The intestinal absorption of triglycerides.

The long controversy over whether triglycerides are hydrolyzed preliminary to their absorption from the intestine may be ascribed to the difficulties in designing an experiment without alternative interpretations. In the present study it was hoped that an unequivocal experiment could be designed by labeling both the glycerol and the fatty acid moieties of ingested fat and examining the glycerides in the resulting lymph. Glycerol was labeled with Cl4 in the CY and a’ positions and esterified with conjugated linoleic acid. It has previously been shown that conjugated linoleic acid may be used as a tracer of fatty acid movements through the body (1, 2). It was considered that there are five possible types of lytic changes fats may undergo in the intestine. These are (a) no hydrolysis, (b) hydrolysis at only the Q( or CY and /3 positions but not at the QI’ position, (c) complete hydrolysis of some fraction of the fat, (d) combinations of (b) and (c), and (e) complete hydrolysis of all the fat. Interpretations of (c), (d), and (e) are further complicated by the possibility that the glycerides in the lymph, resynthesized from ingested fat, may or may not utilize their original glycerol or may do so only to a limited degree. If hydrolysis is complete and none of the labeled glycerol is utilized in the resynthesis of fat from the absorbed conjugated acids, the fact could be determined by the failure of any labeled glycerol to appear in lymph fat after ingestion of labeled conjugated trilinolein. Two experiments of this simple type were performed, but the specific activity of the glycerol of the lymph fat was an appreciable fraction of that in the fat fed. This showed that only a part of the fat fed was completely hydrolyzed and that the glycerol was not used for resynthesis of glycerides of the hydrolyzed fatty acids. There are three possibilities for the apparently unhydrolyzed glyceride: (a) it was absorbed unchanged; (b) it was completely hydrolyzed and the glycerol used for resynthesis (that is, there was 100 per cent hydrolysis and a fraction of the glycerol reused), (c) there was partial hydrolysis and