Effect of fasting on hepatic ligandin, Z protein, and organic anion transfer from plasma in rats.

The effect of fasting on the rate of disappearance from plasma of bromsulphthalein (BSP) and dibromsulphthalein (DBSP), the hepatic content of BSP, and the concentration of ligandin and Z protein, two hepatic organic anion-binding proteins, was studied in the rat. Fasting for 48 h decreased the plasma disappearance of BSP and DBSP and the hepatic content of BSP as well as the amount of ligandin and Z protein. Phenobarbital given prior to fasting partially prevented these changes. A method of quantitation of Z by radioimmunoassay is described. Discrepancies in Z quantiation by dye binding and immunological methods in fasted but not control rats suggest the presence of competitors for organic anion binding to Z in fasting as well as after phenobarbital administration. Results of studies of ligandin turnover during fasting suggest decreased synthesis and increased degradation of the protein. Similar events may be of pathogenetic importance in nonhemolytic unconjugated hyperbilirubinemia observed during fasting in man, horses, and other animals.