Biliary Bile Acid Secretion Research Articles

In liver transplantation, T tube bile represents total bile flow: physiological and scintigraphic studies on biliary secretion of organic anions.

The present study was performed to clarify the recovery of hepatocellular uptake and the biliary secretion of bile acids during the first 14 days after orthotopic liver transplantation (OLT) and to determine the fraction of bile flow appearing outside through the T tube and entering the duodenum. Therefore, we determined primary and secondary bile acids in bile samples obtained from the T tube at day 5 after OLT, while the T tube was permanently open, and at days 10 and 14 after OLT, i.e., 4 and 9 days after closure of the T tube, respectively, thus restoring enterohepatic bile acid circulation. In addition, we performed hepatobiliary scintigraphy using technetium 99m-labeled [2,4,6 trimethyl-3-bromo]imino-diacetic acid (technetium 99m-BRIDA) in 12 patients between days 4 and 17 after OLT. Chromatographic analyses of biliary bile acids showed no secondary bile acids during the first 5 days after OLT, as opposed to 10 and 14 days after OLT when enterohepatic circulation was restored. Eleven patients with an uncomplicated postoperative course after OLT showed a significantly reduced hepatic uptake and biliary secretion of 99mTc-BRIDA during the first days after OLT with progressive recovery. One patient with an acute allograft rejection episode showed almost no uptake and only minimal secretion. The bile fraction appearing outside through the inserted T tube represented 94.6% +/- 6.2% of the injected 99mTc-BRIDA. We conclude that OLT results in markedly impaired hepatocellular uptake and biliary secretion of organic anions. Simultaneously, bile acid synthesis is significantly reduced, which, in addition, diminishes bile secretion of the graft. We show that T tube bile is a valid tool for bile physiological studies in patients in whom transplantation was successfully performed.

Influence of cholestasis on absorption of ursodeoxycholic acid.

Ursodeoxycholic acid (UDCA) has beneficial effects in cholestatic liver diseases. Absorption of UDCA is slow and incomplete. In the present study the effect of cholestasis on absorption was evaluated in 10 patients with pancreatic carcinoma and extrahepatic biliary drainage. At days 3 and 10 after insertion of the biliary drain, all patients received 750 mg UDCA in three divided doses. On both occasions intestinal absorption of UDCA was determined to evaluate the influence of cholestasis. Serum bilirubin was used as indicator of cholestasis. Biliary output of UDCA served as measure of absorption and was determined by gas-liquid chromatography. At days 4 and 11 bile consisted of less than 2% of UDCA, indicating that UDCA excretion was complete within 24 hr and no accumulation of UDCA had occurred. After insertion of the drain, serum bilirubin decreased from 12.2 +/- 2.4 mg/dl at day 3 to 5.4 +/- 0.9 mg/dl at day 10. Biliary secretion of bile acids increased from 2.0 +/- 0.3 to 3.1 +/- 0.4 mmol/day, whereas percentage of ursodeoxycholic acid in bile did not significantly increase (41.1% vs 42.1%). Absorption of UDCA increased from 39.8 +/- 5.0% to 61.1 +/- 6.2% of the administered dose, indicating an improvement of the absorption rate after decrease of cholestasis by 53.65% (P < 0.05). In conclusion, in severe cholestasis absorption of orally administered UDCA is markedly reduced. This may have implications in the treatment of patients with cholestatic disease.

Effect of phloracetophenone on bile flow and biliary lipids in rats

Phloracetophenone is the aglycone part of phloracetophenone glucoside, a naturally-occurring compound from the indigenous plant, Curcuma comosa. The glucoside has previously been identified as the choleretic principle of the plant. In the present study, the effects of synthetic phloracetophenone (2,4,6-trihydroxyacetophenone (THA)) on bile flow and biliary lipid secretion were investigated in male rats, using a bile fistula. A single intraduodenal administration of THA at doses of 10–150 mg kg −1 induced a dose-dependent increase in bile flow rate. The increase in bile flow was associated with increased biliary secretion of bile acid, decreased secretion of cholesterol and phospholipid, and lowered bile lithogenic index. THA at a dose of 100 mg kg b.w. −1 induced a maximal increase of bile flow rate (up to 233.8±6.5% of pre-THA control) and bile acid output (up to 293.4±15.2% of pre-THA control). The stimulation of bile secretion by THA was due to an increase in both bile acid-dependent and bile acid-independent flow. A considerable decrease in plasma cholesterol was also observed, which was attributed to the great choleretic activity with enhancement of biliary bile acid secretion. These findings suggest that THA may have potential for development as a therapeutic agent for treatment of cholestasis, dissolving gallstones, and reducing plasma cholesterol.

