Glycine bile salt metabolism

Bile salts perform an important function and are recycled by the body. The body produces 400 mg of bile salts per day from cholesterol this represents the fate of half of the cholesterol nsed daily in metabolism (800 mg). However, 20 to 30 g of bile acids is maintained in the enterohepatic circnlation. Less than 0.5 g per day is lost to excretion. Bile salts are produced in the liver, stored in the gallbladder, and secreted through the bile duct into the dnodennm where they act on triacylglycerol molecules in the intestines. In the gnt, the glycine or tanrine moiety is removed from the bile salt. It is reabsorbed in the small intestine and retnmed to the liver for rense via the portal vein. Bile salts are absorbed by passive diffnsion along the entire small intestine, and a specialized Na+-bile salt cotransporter is present in the lower ilenm. 

Biochemical studies with isolated rat hepatocytes have largely been concerned with transport mechanisms [15], secretion of bile acids [17-19], or biosynthesis of bile acids [20]. The capacity of cultured hepatocytes to convert tauro- or glyco-chenodeoxycholate to a- and )8-muricholates [19,21] and to produce bile salts (glycine or taurine conjugates) during the dark phase of the diurnal cycle [21] has been established. Demonstrations of other metabolic transformations by hepatocytes are included in the following sections. 

The primary bile salts (those synthesized in the liver) are conjugates of chenodeoxycholic acid and cholic acid with taurine or glycine (Figure 4.16). Intestinal bacteria catalyse deconjugation and further metabolism to yield the secondary bile... 

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