Short communication: Chemical structure, concentration, and pH are key factors influencing antimicrobial activity of conjugated bile acids against lactobacilli.

Effects of chemical structure, concentration, and pH on antimicrobial activity of conjugated bile acids were investigated in 4 strains of lactobacilli. Considerable differences were observed in the antimicrobial activity between the 6 human conjugated bile acids, including glycocholic acid, taurocholic acid, glycodeoxycholic acid, taurodeoxycholic acid, glycochenodeoxycholic acid, and taurochenodeoxycholic acid. Glycodeoxycholic acid and glycochenodeoxycholic acid generally showed significantly higher antimicrobial activity against the lactobacilli, but glycocholic acid and taurocholic acid exhibited the significantly lower antimicrobial activity. Glycochenodeoxycholic acid was selected for further analysis, and the results showed its antimicrobial activity was concentration-dependent, and there was a significantly negative linear correlation (R2 > 0.98) between bile-antimicrobial index and logarithmic concentration of the bile acid for each strain of lactobacilli. Additionally, the antimicrobial activity of glycochenodeoxycholic acid was also observed to be pH-dependent, and it was significantly enhanced with the decreasing pH, with the result that all the strains of lactobacilli were unable to grow at pH 5.0. In conclusion, chemical structure, concentration, and pH are key factors influencing antimicrobial activity of conjugated bile acids against lactobacilli. This study provides theoretical guidance and technology support for developing a scientific method for evaluating the bile tolerance ability of potentially probiotic strains of lactobacilli.

Deoxycholylglycine, a conjugated secondary bile acid, reduces vascular tone by attenuating Ca2+ sensitivity via rho kinase pathway.

Patients with cirrhosis have reduced systemic vascular resistance and elevated circulating bile acids (BAs). Previously, we showed that secondary conjugated BAs impair vascular tone by reducing vascular smooth muscle cell (VSMC) Ca2+ influx. In this study, we investigated the effect of deoxycholylglycine (DCG), on Ca2+ sensitivity in reducing vascular tone. First, we evaluated the effects of DCG on U46619- and phorbol-myristate-acetate (PMA)-induced vasoconstriction. DCG reduced U46619-induced vascular tone but failed to reduce PMA-induced vasoconstriction. Then, by utilizing varied combinations of diltiazem (voltage-dependent Ca2+ channel [VDCC] inhibitor), Y27632 (RhoA kinase [ROCK] inhibitor) and chelerythrine (PKC inhibitor) for the effect of DCG on U46619-induced vasoconstriction, we ascertained that DCG inhibits VDCC and ROCK pathway with no effect on PKC. We further assessed the effect of DCG on ROCK pathway. In ß-escin-permeabilized arteries, DCG reduced high-dose Ca2+- and GTPγS (a ROCK activator)-induced vasoconstriction. In rat vascular smooth muscle cells (VSMCs), DCG reduced U46619-induced phosphorylation of myosin light chain subunit (MLC20) and myosin phosphatase target subunit-1 (MYPT1). In permeabilized VSMCs, DCG reduced Ca2+- and GTPγS-mediated MLC20 and MYPT1 phosphorylation, and further, reduced GTPγS-mediated membrane translocation of RhoA. In VSMCs, long-term treatment with DCG had no effect on ROCK2 and RhoA expression. In conclusion, DCG attenuates vascular Ca2+ sensitivity and tone via inhibiting ROCK pathway. These results enhance our understanding of BAs-mediated regulation of vascular tone and provide a platform to develop new treatment strategies to reduce arterial dysfunction in cirrhosis.

Bile acid flux through portal but not peripheral veins inhibits CYP7A1 expression without involvement of ileal FGF19 in rabbits.

