The effect of allantoin, an active component of yam, on plasma glucose of streptozotocin-induced diabetic rats (STZ-diabetic rats) is investigated. Allantoin decreased plasma glucose levels in a dose-related manner, which was reduced by pretreatment with naloxone or naloxonazine. A concomitant increase in plasma β-endorphin, detected by enzyme-linked immunosorbent assay, was observed. Moreover, allantoin enhanced β-endorphin release from the isolated adrenal medulla of STZ-diabetic rat in a dose-related manner. However, its plasma glucose lowering action was reduced but not totally abolished by bilateral adrenalectomy. Furthermore, allantoin directly increased radioactive glucose uptake in isolated skeletal muscle, and repeated administration for 3 days increased GLUT4 mRNA and protein levels in muscle. This effect was markedly reduced in STZ-diabetic rats with bilateral adrenalectomy. This study suggests that allantoin increases GLUT4 gene expression in muscle by increasing β-endorphin secretion from the adrenal gland in STZ-diabetic rats.
Hyperlipidemia is an important risk factor for cardiovascular diseases. Agents for the treatment of hyperlipidemia are well-developed in the clinic while PPARα is a target for lipid-lowering agents. Shan-Zha (Crataegus pinnatifida) is a traditional Chinese medicine used to increase digestion. Also, Shan-Zha fruit extract showed merit to improve obesity and hyperlipidemia in hamsters; however, the mechanism remained obscure. In the present study, hypertriglycemia and hypercholesterolemia were induced by high fat diet in C57BL/6 J male mice. Then, they were orally administered with Shan-Zha fruit extract at an effective dose of 250 mg/kg for 7 days. The liver was removed to estimate the expressions of PPARα and β-oxidation-related enzyme. Oral intake of Shan-Zha extract significantly improved hyperlipidemia in high fat diet-fed mice with an increase of PPARα expression in liver. Also, expression of PPARα-regulated β-oxidation-related enzymes was raised in liver by Shan-Zha extract. However, adipose tissue and others were not modified by this treatment of Shan-Zha fruit extract. Thus, Shan-Zha can increase the expression of PPARα to facilitate β-oxidation-related enzymes in liver for lipid degradation and blood lipid decrement. Also, this is the first report showing Shan-Zha fruit extract can influence liver to lower hyperlipidemia prior to the action in adipose tissue.
Adipocyte plays an important role in lipid regulation in mammals. Understanding of adipocyte differentiation becomes a key issue for the development of anti-obesity agent. Glucocorticoids (GCs) regulate lipid metabolism through promoting lipogenesis in adipose tissue. Ginsenoside Rh2, with a similar chemical structure as GCs, shows antidiabetic, anti-inflammatory, and anticancer actions both in vivo and in vitro. However, effect of Rh2 on glucocorticoid receptor (GR) for an increase of adipogenesis like GCs remains unclear. In the present study, we employed ginsenoside Rh2 to investigate the changes in adipogenetic process of 3T3-L1, one of the widely used preadipocytes, through activating GR or not. In leuciferase assay, we found that ginsenoside Rh2 induced GRs transitivity in a way as dexamethasone, which was deleted by RU486 at concentrations sufficient to block GR. Moreover, 3T3-L1 preadipocytes were differentiated into adipocytes by adipogenic induction medium containing 0.01 to 1 microM of ginsenoside Rh2. Also, RU486 blocked this adipogenesis induced by ginsenoside Rh2 or dexamethasone. The obtained results suggest that ginsenoside Rh2 can promote preadipocytes differentiation through activating GR. This finding seems helpful for the understanding of ginsenosides in the regulation of lipid metabolism.
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