Feeding diets containing 2% cheno- or urso-deoxycholic acid or cholestyramine to rats for two weeks alters intestinal morphology and bile acid absorption

This study was undertaken to examine the effect of supplementing chow for 2 weeks with 2% cheno- (CDC) or ursodeoxycholic (UDC) acid or cholestyramine (CHOL) on the intestinal morphology and in vitro uptake of bile acids in adult rats. Food intake was higher in UDC and CHOL as compared with animals fed chow or CDC, or in animals pair-fed a chow-restricted diet (CRD). Body weight gain was lower in CDC and CRD but was unchanged by feeding UDC or CHOL. Jejunal mucosal surface area was similar in the five groups, although the ileal mucosal surface area was lower in UDC than in the other animals. Feeding UDC reduced the ileal uptake of cholic acid (C), taurocholic acid (TC), and glycocholic acid (GC). Feeding CDC had no effect on bile acid uptake except when compared with animals fed a chow-restricted diet. Feeding CHOL reduced the active ileal uptake of C, had no effect on the uptake of TC or GC or CDC, and was associated with increased uptake of stearic, linoleic, and linolenic acids. These effects were likely related to a direct effect of changes in the luminal bile acids rather than due to an indirect effect of the reduced food intake, since the ileal uptake of CDC and GC was greater in animals fed CDC than in those fed a chow-restricted diet with comparable weight gain. Thus, 2 weeks of feeding bile acids or bile acid binding agents may alter the form and function of the rat intestine, and as well may lead to changes in food intake and body weight gain.

Inhibitors of the lipoxygenase arachidonic acid pathway impair glycocholate efflux in isolated rat hepatocytes

Lipoxygenase arachidonic acid metabolites mediate secretory processes in several tissues, but their possible involvement in liver transport functions is still unknown. This study evaluated the influence of the lipoxygenase inhibitor nordihydroguayaretic acid (NDGA), the cyclooxygenase inhibitor indomethacin (INDO), and the dual cyclo and lipoxygenase inhibitors 3-amino-1-[m-(trifluoromethyl)-phenyl]-2-pyrazoline (BW 755c) and eicosatetraynoic acid (ETYA) on the handling of glycocholic acid (GC) by isolated rat hepatocytes. No drug modified cell viability or oxygen consumption in hepatocytes. In 30-min incubations with 50 microM GC the initial rate of GC uptake (V0) in control hepatocytes was 1.15 +/- 0.09 nmol.mg protein-1.min-1. The cellular GC content remained constant from 10 to 30 min (steady-state phase), the 30-min value being 6.63 +/- 0.35 nmol.mg protein-1. NDGA (10-50 microM), BW 755c (25-200 microM) and ETYA (5-100 microM), prevented the steady-state phase occurring, thus determining a progressive accumulation of GC in cells with time. As compared to controls, 50 microM NDGA (+37%, p less than 0.01), 200 microM BW 755c (+39%, p less than 0.01) and 5 microM ETYA (+19%, p less than 0.05) induced the highest increases in the amount of GC in cells at 30 min, in all cases V0 being unchanged. Concentrations of BW 755c and ETYA above those indicated also decreased V0. Both V0 and the amount of cellular GC in the steady-state phase were proportionally decreased by high INDO concentrations (25-100 microM) which did not modify the morphology of the uptake curve. Since experiments with dual and lipoxygenase inhibitors suggested an impairment of GC efflux, the initial rate of GC efflux (V0ef) was measured in hepatocytes preloaded with 50 microM GC and transferred to a GC-free medium. In controls, V0ef was 1.12 +/- 0.12 nmol.mg protein-1.min-1. BW 755c (200 microM) and NDGA (50 microM) reduced V0ef by 45 and 38%, respectively. The kinetic analysis of the effect of 200 microM BW 755c on the efflux process using hepatocytes preloaded with GC from 5 to 200 microM disclosed a non-competitive inhibition. Vmax was reduced from 1.37 +/- 0.15 to 0.89 +/- 0.10 (p less than 0.01), whereas Km was unchanged (3.79 +/- 0.33 vs. 4.25 +/- 0.54, N.S.). In summary, inhibitors of the lipoxygenase arachidonic acid pathway impaired the efflux of GC from isolated rat hepatocytes. The hypothesis is raised that oxidized metabolites of arachidonic acid may participate on the secretion of bile salts in these cells.

