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Study of the Biotransformation of Benfluron Using the Isolated Perfused Rat Liver

Study of the Biotransformation of Benfluron Using the Isolated Perfused Rat Liver

Summary: The isolated perfused rat liver method (IPRL) was used to find, isolate and identify further metabolites of Phase I and Phase II biotransformation of the potential cytostatic agent benfluron with special regard to the conjugation pro- cesses. Its pharmacokinetic profile during the perfusion was also estimated. The rat liver was isolated from the body and perfused in vitro using a recirculating perfusion system. Benfluron was added to the reservoir as a bolus in doses of 200, 100, 30 mg/kg of body weigh and 1 mg/perfusate volume and also as a continual infusion in a dose of 0.1 mg/min in se- parate series of experiments. The following metabolites formed during Phase I biotransformation were found in the per- fusion liquid as well as in the bile: benfluron N-oxide, 9-hydroxy benfluron, demethylated 9-hydroxy benfluron, demethylated benfluron, and reduced benfluron. The major Phase II metabolite found in the bile samples was the glucu- ronide of 9-hydroxy benfluron. The pharmacokinetic profile of benfluron in IPRL indicated its main disposition and me- tabolic pathway, i.e. its rapid extraction from perfusate by the liver (t 1/2 α = 3.76 min), 9-hydroxylation followed up O-glucuronidation and excretion to the bile. It was revealed that 12 % of the total dose of the parent compound was exc- reted to the bile in the form of conjugates during the first hour of perfusion, 32 % during 1.5 hour, and 70 % during 2 hours after the administration of benfluron. The conjugates with glucuronic acid represented 96-98 % of all metabolites found in the bile.

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Synthesis and release of Hageman factor (Factor XII) by the isolated perfused rat liver

Synthesis and release of Hageman factor (Factor XII) by the isolated perfused rat liver

isolated perfused rat liver and have compared rates of synthesis in this system with absolute rates of degradation measured in vivo. Rat livers, perfused for 5 h with a recycling fluid consisting of a perfluorochemical emulsion (Fluosol 43), were used to demonstrate a cumulative increase of HF in the perfusate as measured by a specific and sensitive radioimmunoassay. The rate of increase in the perfusate pool of HF during the final 4 h of perfusion yielded a mean synthetic rate of 3.5 micrograms/h per 100 g body wt, which was approximately 0.2% of the synthetic rate of albumin in the same system. The cumulative appearance of albumin and transferrin was linear after 1 h and calculated rates of synthesis were 2,012 micrograms/h per 100 g and 263 micrograms/h per 100 g body wt, respectively. De novo synthesis of HF was confirmed by demonstrating incorporation of [14C]lysine into specific immunoprecipitates of HF, and by the observations that both specific incorporation of labeled amino acid and net release of immunoassayable HF were inhibited by the administration of cycloheximide. Finally, it was evident that the rates of synthesis observed in the isolated perfused liver agreed […]

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Hepatic bilirubin uptake in the isolated perfused rat liver is not facilitated by albumin binding

Hepatic bilirubin uptake in the isolated perfused rat liver is not facilitated by albumin binding

albumin. Rat liver was perfused with a protein-free fluorocarbon medium, and single-pass uptake of 1, 10, or 200 nmol of [3H]bilirubin was determined after injection as an equimolar complex with 125I-albumin, with 125I-ligandin, or free with only a [14C]sucrose reference. Uptake of 10 nmol of [3H]bilirubin was 67.5 +/- 3.7% of the dose when injected with 125I- albumin, 67.4 +/- 6.5% when injected with 125I-ligandin, and 74.9 +/- 2.4% when injected with [14C]sucrose (P greater than 0.1). At 200 nmol, uptake fell to 46.4 +/- 3.1% (125I-

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Influence of Cl  on organic anion transport in short term cultured rat hepatocytes and isolated perfused rat liver

Influence of Cl on organic anion transport in short term cultured rat hepatocytes and isolated perfused rat liver

substitution. To confirm these results in a more physiologic system, transport of [3H]bilirubin was studied in isolated livers perfused with control medium or medium in which Cl- was replaced by gluconate-. Perfusion data analyzed by the model of Goresky, revealed 40-50% reductions in influx and efflux with gluconate- substitution. These results are consistent with existence of a Cl-/organic anion-exchange mechanism similar to that described by others in renal tubules.

