Studies on the in vivo synthesis of triacylglycerol in mouse liver

The in vivo biosynthesis of hepatic glycerolipids was examined by studying the incorporation of [2-3H] glycerol into triacylglycerol in the mouse. The isotope was administered by rapid injection into the portal vein. The incorporation of glycerol was linear for about 1 min and maximal rates were seen in the presence of additional oleic acid. At 20 mumol of oleic acid bound to 1 mumol of bovine serum albumin, the highest level tested, glycerol incorporation was still increasing linearly, whereas a plateau was reached at 4 mumol of glycerol. The liver incorporated 200-300 nmol of [2-3H] glycerol into triacyglycerol per min when 20 mumol of albumin-bound oleic acid plus 4 mumol of glycerol were injected in a 0.2 ml volume. Studies on the uptake by the liver after intraportal injection revealed that at 0.5 min the liver retained 2 mumol of glycerol and 5 mumol of oleic acid, indicating that the uptake of substrate was not rate-limiting. The results suggest that the availability of substrate is a major factor in the regulation of triacyglycerol biosynthesis by the liver.