PRIMARY ACTIVE TRANSPORT OF PRAVASTATIN ACROSS THE LIVER CANALICULAR MEMBRANE IN NORMAL AND MUTANT EISAI HYPERBILIRUBINEMIC RATS

We have previously demonstrated that the HMG-CoA reductase inhibitor pravastatin is efficiently taken up by the liver via the ‘multispecific anion transporter’ in an active manner.³ To further examine the fate of pravastatin within the liver, its biliary excretion was studied in a single-pass liver perfusion system and isolated liver canalicular membrane vesicles (CMVs) using normal (Sprague–Dawley rats; SDRs) and mutant Eisai hyperbilirubinemic rats (EHBRs). In the liver perfusion experiments, the outflowing drug concentration reached a steady state at 30 min and the extraction ratio was approximately 0·7 in both rat strains. Both the steady-state biliary excretion rate and bile flow rate of the EHBR group were 40% those of SDRs. At steady state, the fraction of unchanged drug in bile was 25–34% in both groups. The concentration ratios of unbound drug in cytosol versus that in sinusoid and in bile versus cytosol were, respectively, 11 and 87 in SDRs, and 13 and 94 in EHBRs. After correction for membrane potential (−40 mV in cytosol), the ratios became 49 and 19 in SDRs and 58 and 21 in EHBRs, respectively. The finding that all of these values were much larger than unity suggested that active transport occurred from liver to bile, as well as from plasma to liver, in both rat strains. Furthermore, ATP-dependent uptake of pravastatin was clearly observed in CMVs prepared from EHBRs as well as SDRs, whereas the stimulation by ATP of DNP-SG transport in CMV was observed only in SDRs. It was concluded that pravastatin is excreted into bile in high concentrations and a primary active transport mechanism which is maintained in EHBRs contributes to the biliary excretion of this drug.     

Biliary Excretion of Glycyrrhizin in Rats: Kinetic Basis for Multiplicity in Bile Canalicular Transport of Organic Anions

Purpose. To examine the presence of multiplicity for the biliary excretion of xenobiotic conjugates, we studied the disposition of glycyrrhizin (GR), which has glucuronide within its molecular structure and has the ability to inhibit the biliary excretion of liquiritigenin (LG) glucuronides. Methods. GR was administered intravenously as a bolus to Sprague-Dawley (SD) rats which received an i.v. infusion of inhibitors (dibromo-sulfophthalein (DBSP) and indocyanine green (ICG)) at their transport maximum rates. Biliary excretion of GR was also examined in Eisai hyperbilirubinemic rats (EHBR), which have a hereditary defect in the canalicular transport system of several organic anions. Results. Infusion of ICG did not affect the biliary excretion of GR, whereas infusion of DBSP reduced it significantly. The plasma concentration of GR was increased by DBSP but not by ICG. In EHBR, the biliary excretion of GR was severely impaired, resulting in an increase in the plasma concentration of GR. Conclusions. These findings suggest (1) that the biliary excretion of GR is mediated by the system which is shared by DBSP and LG glucuronides but not by ICG and (2) that this system is hereditarily defective in EHBR. Together with our previous findings, the multiplicity for the biliary excretion of organic anions is shown.     

D—聚甘酯在各脏器的分布特点及其透过血脑屏障机制的研究

利用＾３Ｈ标记Ｄ－聚甘酯,观察了小鼠口服Ｄ－聚甘酯后在各组织和器官尤其是脑的分布特点,并对春血脑屏障的机制进行了初步探讨。实验结果显示,Ｄ－了矣甘酯可以迅速透过血脑屏障,并且除肾脏外,其在脑中的显著性地高于其他组织与器官。Ｄ－聚甘酯在中脑的２显著的高于脑的其他部位。给药３ｈ以后,脑内的Ｄ－聚甘酯９５．８％以原形存在。给小鼠等量的＾３Ｈ－Ｄ－聚甘酯和不同量的Ｄ－聚甘酯,随着Ｄ－聚甘酯量的增加,脑内的     

