Biliary transport maximum of tauroursodeoxycholate is twice as high as that of taurocholate in the rat

Biliary excretory transport maximum (Tm) and choleretic efficiency were compared for tauroursodeoxycholate and taurocholate in Wistar male rats. Under a continuous iv infusion of bile salts with a stepwise increase in infusion rate, the Tm of tauroursodeoxycholate was found to be two times higher (2.25±0.07 μmole/min/100 g body weight, n=8, mean±SD) than that of taurocholate (0.97±0.05 μmole/min/100 g body weight, n=14, p<0.001). On the other hand, the amount of bile water obligated by the excretion of 1μmole of tauroursodeoxycholate was significantly lower than that of taurocholate. (4.71±0.08 μl/μmole for tauroursodeoxycholate, vs. 9.27±0.76 μl/μmole for taurocholate, mean±SD, p<0.001). It was concluded that tauroursodeoxycholate can be excreted into the bile in male rats twice as efficiently as taurocholate. Furthermore, the higher efficiency in the choleretic property of ursodeoxycholate previously reported by Dumont et al. appears to be specific to free ursodeoxycholate and not to its taurine conjugate used in the present experiment.     

The bile flow and biliary excretion of ursocholate in the rat

Several studies reported that ursodeoxycholate (but not its conjugates), when administered intravenously, increased the biliary bicarbonate concentration in the rat (1–3). At the same time, a complete dissociation between bile flow and the bile salt excretion rate was produced in the second hr of infusion (2). In order to examine whether this property was due to the 7β-hydroxy group in its molecular structure, the choleretic property of ursocholate (3α, 7β, 12α-trihydroxy-5β-cholanoic acid) was investigated in male Wistar rats. Immediately after the start of iv infusion of ursocholate at a rate of 1.2 μmole/min/100 g b. wt., both the bile flow and bile salt excretion rate began to increase. However, unlike with ursodeoxycholate, the bile salt excretion rate continued to be high in the second and third hr of infusion, while the bile flow rate gradually increased. Furthermore, the bicarbonate concentration in the bile fell slightly 10 min after the start of ursocholate infusion. Although the concentration tended to return to the baseline value before the bile salt infusion in the later period of observation, no significant increase in bicarbonate concentration was observed during the whole observation period. These properties were quite similar to those of cholate rather than those of ursodeoxycholate. However, a cholate infusion at the same rate of 1.2 μmole/min/100 g b.wt. caused a cholestasis as early as 20 to 30 min after the start of an infusion. These results suggest that the previously reported properties of ursodeoxycholate (that it causes a complete dissociation between the bile flow and bile salt excretion rate in the second hr and that it increases the biliary bicarbonate concentration) were not due to the 7β-hydroxy group in its steroidal structure, and that the choleretic property of ursocholate is similar to its 7α-hydroxy epimar, cholate. However, the much lower cytotoxicity of ursocholate compared to cholate appears to be due to the 7β-hydroxy group that ursocholate has.     

Role of the hepatocyte microtubular system in the excretion of bile salts and biliary lipid: implications for intracellular vesicular transport

The role of the hepatocyte microtubular system in the transport and excretion of bile salts and biliary lipid has not been defined. In this study the effects of microtubule inhibition on biliary excretion of micelle- and non-micelle-forming bile salts and associated lipid were examined in rats. Low-dose colchicine pretreatment had no effect on the baseline excretion of biliary bile salts and phospholipid in animals studied 1 hr after surgery (basal animals), but slightly retarded the excretion of tracer [14C]taurocholate relative to that of lumicolchicine-pretreated (control) rats. However, colchicine pretreatment resulted in a marked reduction in the excretion of 2 mumol/100 g doses of a series of four micelle-forming bile salts of differing hydrophilicity, but had no significant effect on the excretion of the non-micelle-forming bile salt, taurodehydrocholate. Continuous infusion of 0.2 mumol of taurocholate/(100 g.min) following 24 hr of biliary drainage (depleted/reinfused animals) resulted in physiologic bile flow with biliary excretion rates of bile salts, phospholipid, and cholesterol that were markedly inhibited (mean 33, 39, and 42%, respectively) by colchicine or vinblastine pretreatment. Excretion of tracer [14C]taurocholate also was markedly delayed by colchicine in these bile salt-depleted/reinfused animals. In contrast, colchicine did not inhibit bile salt excretion in response to reinfusion of taurodehydrocholate. Thus, under basal conditions, the microtubular system appears to play a minor role in hepatic transport and excretion of bile salts and biliary lipid. However, biliary excretion of micelle-forming bile salts and associated phospholipid and cholesterol becomes increasingly dependent on microtubular integrity as the transcellular flux and biliary excretion of bile salts increases, in both bile salt-depleted and basal animals. We postulate that cotransport of micelle-forming bile salts and lipids destined for biliary excretion, via an intracellular vesicular pathway, forms the basis for this microtubule dependence.     

