Preparation and use of a glyceryl triether as an indicator of fat absorption

I .Tridodecyl glyceryl ether (I ,z,3-tridodecoxypropane) was prepared and purified for use as a lipid-soluble indicator of fat absorption.It was separated from other lipids present in samples of diet, digesta and faeces by thin-layer chromatography and determined by gasliquid chromatography. 2.In balance studies using rats which received a semi-purified diet containing beef tallow, 97-98 "/o of both the dietary tridodccyl glyceryl ether and of thc chromic oxide (Cr,O,) from the diet were recovcrcd unaltered from the faeces.This suggests that both compounds are equally good as digestibility indicators.3. When the rats werc killed, analyses of digesta taken from different regions of the gastrointestinal tract showed that, although the Cr,Os passed from the stomach faster than did the fat, the triethcr and fat left the stomach together.This suggested that the triether was more suitable as an indicator of fat absorption in thc digcstive tract than is Cr,O,.4. Comparisons of the digesta removed from the stomach, jejunum, and ileum of piglets receiving a semi-purified diet containing beef tallow, tridodecyl glyceryl ether, Cr,O, and l4C-labellcd oleic acid also supported the conclusion that the tricther was a suitable indicator of fat absorption from different regions of the digestive tract.Studies of nutrient absorption in vivo require comparison of the amounts of nutrient in the food and unabsorbed food residues.The obvious way of achieving this comparison is to make a total collection of the residues derived from a particular quantity of food.Edin (1926) found that since chromium sesquioxide (chromic oxide, Cr,Q,) was a nutritionally inert, and non-absorbed indicator, it was suitable as an indicator for use in studies in which the progress of absorption was to be detcrmined by comparing the ratios of nutrient to indicator in food and food residues.Carlson & Bayley (1968), however, were unable to use Cr,O, as an indicator because it separatcd from the lipid phase of the digesta in thc stomach.Borgstrom (1960) suggestcd that cholesterol, which is poorly absorbed and is lipidsolublc, could be used to indicate the progress of fat absorption through the intestinal tract; however, the poor recovery of cholesterol limits its usefulness.Sie, Valkema & Loorneijer (1967) suggested using a silicone oil, but the quantitative determination of the silicone oil was tedious.Spener, Paltauf & Holasek (1968) used glyceryl trioleyl ether as a model for triglycerides in studies of fat absorption and found that this compound was not absorbed.Thus it could possibly be useful as an indicator of lipid absorption, particularly if it did not separate from the lipid component of the digesta in the stomach.T h e present study describes the synthesis and purification of tridodecyl glyceryl ether (1,~,3-tridodecoxypropane) (DGE) and its quantitative determination by gas-