Suppressive effects of polygonati rhizoma on hepatic glucose output, GLUT2 mRNA expression and its protein content in rat liver.

The intraperitoneal administration of the methanol extract of Polygonati Rhizoma (OM) into normal rats caused a significant decrease in the blood glucose level at 4 h after its administration of 800 mg/kg (P < 0.01), but not the serum insulin level. Using the perfused rat liver in vitro, a significant decrease of the hepatic glucose output was observed by the infusion of OM (P < 0.05 at 250 micrograms/ml OM). In addition, the hepatic content of facilitative glucose transporter isoform 2 (GLUT2) mRNA and its protein content in the total membrane fraction from rat liver significantly decreased in the intraperitoneally OM-treated rats when compared to that in the controls (mRNA P < 0.01, protein P < 0.001). On the other hand, OM (500 micrograms/ml) exhibited no apparent stimulatory effect on the insulin secretion from the isolated rat pancreatic islets. These results suggest that the hypoglycemic effect of OM is derived, at least in part, from the decrease in hepatic glucose output, due presumably to the reduction of GLUT2 mRNA expression and its protein content in total membrane of the liver, and that because of its unique therapeutic mechanism, OM could be a new category of therapeutic agent for non-insulin-dependent diabetes mellitus.