Bile secretory characteristics of beta-muricholate and its taurine conjugate are similar to those of ursodeoxycholate in the rat

Ursodeoxycholate (UDC) has very high biliary transport maxima values (Tm) for its conjugates as well as the capability of inducing choleresis rich in bicarbonate concentration in the bile in rats. We examined in the present study whether these properties are shared by beta-muricholate (beta-MC), using beta-MC, alpha-muricholate (alpha-MC) and tauro-beta-MC (T beta-MC) in the rat. Bile samples were collected every 20 min for 2 hr in male rats under the infusion of alpha- or beta-MC (1.2 mumol/min/100g). The choleretic response was quicker in beta-MC infused rats than in rats infused with alpha-MC. Bile salt excretion rates increased radically in both experiments. However, in beta-MC infused rats, the bile salt excretion rate began to decrease after 40 min, whereas in alpha-MC infused rats, it continued to increase after 1 hr. Bile bicarbonate concentration significantly increased in beta-MC infused rats but not in alpha-MC infused rats. The Tm of T beta-MC was 2 times higher than the Tm value for taurocholate and was comparable to that of tauroursodeoxycholate (TUDC) which was previously found by the authors. The bile flow (Y, microliter/min/100 g) was significantly correlated with the bile salt excretion rate (X, mumol/min/100 g) [Y = (6.90 +/- 0.24) X + (5.5 + 1.06), n = 41, -0.98, P less than 0.01)], the slope value being higher than that found for TUDC. The results suggest that UDC and beta-MC (and their conjugates) have very similar bile secretory characteristics and may probably share the same transport system in the rat.     

Bile flow and electrolyte composition of bile associated with maximum bilirubin excretion in sheep.

Changes in the composition of bile accompanying the maximum biliary excretion (Emax) of bilirubin were investigated in sheep. Sheep fitted with chronic 'T-tubes' in the common bile duct were infused with taurocholate and bilirubin at various rates. Bile collected during both pre- and post-bilirubin steady-state periods was analyzed for the biliary concentration of electrolytes, bile salts, and bilirubin. Bilirubin Emax was 24.6 mumol/min while bile salt excretion during this period was 103 mumol/min. At Emax bilirubin entry into bile reached a concentration of 16.1 mumol/mL, increased the biliary concentration of sodium, did not change osmolarity of bile, and did not increase bile flow. The data suggest that bilirubin either interacts with mixed micelles in bile or forms molecular aggregates.     

The biliary excretion of {3H}-25-hydroxyvitamin D3 following chronic ethanol administration in the rat

