Conjugation reactions in hepatocytes isolated from streptozotocin-induced diabetic rats

Vitamin E (α-Tocopherol) Does Not Ameliorate the Toxic Effect of Bisphenol S on the Metabolic Analytes and Pancreas Histoarchitecture of Diabetic Rats

This study investigated whether the coadministration of vitamin E (VitE) diminishes the harmful effects provoked by plasticizer bisphenol S (BPS) in the serum metabolites related to hepatic and renal metabolism, as well as the endocrine pancreatic function in diabetic male Wistar rats. Rats were divided into five groups (n = 5-6); the first group was healthy rats (Ctrl group). The other four groups were diabetic rats induced with 45 mg/kg bw of streptozotocin: Ctrl-D (diabetic control); VitE-D (100 mg/kg bw/d of VitE); BPS-D (100 mg/kg bw/d of BPS); The animals from the VitE + BPS-D group were administered 100 mg/kg bw/d of VitE + 100 mg/kg bw/d of BPS. All compounds were administered orally for 30 days. Body weight, biochemical assays, urinalysis, glucose tolerance test, pancreas histopathology, proximate chemical analysis in feces, and the activity of antioxidants in rat serum were assessed. The coadministration of VitE + BPS produced weight losses, increases in 14 serum analytes, and degeneration in the pancreas. Therefore, the VitE + BPS coadministration did not have a protective effect versus the harmful impact of BPS or the diabetic metabolic state; on the contrary, it partially aggravated the damage produced by the BPS. VitE is likely to have an additive effect on the toxicity of BPS.

Expression of hepatic antioxidant enzymes in non-obese type-2 diabetic Goto-Kakizaki rats

Diabetes mellitus and its complications have been attributed in part to oxidative stress, against which antioxidant enzymes constitute a major protective mechanism. The present study was performed to investigate the effects of early stage type 2 diabetes in the absence of obesity and liver damage on hepatic antioxidant enzyme expression and oxidative stress using 9-week-old Goto-Kakizaki (GK) rats. Hepatic total antioxidant capacity determined by total oxygen radical scavenging capacity and lipid peroxidation determined by malondialdehyde in plasma and liver were not significantly different between normal Wistar rats and GK rats. These results indicated that oxidative stress is not evident in these type 2 diabetic rats. Hepatic expression levels of antioxidant enzymes, including superoxide dismutase-1, catalase, glutathione peroxidase and reductase, thioredoxin-1, mu- and pi-class glutathione S-transferase (GST), and the gamma-glutamylcysteine ligase catalytic subunit, were not different between normal rats and GK rats. But, hepatic level and activity of alpha-class GST were decreased and peroxiredoxin-1 level was increased in GK rats, suggesting that upregulation of peroxiredoxin-1 compensates for downregulation of alpha-class GST. These results suggest that alpha-class GST and peroxiredoxin-1 in liver can be altered during the early stages of type 2 diabetes in the absence of obesity and severe oxidative stress.

Influence of gestational diabetes mellitus on the stereoselective kinetic disposition and metabolism of labetalol in hypertensive patients

PURPOSE

This study investigated the influence of gestational diabetes mellitus on the kinetic disposition and stereoselective metabolism of labetalol administered intravenously or orally.

METHODS

Thirty hypertensive women during the last trimester of pregnancy were divided into four groups: non-diabetic and diabetic women treated with intravenous or oral labetalol.

RESULTS

The pharmacokinetics of labetalol was not stereoselective in diabetic or non-diabetic pregnant women receiving the drug intravenously. However, oral administration of labetalol resulted in lower values of the area under the plasma concentration versus time curve (AUC) for the β-blocker (RR) than for the other enantiomers in both diabetic and non-diabetic women. Gestational diabetes mellitus caused changes in the kinetic disposition of the labetalol stereoisomers when administered orally. The AUC values for the less potent adrenoceptor antagonist (SS) and for the α-blocking (SR) isomers were higher in diabetic than in non-diabetic pregnant women.

CONCLUSIONS

The approximately 100% higher AUC values obtained for the (SR) isomer in diabetic pregnant women treated with oral labetalol may be of clinical relevance in terms of the α-blocking activity of this isomer.

