The effect of partition of fatty acid between oil and micelles on its uptake by everted intestinal sacs

1. 1. Everted sacs of rat jejunum were used to measure the effect on uptake of labelled oleic acid, 1 mM, when an unabsorbable oil (glyceryl-trioleyl ether) was present. The incubation medium also contained monoolein 1 mM, and pure bile salts (sodium taurocholate-sodium taurodeoxycholate, 4:1 on a molar basis). 2. 2. Increasing concentrations of triether had no effect on the low uptake of oleic acid in the absence of a micellar phase, bile salts 1 mM, when virtually all the lipid was in emulsified particles. 3. 3. When most of the oleic acid (and monoolein) was present in a micellar phase, bile salts 4 mM or 5 mM, uptake was greatly accelerated. Addition of increasing amounts of triether now led to partition of an increasing proportion of oleic acid into the emulsified oil particles with a corresponding reduction in concentration of oleic acid in the micellar or isotropic phase. Uptake of oleic acid was reduced in linear proportion to reduction in micellar concentration. 4. 4. The regression of oleic acid uptake on isotropic aqueous concentration was the same in these experiments, in which bile salt concentration remained constant, as in previous experiments in which the isotropic concentration was varied by altering the bile salt concentration. 5. 5. These experiments provide further evidence that uptake in vitro depends on the concentration of fatty acid in the isotropic aqueous phase, and not on the concentration of bile salts per se .