The biliary excretion of {³H}-25-hydroxyvitamin D₃ was studied in rats fed a diet containing 36% of total calories as ethanol and in pair-fed controls. {³H}-25-hydroxyvitamin D₃ was injected i.v. and the biliary appearance of {³H}-compounds studied over a period of 80 minutes. Choleresis was not affected by chronic ethanol feeding averaging 98.7±10.3 μl min^?1 kg^?1 in Controls and 101.8±8.7 μl min^?1 kg^?1 in ethanol-fed animals. The total biliary excretion of {³H} was found to be 29% higher in ethanol-treated than control rats and represented 6.3±0.4% and 4.9±0.4% (p<0.05) of the injected dose at the end of the experiment. The biliary excretion rate as well as the biliary concentration of {³H}-25-hydroxyvitamin D³ congeners were significantly increased by the ethanol treatment from the 25th to the 80th minute after the i.v. injection of {³H}-25-hydroxyvitamin D₃. The plasma and liver {³H} concentrations were not significantly affected by the ethanol treatment. These results suggest that, in the rat, chronic ethanol ingestion promotes the biliary loss of {³H}-25-hydroxyvitamin D₃. The higher concentration of {³H}-compounds into the bile of ethanol treated rats also suggests the presence of excretory pathway(s) which could be, at least in part, independent of bile flow. This increased loss of {³H}-25-hydroxyvitamin D³ into the bile may be a contributing factor in the impaired vitamin D status in alcoholics.     

Taurine supplementation induces multidrug resistance protein 2 and bile salt export pump expression in rats and prevents endotoxin-induced cholestasis

The effect of oral taurine supplementation on endotoxin-induced cholestasis was investigated in rat liver. At 12h following lipopolysaccharide (LPS) injection (4mg/kg body weight i.p.) bile flow and bromosulfophthalein (BSP) and taurocholate (TC) excretion were determined in the perfused liver and the expression of the canalicular transporters multidrug resistance protein 2 (Mrp2) and bile salt export pump (Bsep) was analyzed. Injection of LPS induced a significant decrease of bile flow ( 2.2+/-0.2 microl/g liver wet weight/min vs 3.3+/-0.1 microl/g liver wet weight in controls), biliary BSP excretion (10.8+/-2.2 nmol/g/min vs 21.0+/-3.8 nmol/g/min), and biliary TC excretion (114+/-23 nmol/g/min vs 228+/-8 nmol/g/min). These effects were due to transporter retrieval from the canalicular membrane and downregulation of Mrp2 and Bsep expression. In taurine-supplemented rats bile flow was 30% higher than that in untreated rats and the expression of Mrp2 and Bsep protein was increased two- to threefold. In taurine-supplemented rats there was no significant reduction of bile flow or of BSP and TC excretion at 12h following LPS injection. This protective effect of taurine was due to higher Mrp2 and Bsep protein levels compared to nonsupplemented LPS-treated rats, whereas relative Mrp2 retrieval from the canalicular membrane induced by LPS was not significantly different. LPS-induced tumor necrosis factor alpha and interleukin-1beta release were lower in taurine-fed rats; however, downregulation of Mrp2 and Bsep expression by LPS was delayed but not prevented. The data show that oral supplementation of taurine induces Mrp2 and Bsep expression and may prevent LPS-induced cholestasis.     

Taurolithocholate-induced inhibition of biliary lipid and protein excretion in the rat.

Taurolithocholate (TLC), a natural bile salt, induces selective impairment on canalicular membrane of the hepatocyte, which seems to be a major determinant of its cholestatic effect in experimental animals. In order to extend existing studies about the effects of TLC on bile secretion, we examined in TLC-treated rats the biliary excretion of compounds that are transported to canalicular membrane via vesicles, such as lipids and proteins. The single intravenous injection of TLC (3 mumol/100 g body wt.) inhibited transiently the biliary bile salt excretion, while the biliary excretion of lipids (i.e., cholesterol and phospholipids) and proteins remained inhibited even though the biliary excretion and composition of bile salts were normalized. Under such a condition, TLC also inhibited the transcellular vesicular pathway to the exogenous protein horseradish peroxidase entry into bile, without altering the paracellular biliary access of the protein. The hepatic uptake of horseradish peroxidase was unaffected by TLC-treatment. The results indicate that TLC can inhibit the biliary excretion of compounds that reach the canaliculus via a vesicular pathway, such as lipids and proteins, by a mechanism not related to a defective bile salt excretion. Possible explanations for these findings are discussed.     