SENSITIVITY OF PROPRANOLOL ELIMINATION TO HYPOXIA IN THE ISOLATED PERFUSED RAT LIVER PREPARATION

1. The relationship between the hepatic elimination of propranolol and hepatic oxygen delivery was examined in the single-pass isolated perfused rat liver preparation. Varying rates of oxygen delivery were produced (1.35–8.10 μmol/min per g liver) by equilibrating the perfusate with O₂/N₂ mixtures. 2. In two experiments, in which the rate of oxygen delivery was increased or decreased within the hypoxic range (< 4–5 μmol/min per g liver) every 5 min for 120 min, propranolol clearance responded very rapidly in the same direction as the change in oxygen delivery. 3. In five experiments, propranolol clearance, measured at steady state during an initial 30 min normoxia phase and three subsequent 30 min hypoxia phases (oxygen delivery in the range 1.35–5.89 μmol/min per g liver), was linearly related to hepatic oxygen delivery and consumption (r= 0.92 ± 0.07). 4. These data, combined with those from six further experiments that used one normoxia phase followed by one hypoxia phase, showed that there was a threshold for oxygen delivery of about 6 μmol/min per g liver, below which propranolol clearance decreased with decreasing oxygenation. 5. This study shows that in the intact liver propranolol elimination is very sensitive to hepatic oxygen supply, with impairment in clearance occurring at the lower limit of what is considered normal hepatic oxygenation in the rat.     

A PRIMING DOSE OF PROPRANOLOL REDUCES THE AVAILABILITY OF A SUBSEQUENT DOSE IN THE ISOLATED PERFUSED RAT LIVER PREPARATION

1. A 50 μL bolus dose containing (±)-propranolol hydrochloride (200 μg) and [¹⁴C]-sucrose, or antipyrine (2 mg) and [¹⁴C]-sucrose, or [¹⁴C]-taurocholate sodium was injected into the portal vein of the isolated perfused rat liver preparation and perfusate outflow samples were collected frequently for the next 30min. After a 20 min washout period this procedure was repeated. 2. [¹⁴C]-Sucrose, antipyrine and [¹⁴C]-taurocholate each eluted as a single peak at 18, 31 and 28 s, respectively, after each dose. In contrast, propranolol eluted with two peaks at approximately 18 and 128 s after dosing. 3. There was no significant difference in dose-corrected area under the outflow curve (AUC) for [¹⁴C]-sucrose, antipyrine or [¹⁴C]-taurocholate between the first and second doses whereas the mean propranolol AUC for the second dose was only 0.577 ± 0.439 that for the first dose (P <0.05). 4. Unmetabolized propranolol accounted for more than 80% of the drug in hepatic tissue for the first and second doses at 18 s and greater than 50% at 128 s, and there was no significant difference in these values at each time between the first and second doses. 5. These findings suggest that for an avidly extracted drug, such as propranolol, systemic availability of orally administered drug will be highly dependent on factors that influence the hepatic tissue binding of the drug.     

ACTIVITIES OF NAD+-DEPENDENT ALDEHYDE DEHYDROGENASE AND ALCOHOL DEHYDROGENASE IN THE LIVER OF SPONTANEOUSLY HYPERTENSIVE RATS IN THE PROCESS OF DEVELOPMENT

The difference in the basal activities of NAD+-dependent aldehyde dehydrogenase (ALDH) and alcohol dehydrogenase (ADH) was investigated in the liver of age-matched spontaneously hypertensive (SH) and normotensive Wistar Kyoto (WK) rats. A significant difference between the SH and WK rats in the basal ALDH activity, ADH activity and the protein content of subcellular fractions was observed. The activities of mitochondrial low Km- and high Km-ALDH in the SH rats at 5-8 weeks of age were higher than those in the WK rats. The microsomal high Km-ALDH activity in the SH rats at 5 and 11 weeks of age was higher than that in the WK rats. The ADH activities in the SH rats at 5-14 weeks of age were lower than those in the WK rats. The mitochondrial protein content in the SH rats at 5-14 weeks of age was higher than those in the WK rats. At 14 weeks of age, an increase in the blood acetaldehyde level was observed after an intraperitoneal injection of 1.5 g/kg of ethanol in the SH rats. No difference in blood ethanol level was observed between the SH and WK rats.     

来氟米特及其活性代谢物对关节炎模型大鼠TNF-α分泌及mRNA表达的影响

目的观察免疫抑制剂来氟米特(leflunomide,LEF)及其活性代谢产物A771726(A77)对佐剂性关节炎(AA)模型大鼠TNF-α分泌活性及mRNA表达的影响。方法TNF-α活性及mRNA表达用ELISA法和RT-PCR方法。结果 AA大鼠腹腔巨噬细胞(PMφ)呈高度活化状态,TNF-α分泌水平明显升高。LEF明显抑制LPS诱导的大鼠PMφ TNF-α释放且呈剂量依赖关系。体外用A77后TNF-α mRNA表达量降低。结论LEF和A77对AA模型大鼠TNF-α分泌活性及mRNA表达有抑制作用,此可能为其抗炎和免疫抑制作用的机制之一。