Bilirubin UDP-glucuronyltransferase Activity Research Articles

Association of human liver bilirubin UDP-glucuronyltransferase activity with a polymorphism in the promoter region of the UGT1A1 gene

Background/Aims: Gilbert's syndrome is a benign form of a deficiency in bilirubin glucuronidation. It is associated with a homozygous polymorphism, A(TA) 7TAA instead of A(TA) 6TAA, in the TATA-box of the promoter region of the bilirubin UDP-glucuronyltransferase gene. In this study the correlation between this promoter region polymorphism and in vitro human liver bilirubin UDP-glucuronyltransferase enzyme activity was investigated. Methods: Liver samples from organ transplant donors ( n=39) and two known Gilbert's syndrome patients were used for measuring bilirubin UDP-glucuronyltransferase enzyme activity and for isolation of DNA followed by detection of the promoter region polymorphism by polymerase chain reaction. Genotypes were assigned as follows; 6/6: homozygous for the A(TA) 6TAA-allele, 7/7: homozygous for the A(TA) 7TAA-allele, and 6/7: heterozygous with one of each alleles. Results: Seventeen out of 39 subjects (44%) had the homozygous 6/6 genotype, 18 subjects (46%) had the heterozygous 6/7 genotype, whereas four individuals (10%) and the two individuals with Gilbert's syndrome had the 7/7 genotype correlated with Gilber's syndrome. This resulted in an allele frequency of 0.33 for the A(TA) 7TAA-allele. The median bilirubin UDP-glucuronyltransferase enzyme activity of the 17 subjects with the 6/6 genotype (1565 nmol/g liver/h) was significantly higher than the activity of the 18 subjects with the 6/7 genotype (985 nmol/g liver/h; p<0.05) and the six individuals with the 7/7 genotype (749 nmol/g liver/h; p<0.005). No significant differences in enzyme activity were found between the 6/7 and the 7/7 genotype groups. Conclusions: The results indicate a close association between the promoter region genotype and the expression of hepatic bilirubin UDP-glucuronyltransferase enzyme activity. Subjects who have a 7/7 genotype have the lowest enzyme activity, whereas subjects with the heterozygous 6/7 genotype have an intermediate enzyme activity.

Dose-related increase in liver heme catabolism during rabbit aflatoxicosis

Aflatoxin B1 (AFB1) has been reported to decrease microsomal hepatic cytochrome P450 (P450) content and increase both total plasma bilirubin concentration and liver heme oxygenase activity. The purposes of this study were to determine whether liver hemoproteins contents and heme catabolizing enzymes were affected by the mycotoxin and whether these alterations were linked to hyperbilirubinemia. Male New Zealand rabbits were divided into three groups of five animals, each receiving for 5 days either arabic gum as vehicle or AFB1 at a daily oral dose of 0.05 or 0.10 mg/kg. These treatments affected neither cytochrome b5 content nor NADPH-cytochrome reductase activity. A linear dose-dependent decrease in cytochrome P450 content and increases in both heme oxygenase and biliverdin reductase activities were observed. Bilirubin UDP-glucuronyltransferase activity was dramatically decreased at both doses, whereas cholestasis occurred only at 0.10 mg/kg. An exponential dose-dependent increase in plasma bilirubin concentration was also observed. Both the simultaneous exponential increase in bilirubinemia associated to a reduced bilirubin UDP-glucuronyltransferase activity and the absence of cholestasis at 0.05 mg/kg, suggested that the hyperbilirubinemia is more probably related to an increased heme catabolism than to an altered bile duct permeability.