Biliary excretion of foreign compounds. Benzene and its derivatives in the rat

1. The extent of the excretion in the bile of the rat of benzene and 21 of its simple derivatives was studied. 2. Some 16 compounds of molecular weight less than 200, and including neutral molecules (benzene and toluene), aromatic acids, aromatic amines and phenols, were injected in solution intraperitoneally into biliary-cannulated rats. Metabolites in the bile were identified and estimated. The extent of biliary excretion of these compounds was low, i.e. 0–10% of the dose in 24hr., and most appeared in the bile mainly as conjugates. 3. The biliary excretion of six conjugates of molecular weight less than 300, including three glycine conjugates, one sulphate conjugate, one glucuronic acid conjugate and two acetyl derivatives, was low (less than 3% of the dose). 4. It is concluded that simple benzene derivatives of molecular weight less than about 300 are poorly excreted in rat bile.     

The biliary excretion of sulfbromophthalein in the pig

The characteristics of the hepatic metabolism of Sulfbromophthalein (BSP) have not been described previously for the pig. This is an important deficiency, since the pig is particularly suitable for studies of hepatic physiology and pharmacology which might apply to man. The aim of these experiments was to establish the pattern of serum clearance and biliary excretion of BSP and to determine that dose which would produce a maximal concentration in bile. A dose response and pattern of biliary excretion of BSP was studied at three dose levels administered either as a single bolus of a continuous infusion. All experiments were performed in conscious, conditioned pigs. The patterns of serum clearance and biliary excretion were found to be similar to other laboratory animals and to man. Maximary biliary concentration of BSP was achieved by a single bolus of 5-9 mumol/kg or a constant infusion of 0-59 mumol/kg/min. At these dose levels no significant alteration in bile flow was demonstrated nor was there any correlation between bile flow and BSP excretion. Supra-maximal doses produced a significant increase in bile flow and with these doses there was a significant positive correlation between bile flow and BSP excretion.     

Physical and biological properties of fluorescent dansylated bile salt derivatives: the role of steroid ring hydroxylation

The hydroxyl groups of bile salts play a major role in determining their physical properties and physiologic behavior. To date, no fluorescent bile salt derivatives have been prepared which permit evaluation of the functional role of the steroid ring. We have prepared five fluorescent cholanoyl derivatives using a dansyl-ethylene diamine precursor linked to the sulfonyl group of taurine; N-(5-dimethylamino-1-naphthalenesulfonyl)-N'-(2-aminoethanesulf onyl)- ethylenediamine. The fluorescent dansyl-taurine was conjugated to the carboxyl group of free bile acids, enabling the labeling of the series: dehydrocholate, ursodeoxycholate, cholate, chenodeoxycholate and deoxycholate. Despite a systematic hydrophobic shift compared with the native bile salts (aqueous solubility and water:octanol partitioning), the influence of steroid ring hydroxylation was retained, with the dehydrocholate and cholate derivatives more water soluble than the dihydroxy derivatives. Similarly, the sequence of HPLC mobilities, reflecting relative hydrophilicity, was identical in the dansyl-taurine derivatives and the native taurine-conjugated bile salts. Cellular uptake of all five steroid derivatives was rapid, and partial inhibition of [3H]taurocholate uptake was observed in isolated hepatocytes. Rates of biliary excretion of the dansylated derivatives by the isolated perfused rat liver correlated closely with hydrophilicity. Collectively, these findings indicate that the influence of the hydroxyl groups is retained in this series of dansylated steroids, and that hydroxylation is a key determinant of their hepatocellular transport and biliary excretion. These fluorescent bile salt derivatives may thus serve as unique probes for investigating structure-function relationships in hepatic processing of steroid-based compounds.     

