In vitro determination of active bile acid absorption in small biopsy specimens obtained endoscopically or surgically from the human intestine

BACKGROUND: In the construction of a Kock reservoir for continent urinary diversion, 70 cm of the distal ileum are used. Impaired absorption of bile acids in these patients might cause diarrhoea. Data on the absorption of bile acids in different parts of the human intestine are limited. METHODS: Biopsies were taken during endoscopy from the duodenum, the terminal ileum or the right colon, and during surgery 10, 50, 100 and 150 cm proximally to the ileo-caecal valve using standard endoscopy biopsy forceps. The biopsy specimens were incubated in vitro with radio-labelled taurocholic acid at 37 degrees C for 22 or 45 min The radioactivity was determined using the liquid scintillation technique. RESULTS: A linear increase in the uptake was observed, with increased concentrations of taurocholic acid between 100 and 500 microm in all specimens tested, that represented passive uptake or unspecific binding. The active uptake could be calculated from the intercept of the line representing passive uptake with the ordinate. The active uptake in the terminal ileum was 3-4 times greater than 100 cm proximal to the valve. CONCLUSIONS: The active absorption of bile acids in humans can be determined in small biopsy specimens taken using standard biopsy forceps during endoscopy or surgery. This method is suitable for clinical studies of bile acid absorption. Active uptake of bile acids not only takes place in the very distal part of the ileum but also to a considerable degree 100 cm proximally to the ileo-colonic valve. This should be taken into account when selecting the ileal segment for continent urinary diversion.     

Active and Passive Bile Acid Absorption in Man. PERFUSION STUDIES OF THE ILEUM AND JEJUNUM

Absorption of the major human bile acids was studied in 12 healthy volunteers by steady state perfusion of the ileum in 112 experiments and of the jejunum in 48 experiments. Use of a randomized order of four perfusions on 1 day of study and use of up to 4 consecutive days of study in a subject allowed important comparisons of data from the same individuals. That there is active ileal absorption of chenodeoxycholic, glycochenodeoxycholic, and taurocholic acids in man was supported by the finding of saturation kinetics and of competition for absorption among conjugated bile acids. Values for apparent kinetic constants (apparent maximal transport velocity [(*)V(max)] and apparent Michaelis constant) in man are similar to those in other species. The ileum absorbed chenodeoxycholic acid more rapidly than its glycine conjugate, due mainly to a ninefold greater permeability for the free acid. Taurocholate had the highest (*)V(max) and was absorbed more rapidly than glycochenodeoxycholate. Passive permeability of the jejunum to bile acids was twice that of the ileum, and the permeabilities to free and glycine-conjugated chenodeoxycholate were in the same ratio as in the ileum (9: 1). Jejunal permeability to chenodeoxycholic acid was three times that to cholic acid. Variation of intraluminal pH by up to 1.4 units did not influence jejunal uptake of free bile acids. These results, which are comparable with those from animal experiments, provide a basis for estimation of intestinal reabsorption of bile acids in intact man.     

Biological and medical aspects of active ileal transport of bile acids

The active transport of conjugated bile acids by the ileum is responsible for the enterohepatic circulation of bile acids, a physiological process that ensures an ample supply to the intestine of these key biological surfactants, irrespective of the rate of their biosynthesis from cholesterol. The ileal bile acid transport system is a high capacity, low affinity secondary active Na+ co-transport system that differs in substrate specificity from that present in the hepatocyte. Ileal transport is homeostatically regulated by feedback inhibition of the bile acids that are transported. The enterohepatic circulation is responsible for the concentration profile present in the intestine--high concentrations in the small intestine and low concentrations in the large intestine. Loss of ileal absorption, when mild, leads to a sequence of events that result in increased concentrations in the large intestine causing diarrhea. Severe bile acid malabsorption causes decreased concentrations in the small intestine which in turn lead to fat maldigestion and fat malabsorption. The increased passage of fatty acids into the colon contributes to diarrhea. Fat maldigestion and malabsorption also causes increased absorption of dietary oxalate from the colon which causes hyperoxaluria and contributes to nephrolithiasis. In cholestatic liver disease, inappropriate upregulation of ileal bile acid transport is likely to cause retention of hepatotoxic endogenous bile acids. In familial hypercholesterolemia, efficient bile acid absorption contributes to downregulation of LDL receptors and the maintenance of elevated plasma cholesterol levels; upregulation of bile acid transport during bile acid sequestrant therapy could diminish its efficacy. Efforts are in progress to develop a suitable bile acid analogue to be administered orally for conditions of bile acid deficiency in the small intestine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of the fasting enterohepatic circulation of bile acids by the migrating myoelectric complex in dogs.