Glucuronidation of thyroid hormone in rat liver: effects of in vivo treatment with microsomal enzyme inducers and in vitro assay conditions

We investigated the effects of in vivo treatment with different microsomal enzyme inducers, including clofibrate (CLOF), hexachlorobenzene (HCB), 3-methylcholanthrene (MC), 3,3',4,4'-tetrachlorobiphenyl (TCB), and 2,3,7,8-tetrachloro-p-dioxin, as well as of in vitro addition of the detergent Brij 56 on the glucuronidation of T4, T3, and rT3 by UDP-glucuronyltransferase (UGT) activities of rat liver microsomes. The results were compared with measurements of UGT activities for bilirubin, p-nitrophenol (PNP), and androsterone. In general, glucuronidation rates were 5-fold or more higher with rT3 than with T4 or T3 as substrate. In liver microsomes from untreated rats, T4 UGT activity was stimulated by Brij 56 to a maximum of about 2-fold at 0.025% detergent. Treatment of Wistar rats for 4 days with CLOF (200 mg/kg BW.day) resulted in significant increases in UGT activities for T4 (to 154%), rT3 (to 155%), and bilirubin (to 194%), in particular if assayed in the presence of 0.025% Brij 56, but had little effect on the UGT activities for T3, PNP, and androsterone. The CLOF-induced increases in T4 and rT3 UGT activities were not observed in Gunn rats, which have a complete lack of bilirubin UGT activity and greatly impaired PNP UGT activity. Treatment of Wistar rats with a single injection of MC (50 mg/kg BW), TCB (50 mg/kg BW), or 2,3,7,8-tetrachloro-p-dioxin (6.25 micrograms/kg BW) resulted, after 4 days, in 6.3- to 7.3-fold increases in T4 UGT activity and 15.1- to 16.7-fold increases in rT3 UGT activity if determined in the absence of Brij 56, whereas T4 UGT activity was only increased by 33-68% when assayed in the presence of Brij 56. T3 glucuronidation was not affected (with Brij 56) or was increased by only 33-68% (without Brij 56) after treatment with these MC-type inducers. PNP UGT activity was induced 3.6- to 4.3-fold, whereas bilirubin and androsterone UGT activities were changed little by these treatments. Similar findings regarding T4, rT3, PNP, and bilirubin UGT activities were obtained after chronic treatment of WAG rats with HCB, another MC-type inducer. However, WAG rats lack androsterone UGT and show low T3 UGT activity, which was increased about 2.3-fold by HCB treatment. On the basis of these and previous findings it is concluded that at least three UGT isoenzymes are involved in the glucuronidation of thyroid hormone.

Glucuronidation of thyroid hormone in rat liver: effects of in vivo treatment with microsomal enzyme inducers and in vitro assay conditions.

We investigated the effects of in vivo treatment with different microsomal enzyme inducers, including clofibrate (CLOF), hexachlorobenzene (HCB), 3-methylcholanthrene (MC), 3,3',4,4'-tetrachlorobiphenyl (TCB), and 2,3,7,8-tetrachloro-p-dioxin, as well as of in vitro addition of the detergent Brij 56 on the glucuronidation of T4, T3, and rT3 by UDP-glucuronyltransferase (UGT) activities of rat liver microsomes. The results were compared with measurements of UGT activities for bilirubin, p-nitrophenol (PNP), and androsterone. In general, glucuronidation rates were 5-fold or more higher with rT3 than with T4 or T3 as substrate. In liver microsomes from untreated rats, T4 UGT activity was stimulated by Brij 56 to a maximum of about 2-fold at 0.025% detergent. Treatment of Wistar rats for 4 days with CLOF (200 mg/kg BW.day) resulted in significant increases in UGT activities for T4 (to 154%), rT3 (to 155%), and bilirubin (to 194%), in particular if assayed in the presence of 0.025% Brij 56, but had little effect on the UGT activities for T3, PNP, and androsterone. The CLOF-induced increases in T4 and rT3 UGT activities were not observed in Gunn rats, which have a complete lack of bilirubin UGT activity and greatly impaired PNP UGT activity. Treatment of Wistar rats with a single injection of MC (50 mg/kg BW), TCB (50 mg/kg BW), or 2,3,7,8-tetrachloro-p-dioxin (6.25 micrograms/kg BW) resulted, after 4 days, in 6.3- to 7.3-fold increases in T4 UGT activity and 15.1- to 16.7-fold increases in rT3 UGT activity if determined in the absence of Brij 56, whereas T4 UGT activity was only increased by 33-68% when assayed in the presence of Brij 56. T3 glucuronidation was not affected (with Brij 56) or was increased by only 33-68% (without Brij 56) after treatment with these MC-type inducers. PNP UGT activity was induced 3.6- to 4.3-fold, whereas bilirubin and androsterone UGT activities were changed little by these treatments. Similar findings regarding T4, rT3, PNP, and bilirubin UGT activities were obtained after chronic treatment of WAG rats with HCB, another MC-type inducer. However, WAG rats lack androsterone UGT and show low T3 UGT activity, which was increased about 2.3-fold by HCB treatment. On the basis of these and previous findings it is concluded that at least three UGT isoenzymes are involved in the glucuronidation of thyroid hormone.(ABSTRACT TRUNCATED AT 400 WORDS)