Endotoxin-induced reduction in biliary indocyanine green excretion rate in a chronically catheterized rat model

Using a nonstressed chronically catheterized rat model in which the common bile duct was cannulated, we studied endotoxin-induced alterations in hepatic function by measuring changes in the maximal steady-state biliary excretion rate of the anionic dye indocyanine green (ICG). Biliary excretion of ICG was calculated from direct measurements of biliary ICG concentrations and the bile flow rate during a continuous vascular infusion of ICG. Despite significant elevations in mean peak serum tumor necrosis factor-alpha (TNF-alpha) concentrations (90.9 +/- 16.2 ng/ml), there was no effect on mean rates of bile flow or biliary ICG clearance after administration of 100 microg/kg endotoxin at 6 or 24 h. Significant differences from mean baseline rates of bile flow and biliary ICG excretion did occur after administration of 1,000 microg/kg endotoxin (mean peak TNF-alpha 129.6 +/- 24.4 ng/ml). Furthermore, when rats were treated with up to 16 microg/kg of recombinant TNF-alpha, there was no change in mean rates of bile flow or ICG biliary clearance compared with baseline values. These data suggest that the complex regulation of biliary excretion is not mediated solely by TNF-alpha.     

Hepatic organic anion transport kinetics and bile flow during short-term total parenteral nutrition in the rabbit

Plasma disappearance of sulfobromophthalein (BSP) after an intravenous bolus (5 mg/kg) was determined in six lab chow-fed (LCF) rabbits and in six rabbits maintained on total parenteral nutrition (TPN) for 5 days. A common bile duct cannula enabled measurements of bile flow and biliary BSP excretion. Compartmental analysis of the biexponential plasma disappearance curve yielded three fractional transfer rates, plasma to liver (hepatic uptake), liver to plasma (reflux), and liver to bile (canalicular excretion). The transfer rates for hepatic uptake were 0.253 +/- 0.061/min for LCF and 0.147 +/- 0.040/min for TPN (P less than 0.01) and for the canalicular excretion of BSP were 0.038 +/- 0.019/min for LCF and 0.019 +/- 0.002/min for TPN (P less than 0.05). Model-computed rates for BSP excretion in bile over 60 min were lower with TPN (61%) than with LCF (80%); the measured excretory rates were 53% for TPN rabbits and 75% of injected dose for LCF animals. Basal biliary flow was reduced by 50% in the TPN group. With a two-compartmental model, assuming two pools and three transfer rates, we have demonstrated for the first time significant decreases in hepatic uptake and canalicular excretion of the organic anion BSP during TPN. A decrease in hepatic blood flow due to the enteral fast of TPN could have contributed in part to the decreased hepatic uptake. But, because the second exponent of the biexponential curve is independent of hepatic blood flow, the decrease in liver to bile transfer rate is a true approximation of a diminished canalicular excretory capacity during TPN. It is concluded that the movement of organic anions along the hepatic BSP/bilirubin transport system is impaired early during TPN.     

Study of the heme catabolism of fish

• 1.1. The composition of bile pigments in the blood and bile of 39 species were studied.
• 2.2. Conjugated bilirubin (trace to 4.62 mg/100 ml) was detected in the serum of most fish, while biliverdin (trace to 2.0 mg/100ml) was detected only in Anguilla Japonica, Thalassoma lunare and Clinocottus analis.
• 3.3. Analysis showed tht there are two types of bile pigments excretion pattern in these fishes. The first pattern excretes bilirubin (most conjugate) predominantly, the other excretes mostly biliverdin with some bilirubin. However, during starvation, the excretion of conjugate bilirubin gradually shifted to unconjugated biliverdin. The rate of shifting varies with species.
• 4.4. Introduction of bilirubin into Anguilla japonica produced an initial excretion of mono-conjugates, followed by di-conjugates. Introduction of biliverdin caused an increased in the excretion of unconjugated biliverdin, but no significant increase of bilirubin in the bile was detected.
• 5.5. A binary excretion pathway of bile pigments in fish is proposed. The evolutionary characteristics of heme catabolism in terrestrial animals with respect to this pathway is discussed.

