Main Article Content

Anti-hyperglycaemic and anti-oxidant activities of five Nigerian antidiabetic plants

M. D. Ayoola
A. C. Adebajo
E. M. Obuotor
T. O. Oladapo
T. C. Fleischer


Leaves of Olax subscorpioidea, Hoslundia opposita, Cleistopholis patens, Plumbago zeylanica and Dioscoreophyllum cumminsii that are used as anti-diabetics were evaluated for hyperglycaemic-lowering and antioxidant activities to justify their Nigerian ethnomedicinal usage. Leaf methanolic extracts (100, 200 and 400 mg/kg, p.o.) were assayed in normal, glucose- and alloxan-induced diabetic rats, while 1,1,-diphenyl-2-picrylhydrazyl, total antioxidant capacity, ferric reducing antioxidant power and hydroxyl radical scavenging tests were used for their antioxidant activity. Effects of n-hexane, dichloromethane, ethylacetate and aqueous partition fractions of the three most active anti-hyperglycaemic extracts were also tested in glucose-loaded rats. In normoglycaemic rats, all extracts generally lacked activity, while with glucose-loaded rats, only O. subscorpioidea (200mg/kg) and C. patens (400 mg/kg) at 1 h and O. subscorpioidea (200, 400 mg/kg) and C. patens (400 mg/kg) at 2-4 hours gave lowered (p < 0.05) blood glucose levels than glibenclamide (5 mg/kg), while activity of H. opposita and P. zeylanica (200 mg/kg) were only comparable to glibenclamide. When daily fed for fourteen days to alloxan-induced diabetic rats, all extracts, at their most active doses, gave significantly higher activity than glibenclamide. Olax subscorpioidea leaf extract had the highest hyperglycaemic-lowering and least antioxidant activities. Highest antioxidant activity of H. opposita may suggest some contribution of antioxidant property to its hyperglycaemic-lowering activity. The glucose-lowering and insulinotropic constituents of O. subscorpioidea, H. opposita and C. patens should be concentrated in their aqueous, aqueous and dichloromethane fractions, respectively. Anti-hyperglycaemic ethnomedicinal use of these plants was justified and H. opposita has additional antioxidant property.

 Keywords: Antioxidant activity; Diabetes mellitus; Nigerian anti-diabetic plants