A validated technique for the analysis of biliary bile acid secretion in donor livers prior to transplantation.

Many parameters currently used for the pre-transplant assessment of liver allografts, are not reliable enough in predicting the likelihood of early graft dysfunction or non-function. It is generally accepted that bile secretion is a sign of hepatic function post-transplant and that bile flow shows a close linear relationship to the secretion of bile acids ("apparent choleretic activity"). We have studied bile flow, biliary bile acid concentrations and composition and measured apparent choleretic activity from hepatic bile collected with a new technique under controlled conditions at the time of retrieval from 18 donor livers. More than three samples were collected from each of 13 donors and a total of 65 samples of hepatic bile were analysed. Of these, ten showed typical apparent choleretic activity with a positive slope in the regression line analysis (correlation coefficient of 0.9), validating our collection technique.

Liver transplantation and bile analysis: a parallel evolution.

Liver transplantation and bile analysis: a parallel evolution.

A validated technique for the analysis of biliary bile acid secretion in donor livers prior to transplantation

Abstract Many parameters currently used for the pre-transplant assessment of liver allografts, are not reliable enough in predicting the likelihood of early graft dysfunction or non-function. It is generally accepted that bile secretion is a sign of hepatic function post-transplant and that bile flow shows a close linear relationship to the secretion of bile acids (“apparent choleretic activity”). We have studied bile flow, biliary bile acid concentrations and composition and measured apparent choleretic activity from hepatic bile collected with a new technique under controlled conditions at the time of retrieval from 18 donor livers. More than three samples were collected from each of 13 donors and a total of 65 samples of hepatic bile were analysed. Of these, ten showed typical apparent choleretic activity with a positive slope in the regression line analysis (correlation coefficient of 0.9), validating our collection technique.

Impaired absorption of cholesterol and bile acids in patients with an ileoanal anastomosis

Background—No data exist on cholesterol absorption in patients with an ileoanal anastomosis (IAA).Aims—To study cholesterol absorption and its effects on cholesterol and bile acid metabolism in patients with an IAA.Patients...

Effect of maternal cholestasis on biliary lipid and bile acid secretion in the infant rat

Partial and reversible impairment of bile formation has been reported to occur in the offspring of rats undergoing common bile duct ligation during the last third of pregnancy. This situation was defined as latent cholestasis of the neonate and was suggested to be related to the multilamellar bodies partially occupying the canalicular lumen. The current study was undertaken to investigate the presence of alterations in the secretion of biliary lipids in these infant rats. Using both high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) analyses, no changes caused by maternal cholestasis were found in either the conjugation pattern, or in the ratio of primary to secondary major bile acids in bile samples collected from 4-week-old and 8-week-old rats. However, a decrease in the proportion of cholate together with an increase in the amount of alpha- and omega-muricholate were found at 4 weeks of age. These changes were different from those observed in the pattern of maternal plasma bile acids, in which beta-, but not alpha-muricholate, concentrations were increased. Moreover, studies performed by labeling the bile acid pool of the cholestatic mother-fetus tandem with [14C]glycocholic acid (GC) at day 16 of pregnancy indicated that only a minor proportion (approximately 10%) of bile acids found in 4-week-old pups was of maternal origin. Changes in the bile acid pool composition were fully reversed by 8 weeks of age. Bile lecithin and cholesterol output were determined by enzymatic techniques, both under basal conditions and during stepwise taurocholate (TC) infusion. At the time when multilamellar bodies were found, i.e., 4 weeks after birth, no change in either nonstimulated or TC-induced cholesterol output was observed. By contrast, both spontaneous and TC-induced lecithin secretion were markedly higher (+200%) in pups of cholestatic mothers as compared with control rats. These differences were abolished at 8 weeks of age. At this time, cholesterol output was significantly lower than that found in younger animals. This reduction was more pronounced in the control than in the cholestatic group. Histological examination of liver samples collected from the cholestatic group at 4 weeks of age revealed the presence of multilamellar bodies not only in the canalicular lumen but also within vesicular structures located in the pericanalicular area or near the Golgi apparatus. Both intracellular and intracanalicular bodies were present before and after TC infusion for 2 hours. These results indicate that maternal cholestasis in rats induces profound alterations in biliary lipids and bile acid secretion in their pups. Because bile acids are important activators of different steps responsible for biliary lipid secretion (intracellular trafficking, releasing into bile, and solubilization), alterations in maternal bile acid pool size and composition may affect the fetal development of biliary lipid secretion mechanisms, which may result in the appearance of multilamellar bodies within bile canaliculi, which in turn may be involved in the reversible latent cholestasis observed in these infants rats. (Hepatology 1997 Sep;26(3):527-36)

