Possible Role of Triacylglycerol-Rich Lipoproteins in the Down-Regulation of Adipose Obese mRNA Expression in Rats Re-Fed a High-Fat Diet

The large amount of absorbed dietary lipid after feeding a high-fat diet is mainly transported as triacylglycerol (TG)-rich lipoproteins (TRL) in the post-prandial blood and is subsequently distributed to peripheral tissues including adipose and muscle tissues. An in vivo and an in vitro study were conducted to investigate the possible role of post-prandial TRL after high fat feeding in the regulation of obese (ob) gene expression. Adult male Wistar rats were fasted for 48 h and re-fed either a fat-free/high-carbohydrate diet or a high-fat diet for 2, 4, or 8 h and plasma glucose, insulin, TG, and leptin as well as ob mRNA expression in epididymal fat pads were examined. Rats re-fed the high-fat diet had significantly higher plasma TG (p<0.05) and lower plasma leptin and adipose ob mRNA (p<0.05) than those fed the fat-free/high-carbohydrate diet; however, plasma glucose and insulin concentrations were not significantly different between the two groups. Plasma lipid analysis found large amount of TRL in rats fed with high-fat diet; however, only very small amount of the TRL was found in rats fed with fat-free/high-carbohydrate diet. We speculated that TRL might involve in regulation of ob gene expression. To further examine the regulation of TRL on ob mRNA expression, differentiated 3T3-L1 adipocytes were treated with TRL collected from rats fed 5 ml soybean oil by gastric intubations. TRL down-regulated ob mRNA not only in a dose and time dependent manner but also in the presence of insulin in 3T3-L1 adipocytes. These results suggest a possible role of TRL in the down-regulation of adipose ob mRNA expression and may account, at least in part, for the previous observations that short-term high fat feeding resulted in lower plasma leptin.