The physicochemical basis of cholesterol gallstone formation in man

Composition of biliary lipids and kinetics of bile acids after cholecystectomy in man

Postcholecystectomy biliary lipid composition and bile acid kinetics were studied in 24 women and 4 men. Hepatic bile was collected periodically for as long as 4 months without interrupting the enterohepatic circulation and without infecting the biliary system. In 23 patients with cholesterol gallstones, fasting biliary cholesterol made up 10.2% of total lipids in the steady state; in 5 patients with bilirubinate stones, saturation of fasting hepatic bile with cholesterol was lower (8.7% of total lipids). The percentage of deoxycholic acid after cholecystectomy was not higher than that of seven healthy, noncholecystectomized controls. Postcholecystectomy studies of diurnal variation of biliary lipids (7 patients) showed that postprandial hepatic bile had a significantly lower cholesterol saturation than fasting bile. Pool sizes of cholic and chenodeoxycholic acids were low (average 0.4 g/70 kg, each); total synthesis for both bile acids was normal (average 460 mg/day/70 kg), but fractional turnover rates of the two primary bile acids increased after cholecystectomy, probably due to more frequent recycling of the small bile acid pool.

Phenobarbital as a hypocholesterolemic agent in the rat and rabbit

The administration of phenobarbital was observed to inhibit the rise in serum cholesterol that occurred in rats after thyroidectomy or hypophysectomy and in rabbits after inclusion of cholesterol in their diet. This hypocholesterolemic effect of phenobarbital was found to be due to its capacity to inhibit the intestinal absorption of cholesterol in both these species. We found no evidence to suggest that phenobarbital altered the endogenous process of cholesterol metabolism in either of these two species of animals.

The effect of wheat bran upon bile salt metabolism and upon the lipid composition of bile in gallstone patients

When raw wheat bran was added to the diet of six subjects for 4-6 weeks, chenodeoxycholate (CDC) synthesis increased from 0.46 +/- 0.12 to 0.57 +/- 0.17 mmol/day pool increased from 1.72 +/- 0.47 to 2.19 +/- 0.74 mmol (rho less than 0.05). Deoxycholate (DC) pool size diminished from 1.20 +/- 0.29 to 0.80 +/- 0.16 mmol, but cholate synthesis and pool size were unaffected. Overall, the size of the bile salt pool did not change. In spite of this, when 10 patients with probable cholesterol gallstones took bran supplements for 4-6 weeks, their gallbladder bile aspirated from the duodenum became less saturated with cholesterol. The molar percentage of cholesterol fell from 10.1 +/- 3.1% to 8.6 +/- 2.7% (rho less than 0.01), and the saturation index of bile fell from 1.49 +/- 0.40 to 1.29 +/- 0.38 (rho less than 0.005). Bran probably operates primarily on the colon, reducing the formation or absorption of the bacterial metabolite DC, a substance which impairs CDC synthesis.

Lipid composition of bile in morbid obesity before and after jejunoileal bypass surgery

Bile cholesterol, phospholipids, total bile acids, individual bile acids, and fatty acid compositions of bile neutral lipids and phospholipids were analyzed before, at one month and at six months following jejunoileal bypass surgery in a series of morbidly obese patients. Preoperative mole percentages of cholesterol and lithogenic indices were high, indicating that biles were supersaturated with cholesterol and outside the micellar solubility zone when plotted on triangular coordinates. At the one month post-operative period percentages of cholesterol and lithogenic indices were significantly increased as compared to the pre-operative state. At six months post-operatively these values had decreased to approximately the pre-operative levels. No changes were observed in percentages of lithocholic acid, but deoxycholic acid decreased to markedly low levels at one month and remained low at the six month post-operative interval. Relative proportions of cholic acid increased, and the ratio of cholic to chenodeoxycholic acid was significantly increased at both post-operative intervals. No significant changes were noted in bile neutral lipid or phospholipid fatty acid composition, indicating that no depletion of essential fatty acids had occurred.