Effect of maternal cholestasis on biliary lipid and bile acid secretion in the infant rat.

Partial and reversible impairment of bile formation has been reported to occur in the offspring of rats undergoing common bile duct ligation during the last third of pregnancy. This situation was defined as latent cholestasis of the neonate and was suggested to be related to the multilamellar bodies partially occupying the canalicular lumen. The current study was undertaken to investigate the presence of alterations in the secretion of biliary lipids in these infant rats. Using both high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) analyses, no changes caused by maternal cholestasis were found in either the conjugation pattern, or in the ratio of primary to secondary major bile acids in bile samples collected from 4-week-old and 8-week-old rats. However, a decrease in the proportion of cholate together with an increase in the amount of alpha- and omega-muricholate were found at 4 weeks of age. These changes were different from those observed in the pattern of maternal plasma bile acids, in which beta-, but not alpha-muricholate, concentrations were increased. Moreover, studies performed by labeling the bile acid pool of the cholestatic mother-fetus tandem with [14C]glycocholic acid (GC) at day 16 of pregnancy indicated that only a minor proportion (approximately 10%) of bile acids found in 4-week-old pups was of maternal origin. Changes in the bile acid pool composition were fully reversed by 8 weeks of age. Bile lecithin and cholesterol output were determined by enzymatic techniques, both under basal conditions and during stepwise taurocholate (TC) infusion. At the time when multilamellar bodies were found, i.e., 4 weeks after birth, no change in either nonstimulated or TC-induced cholesterol output was observed. By contrast, both spontaneous and TC-induced lecithin secretion were markedly higher (+200%) in pups of cholestatic mothers as compared with control rats. These differences were abolished at 8 weeks of age. At this time, cholesterol output was significantly lower than that found in younger animals. This reduction was more pronounced in the control than in the cholestatic group. Histological examination of liver samples collected from the cholestatic group at 4 weeks of age revealed the presence of multilamellar bodies not only in the canalicular lumen but also within vesicular structures located in the pericanalicular area or near the Golgi apparatus. Both intracellular and intracanalicular bodies were present before and after TC infusion for 2 hours. These results indicate that maternal cholestasis in rats induces profound alterations in biliary lipids and bile acid secretion in their pups. Because bile acids are important activators of different steps responsible for biliary lipid secretion (intracellular trafficking, releasing into bile, and solubilization), alterations in maternal bile acid pool size and composition may affect the fetal development of biliary lipid secretion mechanisms, which may result in the appearance of multilamellar bodies within bile canaliculi, which in turn may be involved in the reversible latent cholestasis observed in these infants rats.

