BIOSYNTHESIS OF TRIGLYCERIDES FROM DOUBLY-LABELED 2-MONOPALMITIN IN INTESTINAL MUCOSA OF RAT

Triglyceride biosynthesis from 2-monopalmitin (consisting of [2-3H]glycerol and [1-14C]palmitic acid) and unlabeled free oleic and palmitic acids was studied when this mixture was introduced into an isolated loop of rat intestine in situ. 1. 1. Hydrolysis and isomerisation of the introduced 2-monopalmitin did not occur in the intestinal lumen during a 30-min period under our experimental conditions. 2. 2. About 70% of labeled 2-monopalmitin was absorbed, and the proportions of 1 and 2 isomers and their isotopic ratios in the monoglyceride fraction of mucosal and intestinal contents showed that the 2-monopalmitin had been absorbed intact. 3. 3. Data suggest that 18% of the absorbed monopalmitin is split in the mucosal cells; the resulting free palmitic acid is incorporated into higher glycerides while a relatively important portion of the freed glycerol is recovered in lecithins and cephalins. 4. 4. Calculations made from the distribution of labeled palmitic acid in the mucosal triglycerides after pancreatic lipolysis suggest that about 85% of these tri-glycerides are synthesized by direct acylation of the 2-monopalmitin and 15% by the α-glycerophosphate pathway; large amounts of the acylated α-glycerophosphate seem to have an endogenous origin. 5. 5. Both phosphatidic and lysophosphatidic acids are labeled but isotopic ratios do not bring to light any evidence on the phosphorylation of 2-monopalmitin as previously shown with 1-monopalmitin. © 1968.