Regulation of biliary cholesterol secretion. Functional relationship between the canalicular and sinusoidal cholesterol secretory pathways in the rat.

The functional interrelationship between biliary cholesterol secretion, sinusoidal lipoprotein cholesterol secretion and bile salt synthesis was studied in the rat. Diosgenin, fructose, and colestipol in the diet were used to, respectively, influence biliary cholesterol output, VLDL production and bile salt synthesis. In the acute bile fistula rat, biliary cholesterol output was 700% increased by diosgenin and 50% decreased by fructose. In the rats fed both diosgenin and fructose, biliary cholesterol secretion was increased only by approximately 200%, whereas biliary bile salts and phospholipid outputs were unchanged. In the isolated perfused liver, VLDL-cholesterol output was 50% reduced by diosgenin alone, but was unchanged following feeding of diosgenin plus fructose. However, the livers of rats fed diosgenin plus fructose exhibited a 700% increase in VLDL-triglyceride production and a 200% increase in VLDL-cholesterol output. A significant reciprocal relationship between VLDL-cholesterol secretion and the coupling ratio of cholesterol to bile salts in bile was observed. Colestipol added to the diet maintained both sinusoidal and biliary cholesterol outputs within the normal range. In the chronic bile fistula rat, colestipol increased bile salt synthesis by 100% while diosgenin and fructose diets had no effect. Similarly, the addition of fructose to the colestipol diet did not decrease bile salt synthesis. These data suggest a reciprocal relationship between biliary cholesterol secretion and hepatic secretion of cholesterol as VLDL particles. The free cholesterol pool used for bile salt synthesis seems functionally unrelated to the pool from which VLDL-cholesterol and biliary cholesterol originate. These findings support the idea that metabolic compartmentalization of hepatic cholesterol is a major determinant of the quantity of cholesterol available for recruitment by the bile salt-dependent biliary cholesterol secretory mechanism.     

Narcotic effects on hepatic disposition of sulfobromophthalein in rats

Ascending morphine doses above 5 mg/kg s.c. progressively reduced plasma clearance of sulfobromophthalein (BSP) and raised hepatic levels of this dye in rats. The narcotic reduced the elimination constant of BSP without affecting its volume of distribution. Because abdominal surgery markedly reduced plasma clearance of BSP, no further effect of morphine could be shown in rats with bile cannulas. In duct-cannulated animals morphine had no effect on BSP concentration in bile, but did raise hepatic BSP levels while reducing bile flow and biliary BSP content. The narcotic also lowered the biliary transport maximum of BSP. The effects on BSP disposition were demonstrated acutely after morphine administration but had subsided completely by 1 and 2 days after giving narcotic. The present findings suggest that morphine impaired the secretion of BSP into bile by a mechanism not involving biliary occlusion and thereby enhanced retention of this dye in liver and plasma.     

The Relation between Plasma Cholesterol and Cholesterol Synthesis in Rats with Experimental Biliary Obstruction

Summary. The relationship between serum cholesterol and the rate of cholesterol synthesis in liver and intestine was studied in rats with experimental ligation of the bile duct. In the acute stages of biliary obstruction the level of plasma cholesterol increased several fold above the control level and was accompanied by a similar rise in the rate of hepatic and intestinal cholesterogenesis.
Feeding a high cholesterol diet before the ligation of the bile duct resulted in a marked reduction in the absolute rate of cholesterol synthesis in both liver and intestine of obstructed rats, but it had no effect on the plasma cholesterol level.
The administration of cycloheximide completely prevented the increase in hepatic and intestinal cholesterogenesis in obstructed rats but did not cause a fall in the level of total plasma cholesterol.
These results would suggest that the accumulation of cholesterol in the plasma of rats with acute biliary stasis is not dependent upon the increased rate of cholesterol synthesis in liver and intestine.     