Expression and therapeutic response related to apolipoprotein E polymorphism in primary biliary cirrhosis

Background/Aims/Methods: Apolipoprotein E polymorphism, affecting intestinal absorption and biliary secretion of bile acids, might also contribute to the variable course and response to drug treatment of primary biliary cirrhosis. To test this possibility, we studied the apo E gene frequency, and the expression and response to drug therapy in different apo E isoforms of 88 patients with primary biliary cirrhosis, randomized to ursodeoxycholic acid, colchicine or placebo treatments for 2 years.Results: The frequency of the ε2 allele was 2.4 times higher (p<0.01) in the patients with primary biliary cirrhosis compared with the Finnish population. At entry the patients with the ε4 allele were significantly younger (p<0.01) than those with other ε alleles, while the severity of primary biliary cirrhosis was similar in the three apolipoprotein E phenotypes. Liver enzymes, acute hepatic inflammation, serum total and low density lipoprotein cholesterol were decreased by ursodeoxycholic acid only in the patients with the ε4 and homozygous ε3 alleles, but not in those with the ε2 allele. Improvements of liver enzyme tests by ursodeoxycholic acid were more marked in the patients with the ε4 than other ε alleles.Conclusions: The present data show that in primary biliary cirrhosis the ε2 allele is overrepresented, and suggest that the expression of primary biliary cirrhosis and response of the disease to ursodeoxycholic acid treatment are closely related to the apo E polymorphism.

Effect of ileal autotransplantation on cholesterol, bile acids, and biliary lipids in pigs with proximal small bowel resection

Our major aim was to investigate the consequences of ileal autotransplantation in pigs with proximal small intestinal resection on biliary lipids and metabolism of bile acids. Biliary lipid secretion rates and bile acid absorption were assessed by measuring dietary and biliary lipids, fractional cholesterol absorption, and fecal excretion of cholesterol and bile acids. In addition, serum bile acids and cholesterol, biliary and fecal bile acid species, and ileal villus height were determined after resection of the proximal 75% of the jejunoileum (n = 15) and autotransplantation of the remaining ileum with systemic venous drainage (n = 15) or transection (n = 5). Autotransplantation further increased fecal excretion of neutral and acidic steroids and serum concentration of bile acids after proximal resection (P < .05 for all); autotransplantation significantly decreased serum cholesterol, ileal villus height, fractional bile acid and cholesterol absorption, and biliary molar percentage of total and primary bile acids, whereas biliary secretion of bile acids, enriched by secondary bile acids, and cholesterol remained unchanged. At 14 weeks, ileal villus height, fractional bile acid and cholesterol absorption, biliary molar percentage of bile acids, and proportion of secondary biliary bile acids were altered by transplantation from the respective postresection values of 864 +/- 22 microm, 97.9 +/- 0.6%, 26.9 +/- 3.9%, 91.8 +/- 1.2% and 9.2 +/- 1.3% to 428 +/- 21 microm, 91.1 +/- 1.5%, 9.5 +/- 1.1%, 83.9 +/- 1.4% and 52.5 +/- 3.5% (P < .005 for all). Posttransplantation biliary bile acid secretion correlated positively with fractional reabsorption (r = .70) and biliary molar percentage (r = .73) of bile acids and ileal villus height (r = .65; P < .01 for all). Decreased absorption efficiency and biliary molar percentage of bile acids, increased biliary secondary bile acids, and short ileal villi point to bacterial overgrowth-induced bile acid malabsorption, which with decreased absorptive area may contribute to malabsorption of other lipids after ileal autotransplantation. Compensatory increase in cholesterol synthesis in the pigs with autotransplanted ileum appeared sufficient for constant biliary secretion of cholesterol and bile acids.

Bile acid metabolism in young-old parabiotic rats.

