Biliary Bile Acid Output Research Articles

In Vivo Biliary Function in the Adult Rat: The Effect of Parenteral Glucose and Amino Acids

Parenteral glucose and glucose-amino acid mixtures are used in the nutritional support of infants, children, and adults when enteral feedings are precluded for any reason. During the first week of such nutritional support, the total energy intakes are generally low and glucose and electrolytes are the only nutrients provided. To assess the effects of such "hypocaloric" regimens, we determined the hepatic responses to parenteral infusions of either glucose or glucose-amino acid mixtures in rats. Further, to illustrate the magnitude of these changes in comparison to normally fed animals, we included a group of sham-operated, chow-fed rats. Bile flow, biliary bile acid output, bile osmolarity, serum bile acids, and plasma amino acids were measured in adult rats following 5 days of the respective dietary regimens. Liver histology was also assessed. Bile acid output, but not bile flow, was significantly decreased by the infusion of glucose compared to glucose-amino acid mixtures. However, in comparison to the chow-fed rats, bile acid output was significantly reduced in both groups of parenterally fed animals, whereas bile flow was significantly reduced only in the glucose-infused animals. Plasma amino acids were markedly different between the groups; concentrations of essential amino acids were greater in the glucose-amino acid infused animals than in the glucose infused animals. Nonessential gluconeogenic amino acids were significantly higher in the glucose-infused animals compared to the other groups; plasma valine was significantly lower in the glucose-infused animals reflecting the lack of protein intake. Liver histology was markedly abnormal in all of the glucose-infused animals, whereas only half the glucose-amino acid infused animals had abnormal pathology.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of bilirubin on biliary lipid secretion: analysis by horseradish peroxidase associated intrahepatic vesicular transport system.

The mechanism of biliary lipid secretion is still controversial and there is no definite information regarding how bilirubin inhibits biliary phospholipid and cholesterol secretions without affecting bile salt secretion. In this study, the effects of bilirubin on intrahepatic vesicular transport and biliary lipid secretion were examined using bile-fistula rats. Horseradish peroxidase (HRP) was used as a tracer of intrahepatic vesicular transport. Bilirubin (5 mg/100 g BW) and/or HRP (5 mg/100 gBW) were injected through the mesenteric vein. Bile flow, biliary bile acid, biliary phospholipid and cholesterol outputs were examined in saline, HRP and HRP + bilirubin groups, respectively. Bile flow and biliary bile acid output were not affected by bilirubin administration. Biliary phospholipid and cholesterol as well as biliary HRP outputs were inhibited just after bilirubin administration, 42.8 +/- 6.1 SD% 47.7 +/- 5.1 SD%, and 33.4 +/- 3.8 SD%, respectively. These results suggested the participation of intrahepatic vesicular transport system in the inhibition of biliary lipid secretion by bilirubin and in its secretory mechanism.

INFLUENCE OF BILE ACIDS ON THE BILIARY TRANSPORT MAXIMUM OF PHENOLSULPHONPHTHALEIN IN THE RAT

1. The effect of changes in bile acid secretion induced by cholestyramine treatment or taurocholate infusion on the biliary transport maximum (Tm) of phenolsulfonphthalein (PSP) was studied in Wistar rats. 2. Five hours after oral administration of cholestyramine (1.5 g/kg bodyweight) the biliary output of bile acids decreased to 51% and bile flow to 76% of control values. The percentage of conjugated and unconjugated PSP excreted into bile and the Tm of the dye were not significantly modified by cholestyramine pretreatment. 3. Administration of sodium taurocholate at increasing rates (60-480 nmol/100 g bodyweight per min) enhanced bile flow and the biliary output of bile acids in a linear dose-related fashion. The Tm of PSP increased progressively until a maximum of 29% above the control values was reached at a taurocholate dose of 240 nmol/100 g bodyweight per min). The enhancement corresponded mainly to the unconjugated dye, the excretion of conjugated PSP not being significantly modified by the infusion of the bile acid. 4. The results indicate that bile acids can influence to some extent biliary excretion of PSP in the rat, although this component is of minor importance at low bile acid secretory rates.

Separate transport systems for biliary secretion of sulfated and unsulfated bile acids in the rat.