Failure of expression of the phenobarbital-induced enhancement of UDP-glycosyltransferases in native, sealed endoplasmic reticulum vesicles from rat liver.

Conflicting data have been published regarding the effects of phenobarbital treatment on bilirubin UDP-glucuronyltransferase activity in native liver microsomes. Recent evidence suggests that the bilirubin UDP-glycosyltransferase system faces the interior of microsomal vesicles, and that expression of its activities in sealed microsomes may be rate-limited by transport of UDP sugars across the membrane. These observations raise the possibility that the reported variability in the effects of phenobarbital may reflect differences in integrity of the membrane in microsomal preparations. We examined the effect of phenobarbital on bilirubin UDP-glucosyltransferase and the UDP-glucuronyltransferase activities towards bilirubin, 4-nitrophenol, and 1-naphthol using native rat liver microsomes with verified vesicle integrity. Phenobarbital-induced microsomes in which the membrane permeability barrier was eliminated by pretreatment with detergent displayed markedly higher UDP-glycosyltransferase activities towards all tested substrates compared with activities in similarly disrupted microsomes from untreated rats. In contrast, none of the transferase activities tested were significantly enhanced by phenobarbital treatment when the enzymic activities were assayed in sealed microsomes. Addition to the enzyme assay mixture of UDPGlcNAc, a presumed physiological activator of the UDP-glucuronyltransferases, failed to expose the enhanced UDP-glucuronyltransferase concentration in phenobarbital-induced sealed microsomes. Our findings are consistent with the idea that transport of UDP sugar across the membrane may be rate-limiting for expression of UDP-glycosyltransferase activities in sealed microsomes. Quantitative assessment of membrane integrity is an essential prerequisite in experiments designed to study the regulation of the microsomal UDP-glycosyltransferase system.

Proportion of conjugated bilirubin in bile in relation to hepatic bilirubin UDP-glucuronyltransferase activity

To elucidate the diagnostic relevance of biliary conjugated bilirubin, biliary bilirubin from normal volunteers (NV), patients with Gilbert's syndrome (GS) and Crigler-Najjar syndrome type II (C-N II), and from various rat strains was fractionated. Biliary bilirubin diglucuronide (BDG) was present at lower levels, and bilirubin monoglucuronide (BMG) and unconjugated bilirubin were present at higher levels in GS and C-N II compared with NV, which is consistent with decreased hepatic bilirubin UDP-glucuronyltransferase activity (BGTA). The level of biliary BDG was higher in Wistar-Kyoto rats and lower in heterozygous (Jj) Gunn rats than in SD and Wistar rats. The hepatic BGTA level in heterozygous (Jj) Gunn rats was decreased to 60% of that in Wistar rats, in accordance with decreased biliary BDG. On the other hand, BGTA in Wistar-Kyoto rats whose biliary BDG level was high, was not different from that of Wistar and SD rats. Thus, a correlation between BGTA and biliary bilirubin fractions may not exist on some occasions.

Increase in the relative amount of bilirubin diconjugates in rat bile and serum under infusion of phthaleins and indocyanine green

The effect of organic anions on bilirubin metabolism and excretion was investigated in rats. Biliary excretion of bromosul-fophthalein, bromocresol green and indocyanine green led to a significant decrease in excretion of bilirubin pigments and to an increase of their concentration in serum. This was concomitant with a marked increase in the ratio of bilirubin diconjugates to monoconjugates in bile and serum. These changes were unrelated to either bile flow, biliary lipid output, or hepatic activity of bilirubin UDP-glucuronyl transferase. Following bolus injection of [ 14C]bilirubin, peak excretory rate of radioactivity was markedly delayed in rats infused with bromosulfophthalein, as compared to controls. It is concluded that administration of the organic anions increased the ratio of bilirubin diconjugates to monoconjugates in bile and serum, by slowing down the intrahepatic transit of bilirubin pigments. This, in turn, allowed more efficient enzyme-catalyzed formation of bilirubin diconjugates from the intermediate bilirubin monoconjugates.

