Quantitative aspects of free fatty acid metabolism in the fasted rat

Abstract

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.

Keywords

• bicarbonate-14C
• Co2
• extrahepatic
• fasted rats
• fatty acid oxidation
• free fatty acid turnover