Effect of bile acids on calcium efflux from isolated rat hepatocytes and perfused rat livers

The changes in intracellular Ca2+ concentration [( Ca2+]i) of hepatocytes induced by certain bile acids are biphasic: an initial increase is followed by a more gradual decrease. This latter decline in [Ca2+]i may be due to an efflux of Ca2+ across the plasma membrane. This hypothesis was tested by studying the effect of different bile acids on the efflux of 45Ca from preloaded rat hepatocytes and isolated perfused rat livers. The following bile acids were studied: cholic (C), ursodeoxycholic (UDC), chenodeoxycholic (CDC), and deoxycholic (DC) acids; their taurine (T) conjugates (TC, TUDC, TCDC, and TDC); and the taurine, sulfate (S), and glucuronide (Glu) derivatives of lithocholic acid (TLC, LS, TLS, and LGlu, respectively). At 0.3 mM, all bile acids except C, TC, TCDC, UDC, and TUDC significantly increased 45Ca efflux from preloaded hepatocytes without affecting cell viability. Dose-response studies revealed that the minimum effective concentration needed to induce 45Ca efflux was 0.06 mM for LS, 0.8 mM for TCDC, and 10 mM for TC. Efflux of 86Rb from preloaded hepatocytes was not significantly altered by 0.1 mM LS, indicating relative specificity for calcium. TDC and DC, but not TC, increased 45Ca efflux from preloaded perfused rat livers. These results showed that bile acids known to increase [Ca2+]i (CDC, DC, TDC, and TLC) also increased 45Ca efflux from hepatocytes and perfused livers and that efflux was also stimulated by LS, TLS, and LGlu. The extent of this efflux was related to the hydrophobicity of the steroid nucleus of the bile acid. It is speculated that bile acid-induced increases in [Ca2+]i activate the plasma membrane Ca2+ pump resulting in increased Ca2+ efflux.

Intestinal absorption of bile acid glucuronides in rats

While the intestinal absorption of taurine, glycine, and sulfate conjugates of bile acids has been studied extensively, nothing is known about the absorption of bile acid glucuronides. In the present study, the intestinal phase of the enterohepatic circulation of two bile acid glucuronides was examined. [3 beta-3H]cholic acid 3-O-beta-D-glucuronide or [3 beta-3H]lithocholic acid 3-O-beta-D-glucuronide was perfused through isolated segments of ileum or jejunum with intact blood supply in rats prepared with a biliary fistula. [14C]Taurocholic acid was perfused simultaneously with each glucuronide to compare glucuronide absorption with that of an actively transported bile acid. Intestinal absorption was determined by measuring the rate of secretion of labeled bile acid in bile. The absorption of [3H]cholic acid glucuronide by the ileum and jejunum was one fortieth and one eighth, respectively, that of [14C]taurocholic acid. Comparison of the two glucuronides show that [3H]lithocholic acid glucuronide absorption was 18 and 10 times greater than [3H]cholic acid glucuronide absorption from the jejunum and ileum, respectively. Collectively, the above observations suggest that glucuronidation of bile acids markedly reduces absorption from the small intestine.

Efficacy of esmolol in the treatment and transfer of patients with supraventricular tachyarrhythmias to alternate oral antiarrhythmic agents

The efficacy and safety of esmolol, a titratable intravenous beta-adrenergic blocking agent with a short elimination half-life (t 1/2 = 9.0 min) was evaluated in a multicenter open-label study for the treatment of supraventricular tachyarrhythmias (heart rate greater than 100 bpm). The study also investigated the feasibility of transferring patients from esmolol to alternate oral antiarrhythmic agents without loss of therapeutic response. Of the 113 patients studied, 95 (84%) achieved therapeutic response (reduction in heart rate of 15% or more or conversion to sinus rhythm). Most of these patients (93%) achieved the therapeutic response at esmolol doses of 200 micrograms/kg/min or lower. Transfer from esmolol to an oral antiarrhythmic agent(s) was studied in 76 patients. Alternate antiarrhythmic agents used in this study were digoxin (N = 25), propranolol (N = 21), verapamil (N = 10), metoprolol (N = 11), quinidine (N = 2), and a combination of two antiarrhythmic agents (N = 7). Sixty-seven (88%) patients were successfully transferred to oral antiarrhythmic agents without loss of the therapeutic response obtained with esmolol. The most frequent adverse effect observed during the study was hypotension, which resolved quickly (16 +/- 14 min) either by decreasing the dose or by discontinuation of esmolol infusion. This study supports previous observations concerning the safety and efficacy of esmolol in the treatment of supraventricular tachyarrhythmias. Furthermore, it demonstrates that the majority of patients successfully treated with esmolol can be safely and effectively transferred to oral therapy with alternate antiarrhythmic agents.