Endoscopic management of liver abscesses and cysts that communicate with intrahepatic bile ducts

BACKGROUND AND STUDY AIMS: The formation of a communication between liver abscesses or cysts and intrahepatic bile ducts is an uncommon cause of significant bile leak. Surgical management of biliary fistulas is associated with high morbidity and mortality. We performed a prospective study of endoscopic management of this type of biliary fistula. PATIENTS AND METHODS: We studied 26 patients who had either liver abscesses or hepatic cysts that had ruptured into the intrahepatic bile ducts. The presence of a biliary fistula was suspected by jaundice and/or by the appearance of bile in percutaneous drainage effluent from a liver abscess and was confirmed by endoscopic retrograde cholangiopancreatography. Once the route of the fistula between the liver abscess or cyst and the intrahepatic bile duct had been defined by cholangiography, patients underwent treatment by sphincterotomy, and either biliary stenting or nasobiliary drainage. Nasobiliary drains or biliary stents (both 7 Fr) were placed according to standard techniques. Nasobiliary drains were removed when bile leakage stopped and closure of the fistula was confirmed by cholangiography; stents were removed after an interval of 4-6 weeks. RESULTS: Of a total of 525 patients with hepatic abscesses or cysts who were seen over a 5-year period, there were 26 patients who developed a demonstrable communication between liver abscesses (n = 20; 16 amebic, four pyogenic) or hydatid cysts (n = 6) and intrahepatic bile ducts (right intrahepatic bile ducts in 22 patients, left intrahepatic bile ducts in four patients). We performed either sphincterotomy with insertion of a nasobiliary drain (n = 20) or sphincterotomy with biliary stenting (n = 6). The fistulas healed in all patients after a mean time of 4 days (range 2-20 days) after endoscopic treatment. We were able to remove the nasobiliary drainage catheters and stents 6-34 days after their placement. CONCLUSIONS: In this case series, endoscopic therapy appears to be an effective mode of treatment for biliary fistulas complicating liver abscesses and cysts.     

Effects of troleandomycin administration on cholesterol 7 alpha-hydroxylase activity and bile secretion in rats

Repeated administration of troleandomycin increased bile flow but decreased the biliary secretion of bile acids in rats. The increased bile flow was associated with a parallel increase in the biliary clearance of [14C]erythritol. Analysis of the relationship between bile flow and bile acid secretion indicated that, for any given rate of bile acid secretin, bile flow was higher in troleandomycin-treated rats than in control rats. The increased bile flow was associated with an increased activity of Na+,K+-adenosine triphosphatase in liver plasma membranes. The decreased bile acid secretion into bile was associated with a similar decrease in the bile acid pool size, a decreased bile acid synthesis rate and a decreased activity of microsomal cholesterol 7 alpha-hydroxylase. The concentration of bile acids in serum, the hepatic extraction ratio of [3H]taurocholate and its biliary transport maximum were not modified. It is concluded that repeated administration of troleandomycin increases the canalicular bile acid-independent flow but decreases the activity of cholesterol 7 alpha-hydroxylase, the synthesis, the pool size and the biliary secretion rate of bile acid in rats.     

Biliary copper excretion by hepatocyte lysosomes in the rat. Major excretory pathway in experimental copper overload.

We investigated the hypothesis that lysosomes are the main source of biliary copper in conditions of hepatic copper overload. We used a rat model of oral copper loading and studied the relationship between the biliary output of copper and lysosomal hydrolases. Male Sprague-Dawley rats were given tap water with or without 0.125% copper acetate for up to 36 wk. Copper loading produced a 23-fold increase in the hepatic copper concentration and a 30-65% increase in hepatic lysosomal enzyme activity. Acid phosphatase histochemistry showed that copper-loaded livers contained an increased number of hepatocyte lysosomes; increased copper concentration of these organelles was confirmed directly by both x ray microanalysis and tissue fractionation. The copper-loaded rats showed a 16-fold increase in biliary copper output and a 50-300% increase in biliary lysosomal enzyme output. In the basal state, excretory profiles over time were similar for biliary outputs of lysosomal enzymes and copper in the copper-loaded animals but not in controls. After pharmacologic stimulation of lysosomal exocytosis, biliary outputs of copper and lysosomal hydrolases in the copper-loaded animals remained coupled: injection of colchicine or vinblastine produced an acute rise in the biliary output of both lysosomal enzymes and copper to 150-250% of baseline rates. After these same drugs, control animals showed only the expected increase in lysosomal enzyme output without a corresponding increase in copper output. We conclude that the hepatocyte responds to an increased copper load by sequestering excess copper in an increased number of lysosomes that then empty their contents directly into bile. The results provide direct evidence that exocytosis of lysosomal contents into biliary canaliculi is the major mechanism for biliary copper excretion in hepatic copper overload.     