Metabolism of troglitazone in hepatocytes isolated from experimentally induced diabetic rats

Troglitazone (TGZ), the prototype 2,4-thiazolidinedione antidiabetic agent, is associated with hepa-totoxicity in patients with Type 2 diabetes. Although the mechanism of toxicity has not been established, alterations in the clearance of TGZ from in-vitro hepatocyte cultures through metabolic conjugation reactions are believed to modulate the toxicity of the compound. In this study, the metabolism of TGZ in freshly isolated hepatocytes from the fat-fed streptozotocin-treated rat model of Type 2 diabetes is described. Biochemical parameters such as cellular reduced glutathione content, content of cytochromes P450 and b5, and the expression of glutathione-S-transferase α (subunits Ya and Yc2) were not affected by the induced diabetes. TGZ was metabolized primarily to a sulfonate, a quinone and a glucuronide in both control and experimentally diabetic animals. However, metabolism after induction of diabetes was characterized by a moderate increase in sulfation, a decrease in the elimination half-life of TGZ and the absence of the minor metabolites of TGZ, notably the glutathione adduct of the putative reactive intermediate (m/z = 747 (M + H)+; m/z = 745 (M — H)−).

Mechanisms and outcomes of drug- and toxicant-induced liver toxicity in diabetes

Increase dincidences of hepatotoxicity have been observed in diabetic patients receiving drug therapies. Neither the mechanisms nor the predisposing factors underlying hepatotoxicity in diabetics are clearly understood. Animal studies designed to examine the mechanisms of diabetes-modulated hepatotoxicity have traditionally focused only on bioactivation/detoxification of drugs and toxicants. It is becoming clear that once injury is initiated, additional events determine the final outcome of liver injury. Foremost among them are two leading mechanisms: first, biochemical mechanisms that lead to progression or regression of injury; and second, whether or not timely and adequate liver tissue repair occurs to mitigate injury and restore liver function. The liver has a remarkable ability to repair and restore its structure and function after physical or chemical-induced damage. The dynamic interaction between biotransformation-based liver injury and compensatory tissue repair plays a pivotal role in determining the ultimate outcome of hepatotoxicity initiated by drugs or toxicants. In this review, mechanisms underlying altered hepatotoxicity in diabetes with emphasis on both altered bioactivation and liver tissue repair are discussed. Animal models of both marked sensitivity (diabetic rats) and equally marked protection (diabetic mice) from drug-induced hepatotoxicity are described. These examples represent a remarkable species difference. Availability of the rodent diabetic models offers a unique opportunity to uncover mechanisms of clinical interest in averting human diabetic sensitivity to drug-induced hepatotoxicities. While the rat diabetic models appear to be suitable, the diabetic mouse models might not be suitable in preclinical testing for potential hepatotoxic effects of drugs or toxicants, because regardless of type 1 or type2 diabetes, mice are resistant to acute drug-or toxicant-induced toxicities.

The role of intracellular signaling in insulin-mediated regulation of drug metabolizing enzyme gene and protein expression

Endogenous factors, including hormones, growth factors and cytokines, play an important role in the regulation of hepatic drug metabolizing enzyme expression in both physiological and pathophysiological conditions. Diabetes, fasting, obesity, protein-calorie malnutrition and long-term alcohol consumption produce changes in hepatic drug metabolizing enzyme gene and protein expression. This difference in expression alters the metabolism of xenobiotics, including procarcinogens, carcinogens, toxicants and therapeutic agents, potentially impacting the efficacy and safety of therapeutic agents, and/or resulting in drug-drug interactions. Although the mechanisms by which xenobiotics regulate drug metabolizing enzymes have been studied intensively, less is known regarding the cellular signaling pathways and components which regulate drug metabolizing enzyme gene and protein expression in response to hormones and cytokines. Recent findings, however, have revealed that several cellular signaling pathways are involved in hormone- and growth factor-mediated regulation of drug metabolizing enzymes. Our laboratory has reported that insulin and growth factors regulate drug metabolizing enzyme gene and protein expression, including cytochromes P450 (CYP), glutathione S-transferases (GST) and microsomal epoxide hydrolase (mEH), through receptors which are members of the large receptor tyrosine kinase (RTK) family, and by downstream effectors such as phosphatidylinositol 3-kinase, mitogen activated protein kinase (MAPK), Akt/protein kinase B (PKB), mammalian target of rapamycin (mTOR), and the p70 ribosomal protein S6 kinase (p70S6 kinase). Here, we review current knowledge of the signaling pathways implicated in regulation of drug metabolizing enzyme gene and protein expression in response to insulin and growth factors, with the goal of increasing our understanding of how disease affects these signaling pathways, components, and ultimately gene expression and translational control.

