Intestinal uptake of fatty acids complexed to proteins in the chick intestine

Intestinal mucosal uptake of protein complexed-fatty acids was studied in ligated duodenal loops in the chick. Increasing the concentration of an albumin oleic acid-complex resulted in a linear increase in uptake of oleic acid. Varying the albumin-to-oleic-acid ratio with constant albumin concentration resulted in depressed oleic acid uptake when the ratio was below 1:3. Uptake of oleic acid complexed to albumin was increased by some 60% on addition of taurocholic acid above its critical micellar concentration. In the absence of albumin, oleic acid uptake was some 60% high from a micellar solution. Uptake of lauric acid from aqueous solution was linear with concentration until its maximum solubility was reached, whereas uptake from albumin complexes at varying lauric acid concentrations was not linear with increasing concentration. Stearic acid exhibited lowest uptake and linoleic and linolenic acid highest uptake both when complexed to albumin or from micellar solution, although albumin-complexed fatty acids were transported at about half the rate of micellar fatty acids. We concluded that some proportion of fatty acids complexed to lipophilic proteins can be absorbed in the intestine in the absence of bile acids. When oleic acid was complexed to casein, bovine serum albumin or beta-lactoglobulin at protein:oleic acid ratio of 1:10 serosal transport was 40 to 50% of mucosal uptake.