Biliary secretion of 3 alpha-sulfated bile acids has been studied in Wistar rats with an autosomal recessive defect in the hepatic transport of bilirubin. Liver function, established by measurement of various enzymes in plasma, by enzyme histochemical methods, and by electron microscopy, appeared to be normal in these rats. Serum levels of unconjugated, monoglucuronidated, and diglucuronidated bilirubin were 0.62, 1.62, and 6.16 mumol/liter, respectively, compared with 0.17, 0.08, and 0.02 mumol/liter in control rats. Biliary bilirubin secretion was strongly reduced in the mutant animals: 0.21 +/- 0.03 vs. 0.39 +/- 0.03 nmol/min per 100 g body wt in control rats. Despite normal biliary bile acid output, bile flow was markedly impaired in the mutant animals, due to a 53% reduction of the bile acid-independent fraction of bile flow. The transport maximum for biliary secretion of dibromosulphthalein (DBSP) was also drastically reduced (-53%). Biliary secretion of intravenously administered trace amounts of the 3 alpha-sulfate esters of 14C-labeled taurocholic acid (-14%), taurochenodeoxycholic acid (-39%), taurolithocholic acid (-73%), and glycolithocholic acid (-91%) was impaired in the jaundiced rats compared with controls, in contrast to the biliary secretion of the unsulfated parent compounds. Hepatic uptake of sulfated glycolithocholic acid was not affected in the jaundiced animals. Preadministration of DBSP (15 mumol/100 g body wt) to normal Wistar rats significantly impaired the biliary secretion of sulfated glycolithocholic acid, but did not affect taurocholic acid secretion. We conclude that separate transport systems in the rat liver exist for biliary secretion of sulfated and unsulfated bile acids; the sulfates probably share secretory pathways with the organic anions bilirubin and DBSP. The described genetic defect in hepatic transport function is associated with a reduced capacity to secrete sulfated bile acids into bile; this becomes more pronounced with a decreasing number of hydroxyl groups on the sulfated bile acid's molecule.

Triton WR-1339-induced changes in serum lipids and biliary lipid secretion.

Biliary lipid secretion rates were measured in fed rats after an intravenous injection of Triton WR-1339 (TWR, 60 mg/100 g body wt), an agent that inhibits lipoprotein removal from the circulation. Serum triglyceride, phospholipid (PL), and cholesterol (CH) concentrations rose within 3 h of TWR to 45, 6.6, and 10 times control values, respectively, at 24-36 h. Serum lipids fell rapidly at 48 h and were normal by 72-96 h after TWR. TWR did not alter bile flow, hepatic bile acid transport, or biliary bile acid output. Within 0.5 h of TWR, biliary PL and CH outputs fell greater than 70%, and taurocholate-stimulated biliary PL secretion was markedly reduced. Biliary PL and CH secretion rates were approximately 30 and approximately 40% suppressed, respectively, 24 h after TWR, 160 and 330% elevated, respectively, at 48 h, and normally by 72 h, despite normal taurocholate-stimulated biliary PL secretion. Biliary beta-glucuronidase secretion (a lysosomal enzyme) was unchanged for 3 h after TWR but was increased at 24, 48, and 72 h, independent of biliary lipid secretion. Thus TWR acutely dissociates bile acid from lipid secretion without impairing bile acid transport or biliary lysosomal discharge. Late changes in biliary lipid secretion relate closely to TWR-induced change in serum lipid metabolism but not to stimulation of biliary lysosomal discharge.

The effect of methimazole on bile flow and bile acid secretion in the rat

The effect of methimazole on bile flow and composition was studied in male Wistar rats. Administration of methimazole as a single bolus (175–700 μmol/kg body wt) or infusion over three hours (1 μmol/100 g body wt/min) significantly increased bile flow and the biliary output of bile acids and inorganic electrolytes. Choleresis was a transient phenomenon and at the end of the experiments bile flow had returned to control values, although bile acid output was significantly lowered. When the amounts of bile acids arriving into the liver were increased by taurocholate infusion or decreased by cholestyramine pretreatment, a transitory enhancement was also found in bile flow and bile acid output, but the amounts of bile acid secreted and the choleretic effect induced were different according to the bile acid secretory rate found before methimazole administration. The bile acid content in the liver of taurocholate-infused rats was reduced during methimazole-induced choleresis. Our data indicate that the higher bile flow in methimazole-treated rats is related to an enhanced biliary secretion of bile acids probably due to a transitory stimulating effect on the transport into bile of the intrahepatocytary bile acid pool. The choleretic effect is not apparently shared by other thiocarbamide compounds.