The purpose of this study was to correlate the fasting enterohepatic circulation (EHC) of bile acids with the migrating myoelectric complex. Four dogs were surgically provided with a functional cholecystectomy, a duodenal cannula for direct vision cannulation of the common bile duct, and 12 bipolar electrodes implanted from stomach to terminal ileum. Bile was collected in equal-volume, timed aliquots over 6 to 10 h. Aliquots were sampled and either returned to the duodenum for study of the intact EHC, or collected and retained in order to study the time course of the bile acid pool washout. In the washout experiments boluses of radiolabeled taurocholic acid were instilled into the duodenum before and after duodenal phase III of the migrating motor or myoelectric complex (MMC). In another group of experiments the bile acid pool was washed out and during a continuous duodenal infusion of taurocholic acid bile was collected to study the pattern of hepatic secretion. Results: (a) In all experiments, a single broad peak of bile flow and bile acid secretion occurred at 35-55% of the MMC migration time. At this time the MMC had migrated to a point 70-85% of the distance along the small intestine. (b) During bile acid pool washout the peak of bile flow and bile acid secretion occurred with the distal migration of the first MMC and then bile flow and bile acid secretion rates decreased to a minimum and stabilized. (c) In bile acid pool washout experiments the radiolabeled bile acids instilled into the duodenum prior to duodenal phase III were secreted and peaked with peak endogenous bile acid secretion. The secretion of radiolabeled bile acids instilled into the duodenum after duodenal phase III was delayed until the subsequent cycle of the MMC. 88% of the bile acid pool collected over 6 h was secreted during the distal migration of the first MMC (2.4 +/- 0.4 h). (d) After bile acid pool washout and during continuous duodenal infusion of taurocholic acid, hepatic bile flow and bile acid secretion continued to fluctuate with the same pattern observed with the EHC intact. Conclusions: (a) In the fasting state, the transport of intestinal bile acids to the liver is pulsatile rather than continuous and is determined by the MMC. Maximum hepatic secretion occurs when phase III of the MMC propels the intraluminal bile acid pool to its site of absorption in the distal small bowel. (b) The "housekeeping" action of the MMC is very efficient and clears 88% of the 6-h washout bile acid pool in one pass.     

Morphofunctional alterations of the small intestine in patients with psoriasis and concomitant chronic opisthorchiasis

To characterize the small intestine clinically and functionally in psoriasis combination with chronic opisthorhiasis, 60 patients were examined with this combination, 45 with psoriasis but no helminthosis, 30 patients with chronic opisthorchiasis and 15 healthy subjects. Small intestinal absorption was studied by fat and carbohydrates absorption; bioelectric small intestinal activity--by electroenterography. Absorption in the small intestine of patients with mixed pathology was impaired. Pathogenetic mechanisms of such impairment were the following: low amplitude of bioelectrical activity of the small intestine, subnormal concentration of bile acids in the vesical bile, defects in microbial biocenosis of the intestine, structural disorders of the upper small intestine. Abnormal absorption in the small intestine correlated with psoriasis clinical picture (stages, duration, size of the lesion, disease severity).     

Role of primary and secondary bile acids as feedback inhibitors of bile acid synthesis in the rat in vivo.

The effect of various primary and secondary bile acids on the rates of synthesis of all major bile acids was studied in the live rat with an extracorporal bile duct. Bile acid synthesis was determined using HPLC based on mass or by isotope dilution. Derepressed rates of bile acid synthesis (30-54 h) were inhibited by an infusion of taurocholic acid only at a supraphysiological dose of 500 mumol/kg per h, but not at 300 mumol/kg per h, which approximates the initial bile acid secretion (250 mumol/kg per h). When administered together with taurocholic acid (200 mumol/kg per h) only a high dose of taurochenodeoxycholic acid (100 mumol/kg per h) decreased taurocholic but not tauromuricholic or taurochenodeoxycholic acid synthesis. The only bile acid suppressing taurocholic acid (36-71%) and taurochenodeoxycholic acid (up to 33%) formation at an infusion rate close to the normal portal flux was deoxy- or taurodeoxycholic acid at 15-50 mumol/kg per h. It may be concluded that deoxycholic acid and possibly other secondary bile acids are much more potent inhibitors than primary bile acids.     

