Primary Bile Salts in Man

There are two 24-carbon primary bile acids in man, cholic and chenode-oxycholic acids, shown as compounds I and II, respectively, in Fig. 1. There are two 27-carbon bile acids in human bile, trihydroxycoprostanic acid. III, and dihydroxycoprostanic acid, IV. These may also be regarded as primary bile acids, but they occur in very small quantities compared to the amounts of 24-carbon bile acids and consequently the term primary bile acids usually refers to the two 24-carbon bile acids in man, cholic and chenode-oxycholic. 

Cholate and chenodeoxycholate are the only two 24-carbon bile salts which can be isolated from the bile of patients with total external bile fistula (2), an observation which supports the validity of the primary and secondary bile salt concept. 

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The two primary bile salts in man, cholate and chenodeoxycholate, are synthesized exclusively in the liver, and consequently measurement of their concentrations in blood or bile often yields useful information about the liver and its response to injury. Bile salt metabolism is altered in two important ways with liver injury. The concentrations of bile salts in the blood increase, and the concentration ratio in both blood and bile changes. 

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