Chenodeoxycholic acid, conjugates quantitation

Cholic acid and chenodeoxycholic acid, known as the primary bile acids, are quantitatively the most important metabolites of cholesterol. After being biosynthesized, they are mostly activated with coenzyme A and then conjugated with glycine or the non-pro-teinogenic amino acid taurine (see p. 62). The acid amides formed in this way are known as conjugated bile acids or bile salts. They are even more amphipathic than the primary products. 

Since free and conjugated dihydroxy cholanic acids cannot be separated completely by paper and thin-layer chromatography they must be differentiated by specific reactions. The following procedures are suitable for quantitative determination of free bile acids reaction with concentrated sulfuric acid for determination of cholic acid (Hammarsten 1925), reaction with salicylic aldehyde and sulfuric acid for determination of deoxycholic acid (Szalkowski and Mader 1952), reaction with ethyl acetate, concentrated sulfuric acid and acetic acid anhydride for chenodeoxycholic acid (Isaksson 1954). 

Quantitation of bile acid synthesis. Bulk measurement of fecal bile acids with GLC (cf. 5) is quite simple at the moment and has been widely used for quantitation of total bile acid synthesis. The use of nonpolar capillary column is preferable for routin work. The complexity of the fecal bile acid mixture requires extensive technique for quantitation of individual bile acids of cholic acid and chenodeoxycholic acid origin or their different conjugates. According to our experience about 80% of the fecal bile acids in normal feces can be identified with a reasonable accuracy from the GLC run on capillary column to originate from either cholic or chenodeoxycholic acid. Usually litho and deoxycholic acids are major fractions but sometimes 38-OH bile acids can predominate. In bile acid malabsorption 7-dehydr-oxylated derivatives are frequentl3 lacking or small and the presence of 7 3-011 and/or ketonic transformation products can be conspicious (see Fig. 1). 

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