Bile acid conjugation pattern in the isolated perfused rat liver during infusion of an amino acid formulation

The influence of the taurine-containing amino acid mixture Trophamine on the pattern of bile acid conjugation was examined in the isolated perfused rat liver using cholic acid as the bile acid substrate. In all experiments, greater than 97% of the cholic acid appearing in bile was conjugated with taurine or glycine. The pattern of taurine and glycine bile acid conjugation, however, was dependent on the availability of taurine in the perfusate medium. Thus, in the absence of Trophamine infusion, the percentage of cholic acid conjugated with taurine (ie, taurocholate) declined throughout the course of the cholic acid infusion. Trophamine infusion increased the ratio of biliary taurocholate/glycocholate by 4.5-fold over that observed in the absence of the amino acid infusion. Increasing the amount of taurine in Trophamine by 2- or 5-fold resulted in a 1.8- and 4.3-fold increase, respectively, in the taurocholate/glycocholate ratio over that observed during the Trophamine infusion. Infusion of taurine alone, at an equimolar concentration of taurine as that in Trophamine, resulted in a similar taurocholate/glycocholate ratio as that observed during the Trophamine infusion. These data indicate that taurine availability, even in the presence of high concentrations of glycine and other amino acids in Trophamine, appears to be the most important factor in determining the pattern of bile acid conjugation in the isolated perfused rat liver.

Bile composition of adult baboons is influenced by breast versus formula feeding

We tested the hypothesis that infant cholesterol intake and breast- versus formula-feeding influence the bile cholesterol saturation index and bile acid conjugate composition in adult baboons at 7-8 years of age. We also measured the influence of the postweaning intake of dietary cholesterol and fat (saturated and unsaturated) on the effects of the infant diets. The 80 baboons were derived from six sires and 80 dams and randomly assigned at birth to breast-feeding or to one of three formulas containing about 2, 30, or 60 mg cholesterol/dl. After weaning at 16 weeks of age the animals were assigned to one of four adult diets, which contained 0.01 or 1.0 mg/kcal of cholesterol containing 40% of calories from saturated or unsaturated fat. The bile cholesterol saturation index was significantly higher at 7-8 years of age in baboons breast-fed as infants compared with those fed formula (87.0% versus 72.8%, p less than 0.004). The cholesterol saturation index was not significantly different among the three formula groups. Among baboons who were breast-fed and subsequently fed saturated fat as adults, the glycine/taurine (G/T) ratios of the bile acid conjugates were about three times those of baboons fed unsaturated fat (1.53 versus 0.47); whereas among formula-fed animals the type of fat did not influence the G/T ratio (interaction, p = 0.022). Adult baboons fed the three formulas in infancy had an inverse relationship of the G/T ratio to the level of formula cholesterol (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Side chain conjugation prevents bacterial 7-dehydroxylation of bile acids

The effect of side chain conjugation on 7-dehydroxylation of bile acids has been investigated. C24-bile acids and their glycine and taurine conjugates and keto bile acids were incubated with pure strains of Eubacterium sp. VPI 12708. Bile acids of the 5 alpha- or 5 beta-series with a free terminal carboxyl group and a 3 alpha, 7 alpha-dihydroxy system were very effectively 7 alpha-dehydroxylated, whereas 7 beta-hydroxy bile acids resisted 7-dehydroxylation. Oxo bile acids were metabolized at the oxygen function also. Glycine- and taurine-conjugated bile acids were neither deamidated nor 7-dehydroxylated by the bacteria. Thus, side chain conjugation prevents 7-dehydroxylation of bile acids by Eubacterium sp. VPI 12708.

