Journal of Lipid Research, Vol. 8, 646-660, November 1967
Copyright © 1967 by Lipid Research, Inc.

Quantitative aspects of free fatty acid metabolism in the fasted rat

Nome Baker and Michael C. Schotz

Radioisotope Research, Veterans Administration Center, Los Angeles, California 90073 and Department of Biological Chemistry, University of California at Los Angeles School of Medicine, Los Angeles, California 90024

Palmitate-1-¹⁴C was injected intravenously into unanesthetized, fasted rats. Disappearance of tracer from plasma free fatty acids was studied. A large component of free fatty acid (FFA) recycling was directly demonstrated by reinjection experiments. The latter studies also indicated the existence of an unidentified, rapidly turning over polar lipid in plasma which was synthesized from palmitate-¹⁴C. The appearance of ¹⁴C in hepatic and extrahepatic triglycerides, in other esters, and in respired CO₂ was also followed. The data were analyzed using a multicompartmental model and a digital computer.

Only a small fraction of the triglycerides formed in liver was derived directly from plasma free fatty acids. The major portion of net triglyceride formation appeared to be by way of an intermediate nontriglyceride ester pool which turned over relatively slowly compared to plasma free fatty acids. Initial approximations are as follows (µmoles of fatty acid per min per 100 g body weight): net free fatty acid mobilization (irreversible disposal) = 2.4; hepatic triglyceride formation directly from plasma free fatty acid = 0.1; total hepatic lipid formation from plasma free fatty acids = 0.5; oxidation of free fatty acids to CO₂ = 0.8; percentage of respired CO₂ from direct oxidation of fatty acids = 12%; extrahepatic triglyceride formation directly from fatty acids = 0.4; total extrahepatic lipid formed directly from fatty acids = 1.2.

Supplementary key words bicarbonate-¹⁴C • CO₂ • extrahepatic • fasted rats • fatty acid oxidation • free fatty acid turnover • liver • irreversible disposal • lipid esters • multicompartmental analysis • palmitate-1-¹⁴C • recycling • triglycerides • triglyceride secretion

Submitted on May 24, 1967
Accepted on August 7, 1967

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