Serum cholesterol, triglyceride and phospholipid levels, liver cholesterol concentration, bile flow, biliary cholesterol, phospholipid and bile acid secretion rates, fecal sterol and bile acid levels and their bile acid compositions were examined in young-old parabiotic rats and compared with those in young and old control rats and young-young parabiotic rats. Bile acid composition was expressed in terms of the cholic acid group/chenodeoxycholic acid group (CA/CDCA) ratio. Body weight (BW) gain decreased after parabiosis especially in old rats, but the liver weight (g/100 g BW), diet-intake, feces dry weight, liver cholesterol concentration and fecal sterol level were almost the same in all the groups. The biliary bile acid secretion rate was higher and the fecal bile acid level was lower in old rats than those in young rats but both the levels became comparable with those in young rats after parabiosis of old rats with young rats. Young rats, however, showed no changes in these levels after parabiosis. The serum cholesterol level and the biliary and fecal CA/CDCA ratios in old rats were higher than those in young rats but decreased after parabiosis with young rats, although they were still higher than those in young rats. The serum cholesterol level in young rats increased after parabiosis with old rats, but not after parabiosis with young rats, and the fecal bile acid level and the CA/CDCA ratio were not changed in either case. It is concluded from these findings that the serum cholesterol level and the CA/CDCA ratio increased with age and that these increases were prevented after parabiosis with young rats while young rats, although their serum cholesterol level was increased, showed no increase in the CA/CDCA ratio after parabiosis with old rats.

Reduced cholesterol absorption in hamsters by crilvastatin, a new 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor

Crilvastatin, a new drug from the pyrrolidone family, has been previously shown to inhibit the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase, in vitro and in vivo, to reduce the absorption of dietary cholesterol and to stimulate the activity of cholesterol 7α-hydroxylase in the rat. The aim of this study was to evaluate the effects of crilvastatin on cholesterol and bile acid metabolism in the hamster. In hamsters fed on a lithogenic diet for 8 weeks, crilvastatin treatment (200 mg/day per kg body weight) did not change plasma lipid levels, failed to improve bile parameters and did not prevent gallstone formation. In hamsters fed on a basal cholesterol-rich (0.2%) diet for 8 weeks, crilvastatin at the same dose reduced the cholesterol level in the plasma by 20%, with a decrease of both low-density and high-density lipoprotein cholesterol. The drug did not significantly stimulate the biliary secretion of bile acids but significantly decreased the activity of acyl coenzyme A:cholesterol acyltransferase in the small intestine by 64%. This effect was enhanced when cholestyramine, a bile acid-sequestering resin, was given in combination with crilvastatin. Crilvastatin alone did not change the activity of cholesterol 7α-hydroxylase in the liver, despite the marked reduction in both hepatic cholesterogenesis and intestinal absorption of dietary cholesterol (the absorption coefficient was 44±2% in treated hamsters vs. 61±7% in controls).

Biliary secretion of anionic polypeptide fraction is not coupled to that of phospholipids and cholesterol in rats.

Anionic polypeptide fraction (APF) is a phospholipid- and calcium-binding apoprotein present in animal and human bile, predominantly associated with cholesterol-phospholipid vesicles. In bile, the protein may play a physiological role in preventing precipitation of calcium salts. APF has also been suggested to be of regulatory importance in the process of biliary lipid secretion. The aim of the present study was to investigate whether the secretion rates of APF and that of biliary lipids are coupled, which would support a physiological role of APF in biliary lipid secretion. Biliary secretion rates of bile acids, phospholipids, and cholesterol were experimentally modulated in three different rat models. Secretion rates of APF were compared with that of bile acids, lipids, and with that of two other biliary proteins, the lysosomal protein beta-glucuronidase and apolipoprotein A-I (apo A-I). Model 1: diurnal variation in bile formation during chronic bile diversion; model 2: specific inhibition of biliary phospholipid and cholesterol, but not of bile acid secretion by infusion of the organic anion, sulfated lithocholyltaurine; model 3: acute interruption of the enterohepatic circulation in unanesthetized rats. The diurnal variation in bile formation involved a parallel increase of the biliary secretion rates of bile acids (+56 +/- 7%, mean +/- SD), phospholipids (+53 +/- 29%), cholesterol (+73 +/- 54%), and APF (+72 +/- 86%) during the night phase of the cycle. Infusion of sulfated lithocholyltaurine inhibited biliary phospholipid and cholesterol secretion (-78 +/- 15%, and -54 +/- 25%, respectively), but did not affect biliary bile acid or APF secretion rate (-19 +/- 14%, and +12 +/- 107%, respectively). Within 4 hours after interruption of the enterohepatic circulation, bile secretion rates for bile acids (-92 +/- 3%), phospholipids (-74 +/- 13%), cholesterol (-64 +/- 8%), and APF (-58 +/- 24%) rapidly declined to a new steady-state level. Correlation analysis using the data from the three experimental models indicated that the biliary secretion rate of APF was independent from that of phospholipids, cholesterol, beta-glucuronidase, and, presumably, apolipoprotein A-I, and positively correlated to bile acid secretion rate and bile flow. The data from three experimental models indicate that the biliary secretion rates of APF and of phospholipids/cholesterol are not coupled and, therefore, do not support a direct physiological role of APF secretion in biliary lipid secretion. APF secretion into bile may, at least partially, be controlled by biliary bile acid secretion.