It was proposed that CYP7A1 expression is suppressed through the gut-hepatic signaling pathway fibroblast growth factor (FGF) 15/19-fibroblast growth factor receptor 4, which is initiated by activation of farnesoid X receptor in the intestine rather than in the liver. The present study tested whether portal bile acid flux alone without ileal FGF19 could downregulate CYP7A1 expression in rabbits. A rabbit model was developed by infusing glycodeoxycholic acid (GDCA) through the splenic vein to bypass ileal FGF19. Study was conducted in four groups of rabbits: control; bile fistula + bovine serum albumin solution perfusion (BF); BF + GDCA (by portal perfusion); and BF + GDCA-f (by femoral perfusion). Compared with only BF, BF + GDCA (6 h portal perfusion) suppressed CYP7A1 mRNA, whereas BF + GDCA-f (via femoral vein) with the same perfusion rate of GDCA did not show inhibitory effects. Meanwhile, there was a decrease in ileal FGF19 expression and portal FGF19 protein levels, but an equivalent increase in biliary bile acid outputs in both GDCA perfusion groups. This study demonstrated that portal bile acid flux alone downregulated CYP7A1 expression with diminished FGF19 expression and protein levels, whereas the same bile acid flux reaching the liver through the hepatic artery via femoral vein had no inhibitory effect on CYP7A1. We propose that bile acid flux through the portal venous system may be a kind of "intestinal factor" that suppresses CYP7A1 expression.

L-Malic Acid Protects Lacticaseibacillus paracasei L9 from Glycodeoxycholic Acid Stress via the Malolactic Enzyme Pathway.

Bile stress tolerance is a crucial characteristic of probiotics for surviving in the human gastrointestinal tract. The mechanism underlying the effect of l-malic acid on enhancing the glycodeoxycholic acid (GDCA) tolerance of Lacticaseibacillus paracasei L9 was investigated herein. Bile tolerance specificity assays revealed that Lc. paracasei L9 was more sensitive to GDCA than to taurocholic acid, glycocholic acid, and taurodeoxycholic acid. Notably, l-malic acid significantly enhanced the GDCA tolerance of Lc. paracasei L9 by increasing the pH of the medium. The role of the malolactic enzyme pathway in enhancing GDCA resistance was investigated using molecular techniques. Confocal laser scanning and scanning electron microscopy revealed that l-malic acid preserved membrane permeability and cellular morphology, thereby protecting bacterial cells from GDCA stress-induced damage. The study also demonstrated that l-malic acid enhanced bile tolerance in different species of lactobacilli. These findings provide a novel protective mechanism for coping with bile stress in lactobacilli.

Glycine-Conjugated Bile Acids Protect RPE Tight Junctions against Oxidative Stress and Inhibit Choroidal Endothelial Cell Angiogenesis In Vitro.

We previously demonstrated that the bile acid taurocholic acid (TCA) inhibits features of age-related macular degeneration (AMD) in vitro. The purpose of this study was to determine if the glycine-conjugated bile acids glycocholic acid (GCA), glycodeoxycholic acid (GDCA), and glycoursodeoxycholic acid (GUDCA) can protect retinal pigment epithelial (RPE) cells against oxidative damage and inhibit vascular endothelial growth factor (VEGF)-induced angiogenesis in choroidal endothelial cells (CECs). Paraquat was used to induce oxidative stress and disrupt tight junctions in HRPEpiC primary human RPE cells. Tight junctions were assessed via transepithelial electrical resistance and ZO-1 immunofluorescence. GCA and GUDCA protected RPE tight junctions against oxidative damage at concentrations of 100-500 µM, and GDCA protected tight junctions at 10-500 µM. Angiogenesis was induced with VEGF in RF/6A macaque CECs and evaluated with cell proliferation, cell migration, and tube formation assays. GCA inhibited VEGF-induced CEC migration at 50-500 µM and tube formation at 10-500 µM. GUDCA inhibited VEGF-induced CEC migration at 100-500 µM and tube formation at 50-500 µM. GDCA had no effect on VEGF-induced angiogenesis. None of the three bile acids significantly inhibited VEGF-induced CEC proliferation. These results suggest glycine-conjugated bile acids may be protective against both atrophic and neovascular AMD.

