Interfacial barriers to the transport of sterols and other organic compounds at the aqueous polysorbate 80-hexadecane interface.

I. The interfacial barrier controlled transport of some biologically important solutes in the aqueous polysorbate 80 hexadecane system were investigated by means of the multiparticulate dispersion technique. 2. It was shown that the resistances to transport of cholesterol, /3-sitosterol, desmosterol, 2oa-hydroxycholesterol, and vitamin D 3 across the oil/water interface, were of the order of IO~-IO 7 times greater than those for diffusion controlled mechanisms. 3. The effects of changing the polysorbate-8o concentration upon the transport rates of the solutes were investigated. Cholesterol,/5-sitosterol, and desmosterol showed little or no change of their permeability coefficients in the o . I I % range of the surfacrant concentration. These results suggest that for these compounds the drug micelle complex is involved in the "transition" state. The data further suggest that a two-step mechanism is involved, viz. the approach of the solute loaded micelle to the interface and the unloading of the solute at the interface. 4. One of the interesting findings of this research relevant to biology is the possible correlation of these experiments to the intestinal absorption of cholesterol and /~-sitosterol. The present studies show that the interfacial resistance for fl-sitosterol is about IO times greater than that for cholesterol, while rat intestinal absorption studies how that cholesterol is absorbed 5 io times more rapidly than fl-sitosterol.