Effects of co-administration of methanol leaf extract of Catharanthus roseus on the hypoglycemic activity of metformin and glibenclamide in rats

ObjectiveTo investigate the interacting effects of co-administration of methanol leaf extract of Catharanthus roseus (C. roseus) on the hypoglycemic activity of metformin as well as glibenclamide using experimental rats.MethodsPhytochemical analysis as well as acute toxicity and lethality (LD₅₀) test were carried out on its methanol leaf extract. The alloxan model for experimental induction of diabetes in rats was employed. Six groups comprising five rats each were used. Groups II, III and IV received 250 mg/kg of extract, 100 mg/kg of metformin and 1 mg/kg of glibenclamide respectively, while V and VI were administered metformin-extract and glibenclamide-extract combinations respectively at doses as above. Group I served as negative control and received only distilled water. All administration was done once daily for seven days. Fasting blood glucose was determined at 2, 12, 24, 72 and 168 h using a glucometer. One-way ANOVA with post-hoc tests was used to assess for significant difference due to administration of drug alone and with co-administration of drug and extract.ResultsThe LD₅₀ was 2 121.32 mg/kg. The phytochemical studies indicated the presence of saponins, tannins, alkaloids, phlotatannins, flavonoids, triterpenoids, reducing sugars, anthraquinones and glycosides. All medicaments significantly reduced blood glucose levels when compared with control alone (P<0.05) with the highest percentage reduction in blood glucose (64.86%) exhibited by metformin-extract combination.ConclusionsThe leaf extract of C. roseus significantly increases the hypoglycemic effect of metformin.