The composition of lipid from jejunal contents of the dog after a fatty meal

Abstract

It is generally accepted that lipase splits fat to some extent in the intestine, but the degree of lipolysis is still uncertain. It has been suggested (Frazer, 1946) that not more than 30 % of the total fatty acid is liberated in the intestine and that no glycerol is formed: and it was also maintained that more than 60 % of ingested fat is absorbed as unsplit triglyceride in the form of particles of less than 05,u in diameter, stabilized as an emulsion by monoglyceride, fatty acid and bile salts. The evidence adduced in support of these contentions was largely indirect, being based on in vitro studies of lipolysis, on the composition of fat from the intestinal contents of rats after fat administration, on in vitro studies of emulsification and on changes in chylomicron counts in blood during fat absorption.In vitro studies on lipolysis have been carried out by Desnuelle who summarized (1951) the results obtained by his group. They found that at pH 8 the extent of fat hydrolysis by pancreatic extracts was low, except in the presence of calcium salts and of large amounts of bile, when hydrolysis proceeded to completion. Borgstr6m (1952) used as a source of lipase a physiological mixture of bile and pancreatic juice obtained by cannulating the duodenal papilla of the rat and subsequently adjusted to pH 6-5. Added corn oil was rapidly hydrolysed, 50 % of the fatty acid being liberated in 3 hr and 70 % in 6 hr.Many workers on fat digestion have analysed the fat obtained from intestinal contents of animals killed after having been fed with olive oil by stomach tube. Desnuelle & Constantin (1952) found 16-24% fatty acid, Borgstrom (1952) found 37 and 43 % and Mattson, Benedict, Martin & Beck (1952) 15-25% in fat from rats killed 3 hr after feeding on olive oil. In similar experiments with dogs Desnuelle & Constantin (1952) found 17 % fatty acid 3 hr after feeding and 49 % after 5 hr. These analyses are all of the unabsorbed 33-2 C. M. DOWSE AND OTHERS residue of fat in the intestine and can provide little evidence as to the degree of lipolysis of absorbed material.Blankenhorn & Ahrens (1955) used a continuous aspiration technique to obtain jejunal contents throughout the whole period offat digestion in humans.They found that 58 and 60 % of the fat isolated was fatty acid. This method of collection provides more valuable evidence as to events in the intestine than the collection of intestinal contents at a fixed time interval after fat feeding.Several workers have fed rats on fats labelled in the fatty acid and/or glycerol part of the molecule, collected lymph and deduced the amount of lipolysis which had taken place in the intestine from distribution of labelled material in the fat isolated from lymph. Favarger, Collet & Cherbuliez (1951) deduced that the maximum hydrolysis varied between 12 and 45 %. Reiser, Bryson, Carr & Kuiken (1952) claimed that 25-45% of triglyceride is completely hydrolysed to glycerol, the remaining 55-75 % being hydrolysed to monoglyceride: this is equivalent to 75-80 % of the fatt...

The Intraluminal Phase of Fat Digestion in Man: The Lipid Content of the Micellar and Oil Phases of Intestinal Content Obtained during Fat Digestion and Absorption*

“…The negligible volume of the oil phase in intestinal content has already been noted. Moreover, inspection of intestinal content by ordinary illumination as well as dark field microscopy indicates that emulsification is quite incomplete (38). It would seem therefore that the interfacial area should be small relative to the concentration of surface active materials present in intestinal content-lecithin, lysolecithin (40,41), bile salts, unionized fatty acid, fatty acid anions, monoglycerides, and proteins, among others.…”