S. Hurwitz

Absorption of oleic and taurocholic acids from the intestine of the chick. Interactions and interference by proteins.

Abstract The interaction between fatty acids, bile acids and proteins in the intestinal lumen and its effect on the mucosal uptake of fatty acids and bile acids in chicks were studied in situ by means of ligated duodenal loops. The basal medium introduced into the loops contained oleic and taurocholic acids in bicarbonate buffer at pH 6.5, with trace amounts of [14C]oleic acid and [14C]-taurocholic acid, [3H]dextran serving as a nonabsorbable reference substance. Tests conducted with varying initial concentrations of oleic acid and taurocholic acid pointed to an optimal molar ratio of oleic acid to taurocholic acid at which the rates of mucosal uptake of both compounds were highest and numerically equal. Addition of casein, albumin or soy protein to the medium caused considerable inhibition of both oleic acid and taurocholic acid uptake. Taurocholic acid uptake alone, or that of the slightly water-soluble lauric acid alone, was similarly decreased by protein. Predigestion of the proteins with pepsin A (EC 3.4.23.1) or elastase (EC 3.4.21.11) eliminated the inhibitory effect on uptake of oleic acid and taurocholic acid. It was shown that casein is able to bind both oleic acid and taurocholic acid. Thus the presence of undigested protein in the upper small intestine of the chick may interfere with the mucosal uptake of lipids by a double action involving direct binding of fatty acids to the protein and disturbance of micellar solubilization of the lipids because of binding of bile acids.

Site of bile acid absorption in the rat

Bile acid absorption was measured in the small intestine of the rat using91Y as a nonabsorbed reference substance. Some 50% of the secreted bile acids were absorbed in the proximal half of the small intestine. In situ incubations of ligated intestinal segments into which tauro(14C-carbonyl)cholic acid was introduced confirmed the considerable uptake of bile acids in the jejunum. The in situ experiments indicated that serosal transport is the limiting stage of bile acid absorption in the jejunum but not in the ileum. Increasing bile acid concentrations in the in situ experiments did not affect the percentage disappearance of dose from the jejunum but reduced the percentage mucosal uptake in the ileum. It is concluded that, in the rat, the proximal small intestine is as important in the absorption of bile acids as the distal small intestine.