Studies on micellar fatty acid uptake by rat intestine in vitro with reference to the role of bile

Abstract

1. The uptake and esterification to trigylceride of oleic acid in micellar form was studied in rat intestine in vitro. Sacs of the upper half of the everted intestine taken from bile fistula rats were incubated in a buffered solution containing mono‐olein, 14C‐labelled oleic acid and bile salt (sodium taurocholate (NaTch) in concentrations exceeding the critical micellar concentration). 2. At 37° C incubation temperature increasing the NaTch concentration enhanced both uptake and esterification. Adding whole rat bile caused uptake to decrease at all NaTch concentrations but had only a slight and variable effect on esterification. 3. Lowering the incubation temperature to 0° C suppressed esterification but had no effect on uptake. 4. At 0° incubation temperature adding whole bile still decreased fatty acid uptake but had no effect on esterification. 5. It is concluded that intestinal fatty acid uptake from micelles is a non‐energy requiring process and that a non‐bile salt component in bile exists which can suppress this process. 6. It is suggested that lecithin may be the non‐bile salt component and that it suppressed uptake by interacting either with the micelles or with the epithelial membrane to reduce fatty acid permeability.

The effect of lecithin on intestinal cholesterol uptake by rat intestine in vitro

“…The existence of the additional active component was established when it was shown that uptake of micellar lipids by intestinal sacs in vitro was strongly suppressed in the presence of whole bile, whereas uptake was increased when the bile salt concentration per se was elevated. Whole bile still suppressed uptake when cell metabolism was depressed by cooling the tissue to 0°C (Rampone, 1973). Thus the non-bile salt component acted by interfering with a non-energy requiring step in the absorptive process.…”

“…It is likely that it would also have a bearing on the absorption of some of the other component parts of mixed micelles. For example, it has been shown that whole bile suppresses intestinal oleic acid uptake from micelles and this response may take place by a mechanism similar to that influencing cholesterol absorption (Rampone, 1972a(Rampone, , 1973.…”

“…It has been suggested that micelles do not penetrate the epithelial membrane directly but are intermediate between an oil (emulsion) phase and an aqueous penetrable monomer phase (Hoffman, 1970). Uptake in either case appears to take place by means of a non-energy requiring process (Johnston & Borgstrom, 1964;Rampone, 1973).…”

Lecithin inhibits fatty acid and bile salt absorption from rat small intestine in vivo

“…Might an impairment in lecithin hydrolysis affect FFA absorption? Rampone (7,8), and Rodgers and O'Connor (9) reported that lecithin could depress uptake of FFA and cholesterol by rat jejunum in vitro. Lecithins form mixed micelles with bile salts and FFA.…”