Hepatotoxic bile acids increase cytosolic Ca++ activity of isolated rat hepatocytes

Effects of bile acids on cystolic Ca++ activity and cell viability of isolated rat hepatocytes were studied to test the hypothesis that bile acids may produce hepatotoxicity by increasing cystolic Ca++ activity. Changes in cystolic Ca++ activity were calculated from time-dependent changes in fluorescence of quin-2 loaded hepatocytes. Release of lactate dehydrogenase and changes in propodium iodide fluorescence were used to assess cell viability. Bile acids studied were unconjugated and taurine-conjugated cholate, chenodeoxycholate (and taurochenodeoxycholate), deoxycholate (and taurodeoxycholate) and lithocholate (and taurolithocholate). With the exception of cholate and taurocholate, bile acids increased cystolic Ca++ activity within 10 to 30 sec in a concentration-dependent fashion (0.05 to 1.0 mM) and in the order lithocholate = taurolithocholate greater than chenodeoxycholate = taurochenodeoxycholate = deoxycholate = taurodeoxycholate. The initial increase in cystolic Ca++ activity by bile acids was not due to cell damage, since bile acid-induced decreases in cell viability were not significant until 2 to 3 min. At higher concentrations of unconjugated bile acid, there was a secondary increase in quin-2 fluorescence corresponding temporally to the increase in propodium iodide fluorescence, indicating cell damage after the initial increase in cystolic Ca++ activity. The ability of conjugated and unconjugated bile acids to increase cystolic Ca++ activity was abolished and decreased (60 to 90%), respectively, in the absence of extracellular Ca++, indicating that extracellular Ca++ is the major source of the bile acid-induced increase in cystolic Ca++ activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Bile acids increase cellular free calcium in cultured kidney cells (LLC-PK)

Suspensions of LLC-PK1 cells were used to determine the effect of bile acids on the cellular homeostasis of inorganic ions. It is determined that bile acids alter cellular free calcium (Cai) levels in LLC-PK1 cells. A series of bile acids were compared and found to produce increases in Cai in the order: lithocholate sulfate (LCS) greater than deoxycholate greater than chenodeoxycholate greater than lithocholate glucuronide greater than cholate. LCS (300 microM) produces changes in Cai (measured using Fura-2) qualitatively similar to those produced by 1 microM ionomycin, except that only ionomycin is able to release calcium from intracellular stores. The effect on Cai is roughly proportional to LCS concentration between 50 and 300 microM. The presence of 40 mM Na in the extracellular medium reduces the LCS-induced rise in Cai to 20% of that observed in the absence of Na. This effect is specific for Na versus 150 mM extracellular K, Li, or TMA. The effect is not dependent on the Na gradient across the membrane. At concentrations of LCS which induce changes in Cai, no significant effect of LCS is observed on either cellular Na or K levels, or intracellular pH.

ATP-dependent Ca2+ uptake and Ca2+-dependent protein phosphorylation in basolateral liver plasma membranes

ATP-dependent Ca2+ uptake was measured in vesicles of rat liver cell basolateral plasma membranes. Nucleotide-dependent uptake was specific for ATP and observed at pH 7.0 and 7.4/7.5 but not at pH 8.0. ATP-dependent Ca2+ transport was only observed in the presence of Mg2+. Kinetic analysis of ATP-dependent transport revealed an apparent Km in the submicromolar region. Addition of calmodulin and trifluoperazine had no effect on ATP-dependent uptake. A Ca2+-dependent, phosphorylated intermediate with the apparent molecular weight of 135,000 could be demonstrated in the basolateral plasma membranes. Phosphorylated intermediates with apparent molecular weights of 200,000 and 110,000 were demonstrated in microsomes and appeared to contaminate 'basolateral' membrane protein phosphorylation. The results suggest that a 135,000 molecular weight protein is a Ca2+-ATPase and the enzymatic expression of the liver cell basolateral membrane Ca2+ pump.