Coordinate Secretion of Acid Hydrolases in Rat Bile: HEPATOCYTE EXOCYTOSIS OF LYSOSOMAL PROTEIN?

Three lysosomal glycosidases, beta-glucuronidase (EC 3.2.1.31), beta-galactosidase (EC 3.2.1.23), and N-acetyl-beta-glucosaminidase (EC 3.2.1.30) have been investigated in bile that was freshly collected from rats through a complete bile fistula. Assay conditions have been established on the basis of appropriate kinetic studies. The biliary excretion patterns for these enzymes were found to vary considerably from rat to rat during the 24-h collection period. In a given animal, however, the three hydrolases were excreted in parallel and showed a gradual increase in activity with time, most marked after 10- 12 h of collection. 24-h biliary outputs of the three hydrolases averaged congruent with3% of their respective contents in total liver, and bile diversion had no effect on hepatic glycosidase activity or total protein content. Other enzymes known to be associated primarily with mitochondria, endoplasmic reticulum, and cell sap were also detected in bile, generally in smaller amounts. The biliary excretion of the plasma membrane markers, alkaline phosphodiesterase I and 5'-nucleotidase, however, was comparable to that of the lysosomal hydrolases. Biliary excretion of total protein was relatively constant and corresponded to 3.0% of the total hepatic protein content per day, whereas biliary bile acid secretion decreased during the first 12 h and then remained constant. Exocytic bulk discharge of hepatocyte lysosomes is proposed as the most likely mechanism for the biliary excretion of lysosomal enzymes. These results call attention to the possible pathophysiologic significance of biliary excretion of hepatic lysosomal contents as a means of residue disposal.     

Rapid active transport of immunoglobulin A from blood to bile

Immunoglobulins were isolated from the serum or ascitic fluid of Lou/Wsl rats bearing plasmacytomas and labeled with 125I. When labeled IgA was injected i.v. it disappeared from the blood serum much more rapidly than IgG2 so that after 3 h less than 10% remained. This rapid disappearance of the injected IgA was not seen in rats with ligated bile ducts. In rats with cannulated bile ducts, the labeled IgA appeared rapidly in the bile so that 25% of the injected dose was recovered in 3 h; at the peak of this biliary excretion the specific radioactivity of the bile (cpm/milligram protein) was about 200 times greater than that of the blood serum. Thus much of the IgA which finds its way into the blood is rapidly and actively transported across the liver so that it enters the gut lumen via the biliary tract.     

Cholestatic effect of carmustine in rats

A single i.p. dose of 20 mg/kg of carmustine [1,3-bis-(2-chloroethyl)-1-nitrosourea; BCNU] caused intrahepatic cholestasis in rats within 48 hr of administration. Cholestasis was characterized by a selective reduction of the bile salt independent fraction of bile flow. Increased plasma K+ and decreased plasma Na+ concentrations, consistent with this effect, were observed. Because bile: plasma osmolality and biliary bile salt concentrations were elevated, increased permeability to bile salts and other osmotically active solutes between bile and plasma is unlikely. Bile salt excretion was normal despite the reduced bile flow because biliary bile salt concentration was increased. In contrast, the treated rats were unable to concentrate bromosulfophthalein in bile before, during and after the onset of cholestasis. Because no reduction in hepatic perfusion was observed in vivo in BCNU-treated rats, reduced xenobiotic organic anion excretion may be a selective effect of the drug. The cholestatic effects of BCNU appear to be different from either alpha-naphthylisothiocyanate or estrogenic steroids.     

