been shown to reduce
plasma glucose levels in moderately diabetic rats,10 ascribable to
its stimulus efficacy on β cell insulin release.11 Further
characterization of the insulinotropic activity of this extract,
using HIT-T15 cells11 as an insulin-secreting cell model, has
demonstrated its influence on Ca2+ handling in β cells.12 Also, it
has been found that such insulin release at the basal condition
may be mediated by closure of the ATP-sensitive K+ channels
to depolarize the membrane of β cells and in turn open the
voltage-sensitive Ca2+ channels. These results suggest a
potential for this natural substance to be developed as an oral
antihyperglycemic agent. Diterpenoids, such as borapetosides
A−G and borapetols A−C,13−16 have been isolated from this
plant. However, the active components of this plant remained
poorly understood. Hence, this study was initiated to isolate the
active compounds for further pharmacological studies.