FURTHER EVALUATION OF THE INTERRELATIONSHIP BETWEEN THE HEPATOCELLULAR TRANSPORT OF BILE-ACIDS AND ENDOCYTOSED PROTEINS

Experiments on the relationship between the hepatocellular transport o f endogenous or exogenously loaded bile acids (sodium taurocholate, TC , 0.5-mu-mol/min/100 g body wt) and horseradish peroxidase (HRP) or im munoglobulin A (IgA) (0.5 mg/100 g body wt) were carried out on anaest hetized Wistar rats. The time course of HRP excretion into bile (accel eration in the secretory peak), but not the total amount of HRP output , was affected by TC infusion. Administration of HRP was found to have no stimulatory effect on either spontaneous or TC-induced bile flow, bile acid, lecithin or cholesterol output. Spontaneous bile acid outpu t was increased (25 and 67%, respectively) in rats that were treated f or 12-h fasting or by oral administration of TC (45 mg/100 g body wt, every 12 h, for 2 days). These manoeuvres did not change the inability of HRP and IgA to increase bile acid output. Exogenous TC load had no stimulatory effect on the hepatocellular transport of endogenous bile acid pool, that was labelled by a combination of fasting and oral adm inistration of C-14-glycocholic acid 12 h before the experiments. Ther efore, exogenous bile acid load-induced stimulation of transcytosis ha d no effect on endogenous bile acid output. Moreover, bile secretion o f both endogenous and exogenously loaded bile acids is unaffected by t he administration of proteins, irrespective of whether they are endocy tosed by a receptor or nonreceptor mediated process.