A physicochemical study of fat absorption in rats limitation of methods in vitro

Abstract

1. 1. The hypothesis that the first stage of normal fatty acid absorption represents a partition between a luminal bile salt mixed micellar phase and mucosal membrane lipid phase has been investigated. 2. 2. Everted segments of rat jejunum incubated with [ 14C]oleic acid in 10 mM sodium taurocholate accumulated a greater amount of 14C-labelled free fatty acid when incubated at pH 5.8 then at pH 7.3 but this was unrelated to incorporation into jejunal [ 14C]triglyceride. 3. 3. Uptake of [ 14C]oleic acid into mucosal free fatty acid from 15 mM taurocholate (20 μmoles/ml) in vitro was less than from 6 mM taurocholate, but the triglyceride accumulation was greater. 4. 4. pH had no effect on the uptake in vitro of the non-ionized oleyl alcohol from taurocholate mixed micellar solution but with increasing taurocholate concentration there was decreased uptake of [ 14C] oleyl alcohol. 5. 5. Increasing concentrations of [ 14C]oleic acid in bile salt mixed micelles caused an increase both of 14C-labelled free fatty acid and [ 14C]triglyceride in vitro. 6. 6. Absorption of [ 14C]oleic acid from perfused or closed loops of jejunum in vivo was increased with increased oleic acid concentration but was not influenced by pH or bile salt concentration. 7. 7. These findings suggest that although uptake of free fatty acid by the mucosal cell in vitro may be predicted on the basis of a partition between micelle and lipid membrane via a molecular phase, this is not an important mechanism during normal fatty acid absorption.