Bile salt-fatty acid mixed micelles as nasal absorption promoters of peptides. I. Effects of ionic strength, adjuvant composition, and lipid structure on the nasal absorption of [D-Arg2]kyotorphin

Bile salts and synthetic surfactants have been used to promote nasal absorption of peptide drugs. Although a marked increase in nasal absorption has been achieved, this may not be adequate and the possibility of adjuvant-induced membrane toxicity exists. The present study employs a rat in situ nasal perfusion technique and mixed micelles between sodium glycocholate (NaGC) and various lipids as potential nasal absorption enhancers of a stable model dipeptide, [D-Arg2]kyotorphin. NaGC alone enhanced the nasal absorption of the dipeptide in a concentration-dependent manner. When linoleic acid was added to form mixed micelles with NaGC, the absorption was further enhanced (P less than 0.01). The effect of mixed micelles was synergistic and much greater than with single adjuvants. Increasing ionic strength was found to increase the adjuvant activity of both NaGC and NaGC-lipid mixed micelles. Structure of the lipid component of the mixed micelles also affected the adjuvant potency. Oleic acid, a cis-unsaturated fatty acid, was more effective than elaidic acid, the trans-isomer, whereas cis-linoleic acid and trans-linolelaidic acid were equally effective (alpha = 0.05). Mixed micelles of mono-glycerides such as monoolein and monolinolein were also more effective than NaGC alone (alpha = 0.05). Micellar solubilization of these polar lipids by NaGC appears to be important for nasal absorption enhancement to occur. Reversal of the membrane permeability was also observed within approximately 20-40 min after removal of the adjuvants from the rat nasal cavity. These observations are similar to the effects of mixed micelles on the rectal mucosa and may involve the same mechanism.

Peroxisomal bile acid-CoA:amino-acid N-acyltransferase in rat liver

Bile acid-CoA:amino-acid N-acyltransferase activity was measured in subcellular fractions of rat liver homogenate. The conversion of [14C]choloyl-CoA and [14C]chenodeoxycholoyl-CoA into the corresponding [14C]tauro- and glyco-bile acids was calculated after isolation of the product by high performance liquid chromatography. There was an enrichment of bile acid-CoA:amino-acid N-acyltransferase activity in the light mitochondrial (L) fraction and to a lesser extent in the microsomal fraction. Surprisingly, no enrichment was found in the cytosolic fraction. Subfractionation of the L-fraction by Nycodenz gradient centrifugation, showed that the activity of the N-acyltransferase had a bimodal distribution and co-sedimented with peroxisomes (particulate catalase) and microsomes (esterase). The highest specific amidation activity of both choloyl-CoA and chenodeoxycholoyl-CoA was always found in the most peroxisome-rich fractions. [14C]Taurocholate formation in the peroxisomal fraction was 2.2 mumol/mg of protein/min. Striking differences were observed in the Km values and the saturation concentrations for glycine and taurine. The peroxisomal amidation of [14C]choloyl-CoA had a Km for taurine of 0.9 x 10(-3) M and for glycine of 17 x 10(-3) M. The results are consistent with the possibility that most of de novo synthesized bile acids conjugate to taurine by a peroxisomal bile acid-taurine N-acyltransferase in rat liver. The bile acids deconjugated in the gut and recirculating to the liver may be activated and amidated by the microsomal enzyme system prior to biliary secretion.

The rapid evaluation of intestinal bacterial growth using a conjugate of ursodeoxycholic acid with para-aminobenzoic acid

From the standpoint of utilizing the distinctive feature of para-aminobenzoic acid (PABA) and the metabolism of intestinal bile acid, a conjugate of ursodeoxycholic acid with PABA (PABA-UDCA) was newly synthesized to study whether it can be a good material or not for the evaluation of the activity of intestinal bacterial growth. This compound was efficiently deconjugated in an incubation experiment with cholylglycine hydrolase resulting in the release of PABA. In a cultivation experiment, this compound was deconjugated by the same species of aerobic and anaerobic bacteria that deconjugated glycocholic acid. In an animal experiment, urinary excretions of PABA during 6 h following oral administration of 10 mg PABA-UDCA were determined. The control rat (n = 10) excreted 338.5 +/- 13.8 micrograms (mean +/- S.E.) of PABA. In contrast with this, the rats (n = 10) with intestinal antisepsis by the administration of polymyxin B and tinidazole excreted less PABA (14.0 +/- 2.5 micrograms; p less than 0.001), whereas the rats with intestinal bacterial overgrowth owing to the artificially made enteric blind loop excreted more PABA than the control rats did (673.6 +/- 70.2 micrograms; p less than 0.01). These observations indicate that this new compound is likely to offer a simple and rapid method for evaluation of intestinal bacterial growth.

