Elevation of liver diacylglycerols and molecular species of diacylglycerols in rats fed a lipogenic diet.

The concentration of diacylglycerols in rat liver was measured by a newly developed procedure that entailed a) freeze-clamping of the liver in situ, b) lipid extraction with dimyristoylglycerol as an internal standard, c) thin-layer chromatography, and d) gas-liquid chromatography. Molecular species of diacylglycerol and total diacylglycerols were quantified. The average level of diacylglycerol in livers of chow-fed rats was 102 micrograms/g wet wt, equivalent to about 180 nmol/g wet wt. A high-carbohydrate fat-free diet, known to increase the rate of fatty acid synthesis, greatly increased the liver diacylglycerol concentration relative to the level observed in rats fed laboratory chow. Diacylglycerol molecular species that contained 16-carbon fatty acids were most markedly elevated. Liver triacylglycerol, free cholesterol, and esterified cholesterol were concurrently increased. Molecular species of triacylglycerols and cholesteryl esters that contained 16-carbon fatty acids were elevated to the greatest degree. The concentrations of total triacylglycerol and cholesteryl esters exhibited a high correlation in the livers of all animals studied, suggesting their coexistence in metabolic pools, predominantly the cores of lipid droplets and newly assembled very low density lipoprotein particles. The correlation of liver diacylglycerol and triacylglycerol contents in the chow-fed rats suggests that the diacylglycerol concentration may be a rate-determining factor in triacylglycerol synthesis when diacylglycerol levels are in the observed range of 70-150 micrograms/g wet wt. In conclusion, when the rates of fatty acid synthesis and hence triacylglycerol synthesis are increased in the liver, the steady state concentrations of diacylglycerols are also elevated.(ABSTRACT TRUNCATED AT 400 WORDS)