Inhibitory mechanisms of oleanolic acid 3-O-monodesmosides on glucose absorption in rats

We examined the action mechanism of oleanolic acid 3-O-monodesmoside, momordin Ic (1), and oleanolic acid 3-O-glucuronide (2) for the inhibitory effect on the increase in serum glucose levels in oral glucose-loaded rats. Although 1 and 2 dose-dependently inhibited the increase in serum glucose levels in oral glucose-loaded rats, these compounds showed no significant effects on serum glucose levels in normal rats, intraperitoneal glucose-loaded rats, and alloxane-induced diabetic mice. Furthermore, 1 and 2 were found to suppress gastric emptying in rats, and also to inhibit the glucose uptake in rat small intestine concentration dependently in vitro. These results indicate that 1 and 2 given orally have neither insulin-like activity nor insulin releasing-activity. 1 and 2 apparently inhibited glucose absorption by suppressing the transfer of glucose from the stomach to the small intestine and by inhibiting the glucose transport system at the small intestinal brush border.