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PubMed1978

Effects of dihydroxy bile acids and hydroxy fatty acids on the absorption of oleic acid in the human jejunum.

Perfusion studies of the normal human jejunum were performed to test whether dihydroxy bile acids and hydroxy fatty acids inhibit the absorption of oleic acid, since previous reports documented their inhibitory effects on the absorption of several other organic solutes. 3 mM deoxycholate and 7 mM glycodeoxycholate inhibited the absorption of 3 mM oleic acid in isotonic micellar solutions while inducing net fluid secretion. Similarly, fractional absorption of oleic acid decreased in the presence of hydroxy fatty acids. However, only the changes induced by 2 mM ricinoleic acid could be distinguished from changes induced by an increase in total fatty acid concentration. Under all experimental conditions, close linear relationships existed between net water movement and fractional absorption of glucose, xylose, and fatty acids, as well as between the absorption rates of these solutes. In contrast, net fluid secretion induced by hypertonic D-mannitol (450 mosmol/liter) had no effect on solute absorption. Our data and observations in the literature do not allow formulation of a hypothesis which would adequately define all effects of dihydroxy bile acids and fatty acids on intestinal transport processes. The observations help explain the malabsorption of fat and other nutrients in patients with the blind loop syndrome.

Adult↗
PubMed1994

Bile salts stimulate mucous glycoprotein secretion from cultured rabbit gastric mucosal cells.

Resistance of gastric mucosa to damage is increased after exposure to mild irritants such as bile salts (adaptive cytoprotection). Mucus secretion also contributes to gastric cytoprotection. We investigated whether bile salts stimulate mucous glycoprotein secretion from cultured rabbit gastric mucosal cells. Because prostaglandins (PGs) stimulate mucus secretion, we assessed the role of endogenous PG release in bile salt-stimulated mucus secretion. Because Ca2+ plays a role in PGE2 release, the role of extracellular Ca2+ on PGE2 release and mucus secretion by bile salts was also studied. Rabbit gastric mucosal cells were prepared with collagenase and ethyl-enediaminetetraacetic acid. These cells were cultured as described previously. Cytotoxicity of bile salts was quantified by measuring chromium 51 release from prelabeled cells. PGE2 was measured by radioimmunoassay. Mucous glycoprotein secretion was assessed by tritiated glucosamine release assay. Deoxycholate (DC) and glycodeoxycholate (GDC) stimulated tritiated glucosamine release in doses that were not cytotoxic to the cultured cells. DC stimulated PGE2 release that was blocked by deprivation of extracellular Ca2+. GDC did not stimulate PGE2 release. Neither DC-stimulated nor GDC-stimulated mucus secretion was affected by indomethacin. Deprivation of extracellular Ca2+ did not affect DC-stimulated or GDC-stimulated mucus secretion. Bile salts stimulated mucous glycoprotein secretion from cultured rabbit gastric mucosal cells. This effect occurred independently of changes in endogenous PGE2 or extracellular Ca2+ concentrations.

Animals↗
PubMed2002

cAMP inhibits bile acid-induced apoptosis by blocking caspase activation and cytochrome c release.

We have previously shown that cAMP protects against bile acid-induced apoptosis in cultured rat hepatocytes in a phosphoinositide 3-kinase (PI3K)-dependent manner. In the present studies, we investigated the mechanisms involved in this anti-apoptotic effect. Hepatocyte apoptosis induced by glycodeoxycholate (GCDC) was associated with mitochondrial depolarization, activation of caspases, the release of cytochrome c from the mitochondria, and translocation of BAX from the cytosol to the mitochondria. cAMP inhibited GCDC-induced apoptosis, caspase 3 and caspase 9 activation, and cytochrome c release in a PI3K-dependent manner. cAMP activated PI3K in p85 immunoprecipitates and resulted in PI3K-dependent activation of the survival kinase Akt. Chemical inhibition of Akt phosphorylation with SB-203580 partially blocked the protective effect of cAMP. cAMP resulted in wortmannin-independent phosphorylation of BAD and was associated with translocation of BAD from the mitochondria to the cytosol. These results suggest that GCDC-induced apoptosis in cultured rat hepatocytes proceeds through a caspase-dependent intracellular stress pathway and that the survival effect of cAMP is mediated in part by PI3K-dependent Akt activation at the level of the mitochondria.

