Ileal uptake of oleic acid: evidence for adaptive response to high fat feeding.

When I-14C oleic acid at 120 micron Eq/hr was infused into the duodenum in normal rats in a micellar solution with mono-olein (60 mu moles/hr) in 15 mM taurocholate over 6 hr uptake was nearly complete (97%). However, when this same solution was infused into the mid small bowel in control animals uptake was incomplete (88.9 +/- 2.6%, mean +/- SEM, P < 0.01). After 4 weeks on a high fat diet, containing 45% vegetable oil by weight, oleic acid uptake increased to 98.1 +/- 0.1% (P < 0.01 compared to controls). The improved uptake of oleic acid was associated with increased dry weight of mucosa in the proximal half of the ileum from 109 +/- 8.8/20 cm in controls to 135.6 +/- 7.3 mg/20 cm in high fat diet fed rats (P < 0.05), while protein increased from 107.4 +/- 6.5 to 124.9 +/- 4.8 mg/20 cm (P < 0.05). There was no increase in DNA expressed as mg/g wet weight of mucosa or in number of cells per villus. Lipid content of the mucosa and degree of esterification of absorbed oleic also were unaltered. These results indicate that the mucosa of the proximal ileum responds to high fat feeding by hypertrophy (increased mass and protein, with no change in DNA content or cell number) and that this change is associated with more complete uptake of oleic acid reaching this part of the small bowel.