Enhanced biliary gamma-glutamyltransferase excretion following prolonged alcohol consumption in rats.

In order to study the question of whether chronic ethanol consumption may alter the biliary excretion of gamma-glutamyltransferase (gamma-GT), female rats were pair-fed nutritionally adequate liquid diets containing either ethanol (36% of total calories) or isocaloric carbohydrates for 24 days. Compared to pair-fed controls, the administration of the alcohol-containing diet resulted in an increased biliary excretion of gamma-GT (5.84 +/- 0.73 mU 6 h-1 100 g-1 b.w. vs. 8.82 +/- 0.79, P less than 0.001). This was associated with a corresponding enhanced biliary output of total bile acids. An apparent linear relation between the biliary output rates of gamma-GT and those of total bile acids was observed both in alcohol-fed animals (r = 0.83) and in their pair-fed controls (r = 0.95). In addition, there was a significant increase of gamma-glutamyltransferase activities in the liver homogenate and in liver plasma membranes, both in fractions rich in bile canalicular and basolateral membranes and in those rich in blood sinusoidal site. Serum gamma-glutamyltransferase activities as well as serum bile acid concentrations were also enhanced by 96.8% (P less than 0.001) and 233% (P less than 0.001), respectively. These data show that chronic alcohol consumption enhances hepatic gamma-GT activities, leading to an increased efflux of gamma-GT into the bile and possibly into the blood out of the liver cell. Furthermore, these data suggest the involvement of bile acids with their solubilizing properties for the biliary excretion of gamma-GT.

TISSUE AMINO ACID RESPONSES TO PARENTERAL NUTRITION

We have previously described significant differences in plasma amino acids, bile flow and biliary bile acid output between animals infused either glucose or glucose+amino acids. The present study was undertaken to determine liver, bile and brain amino acid responses to the infusion of these various nutrients. Adult male Sprague-Dawley rats (225-325g) were cannulated via the jugular vein and infused with either glucose (GLU) or glucose+amino acids (TPN) or were chow-fed (CHOW). After 5 days of the respective regimens, bile was collected for 4h, animals were killed and brain and liver obtained. The GLU animals received 164 (SD 7) kcal/kg/d, whereas TPN animals received 9.4 (0.5)g AA and 154 (8) kcal/kg/d. Both GLU and TPN animals lost weight and CHOW animals gained weight. In general, the tissue amino acid patterns were similar to those in plasma; most individual amino acids were different among groups in liver and bile whereas only threonine, valine and isoleucine concentrations were different among the groups in the brain. Essential to non-essential amino acid ratios (markers of protein nutritional status) were: 0.59, 0.51 and 0.36 in the plasmas; 0.18, 0.11 and 0.09 in the livers; and 0.29, 0.29 and 0.22 in the bile of TPN, CHOW and GLU animals respectively. The branch chain amino acids are actively accumulated in the liver from the plasma and then appear to be passively tranported down a concentration gradient into the bile. Thus, the amino acid responses to these nutritional manipulations indicate that tissues (primarily the liver) may be susceptible to the trophic and toxic effects of amino acids.

Effects of Na+ replacement and amiloride on ursodeoxycholic acid-stimulated choleresis and biliary bicarbonate secretion.

