Influence of concurrent administration of the methanol leaf extract of Leptadenia hastata (Pers) decne (Apocynaceae) with metformin on blood glucose in diabetic rats

Abstract

Leptadenia hastata (Pers) Decne (Apocynaceae) is a common medicinal plant used in northern Nigeria either singly or together with conventional drugs to treat diabetes. This study investigated the influence of concurrent administration of the methanol leaf extract of L. hastata with metformin in streptozotocin/ nicotinamide-induced diabetic rats. Possible synergistic activity between the extract and metformin was assessed using 3 models of synergy analysis (Loewe additivity, Bliss independent and highest single agent [HSA] models). Eleven groups of Wistar rats (eight animals per group) consisting of ten groups of diabetic rats and one normal control group were used in this study. Six groups were administered with either the extract or metformin at three different doses each (50, 150 and 500 mg/kg for the extract and 30, 100 and 300 mg/kg for metformin), while another three groups were co-administered with the extract and metformin at three different ratios each (50 mg/kg: 30 mg/ kg, 150 mg/kg: 100 mg/kg and 500 mg/kg: 300 mg/kg). An oral glucose tolerance test (OGTT) was conducted at baseline and on day 14. The results revealed that the extract-metformin combination brought about a synergistic reduction in the total area under the OGTT curve (based on Loewe and HSA models) as well as a synergistic reduction in blood glucose (based on Loewe, Bliss and HSA models). The methanol leaf extract of L. hastata produced a synergistic antidiabetic activity in streptozotocin/ nicotinamide-induced diabetic rats when combined with metformin.