Effect of indomethacin on bile acid-phospholipid interactions: implication for small intestinal injury induced by nonsteroidal anti-inflammatory drugs.

The injurious effect of nonsteroidal anti-inflammatory drugs (NSAIDs) in the small intestine was not appreciated until the widespread use of capsule endoscopy. Animal studies found that NSAID-induced small intestinal injury depends on the ability of these drugs to be secreted into the bile. Because the individual toxicity of amphiphilic bile acids and NSAIDs directly correlates with their interactions with phospholipid membranes, we propose that the presence of both NSAIDs and bile acids alters their individual physicochemical properties and enhances the disruptive effect on cell membranes and overall cytotoxicity. We utilized in vitro gastric AGS and intestinal IEC-6 cells and found that combinations of bile acid, deoxycholic acid (DC), taurodeoxycholic acid, glycodeoxycholic acid, and the NSAID indomethacin (Indo) significantly increased cell plasma membrane permeability and became more cytotoxic than these agents alone. We confirmed this finding by measuring liposome permeability and intramembrane packing in synthetic model membranes exposed to DC, Indo, or combinations of both agents. By measuring physicochemical parameters, such as fluorescence resonance energy transfer and membrane surface charge, we found that Indo associated with phosphatidylcholine and promoted the molecular aggregation of DC and potential formation of larger and isolated bile acid complexes within either biomembranes or bile acid-lipid mixed micelles, which leads to membrane disruption. In this study, we demonstrated increased cytotoxicity of combinations of bile acid and NSAID and provided a molecular mechanism for the observed toxicity. This mechanism potentially contributes to the NSAID-induced injury in the small bowel.

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.

Effects of dual inhibitor of cyclooxygenase and 5-lipoxygenase on acute necrotizing pancreatitis in rats.

BACKGROUND/AIMS: The aim of this study was to investigate the influence of dual inhibitor of cyclooxygenase and 5-lipoxygenase (ER-34122) on acute necrotizing pancreatitis (ANP) induced by glycodeoxycholic acid in rats. METHODOLOGY: ANP was induced in 96 rats by standardized intraductal glycodeoxycholic acid infusion and intravenous cerulein infusion. Rats were divided into six groups (6 rats in each group): Sham + saline, sham + ER-34122, which was dissolved in hydroxypropylmetylcellulose (TC-5RW), sham + TC-5RW, ANP + saline, ANP + ER-34122 and ANP + TC-5RW. Six hours after ANP induction ER-34122 (30 mg/kg), saline or TC-5RW was given by feeding tube. At the 12th hour, routine cardio-respirator, renal parameters were monitored to assess organ function. Serum amylase, alanine amino transferase (ALT), interleukin 6 (IL-6), lactate dehydrogenase (LDH) in bronchoalveolar lavage (BAL) fluid, serum concentration of urea, tissue activity of myeloperoxidase (MPO) and malondialdehyde (MDA) in pancreas and lung were measured. Pancreas histology was examined. In the second part of the study 60 rats were studied in four groups similar to first part. Survival of all rats was monitored for 24 hours. RESULTS: The induction of ANP resulted in significant increase in mortality rate, pancreatic necrosis and serum activity of amylase, ALT, IL-6, LDH in BAL fluid, serum concentration of urea, tissue activity of MPO and MDA in pancreas and lung, and significant decrease of serum concentrations of calcium, blood pressure, urine output and pO2. NAC did not change serum activity of amylase. The use of ER-34122 inhibited the changes in blood pressure, pO2, serum activity of ALT, pancreatic MPO and MDA levels, partially urine output, LDH level in BAL fluid and pancreatic damage. But ER-34122 could not effect the changes, such as serum activity of amylase, IL-6, serum concentration of urea and calcium, MPO and MDA levels in lung and the mortality rate. CONCLUSIONS: The use of ER-34122 has a limited value on the course of ANP. It has no role in the treatment of ANP.