In these studies, we have tested the hypothesis that bile acid-dependent bile formation is attributable, in part, to the stimulation of active bicarbonate secretion and have further explored the cellular mechanism(s) possibly involved in this process using the isolated perfused rat liver. Under control conditions, ursodeoxycholic acid (UDCA) infusion (3 mumol/min X 20 min) produced a 3.7-fold increase in bile flow and a 7.4-fold increase in HCO3- output. Amiloride (an inhibitor of Na+-H+ exchange) decreased UDCA-stimulated bile flow by 20.6% and decreased biliary HCO3- output by 24.9% but increased biliary UDCA output by 42.9%. Thus amiloride decreased UDCA choleretic efficiency (microliter UDCA-stimulated bile/mumol UDCA output) by 45% and UDCA-stimulated increase in HCO3- output per unit UDCA secreted by 48%. Substitution of Li+ for Na+ in perfusate virtually abolished (greater than 95% decrease) both the UDCA choleresis and increase in biliary HCO3- output but modestly decreased (39.6%) biliary bile acid output. Li+ substitution thus decreased UDCA choleretic efficiency by 98% and the UDCA-stimulated increase in HCO3- output by 96%. Amiloride had no effect and Li+ substitution produced a modest decrease in basal bile flow (26.0%) and HCO-3 output (33.5%). Neither amiloride nor Li+ substitution significantly affected UDCA uptake by cultured hepatocytes or by perfused liver. Amiloride (1 mM) also decreased taurocholate (TC)-stimulated choleresis by 48.5%, biliary TC output by 7.2%, and the choleretic efficiency of TC by 45%.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of hypothyroidism and thyroxine replacement on hepatic and intestinal HMG-CoA reductase and ACAT activities and biliary lipids in the rat

Hepatic and intestinal cholesterol metabolism were investigated in the hypothyroid and thyroxine-treated hypothyroid rat. Plasma cholesterol levels were significantly increased in hypothyroid animals. After thyroxine administration, plasma cholesterol levels were reduced to levels observed in euthyroid controls. Hypothyroidism caused a significant decrease in biliary cholesterol output, which was reversed with thyroxine treatment. In contrast, biliary bile acid output was unchanged by the thyroid status. Cholesterol synthesis, as estimated by HMG-CoA reductase activity, was decreased in the liver of hypothyroid animals. Thyroxine administration, however, significantly increased reductase activity returning it to control levels. Hypothyroidism did not affect HMG-CoA reductase activity in the intestine, but thyroxine administration markedly stimulated the activity of this enzyme in this organ. Cholesterol esterification, as estimated by ACAT activity, was decreased in the liver of hypothyroid rats, while intestinal ACAT activity was greatly increased. Thyroxine treatment reversed these effects of hypothyroidism on ACAT activity in both organs. An increase in microsomal cholesterol content in the intestine of hypothyroid rats was associated with the observed increase in intestinal ACAT activity. The percent of cholesterol that was absorbed in the intestine was not changed by the thyroid status of the animal. The data suggest that the changes observed in cholesterol metabolism in hypothyroid rats or hypothyroid rats treated with thyroxine for 1 week cannot account for the increase in plasma cholesterol levels observed in the hypothyroid rat. This implies that other factors that were not studied, such as changes in lipoprotein catabolism, are likely to contribute to the hypercholesterolemia of hypothyroidism.

Ketoconazole blocks bile acid synthesis in hepatocyte monolayer cultures and in vivo in rat by inhibiting cholesterol 7 alpha-hydroxylase.

In cultured hepatocytes conversion of [4-14C]cholesterol into bile acids was dose dependently reduced by the antimycotic drug ketoconazole, giving half-maximal inhibition at 10 microM ketoconazole in rat hepatocytes and at 1 microM in human hepatocytes. No change was observed in the ratio of produced cholic, beta-muricholic, and chenodeoxycholic acid with increasing amounts of the drug. Conversion of [4-14C]7 alpha-hydroxycholesterol, an intermediate of bile acid pathway, to bile acids was not affected by ketoconazole. These results together with kinetic studies with rat liver microsomes, demonstrating noncompetitive inhibition (Ki = 0.4 microM), indicate that cholesterol 7 alpha-hydroxylase is the main site of inhibition. In bile-diverted rats a single dose of ketoconazole (50 mg/kg) dramatically impaired bile flow and biliary bile acid output (92% inhibition). A similar blockade was observed using [4-14C]cholesterol as precursor for bile acid synthesis. Therefore, treatment of patients with this drug may inhibit bile acid synthesis, resulting in a reduction of the bile acid pool size after long-term ketoconazole therapy.

Intestinal absorption of lithocholic acid sulfates in the rat: inhibitory effects of calcium.

