The effect of portal blood bile salt concentrations on bile salt synthesis in rat liver (original) (raw)
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Biochimica et Biophysica Acta (BBA) - Lipids and Lipid Metabolism, 1981
1. Rats were maintained in a strictly controlled environment of 12 h illumination and 12 h darkness. At regular intervals during the light/dark cycle the portal blood conjugated cholic acid and conjugated chenodeoxycholic acid concentrations were measured. The bile salt concentrations exhibited similar diurnal rhythms, the highest concentrations occurring in the middle of the dark phase. 2. The concentrations of conjugated cholic and chenodeoxycholic acids in the portal blood of rats fed a diet containing the bile salt sequestrant, cholestyramine, were significantly lower than those found in rats given a control diet. 3. During total biliary drainage the portal blood concentrations of conjugated cholic and chenodeoxycholic acids fell to a minimum 6-8 h after the start of the experiment, whereas bile salt synthesis in hepatocytes isolated from the rats was not increased until at least 13 h afer the commencement of total bilii drainage. 4. These results suggest that the concentrations of bile salts in the portal blood do not affect directly the diurnal fluctuation in rates of bile salt synthesis, as the response of synthesis to a change in portal blood bile salt concentrations is too slow. 5. When the rats were given a small supplement of cholesterol in the diet to suppress hepatic cholesterologenesis prior to being subjected to total biliary drainage, the changes in the portal blood concentrations of conjugated cholic and chenodeoxycholic acids and the synthesis of the two bile salts by isolated hepatocytes were similar to those found in rats given the control diet. 6. The rise in bile salt production seen during biliary drainage may not be dependent exclusively on a preceding increase in cholesterol synthesis.
Bile acid formation in primary human hepatocytes
World journal of gastroenterology : WJG, 2000
AIM:To evaluate a culture system for bile acid formation in primary human hepatocytes in comparison with HepG2 cells.METHODS:Hepatocytes were isolated from normal human liver tissue and we re cultured in serum-free William's E medium.The medium was collected and re newed every 24 h. Bile acids and their precursors in media were finally analysed by gas chromatography mass spectrometry.RESULTS:Cholic acid (CA) and chenodeoxycholic acid (CDCA) conjugated with glycine or taurine accounted for 70% and 25% of total steroids. A third of CDC A was also conjugated with sulphuric acid. Dexamethasone and thyroid hormone alone or in combination did not significantly effect bile acid formation. The addition of cyclosporin A (10&mgr;mol/L) inhibited the synthesis of CA and CDCA by about 13% and 30%, respectively.CONCLUSION:Isolated human hepatocytes in primary culture behave as in the intact liver by converting cholesterol to conjugated CA and CDCA.This is in contrast to cultured HepG2 cells,...
Comparative Biochemistry and Physiology Part A: Physiology, 1996
Dose-response curves for taurocholate and tauroursodeoxycholate were performed in rat and rabbit livers to get more insight into species differences in the hepatic bile acid uptake. The bile acids showed saturation kinetics in both animals, the V,,, in rat being higher than in rabbit and the K, being lower in the rat than in the rabbit for both the bile acids, with no significant difference in the hepatic cells morphometric parameters. Therefore, it is possible that differences in the kinetic parameters are related to the number and, to a lesser extent, to the affinity of the transporters on the sinusoidal plasma membranes. COMP BIOCHEM PHYSIC),. 113A:2:157-164. 1996.
Excretion of taurocholate from isolated hepatocytes
European journal of biochemistry / FEBS, 1976
Efflux of taurocholate from isolated rat hepatocytes was studied to characterize the mechanism of bile acid secretion. Cells were incubated with taurocholate for 15 min. The amount of the intracellularly accumulated bile acid was directly related to the concentration in the medium. Transfer of the loaded cells from the incubation medium to a medium without taurocholate led to taurocholate efflux. Efflux was saturable, its activation energy amounted to 12 kcal/mol (50 kJ). It was strongly inhibited by the metabolic inhibitor antimycin A and to a lesser extend by the uncoupler carbonylcyanide-m-chlorophenylhydrazone. Dinitrofluorobenzene and mersalyl, reagents which react with amino acids, inhibited efflux by about 30% when applied at concentrations of 50 muM. Ouabain increased the rate of efflux. The observations indicate that secretory functions are maintained in isolated liver cells.