Lithogenic bile

So-called authors' lithogenic bile [Ch greater than 7.5 mg/ml, (TBS + PL)/Ch weight ratio less than 20] corresponds to the bile which falls well above the micellar zone boundary on triangular coordinates with high concentration of cholesterol. The authors supposed that, in man like hamsters and squirrel monkeys, in the process of alimentary formation of cholesterol gallstones gallbladder bile of which cholesterol concentration was high, and (TBS + PL)/Ch ratio was as low as that of gallbladder bile with cholestrol gallstones seemed to be lithogenic.

Gallbladder disease. Prevalence in a South Wales industrial town

In a weighted random sample of the specially enumerated population of a South Wales industrial town, examined by cholecystography for gallstones, the overall prevalence rates were 6.2 per cent for men 45 to 69 years of age and 12.1 per cent for women of the same ages. Contrary to our expectation there was no marked increase in prevalence with age in either sex. Symptoms of dyspepsia said to be suggestive of gallstones were found with approximately equal frequency in those with and without gallbladder disease.

The effect of phenobarbital on biliary lipid metabolism and hepatic microsomal drug metabolism in patients with cholesterol cholelithiasis

Six patients with cholesterol cholelithiasis were studied before and after 3 weeks treatment with phenobarbital, 120 mg/day. The kinetics of cholic and chenodeoxycholic acid and biliary lipid composition were not significantly affected by phenobarbital treatment although hepatic mixed-function oxidase was stimulated by the treatment as shown by increased breath output of 14CO2 after administration of (14C)aminopyrine. It is concluded that treatment with phenobarbital is unlikely to be effective therapy for patients with cholesterol cholelithiasis.

The estimation of phospholipids in bile

Total and lipid phosphorus were measured in the duodenal aspirate of 24 fasting subjects following an injection of cholecystokinin. The lipid phosphorus values were lower than the total phosphorus, a difference most pronounced in dilute samples. Storage at -20 degrees C over 4 weeks resulted in a loss of over 50% lipid phosphorus. Such alterations in the lipid phosphorus affected the calculation of biliary phospholipid and hence the saturation index of cholesterol in bile causing it to be erroneously elevated. It is concluded that analysis of bile samples should be undertaken on freshly obtained samples and include a preliminary step for the extraction of lipids.

A study of the physicochemical interactions between biliary lipids and chlorpromazine hydrochloride. Bile-salt precipitation as a mechanism of phenothiazine-induced bile secretory failure

Since chlorpromazine hydrochloride [2-chloro-10-(3-dimethylaminopropyl)-phenothiazine hydrochloride] is commonly implicated in causing bile-secretory failure in man and is secreted into bile, we have studied the physicochemical interactions of the drug with the major components of bile in vitro. Chlorpromazine hydrochloride molecules are amphiphilic by virtue of possessing a polar tertiary amine group linked by a short paraffin chain to a tricyclic hydrophobic part. At pH values below the apparent pK (pK'a 7.4) the molecules are water-soluble cationic detergents. We show that bile salts in concentrations above their critical micellar concentrations are precipitated from solution by chlorpromazine hydrochloride as insoluble 1:1 salt complexes. In the case of mixed bile-salt/phosphatidylcholine micellar solutions, however, the degree of precipitation is inhibited by the phospholipid in proportion to its mole fraction. With increases in the concentration of chlorpromazine hydrochloride or bile salt, micellar solubilization of the precipitated complexes results. Sonicated dispersions of the negatively charged phospholipid phosphatidylserine were also precipitated, but dispersions of the zwitterionic phospholipid phosphatidylcholine were not. Chlorpromazine hydrochloride efficiently solubilized these membrane phospholipids as mixed micellar solutions when the drug:phospholipid molar ratio reached 4:1. Polarizing-microscopy and X-ray-diffraction studies revealed that the precipitated complexes were amorphous and potentiometric studies confirmed the presence of a salt bond. Some dissociation of the complex occurred in the case of the most polar bile salt (Ks 0.365). As canalicular bile-salt secretion determines much of bile-water flow, we propose that complexing and precipitation of bile salts by chlorpromazine hydrochloride and its metabolites may be physicochemically related to the reversible bile-secretory failure produced by this drug.