Biosynthesis of hydroxyl-linked glucuronides of short-chain bile acids by rat liver 3-hydroxysteroid UDP-glucuronosyltransferase

Microsomal preparations from livers of Sprague-Dawley rats catalyze the glucuronidation of 3 alpha-hydroxy-5 beta-H (3 alpha, 5 beta) short-chain bile acids (C20-C23), predominantly at the hydroxyl group, while the glucuronidation of 3 beta, 5 beta short-chain bile acids occurs exclusively at the carboxyl group. A similar pattern of conjugation was also observed in Wistar rats having normal levels of 3-hydroxysteroid UDP-glucuronosyltransferase. Significant reductions of formation rates for hydroxyl-linked, but not carboxyl-linked, short-chain bile acid glucuronides were observed in hepatic microsomes from Wistar rats with low 3-hydroxysteroid UDP-glucuronosyltransferase activity. 3-Hydroxysteroid UDP-glucuronosyltransferase, purified to homogeneity from Sprague-Dawley liver microsomes, catalyzed the 3-O-glucuronidation of 3 alpha, 5 beta C20-23 bile acids, as well as of lithocholic and isolithocholic acids (C24). The apparent Michaelis constants (KM) for short-chain bile acids were similar to the value obtained for androsterone. 3 alpha, 5 beta-C20 and 3 beta, 5 beta-C20 competitively inhibited glucuronidation of androsterone by the purified 3-hydroxysteroid UDP-glucuronosyltransferase. Purified 17 beta-hydroxysteroid and p-nitrophenol UDP-glucuronosyltransferases did not catalyze the glucuronidation of bile acids. In addition, none of the purified transferases catalyzed the formation of carboxyl-linked bile acid glucuronides. The results show that 3-hydroxysteroid UDP-glucuronosyltransferase, an enzyme specific for 3-hydroxyl groups of androgenic steroids and some conventional bile acids, also catalyzes the glucuronidation of 3 alpha-hydroxyl (but not carboxyl) groups of 3 alpha, 5 beta short-chain bile acids.

Formation of three types of glucuronides of 6-hydroxy bile acids by rat liver microsomes

The glucuronidation of 6-hydroxylated bile acids by rat liver microsomes was studied in vitro; for comparison, several major bile acids lacking a hydroxyl group in position 6 were also investigated. The highest reaction rates were found for lithocholic and deoxycholic acid (10.2 +/- 0.2 and 7.3 +/- 1.4 nmol/mg.min, respectively); our results for these substrates agree well with published values. Glucuronidation rates for the 6 beta-hydroxylated bile acids 3 alpha, 6 beta-dihydroxy-5 beta-cholanoate (murideoxycholate) and 3 alpha, 6 beta, 7 beta-trihydroxy-5 beta-cholanoate (beta-muricholate) were only slightly lower (3.7 +/- 0.3 and 3.6 +/- 0.3 nmol/mg.min). 6 alpha-Hydroxylated bile acids were glucuronidated at rates that were lower than those for their 6 beta-hydroxy counterparts. Rigorous product identification by high-field proton NMR of methyl/acetyl derivatives revealed that while bile acids lacking a 6-hydroxyl group gave rise exclusively to the typical 3-O-glucuronide, the presence of a hydroxyl group in position 6 led to the formation, in ratios depending on the substrate, of three types of conjugate: the 3-O-, the 6-O-, and the carboxyl-linked (acyl-) glucurnide. The latter is the first example of an acyl glucuronide of a bile acid of conventional (C24) size.

Bile salt-induced calcium fluxes in artificial phospholipid vesicles

The ionic permeability of selected biological membranes is increased by bile salts. To examine changes in calcium permeability during the exposure of artificial membranes to bile salts, we investigated calcium uptake by unilamellar and multilamellar phospholipid vesicles. In the presence of 750 microM taurodeoxycholate, uptake of radiolabelled calcium by unilamellar vesicles increased 2.5-fold over control values. Calcium uptake by multilamellar vesicles as measured with a free calcium indicator, arsenazo III, increased 2.2- or 21-fold in the presence of 60 microM lithocholate or 3 beta-hydroxy-5-cholenoate, respectively. Results were directly influenced by experimental variables such as bile salt hydrophobicity, external calcium concentration, and the bile salt/lipid molar ratio. Observed membrane solubilization was minimal despite increased calcium permeability. Comparison of radiolabelled calcium uptake with radiolabelled sodium or radiolabelled rubidium uptake indicated that bile salt-dependent calcium uptake was 60-140-times greater than bile salt-dependent uptake of either monovalent cation. In an effort to delineate forces affecting calcium translocation, vesicles were exposed either to valinomycin, which induced an electrochemical gradient across the membrane, or to nigericin, which induced a proton gradient. Exposure to valinomycin minimally influenced bile salt-induced calcium uptake while exposure to nigericin significantly promoted uptake by 40-70%. The results suggest that bile salts promote calcium uptake by a mechanism which may be similar to those of other carboxylic ionophores.

