Native bile and intestinal content

Recent physical-chemical observations on native mammalian systems reveal that the proposed mixed micellar mechanism of lipid solubilization and transport in both bile and in upper small intestinal contents is incomplete [1,260-263]. Bile is predominantly a mixed micellar solution but, particularly when supersaturated with Ch, also contains small liquid-crystalline vesicles which, as suggested from model systems [239], are another vehicle for Ch and L transport. In dog bile which is markedly unsaturated with Ch [258], these vesicles exist in dilute concentrations and may be markers of the detergent properties of BS on the cells lining the biliary tree and/or related to the mode of bile formation at the level of the canaliculus. In human hepatic bile, which is generally dilute and markedly supersaturated with Ch, these vesicles may be the predominant form of Ch and L solubilization and transport [261]. If hepatic bile is extremely dilute, it is theoretically possible that no BS-L-Ch micelles may be present [268] all of the lipid content may be aggregated 

Both micelles and unilamellar liquid-crystalline vesicles coexist during human fat digestion in the aqueous portions of upper intestinal content [262,263, Chapter 14]. In terms of composition and size, the micelles are not like biliary micelles, as has been traditionally believed, but are considerably larger 100 A) with relative lipid compositions which fall on the limits of the mixed lipids/Ch-BS phase boundary. The liquid-crystalline vesicle (or liposomal) phase of upper small intestinal contents is less well defined physico-chemically [262,263] its crucial importance in fat digestion and absorption is obvious in view of the fact that fat absorption proceeds efficiently in the total absence of BS micelles [262]. 

23 Haslewood, G.A.D, (1978) The Biological Importance of Bile Salts, pp. 1-206, North-Holland, Amsterdam. 

24 Heaton. K.W, (1972) Bile Salts in Health and Disease, pp. 1-252, Churchill-Livingstone, London. 

30 Elliott, W.H. and Shaw, R. (1981) in Steroid Analysis by HPLC (Kautsky, M.P., Ed.) pp. 1-40, Marcel Dekker, New York. 

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