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Effects of Ranolazine on Carbohydrate  Metabolism in the Isolated Perfused Rat Liver

Effects of Ranolazine on Carbohydrate Metabolism in the Isolated Perfused Rat Liver

An important cause for the increased glycolysis and diminished gluconeogenesis is probably the inhibition of oxygen uptake caused by ranolazine and the consequently diminished rate of oxidative phosphorylation. It is well established by studies with other inhibitors that such an action usually causes stimulation of glycolysis and inhibition of gluconeogenesis [13] [26]. Inhibition of mitochondrial oxygen uptake, in turn, may have two caus- es. The first one is a direct inhibition of electron transfer at complex I [27]; the second cause is a direct inhibi- tion of fatty acid oxidation, as suggested by experiments in which the oxidation of palmitoyl-CoA and oleoyl- CoA by isolated mitochondria was measured [10]. The fact that ranolazine inhibited the ketone body production from endogenous sources strongly corroborates the view of a direct inhibition of fatty acid oxidation. The latter may be even more important than complex I inhibition as suggested by the observation that the infusion of lac- tate or pyruvate in the presence of ranolazine still increased oxygen uptake to levels close to those found before the infusion of ranolazine suggesting that the reducing equivalents generated by the oxidation of lactate or py- ruvate were still partly able to reach the cytochrome c oxidase system, a phenomenon that requires the participa- tion of complex I. Even so, it is likely that complex I is inhibited to a certain extent, because the increased β -hydroxybutyrate to acetoacetate ratios in the presence of ranolazine indicate a diminished capacity of oxidiz- ing the mitochondrial NADH [22].

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The regulation of 3 hydroxy 3 methylglutaryl coenzyme A reductase in the isolated perfused rat liver

The regulation of 3 hydroxy 3 methylglutaryl coenzyme A reductase in the isolated perfused rat liver

coenzyme A reductase was studied. In liver removed during the basal period of the diurnal cycle of enzyme activity, a 227 +/- 41% increase in enzyme activity occurred after 3 h of a plasma-free perfusion. This could be prevented by the addition of cycloheximide or pure cholesterol (dispersed with lecithin) to the perfusate. In contrast, the continuous addition of taurocholate or taurochenodeoxycholate, alone or in combination, at a variety of rates did not prevent the increase in enzyme activity. The added bile salts were efficiently extracted from the perfusate and excreted in the bile. The addition of these bile salts to a cholesterol- enriched perfusate did not alter the effect obtained with cholesterol alone. If the perfusate contained whole serum, the increase induced by perfusion in the basal period was smaller (88 +/- 27%) than with plasma-free perfusate. Again, the major bile salts of the rat failed to prevent the increase in enzyme activity induced by liver perfusion. If livers were removed and perfused at the height of the diurnal cycle of enzyme activity, the enzyme activity remained high (2 +/- 10% increase) rather than decreasing, as occurs in vivo. If cholesterol was added to these perfusions, a 52 +/- 4% decrease was induced. Bile salt addition induced no […]

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Biliary secretion of fluid phase markers by the isolated perfused rat liver  Role of transcellular vesicular transport

Biliary secretion of fluid phase markers by the isolated perfused rat liver Role of transcellular vesicular transport

contribution of transcellular vesicular transport (transcytosis) to the blood-to-bile movement of inert fluid-phase markers of widely varying molecular weight. First, under steady-state conditions, the perfused rat liver secreted even large markers in appreciable amounts. The bile-to-plasma (B/P) ratio of these different markers, including microperoxidase (B/P ratio = 0.06; mol wt = 1,879), insulin (B/P ratio = 0.09, mol wt = 5,000), horseradish peroxidase (B/P ratio = 0.04, mol wt = 40,000), and dextran (B/P ratio = 0.09, mol wt = 70,000), exhibited no clear ordering based on size alone, and when dextrans of two different sizes (40,000 and 70,000 mol wt) were studied simultaneously, the relative amounts of the two dextran

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Reactive oxygen species during ischemia reflow injury in isolated perfused rat liver

Reactive oxygen species during ischemia reflow injury in isolated perfused rat liver

The hypothesis that intracellular generation of reactive oxygen species in hepatocytes or reticuloendothelial cells may cause ischemia-reperfusion injury was tested in isolated perfused livers of male Fischer rats. GSSG was measured in perfusate, bile, and tissue as a sensitive index of oxidative stress. After a preperfusion phase of 30 min, the perfusion was stopped (global ischemia) for various times (30, 120 min) and the liver was reperfused for another 60 min. The bile flow (1.48 +/- 0.17 microliters/min X gram liver weight), the biliary efflux of total glutathione (6.54 +/- 0.94 nmol GSH eq/min X g), and GSSG (1.59 +/- 0.23 nmol GSH eq/min X g) recovered to 69-86% after short-term ischemia and to 36-72% after 2 h of ischemia when compared with values obtained from control livers perfused for the same period of time. During reperfusion, the sinusoidal efflux of total glutathione (16.4 +/- 2.1 nmol GSH eq/min X g) and GSSG (0.13 +/- 0.05 nmol GSH eq/min X g) did not change except for an initial 10-30-s increase during reperfusion washout. No increased GSSG secretion into bile was detectable at any time during reperfusion. The liver content of total glutathione (32.5 +/- 3.5 nmol GSH eq/mg protein) and GSSG (0.27 +/- 0.09 nmol GSH eq/mg protein) did not change significantly during any period of ischemia or reperfusion. We […]