     

Urinary prostaglandin and kallikrein excretion are not flow dependent in the rat

To study the relationship between urine flow, urinary prostaglandin (PG) and kallikrein excretion in the rat high urine flow was induced in hydropenic Long-Evans rats by either hypotonic volume expansion or with manniitol or with furosemide. PGE, excretion remained unchanged during hypotonic volume expansion (134.5 ± 29.7 before and 153.0 ± 48.9 pg/min after) while it decreased significantly with mannitol (from 166.3 ± 32.4 to 45.2 ± 8.2 pg/min, p<0.01) and with furosemide (from 170.0 ± 20.4 to 29.5 ± 5.3 pg/min, p<0.001). PGF_2α excretion rates were slightly reduced following all three interventions. Urinary kallikrein excretion remained unchanged in all three groups of animals. It is concluded that, in contrast to human and dogs in the rat urine flow and urinary PG excretion are not interlinked.     

Biliary excretion of proteins in the rat during dehydrocholate choleresis

Choleresis induced by dehydrocholate (DHC) stimulates the discharge into bile of lysosomes, which are implicated in the biliary excretion of proteins. Contrary to taurocholate-induced choleresis, DHC choleresis is not affected by microtubule (mt) inhibition. Therefore, the role of mt's in the biliary protein excretion during bile salt choleresis was analyzed in this study. Normal rats and rats treated with the mt poisons colchicine or vinblastine or with the acidotropic agent chloroquine (Cq) were used. The analysis of the protein component in bile was made on SDS-polyacrylamide gel, and the individual polypeptides were quantitated by densitometry. The excretion of bile polypeptides were compared with that of lysosomal acid phosphatase. Bile flow and bile salt output did not show changes on account of treatments. The biliary excretion of acid phosphatase was stimulated by DHC, and it was not affected by mt inhibitors but was markedly diminished by Cq. DHC choleresis produced different effects on the bile polypeptides. The biliary excretion of polypeptide of high molecular mass (84-140 kDa) was stimulated by DHC. Cq treatment increased their basal biliary excretions, whereas DHC-induced secretion was qualitatively and quantitatively similar to that of controls. The 69-kDa polypeptide (albumin) also increased during DHC-induced choleresis, but it showed a different excretory pattern. Cq treatment inhibited such an increase but no correlation with the excretory pattern of the lysosomal marker was found. The biliary excretion of polypeptides of low molecular mass (down to 14 kDa) suffered a transitory decrease and then a subsequent increase over basal values during the DHC choleresis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cholestasis induced by lithocholate and its glucuronide: their biliary excretion and metabolism

We studied the effects of the infusion of lithocholate and lithocholate-3-sulfate and 3-glucuronide in rats (0.29 mumol/min per 100 g body weight for 40 min) on bile flow, together with their biliary excretion and metabolism. Lithocholate-glucuronide had a higher cholestatic effect than lithocholate, whereas lithocholate-sulfate had almost no effect on bile flow. Lithocholate was mainly converted to taurine or glucuronide conjugates in the bile, serum and liver and hydroxylation of the tauro-conjugate proceeded. Lithocholate-sulfate was almost completely excreted in the bile, mainly as tauro-conjugate. Lithocholate-glucuronide was excreted in bile almost without conjugation, while some taurine conjugation occurred in the serum and liver. These results suggest that the poor biotransformation of lithocholate-glucuronide is related to its higher cholestatic potency than lithocholate.     

Solubilization of lipids from hamster bile-canalicular and contiguous membranes and from human erythrocyte membranes by conjugated bile salts.