Animals↗
PubMed1993

Modulating effects of bile salt hydrophobicity on bile secretion of the major protein of the bile lipoprotein complex.

Bile lipids are secreted in association with a newly identified major apoprotein called anionic polypeptide fraction-calcium binding protein (APF-CBP), which is synthesized in the hepatocytes and has been detected in both bile and plasma and characterized. The secretion of the lipids in bile depends both on the concentration and the hydrophobicity of the bile salts (BS) secreted. The present study was undertaken to determine whether the synthesis and the secretion of APF-CBP are similarly regulated by BS, using two methods. The synthesis and secretion of labelled, newly synthesized APF-CBP by isolated rat hepatocytes were monitored by solid-phase immunoassay. For this purpose, hepatocytes were incubated with either glycodeoxycholate (GDC) or taurocholate (TC). The synthesis and secretion of labelled, newly synthesized APF-CBP by perfused rat liver were measured by immunological enzyme-linked assay (ELISA) upon perfusing the liver with either GDC or TC. We found that (i) the synthesis and the secretion of APF-CBP were increased during either TC or GDC perfusion, but the increase was more pronounced with TC; (ii) in GDC perfusion the APF-CBP levels measured were more closely related to the levels of bile salts and not to phospholipid levels, (iii) when the two bile salts were perfused in reverse order, i.e., first GDC and then TC, the secretion of APF-CBP in bile decreased when GDC was perfused, but increased when TC was perfused. Similar results were obtained in experiments with isolated hepatocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Effect of bilirubin and bile acids on biliary phospholipid secretion during bromobenzene-induced hepatic injury in the rabbit.

The interrelationship between the biliary secretion of phospholipids, bilirubin and bile acids was studied in New Zealand rabbits after acinar zone 3 hepatocyte damage induced by bromobenzene (4 mmol/kg body wt; i.p.). Treatment with the toxin did not significantly modify biliary phospholipid secretion, suggesting that the transport of phospholipids is mainly a zone 1 function. Bilirubin infusion at 1 mumol/min kg body wt induced a significant inhibition in biliary phospholipid secretion both in control and treated animals. This effect was overcome by the additional infusion of sodium glycodeoxycholate at 1.6 mumol/min kg body wt, although higher increases in phospholipid output were found in the control than in the treated rabbits. This would be related to the lowered recruitment of zone 3 cells for secretion in bromobenzene-damaged livers.

Animals↗
PubMed1994

Increases of intracellular magnesium promote glycodeoxycholate-induced apoptosis in rat hepatocytes.

Retention of bile salts by the hepatocyte contributes to liver injury during cholestasis. Although cell injury can occur by one of two mechanisms, necrosis versus apoptosis, information is lacking regarding apoptosis as a mechanism of cell death by bile salts. Our aim was to determine if the bile salt glycodeoxycholate (GDC) induces apoptosis in rat hepatocytes. Morphologic assessment included electron microscopy and quantitation of nuclear fragmentation by fluorescent microscopy. Biochemical studies included measurements of DNA fragmentation, in vitro endonuclease activity, cytosolic free Ca2+ (Cai2+), and cytosolic free Mg2+ (Mgi2+). Morphologic studies demonstrated typical features of apoptosis in GDC (50 microM) treated cells. The "ladder pattern" of DNA fragmentation was also present in DNA obtained from GDC-treated cells. In vitro endonuclease activity was 2.5-fold greater with Mg2+ than Ca2+. Although basal Cai2+ values did not change after addition of GDC, Mgi2+ increased twofold. Incubation of cells in an Mg(2+)-free medium prevented the rise in Mgi2+ and reduced nuclear and DNA fragmentation. In conclusion, GDC induces apoptosis in hepatocytes by a mechanism promoted by increases of Mgi2+ with stimulation of Mg(2+)-dependent endonucleases. These data suggest for the first time that changes of Mgi2+ may participate in the program of cellular events culminating in apoptosis.

Animals↗
PubMed1991

Lysosomal and plasma membrane ganglioside GM3 sialidases of cultured human fibroblasts. Differentiation by detergents and inhibitors.

