Influence of phenobarbital pretreatment on biliary rose bengal excretion in rats.

Plasma concentration, hepatic uptake and biliary excretion of intravenously administered rose bengal was determined in rats pretreated with phenobarbital (50 mg/kg) daily, for four days). After an initial (0--16 min) rapid fall in plasma rose bengal concentration caused by hepatic uptake of the dye, the curves in control and pretreated rats did not differ from each other either after administration of a small (5 mg/kg) or a large (50 mg/kg) dose. Hepatic rose bengal concentration was significantly lower in pretreated animals than in the control group. Since liver weight was higher in the phenobarbital pretreated animals than in the controls, the total amount of rose bengal taken up by the liver did not differ in the two groups. The biliary excretion of low dose (5 mg/kg) rose bengal was significantly higher in phenobarbital pretreated than in the control rats but with doses of 50 mg/kg and 100 mg/kg no difference was observed. These doses of rose bengal diminished the increased bile flow caused by phenobarbital.