Inhibition of ileal bile acid transport by cyclosporin A in rat

Abstract. Chronic administration of cyclosporin A may induce cholestasis and this effect has been attributed to impaired hepatic bile salt synthesis, metabolism and transport. We investigated the effect of cyclosporin A on intestinal absorption of bile acids in the ileum of rat. Ileal bile acid absorption was measured by in vivo intestinal perfusion with cyclosporin A and the solvent Cremophor EL. During ileal perfusion with 25 μM glycocholic acid, the concentration of 2.8 mm cyclosporin A inhibited intestinal bile acid absorption on average by 34%. Additional experiments were performed with everted gut sacs of the distal ileum to evaluate active absorption. A dose and time dependent inhibition of the active intestinal absorption of bile acids was found, with a 50% transport inhibition at an average cyclosporin A concentration of 2.69mmolL^-'. Thus, cyclosporin A inhibits the active intestinal absorption of bile acids which may influence bile acid synthesis, turnover and secretion and may contribute to cyclosporin A induced cholestasis.     

Pathogenesis of steatorrhea in chronic diseases of the small intestine

Altogether 150 patients with chronic enteritis and celiac disease with a history of resection of a part of the ileum were examined. It was established that in patients with chronic enteritis, of importance for the pathogenesis of steatorrhea was the deficiency of bile acids during digestion because of hypokinesia of the gallbladder and partial deconjugation of bile acids in the presence of bacterial dissemination of the small intestine. During celiac disease, steatorrhea was caused by the decreased enzymatic function of the pancreas, asynchronism of the food and bile supply to the intestinal lumen, disorders of absorption of lipolysis products. In patients with large resection of the ileum, steatorrhea was associated with abnormality of the enterohepatic circulation of bile acids, bacterial dissemination of the small intestine and reduction of the absorption surface. A schedule of differentiated therapy is offered.     

Hepatic uptake and intestinal absorption of bile acids in the rabbit

Abstract The existence of transporters for bile acids (BA) in liver and intestine has been well documented, but information is still needed as to their respective transport capacity. In the present investigation, we compared the hepatic and intestinal transport rates for BA, using perfused livers and intestines. The livers and intestines were separately perfused and dose-response curves (0·25–10 mM) for tauroursodeoxycholate, taurocholate and taurodeoxycholate were obtained. The intestinal and mesenteric concentration and bile acid pattern were also evaluated in six non-fasting rabbits. Taurocholic, tauroursodeoxy-cholic and taurodeoxycholic acid ileal absorption showed saturation kinetics in the intestine as in the liver; the maximal uptake velocity for each bile acid in the liver was tenfold higher than the respective maximal transport velocity in the intestine; the Km values obtained in the liver were of the same order of magnitude, i.e. in the millimolar range. Taurocholic, tauroursodeoxycholic and taurodeoxycholic acid transport differences in the liver paralleled those in the intestine. Although the intestine was not homogeneously filled, the bile acid concentration in the ileal content fell into the range of the Km for the three studied bile acids, while the portal blood total bile acid concentration was inferior to the observed Kms of liver uptake. Therefore, both the hepatic and intestinal systems do not operate at their maximal transport rates at the prevailing concentrations in portal blood and luminal content, and the hepatic transport occurs at its highest efficiency (below the Km values) in physiological conditions.     

Bile salt regulation of fatty acid absorption and esterification in rat everted jejunal sacs in vitro and into thoracic duct lymph in vivo

This study was performed to investigate whether the malabsorption of fat in the blind loop syndrome is due to the presence of free bile acids or to a deficiency of conjugated bile salts produced by bacterial degradation of normal bile salts, as well as to learn something of the mechanisms by which bile salts might regulate fat absorption. In the everted gut sac of the rat in vitro, conjugated bile salts were necessary for maximal rates of fatty acid esterification to triglycerides, whereas free bile acids inhibited this process even in the presence of physiologically normal or higher concentrations of conjugated bile salts. In contrast, in the living animal the addition of similar or higher concentrations of free bile acids to infusions of fatty acids in taurocholate micellar solutions produced no reduction in the amount of fatty acid absorbed into lymph or the amount of fatty acid esterified into lymph triglyceride. Both in vitro and in the living animal, reduction in the conjugated bile salt concentration reduced both the rate of fatty acid uptake by the intestine and the esterification into triglycerides. It is concluded that the steatorrhea of the blind loop syndrome or other conditions in which upper intestinal stasis allows bacterial proliferation is not due to presence of increased gut luminal concentrations of free bile acids, but rather is a consequence of lowered concentrations of conjugated bile salts.     