Effect of anaesthetic agents on bile flow and biliary excretion of 131I-cholylglycyltyrosine in the rat

We have compared in the rat the effects of i.v. anaesthetic agents on bile flow rate and on the biliary excretion of a novel bile acid, 131I-cholylglycyltyrosine (131I-cholylgly.tyr.). Etomidate 1-mg bolus and 2-mg h-1 infusion, Althesin 3-mg bolus and 14.5-mg h-1 infusion and propofol 3.3-mg bolus and 3.3-mg h-1 were given via a tail vein cannula and pentobarbitone 50 mg kg-1 was given by the intraperitoneal route, to groups of six rats. Each animal received only one anaesthetic agent. One hour after cannulation of the common bile duct, 131I-cholylgly.tyr. 5 microCi was injected into the jugular vein and bile was collected every 1 min for 10 min. The mean (SD) percentage cumulative biliary excretion of 131I-cholylgly.tyr. at the end of 10 min was: propofol group 74.1 (5.2)%; Althesin group 82.3 (2.2)%; etomidate group 69.4 (17.6)%; pentobarbitone group 76.4 (3.2)%. Propofol and Althesin were relatively more choleretic, causing bile flow rates twice that produced by pentobarbitone. Only Althesin caused a significant increase in biliary excretion of 131I-cholylgly.tyr. relative to that in rats that received pentobarbitone. Bile flow rates for the respective anaesthetic techniques (microliter min-1/100 g body weight) (mean (SD)) were: propofol group 14.1 (1.8); Althesin group 12.5 (1.7); etomidate 8.5 (1.4); pentobarbitone group 7.3 (1.0). There was a marked metabolic acidosis in all rats except in the propofol group, in which normal acid-base status and oxygenation were observed.

Biliary obstruction dissipates bioelectric sinusoidal-canalicular barrier without altering taurocholate uptake

To study immediate events during extrahepatic cholestasis, we investigated the effect of short-term biliary obstruction on the bioelectrical sinusoidal-canalicular barrier in the rat using molecular weight-matched uncharged and negatively charged inert solute pairs. The bioelectrical barrier averaged -22 +/- 5 and -18 +/- 4 mV (NS) using the pair carboxy-/methoxyinulin and ferrocyanide/sucrose, respectively. After a 20-min biliary obstruction both decreased by 61 and 11%, respectively, but only the large molecular weight pair (the inulins) returned to base line after release of the obstruction. Inert solute clearances were increased after short biliary obstruction depending on molecular size and negative charge (ferrocyanide greater than sucrose greater than carboxyinulin greater than inulin), suggesting that both permeability and bioelectrical barriers were affected by obstruction. The hepatic extraction in vivo of a passively transported drug not excreted into bile (D-propranolol) was not affected by obstruction, whereas that of an actively transported drug (glycocholate) decreased from 66 +/- 8 to 41 +/- 20% during biliary obstruction (P less than 0.01). Unidirectional transfer of glycocholate was not affected by short-term biliary obstruction in the situ perfused rat liver; however, 2 min after [14C]glycocholate administration, increased return was observed in hepatic venous effluent in obstructed animals. Our findings demonstrate a loss of the bioelectrical barrier immediately after short-term biliary obstruction. Decreased hepatic extraction in the view of unaltered sinusoidal uptake demonstrates regurgitation of bile into blood during short-term biliary obstruction.

