Quantitative Fecal Excretion of Bile Acids by Germfree and Conventional Animals

QUANTITATIVE FECAL EXCRETION OF BILE ACIDS BY GERMFREE AND CONVENTIONAL ANIMALS 

The quantitative analysis of the fecal bile acids of rats presents a special problem which does not need to be considered in comparable studies with most other species. The presence of appreciable quantities of muricholic acids, over 50% of the total with germfree feces, requires methods which will not cause destruction of these 3,6,7-trihydroxy bile acids if chromatographic techniques are used. 

It has been shown that the trifluoroacetates of 3,6,7-trihydroxy bile acids are subject to thermal decomposition in gas chromatographs (30). Oxidation of the bile acids to their keto derivatives and subsequent gas chromatography should also be avoided (31). In our laboratory, we have been unable to gas chromatograph any oxidized 3,6,7 bile acid methyl esters they are either destroyed or will not elute in a reasonable amount of time. 

If isotopic techniques are used, care must be taken to ensure that the entire bile acid pool is uniformally labeled. Use of radioactive cholic acid 

Gustafsson et al. (22) studied the fecal excretion of cholic acid-i C metabolites in conventional and germfree rats. The mean daily excretion of labeled cholic acid and its metabolites was 18.9 mg/kg body weight for the conventional group and 8.2 mg/kg body weight for the germfree group. As mentioned above, their techniques would not uniformly label the bile acid pool however, their other techniques may have caused inclusion of the muricholic acids in their assay. 

---