The transport and dynamic state of exogenous glycerol- and palmitic acid-labeled tripalmitin*

Abstract

The radioactivities of the glycerol and fatty acid moieties of plasma, liver, and adipose tissue lipids were determined at intervals after the ingestion of glycerol- and palmitic acid-labeled tripalmitin by rats. The changes in the levels of activities of the glycerol and fatty acids, and in the ratios of those activities, demonstrated the following: Only about half of the glycerol is completely hydrolyzed from fatty acid during digestion and absorption. Plasma lecithin originating from dietary fat is synthesized extrahepatically. Plasma triglycerides are removed by the liver without change but are hydrolyzed before incorporation into adipose tisaue. Liver lecithins originate from liver triglycerides. Triglycerides are metabolically more active than lecithins and the latter more active than cephalins. In the postabsorptive period, glycerol disappears from adipose tissue triglycerides more rapidly than do the fatty acids, indicating hydrolysis and renewal of glycerol. In the liver, on the other hand, glycerol and fatty acid disappear from both triglycerides and phospholipids at the same rates, indicating that they are removed as units.