Bile acid conjugation in fetal hepatic organ cultures

A new technique has been developed in which mammalian fetal liver can be maintained in organ culture for prolonged periods with intact structure and function. Near-term rat fetal liver explants were incubated in vitro for periods of up to 3 wk with preservation of normal cellular morphology and intercellular (organ) relationships. [14C]cholate was incorporated into tissue and medium conjugates at a constant rate during 21 days in vitro. During a 24-h incubation with radioactively labeled cholic acid, bile acid conjugates accumulated in tissues to a maximum value by 6 h and maintained this value through 24 h. During the same 24-h incubation with [14C]cholate, conjugates were secreted into the medium at a constant rate. Addition of 8 X 10(-4) M taurine to the medium during a 4-day incubation produced a threefold enhancement in the rate of conjugate formation in tissues and medium. Enhanced conjugation in the presence of additional taurine was due almost entirely to increased taurocholate formation and no significant difference was observed in the amount of glycocholate formed. Exposure of explants to 3.6 X 10(-4) M cycloheximide for prolonged periods resulted in inhibition of conjugate formation, but when this concentration of cycloheximide was maintained for only 24 h a significantly (P less than 0.001) increased rate of conjugate formation was observed. The results indicate that metabolic processes in the organ-culture system are in a state of dynamic equilibrium and that morphologic integrity and specific hepatocytic function are maintained after 21 days in vitro. Preferential taurocholate formation was demonstrated in rat fetal liver, and the data suggest that glycine and taurine interact with separate enzymatic systems in bile acid conjugation. The possible mechanisms that mediate the effect of cycloheximide are discussed.