Digestive Diseases and Sciences, 1994
Taurohyodeoxycholic acid is a natural 6et-hydroxylated bile acid with an apparent hydrophilicity intermediate between those of tauroursodeoxycholic and taurocholic acids. We investigated in the rat the hepatobiliary metabolism, choleretic properties, and biliary maximum secretory rate (SRmax) of taurohyodeoxycholic in comparison with these two bile salts. Each compound was infused intravenously, at a rate increased in a stepwise manner from 100 to 300 nmol/min/100 g body wt, in bile salt-depleted bile fistula rats. The three bile salts appeared rapidly starting with the infusion and increased to represent more than 95% of the total bile salts. No apparent biliary metabolites were formed. All the bile salts caused a dose-dependent increase in bile flow and biliary lipid output. The absolute increase in bile flow was lower in rats infused with taurohyodeoxycholic acid, yet the volume of bile formed per nanomole of secreted bile salt was 13.8 nl for taurohyodeoxycholic, 6.4 nl for tauroursodeoxycholic acid, and 10.9 nl for taurocholic. The SRm~, , values were 1080, 3240, and 960 nmol/min/100 g, respectively. At all infusion rates, taurohyodeoxycholic acid caused a greater (P < 0.001) secretion of biliary lecithin compared to the other bile salts. There were no significant differences in the biliary secretion of cholesterol and proteins. Electron microscopy showed the recruitment of vesicles and lamellar bodies around and within bile canaliculi. In conclusion, taurohyodeoxycholic promotes a biliary lecithin secretion greater than expected from physicochemical predictions, representing a novel secretory property with potential pharmacological relevance.
Bile acid synthesis in primary cultures of rat and human hepatocytes
Hepatology, 1998
The regulation of hepatic bile acid formation is incompletely understood. Primary cultures of mammalian hepatocytes offer an opportunity to examine putative regulatory factors in relative isolation. Using rat and human hepatocytes in primary culture, we examined bile acid composition and the expression of the rate-limiting enzyme of formation, cholesterol 7␣-hydroxylase. Control rat hepatocytes showed a declining bile acid production over 4 days, from 156 ؎ 24 ng/mL (67% cholic acid) on day 1 to 55 ؎ 11 ng/mL (55% cholic acid) on day 4. In addition to cholic acid, chenodeoxycholic acid, ␣-muricholic acid, and -muricholic acid were formed. Treatment with triidothyronine (T 3 ) or dexamethasone alone had no significant effect on bile acid production. A combination of T 3 and dexamethasone significantly increased the total bile acid production on day 4 (224 ؎ 54 ng/mL) and resulted in a marked change in composition to 23% cholic acid and 77% non-12␣hydroxylated bile acids. Control rat hepatocytes had a cholesterol 7␣-hydroxylase activity of 3.3 ؎ 0.6 pmol/mg protein/min after 4 days in culture. Cells treated with the combination of dexamethasone and T 3 had an activity of 16.4 ؎ 3.6 pmol/mg protein/min. The cholesterol 7␣hydroxylase messenger RNA (mRNA) levels, determined by solution hybridization after 4 days of culture, showed results similar to those for the activity data; control cells had 5.3 ؎ 0.9 cpm/g total nucleic acids (tNAs). T 3-or dexamethasone-treated cells did not differ from control cells, whereas the combination of T 3 and dexamethasone increased the mRNA levels to 20.6 ؎ 2.8 cpm/g tNAs. In human hepatocytes, isolated from donor liver, bile acid formation increased from 206 ؎ 79 ng/mL on day 2 to 1490 ؎ 594 ng/mL on day 6 and then declined slightly. Cholic acid and chenodeoxycholic acid were formed, constituting about 80% and 20%, respectively. The combined addition of T 3 and dexamethasone had a tendency to Abbreviations: mRNA, messenger RNA; T 3 , triidothyronine; HDL, high-density lipoprotein; LDL, low-density lipoprotein; EDTA, ethylenediaminetetraacetic acid; tNA, total nucleic acids.