Sulfation of lithocholic acid has been proposed as a mechanism for elimination of this hepatotoxic bile acid from the body by accelerating its fecal excretion. However, quantitative data on the absorption characteristics of sulfated lithocholic acid conjugates in vivo are scarce. We studied the intestinal absorption of 14C-labeled glycolithocholic acid (GLC), taurolithocholic acid (TLC), and their 3 alpha-sulfate esters, SGLC and STLC, respectively. Studies were performed in unanesthetized rats with a permanent biliary drainage. At an intestinal infusion rate of 125 nmol/min, which is comparable to 7% of the normal biliary bile acid output in the rat, the absorption of sulfated lithocholic acid conjugates was delayed when compared with their unsulfated precursors but quantitatively only slightly reduced over a 24-h period: SGLC 90.9 +/- 3.6%, GLC 94.4 +/- 1.1%, STLC 84.4 +/- 3.0%, and TLC 94.2 +/- 2.1%. Urinary excretion of sulfated and unsulfated bile acids was similar and never exceeded 2% of the dose. SGLC absorption was dose dependent, was not altered by coinfusion of rat bile, and was only slightly reduced by a sixfold overdose of taurocholic acid. SGLC and STLC were excreted into bile largely unchanged in form. In contrast, GLC and TLC were extensively metabolized to more polar bile acids, predominantly to beta-muricholic acid conjugates. Replacement of NaCl in the infusion fluid by CaCl2 reduced the absorption of SGLC and STLC by 63 and 52%, respectively. This calcium effect was less pronounced for the unsulfated bile acids: GLC -22%, and TLC -19%. Absorption of taurocholic acid was unaffected by CaCl2.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Gomisin A on Liver Functions in Hepatotoxic Chemicals-Treated Rats

The effects of gomisin A, which is a lignan component of schizandra fruits, on liver functions in various experimental liver injuries and on bile secretion in CCl4-induced liver injury were studied. Gomisin A weakly accelerated the disappearance of plasma ICG by itself at a high dose (100 mg/kg, i.p.). All of the hepatotoxic chemicals used in this study inhibited the excretion of ICG from plasma. Gomisin A showed a tendency to prevent the delays of the disappearance of plasma ICG induced by CCl4, d-galactosamine and orotic acid, but not that by ANIT. Bile flow and biliary outputs of total bile acids and electrolytes (Na+, K+, Cl− and HCO3−) were decreased in CCl4-treated rats. Gomisin A maintained bile flow and biliary output of each electrolyte nearly to the level of the vehicle-treated group, but did not affect biliary output of total bile acids. These findings suggest that gomisin A possesses a liver function-facilitating property in normal and liver injured rats and that its preventive action on CCl4-induced cholestasis is due to maintaining the function of the bile acids-independent fraction.

Altered effect of 3% dietary cholestyramine on plasma lipids and biliary bile acid output in the pregnant rat

The effects of a diet containing 3% (ww) cholestyramine on plasma total, free, and high-density lipoprotein cholesterol and triglycerides and on bile flow and composition were compared between pregnant rats fed the resin from before mating until the twentieth day of gestation and virgin rats fed the resin for an equivalent length of time. Pregnant and virgin rats consuming a similar diet but not receiving cholestyramine were also studied. In the nonpregnant rat the usual response to cholestyramine was observed as a significantly elevated plasma high-density lipoprotein cholesterol level and biliary bile acid secretion. Plasma cholesterol levels and bile composition were not altered by cholestyramine in the pregnant rat. The inability of resin therapy to change plasma high-density lipoprotein cholesterol and bile composition during pregnancy is likely to be causally related to a reduced efficacy of cholestyramine treatment when administered during gestation.

Effects of phenobarbital on biliary lipid metabolism in children with chronic intrahepatic cholestasis.

The effects of phenobarbital (5.4-7.5 mg/kg body weight) for 14 days were studied in four children with severe intrahepatic cholestasis (group I) and in four with a syndromatic type of paucity of intralobular bile ducts (group II). Phenobarbital administration resulted in a moderate improvement of pruritus in all patients. There was a significant decrease of bilirubin in serum (group I: from 4.8 to 2.7 mg/dl; group II: from 6.1 to 2.1 mg/dl); total bile acids (group I: from 416 to 337 mumol/l; group II: from 156 to 123 mumol/l) and cholesterol (group I: from 248 to 207 mg/dl; group II: from 351 to 292 mg/dl). Alkaline phosphatase activity increased from 929 to 1126 U/l in group I and from 1751 to 2360 U/l in group II. SGOT and SGPT activities remained unchanged in both groups. In group I total biliary lipid concentration and bile acid output increased from 0.09 to 0.17 g/dl and from 3.9 to 7.2 mumol/kg per 30 min, respectively. Molar percentages of cholesterol, phospholipids and bile acids in bile remained unchanged. In group II total lipid concentrations and bile acid output increased from 1.62 to 2.0 g/dl and from 27.8 to 39.1 mumol/kg per 30 min, respectively. The molar percentage of cholesterol decreased from 5.6 to 3.5 mol%. The present results indicate that short term administration of phenobarbital has only minimal effects on biliary lipid metabolism in children with chronic intrahepatic cholestasis.