[Bile salts induce differentiation in cultured human normal esophageal mucosal epithelial cells].

OBJECTIVE: To investigate the effects of bile salts on the proliferation and differentiation of human normal esophageal mucosal epithelial cells on cultured. METHODS: Normal human esophageal mucosa was obtained during operation. The esophageal epithelial cells were isolated, cultured, and treated with 6 different conjugated bile salts [glycocholate (GC), glycochenodeoxycholate (GCDC), glycodeoxycholate (GDC), taurochenodeoxycholate (TCDC), and taurodeoxycholate (TDC), all of the concentration of 50 micromol/L, and taurocholate (TC) of the concentration of 20 micromol/L], and their mixtures the concentration of 50 micromol/L respectively. One, three, and five days later MTT assay was applied to detect the cell proliferation. The cell cycle was assayed by flow cytometry with propidium iodide staining 1 and 3 d after treating with the bile salts. The cytokeratin 13 (CK13) in the differentiated cells and cytokeratin 14 (CK14) in the proliferating cells were detected by immunocytochemical assay. The concentration of intercellular calcium ([Ca(2+)]i) was analyzed by Laser Scanning Confocal Microscope (LSCM) in cells with TC, mixed bile salts and GC. RESULTS: The cultured esophageal epithelial cells treated by the bile salts, except those treated by GC for 1 - 3 days, became larger and shuttle-like, with the cell proliferation inhibited, the percentages of cells in G(0)-G(1) phase increased and percentages of cells in S phase decreased. The percentages of CK14 positive cells were increased, but the percentages of CK13 positive cells were decreased time-dependently in cells treated for 1 - 5 days. The most obvious effects were seen in those cells treated with TC. The percentage of CK13 positive cells reached 74% +/- 8% in those cells treated with TC for 5 days, higher significantly than the percentage in the control cell (22% +/- 7%), (P < 0.01). The [Ca(2+)]i increased significantly only several minutes after treatment of TC and mixed bile salts, however, GC failed to cause the increase of [Ca(2+)]i. CONCLUSION: GCDC, GDC, TC, TCDC, TDC and their mixture all induce differentiation of cultured human normal esophageal mucosal epithelial cells, but nor does GC. Increased [Ca(2+)]i is related to the TC-induced differentiation in those esophageal mucosal epithelial cells.

Ca2+-mediated activation of human erythrocyte membrane Ca2+-ATPase.

Ca2+-ATPase of human erythrocyte membranes, after being washed to remove Ca2+ after incubation with the ion, was found to be activated. Stimulation of the ATPase was related neither to fluidity change nor to cytoskeletal degradation of the membranes mediated by Ca2+. Activation of the transport enzyme was also unaffected by detergent treatment of the membrane, but was suppressed when leupeptin was included during incubation of the membranes with Ca2+. Stimulation of the ATPase by a membrane-associated Ca2+-dependent proteinase was thus suggested. Much less 138 kDa Ca2+-ATPase protein could be harvested from a Triton extract of membranes incubated with Ca2+ than without Ca2+. Activity of the activated enzyme could not be further elevated by exogenous calpain, even after treatment of the membranes with glycodeoxycholate. There was also an overlap in the effect of calmodulin and the Ca2+-mediated stimulation of membrane Ca2+-ATPase. While Km(ATP) of the stimulated ATPase remained unchanged, a significant drop in the free-Ca2+ concentration for half-maximal activation of the enzyme was observed.

Activation of erythrocyte membrane Ca2+-ATPase by calpain.