Hyodeoxycholate-6-O-glucuronide cannot be quantitated with 3 alpha-hydroxysteroid dehydrogenase

The reaction of the 6-hydroxylated bile acid, hyodeoxycholic acid, and its 6-O-glucuronide conjugate with 3 alpha-hydroxysteroid dehydrogenase was examined. A standard end-point assay and determination of the initial rates of reaction showed only minimal activity of the enzyme toward hyodeoxycholate-6-glucuronide in spite of the presence of a free 3 alpha-hydroxyl group. It was established that 6-hydroxylation itself did not significantly affect the enzyme reaction. It is concluded that the 6-glucuronide either blocks or hinders enzyme access to the 3-hydroxyl group.

Two laboratory methods for diagnosis of herpes simplex keratitis

Two techniques are described which enable a rapid diagnosis of herpes simplex keratitis to be made. The tests, antibody/antigen reactions, were shown to be accurate and sensitive in the 119 patients examined. A result is available within four hours with the indirect peroxidase-antiperoxidase method and within one hour with the direct method. The techniques are relatively inexpensive, though labour intensive. Negative reactions were found in treated cases and in those with some delay in the histochemical staining.

Taurodeoxycholate and the developing rabbit distal colon: absence of secretory effect

Failure to absorb bile acids by the ileum leads to fluid secretion by the colon and diarrhea in adults. The infant ileum, however, does not actively transport bile acids. Therefore, we investigated the effect of taurodeoxycholic acid (TDCA) on ion transport in the colon of rabbits 7-10 days old. We mounted distal colon from infant and adult rabbits in modified Ussing chambers and exposed the mucosal or serosal surfaces to TDCA. In the adult, 50 microM TDCA produced an increase in short-circuit current (delta Isc = 1.0 +/- 0.3 mu eq . h-1 . cm-2, P less than 0.05) and Cl secretion. In the infant, the effect was different, Isc was reduced (delta Isc = -1.1 +/- 0.2 mu eq . h-1 . cm-2, P less than 0.01) and ion flux was not altered. Microscopy demonstrated that the infant epithelium was not significantly damaged by exposure to TDCA at these concentrations. The infant colon was, however, capable of a secretory response to a variety of agonists including theophylline, carbachol, bradykinin, serotonin, and 12,13-dibutyryl phorbol ester. The infant rabbit distal colon lacks a secretory response to TDCA during that period when the ileum cannot transport bile acids.

Glucuronidation of 6 alpha-hydroxy bile acids by human liver microsomes

The glucuronidation of 6-hydroxylated bile acids by human liver microsomes has been studied in vitro; for comparison, several major bile acids lacking a 6-hydroxyl group were also investigated. Glucuronidation rates for 6 alpha-hydroxylated bile acids were 10-20 times higher than those of substrates lacking a hydroxyl group in position 6. The highest rates measured were for hyodeoxy- and hyocholic acids, and kinetic analyses were carried out using these substrates. Rigorous product identification by high-field proton nuclear magnetic resonance and by electron impact mass spectrometry of methyl ester/peracetate derivatives revealed that 6-O-beta-D-glucuronides were the exclusive products formed in these enzymatic reactions. These results, together with literature data, indicate that 6 alpha-hydroxylation followed by 6-O-glucuronidation constitutes an alternative route of excretion of toxic hydrophobic bile acids.

