Meanwhile, we found Corosolic acid was able to enhance glucose uptake stimulated by submaximal concentration of insulin (1 or 10 nM) and this synergic effect was covered by maximal concentration of insulin (100 nM). These results hinted us that it could improve the sensitivity of L6 myotubes to insulin. In order to validate the hypothesis, we used Wortmannin, a PI3 Kinase specific inhibitor, to block intrinsic insulin pathway. The compound induced enhancement on glucose uptake was abolished by Wortmannin completely. This hinted us that it might enhance glucose uptake via insulin pathway. Meanwhile, we tested the effect of Corosolic acid on AMPK pathway, the other distinct signaling pathway to stimulate glucose uptake which can be activated by muscle contraction/exercise in physiological condition, and the result showed AMPK could not be activated by Corosolic acid.