Biliary secretion of anionic polypeptide fraction is not coupled to that of phospholipids and cholesterol in rats

Anionic polypeptide fraction (APF) is a phospholipid- and calcium-binding apoprotein present in animal and human bile, predominantly associated with cholesterol-phospholipid vesicles. In bile, the protein may play a physiological role in preventing precipitation of calcium salts. APF has also been suggested to be of regulatory importance in the process of biliary lipid secretion. The aim of the present study was to investigate whether the secretion rates of APF and that of biliary lipids are coupled, which would support a physiological role of APF in biliary lipid secretion. Biliary secretion rates of bile acids, phospholipids, and cholesterol were experimentally modulated in three different rat models. Secretion rates of APF were compared with that of bile acids, lipids, and with that of two other biliary proteins, the lysosomal protein β-glucuronidase and apolipoprotein A-I (apo A-I). Model 1: diurnal variation in bile formation during chronic bile diversion; model 2: specific inhibition of biliary phospholipid and cholesterol, but not of bile acid secretion by infusion of the organic anion, sulfated lithocholyltaurine; model 3: acute interruption of the enterohepatic circulation in unanesthetized rats. The diurnal variation in bile formation involved a parallel increase of the biliary secretion rates of bile acids (+56 +/- 7%, mean +/- SD), phospholipids (+53 +/- 29%), cholesterol (+73 +/- 54%), and APF (+72 +/- 86%) during the night phase of the cycle. Infusion of sulfated lithocholyltaurine inhibited biliary phospholipid and cholesterol secretion (-78 +/- 15%, and -54 +/- 25%, respectively), but did not affect biliary bile acid or APF secretion rate (-19 +/- 14%, and +12 +/- 107%, respectively). Within 4 hours after interruption of the enterohepatic circulation, bile secretion rates for bile acids (-92 +/- 3%), phospholipids (-74 +/- 13%), cholesterol (-64 +/- 8%), and APF (-58 +/- 24%) rapidly declined to a new steady-state level. Correlation analysis using the data from the three experimental models indicated that the biliary secretion rate of APF was independent from that of phospholipids, cholesterol, β-glucuronidase, and, presumably, apolipoprotein A-I, and positively correlated to bile acid secretion rate and bile flow. The data from three experimental models indicate that the biliary secretion rates of APF and of phospholipids/cholesterol are not coupled and, therefore, do not support a direct physiological role of APF secretion in biliary lipid secretion. APF secretion into bile may, at least partially, be controlled by biliary bile acid secretion.(Hepatology 1997 Jan;25(1):38-47)

Changes in biliary lipid output after interruption of pravastatin treatment in humans