Stimulation of taurocholate and glycocholate efflux from the rat hepatocyte by arginine vasopressin

Vasopressin induces alterations in the transmembrane distribution of the bile salts taurocholate and glycocholate but not of cholate, chenodeoxycholate, or chenodeoxycholate derivatives in isolated rat hepatocytes in suspension. Studies were conducted to define the specific transport events modulated by vasopressin. Unidirectional uptake of cholate, taurocholate, and glycocholate, monitored within a 15-s time frame, is not altered by vasopressin. Km values for cholate, taurocholate, and glycocholate influx were found to be 57, 12, and 26 microM, respectively. Vmax values for influx of cholate, taurocholate, and glycocholate were 1.7, 1.8, and 2.4 nmol.mg protein-1.min-1, respectively. At half-maximal effective concentrations, arginine vasopressin increases unidirectional efflux of taurocholate by 34% (EC50 = 1.5 X 10(-9) M) and glycocholate by 17% (EC50 = 5 X 10(-9) M). In the presence of 0.05 microM arginine vasopressin, the apparent Km value for taurocholate efflux decreases from 1.57 mM (control) to 0.94 mM; for glycocholate, the apparent Km decreases from 5.19 mM (control) to 3.22 mM. Vasopressin does not significantly change the Vmax values for taurocholate and glycocholate efflux (0.40 and 1.05 nmol.mg protein-1.min-1, respectively). These studies suggest that modulation of bile salt efflux by vasopressin may be utilized to probe bile salt transport pathways in the rat hepatocyte.

Deconjugation of glycine-amidated bile salts does not occur in germfree rats

After oral administration to germfree rats of cholyl-glycine-1-14C, deoxycholyl-glycine-1-14C and nor-ursocholyl-glycine-1-14C no significant amounts of 14CO2 are expired. This indicates that these bile salts are not significantly deamidated under physiological conditions in the rat organism outside the gastro-intestinal tract.

Absence of an acinar gradient for bile acid uptake in developing rat liver

We studied the acinar distribution for uptake of the bile acid analogue [125I]-cholylglycyltyrosine in livers from adult and 14-day-old suckling rats. Portal and peripheral (systemic) serum bile acid concentrations were also measured by combined gas chromatography-mass spectrometry as an independent index of hepatic bile acid clearance from portal blood. Utilizing light microscopic autoradiography, a steep, decreasing portal to centrilobular gradient for cholylglycyltyrosine uptake was noted in adult rat liver. In contrast, there was no lobular gradient for cholylglycyltyrosine uptake visible in the 14-day-rat liver; all hepatocytes within the acinus contained a similar number of silver grains. Portal vein total bile acid concentrations were significantly higher in serum of adult compared to 14-day-old rats. In contrast, bile acid concentrations were 10-fold higher in the peripheral serum of developing versus adult rats. The peripheral to portal serum bile acid concentration ratio was 0.23 in the adult and 6.48 in the 14-day-old rat. We conclude that the entire hepatic lobule participates in the uptake of bile acids in the 14-day-old rat even under the basal conditions of this study. The normal "reserve" function of centrilobular hepatocytes is not sufficient to compensate for the decreased transport capacity of the developing liver with the result that increased concentrations of bile acids enter and accumulate in the systemic circulation.

[Binding of bile salts and lysolecithin by various antacids in biological media]

The in vitro capacity of several commercial antacids to bind bile acids and lysolecithin was measured in three different test media: 0.1 n HCl, natural human gastric juice and human gastric juice enriched with 5% protein. Antacids bind bile salts variably. In HCl and in natural and protein-enriched gastric juice the capacity to bind conjugated bile salts was higher (47-72%) for antacids with high aluminium content, such as Alucol, Andursil, Muthesa than for antacids with less aluminium such as Calamox and Riopan (17-18%). Binding of unconjugated bile salts did not show any corresponding difference. The test medium had little effect on binding capacity when pH was comparable. Natural gastric juice was slightly better with regard to binding of conjugated bile salts. The addition of protein had only minimal effect. Lysolecithin was equally heavily adsorbed by all tested antacids and in all three test conditions (85-100%). Since duodenogastral reflux contains mainly unconjugated bile salts, our results suggest that antacids with higher aluminium content should be preferred if binding of bile salt reflux is attempted.

