500 mg/kg of MLASE, respectively, for 8 days after which the rats were sacrificed humanely under inhaled diethyl ether. FBG were determined in the treated diabetic rats on the 1st and 8th day of oral extract treatments while the blood samples for the lipid assays of were obtained directly from heart chambers through cardiac puncture on the 8th day after an overnight fasting. In addition, preliminary qualitative and quantitative analyses of the aqueous stem bark of Morinda lucida were conducted using standard procedures. Results showed that the preliminary qualitative analysis of MLASE revealed the presence of presence of flavonoids, alkaloids, saponin, terpenoids, phenols, tannins and phlobatinnins while cardiac glycosides, steroid glycosides and anthraquinones were absent. Similarly, quantitative analysis of MLASE showed the presence of tannin, alkaloids, phenols, sugar and saponin at the concentrations of 29.73 ± 0.38 mg/100 g, 25.69 ± 0.10 mg/100 g, 37.15 ± 0.10 mg/100 g, 37.38 ± 0.08 mg/100 g and 54.84 ± 0.21 mg/100 g of MLASE, respectively. Repeated daily oral treatments with 125-500 mg/kg of MLASE significantly (p<0.01 and p<0.001) lowered the FBG dose dependently with highest antidiabetic effect recorded for the highest dose. Similarly, 125-500 mg of MLASE significantly (p<0.05, p<0.01 and p<0.001) decreased serum TG, TC, LDL-c and VLDL-c levels while significantly increasing serum HDL-c levels. Overall, results of this study showed MLASE to possess antihyperglycemic and antihyperlipidemic effects in experimental diabetic rats which was probably mediated via enhanced peripheral glucose utilization and/or enhanced insulin secretion.
Keywords: Morinda lucida, aqueous stem bark extract, alloxan-induced diabetes, antihyperglycemia, antihyperlipidemia