Hepatic bilirubin and UDP-glucuronate levels in bolivian squirrel monkeys exhibiting fasting hyperbilirubinemia

1. 1. Bolivian squirrel monkeys (BoSMs), which are animal models for Gilbert's syndrome, have 40% less hepatic bilirubin UDP-glucuronyltransferase (BR-UPPG-T) activity than Brazilian squirrel monkeys (BrSMs). 2. 2. Although fasting results in similar decreases in hepatic UDP-glucose and UDP-glucuronate levels in both simian subspecies, increased activities (55%) of BR-UDPG-T are induced only in the fasted control BrSMs, which do not exhibit the marked fasting hyperbilirubinemia (FH). 3. 3. Total hepatic bilirubin (BR) concentrations were 50% greater in both fed and fasted BoSMs when compared to BrSMs. 4. 4. Hepatic unconjugated BR levels increase upon fasting only in Gilbert-like BoSMs, reaching concentrations twice that observed in BrSMs. 5. 5. Elevated hepatic BR levels in lasted BoSMs may reflect BR overproduction or inadequate glucuronidation. 6. 6. The increased BR-UDPG-T activity induced in BrSMs during fasting could compensate in-part for the UDPGA depletion and prevent the marked FH as observed in BoSMs.

A case of Gilbert’s syndrome combined with macroamylasemia

A 30-year-old Japanese male, who had no remarkable family history, visited our hospital with a complaint of abdominal pain, and unconjugated hyperbilirubinemia and hyperamylasemia were observed. He showed negative hemolysis tests, positive nicotinic acid test, low hepatic bilirubin UDP-glucuronyltransferase activity, decreased bilirubin diglucuronide and increased bilirubin monoglucuronide in bile, and a decrease in serum bilirubin after phenobarbital administration. He also showed high serum amylase level, low urine amylase level, and low amylase-creatinine clearance ratio. Gel filtration of serum with Sephadex G-200 revealed the existence of macroamylase. Countercurrent immunoelectrophoresis proved binding of serum amylase to lambda type IgA. From these results, the case was diagnosed as Gilbert's syndrome combined with macroamylasemia.

Topology and regulation of bilirubin UDP-glucuronyltransferase in sealed native microsomes from rat liver

Bilirubin UDP-glucuronyltransferase displays marked latency in native microsomes. To examine whether this latency correlates with structural integrity of the microsomal vesicles and reflects lumenal orientation of the enzyme's catalytic center, we analyzed the relationship between transferase activity and the degree of expression of mannose (Man)-6-phosphatase, which is a marker enzyme of the cisternal face of the ER membrane. Using detergent, sonication, or the pore-forming Staphylococcus aureus α-toxin to breach the microsomal membrane permeability barrier, we found that after each of these pretreatments a remarkably close direct relationship existed between latency changes for bilirubin UDP-glucuronyltransferase and Man-6-phosphatase. This finding suggested that the transferase may have the same transverse topology as the phosphohydrolase. We also compared the effects of membrane-impermeant proteinases on bilirubin UDP-glucuronyltransferase activity in native and disrupted microsomes. Whereas the unspecific proteinase nagarse markedly inactivated (to <30% of activities in controls) the transferase in disrupted microsomes, treatment with the proteinase had little effect on transferase activity in sealed microsomal vesicles. The results suggest that the active site of bilirubin UDP-glucuronyltransferase is on the lumenal face of the endoplasmic reticulum membrane. It was also found that activation of transferase activity by UDP N-acetylglucosamine, which is the presumed allosteric effector of UDP-glucuronyltransferase, was markedly altered by relatively small changes in structural integrity of the microsomes and totally abolished when latency of Man-6-P hydrolysis fell below 8 ̃ 0%. Collectively, these findings demonstrate that the microsomal membrane permeability barrier is a major determinant of expression of microsomal UDP-glucuronyltransferase activity and that quantitative assessment of integrity of the microsomes is essential for studying kinetic properties and regulation of microsomal UDP-glucuronyltransferase.