Cultured human fibroblasts contain two sialidases that degrade gangliosides such as GM3: a lysosomal activity that appears identical with the activity towards water-soluble substrates and that is deficient in the genetic lysosomal disorder sialidosis, and another enzyme that seems localized on the external surface of the plasma membrane. In this report we show that both enzymes can be differentiated in the presence of each other by choice of the detergent used for activation, and also by the inhibitory action of some polyanionic compounds such as sulphated glycosaminoglycans. The lysosomal ganglioside GM3 sialidase is greatly stimulated by sodium glycodeoxycholate and, to lesser degrees, by sodium glycocholate and sodium cholate. The ganglioside GM3 sialidase of the plasma membrane is not measurably active under the conditions of the lysosomal enzyme but is specifically activated by the non-ionic detergent Triton X-100. The glycodeoxycholate-stimulated, but not the Triton-activated, ganglioside GM3 sialidase activity was profoundly diminished in cell lines from patients with the lysosomal disorders sialidosis and galactosialidosis; however, both activities were normal in fibroblasts from patients with mucolipidosis IV, previously thought to be a ganglioside sialidase deficiency disorder. Both the lysosomal and the plasma membrane ganglioside GM3 sialidases were inhibited by sialic acids, suramin, dextran sulphate and sulphated glycosaminoglycans. Among the latter, heparin and heparan sulphate showed a much higher inhibitory potency towards the plasma membrane ganglioside GM3 sialidase than towards the lysosomal onw.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbohydrate Metabolism, Inborn Errors↗
PubMedDate not supplied

Solubilization in good yield of active opiate binding sites from mammalian brain.

Active opiate binding sites have been solubilized from mammalian brain cell membranes. The presence of 0.5-0.1 M NaCl during treatment of membranes from rat brain, human frontal cortex, and bovine corpus striatum with glycodeoxycholate or digitonin resulted in the extraction of active opiate binding sites in yields ranging up to 43%. The criteria for solubility of the sites were their inability to sediment at 10(5) x g after 2 hr and their apparent molecular weight of 3- 4 x 10(5) as determined by gel filtration. The receptors in solution resemble the membrane-bound sites with respect to saturability, stereo-specificity, sensitivity to heat and reagents, and high affinity for opioid ligands. The interaction of solubilized sites with immobilized lectins was used to demonstrate the glycoprotein nature of the opiate receptor. Soluble receptors from all species studied were retained by wheat germ agglutinin(WGA)-agarose and could be specifically eluted with N-acetylglucosamine. No retention of solubilized material was observed with eight other lectins examined, including horseshoe crab lectin, a sialic acid specific agglutinin. The receptor protein eluted from WGA columns was enriched 25-50-fold over the crude soluble fraction.

Animals↗
PubMed1968

Experimental cholelithiasis in the rabbit induced by cholestanol feeding: effect of neomycin treatment on bile composition and gallstone formation.

Fed cholestanol is converted by the rabbit to 5alpha-bile acids which coprecipitate with the normally occurring 5beta-bile acids to form gallstones composed of calcium and sodium glycoallodeoxycholate and glycodeoxycholate. The present study shows that oral administration of large doses of neomycin prevents gallstone formation in the cholestanol-fed rabbit and reduces the elevated concentration of allodeoxycholic acid in bile, with a reciprocal increase in allocholic acid concentration. The reduction in the concentration of allodeoxycholic acid and in the incidence of gallstones is proportional to the dose of neomycin; at a concentration of allodeoxycholic acid below about 20% of total bile acids, gallstone formation does not occur. Neomycin probably exerts its action by modifying the anerobic intestinal flora which dehydroxylate allocholic acid to allodeoxycholic acid; if so, this suggests that both hepatic and bacterial transformations are essential steps in the pathogenesis of cholestanol-induced cholelithiasis. The bile of rabbits on a normal diet contains allodeoxycholic acid (5% of total bile acids). A similar decrease in allodeoxycholic acid concentration and reciprocal increase in allocholic acid concentration is observed when neomycin is administered to rabbits on a normal diet.

Animals↗
PubMed1971

Bile acid synthesis in the isolated, perfused rabbit liver.