Excretion, deconjugation, and absorption of bile acids after colectomy for ulcerative colitis. Comparative studies in patients with conventional ileostomy and patients with Kock's reservoir

Bile acid metabolism was studied in 26 patients with a continent ileostomy (Kock's reservoir) and 32 patients with conventional ileostomy. All had been colectomized for ulcerative colitis. In patients with a continent ileostomy the 14C-glycocholic acid breath test showed increased pulmonary 14CO2 excretion as evidence of abnormal bacterial deconjugation of bile acids and increased faecal 14C excretion as evidence of bile acid malabsorption. Faecal bile acid excretion, determined chemically, and, by inference, bile acid synthesis were only moderately increased (median, 1.8 mmol/day). The disturbance of bile acid metabolism was similar to that found in 32 patients with conventional ileostomy, but more pronounced with higher faecal 14C. A significant difference was that no abnormal bacterial deconjugation took place in patients with conventional ileostomy, since their pulmonary 14CO2 excretion was subnormal. Stool mass was almost identical in the two groups, with median values of 665 and 663 g/day, respectively. Faecal fat excretion was normal in most in both groups. Thus bile acid metabolism is slightly more disturbed in patients with a continent ileostomy than in patients with conventional ileostomy. The resulting malabsorption was modest in both groups.

Intestinal absorption of lithocholic acid sulfates in the rat: inhibitory effects of calcium

Sulfation of lithocholic acid has been proposed as a mechanism for elimination of this hepatotoxic bile acid from the body by accelerating its fecal excretion. However, quantitative data on the absorption characteristics of sulfated lithocholic acid conjugates in vivo are scarce. We studied the intestinal absorption of 14C-labeled glycolithocholic acid (GLC), taurolithocholic acid (TLC), and their 3 alpha-sulfate esters, SGLC and STLC, respectively. Studies were performed in unanesthetized rats with a permanent biliary drainage. At an intestinal infusion rate of 125 nmol/min, which is comparable to 7% of the normal biliary bile acid output in the rat, the absorption of sulfated lithocholic acid conjugates was delayed when compared with their unsulfated precursors but quantitatively only slightly reduced over a 24-h period: SGLC 90.9 +/- 3.6%, GLC 94.4 +/- 1.1%, STLC 84.4 +/- 3.0%, and TLC 94.2 +/- 2.1%. Urinary excretion of sulfated and unsulfated bile acids was similar and never exceeded 2% of the dose. SGLC absorption was dose dependent, was not altered by coinfusion of rat bile, and was only slightly reduced by a sixfold overdose of taurocholic acid. SGLC and STLC were excreted into bile largely unchanged in form. In contrast, GLC and TLC were extensively metabolized to more polar bile acids, predominantly to beta-muricholic acid conjugates. Replacement of NaCl in the infusion fluid by CaCl2 reduced the absorption of SGLC and STLC by 63 and 52%, respectively. This calcium effect was less pronounced for the unsulfated bile acids: GLC -22%, and TLC -19%. Absorption of taurocholic acid was unaffected by CaCl2.(ABSTRACT TRUNCATED AT 250 WORDS)

Conjugation of cholic acid with taurine and glycine by rat liver peroxisomes

We have previously shown that rat liver peroxisomes catalyze conversion of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid into cholic acid as the CoA-ester (1). In the present work it is shown that addition of taurine or glycine to the reaction mixture, choloyl-CoA is further converted to taurocholic or glycocholic acid, respectively. The identity of these products was verified by fast atom bombardment-mass spectrometry. The peroxisomal fraction catalyzed conjugation of cholic acid with taurine (22.3 nmol X mg-1 X h-1) or glycine (18.6 nmol X mg-1 X h-1) at rates twice those observed with the microsomal fraction. The results indicate that conjugation of newly formed bile acids may be an important function of liver peroxisomes.

Human breast milk stimulates bile acid secretion by fetal rabbit liver in organ culture

Fetal livers from rabbits at 30 days of gestation were grown in organ culture and the effect of human milk added to the culture medium on the ability of liver to excrete bile acids (cholylglycine) was examined. Human breast milk promoted a concentration related increase in cholylglycine accumulation in the medium. The factor(s) present in milk responsible for this effect appear to be non-protein in nature and is associated with the floating lipid fraction. Furthermore, milk enhances the integrity of liver explants, as established by light microscopy.