Comparison of hepatic, renal and intestinal bilirubin UDP-glucuronyl transferase activities in rat microsomes

1. 1. Bilirubin UDP-glucuronyltransferase activity and its dependence on substrate concentrations in rat liver, renal cortex and intestinal mucosa microsomes were studied. 2. 2. Bilirubin monoglucuronide synthesis from unconjugated bilirubin was a higher capacity, lower affinity step in comparison with bilirubin diglucuronide formation in the three tissues tested. 3. 3. Bilirubin glucuronide formation in liver microsomes showed a higher capacity but a lower affinity than extrahepatic ones. Renal cortex and intestinal mucosa exhibited similar kinetics parameters. 4. 4. In vitro bilirubin glucuronidation in renal cortex and intestinal mucosa was quantitatively important as compared with the hepatic one.

Partial defect in hepatic glutathione S-transferase activity in a case of Rotor’s syndrome

In a 17 year-old male patient with Rotor's syndrome, hepatic glutathione S-transferase activity toward 1-chloro-2,4-dinitrobenzene reduced to about 0.2% of the mean activity of patients with other diseases. The activities toward sulfobromophthalein and 1,2-dichloro-4-nitrobenzene were low (44% and 47%, respectively, of those controls), but basically present. Bilirubin UDP-glucuronyltransferase activity in this Rotor's syndrome case was in the normal range.

The congenic normal R/APfd and jaundiced R/APfd-j/j rat strains: a new animal model of hereditary non-haemolytic unconjugated hyperbilirubinaemia due to defective bilirubin conjugation.

In this paper the production of the R/APfd-j/j strain which is congenic with the R/APfd strain is reported. The R/APfd-j/j completely lacks hepatic bilirubin UDP-glucuronyltransferase activity, as do our GUNNXR/Pfd-j/j rat strain and various other stocks of GUNN rats (j/j) described in the literature. Our recombinant inbred strain GUNNXR/Pfd-j/j was produced from non-inbred GUNN (j/j) rats. This GUNNXR/Pfd-j/j rat was used as a donor of the jaundice gene j, the R/APfd rat serving as the recipient. After eight backcross-intercross cycles (16 generations) the R/APfd-j/j strain was obtained which is congenic with the R/APfd strain. Congenicity was demonstrated by various techniques including transplantation of skin tissue, strain-specific tumour cells and hepatocytes, the mixed lymphocyte reaction, and comparison of biochemical markers. The potential of the novel inbred strain of jaundiced rat, R/APfd-j/j, and the corresponding control strain R/APfd for biochemical and clinical studies of bilirubin metabolism are briefly discussed.

Treatment of enzyme deficiency by hepatocyte transplantation in rats

The inbred, homozygous Gunn rat exhibits unconjugated hyperbilirubinemia due to a hereditary absolute deficiency of bilirubin UDP-glucuronyltransferase activity. The mechanism of action of hepatocyte transplantation (HTX) in the treatment of enzyme deficiency has been investigated in this study. Gunn rats underwent HTX by the injection of isolated hepatocytes from a nondeficient donor rat (Wistar) into the spleen. A transient, statistically significant decrease in total plasma bilirubin (TB) levels was observed. Gunn rats receiving Gunn hepatocytes did not show such a decrease. Histological examination 2–3 months post-HTX of the recipient spleens showed the absence of grafted hepatocytes in the first group and graft survival in the second. Bile specimens from sublethal irradiated Gunn rats, collected 6 days after HTX with viable Wistar hepatocytes, all contained bilirubin mono- and diglucuronides. Control groups consisting of Gunn rats receiving nonviable Wistar hepatocytes or Gunn hepatocytes, and sham-operated Gunn rats did not excrete bilirubin glucuronides in bile. It was also demonstrated that bilirubin UDP-glucuronyltransferase activity, which appeared in Gunn rats after HTX with Wistar hepatocytes, was only transient. It is concluded that the decrease of TB in the Gunn rat after HTX with nondeficient hepatocytes is explained by the appearance of the enzyme, which was absent in the recipient animal. Viable, nondeficient hepatocytes are required for the elicited bilirubin conjugation. Rejection of the transplanted hepatocytes abolishes this effect.