Characterization of the kinetics of the passive and active transport mechanisms for bile acid absorption in the small intestine and colon of the rat

Bile acid uptake occurs via passive diffusion in all regions of the intestine and via active absorption in the ileum. Determination of the passive permeability coefficient for ionized monomers ((*)P(-)) demonstrated that permeability decreased by a factor of 3.4, 6.8, and 8.1 for the addition of a hydroxyl, glycine, or taurine group, respectively, to the steroid nucleus. Removal of the negative charge increased permeation by a factor of 4.4; however, permeability coefficients for the protonated monomers showed the same relative decrease with addition of a hydroxyl group. The calculated incremental free energies of solution (deltaDeltaF(W-->1)) associated with these additions equaled + 757 (hydroxyl), + 1178 (glycine), and + 1291 (taurine) cal/mole. Passive permeability coefficients for the transverse colon showed the same relative relationships among the various bile acids. After making appropriate corrections for passive permeability across the ileum, apparent values for the maximal transport velocity ((*)V(max)) and Michaelis constant ((*)K(m)) of the active transport system were measured. (*)V(max) depended upon the number of hydroxyl groups on the steroid nucleus; values for the trihydroxy bile acids were high (1543-1906 pmoles/min per cm) while those for the dihydroxy (114-512 pmoles/min per cm) and monohydroxy (45-57 pmoles/min per cm) acids were lower. In contrast, (*)K(m) values were related to whether the bile acid was conjugated; unconjugated bile acids had values ranging from 0.37 to 0.49 mM, while values for the conjugated bile acids were approximately half as high (0.12-0.23 mM).     

Serum unconjugated bile acids: qualitative and quantitative profiles in ileal resection and bacterial overgrowth

Qualitative and quantitative profiles of unconjugated bile acids in the serum obtained over a 24-h period from three patients with ileal resections and one with a bacterial overgrowth are described. Unconjugated serum bile acids were determined using the high sensitivity and resolution of capillary column gas liquid chromatography after their rapid extraction and isolation using reverse phase octadecylsilane bonded silica cartridges and the lipophilic gel Lipidex 1000. Unconjugated serum bile acid concentrations were elevated throughout the day in both ileum resected patients and in conditions involving bacterial overgrowth when compared to healthy subjects. Total conjugated cholic acid concentrations were expectedly low in both intestinal disorders and were without the postprandial increases generally observed in healthy subjects. Qualitative gas chromatographic profiles of serum unconjugated bile acids in bacterial overgrowth distinctly revealed a predominance of deoxycholic acid and other secondary bile acids in all samples, while, in conditions of an impaired enterohepatic circulation, deoxycholic acid was absent or present in only trace amounts. The potential significance of measuring serum unconjugated bile acids in intestinal disorders is discussed.     

Intestinal solubilization, absorption, pharmacokinetics and bioavailability of chenodeoxycholic acid*

Abstract. Little is known about the physical state, intestinal solubilization, absorption and bioavailability of chenodeoxycholic acid used in the medical treatment of gallstones. Therefore the concentrations of unconjugated chenodeoxycholic acid were measured in the supernatant and precipitate phases of intestinal contents aspirated from stomach, duodenum and jejunum of nine control subjects who took 500 mg chenodeoxycholic acid (4 times 125 mg gelatin-coated capsules) either fasting or together with a standard liquid meal. Chenodeoxycholic acid solubility was markedly influenced by luminal pH but was little affected by endogenous conjugated bile acids when their concentrations were > 1–2 mmol/1.
Systemic bioavailability of 250, 500 and 750 doses of chenodeoxycholic acid was measured in five subjects by comparing areas under 4 h serum concentration-time curves after giving the bile acid first as a bolus intraduodenal aqueous infusion of ³H-labelled chenodeoxycholic acid containing either ¹⁴C-polyethylene glycol or bromsulphthalein as non-absorbable markers, and then as gelatin-coated capsules by mouth.
Absorption was assessed by measuring the ratio of marker: bile acid in intestinal contents aspirated for 2 h from sites 60 and 120 cm distal to the duodenal infusion port and in three subjects quantitative recovery of marker was measured proximal to an occluding intestinal balloon. Absorption of duodenally-infused chenodeoxycholic acid was 96–99% complete and bioavailability was complete with the 250 and 500 mg doses but fell to 81% with the 750 mg dose.     