Ca2+-ATPase of erythrocyte membranes, prepared from erythrocytes substantially removed of contaminating leukocytes, was found to be activated by calpain isolated from the same source. Saponin or glycodeoxycholate treatment of membranes was essential for elicitation of the calpain response. Unlike the membrane bound ATPase, solubilized ATPase was inactivated by calpain. Digestion of membranes with the protease did not affect the Km (ATP) of Ca2+-ATPase though stimulation of the membrane ATPase by calmodulin could be partially substituted by calpain treatment. As compared with control, Ca2+-ATPase of calpain-digested membranes attained maximal activity at a lower free Ca2+ concentration.

Membrane fluidity and bile salt damage.

The lysis, by bile salts, of membranes of different fluidities was studied; it was shown that membranes of low fluidity were less readily lysed than membranes of higher fluidity. Membrane fluidity levels were controlled (i) by the use of erythrocytes, from different species, systematically differing in their lipid composition; (ii) by using each membrane at a range of temperatures; and (iii) by incorporating into the membranes the fluidizing agent, benzyl alcohol, at a range of concentrations. Membrane fluidity (and order) in each case was monitored by measuring the degree of polarization of fluorescence from the hydrophobic probe molecule, 1,6-diphenyl-1,3,5-hexatriene. The response of lytic behaviour to modulations of membrane fluidity also indicated a difference between the bile salts, glycodeoxycholate and glycocholate; the former initiates lysis close to (at or below) its critical micellar concentrations whereas the latter only causes lysis above, and often substantially above, its critical micellar concentration. In their respective ranges of lytic concentrations, both bile salts are far less effective with membranes of low fluidity. The results are discussed with regard to the features of a membrane which would be expected to be resistant to high concentrations of bile salts in vivo, i.e., the plasma membranes of the bile canaliculus and lumenal surface of biliary tract cells.

Comparison of the effects of bile acids on cell viability and DNA synthesis by rat hepatocytes in primary culture.

Bile acid-induced inhibition of DNA synthesis by the regenerating rat liver in the absence of other manifestation of impairment in liver cell viability has been reported. Because in experiments carried out on in vivo models bile acids are rapidly taken up and secreted into bile, it is difficult to establish steady concentrations to which the hepatocytes are exposed. Thus, in this work, a dose-response study was carried out to investigate the in vitro cytotoxic effect of major unconjugated and tauro- (T) or glyco- (G) conjugated bile acids and to compare this as regards their ability to inhibit DNA synthesis. Viability of hepatocytes in primary culture was measured by Neutral red uptake and formazan formation after 6 h exposure of cells to bile acids. The rate of DNA synthesis was determined by radiolabeled thymidine incorporation into DNA. Incubation of hepatocytes with different bile acid species - cholic acid (CA), deoxycholic acid (DCA), chenodeoxycholic acid (CDCA) and ursodeoxycholic acid (UDCA), in the range of 10-1000 microM - revealed that toxicity was stronger for the unconjugated forms of CDCA and DCA than for CA and UDCA. Conjugation markedly reduced the effects of bile acids on cell viability. By contrast, the ability to inhibit radiolabeled thymidine incorporation into DNA was only slightly lower for taurodeoxycholic acid (TDCA) and glycodeoxycholic acid (GDCA) than for DCA. When the effect of these bile acids on DNA synthesis and cell viability was compared, a clear dissociation was observed. Radiolabeled thymidine incorporation into DNA was significantly decreased (-50%) at TDCA concentrations at which cell viability was not affected. Lack of a cause-effect relationship between both processes was further supported by the fact that well-known hepatoprotective compounds, such as tauroursodeoxycholic acid (TUDCA) and S-adenosylmethionine (SAMe) failed to prevent the effect of bile acids on DNA synthesis. In summary, our results indicate that bile acid-induced reduction of DNA synthesis does not require previous decreases in hepatocyte viability. This suggests the existence of a high sensitivity to bile acids of cellular mechanisms that may affect the rate of DNA repair and/or proliferation, which is of particular interest regarding the role of bile acids in the etiology of certain types of cancer.

The influence of bile salts and mixed micelles on the pharmacokinetics of quinine in rabbits.