Enterohepatic circulation: physiological, pharmacokinetic and clinical implications

Enterohepatic recycling occurs by biliary excretion and intestinal reabsorption of a solute, sometimes with hepatic conjugation and intestinal deconjugation. Cycling is often associated with multiple peaks and a longer apparent half-life in a plasma concentration-time profile. Factors affecting biliary excretion include drug characteristics (chemical structure, polarity and molecular size), transport across sinusoidal plasma membrane and canniculae membranes, biotransformation and possible reabsorption from intrahepatic bile ductules. Intestinal reabsorption to complete the enterohepatic cycle may depend on hydrolysis of a drug conjugate by gut bacteria. Bioavailability is also affected by the extent of intestinal absorption, gut-wall P-glycoprotein efflux and gut-wall metabolism. Recently, there has been a considerable increase in our understanding of the role of transporters, of gene expression of intestinal and hepatic enzymes, and of hepatic zonation. Drugs, disease and genetics may result in induced or inhibited activity of transporters and metabolising enzymes. Reduced expression of one transporter, for example hepatic canalicular multidrug resistance-associated protein (MRP) 2, is often associated with enhanced expression of others, for example the usually quiescent basolateral efflux MRP3, to limit hepatic toxicity. In addition, physiologically relevant pharmacokinetic models, which describe enterohepatic recirculation in terms of its determinants (such as sporadic gall bladder emptying), have been developed. In general, enterohepatic recirculation may prolong the pharmacological effect of certain drugs and drug metabolites. Of particular importance is the potential amplifying effect of enterohepatic variability in defining differences in the bioavailability, apparent volume of distribution and clearance of a given compound. Genetic abnormalities, disease states, orally administered adsorbents and certain coadministered drugs all affect enterohepatic recycling.

Alterations in susceptibility to carbon tetrachloride toxicity and hepatic antioxidant/detoxification system in streptozotocin-induced short-term diabetic rats: effects of insulin and Schisandrin B treatment

The streptozotocin-induced short-term (2 week) diabetic rats showed an increase in susceptibility to carbon tetrachloride (CCl4)-induced hepatocellular damage. This diabetes-induced change was associated with a marked impairment in the hepatic glutathione antioxidant/detoxification response to CCl4 challenge, as indicated by the abrogation of the increases in hepatic reduced glutathione (GSH) level, glucose-6-phosphate dehydrogenase and microsomal glutathione S-transferases (GST) activities upon challenge with increasing doses of CCl4. While the hepatic GSH level was increased in diabetic rats, the hepatic mitochondrial GSH level and Se-glutathione peroxidase activity were significantly reduced. Insulin treatment could reverse most of the biochemical alterations induced by diabetes. Both insulin and schisandrin B (Sch B) pretreatments protected against the CCl4 hepatotoxicity in diabetic rats. The hepatoprotection was associated with improvement in hepatic glutathione redox status in both cytosolic and mitochondrial compartments, as well as the increases in hepatic ascorbic acid level and microsomal GST activity. The ensemble of results suggests that the diabetes-induced impairment in hepatic mitochondrial glutathione redox status may at least in part be attributed to the enhanced susceptibility to CCl4 hepatotoxicity. Sch B may be a useful hepatoprotective agent against xenobiotics-induced toxicity under the diabetic conditions.

Glucose formation from methylglyoxal in hepatocytes from streptozotocin-induced diabetic mice: the effect of insulin

Acetol and methylglyoxal are intermediates of the intrahepatic metabolism of acetone leading to pyruvate formation. In hepatocytes prepared from fasted streptozotocin-induced diabetic mice, net glucose production could be measured from methylglyoxal but not from acetone or acetol. Insulin increased glucose formation from methylglyoxal in a concentration-dependent manner, whereas it was ineffective when pyruvate was used as substrate. Drug oxidation, as evidenced by p-aminophenol formation from aniline, was enhanced by methylglyoxal, and insulin proved to be stimulatory in this case as well. It is concluded that insulin might be involved in the regulation of glucose formation from methylglyoxal, but its mode of action is not yet clear.