Effects of ioglycamide on the hepatic transport of bilirubin and its mono- and diconjugates in the rat.

Bilirubin seems to share the biliary excretion pathway with other organic anions, but not with bile acids. We studied the effects of the organic anion ioglycamide, an iodinated contrast agent, on bilirubin metabolism in Wistar rats. This compound does not undergo conjugation and is characterized by a maximal biliary secretory rate (Tm). The results show that in spite of producing a 3-fold increase in bile flow, ioglycamide excretion under Tm conditions decreased the output of unconjugated bilirubin and its monoconjugate by approximately 90%. Diconjugated bilirubin decreased by only 50% and became by far the predominant pigment in bile (86.5 +/- 6.0% of total pigment vs. 61.0 +/- 4.0% in basal conditions, n = 12). Unconjugated and monoconjugated bilirubins changed in parallel suggesting that the former arises from the monoconjugates. In serum, diconjugated bilirubin augmented from trace amounts to 1.15 +/- 0.17 mumole per liter. Total conjugated pigments in serum increased from 5 to 85% of total bilirubin. Bile acid output remained unchanged. Pretreatment of rats with ioglycamide altered neither the activity of bilirubin UDP-glucuronyltransferase nor the ratio of diconjugate to monoconjugate formed at both low (25 microM) and high (164 microM) bilirubin concentrations. The observed biological effects of ioglycamide were dose-dependent and fully reversible. We suggest that ioglycamide interferes with the excretion of conjugated bilirubins ("bilirubinostasis"). The monoconjugates retained in the hepatocyte might then undergo more efficient transformation to diconjugates, the latter thus becoming the most important bile pigments in serum and bile.

Liver microsomal bilirubin UDP-Glucuronyltransferase disturbances in bile duct ligated rats

The activity of bilirubin UDP-Glucuronyltransferase was determined in microsomes from normal and bile duct ligated rats. It was measured after 2 and 8 days following bile duct ligation and compared with normal rats. A decrease of 33% in the total enzyme activity was observed on day 2; a fall of 70% was founded on day 8. Bilirubin diglucuronide represented approximately 20% of total conjugates in both groups of cholestatic rats, as compared with 65% found in normals. It was concluded that bilirubin microsomal conjugating capacity is markedly altered during cholestasis. This can be attributed to microsomal membrane damage produced by stagnant bile.

Subcellular distribution and regulation of hepatic bilirubin UDP-glucuronyltransferase.

We have investigated the subcellular location and regulation of hepatic bilirubin UDP-glucuronyltransferase, which has been presumed to be located largely in the smooth endoplasmic reticulum. Purity of subcellular membrane fractions isolated from rat liver was assessed by electron microscopy and marker enzymes. Bilirubin UDP-glucuronyltransferase activity was measured by radiochemical assay using a physiologic concentration of [14C]bilirubin, and formation rates of bilirubin diglucuronide and monoglucuronides (C-8 and C-12 isomers) were determined. Activity of the enzyme was widely distributed in subcellular membranes, the majority being found in smooth and rough endoplasmic reticulum, with small amounts in nuclear envelope and Golgi membranes. No measurable activity was found in plasma membranes or in cytosol. Synthesis of bilirubin diglucuronide as a percentage of total conjugates and the ratio of C-8/C-12 bilirubin monoglucuronide isomers formed were comparable in all membranes, suggesting that the same enzyme is present in all locations. However, the regulation of bilirubin UDP-glucuronyltransferase activity differed among intracellular membranes; enzyme activity measured in the presence of the allosteric effector uridine 5'-diphospho-N-acetylglucosamine exhibited latency in smooth endoplasmic reticulum and Golgi membranes, but not in rough endoplasmic reticulum and nuclear envelope. Since rough membranes comprise 60% of hepatocyte endoplasmic reticulum and bilirubin UDP-glucuronyltransferase activity in vitro is maximal in this membrane fraction under presumed physiologic conditions, it is likely that the rough endoplasmic reticulum represents the major site of bilirubin glucuronidation in hepatocytes.