Synthesis and biliary excretion of tyrosine-conjugated bile salts in Wistar rats

Tyrosine-labelled free and glycine-conjugated bile acids were synthesized and radiolabelled with 125I to high purity. The synthetic method utilized excess tyrosine methyl ester hydrochloride (1.4 equiv.) and bile acid (one equiv.) via dicyclohexylcarbodiimide (1.4 equiv.) with yields of 90-93% for tyrosine bile acid conjugates and glycyltyrosine conjugates and 56-60% yields for the glycylglycyltyrosine conjugates. All of the eight iodinated tyrosine bile acids tested were rapidly excreted into bile following intravenous injection. In bile duct-cannulated rats with ligated renal pedicles under pentobarbital anaesthesia the percentages of injected dose recovered from bile within 20 min were as follows: cholylglycine ([14C]cholylGly), 81.2 +/- 1.3%; taurocholate ([14C]taurocholate), 94.3 +/- 1.0%; cholyltyrosine (125I-cholylTyr), 85.5 +/- 3.3%; deoxycholyltyrosine (125I-deoxycholylTyr), 87.9 +/- 6.3%; chenodeoxycholyltyrosine (125I-chenodeoxycholylTyr), 93.4 +/- 2.9; cholylglycyltyrosine (125I-cholylGlyTyr), 95.7 +/- 6.7%; deoxycholylglycyltyrosine (125I-deoxylcholylGlyTyr), 92.5 +/- 3.2%; chenodeoxycholylglycyltyrosine (125I-chenodeoxycholylGlyTyr), 94.1 +/- 3.1%; cholyldiglycyltyrosine (125I-cholylGlyGlyTyr), 85.2 +/- 3.6%, and deoxycholyldiglycyltyrosine (125I-deoxycholylGlyGlyTyr), 85.5 +/- 2.7%. Values are means +/- SD. Thus the biliary excretion of 125I-chenodeoxycholylGlyTyr, 125I-chenodeoxycholylTyr, 125I-deoxycholylGlyTyr and 125I-cholylGlyTyr was similar to that of [14C]taurocholate, the major naturally occurring bile acid in the rat, and the biliary excretion of all the tyrosine conjugates was similar to or exceeded that of [14C]cholylglycine. Conjugation with tyrosine enhanced the efficiency of plasma-to-bile transport of most naturally occurring bile acids. Comparison of glycyltyrosine conjugates with glycylglycyltyrosine conjugates suggests that any additional benefit derived by elongation of the side-chain is probably negated by obscuring the 12 alpha-hydroxyl function on the steroid nucleus in the bile acid glycylglycyltyrosine conjugates.

Hepatic transport of fluorescent molecules: in vivo studies using intravital TV microscopy

Experiments were undertaken to evaluate the role of intravital epifluorescent TV microscopy in the study of the hepatic transport of sodium fluorescein and fluorescently labeled sodium glycocholate in rats and hamsters. It was found that the apparent sinusoid to canaliculus transport time for fluorescently labeled sodium glycocholate was only half of that for sodium fluorescein, 0.50 and 0.92 sec, respectively. The sinusoid to bile transport time was 35 sec for fluorescently labeled sodium glycocholate and 90 sec for sodium fluorescein. There were also marked differences in zonal clearance of these two substances. Sodium fluorescein was removed from Zone 1 much faster than from Zone 3, while fluorescently labeled sodium glycocholate was cleared at the same rate by hepatocytes in all three acinar zones. This study provides direct evidence that there are zonal differences in hepatic transport rates for certain compounds. It also demonstrates that epifluorescent TV microscopy has the potential to provide quantitative data on the transport rates of bile acids and other molecules into, through and out of the liver.

Studies on the relationship between glutathione S-transferase phenotype and bile acid binding by human liver cytosol

The possibility that the GST1 phenotype of human liver cytosol is a determinant of bile salt binding has been investigated by using equilibrium dialysis and gel-exclusion chromatography. Binding of bile salts was non-saturable and whereas the glutathione S-transferases did not appear to be major bile salt binders, other binding components with molecular weights of 35 000 and 11 000 were identified in both fetal and adult cytosols.

