The intestinal absorption of cholesterol and sitosterol was compared in rats. The intragastric administration of a single emulsified lipid meal containing either 50 mg of [4-14C]cholesterol or [4-14C]sitosterol resulted in the lymphatic absorption of 18.2% and 0.42% of each sterol, respectively, in 6 hr. This difference was unaltered when the mucosal sterol load was equalized by reducing the cholesterol to 1 mg in the emulsified lipid meal while maintaining the same sitosterol load or when the physical state in the lumen was equalized by infusion of a micellar solution containing both sterols into bile-diverted intestine. Lymphatic cholesterol was 90% esterified compared to 12% for sitosterol. Both sterols were associated predominantly (>70%) with the chylomicron fraction. Eighty percent of the chylomicron cholesterol as recovered as ester with the core lipids, while 77% of the sitosterol was recovered as free sterol with the chylomicron coat. In mucosal homogenates at 6 hr, sitosterol recovery was one-eleventh that of cholesterol. When [3H]cholesterol (10 mg) and [14C]sitosterol (10 mg) were co-administered in an emulsified intragastric lipid meal, sitosterol associated with the brush border isolated 2 hr later was one-fifth that of cholesterol. Similar differences were seen when brush border membranes were incubated in vitro with micellar solution containing either 50 μM [14C]cholesterol or [14C]sitosterol and the relative uptake of each sterol was unaffected by micellar phospholipid type (egg yolk phospholipids, phosphatidylcholine, or phosphatidylethanolamine). When the affinity of several absorbable and nonabsorbable sterols for the mixed taurocholate micelle was compared in an in vitro model system which assessed sterol movement from the micellar to the oil phase, there was preferential movement of cholesterol and other absorbable sterols while unabsorbable sterols including sitosterol were retained. The differential sterol affinity was dependent on the bile salt composition of the micelle with the glycine or taurine conjugates of cholate most effective. Transfer to the two sterols was equivalent from Triton X-100 and phospholipid emulsions. These studies suggest two major sites of discrimination between absorbable and nonabsorbable sterols for absorption, differential uptake at the brush border and differential affinity for bile salt in micelles. Other minor sites of discrimination may be expressed intracellularly since mucosal cholesterol and sitosterol, although present in limited amounts, are processed differently with respect to esterification and chylomicron incorporation.
|Number of pages||9|
|Journal||Journal of lipid research|
|Publication status||Published - 1988|
ASJC Scopus subject areas
- Cell Biology