Effects of acute changes of bile acid pool composition on biliary lipid secretion.

To elucidate the mechanism responsible for the bile acid-induced changes of biliary lipid secretion, we evaluated bile flow and biliary output of bile acids, cholesterol, phospholipids, and alkaline phosphatase activity in seven cholecystectomized subjects with a balloon occludable T-tube during two experimental periods: (a) depletion of the endogenous bile acid pool and (b) replacement of the pool by means of duodenal infusion with individual bile acids, such as deoxycholic (DCA), chenodeoxycholic (CDCA), cholic (CA), and ursodeoxycholic (UDCA) acids. Bile flow, cholesterol, and phospholipid output were linearly related to bile acid secretion in all experimental periods. During the replacement periods, the amount of cholesterol and phospholipids coupled to bile acids was significantly different (at 1% level at least) for each individual bile acid secreted; it was the highest during DCA secretion (slope value: 0.209 for cholesterol and 0.434 for phospholipids) followed, in the order, by CDCA (0.078 and 1.794), CA (0.044 and 0.127), and UDCA (0.030 and 0.122). The phospholipid to cholesterol ratio was higher during secretion of CA and UDCA as compared with DCA and CDCA. The secretion of CA seemed to stimulate a greater bile flow than the other bile acids did. The infusion of all bile acids, except UDCA, induced an increase of biliary alkaline phosphatase activity as compared with the values of the depletion period. The mean highest increase (13-fold the pretreatment value) was observed during DCA secretion followed by CDCA (fivefold) and CA (1.5-fold). These results would suggest that the physical chemical properties, namely the lipid-solubilizing capacity, of bile acids could directly contribute to the regulation of biliary lipid secretion. The observed changes in biliary alkaline phosphatase activity lend support to the view that bile acid-induced lipid secretion may be, at least in part, contributed by membrane solubilization.

Biliary Steroid Excretion in Rats Fed Soybean Protein and Casein or their Amino Acid Mixtures

Male Wistar rats were fed 1% fat, cholesterol-free semipurified diets containing soybean protein isolate and casein or amino acid mixtures simulating these proteins for 28–30 days. The animals then underwent surgery for biliary diversion, and bile was collected for 2 hours. The rate of bile flow was not influenced by the type of dietary protein. The concentration and output of biliary cholesterol in rats fed soybean protein were significantly higher than in those fed casein, while biliary bile acid excretion was comparable. The group given the soy protein-type amino acid mixture also tended to excrete more biliary cholesterol relative to the casein-type amino acid mixture, although the difference was not significant, while biliary bile acid output was comparable. When 5% fat diets containing 0.5% cholesterol were given to rats, concentrations of both biliary cholesterol and bile acid were elevated significantly on a vegetable protein diet. In these experiments, there was a significant negative correlation between serum cholesterol and biliary cholesterol levels. Stimulation of the biliary excretion of cholesterol seems at least relevant to the cholesterol-lowering action of soybean protein.

Relationship between hepatic cholesterol synthesis and biliary cholesterol secretion in man: hepatic cholesterol synthesis is not a major regulator of biliary lipid secretion.

1. To examine the role of newly synthesized cholesterol as a determinant of bile lipid secretion, both hepatic cholesterol synthesis (as judged by the activity of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, EC 1.1.1.34; HMGCoAR) and steady state biliary cholesterol output were measured in nine patients. 2. HMGCoAR levels varied four fold (9-40 pmol min-1 mg-1) and biliary cholesterol secretion 2.5-fold (0.60-1.15 mumol h-1 kg-1) but there was no correlation between these two variables (r = 0.18; P greater than 0.05) nor between biliary bile acid output and HMGCoAR activity (r = 0.34; P greater than 0.05). 3. There was, however, a linear relationship between bile acid and phospholipid secretion (r = 0.77; P less than 0.001) and between bile acid and cholesterol secretion (r = 0.69; P less than 0.05). 4. These results suggest that HMGCoAR activity is not a major determinant of cholesterol secretion nor at these secretion rates is HMGCoAR activity related to bile acid return to the liver.

