The leaf of Lagerstroemia speciosa L. is used as an anti-diabetic herbal remedy in many
countries. In an attempt to discover mechanisms of action of the L. speciosa extract that stimulate
glucose uptake, a cell-based radioactive assay of glucose uptake was performed using L8 muscle cells.
In this study, the methanol fraction of L. speciosa leaves (LSE) contained a high level of phenolic
compounds and showed strong capability to stimulate glucose uptake in a dose-dependent manner. The
LSE stimulation was slightly inhibited (8.8%) by SB203580. The inhibitory effect (23.6%) of
wortmannin on LSE-stimulated glucose uptake was demonstrated, suggesting LSE action on glucose
transporter translocation. LSE-induced glucose uptake was completely reversed by cycloheximide. In
addition, an increased amount of total glucose-transporter-1 protein was observed indicating that new
protein synthesis is necessary for elevated glucose transport. LSE also enhanced insulin-stimulated
glucose transport. These results suggest that LSE action may be mediated primarily via the synthesis of
new transporters and involve both insulin-dependent and independent pathways.