Properties of glycerol-75Se-triether: A lipid-soluble marker for the estimation of intestinal fat absorption

The properties of a 75Se-labeled glycerol triether were investigated in rat experiments designed to test this substance as a nonabsorbable marker for the assessment of intestinal fat absorption. After oral administration of 75Se-triether, the radioactivity was excreted almost completely with the feces. Amounts in excess of the quantity required tor clinical use did not interfere with overall fat absorption. No evidence for toxicity of 75Se-triether was observed. 131l-triolein was used as tracer fat and fat absorption was calculated by the following methods: (1) isotope balance method-oral intake minus fecal excretion of 131L; (2) isotope ratio method-comparison of the 131L to 75Se ratios in the test dose and in a stool sample. Results obtained from the isotope ratio method were in close agreement with those of the isotope balance method over a range of fat absorption of 80 to 95 per cent, thus indicating that the marker and the radioactive fat pass the gastrointestinal tract at the same rate under these experimental conditions. These results show that 75Se-triether possesses several of the properties of an ideal marker for fat absorption studies. Its advantages over other proposed markers for fat absorption studies are discussed. Simultaneous administration of 131L-TRIOLEIN AND 75Se-triether in a single dose may provide a reliable, rapid, and simple method to estimate intestinal fat absorption in man.