Intrahepatic cholestasis and hyperbilirubinemia in ethynyl estradiol and chlorpromazine-treated rats.

Intrahepatic cholestasis associated with hyperbilirubinemia was induced by the simultaneous administration of ethynyl estradiol (EE) and chlorpromazine hydrochloride (CPZ) for 7 days to female Sprague-Dawley rats. Increases in direct serum bilirubin levels and alkaline phosphatase activities were observed concomitantly with diminished bile flow and bile acid excretion. However, the bilirubin output in the bile remained unchanged. [14C]Erythritol clearance decreased in parallel with the diminished bile flow, while [14C]sucrose biliary clearance increased, suggesting that the decrease in bile flow was of canalicular origin and also due to increased permeability in the biliary tract. There was a prominent decrease in the bile acid-independent flow, and the bile acid-dependent flow also decreased concomitantly with the diminished bile acid excretion. Slight increases in cytochrome P-450 and anilin hydroxylase activities in liver microsomes were observed, and bilirubin UDP-glucuronyl transferase activity increased significantly. Indirect bilirubin clearances determined by a bilirubin load test were markedly reduced in the icteric rats. The bilirubin load test also suggested that bilirubin flowed back into the circulating blood and that gluculonidation of bilirubin mono-gluculonide (BMG) to bilirubin diglucuronide (BDG) was impaired. Light microscopic examinations of the liver revealed marked proliferation of the bile ductules and numerous vacuoles in the hepatocytes. Dilatation of the bile canaliculi with diminished microvilli was also detected by scanning electron microscopy.

Bile pigments and bilirubin UDP-glucuronyl transferase during the metamorphosis of Rana catesbeiana tadpoles

1. 1. The major bile pigments in Rana catesbeiana tadpoles was bilirubin IXα. 2. 2. The concentration of bilirubin IXα increases in bile and plasma during metamorphosis. 3. 3. Bilirubin IXα and biliverdin IXα were also present in the bile of tadpoles. 4. 4. Bilirubin UDP-glucuronyl transferase activity was present in the livers of all tadpoles examined. 5. 5. Bilirubin UDP-glucuronyl transferase activity increases slightly during spontaneous metamorphosis and increases approximately 2-fold during T 3-induced metamorphosis.

Hepatic bilirubin-conjugating enzymes of man in the normal state and in liver disease.

Bilirubin UDP-glucuronyl transferase (BGT), bilirubin UDP-glucosyl transferase (BGLT) and bilirubin UDP-xylosyl transferase (BXT) activities were measured in wedge-biopsied liver specimens obtained from patients with various liver diseases, and compared with those in controls with normal liver histology. BGT was measured alone using needle biopsy liver specimens from the patients with Gilbert's syndrome (15 patients). Rotor's syndrome (one) and posthepatitic hyperbilirubinemia (3). BGT was decreased to about 30% of controls in Gilbert's syndrome, but showed no change in posthepatitic hyperbilirubinemia and Rotor's syndrome. About 90% decrease in BGT, and BGLT and BXT were observed in Crigler-Najjar syndrome type II (3 patients). In patients with cholelithiasis and chronic hepatitis, statistically significant changes of these three enzymes were not observed, except the statistically significant increase in BGT activity in chronic hepatitis. Slight increases in BGT and BXT activities were observed in anicteric cases with cholelithiasis. The ratio of BGT, BGLT and BXT activities in controls was 1:0.50:0.98 (expressed as "per mg protein"). Slight differences existed between the ratios of BGT, BGLT and BXT in various liver diseases, and this may suggest the separate identities of BGLT and BXT from BGT. Determination of bilirubin-conjugation is essential in the diagnosis of Gilbert's syndrome and Crigler-Najjar syndrome type II, but shows no specific change in the other chronic liver diseases.