Regulatory roles of taurine and glycine in the formation of bile acid conjugates—Analyses using freshly isolated hepatocytes and hepatocytes in primary culture.

The regulatory roles of taurine and glycine, which were transported or biosynthesized in hepatocytes, in the formation of bile acid conjugates were studied using freshly isolated rat hepatocytes(fresh hepatocytes) and rat hepatocytes maintained in primary culture(cultured hepatocytes). In the formation of taurocholic acid, transported taurine significantly increased the rate of taurocholic acid formation both in fresh and cultured hepatocytes. Similarly, the formation of taurocholic acid in these cells was facilitated by the addition of cysteine and hypotaurine which were metabolically converted to taurine. On the other hand, glycine which was added exogenously into the incubation medium had no effect on the formation of glycocholic acid in fresh and cultured hepatocytes. In contrast, the addition of serine and threonine which were metabolically converted to glycine in hepatocytes significantly increased the formation of glycocholic acid in fresh hepatocytes. These results indicate that the formation of taurine-conjugated bile acids in hepatocytes is maintained by both transported and biosynthesized taurine, while that of glycine-conjugated bile acids is regulated by biosynthesized glycine in hepatocytes, but not by transported glycine.