Biliary excretion of pravastatin in rats: contribution of the excretion pathway mediated by canalicular multispecific organic anion transporter.

The biliary excretion of pravastatin in normal rats and Eisai hyperbiliruminemic rats (EHBRs) was examined in vivo and in vitro using bile canalicular membrane vesicles (CMVs). In vivo, the total body clearances at steady-state (CLtot) for both rat strains decreased as the infusion rate increased. At the lowest infusion rate, CLtot for normal rats was 1.6 times higher than that for EHBRs. Under this set of conditions, the biliary excretion clearance (CLbile), defined as the biliary excretion rate at steady-state divided by the concentration in the liver (Cliver), for normal rats was 3-fold higher than that for EHBRs. The CLbile fell markedly with increasing Cliver for normal rats and the Michaelis constant (KM) for Cliver was 180 microM; in contrast, the degree of saturation was slight if any in EHBRs. In vitro, the uptake of pravastatin by CMVs prepared from normal rats exhibited clear ATP-dependence, whereas only a minimal effect of ATP was observed on the uptake by CMVs from EHBRs. Transport kinetic studies were performed over a wide range of pravastatin concentration (0.2-10,000 microM) with a tracer tritium-labeled pravastatin. Saturation was observed both in the ATP-dependent (KM: 220 microM) and ATP-independent (KM: 480 microM) uptake by CMVs prepared from normal rats. ATP-dependent uptake of 2, 4-dinitrophenyl glutathione, a typical substrate for the canalicular multispecific organic anion transporter (cMOAT), was inhibited by pravastatin in a concentration-dependent manner and the resultant inhibitory constant of pravastatin (170 microM) was comparable with the KM value of ATP-dependent pravastatin uptake itself. In conclusion, biliary excretion of pravastatin is mediated mainly by cMOAT in normal rats. This can explain the decrease in the biliary excretion of pravastatin in EHBRs.

Methotrexate is excreted into the bile by canalicular multispecific organic anion transporter in rats.

Methotrexate [(+) amethopterin, L-MTX] has two carboxyl groups in its structure and is eliminated mainly by excretion into urine and bile. To investigate the biliary excretion mechanism of L-MTX, we performed in vivo and in vitro studies using mutant rats, Eisai hyperbilirubinemic rats (EHBRs), whose canalicular multispecific organic anion transporter (cMOAT) is defective as a consequence of heredity. After i.v. administration of L-MTX to EHBRs, its plasma disappearance and biliary excretion was slower than in normal Sprague Dawley rat (SDR). ATP-dependence and overshoot phenomena were observed in the uptake of [3H]L-MTX by canalicular membrane vesicles (CMV) prepared from SDR, whereas no ATP-dependence was observed in CMV from EHBRs. The ATP-dependent uptake of L-MTX by SDR CMV exhibited saturable kinetics with a Km of 295 microM. L-MTX competitively inhibited the ATP-dependent uptake of [3H]2,4-dinitrophenyl-S-glutathione, a typical substrate for cMOAT, and the inhibition constant (Ki) of L-MTX was comparable with its own Km. These results suggest that L-MTX is excreted into bile by cMOAT. The inhibitory effects of L-MTX and its optical isomer, (-) amethopterin (D-MTX), on the uptake of [3H]L-MTX differed with Kis of 326 and 93 microM, respectively, indicating that the biologically inactive D form has a higher affinity for cMOAT than L-MTX.

Electroencephalographic study of an infant with phosphoribosylpyrophosphate synthetase deficiency.

In a hypouricemic and mentally retarded infant due to a defect of 5-phosphoribosylpyrophosphate synthetase, electroencephalograms were recorded at the age of 4, 7, 10 and 11 months. Hypsarrhythmia was first observed at the age of 10 months, and markedly improved after ACTH therapy with concomitant increase in the enzyme activity of erythrocytes.