The intestinal absorption and metabolism of micellar solutions of lipids

Ultracytochemical study of fatty acid absorption in the rat small intestine by performic acic-phosphotungstic acid (PFP) reaction.

“…The free fatty acid without the envelope would be diffusing the microvilli and the terminal web to the underlining ER. Now it is evident ultracytochemically that fatty acid is transported to the ER by diffusion, as many workers (1,(3)(4)(5)(6)(7)15) have suggested. It may penetrate the microvillus membranes in the form of a small particle.…”

“…One is the pinocytic mechanism (12,13) and another is the diffusion mechanism across the microvillus membranes and to the teminal web (1,9,14,15). Biochemical (5,6) and physicochemical (3,4,7) investigations seem to support the latter as the primary mechanism of fat absorption. The first prominent morphological alteration in the cells after fat intake was the appearance of electron dense droplets in the endoplasmic reticulum (ER).…”

The ultrastructure of lipid absorption and transport in bovine intestinal mucosa

“…The experiments of Strauss (1966), in which intestinal tissue was incubated in micellar solutions at various temperatures, demonstrated that triglyceride resynthesis (but not lipid absorption) was energy dependent, and confirmed the biochemical data of Johnston and Borgstrom (1964). Triglyceride synthesis at Cc was inhibited, while at 10°C some synthesis occurred as was shown by very small droplets within the SER.…”

“…The absorption of monoglycerides and fatty acids from bile salt mixed micelles was first shown in vitro by Johnston and Borgstrom (1964) using hamster intestinal slices. Employing C^^-oleic acid and H^-l-monoolein, these workers demonstrated penetration of label into the intestinal mucosa and, from the ratios, they concluded that the monoglyceride and fatty acid were absorbed intact.…”

“…Consequently, the authors concluded that penetration was not a rate limiting step. In regard to the mechanism of penetration, Johnston and Borgstrom (1964) studied uptake in slices incubated at 0°C, heat inactivated, or incubated at 37°C in the presence of metabolic inhibitors. These treatments had no effect on uptake of oleic acid and 1-monoolein, and the authors concluded that the transport was enzymatically and energetically independent, suggesting a passive molecular diffusion.…”