The serum activities of AP, gamma-GT, GLDH, GPT and CHE after complete biliary obstruction and choledochocaval fistula in the rat

The activities in serum of alkaline phosphatase, gamma-glutamyltransferase, glutamate dehydrogenase, glutamic pyruvic transaminase and cholinesterase were compared after complete biliary obstruction (CBO) and choledochocaval fistula (CCF) in the rat. CCF was used as a model of complete biliary retention without bile stasis and without increased pressure in the biliary tract. The increases in AP, GLDH and gamma-GT within 24-h post-op. show no difference between the two experimental groups. The conclusion is that the retention of biliary constituents alone is responsible for the increase in the levels of serum activity and that other conditions like bile stasis and increased pressure in the biliary tract do not play an important role in the pathogenesis of these alterations. The rise of GPT activity in CCF is of a lesser degree than in CBO.     

Metabolic fate of SCE-1365, a new broad-spectrum cephalosporin, after parenteral administration to rats and dogs.

Disposition of [14C]SCE-1365 was studied in rats and dogs after intramuscular or intravenous injection. The plasma level of [14C]SCE-1365 peaked at 15 min after intramuscular administration and declined rapidly to give half-lives of 27 and 39 min, respectively, in rats and dogs. After intravenous dosage, half-lives were 22 and 32 min, respectively, in rats and dogs. In both animals, the plasma levels of 14C were made up largely of unchanged antibiotic. Binding to plasma protein was 91 and 31%, respectively, in rats and dogs. Tissue levels of [14C]SCE-1365 administered intramuscularly to rats peaked at 15 min and were highest in the kidney and lowest in the brain, with plasma, liver, lung, heart, intestinal wall, and adrenal gland occupying intermediary positions in the order listed. The concentration of [14C]SCE-1365 in erythrocytes was very low, as was the level of the antibiotic in rat fetuses. The milk of rats given [14C]SCE-1365 intramuscularly contained detectable levels of 14C. [14C]SCE-1365 was completely eliminated from the bodies of rats and dogs within 24 to 48 h. In both animals, a large amount of the dosed 14C was excreted in urine as unaltered antibiotic. The remainder was eliminated in the feces via bile. In rats, [14C]SCE-1365 was eliminated by both glomerular filtration (33%) and tubular secretion (67%). An active transport process appeared to be involved in biliary excretion in rats.     

Effects of chlorpromazine hydrochloride on bile salt synthesis, bile formation and biliary lipid secretion in the Rhesus monkey: a model for chlorpromazine-induced cholestasis

We studied the acute effects of intravenous infusions of chlorpromazine hydrochloride on bile salt synthesis, bile formation and biliary lipid secretion in the alert female Rhesus monkey prepared with a total biliary fistula and in a steady bile salt secretory state. In twelve studies (three animals), five doses of radiolabelled chlorpromazine hydrochloride (1-10 mg identical to 2.8-28 mumol/kg) were infused intravenously for 1 h in random order. Cholestasis was induced within minutes in all experiments. The radiolabel appeared rapidly in bile, with similar recoveries in bile and urine and a 90% total cumulative output in 4 days. Both bile flow, bile salt and other biliary lipid outputs were inhibited in a dose related and reversible manner. The apparent bile salt independent bile flow was consistently abolished, and a prompt return to basal values occurred when biliary concentration of the drug and metabolities fell below 1-2 mM. When chlorpromazine hydrochloride was infused at three doses (2.5, 5.0 and 10.0 mg identical to 7-28 mumol/kg) during constant intravenous infusion of 14C sodium taurocholate (300 mumol/h), bile flow, total bile salt output and 14C taurocholate output decreased within minutes. This was accompanied by a progressive rise in the serum 14C taurocholate concentration. After 90 min the taurocholate specific activity in bile increased significantly indicating that bile salt synthesis was inhibited. Secretion of retained bile salts and reversal of inhibition of bile salt synthesis occurred with time: the course of both events was correlated with the dose of the drug. Thus, in monkeys, chlorpromazine hydrochloride induces reversible, dose related cholestasis suppression of the bile salt dependent and independent flow, inhibition of bile salt synthesis and impairment of biliary lipid secretion. We suggest that these effects are due to both bile salt-chlorpromazine interactions and the effect of the latter on canalicular and other membranes.     