These experiments were carried out to demonstrate the usefulness of the perfused rabbit liver for studies of bile acid metabolism, and to determine the rate-limiting enzyme of bile acid synthesis. Rabbits were fed a semisynthetic diet, with or without the addition of 1% cholestyramine, under controlled conditions. At the end of 2-5 wk, the livers were removed and perfused for 2.5 hr employing various (14)C-labeled precursors to measure de novo cholic acid synthesis. The livers were then analyzed for cholesterol, and the bile collected during the perfusion was analyzed for cholesterol and bile acids. Control bile contained, on the average, 0.34 mg of glycocholate, 7.4 mg of glycodeoxycholate, and 0.06 mg of cholesterol. After cholestyramine treatment of the donor rabbits, the bile contained 3.3 mg of glycocholate, 3.7 mg of glycodeoxycholate, and 0.05 mg of cholesterol. It was assumed that in cholestyramine-treated animals the enterohepatic circulation of the bile acids had been interrupted sufficiently to release the feedback inhibition of the rate-controlling enzyme of bile acid synthesis. Therefore, a given precursor should be incorporated into bile acids at a more rapid rate in livers of cholestyramine-treated animals, provided that the precursor was acted upon by the rate-controlling enzyme. It was found that the incorporation of acetate-(14)C, mevalonolactone-(14)C, and cholesterol-(14)C into cholate was 5-20 times greater in the livers of cholestyramine-treated animals than in the controls. In contrast, there was no difference in the incorporation of 7alpha-hydroxycholesterol-(14)C into cholate regardless of dietary pretreatment. It was concluded that given an adequate precursor pool, the 7alpha-hydroxylation of cholesterol is the rate-limiting step in bile acid formation.

Acetates↗
PubMed1991

Precipitation and 13C-NMR relaxation enhancement measurements of the interactions of bile acids with synthetic cationic bile acid derivatives, and with spin labelled fatty acids.

In an investigation of novel potential bile acid sequestrants, the affinities of the sodium salts of the glycine and taurine conjugates of naturally occurring bile acids (cholate, deoxycholate, chenodeoxycholate and lithocholate) for several cationic ammonium bile acid derivatives have been investigated by measurements of the extent to which the derivatives are able to precipitate the bile acids. This is roughly proportional to the lipophilicity of the interacting species. Thus, amino and ammonium derivatives of cholic acid do not precipitate taurocholate or glycocholate to any great extent, whereas ammonium derivatives of deoxycholate and lithocholate are much more effective. To complement the precipitation measurements, high resolution 13C-NMR has been applied to investigate the weaker interactions between the ammonium cholate derivative and glycocholate, glycodeoxycholate and glycochenodeoxycholate. Addition of either of the latter two bile acids to the cationic ammonium compound results in considerable broadening of the 13C resonances of both species, indicating the formation of relatively rigid structures. In addition, we have used T2 relaxation enhancement induced by spin-labelled fatty acids to examine the mechanism of interaction with bile acids of amphiphilic anions, which might compete with bile acids for sites on bile acid sequestrants. Low concentrations of 16-DOXY L-Stearate dramatically broaden the 13C-NMR resonances of deoxycholate carbons 19, 18 and 7 in particular, while 5-DOXY L-Stearate exerts much less specific effects. These results have been incorporated into a snapshot model of bile acid-fatty acid interactions.

Bile Acids and Salts↗
PubMed1974

The effect of glycine-conjugated bile acids on net transport and potential difference across isolated rat jejunum and ileum.

1. Five mM glycodeoxycholate and glycochenodeoxycholate inhibit net fluid transport across isolated rat jejunum and ileum; 5 mM glycocholate does not affect jejunal segments, but arrests fluid transport across ileal segments.2. Inhibition of fluid transport is accompanied by some diminution of mucosal glucose uptake, but translocation of glucose to the serosal surface of jejunal segments persists in the presence of dihydroxy conjugated bile acids.3. Inhibition of fluid transport is accompanied by a marked fall in the glucose-stimulated transmural electropotential difference, within 5 min of mucosal exposure to the bile acids.4. The lactate concentration gradient normally maintained across isolated intestine is abolished when fluid transport is inhibited by conjugated bile acids, even though lactate formation is not greatly reduced.5. These results suggest that inhibition of intestinal fluid transport is reproducible in vitro, and that the inhibition is not associated with increased permeability of the mucosa, but may be associated with altered permeability of the mucosal pole of the enterocyte.6. Although in vitro and in vivo effects of dihydroxy bile acids on fluid transport are similar, the assumption that the mode of action is likewise similar is not justified on present evidence.

Animals↗
PubMed1998

Effect on the partition equilibrium of various drugs by the formation of mixed bile salt/phosphatidylcholine/fatty acid micelles. A characterization by micellar affinity capillary electrophoresis. Part IV.

