Variations in dietary triacylglycerol saturation alter the lipid composition and fluidity of rat intestinal plasma membranes

Rats were maintained on nutritionally complete diets enriched in unsaturated (corn oil) or saturated (butter fat) triacylglycerols. After 6 weeks, significant differences in the lipid composition and fluidity of a number of intestinal membranes were observed. The corn oil diet (enriched mainly in linoleic acid) increased the overall unsaturation of the acyl chains and enhanced the lipid fluidity, as assessed by the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene, of enterocyte microvillus and basolateral membranes and of colonocyte basolateral membranes. Concomitantly, the cholesterol content and the cholesterol/phospholipid molar ratio were increased in the microvillus but not in the basolateral membranes. The increased cholesterol in ileal microvillus membranes can result from enhanced cellular biosynthesis, since ileal slices from rats fed the unsaturated diet incorporated [¹⁴C]octanoate more rapidly into digitonin-precipitable sterol. Increased fluidity of the enterocyte microvillus and basolateral membranes, respectively, enhanced the enzyme specific activities of p-nitrophenylphosphatase and (Na⁺+K⁺)-dependent adenosine triphosphatase. The results indicate that the lipid composition, fluidity and enzyme activities of intestinal plasma membranes can be altered by dietary means. Moreover, rat enterocytes possess regulatory mechanisms which modulate the cholesterol content of the microvillus membranes so as to mitigate changes in lipid fluidity.