SITES OF INITIAL REMOVAL OF CHYLOMICRON TRIGLYCERIDE FATTY ACIDS FROM THE BLOOD*

Abstract

During a constant 45-minute infusion of a moderate dose of chylomicrons into 4 dogs at a rate designed to simulate conditions of normal fat absorption, the triglyceride fatty acids (TGFA) of liver constantly contained about 1/3 of the radioactivity removed from plasma. Adipose tissue contained 1/5 of the removed radioactivity, and it was assumed that oxidation and deposition into other extrahepatic tissues accounted for the remainder. The findings in two fasted dogs did not differ from those in two that had been eating normally and that received an infusion of glucose immediately before the chylomicrons. The mean turnover rate of hepatic TGFA during the infusions was 1,100 mg/hour. From calculations based on this turnover rate and the concentration of radioactivity in liver and other tissues, we estimated that no more than 2% of the radioactivity deposited in lipids of extrahepatic tissues during the first 5 minutes could have been derived from hepatic TGFA radioactivity, and no more than 15% during the subsequent 40 minutes. It is concluded that under conditions simulating the physiologic rate of influx of chylomicron lipid into the circulation, most of this lipid is removed directly by extrahepatic tissues.