Effects of oral contraceptives on the gallbladder bile of normal women

In view of the reported association between use of oral contraceptives and gallbladder disease, the effects of contraceptive steroids on the lipid composition of gallbladder bile were studied in 22 healthy women. Each subject was studied during routine use of oral contraceptives and also during normal menstrual cycles on no medication. Gallbladder bile was significantly more saturated with cholesterol during contraceptive therapy than during normal menstrual cycling (125 versus 92 per cent, P less than 0.001). Chenodeoxycholic acid accounted for a significantly smaller proportion (35 versus 42 per cent P less than 0.001) and cholic acid a significantly greater proportion (50 versus 41 per cent (P less than 0.001) of total bile acids during contraceptive steroid therapy. These findings show that exogenous sex steroids in doses and formulations routinely prescribed induce important alterations in the composition of human gallbladder bile, and suggest a biochemical basis for the increase in gallbladder disease observed among women using oral contraceptives.

Some observations on gallstones and bile composition

A series of 31 consecutive patients undergoing surgery for gallstone disease has been studied and the composition of the gallstones and bile from the gallbladder and common duct determined. As a result of the stone analysis by the X-ray powder diffraction method, the patients were classified according to whether their stones consisted of cholesterol, calcium salts or a mixture of the two. The mean composition of the common duct bile for the groups with cholesterol and mixed stones was just outside the micellar region of cholesterol solubility. The gallbladder bile from the cholesterol group of stone-formers was also supersaturated, but the gallblader bile from the group of mixed stone-formers was undersaturated with respect to cholesterol. None of the patients forming gallstones of calcium salts showed any abnormality in the cholesterol content of their bile.

Gallbladder function, cholesterol stones, and bile composition

Gallbladder bile obtained at operation from five patients with no symptoms of biliary disease was undersaturated with cholesterol in every case. However, gallbladder bile from patients with stones composed of 97-100% crystalline cholesterol was on average just saturated with cholesterol when the gallbladder was functioning and undersaturated when it was not. Regardless of gallbladder function, the patients with stones had on average significantly more cholesterol in their bile than in the control group, but the differences between the mean composition of bile from functioning and non-functioning gallbladders were not significant. Common duct bile from patients with non-functioning and functioning gallbladders was on average supersaturated with cholesterol, but there was significantly more bile salt and significantly less cholesterol in the bile from patients with non-functioning gallbladders. Only in the case of patients with functioning gallbladders did the mean composition of the common duct and gallbladder biles differ significantly. The former contained significantly more cholesterol and less bile salt than the latter. It is suggested that patients with non-functioning gallbladders may be 'autocholecystectomised' with the duct bile reverting to a more 'normal' composition.

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.

Biliary lipid composition in early childhood

The biliary lipid composition was studied in 11 children without hepatic or gastrointestinal disease who ranged in age from 15 to 54 months. The molar percentages of cholesterol, bile acids and phospholipids in the biliary lipid mixture averaged 5.0 +/- 1.1; 80 +/- 6.1 and 15 +/- 6.2%, respectively. Cholic, chenodeoxycholic, deoxycholic and ursodeoxycholic acid comprised 48; 45; 4 and 3% of total bile acids, respectively. A comparison of the lipid composition with data reported in the literature for the adult reveals that the molar percentage of cholesterol is relatively low in early childhood. This could be one of the factors which is responsible for the low incidence of cholesterol gallstones in this age group.

