This study evaluated the hypoglycemic effect of stem-bark extracts of Anacardium occidentale Linn., of the Anacardiaceae family, in normal (normoglycemic) and in streptozotocin-treated diabetic rats. Young adult, male Wistar rats weighing 250-300 g were used. Diabetes mellitus was induced in the test rats by intraperitoneal injections of streptozotocin (STZ, 90 mg/kg). In one set of experiments, graded doses of the aqueous and methanolic stem-bark extracts of A. occidentale (100-800 mg/kg p.o.) were separately administered to groups of fasted normal and fasted diabetic rats. In another set of experiments, 800 mg/kg p.o. of the aqueous or methanolic extract of the plant, a dose which produced maximal hypoglycemic effects in both fasted normal and diabetic rats in the previous set of experiments, were used. The hypoglycemic effects of single doses (i.e., 800 mg/kg p.o.) of A. occidentale stem-bark aqueous and methanolic extracts were compared with those of insulin (5 microU/kg s.c.) and glibenclamide (0.2 mg/kg p.o.) in both fasted normal and fasted diabetic rats. Following acute treatment, relatively moderate-to-high doses of A. occidentale stem-bark extracts (100-800 mg/kg p.o.) produced dose-dependent, significant reductions (p< 0.05-0.001) in the blood glucose concentrations of both fasted normal and fasted diabetic rats. On their own, both insulin (5 microU/kg s.c.) and glibenclamide (0.2 mg/kg p.o.) produced significant reductions (p< 0.01-0.001) in the blood glucose concentrations of the fasted normal and fasted diabetic rats. At single doses of 800 mg/kg p.o., A. occidentale stem-bark aqueous and methanolic extracts significantly reduced (p< 0.001) the mean basal blood glucose concentrations of fasted normal and fasted diabetic rats. The hypoglycemic effect of the methanolic plant extract was found to be slightly more pronounced than that of the aqueous plant extract in both the normal and diabetic rats examined. A. occidentale contains a diverse group of chemical compounds. Since methanol extractives of plants usually contain many chemical compounds, each of which is capable of producing definite biological activities via different mechanisms, it is difficult to draw any logical conclusion on the mechanism of the hypoglycemic effect of such a diverse mixture of chemical compounds contained in the plant extracts used in this study. While it is possible that the hypoglycemic effects of the plant extracts may be due, at least in part, to their terpenoid and/or coumarin contents, the mechanism of their hypoglycemic action remains largely speculative. However, this is unlikely to be due to the stimulation of pancreatic beta-cells and subsequent secretion of insulin. Although A. occidentale stem-bark aqueous or methanolic extract is less potent than insulin as an antidiabetic agent, the results of this experimental animal study indicate that it possesses hypoglycemic activity, and thus lends credence to the folkloric use of the plant in the management and/or control of adult-onset, type-2 diabetes mellitus among the Yoruba-speaking people of Western Nigeria.
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