The effect of pregnancy and estradiol-17 beta treatment on the biliary transport maximum of dibromosulfophthalein, and the glucuronide conjugates of 5-phenyl-5-p-hydroxyphenyl[14C]hydantoin and [14C]morphine in the isolated perfused rat liver.

The biliary transport maximum (Tm) of three organic axions was determined in the isolated perfused livers of untreated female (control), estradiol-17 beta (E2)-treated female (1 mg/kg/day, s.c. for 14 days), and pregnant (19-21 days of gestation) rats. Dibromosulfophthalein (DBSP), 5-phenyl-5-p-hydroxyphenyl[14C]hydantoin (HPPH) and [14C]morphine were infused continuously into the perfusate for a total dose of 41.2, 18, or 40.5 mumol, respectively. The concentration of [14C]HPPH and [14C]morphine declined in the perfusate, whereas the concentrations of [14C]HPPH glucuronide and [14C]morphine glucuronide increased during the 90-min experiment, indicating that the rate of formation of the glucuronide exceeded its rate of excretion in bile. E2 treatment decreased the Tm (nmol/min/g liver) for [14C]HPPH glucuronide and [14C]morphine glucuronide but not for DBSP, whereas pregnancy decreased the Tm for all three organic anions. Pregnancy, and to a lesser extent E2 treatment, increased liver weight. When expressed per whole liver, the Tm was not altered by pregnancy for any of three organic anions. E2 treatment increased the Tm for DBSP, had no effect on the Tm for HPPH glucuronide and decreased the Tm for [14C]morphine glucuronide. These data suggest the presence of multiple carriers for organic anions which are differentially affected by estrogen treatment and pregnancy.