Metabolism of bile acids has been characterized in vivo and in vitro, the latter in a variety of systems including isolated perfused liver and transformed and normal hepatocytes. We have been exploring the use of precision-cut slices of rat liver to study bile acid metabolism. Initially, secretion of individual bile acids by slices from control rats and rats treated with a-naphthylisothiocyanate (ANIT) or clofibrate was investigated. In each study, bile acids were added to the medium to examine effects on conjugation, metabolism and secretion of bile acids by slices. Bile acids in media were measured using a HPLC/enzymatic method with fluorescence detection. In these experiments (6 to 7 hr incubations in Williams' E medium), secretion of total bile acids by slices from control rats ranged from 160 to 447 pmol/mg protein/hr. These rates are 3 to >30-fold higher than those reported for cultured hepatocytes and compare favorably with those for isolated perfused liver. Secretion rates of individual bile acids from slices from rats treated with ANIT were significantly increased for tauro-a-muricholate, tauroallocholate, taurocholate (strong trend), tauroallochenodeoxycholate, and taurochenodeoxycholate, and decreased for taurohyodeoxycholate. The addition of b-muricholate to the medium increased the secretion of tauro-b- muricholate by approximately 10-fold and increased the formation of an unknown bile acid, identified as D22-tauro-b-muricholate by NMR spectroscopy, by 4-fold. Slices from rats treated with clofibrate had total rates of secretion that were approximately 3-fold less than those from control rats. These lower rates resulted from decreased secretion of glyco-b-muricholate, tauro-b-muricholate, D22-tauro-b-muricholate, taurohyodeoxycholate, and taurocholate. Decreased taurocholate secretion persisted even with the addition of taurine and glycine and/or cholate to the medium. These experiments demonstrate that liver slices can provide a valuable alternative to other in vitro systems for the study of bile acid metabolism and secretion.