Bile salts induce calcium uptake in vitro by human erythrocytes

At high concentrations, bile salts induce hemolysis by comicellization of lipid components of the cell membrane. However, bile salts are also associated with hemolysis at lower concentrations by mechanisms which have not been characterized. To investigate the possibility that bile salts promote calcium uptake by red blood cells and that bile salt-associated hemolysis is, in part, calcium-mediated, calcium uptake by red blood cells was measured in the presence of individual bile salts, and hemolysis dependence upon calcium availability was examined. Washed human red blood cells with or without ATP depletion were incubated with 1 mM CaCl2 and tracer amounts of 45CaCl2 in the presence of selected bile salts at concentrations (0.01 to 0.3 mM) reported to be below critical micellar concentrations. Calcium uptake (defined for the purposes of this study as 45Ca retained in red blood cells) was monitored over 5 hr, after which hemolysis and membrane phospholipid content were determined. The presence of bile salts stimulated calcium uptake 4- to 25-fold--the magnitude of which was partly related to the lipid solubility of the bile salts. ATP depletion or exposure to trifluoperazine, procedures which inhibit calcium pump activity in red blood cells, enhanced bile salt-induced calcium uptake relative to controls. The percentage of associated hemolysis (2 to 14%) at the end of 5 hr correlated directly with the observed calcium uptake. Removal of calcium from the extracellular space reduced hemolysis in the presence of bile salts to control levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Vulpecholic acid (1 alpha, 3 alpha, 7 alpha-trihydroxy-5 beta-cholan-24-oic acid): a novel bile acid of a marsupial, Trichosurus vulpecula (Lesson)

A novel trihydroxylated C24 bile acid was isolated from the gallbladder bile of the Australian opossum, Trichosurus vulpecula (Lesson). This acid, for which the name vulpecholic acid is proposed, was identified as 1 alpha, 3 alpha, 7 alpha-trihydroxy-5 beta-cholan-24-oic. The structure proof included mass spectral and 1H and 13C nuclear magnetic resonance characterization of all crucial derivatives obtained by: oxidation of the methyl ester to a triketone with the enolizable 1,3-diketone function; methylation of this triketone to two isomeric methyl enol ethers; and reductive removal of oxygen functions from this triketone to give 5 beta-cholan-24-oic and 7-oxo-5 beta-cholan-24-oic acids. Vulpecholic acid was found in the bile in the unconjugated form; it accounted for more than 60% of the solid bile material. The marsupial T. vulpecula is the first example of a mammal secreting a 1 alpha-hydroxylated bile acid as well as the first example of a mammal secreting the major bile acid in a free form.

Metabolism of 24-norlithocholic acid in the rat: formation of hydroxyl- and carboxyl-linked glucuronides and effect on bile flow

24-Norlithocholic (3 alpha-hydroxy-24-nor-5 beta-cholan-23-oic) acid is the lower homologue of lithocholic acid, a potent cholestatic agent. In order to characterize its cholestatic potential and metabolic fate, 3 beta-tritiated 24-norlithocholate was infused intravenously into adult male Sprague-Dawley rats prepared with an external biliary fistula. The results demonstrate that 24-norlithocholate does not induce cholestasis in rats when administered in doses in excess of those necessary for lithocholate to produce cholestasis. Hydroxyl- and carboxyl-linked glucuronides were identified as major metabolites secreted in the bile. Especially noteworthy is the identification of carboxyl-linked glucuronides of mono-, di- and trihydroxylated C23 bile acids. Their total amount (25% of recovered radioactive products) is comparable to that of the hydroxyl-linked glucuronide of 24-norlithocholic acid (41%). In this study, for the first time, a bile acid diglucuronide, substituted both at 3-hydroxyl and carboxyl groups, was detected (11%).

Primary biliary cirrhosis

Primary biliary cirrhosis often presents insidiously but progresses relentlessly in its later stages. Asymptomatic patients, however, may have a relatively benign course. Clinical, laboratory and histologic characteristics support an autoimmune pathogenesis. The complications of primary biliary cirrhosis are secondary to severe cholestasis, portal hypertension and progressive hepatocellular dysfunction. Currently, treatment is only supportive; no drug regimen has been shown to alter the disease course.

Cellular mechanisms of cholestasis

Concepts regarding the pathogenesis of cholestasis continue to evolve as investigational techniques improve and molecular mechanisms of bile formation are clarified. With the accumulation of information it is becoming increasingly evident that cholestasis results from not one but multiple disturbances in the sequence of events responsible for bile production. In addition to the inhibition of bile flow attributable to initiating events, cholestasis itself may inhibit bile flow by altering the intra- and extracellular environments of liver cells. Many questions about cholestasis remain unanswered, but future directions for research are suggested by the information currently available.