Effects of obesity and caloric intake on biliary lipid metabolism in man

The effects of obesity and caloric intake on biliary lipid metabolism were investigated in a series of related studies. The degree of saturation of gallbladder bile with cholesterol was found to be significantly higher in a group of 23 obese healthy subjects than in a group of 23 nonobese controls matched for age, sex, and race. Bile was also significantly more saturated in 11 obese subjects before than after weight reduction. To determine whether supersaturated bile in obesity is due to excessive secretion of cholesterol or to deficient secretion of bile acids and phospholipids, the hepatic outputs of these three lipids were measured during constant duodenal infusion of formula in the same 11 subjects before and after weight reduction. Weight reduction resulted in significant reduction of cholesterol output but not of bile acid or phospholipid output. Moreover, very obese subjects were found to have cholesterol secretion rates markedly higher than less obese subjects previously studied by the same method. In obese subjects, bile was supersaturated with cholesterol despite increased bile acid pool sizes and increased secretion rates of bile acids and phospholipids. Supersaturated bile in the obese could therefore be attributed to a single defect in lipid secretion, namely, an excessive output of cholesterol. To determine whether the rate of caloric intake can account for the effects of obesity on biliary lipid composition and secretion, nine obese white men were studied on a weight maintenance diet and then during weight reduction on a 1,000 cal diet. As compared to weight maintenance, chronic caloric restriction resulted in reduced outputs of cholesterol, bile acids, and phospholipids, reduced bile acid pool size, and reduced synthesis and fecal excretion of cholesterol. Saturation of bile with cholesterol did not decrease during weight reduction, evidently because of the mobilization of cholesterol from adipose stores and the marked reduction in bile acid and phospholipid output observed during chronic caloric restriction. Acute alterations in caloric infusion rates did not fully reproduce the effects of chronic administration of high and low calorie diets. Likewise, chronic intake of hypercaloric diets by nonobese subjects did not reproduce the cholesterol hypersecretion characteristic of the obese. Thus, increased cholesterol secretion in obese subjects could not be fully explained by the amount of calories they ingested to maintain stable weight. It is concluded that obesity is characterized by excessive hepatic secretion of cholesterol which results in supersaturated bile.

Isolation and properties of the mixed lipid micelles present in intestinal content during fat digestion in man

To evaluate better the physicochemical characteristics of human fat digestion, a method was developed which allowed characterization of the bile acid-lipid mixed micelles of the aqueous phase of post-prandial duodenal fluid. Duodenal fluid was collected after a 36-g fat breakfast for two 90-min periods and for 60 min after i.v. cholecystokinin and was ultracentrifuged at 15,400,000 g-min. The aqueous phase was isolated, passed through a 200-nm filter, and the mixed micelles were concentrated by an ultrafiltration procedure using a 1.5-nm filter. The 1.5-nm retentate was eluted from Sepharose 6B columns with 1.5-nm filtrate for both preequilibration fluid and eluent. 1.5-nm filtrate approximated the monomer concentrations. Each sample was assayed for bile acid, fatty acid, lecithin, lysolecithin, protein, cholesterol, and counterions (pH, Na+, K+, Ca2+). Constituents were concentrated only on the 1.5-nm filter. On gel permeation chromatography, coincident peaks were observed for bile acid, fatty acid, lysolecithin, and cholesterol; and were eluted with a Kav range of 0.50-0.68 (corresponding to a Stokes radius of 2.3-3.5 nm). An average density of 1.25 and coincident peaks of bile acid and fatty acid were found for the mixed micelles on sucrose density gradients. The regression lines of micellar fatty acid, lysolecithin, and cholesterol vs. bile acid gave a stoichiometry of 1.4 mol fatty acid, 0.15 mol lysolecithin, and 0.06 mol cholesterol for each mole of bile acid. Mixed micelles were homogeneous in composition. These results provide direct evidence for the existence of the postprandial mixed micelle and describe several of its physicochemical properties.

Crustacean intestinal detergent promotes sterol solubilization

Although crustacean tissue cholesterol content is high, Crustacea, like other arthropods; are incapable of cholesterol synthesis, and presumably are dependent for maintaining tissue cholesterol stores on the intestinal absorption of ingested sterol. A detergent, N-(N-dodecanoylsarcosyl)taurine, representative of a set of detergents synthesized by the crustacean hepatopancreas and secreted into the intestine, is capable of efficient cholesterol solubilization, and thus of promoting sterol absorption.

The intermicellar bile salt concentration in equilibrium with the mixed-micelles of human bile

The intermicellar bile salt concentration in equilibrium with the bile salt-lecithin-cholesterol mixed-micelle has been studied in human bile. Equilibrium-dialysis, used to measure the biliary intermicellar bile salt concentration, has been validated as an applicable method by studying the cholate-lecithin mixed-micelle, for which intermicellar bile salt concentration values have previously been reported. The intermicellar bile salt concentration of bile was essentially independent of ionic strength in the range 0.05-0.15 M chloride. Simple dilution of bile lowered the intermicellar bile salt concentration (about 2/3 reduction for each two-fold dilution). This reduction occurred because of a simultaneous decrease in the molar ration of bile salt/phospholipid in the micelle. Dilution of micelles with micellar bile salt/phospholipid held constant did not affect the intermicellar bile salt concentration. The relationship between intermicellar bile salt concentration and micellar bile salt/phospholipid, defined in the dilution studies, was linear in the range of study. For a composite of five biles, this relationship was described by the equation: intermicellar bile salt concentration = 1.27 (bile salt/phsopholipid) + 0.538. Data obtained on an artificial bile agreed closely with the results obtained on bile suggesting that the other constituents of bile did not affect this analysis. These findings may be helpful in understanding the process of micellar cholesterol solubilization in bile.