The bioavailability of orally administered drugs can be influenced by interactions with food components and by physico-chemical conditions in the upper gastrointestinal tract. Normally, bile salts enhance the transport of lipophilic drugs across mucosal membranes. Bile salts are able to form stable mixed micelles consisting of fatty acids and phospholipids. Conventional micellar systems are known to solubilize lipophilic drugs having a low bioavailability. The influence of bile salts and mixed micelles on the pharmacokinetics of the lipophilic drug quinine was investigated in rabbits. Female rabbits were given intraduadenally quinine (5 mg/kg body weight) without and with incorporation into the micellar or mixed micellar systems. Blood was collected every 30 min for 6 h. In plasma, concentration of quinine was measured using HPLC. The plasma concentration-time profiles of quinine were significantly lower within the first 2 h after administration in presence of both the sodium salt of glycodeoxycholic acid (above the critical micellar concentration) as well as of mixed micellar systems consisting of glycodeoxycholic acid and palmitic acid and/or lecithin. The pharmacokinetic parameters AUC (relative bioavailability) and c(max) of quinine were significantly decreased by micellar systems in rabbits. These mixed micellar systems lower and not as expected, increase the absorption of quinine in vivo. Therefore, quinine should be orally administered at least 1h before food intake, particularly before fat intake.

Studies in bile salt solutions. Deoxycholate stimulation of human milk lipase.

Stimulation of human milk lipase by deoxycholate and its taurine and glycine conjugates was demonstrated by measuring the esterolysis reaction of 4-nitrophenylacetate. The steroidal surfactants did not bind strongly to the polar substrate but they did bind effectively to a hydrophobic site on the enzyme and these bile salt-enzyme complexes were effective catalysts. These results are compared with those for stimulation of the enzyme by cholate surfactants and it has been demonstrated that the absence of a 7 alpha-OH substituent on the steroid nucleus does not prevent stimulation of either the esterolytic or lipolytic activity of the enzyme.

Heterogeneity of rabbit hepatocytes for bile secretion after acinar zone 3 damage induced by bromobenzene. Effect of bilirubin and bile salt infusions.

Anaesthetized rabbits were used to study the effect of bromobenzene-induced hepatic damage to the acinar zone 3 on bile flow, bile salt, sodium secretion as well as bilirubin transport in basal conditions or with infusion of sodium glycodeoxycholate. The bromobenzene-pretreated animals exhibited in basal conditions a lower bile flow (44%) than that of the controls, with a smaller decrease in bile salt output (27%) and sodium output (29%), whereas no modification in endogenous bilirubin excretion was observed. The bile salt independent fraction of secretion (BSIF) was reduced significantly after the toxic lesion both in terms of absolute and relative values. The hepatocytes of the periportal zone were capable of excreting the totality of bilirubin presented to the liver, regardless of the extent of bile flow or the input of bile salts. The infusion of bilirubin at 1.0 mumole/kg/min led to a fall in bile flow which was attributed to the interference of the pigment with the BSIF. The maximal bilirubin excretion was significantly smaller in bromobenzene-pretreated animals than in the controls, which could be due to the incapacity of the intoxicated rabbits to recruit quiescent hepatocytes. When glycodeoxycholate was administered under conditions of maximal bilirubin transport, bile flow increased as did bile salt secretion in both controls and animals with damaged livers. However, clear differences persisted between the two, which could be attributed not only to the volume fraction of necrosis but also to an interference by bilirubin with the hepatic handling of bile salts. Maximal bilirubin excretion increased in a similar way in both groups after glycodeoxycholate administration. It is proposed that glycodeoxycholate infusion facilitates the hepatic depletion of bilirubin, probably by stimulating transport processes.

Leukocyte-endothelial adherence correlates with pancreatic nitric oxide production in early cerulein-induced pancreatitis in rats.

