Fat absorption was studied in normal and bile fistula rats using test meals of corn oil containing radioactively labelled triolein. Two types of test meal were used, which would produce differently labelled monoglyceride and fatty acid under the action of pancreatic lipase. Triolein containing 3H labelled oleic acid in the 1 and 3 positions and 14C labelled oleic acid in the 2 position was fed to normal and bile fistula rats with and without lymph fistulae. Short term pancreatic lipolysis of this triolein produced 3H labelled fatty acid and 14C labelled 2‐monoolein. Fat balance studies, Cori type experiments and the recovery of label in the lymph showed that in bile fistula rats 3H was absorbed in excess of 14C during the first few hr after feeding. In contrast, in lymph fistula rats with a normal bile flow 14C was absorbed in excess of 3H except in the earliest sample. These results indicate that after digestion triglyceride is absorbed mainly as fatty acid in the bile fistula rat, but as a mixture of fatty acid and monoglyceride in the normal animal. Analysis of lymph lipids confirmed that the mechanism of absorption is different in the bile fistula and normal animals. A mixture of triolein labelled with 3H in the glycerol moiety and triolein labelled with 14C in the fatty acid moieties was also used as a marker in corn oil test meals fed to lymph fistula rats with and without bile diversion. In bile fistula rats the early lymph samples contained more 3H than 14C, but from 6 hr onward 14C predominated, and overall more 14C than 3H was recovered in the lymph. It seems probable that the early high recovery of 3H was due to the incorporation of free glycerol into lymph lipids in these animals. The overall recovery of 14C in excess of 3H is consistent with the concept that triglyceride is absorbed chiefly as fatty acid in the absence of bile. In animals with a normal bile flow 14C was absorbed in excess of 3H throughout the recovery period. It is concluded that the mechanism of fat absorption in the bile fistula rat is not the same as it is in the presence of bile. Possibly fatty acid may be absorbed as soaps in the absence of bile, but no mechanism for the absorption of intact monoglyceride by these animals can be suggested. © 1969 The Physiological Society
