Preliminary investigations were carried out to evaluate the
antidiabetic effects of the leaves of O. stamineus extracted serially with
solvents of increasing polarity (
petroleum ether,
chloroform,
methanol and water); bioassay-guided purification of
plant extracts using the subcutaneous
glucose tolerance test (SbGTT) was also carried out. Only the
chloroform extract, given at 1 g/kg
body weight (b.w.), significantly reduced (P < 0.05) the
blood glucose level of rats loaded subcutaneously with 150 mg/kg (b.w.)
glucose. The active
chloroform extract of O. stamineus was separated into five fractions using a dry flash column chromatography method. Out of the five fractions tested, only
chloroform fraction 2 (Cƒ2), at the dose of 1 g/kg (b.w.) significantly inhibited (P < 0.05)
blood glucose levels in SbGTT. Active Cƒ2 was split into two sub-fractions Cƒ2-A and Cƒ2-B, using a dry flash column chromatography method. The activities Cƒ2-A and Cƒ2-B were investigated using SbGTT, and the active sub-fraction was then further studied for anti-diabetic effects in a
streptozotocin-induced diabetic rat model. The results clearly indicate that Cƒ2-B fraction exhibited a
blood glucose lowering effect in fasted treated normal rats after
glucose-loading of 150 mg/kg (b.w.). In the acute
streptozotocin-induced diabetic rat model, Cƒ2-B did not exhibit a
hypoglycemic effect on
blood glucose levels up to 7 hours
after treatment. Thus, it appears that Cƒ2-B functions similarly to
metformin, which has no
hypoglycemic effect but demonstrates an
antihyperglycemic effect only in normogycemic models. The effect of Cƒ2-B may have no direct stimulatory effects on insulin secretion or on
blood glucose levels in diabetic animal models. Verification of the active compound(s) within the active fraction (Cƒ2-B) indicated the presence of
terpenoids and,
flavonoids, including sinensitin.