Intestinal solubilization, absorption, pharmacokinetics and bioavailability of chenodeoxycholic acid*

Abstract Little is known about the physical state, intestinal solubilization, absorption and bioavailability of chenodeoxycholic acid used in the medical treatment of gallstones. Therefore the concentrations of unconjugated chenodeoxycholic acid were measured in the supernatant and precipitate phases of intestinal contents aspirated from stomach, duodenum and jejunum of nine control subjects who took 500 mg chenodeoxycholic acid (4 times 125 mg gelatin-coated capsules) either fasting or together with a standard liquid meal. Chenodeoxycholic acid solubility was markedly influenced by luminal pH but was little affected by endogenous conjugated bile acids when their concentrations were > 1–2 mmol/1.
Systemic bioavailability of 250, 500 and 750 doses of chenodeoxycholic acid was measured in five subjects by comparing areas under 4 h serum concentration-time curves after giving the bile acid first as a bolus intraduodenal aqueous infusion of ³H-labelled chenodeoxycholic acid containing either ¹⁴C-polyethylene glycol or bromsulphthalein as non-absorbable markers, and then as gelatin-coated capsules by mouth.
Absorption was assessed by measuring the ratio of marker: bile acid in intestinal contents aspirated for 2 h from sites 60 and 120 cm distal to the duodenal infusion port and in three subjects quantitative recovery of marker was measured proximal to an occluding intestinal balloon. Absorption of duodenally-infused chenodeoxycholic acid was 96–99% complete and bioavailability was complete with the 250 and 500 mg doses but fell to 81% with the 750 mg dose.     

Effects of Bay o 2752, a hypocholesterolemic agent, on intestinal taurocholate absorption and cholesterol esterification

Bay o 2752 [N,N'-(1, 11-undecandiyl)bis(2,3-dihydro-2-methyl-1H-indole-1-carboxamide)] has been demonstrated in rats to inhibit intestinal cholesterol absorption. Studies were carried out in male Wistar rats to determine if the mechanism is inhibition of intestinal bile acid absorption or cholesterol esterification. Bay o 2752 did not alter intestinal bile acid absorption as measured by in vitro uptake of [14C]taurocholic acid into ileal everted sacs (0.01 and 1.0 mg/ml of Bay o 2752) or the biliary excretion of radioactivity after in vivo ileal perfusion of the bile acid and drug (1.0 mg/ml at 1.0 ml/min for 1 hr). Cholesterol esterification was determined by measurement of in vitro activity of acyl coenzyme A:cholesterol acyltransferase from hepatic microsomes and cholesterol ester hydrolase from pancreatic supernatant, and the in vivo lymphatic output of cholesteryl ester after intraduodenal cholesteryl infusion. Addition of Bay o 2752 (0.01-10 micrograms/ml) to hepatic microsomes produced a concentration-dependent decrease in acyl coenzyme A:cholesterol acyltransferase activity with an IC50 of 0.95 micrograms/ml. Cholesterol ester hydrolase activity was unaffected by the drug (1.0-100 micrograms/ml). Intraduodenal infusion of Bay o 2752 (10 mg/ml at 0.9 ml/hr for 8 hr) reduced markedly the flux of cholesterol from the intestinal lumen into the mesenteric lymph, especially the lymphatic output of the esterified form of both radioisotopically labeled and total cholesterol. These data suggest that Bay o 2752-induced reduction in intestinal cholesterol absorption results from its potent inhibitory effect on acyl coenzyme A:cholesterol acyltransferase activity.     

Identification and characterization of a bile acid receptor in isolated liver surface membranes.