Triton WR-1339, a lysosomotropic compound, is excreted into bile and alters the biliary excretion of lysosomal enzymes and lipids.

In these experiments, we tested two hypothesis: first, that Triton WR-1339, a nonionic detergent which is sequestered in hepatocyte lysosomes, undergoes biliary excretion; and second, that Triton WR-1339, which also alters serum lipid levels and modifies hepatic catabolism of lipoproteins, affects the biliary output of proteins and lipids. When 3H-Triton WR-1339 was administered to rats, biochemical and morphologic studies showed that hepatocyte lysosomes sequestered Triton WR-1339: (i) the subcellular distribution of 3H was identical to that of lysosomal enzymes after liver fractionation by differential or isopycnic centrifugation, and (ii) lysosomes appeared engorged with Triton WR-1339 on electron microscopy. 3H was also excreted into bile in parallel to three lysosomal enzymes. Triton WR-1339 administration caused a coordinate increase in the biliary excretion of three lysosomal enzymes and also increased the biliary output of total protein, bile acids, and phospholipid. Triton WR-1339 administration did not affect bile flow or the biliary outputs of cholesterol, plasma membrane, and cytosolic enzymes, but did decrease biliary cholesterol saturation by 50%. These results demonstrate that an exogenous compound which is sequestered in hepatocyte lysosomes may be excreted directly into bile in parallel with endogenous lysosomal constituents. The data also show that such a lysosomotropic agent may also selectively modify the biliary excretion of proteins and lipids. The findings are consistent with the existence of a lysosome-to-bile hepatic excretory pathway and suggest that hepatocyte lysosomes may be important in modulating biliary protein and lipid secretion.

Regulation of biliary cholesterol output in the rat: dissociation from the rate of hepatic cholesterol synthesis, the size of the hepatic cholesteryl ester pool, and the hepatic uptake of chylomicron cholesterol.

These studies were designed to determine the importance of the rate of hepatic cholesterol synthesis, the size of the hepatic cholesteryl ester pool, the amount of chylomicron cholesterol reaching the liver, and the rate of bile acid transport into bile as determinants of the rate of biliary cholesterol output. Female rats that had been subjected to diurnal light cycling, fasting for 48 hr, intravenous administration of chylomicrons, and diets containing either cholestyramine, cholesterol, or bile acid underwent total biliary diversion for 2 hr. The animals were then killed and the rates of hepatic cholesterol synthesis and levels of hepatic esterified cholesterol were measured along with biliary lipid concentrations. Despite a 1000-fold variation in the rate of hepatic cholesterogenesis and a 100-fold variation in the levels of cholesteryl esters, the output and molar percentage of cholesterol in bile remained essentially constant with the exception of an approximate doubling in the output of cholesterol, as well as of bile acid and phospholipid in those animals fed bile acid. However, in this latter group the molar percentage of each component was unchanged. The administration of a bolus of chylomicrons did not alter output or molar percentage of cholesterol. Total biliary diversion for 36 hr and bile acid infusion were used to markedly vary the rate of biliary bile acid output. Cholesterol and phospholipid output remained tightly coupled to bile acid output over almost a 40-fold range. In other experiments it was shown that biliary cholesterol output could be driven by bile acid infusion to a similar extent in rats in which the rate of hepatic cholesterogenesis had been varied over a 26-fold range. It was concluded that the rate of hepatic cholesterol synthesis, the level of hepatic cholesteryl esters, and the amount of cholesterol absorbed from the diet play no role in determining the rate of biliary cholesterol secretion, at least in this species.-Turley, S. D., and J. M. Dietschy. Regulation of biliary cholesterol output in the rat: dissociation from the rate of hepatic cholesterol synthesis, the size of the hepatic cholesteryl ester pool, and the hepatic uptake of chylomicron cholesterol.