Estradiol-17beta-glucuronide (E217G) is a cholestatic agent and is considered to be related to the pathogenesis of
intrahepatic cholestasis of pregnancy. In the current study, we examined the mechanism of the biliary excretion of E217G and
estradiol metabolites in rats. Biliary excretion of tracer doses of [3H]
estradiol-17beta-
glucuronide and [14C]
estradiol or [3H]
taurocholate and ]14C]
vinblastine, a
P-glycoprotein (P-GP) substrate, intravenously administered as a bolus to bile-drained control rats or EHBR was studied. Biliary excretion of E217G and
estradiol metabolites EHBR was markedly delayed. Analyses of biliary metabolites after
estradiol injection showed less polar conjugates in EHBR. In contrast, the excretion of
taurocholate and
vinblastine (VLB) was only slightly delayed in EHBR. Although
phenothiazine treatment to induce the expression of P-GP increased biliary
vinblastine excretion, it did not affect biliary excretion of a tracer dose of [3H]
estradiol-17beta-
glucuronide. However,
phenothiazine treatment inhibited the
cholestasis induced by E217G infused at the rate of 0.075 micromol/min/100g for 20 minutes and increased biliary E217G excretion.
Sulfobromophthalein infusion (0.2 micromol/min/100 g body 0 weight) markedly inhibited the biliary excretion of E217G and
estradiol metabolites, whereas dibromosulfophthalein (DBSP) at the same infusion rate had no effect. These findings indicate that EG17G is excreted into bile by a canalicular organic
anion carrier for sulfobromopthalein (BSP), not for DBSP, under physiological conditions, and that P-GP influences E217G excretion only at a high dose. under physiological conditions, and that P-GP influence s E217G excretion only at a high dose.