Pancreatic carboxypeptidase hydrolysis of bile acid-amino conjugates: selective resistance of glycine and taurine amidates

To find a possible explanation for the selective hepatic conjugation of bile acids with glycine or taurine, the N-acyl amidates of cholic acid and a number of amino acids and amino acid analogues were synthesized, and their susceptibility to hydrolysis by pancreatic juice, gastric juice, serum, or small intestinal mucosal enzymes was measured. Deconjugation by pure carboxypeptidase A and B was also examined, and hydrolysis by these tissue fluids and enzymes was compared with that mediated by a bacterial cholylglycine hydrolase. Human pancreatic juice efficiently hydrolyzed cholyl conjugates of all neutral-L-amino acids (cholyl-L-alanine, cholyl-L-valine, cholyl-L-leucine, and cholyl-L-tyrosine), except cholylglycine. The net hourly rate of hydrolysis (in micromoles per milligram protein per hour) increased when the terminal residue was aromatic or branched aliphatic, and appeared to be specific for L-alpha-amino acids as cholyl-beta-alanine and cholyl-D-valine were not cleaved. From cholyl glycylglycine, only the terminal glycine was efficiently removed. Cholyltaurine and cholyl conjugates with the methyl and propyl analogues of taurine were resistant to hydrolysis. Two basic amino acid conjugates (cholyl-L-lysine and cholyl-L-arginine) were cleaved, whereas conjugates of acidic amino acids (cholyl-aspartate and cholyl-cysteate) were not cleaved. Studies using pure enzymes showed that bovine carboxypeptidase A hydrolyzed the cholyl conjugates of the neutral L-alpha-amino acids with similar specificity as observed for the human pancreatic juice, whereas bovine carboxypeptidase B cleaved the basic amino acid conjugates. Cholyl-L-lysine and cholyl-L-arginine were also cleaved by serum and plasma, which are known to possess carboxypeptidase activity. Cholyl conjugates were not cleaved by gastric juice, by trypsin, or by homogenates of rat small intestinal mucosa. In contrast, all cholyl conjugates were cleaved by a bacterial cholylglycine hydrolase. These experiments indicate that glycine and taurine amidates of cholic acid differ from a number of other conjugates with neutral and basic amino acid in being resistant to hydrolysis by pancreatic and plasma carboxypeptidases.(ABSTRACT TRUNCATED AT 400 WORDS)

Iodinated cholylglycyltyrosine: a new agent for hepatobiliary imaging

The characteristics of radiolabelled cholylglycyltyrosine (CGT), a recently synthesised bile acid, were studied. 125I-CGT-Na was found to have a short plasma half-life of 1.6 +/- 0.4 min in rats and 3.1 +/- 0.7 min in dogs. Biliary clearance studies showed the cumulative biliary output of the tracer over 20 min in rats to be 95.7% of the total dose administered, with a mean biliary transit time (50% retention time) of 4.0 +/- 0.1 min, i.e. similar to the biliary kinetics of taurocholate. 131I-CGT-Na proved to be satisfactory for hepatobiliary imaging in rats and dogs at doses of 35 microCi (1.3 MBq) in rats and 90 microCi (3.3 MBq) in dogs. Satisfactory hepatic images were also obtained in rats that had high bilirubin levels produced by obstruction or the recycling of bile. These results show that CGT has better pharmacokinetics than currently used hepatobiliary imaging agents, and that this new compound may be useful in scintigraphy even in the presence of jaundice.

Formation and secretion of glycolithocholate-3-sulfate in primary hepatocyte cultures

Bile acid sulfation was studied in primary hepatocyte cultures. The primary hepatocyte cultures formed glycolithocholate-3-sulfate (GLC-S) when glycolithocholate (GLC) was added to the medium. The relative percentage of GLC-S formation increased when the GLC concentration was increased from 10 microM to 100 microM. GLC-S formation was linear to 60 min. GLC-S secretion into the medium was detectable at 75 min and linear to 8 hr. In contrast to the effect of GLC concentration, there was no difference in GLC-S formation or secretion when inorganic sulfate in the medium was increased 16-fold (100 microM-1600 microM). We conclude that the rate of bile acid sulfate formation in cultured primary hepatocytes is primarily controlled by bile acid, but not inorganic sulfate, concentration.