Dietary carbohydrate induces lipogenesis and very-low-density lipoprotein synthesis

Hepatocytes obtained from sucrose-fed rats secreted triacylglycerol at a rate that was about twice that of cells from control rats. The increased rate of triacylglycerol secretion by cells from sucrose-fed rats was accompanied by a twofold increase in its rate of synthesis as determined by 3H2O incorporation. In addition, cells from sucrose-fed rats had a two- to threefold increase in apolipoprotein synthesis. Differences between the two groups became even more marked when cells were challenged in vitro with glucose. Double-reciprocal analysis showed that compared with controls, cells from sucrose-fed rats had a fourfold increase in the Vmax that described the glucose stimulation of [3H]triacylglycerol secretion. In contrast to in vivo carbohydrate (sucrose) induction of apolipoprotein synthesis, glucose added in vitro did not affect apolipoprotein synthesis. These data suggest that in vivo induction by dietary carbohydrate requires factors in addition to increased hexose that are not contained within the isolated hepatocyte system. The coinduction by dietary carbohydrate of both lipogenesis and apolipoprotein synthesis is likely to play a role in the increased capacity of cells from sucrose-fed rats to both assemble and secrete triacylglycerol-rich lipoproteins.