Increased tight junction permeability: a possible mechanism of oestrogen cholestasis

Ethinyl oestradiol increased rat biliary permeability for 3H-inulin and 14C-sucrose, and significantly raised serum concentrations of bile acids after 3 and 7 days' treatment (P less than 0.0005) and bilirubin after 7 days (P less than 0.005) but not after 3 days. Following intravenous infusion of bromsulphthalein or phenolphthalein, ethinyl oestradiol-treated rats had elevated plasma concentrations of the three bile constituents, bromsulphthalein (P less than 0.0005 after 3 and 7 days), bromsulphthalein-glutathione conjugate (P less than 0.005 after 3 days; P less than 0.0005 after 7 days) and phenolphthalein glucuronide (P less than 0.005 after 3 days; P less than 0.0005 after 7 days), but the plasma concentration of unconjugated phenolphthalein, which was undetectable in bile, was unchanged. Similar changes followed partial biliary obstruction produced by bile cannula elevation. This pattern suggests that biliary constituents are refluxing from bile to plasma via the paracellular pathway, a concept further supported by structural changes in tight junction morphology in the oestrogen-treated rats. 'Leakiness' of canalicular tight junctions may explain the pathophysiology of oestrogen-induced cholestasis.     

Further studies on the effect of niridazole on urinary and biliary excretion of copper

Administration of niridazole to rats poisoned with copper caused a significant increase in both the urinary and biliary excretion of the metal. Although the urinary excretion of iron was increased by the drug, iron excretion was significantly decreased during the drug-induced excretion of copper after copper poisoning. Formation of a copper-niridazole chelate or chelates before excretion in the bile or urine may explain these findings. Polarity and molecular weights of the metal-drug chelates formed in vivo may be the directing forces not only in the selection of the metal for chelation, but also for its urinary or biliary excretion. The laboratory preparation of two copper-niridazole complexes lends support to these conclusions.     

Effects of taurodihydrofusidate, a bile salt analogue, on bile formation and biliary lipid secretion in the rhesus monkey.

Bile salts play a major role in bile formation and biliary lipid secretion. Sodium taurodihydrofusidate (TDHF), a derivative of the antibiotic fusidic acid, closely resembles bile salts in terms of structure, micellar characteristics, and capacity ot solubilize otherwise insolbule lipids. We have therefore studied the biliary secretion of this bile salt analogue and its influence on bile formation and biliary lipid secretion in primates. Alert, unanesthetized female rhesus monkeys prepared with a total biliary fistula were allowed to reach a steady bile salt secretion rate before each study. In three animals (group I),[14C]TDHF was infused intravenously. Most of the compound was secreted rapidly in bile chemically unchanged. The biliary secretion of this drug produced a twofold increase in bile flow; however, the bile salt output was markedly reduced during the infusion. In spite of this reduction, the phospholipid output remained essentially unchanged whereas the cholesterol output increased almost twofold. In five other animals (group II), the effect of TDHF on the bile salt secretion was further investigated by an intravenous infusion of [14C]taurocholate followed by a combined infusion of [14C]taurocholate and TDHF. When TDHF was added to the infusate, a reduction in the [14C]taurocholate output and a progressive rise in the plasma [14C]taurocholate concentration were observed in each animal. An analysis of the data in both groups indicates that (a) the most likely explanation to account for the decreased bile salt output is that the bile salt analogue, TDHF, interfered with bile salt secretion into the biliary canaliculi; (b) TDHF induces a greater secretion of biliary water than was observed with bile salts, an effect consistent with a stimulation of the bile salt-independent canalicular flow; (c) at similar 3alpha-hydroxysteroid secretion rates TDHF caused a significant increase in cholesterol secretion compared to that induced by bile salt. This finding suggests that TDHF affects cholesterol metabolism or secretion in a way distinct from bile salts. Thus, the solubilization of biliary lipids in mixed micelles, although essential, is only one of the factors which determine their secretion into bile.     