Glucuronides of monohydroxylated bile acids: specificity of microsomal glucuronyltransferase for the glucuronidation site, C-3 configuration, and side chain length

The ability of rat liver microsomes to catalyze UDP-glucuronic acid-dependent glucuronidation of monohydroxy-bile acids was examined. The following bile acids were used as substrates, each as the 3 alpha and 3 beta epimer: 3-hydroxy-5 beta-cholanoic acid (C24), 3-hydroxy-5 beta-norcholanoic acid (C23), 3-hydroxy-5 beta-bisnorcholanoic acid (C22), 3-hydroxy-5 beta-pregnan-21-oic acid (C21), and 3-hydroxy-5 beta-androstane-17 beta-carboxylic acid (C20). The corresponding glucuronides were chemically synthesized to serve as standards and were characterized by thin-layer and gas-liquid chromatography as well as by nuclear magnetic resonance. Enzymatic glucuronidation reactions were optimized with respect to pH for each product formed and the kinetic parameters for each reaction were measured. Analytical techniques necessary to separate products from unreacted substrates and to identify them included thin-layer chromatography, gas-liquid chromatography, and nuclear magnetic resonance. It was found that the 3 alpha epimers of the five bile acids listed above enzymatically formed 3-O-glucuronides, C24 being the best substrate, followed by C21 and C20; C22 and C23 gave rise to only small amounts of this product. The 3 beta epimers of all bile acids tested were poorer substrates, although by a factor that varied widely. In addition to the expected hydroxyl-linked glucuronide, three of the 3 alpha-bile acids (C23, C22, and C20) and at least one 3 beta-bile acid (C20), gave rise to a novel metabolite in which the 1-OH of glucuronic acid was esterified with the steroidal carboxyl group (carboxyl-linked glucuronide).

Preparation and characterization of 3-monohydroxylated bile acids of different side chain length and configuration at C-3. Novel approach to the synthesis of 24-norlithocholic acid

A series of 3-monohydroxylated bile acids, in unlabeled and radioactive form, of varying side chain length and configuration at C-3 has been synthesized and rigorously characterized. They include: 3 alpha- and 3 beta-hydroxy-5 beta-androstane-17 beta-carboxylic acids (C20); 3 alpha- and 3 beta-hydroxy-5 beta-pregnan-21-oic acids (C21); 3 alpha- and 3 beta-hydroxy-23,24-bisnor-5 beta-cholan-22-oic acids (C22); 3 alpha- and 3 beta-hydroxy-24-nor-5 beta-cholan-23-oic acids (C23, norlithocholic and isonorlithocholic acids); and 3 beta-hydroxy-5 beta-cholan-24-oic acid (C24, isolithocholic acid). A novel approach to the degradation of lithocholic acid acetate to 24-norlithocholic acid is described. This degradation involves the photochemical modification of a Hunsdiecker reaction and Kornblum oxidation of the intermediate 23-bromide. The availability of these compounds makes it possible to study the metabolism and biological effects of short chain bile acids.

Excretion of cholate glucuronide

[3-3H]Cholic acid glucuronide [7 alpha,12 alpha-dihydroxy-3 alpha-O-(beta-D-glucopyranosyluronate)-5 beta- cholan-24-oate] was synthesized and administered to rats prepared with either an external biliary fistula or a ligated bile duct. When bile fistula animals were given either microgram or milligram amounts of the glucuronide, biliary secretion of label was rapid and efficient: greater than 90% of the administered label was secreted within 60 min and total recovery of label in bile was 98.6 +/- 1.2%. Studies in which [14C]taurocholate was included in the dose indicated that this bile acid was secreted into bile significantly more rapidly than was the glucuronide. In animals with ligated bile ducts, urinary excretion was the major route of elimination: after 20 hr, 83.4 +/- 9.3% of the administered dose had been excreted in urine. Urinary excretion of cholate glucuronide was significantly more rapid than that of taurocholate. Gas-liquid chromatographic analysis of the methyl ester acetate derivatives of labeled compounds isolated from bile and urine by chromatography established that the bulk (greater than 70%) of the administered material was secreted in bile or excreted in urine as the intact cholate glucuronide. From these results, we conclude that the glucuronidation of cholic acid produces a derivative which is rapidly and effectively cleared from the circulation and excreted.