Emodin, one of the main active components in the root and rhizome of Rheum palmatum L, promoted the conversion of 3T3-L1 fibroblasts to adipocytes, as evidenced by increased glycerol-3-phosphate dehydrogenase (GPDH) activity and the expression of adipocyte aP2 mRNA, as well as accelerated triacylglycerol (TG) accumulation, which was associated with increased mRNA expression levels of both C/EBP alpha and PPAR gamma 2. By using surface plasmon resonance (SPR) experiment, it was showed that emodin exhibited a very high binding affinity to PPAR gamma. In differentiated 3T3-L1 adipocytes, emodin induced a time-and dose-dependent increase in glucose uptake as well as GLUT1 and GLUT4 mRNA expression, and the rate of uptake was partly abrogated by wortmannin (phosphoinositide 3-kinase inhibitor). Meanwhile, insulin-stimulated glucose uptake was increased significantly after treatment with low doses of emodin, and the degree of potentiation was decreased thereafter in response to increasing concentrations. Furthermore, 50 PM emodin profoundly inhibited insulin-stimulated glucose uptake by 25%. These data suggest a new role for emodin as a PPAR gamma agonist in 3T3-L1 cells. Besides, it is possible that emodin may also possess other properties contribute to glucose utilization in the adipocytes. (c) 2006 Elsevier Inc. All rights reserved.