The role of nitric oxide (NO) in microcirculation during the development of acute pancreatitis was not clear. An in vivo microscopic technique was used for evaluating leukocyte-endothelial adherence in the pancreatic microcirculation after induction (cerulein) of acute pancreatitis. Microdialysis was performed to detect pancreatic nitrate concentration (NO level) by high-performance liquid chromatography. Cerulein caused significantly reduced flow velocity in 1 h (31 %) and increased the number of sticking leukocytes in 2 h; both persisted for at least 3 h. Pancreatic NO level was found to be significantly elevated (2.5-fold) in 1 h and also persisted for 3 h. Both microcirculatory changes and NO elevation were significantly alleviated in cerulein-induced animals pretreated with NO synthase inhibitor (NG-nitro-L-arginine), indicating that elevation of NO could precede and account for a major portion of the observed microcirculatory changes. Furthermore, there was a strong positive correlation between numbers of adherent leukocytes and pancreatic NO level, suggesting that during the development of acute pancreatitis, NO could play an adverse role in microcirculation.

Effects of bile salts on bile formation in rabbits.

The effects of different species of bile salts: deoxycholate, taurochenodeoxycholate, ursodeoxycholate, glycodeoxycholate, tauroursodeoxycholate, chenodeoxycholate and cholate (DCA, TCDC, UDCA, GDCA, TUDC, CDCA, CA) on bile secretion were examined in anesthetized rabbits using two different infusion routes. When bile salts were infused intravenously, all bile salts (except for TCDC) significantly increased the volume of bile and bile salt excretion, but their respective efficiency for bile formation was different. The concentration of bicarbonate ion in the bile significantly increased during the choleretic periods induced by DCA, UDCA, GDCA and CDCA but remained unchanged with the other bile salts (CA, TCDC, TUDC). In rabbits, where a bile salt solution was infused in the duodenum and then drained from the intestine through an incision in the distal part of duodenum, none of these bile salts affected bile secretion. The effects of intravenously administered bile salts on rabbit bile secretion are different in terms of their choleretic potency and bicarbonate excretion depending on the species of bile salts used. Furthermore, it was concluded that the intraduodenal infusion of UDCA, which was found to stimulate the pancreatic exocrine function, did not affect bile secretion.

Bile acids are able to reduce blood pressure by attenuating the vascular reactivity in spontaneously hypertensive rats.

Effects of the synthetic bile acids on blood pressure were examined in spontaneously hypertensive rats. Continuous intravenous administration of the bile acids at the rate of 1 mg/min for 20 min significantly lowered the blood pressure by 12 mmHg. In order to examine its blood pressure lowering mechanism, the isolated mesenteric arterial perfusion system was employed. Bile acids in the perfusate inhibited vascular reactivity to norepinephrine and KCl in a dose-dependent manner. This inhibitory action diminished as the concentration of potassium in the perfusate decreased. When the perfusate was free from potassium, its inhibitory action completely disappeared. These results in vivo and in vitro studies strongly suggest that bile acids act directly on the vascular beds and attenuate vascular response to norepinephrine.

Hyodeoxycholic acid: a new approach to gallstone prevention.

Hyodeoxycholic acid and its isomer, 6 beta-hyodeoxycholic acid, when added to a lithogenic diet prevented the formation of cholesterol gallstones and crystals in prairie dogs. This beneficial effect occurred in the presence of bile supersaturated with cholesterol. Hyodeoxycholic acid abolished the feedback inhibition of hepatic hydroxymethylglutaryl coenzyme A reductase activity, the rate-limiting enzyme of cholesterol synthesis, and prevented elevations in serum and liver cholesterol observed in animals fed a 0.4 percent cholesterol diet. The gallbladder bile of the animals fed hyodeoxycholic acid and 6 beta-hyodeoxycholic acid contained abundant liquid crystals. This suggests that these bile acids prevented the transition of cholesterol from its liquid crystalline phase to solid crystals and stones.