The use of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (e.g. pravastatin) has gradually increased in the treatment of hypercholesterolaemia. By inhibiting HMG-CoA reductase (the rate-limiting enzyme in cholesterol synthesis) activity, cholesterol synthesis in the liver is reduced and the plasma level of cholesterol, especially low-density lipoprotein (LDL)-cholesterol, is substantially lowered. Simultaneously, inhibition of HMG CoA reductase activity is associated with increased synthesis and accumulation of larger amounts of HMG CoA reductase enzyme protein. The main purpose of this study was to determine if the cessation of pravastatin treatment causes a rapid increase in the synthesis and biliary secretion of cholesterol, a condition which might lead to a temporarily increased cholesterol saturation of bile. Nine patients undergoing surgery for stones in the common bile duct were fitted with T-tubes in the common bile duct peroperatively; the side arm of the T-tube was left open postoperatively, creating a biliary fistula. All patients were given 6 days' treatment with pravastatin (20 mg b.i.d.) following the operation. Bile was collected from the T-tube, in 12-h fractions during this period and for another 3 days after termination of the treatment. Plasma levels of lipoproteins and lathosterol--reflecting cholesterol synthesis--were determined on several occasions. After cessation of pravastatin treatment, the plasma levels of total cholesterol and LDL-cholesterol increased by 21% and 33% respectively. High-density lipoprotein (HDL)-cholesterol did not change. The plasma level of lathosterol was increased two- to fourfold. Outputs of bile acids and phospholipids were significantly increased (23% and 10% respectively) after termination of treatment, whereas the output of cholesterol was not significantly changed. Cholesterol saturation was reduced by 20%, from 175 +/- 37% to 140 +/- 19%, but this change was not significant. The results indicate that, with the present experimental model (biliary diversion), the synthesis and biliary secretion of bile acids seem to be largely dependent on the de novo synthesis of cholesterol in the liver, whereas the biliary output of cholesterol is not.

Retrograde injections of formaldehyde into the biliary tree induce alterations of biliary epithelial function in rats

Formaldehyde may induce severe lesions of intrahepatic and extrahepatic bile ducts. The purpose of this study was to examine in vivo the functional consequences of an alteration of the biliary epithelium induced by a retrograde intrabiliary injection of formaldehyde in rats. After basal bile collection, a 10% formaldehyde solution was injected into the biliary tree of anesthetized rats, and the cannula was occluded for 30 minutes. Choleresis was then reestablished, and bile flow, bile acid, and bicarbonate secretion were measured both spontaneously and during ursodeoxycholate infusions. Formaldehyde injections induced a significant increase in bile flow and a marked inhibition of ursodeoxycholate-induced increase in biliary bicarbonate concentration and secretion. Biliary glucose secretion, which is normally very low, was increased about 20-fold in animals injected with formaldehyde. Histological and ultrastructural examination of the liver showed alterations of biliary epithelial cells, whereas hepatocytes, bile canaliculi, and canalicular tight junctions remained normal. Hepatocytic excretory function, as assessed by biliary secretion of bile acids, was not affected. It was concluded that short-term formaldehyde intrabiliary injections cause an inhibition of ursodeoxycholate-induced hypersecretion of bicarbonate, an increase in biliary glucose secretion, and selective structural alterations of biliary epithelial cells. These results suggest that formaldehyde retrograde biliary injection may be a useful model to study alterations of biliary epithelial function in vivo. (Hepatology 1996 Nov;24(5):1217-23)

Retrograde Injections of Formaldehyde Into the Biliary Tree Induce Alterations of Biliary Epithelial Function in Rats

Formaldehyde may induce severe lesions of intrahepatic and extrahepatic bile ducts. The purpose of this study was to examine in vivo the functional consequences of an alteration of the biliary epithelium induced by a retrograde intrabiliary injection of formaldehyde in rats. After basal bile collection, a 10% formaldehyde solution was injected into the biliary tree of anesthetized rats, and the cannula was occluded for 30 minutes. Choleresis was then reestablished, and bile flow, bile acid, and bicarbonate secretion were measured both spontaneously and during ursodeoxycholate infusions. Formaldehyde injections induced a significant increase in bile flow and a marked inhibition of ursodeoxycholate–induced increase in biliary bicarbonate concentration and secretion. Biliary glucose secretion, which is normally very low, was increased about 20–fold in animals injected with formaldehyde. Histological and ultrastructural examination of the liver showed alterations of biliary epithelial cells, whereas hepatocytes, bile canaliculi, and canalicular tight junctions remained normal. Hepatocytic excretory function, as assessed by biliary secretion of bile acids, was not affected. It was concluded that short–term formaldehyde intrabiliary injections cause an inhibition of ursodeoxycholate–induced hypersecretion of bicarbonate, an increase in biliary glucose secretion, and selective structural alterations of biliary epithelial cells. These results suggest that formaldehyde retrograde biliary injection may be a useful model to study alterations of biliary epithelial function in vivo .