We have demonstrated in vitro the efficacy of the taurine-conjugated dihydroxy bile salts deoxycholate and chenodeoxycholate in solubilizing both cholesterol and phospholipid from hamster liver bile-canalicular and contiguous membranes and from human erythrocyte membrane. On the other hand, the dihydroxy bile salt ursodeoxycholate and the trihydroxy bile salt cholate solubilize much less lipid. The lipid solubilization by the four bile salts correlated well with their hydrophobicity: glycochenodeoxycolate, which is more hydrophobic than the tauro derivative, also solubilized more lipid. All the dihydroxy bile salts have a threshold concentration above which lipid solubilization increases rapidly; this correlates approximately with the critical micellar concentration. The non-micelle-forming bile salt dehydrocholate solubilized no lipid at all up to 32 mM. All the dihydroxy bile acids are much more efficient at solubilizing phospholipid than cholesterol. Cholate does not show such a pronounced discrimination. Lipid solubilization by chenodeoxycholate was essentially complete within 1 min, whereas that by cholate was linear up to 5 min. Maximal lipid solubilization with chenodeoxycholate occurred at 8-12 mM; solubilization by cholate was linear up to 32 mM. Ursodeoxycholate was the only dihydroxy bile salt which was able to solubilize phospholipid (although not cholesterol) below the critical micellar concentration. This similarity between cholate and ursodeoxycholate may reflect their ability to form a more extensive liquid-crystal system. Membrane specificity was demonstrated only inasmuch as the lower the cholesterol/phospholipid ratio in the membrane, the greater the fractional solubilization of cholesterol by bile salts, i.e. the total amount of cholesterol solubilized depended only on the bile-salt concentration. On the other hand, the total amount of phospholipid solubilized decreased with increasing cholesterol/phospholipid ratio in the membrane.     

Effect of bilirubin infusion on excretion of bilirubin and biliverdin in rabbits

Intravenous infusion of bilirubin (BR) at 171 micrograms/min/kg into rabbits resulted in biliary concentration of BR increasing from 3.8 (control) to 243 mg/dl and BR excretion increasing from 1.7 to 66 micrograms/min/kg. BR infusion resulted in biliary concentrations of biliverdin (BV) increasing from 9.1 to 30 g/dl and BV excretion increasing from 4.2 to 8.2 micrograms/min/kg. BR infusion produced a progressive decline in bile flow. BV was the predominant bile pigment in control rabbits fed either an alfalfa-based or chlorophyll-free diet. These results imply that rabbits can oxidize BR to BV.     

Ursodeoxycholate modulates bile flow and bile salt pool independently from the cystic fibrosis transmembrane regulator (Cftr) in mice

Cystic fibrosis liver disease (CFLD) is treated with ursodeoxycholate (UDCA). Our aim was to evaluate, in cystic fibrosis transmembrane regulator knockout (Cftr(-/-)) mice and wild-type controls, whether the supposed therapeutic action of UDCA is mediated via choleretic activity or effects on bile salt metabolism. Cftr(-/-) mice and controls, under general anesthesia, were intravenously infused with tauroursodeoxycholate (TUDCA) in increasing dosage or were fed either standard or UDCA-enriched chow (0.5% wt/wt) for 3 wk. Bile flow and bile composition were characterized. In chow-fed mice, we analyzed bile salt synthesis and pool size of cholate (CA). In both Cftr(-/-) and controls intravenous TUDCA stimulated bile flow by ～250% and dietary UDCA by ～500%, compared with untreated animals (P < 0.05). In non-UDCA-treated Cftr(-/-) mice, the proportion of CA in bile was higher compared with that in controls (61 ± 4 vs. 46 ± 4%; P < 0.05), accompanied by an increased CA synthesis [16 ± 1 vs. 10 ± 2 μmol·h(-1)·100 g body wt (BW)(-1); P < 0.05] and CA pool size (28 ± 3 vs. 19 ± 1 μmol/100 g BW; P < 0.05). In both Cftr(-/-) and controls, UDCA treatment drastically reduced the proportion of CA in bile below 5% and diminished CA synthesis (2.3 ± 0.3 vs. 2.2 ± 0.4 μmol·day(-1)·100 g BW(-1); nonsignificant) and CA pool size (3.6 ± 0.6 vs. 1.5 ± 0.3 μmol/100 g BW; P < 0.05). Acute TUDCA infusion and chronic UDCA treatment both stimulate bile flow in cystic fibrosis conditions independently from Cftr function. Chronic UDCA treatment reduces the hydrophobicity of the bile salt pool in Cftr(-/-) mice. These results support a potential beneficial effect of UDCA on bile flow and bile salt metabolism in cystic fibrosis conditions.