The availability of different sources of cholesterol for bile acid synthesis by cultured chick embryo hepatocytes

The availability of different sources of cholesterol for bile acid synthesis by cultured chick embryo hepatocytes was studied. (1) Mevalonolactone was taken up by the cells and converted to cholesterol, cholesterol ester and tauroconjugates of bile acids. The addition of mevalonolactone had little effect on the conversion of endogenous cholesterol to taurocholic acid; however, taurochenodeoxycholic acid synthesis was stimulated. 25-30% of the cholesterol synthesized from mevalonolactone was converted taurochenodeoxycholic, taurocholic and two so-far unidentified bile acids. All bile acids were secreted into the incubation medium. (2) When cholesterol was added as mixed liposomes with phosphatidylcholine, it was taken up by the cells and converted to bile acids. At low concentrations of liposomes, the greater part of the cholesterol which was taken up by the cells was converted to bile acids. At higher concentrations, considerable amounts of cholesterol and cholesterol ester accumulated inside the cells. (3) When mevalonolactone and cholesterol liposomes was added together, both substrates were used simultaneously for bile acids synthesis. (4) HDL cholesterol was the best substrate tested, yielding large amounts of two, so-far, unidentified bile acids (possibly allo-bile acids) and smaller amounts of taurocholic and taurochenodeoxycholic acid. Addition of HDL suppressed the conversion of endogenous cholesterol to taurocholic acid; taurochenodeoxycholic acid synthesis, however, was stimulated.