Role of calcium fluxes in the action of glucagon on cytosolic glutathione S-transferase activity in rat liver slices

In a previous study we demonstrated that the administration of 20 micrograms/kg b.wt. of glucagon to rats caused a significant diminution of hepatic cytosolic glutathione S-transferase (GST) activity. This inhibition was non-competitive and reversible. We suggested that the effect would be mediated by cytosolic effectors. The present work was performed to characterize the mechanism involved in this inhibition. Liver tissue slices (170 to 200 mg) were incubated during different periods of time (0, 5, 10, 15, 20 and 30 min.) with several concentrations of glucagon (10(-5) M, 10(-8) M and 10(-10) M), dibutiryl cyclic AMP (10(-4) M, 10(-6) M and 10(-9) M), divalent cation ionophore A23187 (10(-4) M, 10(-6) M and 10(-9) M) or vasopressin (10(-7) M, 5 x 10(-7) M and 10(-8) M). The incubation was done with or without calcium in the medium. In all cases the cytosolic GST activity were determined in liver slices. The percentage of inhibition of GST activity was directly related to the increase of concentration of the test substances. An inhibition between 40% to 45% after 10 min. of incubation with the highest concentrations was observed (except vasopressin which caused 10% of inhibition). 10(-10) M glucagon did not produce a decrease of GST activity. The inhibition disappeared in calcium-free incubated slices, but direct relationship between plasma-membrane calcium influx and inhibition of GST activity (r = 0.950, P < 0.001, n = 24) could be obtained. By using calmodulin antagonists, we conclude that the inhibition process of the enzyme was mediated by calmodulin. In summary, we propose that plasma-membrane calcium influx induced by high concentrations of glucagon activates calmodulin, which promotes a modification (actually a methylation, according to other authors) on GST, thereby causing a decrease in its activity.

Increased oxidation and decreased conjugation of drugs in the liver caused by starvation. Altered metabolism of certain aromatic compounds and acetone

Starvation causes several changes in the various processes of biotransformation. The focus of this review is on biotransformation of various aromatic and other compounds whose metabolism is catalyzed in phase I by isozymes belonging to the CYP2E1 gene subfamily, while in phase II phenol-UDPGT or conjugation with GSH play a dominant role. The other ways of conjugation are beyond the scope of this review. The reason why this aspect has been chosen is that the capacity of these reactions is profoundly altered by nutritional conditions. There is a balance between the two phases of biotransformation. Therefore, under standard circumstances in a well-fed state the intermediate formed in the course of phase I is converted to a conjugated compound rapidly, as a result of phase II. However, in starvation the pattern of drug metabolism is altered and the balance between the two phases is changed. This alteration of drug metabolism upon starvation is partly connected to the changes of cofactor supplies due to the metabolic state.

Acute regulation of hepatic glutathione S-transferase by insulin and glucagon

The intravenous administration of insulin plus glucose in anesthetized rats caused, within 30 min, an increase of about 56% in hepatic cytosolic glutathione S-transferase (GST) activity, but it did not affect the microsomal enzyme. The injection of glucagon resulted, at the same time, in a 43% drop in the hepatic cytosolic GST, without affecting the microsomal GST. The insulin-dependent increase in cytosolic GST activity was abolished by the pretreatment of the animals with an inhibitor of protein synthesis (cycloheximide). A kinetic analysis revealed a non-competitive inhibition caused by glucagon upon the cytosolic enzyme. In addition, the presence of insulin did not interfere with the effectiveness of glucagon, and vice versa. We propose that: (1) the effect of insulin on hepatic cytosolic GST activity requires protein synthesis; (2) glucagon produces an inhibition of hepatic cytosolic GST, which could be mediated by cytosolic effectors such as adenosine 3'-5'-cyclic monophosphate (cAMP); (3) the effects of glucagon and insulin were not mutually exclusive; (4) hepatic microsomal GST is regulated by different mechanism(s).

Paracetamol elimination in patients with non-insulin dependent diabetes mellitus

The pharmacokinetics and metabolism of an intravenous dose (500 mg) of paracetamol were studied in a group of non-insulin dependent diabetic patients (n = 10) and in a group of healthy control subjects (n = 9). Paracetamol clearance, half-life and the partial clearance to paracetamol glucuronide were not significantly different, but the partial clearance to paracetamol sulphate was significantly reduced (62 +/- 18 vs 86 +/- 17 ml h-1 kg-1 (mean +/- s.d.)) and the renal clearance of paracetamol was significantly increased (56 +/- 20 vs 22 +/- 6 ml h-1 kg-1 (mean +/- s.d.)) in the non-insulin dependent diabetic patients, compared with the control group.

