Linoleic acid absorption in the unanesthetized rat: mechanism of transport and influence of luminal factors on absorption.

Linoleic acid intestinal absorption was studied in the unanesthetized rat. At low (21-1260 micrometer) intraluminal concentrations, absorption took place by facilitated diffusion; while at high (1.26-2.5 mM) concentrations, simple diffusion was the predominant mechanism of transport. At low concentrations (840 micrometer), the equimolar additions of oleic, linolenic, and arachidonic acids or lecithin inhibited the absorption of linoleic acid. Substitution of potassium for sodium in the buffer solution, substitution of Tween 80 for sodium taurocholate, or decrease in the hydrogen ion concentration all resulted in decreased rate of linoleic acid absorption. Increase in sodium taurocholate concentration, or perfusate flow rate increased linoleic acid's absorption. These experiments demonstrate that linoleic acid is absorbed by a concentration-dependent dual mechanism of transport. The absorption rate is modified by the pH, surfactant type and concentration, the simultaneous presence of other polyunsaturated fatty acids, and the thickness of the unstirred water layer.