Fecal Excretion of Administered Isotopic Bile Acids

Fecal Excretion of Administered Isotopic Bile Acids 

Measurement of fecal excretion of isotopic bile acids (65) gives only the half-life of the labeled bile acid used. The isotope is injected intravenously, and the daily fecal excretion of radioactivity is measured. According to this procedure, the fractional excretion rate of cholic acid in man is normally about 12-13% per day (66,67). Disadvantages of the method are that the absolute values are not obtained, the cholic and chenodeoxycholic acid excretions must be measured separately or a double label method must be used, and the fecal flow should be regular, though an unabsorbable fecal marker can be used. The method appears to be suitable for screening of ileal dysfunction. 

In the isotope dilution method, described originally by Lindstedt (35), a tracer dose of a labeled bile acid is given orally or intravenously and the disappearance is followed by determining the specific activity of that bile acid in duodenal contents serially for up to 7 days. The specific activitytime curve is exponential. Thus the pool size and turnover (equals synthesis) of that bile salt can be determined. Cholic and chenodeoxycholic acids appear to have slightly different turnover data in some individuals (38,67). Therefore, the metabolism of the two should be measured separately if exact figures are wanted, by using both labeled cholic and chenodeoxycholic acids. A gross estimate of the one can be obtained, however, from the ratio of these two bile acids in the bile if the pool and turnover of the other are measured (35,37). 

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B. Fecal Excretion of Administered Isotopic Bile Acids... 

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