Intestinal absorption in vivo of micellar and nonmicellar lipid.

KNOEBEL, LEON K. Intestinal absorption in vivo of micellar and nonmicellar Zipid. Am. J. Physiol. 223(2) : 255-261. 1972.-Lymphatic transport of absorbed fatty acid and rate and site of uptake from intestinal lumen were measured in bile-fistula rats which received the lipid mixture, 10 mM oleic acid and 10 mM monoolein, by steady intraduodenal infusion. The concentration of fatty acid solubilized in the four infusates used varied from 40 y0 (10 mM bile salts) to monomolecular solubility (2.5 mr+!t and 1 mM bile salts or 1 y0 gum acacia). A model of micellar and nonmicellar absorption, based on the balance between absorption rate per unit area of intestine and utilization of available surface area, is proposed. Fatty acid was completely absorbed from the proximal intestine for the infusate with a large micellar phase. When the diffusion gradient was reduced with the nonmicellar infusates, the ileum acted as a reserve absorptive area. Differences in lymphatic output of fatty acid between groups given nonmicellar infusates are explained on the basis of intraluminar fluid absorption which resulted in intraluminar concentration of bile salts to varying extents, and thus different degrees of solubilization of fatty acid. Studies on metabolism of absorbed fatty acid in mucosa and lymph support the idea that intracellular triglyceride formation is promoted by increased rate of delivery of fatty acid into the mucosa. The data do not support a specific role of the bile salts in intracellular esterification.