Mixed micelles, which mimic the bile containing fatty acids in the gastrointestinal tract, were used as a pseudostationary phase in capillary electrophoresis. The mixed micellar system studied contained the dihydroxy bile salts sodium glycodeoxycholate or sodium taurodeoxycholate or the trihydroxy bile salt sodium taurocholate, in association with different sodium salts of fatty acids including lauric, myristic, palmitic, oleic, stearic and linoleic acid and lecithin or dipalmitoylphosphatidylcholine as phospholipid. The determination of the changing mobilities of ionic analytes in the presence of mixed micelles reflected interactions between the used drugs and the mixed micelles. These were determined as dependence on the fatty acid concentration in the bile salt/fatty acid micelles and the mixed bile salt/phosphatidylcholine/fatty acid micelles. The capacity factor kappa MMC, for the partition between mixed micellar and aqueous phase was calculated. The partition equilibrium of basic and acidic drugs depends considerably on shape and charge of the mixed micelles (dependent on the fatty acid concentration) as well as on the acid-base properties of the drug. The mobility of the micelle aggregates was determined as an important reference value to the calculations of kappa MMC. This paper also describes the use of laser-induced fluorescence detection and electrospray mass spectrometry and tandem mass spectrometry for the characterization of the mixed micelle composition.

Bile Acids and Salts↗
PubMed2005

Bile salts inhibit growth and induce apoptosis of human esophageal cancer cell line.

AIM: To explore the effect of six bile salts, including glycocholate (GC), glycochenodeoxycholate (GCDC), glycodeoxycholate (GDC), taurocholate (TC), taurochenodeoxycholate (TCDC), taurodeoxycholate (TDC), and two bile acids including cholic acid (CA) and deoxycholic acid (DCA) on esophageal cancer Eca109 cell line. METHODS: Eca109 cells were exposed to six bile salts, two bile acids and the mixed bile salts at different concentrations for 24-72 h. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay was used to detect the cell proliferation. Apoptotic morphology was observed by phase-contrast video microscopy and deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay. Sub-G1 DNA fragmentations and early apoptosis cells were assayed by flow cytometry (FCM) with propidium iodide (PI) staining and annexin V-FITC conjugated with PI staining. Apoptosis DNA ladders on agarose were observed. Activation of caspase-3 was assayed by FCM with FITC-conjugated monoclonal rabbit anti-active caspase-3 antibody and expressions of Bcl-2 and Bax proteins were examined immunocytochemically in 500 micromol/L-TC-induced apoptosis cells. RESULTS: Five bile salts except for GC, and two bile acids and the mixed bile salts could initiate growth inhibition of Eca109 cells in a dose- and time-dependent manner. TUNEL, FCM, and DNA ladder assays all demonstrated apoptosis induced by bile salts and bile acids at 500 micromol/L, except for GC. Early apoptosis cell percentages in Eca109 cells treated with GCDC, GDC, TC, TCDC, TDC, CA at 500 micromol/L for 12 h, DCA at 500 micromol/L for 6 h, and mixed bile salts at 1000 micromol/L for 12 h were 7.5%, 8.7%, 14.8%, 8.9%, 7.8%, 9.3%, 22.6% and 12.5%, respectively, all were significantly higher than that in control (1.9%). About 22% of the cell population treated with TC at 500 micromol/L for 24 h had detectable active caspase-3, and were higher than that in the control (1%). Immunocytochemical assay suggested that TC down-regulated Bcl-2 protein level and up-regulated Bax protein level. CONCLUSION: GCDC, GDC, TC, TCDC, TDC, CA and DCA, except for GC, can inhibit growth and induce apoptosis of esophageal cancer Eca109 cells. Activation of caspase-3, decreased Bcl-2 protein and increased Bax protein are involved in TC-induced apoptosis of Eca109 cells.

Apoptosis↗
PubMed1989

Deoxycholate 7 alpha-hydroxylase in the hamster: substrate specificity and effect of phenobarbital.