Techniques for pharmacological and toxicological studies with isolated hepatocyte suspensions

Since its introduction in 1969, the high-yield preparation of isolated hepatocytes has become a frequently used tool for the study of hepatic uptake, excretion, metabolism and toxicity of drugs and other xenobiotics. Basic preparative methods are now firmly established involving perfusion of the liver with a balanced-saline solution containing collagenase. Satisfactory procedures are available for determining cell yields, for expressing cellular activities and for establishing optimal incubation conditions. Gross cellular damage can be detected by means of trypan blue or by measuring enzyme leakage, and damaged cells can be removed from the preparation. Specialized techniques are available for preparing hepatocyte couplets and suspensions enriched with periportal or perivenous hepatocytes. The isolated hepatocyte preparation is particularly convenient for the study of the kinetics of hepatic drug uptake and excretion because the cells can be rapidly separated from the incubation medium. Isolated liver cells have also proved valuable for investigating drug metabolism since they show many of the features of the intact liver. However, they also show important differences such as losses of membrane specialization, some degree of cell polarity and the capacity to form bile. The many consequences of the hepatic toxicity of xenobiotics including lipid peroxidation, free radical formation, glutathione depletion, and covalent binding to macromolecules are also readily studied with the isolated liver cell preparation. A particular advantage is the ease with which morphological changes as a result of drug exposure can be observed in isolated hepatocytes. However, it must be remembered that the isolation procedure inevitably introduces changes that may make the cells more susceptible than the normal liver to damage by xenobiotic agents. Despite its limitations, the isolated hepatocyte preparation is now firmly established in the armamentarium of the investigator examining the interaction of the liver with xenobiotics.

Diabetes-induced alteration of HMGCoA reductase forms in rat livers

The effects of streptozotocin-induced diabetes on the various forms of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCoA reductase), phosphorylated/dephosphorylated and thiolic/disulphide, were studied in rat liver. Animals were treated twice with 65 mg/kg intraperitoneally of streptozotocin to induce diabetes and sacrificed after 5 days. The relative amounts of the four possible forms of the enzyme were determined in control and diabetic rats. As determined from the total activity, and in agreement with previous reports, the enzyme protein was significantly decreased in streptozotocin-treated rats. However, the percentage of the active thiolic dephosphorylated form was higher in these animals than in controls, suggesting a response of the liver to the decrease both total and specific activity of HMGCoA reductase.

Hepatic transport of bilirubin in rats with streptozotocin-induced diabetes

This study was undertaken to evaluate the effects of streptozotocin-induced diabetes on the hepatic transport of bilirubin in male Wistar rats. Rats were pretreated with streptozotocin (60 mg/kg i.p.) to induce uncontrolled diabetes. Six days later endogenous biliary excretion and plasma bilirubin concentration were significantly enhanced compared to control animals (+36% and +46%, respectively), while the blood levels of free hemoglobin remained unchanged. Following a bilirubin load, the maximal biliary excretion of the pigment (Tm) in diabetic animals was significantly enhanced compared to control animals (+49%). Liver and plasma bilirubin concentrations at the end of bilirubin administration were significantly reduced (-28% and -30%, respectively). Bilirubin UDP-glucuronosyltransferase activity and UDP-glucose concentration in liver were significantly enhanced (+31% and +81%, respectively), as was the biliary excretion of unconjugated bilirubin (+37%) and bilirubin mono- (+38%) and diconjugates (+53%). When streptozotocin-diabetic rats were treated with insulin, the parameters of bilirubin transport and metabolism were significantly reduced compared to diabetic animals receiving no hormone replacement. In summary, our data indicate that in short-term streptozotocin-diabetic rats there is increased bilirubin production as well as enhanced hepatic conjugation and subsequent biliary excretion of the pigment. These effects appear to be a direct consequence of diabetes.