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Coordinate pulsatile insulin secretion by chronic intraportally transplanted islets in the isolated perfused rat liver

Coordinate pulsatile insulin secretion by chronic intraportally transplanted islets in the isolated perfused rat liver

transplantation? We studied isolated perfused livers at 10 mM glucose from 27 rats rendered diabetic with streptozotocin and then transplanted with approximately 2 x 10(3) islets, 2 (n = 5), 7 (n = 5), 30 (n = 5), and 200 (n = 12) d after transplantation. 12 out of 12 of the 200-d IHI-Tx secreted insulin in coordinate pulses (frequency 3.9 +/- 0.3 pulses/h,

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Tauroursodeoxycholic acid stimulates hepatocellular exocytosis and mobilizes extracellular Ca++ mechanisms defective in cholestasis

Tauroursodeoxycholic acid stimulates hepatocellular exocytosis and mobilizes extracellular Ca++ mechanisms defective in cholestasis

To assess the effects of tauroursodeoxycholic acid (TUDCA) on bile excretory function, we examined whether TUDCA modulates vesicular exocytosis in the isolated perfused liver of normal rats in the presence of high (1.9 mM) or low (0.19 mM) extracellular Ca++ and in cholestatic rats 24 h after bile duct ligation. In addition, the effects of TUDCA on Ca++ homeostasis were compared in normal and in cholestatic hepatocytes. In the isolated perfused rat liver, TUDCA (25 microM) stimulated a sustained increase in the biliary

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Inhibition of lactate removal by ketone bodies in rat liver  Evidence for a quantitatively important role of the plasma membrane lactate transporter in lactate metabolism

Inhibition of lactate removal by ketone bodies in rat liver Evidence for a quantitatively important role of the plasma membrane lactate transporter in lactate metabolism

We studied the effect of DL-3-hydroxybutyrate and acetoacetate on lactate transport into isolated hepatocytes and on lactate removal in the isolated perfused rat liver. Ketone bodies inhibited lactate transport into isolated hepatocytes (maximum, 35% at concentrations of 10- 20 mM). Lactate removal and glucose production by perfused livers were examined before and after the introduction of a constant infusion of hydroxybutyrate, acetoacetate, or

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Hepatic processing of transforming growth factor beta in the rat  Uptake, metabolism, and biliary excretion

Hepatic processing of transforming growth factor beta in the rat Uptake, metabolism, and biliary excretion

disappearance of 125I-TGF beta by 80%. 60 min after intrafemoral injection, 63% of the recovered label was present in liver and/or bile; by 90 min, most of the label removed by the liver (83%) had been slowly excreted into bile. Nearly all the label in bile (96%) was soluble in trichloracetic acid and not immunoprecipitable by specific antiserum. Colchicine and vinblastine inhibited cumulative biliary excretion of label by 28 and 37%, respectively; chloroquine and leupeptin each increased the amount of label in bile that was precipitable by trichloracetic acid and that coeluted with authentic 125I-TGF beta on molecular sieve chromatography. There was efficient first-pass hepatic extraction of 125I-TGF beta (36%) in the isolated perfused rat liver, which was inhibited by unlabeled TGF beta (but not by epidermal growth factor, EGF) and by lectins in a dose-dependent manner; prolonged fasting also decreased clearance (26%). After fractionation of liver by differential or isopycnic centrifugation, radiolabel codistributed with […]

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Clearance of Immunoreactive Somatostatin by Perfused Rat Liver

Clearance of Immunoreactive Somatostatin by Perfused Rat Liver

commensurate with first-order kinetics. Hepatic clearance was 0.84±0.04 ml/min per g postperfusion wet weight (SE). Hepatic extraction was 36±2%, and t ½ was 20.0±1.3 min. Recovery of IRS from the perfusate without the liver was >85%, excluding significant degradation by the medium. Clearance, extraction, and t ½ of IRS were not changed by an unphysiologic IRS concentration (621,500 pg/ml), or by pharmacologic concentrations of insulin (8.2 µM) or […]

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Excretion and metabolism of catecholamines by the isolated perfused rat kidney

Excretion and metabolism of catecholamines by the isolated perfused rat kidney

medium with no demonstrable tubular maximum at the concentrations studied. The isolated kidney removed catecholamines from the medium by metabolism as well as excretion in the urine. O-Methylation was the major metabolic route and O-methylated metabolites were rapidly excreted and concentrated in urine. Preferential excretion and metabolism of epinephrine were confirmed in double-label experiments in which [14C]epinephrine and [3H]norepinephrine were perfused together. The ratio of 14C:3H in urine exceeded that in perfusion medium for total radioactivity as well as for catecholamines and O-methylated amines. The present study thus provides direct evidence for (a) net tubular secretion of epinephrine and norepinephrine with a direct relationship between secretion and medium concentration; (b) significant renal metabolism of both epinephrine and norepinephrine with O-methylation as the major metabolic route; and (c) preferential excretion and metabolism of epinephrine.