It is generally assumed that hepatic transport of bile acids is a carrier-mediated process. However, the basic mechanisms by which these organic anions are translocated across the liver cell surface membrane are not well understood. Since carrier-mediated transport involved binding of the transported molecule to specific receptor sites, we have investigated the possibility that bile acid receptors are present in liver surface membranes. Isolated liver surface membranes were incubated at 4 degrees C with [14C]cholic acid and [14C]taurocholic acid, and membrane-boudn bile acid was separated from free by a rapid ultrafiltration technique through glass-fiber filters. Specific bile acid binding is rapid and reversible and represents approximately 80% of the total bile acid bound to liver surface membranes. Taurocholic acid binding is independent of the medium pH, while cholic acid binding demonstrates an optimum at pH 6.0. Analysis of equilibrium data for both cholic and taurocholic acid binding indicates that specific binding is saturable and consistent with Michaelis-Menten kinetics, while nonspecific binding is nonsaturable. Apparent maximal binding capacity and dissociation constant values indicate a large capacity system of receptors that have an affinity for bile acids comparable to that of the hepatic transport mechanism. Scatchard analysis of the saturation kinetics as well as inhibition studies suggest that bile acids bind to a single and noninteracting class of anion that competes with bile acids for hepatic uptake, also inhibits cholic acid binding. In contrast, no inhibition was demonstrated with indocyanine green and probenecid. Specific bile acid binding is enriched and primarily located in liver surface membranes and found only in tissues involved in bile acid transport. Specific bile acid binding is independnet of Na+, Ca2+, and Mg2+ and does not require metabolic energy. In addition, thiol groups and disulfide are not required for activity at the binding site. However, specific bile acid binding is markedly decreased by low concentrations of proteolytic enzymes and is also decreased by the action of neuraminidase and phospholipases A and C. These results are consistent with the existence of a homogeneous bile acid receptor protein in liver surface membranes. The primary surface membrane location of this receptor, its binding properties, and its ligand specificity suggest that bile acid binding to this receptor may represent the initial interaction in bile acid transport across liver surface membranes.     

Intestinal morphometry and bile acid-induced mucosal injury in chronic experimental renal failure

To examine whether the intestinal mucosa in uremia is more prone to injury, we studied acute intestinal mucosal injury in rats with experimental chronic renal failure (RF) and sham-operated and starved control animals. Intestinal injury was produced by perfusing intestinal segments in vivo with 5 mmol/L chenodeoxycholic acid. Histologic specimens were then taken from the proximal and distal perfused and unperfused intestinal segments. Quantitative morphometry was done with computerized image analysis, and samples of the unperfused intestine were assayed for protein and DNA content. Chronic RF did not significantly affect the functional or morphologic injury caused by chenodeoxycholic acid. However, it was noted that RF rats had consistently taller villi and deeper crypts in all the samples studied. The protein content and the ratio of DNA to protein was similar among the three groups. The mechanism of the increase in villus height and crypt depth in the RF rats was not related to increases in tissue water content or to alterations in protein or DNA content, and the mechanism thus remains unexplained. This study clearly demonstrates, however, that the intestinal mucosa of rats with chronic renal insufficiency is not more susceptible to mucosal injury by bile acids than is the mucosa of appropriate control animals.     

Metabolism of steroid and amino acid moieties of conjugated bile acids in man: II. Glycine-conjugated dihydroxy bile acids

Chenodeoxycholyl-2,4-(3)H-glycine-1-(14)C and deoxycholyl-2,4-(3)H-glycine-1-(14)C were synthesized and administered orally to 10 healthy subjects. Distribution of radioactivity among bile acids and specific activity of steroid and amino acid moieties were determined in bile samples. (3)H and (14)C were measured in feces. (14)C in breath was calculated from interval (14)CO(2) specific activity determinations.The daily fractional turnover of the glycine moiety of chenodeoxycholyl and deoxycholylglycines was more than three times that of the steroid moiety. Pool size of chenodeoxycholylglycine was about twice that of deoxycholylglycine, but similar fractional turnover rates of steroid and amino acid moieties suggested that intestinal absorption of the two conjugated bile acids was equally efficient (about 95%). The amount of unlabeled deoxycholic acid (newly formed by bacterial 7alpha-dehydroxylation) absorbed from the intestine approximated 30% of the cholic acid that was lost. (3)H radioactivity remained predominantly in administered bile acid implying that, normally, secondary bile acids derived from chenodeoxycholic acid are not appreciably absorbed from the intestine and that deoxycholic acid is not hydroxylated by the liver.Approximately 25% of administered (14)C was recovered in the breath in the first 24 hr and less than 8% in the feces in 8 days; (14)CO(2) excretion correlated highly with fractional turnover of the glycine moiety. (3)H appeared predominantly in feces, and the rate of excretion correlated highly with the fractional turnover of the steroid moiety of bile acids. From the results in this paper plus previous measurements on the metabolism of cholylglycine, we calculated that about 6 mmoles/day of glycine is used for bile acid conjugation in health.