Alprazolam in end-stage renal disease: I. Pharmacokinetics

In a double-blind, randomized, placebo-controlled study, the pharmacokinetics of alprazolam and its active metabolite, alpha-hydroxyalprazolam, were determined in 12 normal subjects and 12 dialysis patients [7 hemodialysis (HD) patients and 5 continuous ambulatory peritoneal dialysis (CAPD) patients]. Blood samples were collected over 48 hours after alprazolam 0.5 mg and alprazolam 2 mg administration. Alprazolam and alpha-hydroxyalprazolam concentrations and alprazolam free fraction were determined. The pharmacokinetics of alprazolam were similar in normal subjects and HD patients with the exception of higher free fraction in HD patients. Differences were detected, however, in the pharmacokinetics of alprazolam in CAPD patients when compared with normal subjects and HD patients. These differences included a higher free fraction and a lower apparent oral clearance and free clearance in CAPD patients than in normal subjects or in HD patients. There was also a tendency for a later Tmax and a longer elimination half-life in CAPD patients than in normal subjects or HD patients. Alpha-hydroxyalprazolam concentrations were less than 15% of corresponding alprazolam concentrations in normal subjects and dialysis patients. Thus, end-stage renal disease is associated with changes in absorption, distribution, and/or elimination of alprazolam.

Effect of diabetes and starvation on the activity of rat liver epoxide hydrolases, glutathione S-transferases and peroxisomal beta-oxidation

The activities of peroxisomal beta-oxidation, cytosolic and microsomal epoxide hydrolase as well as soluble glutathione S-transferases have been determined in the livers of alloxan- and streptozotocin-diabetic male Fischer-344 rats. Five, seven and ten days after initiation of diabetes serum glucose levels were elevated 3.6-, 5.7- to 6.2- and 6-fold, while the activities of peroxisomal beta-oxidation and cytosolic epoxide hydrolase were elevated 1.5- and 2.5-fold, 1.4- and 2.7-fold and 1.3- and 2.0-fold, respectively. The activities of microsomal epoxide hydrolase and glutathione S-transferases were reduced to about 71% and 80% of controls. Application of 10 I.U./kg depot insulin twice a day for 10 consecutive days to alloxan-diabetic individuals approximately restored the initial glucose levels and enzyme activities except for peroxisomal beta-oxidation. Starvation of Fischer-344 rats for 48 hours and 5 days similarly resulted in a 1.3-fold to 2.1-fold and 1.2- to 1.6-fold increase in peroxisomal beta-oxidation and cytosolic epoxide hydrolase activity, respectively. Microsomal epoxide hydrolase was significantly decreased to 57% and 61% of control activity whereas glutathione S-transferase was only marginally reduced to 91% and 92%. Except for glutathione S-transferases initial enzyme activities were restored upon refeeding within 10 days. These results are similar to those obtained upon feeding of hypolipidemic compounds with peroxisome proliferating activity, and may indicate that high levels of free fatty acids or their metabolites which are known to accumulate in liver in both metabolic states may act as endogenous peroxisome proliferators.

Glycogenolysis--and not gluconeogenesis--is the source of UDP-glucuronic acid for glucuronidation

Differences in cofactor (NADPH and UDP-glucuronic acid) supply for various processes of biotransformation were studied by investigating the interrelations between glucose production (gluconeogenesis and glycogenolysis) and drug (p-nitrophenol, aminopyrine, phenolphthalein) biotransformation (hydroxylation and conjugation) in isolated murine hepatocytes. In glycogen-depleted hepatocytes prepared from animals fasted for 48 h (i) p-nitrophenol conjugation was decreased by 80% compared to the fed control, while aminopyrine oxidation was unaltered, (ii) addition of glucose or gluconeogenic substrates failed to increase the rate of p-nitrophenol conjugation, while the rate of p-nitrophenol and also aminopyrine oxidation was increased and (iii) gluconeogenesis was inhibited by 80% by aminopyrine oxidation: it was moderately decreased by p-nitrophenol oxidation and conjugation and remained unchanged by phenolphthalein conjugation. In hepatocytes prepared from fed mice (i) p-nitrophenol conjugation was independent of the extracellular glucose concentration, (ii) it was linked to the consumption of glycogen--addition of fructose inhibited p-nitrophenol glucuronidation only, while sulfation was unaltered and (iii) p-nitrophenol oxidation was not detectable: aminopyrine oxidation was not affected by fructose addition. It is suggested that UDP-glucuronic acid for glucuronidation derives predominantly from glycogen, while the NADPH generation for mixed function oxidation is linked to glucose uptake and/or gluconeogenesis in the liver.