Comparison of cholesterol and beta-sitosterol: effects on jejunal fluid secretion induced by oleate, and absorption from mixed micellar solutions.

Jejunal fluid secretion induced by perfusion with oleic acid can be reduced by the addition of cholesterol. The present study was performed to test the specificity of this effect by comparing the effects of cholesterol with that of a plant sterol, beta-sitosterol during perfusion of the jejunum in healthy volunteers. In addition, we compared the solubilities of cholesterol and beta-sitosterol in micellar solutions and their jejunal absorption rates. One millimolar beta-sitosterol was as effective as 1 mM cholesterol in reducing jejunal fluid secretion induced by 6 mM oleate (n = 7). In mixed micellar solutions consisting of 10 mM taurocholate and 6 mM oleate, solubility of beta-sitosterol is about one third of cholesterol solubility. When cholesterol was gradually replaced by beta-sitosterol in the incubation mixture, beta-sitosterol reduced cholesterol solubility to a greater extent than would be expected from an equimolar replacement of cholesterol by beta-sitosterol. Absorption of beta-sitosterol was limited by its solubility in mixed micellar solutions and both sterols were absorbed at equal rates as long as their solubility limits were not exceeded (n = 5).

Cholesterol reduces the effects of dihydroxy bile acids and fatty acids on water and solute transport in the human jejunum.

Jejunal perfusion studies were performed in 16 healthy volunteers to test the hypothesis that intraluminal cholesterol can mitigate the fluid secretion induced by dihydroxy bile acids and fatty acids. Fluid secretion in the presence of 5 mM taurodeoxycholate was somewhat reduced by 4 mM mono-olein which was used for the solubilization of cholesterol. Addition of 0.8 mM cholesterol reduced fluid secretion further (P less than 0.05). Fluid secretion induced by 4 mM oleic acid was changed to net absorption in a linear fashion with increasing cholesterol concentration in the perfusion solutions. 1 mM cholesterol reduced fluid secretion induced by 6 mM oleic acid (P less than 0.005), but had no effect on fluid secretion induced by 6 mM linolenic acid. Glucose absorption was generally affected in a similar manner as water transport. In vitro, 1 mM cholesterol reduced monomer activity of 6 mM oleic acid to 72.3 +/- 0.9% of control and that of linolenic acid to 81.1 +/- 1.7% of control. Although statistically significant (P less than 0.001), the difference in the effects of cholesterol on monomer activities of the two fatty acids was rather small and it is unlikely that changes in monomer concentration of fatty acids and bile acids account for the protective effect of cholesterol. The in vivo observations point to a new physiological role for biliary cholesterol: the modification of the response of the small intestine to the effects of dihydroxy bile acids and fatty acids.