In a recent publication, we reported that deoxycholic acid is 7 alpha-hydroxylated to yield glycocholate or taurocholate in vivo in the hamster (1987. Kuroki et al. Hepatology. 7: 229-234). In order to explore the possibility that amidation of free deoxycholic acid precedes the 7 alpha-hydroxylation, we assayed 7 alpha-hydroxylase activities of free and conjugated deoxycholates in vitro. 7 alpha-Hydroxylase activities of glycodeoxycholate and taurodeoxycholate were 720 +/- 132 and 640 +/- 160 pmol/mg.min-1, respectively. Activity of 7 alpha-hydroxylation of free deoxycholate was very low (60 +/- 20 pmol/mg.min-1). After treatment with phenobarbital in a dose of 100 mg/kg per day for 6 days, 7 alpha-hydroxylase activities of conjugated deoxycholates were decreased significantly (40%, P less than 0.01, n = 8), whereas that of free deoxycholate was not significantly changed. In the rat, 7 alpha-hydroxylase activities of conjugated deoxycholates were induced significantly (45% increase, P less than 0.05, n = 5) by phenobarbital treatment in sharp contrast to the hamster. There were significant correlations between the 7 alpha-hydroxylase activity of taurodeoxycholate and that of glycodeoxycholate both in the hamster and in the rat (hamsters: n = 16, r = 0.98, P less than 0.01; rats: n = 10, r = 0.82, P less than 0.01). These studies suggested that deoxycholic acid is 7 alpha-hydroxylated after amidation with glycine or taurine in vivo and that the same enzyme may well catalyze the 7 alpha-hydroxylation of glycodeoxycholate and taurodeoxycholate in the hamster.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

High and low affinity binding of [3H]cholate to rat liver plasma membranes.

The transport of bile acids across sinusoidal and canalicular membranes of hepatocytes is characterized as carrier mediated. Such a carrier should specifically bind bile acids at physiological concentrations. We examined the binding of [3H]cholate to rat liver plasma membranes using a microcentrifugation technique and detected high (KD = 1.23 +/- 0.44 microM, Bmax = 21.8 +/- 3.3 pmol/mg protein) and low (KD = 1.97 +/- 1.33 mM, Bmax = 41.5 +/- 25.3 nmol/mg protein) affinity binding sites. Maximal binding was achieved within 15-45 sec and was stable for 2 min at 37 degrees. Binding to the high affinity site was reversible, was not Na+ dependent or attributable to vesicular uptake, and exhibited a broad pH optimum. Binding to this site was negligible or not detected in liver mitochondrial and microsomal fractions, was saturable, and was inhibited by other bile acids. The IC50 values for bile acids as inhibitors of [3H]cholate binding at the high affinity site were: taurocholate, 1.9 nM; glycodeoxycholate, 3.1 nM; chenodeoxycholate, 5.6 nM; taurochenodeoxycholate, 7.3 nM; glycochenodeoxycholate, 11 nM; lithocholate, 13 nM; taurodeoxycholate, 20 nM; glycocholate, 3.6 microM; and deoxycholate, 5.6 microM. [3H]Cholate specific binding was inhibited by 10(-5) M bromosulfophthalein, bilirubin and indocyanin green. These data support the hypothesis that the high affinity binding site represents a carrier which is shared by bile acids and nonbile acid organic anions.

Animals↗
PubMed1994

Inhibition of calcium phosphate precipitation by bile salts: a test of the Ca(2+)-buffering hypothesis.

The ability of bile salts to inhibit the precipitation of either calcium hydroxyapatite or its precursor, amorphous calcium phosphate, by reducing Ca2+ activity or poisoning nascent crystals was determined. When apatite precipitated rapidly (1-4 h), glycocholate and taurine-conjugated bile salts (up to 100 mM) had little effect on apatite formation, but prevented amorphous calcium phosphate precipitation by lowering Ca2+ activity. In contrast, glycodeoxycholate and glycochenodeoxycholate (2-3 mM) inhibited apatite formation for at least 24 h by poisoning embryonic apatite. When apatite precipitated slowly (> 24 h), all the dihydroxy bile salts prevented apatite formation for at least 4 days. At constant initial supersaturation, the phosphate concentration determined the degree of inhibition caused by the six bile salts mixed together in physiologic proportion. At low phosphate concentrations (1.2 mM) total inhibition was achieved by poisoning embryos (approximately -5 mM total bile salt), but with 4.0 mM phosphate only approximately 60% inhibition was attained (150 mM bile salt) by a combination of poisoning and Ca(2+)-buffering. Thus, at low supersaturation all dihydroxy bile salts can prevent apatite formation by reducing free Ca2+ (taurine and glycine conjugates) or poisoning embryos (glycine conjugates). With mixtures of bile salts at higher supersaturation, inhibition of apatite depends on a combination of poisoning and reduction of free Ca2+, mainly caused by glycodeoxycholate and glycochenodeoxycholate.

Bile Acids and Salts↗