BLEEDING TENDENCY AND PROTHROMBIN DEFICIENCY IN BILIARY FISTULA DOGS: EFFECT OF FEEDING BILE AND VITAMIN K

In biliary fistula dogs the plasma prothrombin falls eventually to low levels and bleeding commonly occurs. Faulty absorption of vitamin K from the intestine in these animals is an important causative factor. Feeding bile permits absorption of the traces of this vitamin normally present in mixed diets, and as a result a slow rise in prothrombin level is observed. If a standard diet is supplemented with large amounts of vitamin K concentrate the prothrombin rise is rapid, provided bile or bile salt is supplied to aid in the absorption. Variations in the rate of prothrombin depletion in biliary fistula dogs kept on constant diet indicate the existence of additional factors which require further study. Our experience indicates that vitamin A and vitamin D supplements do not correct the prothrombin deficiency in biliary fistula animals.     

Biliary excretion of iron from hepatocyte lysosomes in the rat. A major excretory pathway in experimental iron overload.

In these experiments, we assessed the role of hepatocyte lysosomes in biliary excretion of iron. We loaded rats with iron by feeding 2% carbonyl iron and collected bile for 24 h via bile fistulae from iron-loaded and control rats. In additional rats, bile was collected before and after the administration of colchicine. Rats were then killed and their livers were homogenized and fractionated for biochemical analyses or processed for electron microscopy and x-ray microanalysis. Inclusion of 2% carbonyl iron in the diet caused a 45-fold increase (P less than 0.001) in hepatic iron concentration compared with controls (1,826 +/- 159 vs. 38 +/- 6.7 micrograms/g liver, mean +/- SE). Electron microscopy with quantitative morphometry and x-ray microanalysis showed that the excess iron was sequestered in an increased number of lysosomes concentrated in the pericanalicular region of the hepatocyte. Iron loading was also associated with a twofold increase in biliary iron excretion (4.06 +/- 0.3 vs. 1.75 +/- 0.1 micrograms/g liver/24 h; P less than 0.001). In contrast, the biliary outputs of three lysosomal enzymes were significantly lower (P less than 0.0005) in iron-loaded rats compared with controls (mean +/- SE) expressed as mU/24 h/g liver: N-acetyl-beta-glucosaminidase, 26.7 +/- 4.6 vs. 66.2 +/- 13.4; beta-glucuronidase, 10.1 +/- 1.3 vs. 53.2 +/- 17.9; beta-galactosidase, 8.9 +/- 1.0 vs. 15.4 +/- 2.3. In iron-loaded rats but not in controls, biliary iron excretion was coupled to the release into bile of each of the three lysosomal hydrolases as assessed by linear regression analysis (P less than 0.001). In contrast, no relationships were found between biliary iron excretion and the biliary outputs of a plasma membrane marker enzyme (alkaline phosphodiesterase I) or total protein. After administration of colchicine, there was a parallel increase in biliary excretion of iron and lysosomal enzymes in iron-loaded rats, but not controls. We interpret these data to indicate that, in the rat, biliary iron excretion from hepatocyte lysosomes is an important excretory route for excess hepatic iron.     

Cyclosporin A, but not tacrolimus, inhibits the biliary excretion of mycophenolic acid glucuronide possibly mediated by multidrug resistance-associated protein 2 in rats

