The goal of the present study was to determine 1) whether the poor digestion and absorption of glycerol tristearate (TS) that we observed previously is due to amount fed and 2) whether the digestion, absorption, and lymphatic transport of TS is affected by the presence of either a saturated fat [glycerol tripalmitate (TP)] or a monounsaturated fat [glycerol trioleate (TO)]. Three groups of intestinal lymph fistula rats were used. Group A was fed a lipid emulsion containing 12.5-mu-mol of TS (labeled as [glyceryl-1,3-C-14]tristearate), 7.8-mu-mol of egg phosphatidylcholine, and 57-mu-mol of sodium taurocholate in 3 ml of phosphate-buffered saline per hour for 8 h. Group B rats were fed the same emulsion as group A, but with 12.5-mu-mol of TO added. Group C rats had 12.5-mu-mol of TP instead of TO added to the group A emulsion. The lymphatic radioactivity and triglyceride outputs were significantly lower in group A, with group C next and group B having the highest outputs. Significantly more TS remained in the lumen of the group A rats compared with groups B and C. The majority of the radioactivity in the lumen was still in the TS from in all three groups, indicating poor lipolysis. However, once the fatty acid and monoglyceride were absorbed, the reesterification process was similar in all three groups. When we studied the ability of the three groups of animals to transport the absorbed lipid into lymph (lymph transport index), both groups B and C were significantly better than group A rats. Thus the presence of both TP and TO greatly enhances the lymphatic transport of TS, with TO more effective. This enhancement was mediated by better lipolysis and also more efficient packaging of absorbed fat into triglyceride-rich lipoproteins.
