Utilization of exogenous free fatty acids for the production of very low density lipoprotein triglyceride by livers of carbohydrate-fed rats

Abstract

High carbohydrate diets enhance the hepatic output of very low density lipoprotein triglycerides. The fatty acids of these triglycerides could come from exogenous sources (i.e., diet or adipose tissue) or from de novo fatty acid synthesis in the liver. The role of exogenous free fatty acids was evaluated in rats fed Purina Chow or diets containing 10% fructose for up to 14 wk. In carbohydrate-fed rats, serum triglycerides were twice normal, and VLDL accounted for about 60% of the increases. Pre-β-lipoprotein was increased and α- and β-lipoprotein were decreased. Phospholipid and cholesterol levels were unchanged.Livers were perfused with glucose and free fatty acids. Perfusate free fatty acids rose from 180 to 1800 μeq/liter as the infused acids increased from 0 to 992 μeq/3 hr; simultaneously, net free fatty acid uptake rose from 13 μeq/g/hr. More lauric and myristic acid appeared in the perfusate than was infused, suggesting the hepatic discharge of free fatty acids.Livers of fructose-fed rats secreted twice as much oleate-14C-labeled triglyceride as controls at all levels of free fatty acid uptake. The ratios of the specific activities of perfusate triglyceride to free oleate-14C were unaffected by diet and were about 0.6 and 1.0 at low and high triglyceride secretion rates, respectively. Thus, carbohydrate feeding did not result in altered uptakes of free fatty acids or preferential secretion of triglycerides containing endogenously synthesized fatty acid. Instead, the increased secretion of triglyceride was accomplished by enhanced formation of VLDL triglyceride from exogenous free fatty acids.

Keywords

• VLDL triglyceride
• fructose
• liver perfusion