The onset of diarrhea after the administration of mycophenolate mofetil (MMF) is possibly associated with the biliary excretion of its metabolite, mycophenolic acid glucuronide (MPAG). This study was undertaken to clarify the mechanism underlying the biliary excretion of MPAG. Intravenously administered mycophenolic acid (MPA, 5 mg/kg) rapidly disappeared from plasma and was efficiently excreted as MPAG in the bile of Wistar (26% of dose) and Sprague-Dawley rats (21% of dose) over 1 h. On the other hand, in spite of the rapid disappearance of MPA from plasma, the biliary excretion of MPAG was very limited in Eisai hyperbilirubinemic rats (EHBRs), which display mutations in multidrug resistance-associated protein 2 (Mrp2)/canalicular multispecific organic anion transporter, and constituted only 0.5% of dose. Instead, high levels of MPA were noted in the plasma of EHBRs. Intravenous administration of CsA (5 mg/kg) to Wistar rats significantly lowered the biliary excretion of MPAG. However, intravenously administered tacrolimus (0.1 mg/kg) failed to produce such effect. In conclusion, it is suggested that there is an efficient MPAG transport mediated by Mrp2 on the bile canalicular membrane of rat hepatocytes and that the therapeutic range of CsA potentially interferes with Mrp2. However, the therapeutic range of tacrolimus does not inhibit the transporter. Thus, it should be noted that MMF coadministered with tacrolimus instead of CsA might increase the occurrence of diarrhea related to the biliary excretion of MPAG in transplant recipients.     

Enterohepatic physiology of 1,25-dihydroxyvitamin D3.

After intravenous administration of radiolabeled 1,25-dihydroxyvitamin D3 to rats, approximately 25% of the administered radioactivity appeared in the bile within 24 h. Instillation of the biliary radioactivity into the duodena of other rats was followed by recovery of 15% of the radioactivity in newly secreted bile within 24 h. The process by which products of 1,25-dihydroxyvitamin D3 were excreted in bile was not saturable in the dose range tested (0.275-650 ng). The metabolites of 1,25-dihydroxyvitamin D3 present in bile were found to be much more polar than 1,25-dihydroxyvitamin D3 and were resolved into three fractions on high performance liquid chromatography. 60% of the radioactivity present in bile was retained selectively by DEAE-cellulose; the radioactive material could be eluted from the gel at a low pH or at high salt concentrations. When bile containing the radiolabeled metabolites was incubated at 37 degrees C and pH 5 with beta-glucuronidase, there was an increase in the amount of radioactivity comigrating with 1,25-dihydroxyvitamin D3. Treatment of the products of radiolabeled 1,25-dihydroxyvitamin D3 in bile with diazomethane, an agent which converts acids into methyl esters, transformed one of the metabolites into a less polar compound. These results demonstrate that there is a quantitatively important enterophepatic circulation of the products of 1,25-dihydroxyvitamin D3 in the rat.     

Relationships between cholesterol gallstones, biliary function, and plasma lipoproteins in squirrel monkeys

We used squirrel monkeys (Saimiri sciureus) as models to investigate human sex differences in susceptibility to cholesterol gallstones, biliary function, and plasma lipoproteins. Cholesterol gallstones developed in a large proportion of intact and gonadectomized male and female Brazilian monkeys maintained on a lithogenic diet, but male Bolivian monkeys were completely resistant. Although the gallbladder bile of nearly all monkeys was saturated with cholesterol, the bile of the Bolivian monkeys had a much greater concentration of total lipids (cholesteriol + phospholipid + bile acids) than did bile of the other groups. The male Bolivian monkeys had the highest percentage of gallbladder bile acids as chenodeoxycholic and the lowest as deoxycholic acids. They also had larger total body pools of cholic and chenodeoxycholic acids than any other group. The lithogenic index of all Brazilian squirrel monkeys with gallstones was greater than that of all Brazilian monkeys that were free of stones. The level of HDLs was much lower in the plasma of Bolivian monkeys than in that of any group of Brazilian monkeys, and the differences were restricted to the HDL2 subfraction. Addition of cholesterol (0.9 mg/Kcal) to the regular semipurified diet containing butter resulted in elevations in the LDLs of all groups and a change in the relative compositions of HDL and LDL (a higher percentage of cholesterol and lower percentage of protein). The occurrence of low plasma HDL2 levels in a population of squirrel monkeys resistant to cholesterol gallstones is consistent with the suggested role of that fraction in net transport of cholesterol to the bile.