A
tritium-labeled
glycerol triether was tested as a nonabsorbable oil-phase marker in studies of fat absorption in normal rats and in rats with
steatorrhea induced by various doses of
cholestyramine. Animals were fed a test meal containing (3)H-labeled triether and (14)C-labeled
trilinolein. Fat absorption was estimated in the following three ways: (a) by
isotope ratios (the change in (3)H/(14)C in the test meal and in feces); (b) by
isotope recovery (the total fecal excretion of (14)C radioactivity); and (c) by chemical recovery (the total fecal fat excretion). Absorption calculated from
isotope ratios agreed well with that calculated from
isotope recovery over a range of fat absorption of 50-100%, thus validating the use of this
lipid marker under these conditions of fat malabsorption. Absorption calculated from chemical recovery was consistently poorer than that calculated from
isotope ratios or
isotope recovery, thus suggesting that
cholestyramine increased the excretion of nondietary (endogenous) fat. Triether may be of value for studying the absorption of compounds present predominantly in the oil phase during digestion and may have significant advantages over other proposed
lipid markers.