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The Handling of Immunoreactive Vasopressin by the Isolated Perfused Rat Kidney

The Handling of Immunoreactive Vasopressin by the Isolated Perfused Rat Kidney

In control kidneys perfused with AVP at concentrations below 116 µU/ml, the organ clearance of AVP (OC AVP ) was 1,145±47 (SE) µl/min, whereas glomerular filtration rate (GFR) averaged 515±37 µl/min. Filtration could thus account for up to 45% of the OC AVP , the balance presumably being cleared from the peritubular circulation. Of the AVP filtered, only 38% could be recovered in the urine (urinary clearance AVP averaged 205±12 µl/min) suggesting that the balance was taken up by the tubular epithelium and degraded.

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Protoporphyrin induced Cholestasis in the Isolated In Situ Perfused Rat Liver

Protoporphyrin induced Cholestasis in the Isolated In Situ Perfused Rat Liver

The pathogenesis of liver disease in protoporphyria has been presumed to result from the hepatic deposition of protoporphyrin. To examine the effects of protoporphyrin on hepatic bile flow and histopathology, studies were performed employing an isolated, in situ, rat liver perfusion system. Rat livers in the control group were perfused with 0-80 µmol sodium taurocholate/h. Rat livers in the experimental group were perfused with sodium taurocholate and (a) sufficient quantities of protoporphyrin to produce maximal canalicular secretion and (b) perfusate protoporphyrin concentrations of 0.01, 0.1, and 1 µM.

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Bile Acid Synthesis in the Isolated, Perfused Rabbit Liver

Bile Acid Synthesis in the Isolated, Perfused Rabbit Liver

These experiments were carried out to demonstrate the usefulness of the perfused rabbit liver for studies of bile acid metabolism, and to determine the rate-limiting enzyme of bile acid synthesis. Rabbits were fed a semisynthetic diet, with or without the addition of 1% cholestyramine, under controlled conditions. At the end of 2-5 wk, the livers were removed and perfused for 2.5 hr employing various 14 C-labeled precursors to measure de novo cholic acid synthesis. The livers were then analyzed for cholesterol, and the bile collected during the perfusion was analyzed for cholesterol and bile acids. Control bile contained, on the average, 0.34 mg of glycocholate, 7.4 mg of glycodeoxycholate, and 0.06 mg of

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Regulation of the Conversion of Thyroxine to Triiodothyronine in the Perfused Rat Liver

Regulation of the Conversion of Thyroxine to Triiodothyronine in the Perfused Rat Liver

physiologic functions of the liver. The perfused liver readily extracted T 4 from perfusion medium and converted it to T 3 . Production of T 3 by the perfused liver was a function of the size of the liver, the uptake of T 4 by the liver, and the presence of T 4 -5¢-deiodinase activity. Production of T 3 was increased by increasing the uptake of T 4 by liver, which could be accomplished by increasing the liver size, by increasing the perfusate T 4 concentration, or by decreasing the perfusate albumin concentration. These changes occurred without altering the conversion of T 4 to T 3 . The liver had a large capacity for extracting T 4 and for T 4 -5¢-deiodination to T 3 , which was not saturated at a T 4 concentration of 60 µg/dl.

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Metabolism of platelet activating factor in isolated perfused rat lung

Metabolism of platelet activating factor in isolated perfused rat lung

The administration of platelet-activating factor (PAF) into the airway system of the lung is known to cause profound effects, yet little is known about the metabolism of this active lipid mediator. 3H-Labeled PAF administered into the airway of isolated rat lungs was rapidly and extensively metabolized. The tissue retained 96% of the administered radiolabel while the perfusate contained 4%. Characterization of the tissue retained lipid indicated

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Influence of Thyroid Status on Lipid Metabolism in the Perfused Rat Liver

Influence of Thyroid Status on Lipid Metabolism in the Perfused Rat Liver

Thyroid disease is often accompanied by changes in the concentrations of serum lipids and lipoproteins. To evaluate the hepatic contribution to the serum abnormalities in thyroid disease, we examined fatty acid metabolism in perfused livers from pair-fed rats made hypothyroid with propylthiouracil (PTU) or made hyperthyroid by treatment with

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