Bile acid-induced liver toxicity: Relation to the hydrophobic-hydrophilic balance of bile acids
Medical Hypotheses, 1986
Hypertransaminasemia is a frequent side effect during chenodeoxycholic administration for gallstone dissolution. Evidence suggests that this effect is not mediated by lithocholic acid, the intestinal metabolite of chenodeoxycholic acid, but that toxicity is due to the chenodeoxychol~c acid itself. In vitro cytotoxicity of bile salts is positively proportional to their detergent effect, which is, on the other hand, related to their hydrophobic-hydrophilic balance. We hypothesize that in vivo also liver injury can occur when the liver is perfused by an high proportion of strongly detergent bile salts. The more detergent bile salts are unconjugated or glycine conjugated, while the lesser are taurine conjugated and sulfated. Within each class the following order of decreasing detergent power can be indicated: lithocholic) deoxycholic) chenodeoxycholic > cholic > ursodeoxycholic acid. Besides chronic exogenous administration of chenodeoxycholic or deoxycholic acids, conditions in which the liver is perfused by an high mass of highly detergent bile salts are those characterized by an enhanced intestinal biodegradation of bile salts. These conditions, which are common features of some chronic inflammatory bowel diseases, are frequently associated with liver damage. On the other hand, a normally detergent bile salt pool can become hepatotoxic for liver cells which have already been injured. In this respect, as already reported for increased sulfation, the increased proportion of taurine conjugates and the reduced formation of deoxycholic acid in liver cirrhosis can be regarded as protective mechanisms. Liver toxicity induced by bile salts' detergency can be prevented by favouring tauroconjugation or reducing the intestinal degradation of bile salts or by administering poorly detergent bile salts.
Transport of drugs in isolated hepatocytes the influence of bile salts
Biochemical Pharmacology, 1978
The influence of bile salts on hepatic transport of drugs was studied using isolated hepatocyte suspensions. Upra~e of the organic anions, dibromosulphthalein (DBSP), indcrcyanine green (ICG) and an organic cation, N4-acetyi procainamide ethobromide (APAEB) was measured. Afte; 60 min incubation the amount of DBSP, ICG and APAEB nresent in the cells was 17. 41 and 4.5 ner cent of the added amount respectively. The release of DBSP, ICG and APAEB from the hepatocytes preincubated with the agents under study, after 60 min incubation in fresh medium was 80.5, 12.5 and 48.9 per cent of the amount initially present respectively. The presence of bile canalicular membranes in the isolated hepatocytes was demonstrated by enzymehistochemistry: 5'nucleotidase activity showed sharp branched bands over the cell surface. When bile salts were present in the incubation medium. the cellular content of DBSP, ICG and APAEB was diminished. The taurocholate concentration which caused 50 per cent of the maximal effect was 0.07mM. O.lOmM and 0.06mM in experiments with DBSP, ICG and APAEB respectively. Pharmacokinetic analysis revealed that the influence of bile salts on cellular content of the three compounds was due to inhibition of the uptake into the isolated hepatocytes, rather than stimulation of release from the cells. The hypothesis, that stimulation of biliary output of organic anions in viw is due to a modifying effect of bile salts on the canalicular membranes. instead of being the result of the increased bile flow, is not supported by this study.
Taurine increases bile acid pool size and reduces bile saturation index in the hamster
Journal of lipid research, 1987
There is evidence that increased availability of taurine enhances the proportion of taurine-conjugated bile acids in bile. To explore the possibility that taurine treatment could also influence hepatic cholesterol and bile acid metabolism, we fed female hamsters for 1 week and measured both the biliary lipid content and the microsomal level of the rate-limiting enzymes of cholesterol and bile acid synthesis. In these animals the cholesterol 7 alpha-hydroxylase activity was significantly greater in respect to controls (P less than 0.05). The total HMG-CoA reductase activity, as well as that of the active form, was similarly increased. The stimulation of 7 alpha-hydroxycholesterol synthesis was associated with an expansion of the bile acid pool size in taurine-fed animals. Taurine feeding was observed to induce an increase in bile flow as well as in the rate of excretion of bile acids, whereas the secretion rate of cholesterol in bile was decreased. As a consequence, the saturation in...
The effect of taurine depletion with guanidinoethanesulfonate on bile acid metabolism in the rat
Life Sciences, 1985
~dministration of guanidinoethanesulfonate (GES) to male rats for 5 weeks resulted in a 90% decrease in the hepatic taurine concentration. This depletion of hepatic taurine was associated with a 570% increase in the concentration of glycine-conjugated bile acids, a 30 % decrease in the concentration of taurine-conjugated bile acids, and an increase in the ratio of glycine-to taurine-conjugated bile acids from 0.046 to 0.45. The total concentration of bile salts in the bile and the turnover of cholic acid were not affected by administration of GE~ The data indicate that the taurine-depleted rat conserves taurine to some extent by using glycine instead of taurine for bile salt synthesis but not by decreasing the daily fractional turnover of bile acids.