Current concepts of hepatic uptake, intracellular transport and biliary secretion of bile acids: physiological basis and pathophysiological changes in cholestatic liver dysfunction.

Hepatic sinusoidal uptake of bile acids is mediated by defined carrier proteins against unfavourable concentration and electrical gradients. Putative carrier proteins have been identified using bile acid photoaffinity labels and more recently using immunological probes, such as monoclonal antibodies. At the sinusoidal domain, proteins with molecular weights of 49 and 54 kDa have been shown to be carriers for bile acid transport. The 49 kDa protein has been associated with the Na(+)-dependent uptake of conjugated bile acids, while the 54 kDa carrier has been involved in the Na(+)-independent bile acid uptake process. Within the hepatocyte, cytosolic proteins, such as the glutathione S-transferase (also designated the Y protein), the Y binders and the fatty acid binding proteins, are able to bind bile acids and possibly facilitate their movement to the canalicular domain. At the canalicular domain a 100 kDa carrier protein has been isolated and it has been shown by several laboratories that this particular protein is concerned with canalicular bile acid transport. The system is ATP-dependent and follows Michaelis-Menten kinetics. Interference with bile acid transport has been demonstrated by several chemicals. The mechanisms by which these chemicals inhibit bile acid transport may explain the apparent cholestatic properties observed in patients and experimental animals treated with these agents. Several studies have shown that Na+/K(+)-ATPase activity is markedly decreased in cholestasis induced by ethinyloestradiol, taurolithocholate and chlorpromazine. However, other types of interference have been described and the cholestatic effects may be the result of several mechanisms. Cholestasis is associated with several adaptive changes that may be responsible for the accumulation of bile acids and other cholephilic compounds in the blood of these patients. It may be speculated that the nature of these changes is to protect liver parenchymal cells from an accumulation of bile acids to toxic levels. However, more detailed quantitative experiments are necessary to answer questions with regard to the significance of these changes and the effect of various hepatobiliary disorders in modifying these mechanisms. It is expected that the mechanisms by which bile acid transport is regulated and efforts to understand the molecular basis for these processes will be among the areas of future research.

Structural and Functional Alterations of Hepatocytes during Transient Phalloidin-Induced Cholestasis in the Rat

To study the relationship between the dynamic actin web and bile secretion, we developed an acute model of cholestasis, using phalloidin, and examined sequential morphologic and biochemical events in rat liver. Biliary function (bile flow, bile, and canalicular membrane components) and cellular integrity (release of hepatic enzymes in serum and bile, canalicular structure, and microfilaments distribution) in rats given a single iv dose of phalloidin (0.8 mg/kg body weight) were assessed at 15, 45, and 90 min, 24 hr, and 5 days postinjection. Bile flow decreased significantly at 45 and 90 min, but cholestasis was transient since bile secretion returned to control levels at 24 hr. The biliary bile acid secretion rate was not modified during the same time period, indicating that cholestasis may have been due to impairment of the bile acid independent component of bile flow. Serum alanine aminotransferase and lactate dehydrogenase as well as biliary alkaline phosphatase and alkaline phosphodiesterase-1 activities were not altered by phalloidin treatment. These data, coupled with morphologic studies, provide no evidence of cell damage. Electron microscopy revealed that the pericanalicular actin web in both centrilobular and periportal hepatocytes was increased at 90 min and further enlarged at 24 hr and 5 days after phalloidin injection. At all time periods, the canalicular structure was well preserved. Na+K+–ATPase and Mg2+–ATPase activities in membrane fractions enriched in bile canalicular complexes decreased significantly at 15 min and remained low up to Day 5. Mg2+–ATPase activity returned to control levels by Day 5. The lipid constituents of liver cell membranes enriched in canalicular complexes showed no significant variations 90 min after toxin treatment but, at 24 hr, phospholipid content rose and membrane fluidity increased. These results clearly indicate that the bile flow variation after a single low dose of phalloidin can be dissociated from specific pericanalicular microfilament distribution, lending further support to the view that normal biliary function is not strictly dependent on the integrity of the actin filament network.