Objective: Alcoholic extract of the bark of Moringa oleifera Lam. (MO), (Moringaceae), has been experimentally evaluated previously for its insulin sensitizing potentials. In the quest to explore the possibility of the class of phytochemical(s) responsible for this experimental claim, the alcoholic extract was fractionated and evaluated for insulin sensitizing effect in rat model for insulin resistance. Methods: Alcoholic extract of MO was fractionated into, non-polar [petroleum ether (PEF)], moderately non-polar [ethyl acetate (EAF)] and polar [aqueous (AQF)] fractions. The fractions obtained were investigated for their insulin sensitizing properties in dexamethasone induced insulin resistance in rats. The bioactive fraction was analysed by spectroscopy for further characterization of phytochemical(s) present. Results: Acute treatment for 4 h with dexamethasone (1 mg/kg i.p.) in rats led to the development of impaired oral glucose tolerance. Treatment with pioglitazone and EAF abolished dexamethasone induced oral glucose intolerance (OGT). Dexamethasone (1 mg/kg s.c., once daily for 11 d) administration led to the development of insulin resistance, characterised by fasting hyperglycemia, hyperinsulinemia, hypertriglyceridemia, impaired OGT and increased HOMA IR index. Treatments with EAF (140 mg/kg p.o.) and pioglitazone [PIO (10 mg/kg p.o.)] significantly prevented dexamethasone induced metabolic changes. Similarly, treatment with AQF (95 mg/kg p.o.) also significantly prevented metabolic changes due to dexamethasone except impaired OGT. In contrast PEF (15 mg/kg p.o.) failed to prevent these metabolic changes except hypertriglyceridemia. Conclusion: The present study reveals that triterpenoid and the polyphenols (procyanidin) class of phytochemicals detected in EAF of alcoholic extract of MO bark may be responsible for the prevention of dexamethasoneinduced insulin resistance in rats.
Key words: Dexamethasone, Insulin resistance, Moringa oleifera, Oral glucose tolerance test, Serum triglyceride.