Anti-diabetic effects of stem bark extract and fractions of Terminalia catappa Linn. (Combretaceae)

The pharmacognostic, toxicity and anti-diabetic profiles of stem bark of Terminalia catappa were evaluated. The plant material was subjected to macroscopy, microscopy and proximate analyses using standard methods. The pulverized sample was extracted using soxhlet apparatus. The methanol extract (CE) was then fractionated into n-hexane fraction (HF), ethyl acetate fraction (EF), n-butanol fraction (BF) and water fraction (WF); the crude extract and the fractions were subjected to phytochemical analysis and screened for toxicity and antidiabetic properties using streptozotocin, alloxan and alloxan-nicotinamide induced diabetic Wistar rats. The chromatographic fingerprints of both the methanol extract and butanol fraction were obtained. The retardation factors (Rf-values) of the individual spots were calculated. The microscopic examination revealed some phloem parenchyma with pits, phelloderm, fibres, parenchyma cells, sclereids, cork cells and calcium oxalate crystals. Phytochemical analysis showed the presence of alkaloids, tannins, flavonoids, saponin, steroids, cardiac glycosides, carbohydrates, proteins and anthraquinones. Acute toxicity test on the crude extract established that at 5000 mg/kg, no toxicity was recorded; the extract and fractions of Terminalia catappa slightly increased WBC concentrations. The crude extract and the fractions administered for 7 days significantly (p < 0.01) reduced the blood glucose levels when compared with control. The potency of the extract and fractions in relation to blood glucose concentration increased in the order WF ˃ BF ˃ CE ˃ EF ˃ HF; with the WF and BF at 500 mg/kg exhibiting fasting blood glucose reduction comparable to that obtained with 500 mg/kg metformin. The results showed that stem bark of Terminalia catappa possess anti-diabetic activity.