Bile protein secretion in the rat stimulated by taurocholate effect of chloroquine

The biliary protein excretion during sodium taurocholate induced choleresis was studied in normal rats and in rats treated with the lysosomotropic agent, chloroquine. The analysis of the protein component in bile was made on SDS–polyacrilamide gel, and the individual polypeptides were quantitated by densitometry. The excretion of bile polypeptides was compared with that of lysosomal acid phosphatase. The biliary excretion of polypeptides of molecular mass lower than and equal to 54 kDa was markedly stimulated by taurocholate-induced choleresis. Chloroquine treatment of rats diminished the biliary excretion of such polypeptides and also inhibited their excretion induced by taurocholate. The behaviour of these polypeptides was well correlated to that of the lysosomal marker. The biliary excretion of polypeptide bands of a higher molecular mass (up to 140 kDa) did not show major changes during taurocholate-induced choleresis in any of the groups. The results indicate that biliary excretion of proteins in the rat may be either stimulated by taurocholate or may be independent of the bile salt. The former requires the functional integrity of chloroquine-sensitive hepatocyte compartments, which may involve the lysosomes.

Influence of hypoproteinemia on bile proteins

Plasmapheresis was performed in dogs to change the serum protein and bile protein. A low caloric diet and plasmapheresis resulted in a diminished plasma albumin, slightly increased α-globulin, and definitely increased ß- and γ-globulins. Simultaneously, B-fraction (albumin-containing-fraction of bile) decreased while the C-fraction (α-globulin-containing-fraction of bile) and D-fraction (ß- and γ-globulin-containing-fraction of bile) increased. When the plasmapheresis was discontinued and a normal caloric diet supplied, there was a gradual reversal of these changes toward the original levels. This is further indication that B-, C- and D-fraction of bile proteins arise from blood proteins. It is apparent that this is not by simple transudation of proteins from capillaries to bile canaliculi because the smallest protein molecular B-fraction comprises a smaller proportion of bile proteins than of serum proteins, whereas the larger molecular D-fraction comprises a larger proportion of bile proteins than of serum proteins, and yet the total bile protein concentration is always much less than the total serum protein concentration. There must be some mechanism regulating the occurrence of the bile proteins, and this may be an additional function of the hepatic cells.