Prolonged secretion of lithogenic bile after cholecystectomy

Hepatic bile samples were obtained from 8 subjects 1 1/2 to 23 years after cholecystectomy for presumed cholesterol gallstones. The content of cholesterol, bile acids and lecithin was determined for each bile sample and compared to the values found in gallbladder bile in 15 control subjects undergoing cholecystectomy for pure and mixed cholesterol stones. Plot of the data on triangular coordinates and subsequent determination of lithogenic index showed that bile was supersaturated with cholesterol in both groups of patients. The cholesterol content of bile remained at supersaturated levels following cholecystectomy and showed no tendency to return toward normal levels with the passage of time.

Bile salts and gallstone disease

Bile salts play an important role in maintaining cholesterol in aqueous solution in bile. There is evidence that in some patients at least gallstones arise as a result of bile salt deficiency. The evidence to date suggests that although oral bile salts may be of use in treating some gallstone patients they are unlikely to replace cholecystectomy in the foreseeable future. The instillation of bile salts via an indwelling T-tube may well be of great use in the management of stones retained in the common duct after choledocholithotomy. There is no doubt that in this branch of medicine as in all others prevention is better than cure and our aim should be to perfect our technique so that we do not leave stones behind. However, should the situation occur we may soon have safe effective physiological solvents to dissolve our mistakes.

Management of gallstones in the aged

Calculous gallbladder disease is the most common indication for intra-abdominal surgery in the elderly. Feeding bile salts may possibly increase the solubility of cholesterol in bile and may cause diminution in the size of radiolucent gallstones, the principal ingredient of which is cholesterol. However, indications for such treatment are still not clear, and long-term effectiveness and safety still have to be evaluated. If the aged patient with gallstones has severe symptoms, is a good medical risk and is not demented, surgical treatment should not be denied because of advanced age. If the patient has "silent" or "dyspeptic" gallstones and is a poor risk or demented, surgical therapy should be postponed at least temporarily, in the hope that medical methods for dissolving gallstones soon will be perfected.

Turnover of plasma cholesterol in patients with cholesterol gallstones

Following the i.v. injection of about 30 muCi of 1-alpha-2-alpha-3H-cholesterol, the specific activity decay of plasma cholesterol has been analysed in terms of a 2-pool model in eight patients with radiolucent gallstones and two healthy controls. In each subject some kinetic parameters were calculated, including the input into and the size of the rapidly exchangeable cholesterol pool. The results were compared with those in 16 controls from another study. Statistical analysis failed to demonstrate significant differences in any of the parameters between the gallstone patients and the combined controls, indicating that patients with cholesterol gallstones have normal input into and size of the rapidly exchangeable cholesterol mass. The conclusion is discussed in relation to similar studies, and it is speculated that gallstone patients may have decreased absorption of exogenous cholesterol.

A modified assay of total faecal bile acid excretion for clinical studies

Faecal bile acid excretion was estimated in a clinical laboratory using gas liquid chromatography. The original method of Grundy et al was simplified so that quantitative thin layer chromatography was not required. Rigid dietary control or inpatient facilities were unnecessary for clinical studies. Control patients studied under these conditions had a daily faecal bile acid excretion of 0.37 +/- 0.13 g/day. Patients with ileal resections varied markedly with bile acid excretions ranging from 0.25--6.32 g/day (mean 2.36 +/- 1.11).

The choleretic effect of iodipamide

It is well established that a number of organic anions are excreted by the liver into bile in association with a marked increase in bile flow. Previous studies have shown that iodipamide (3,3'-(adipoyl-diimino)bis[2,4,6-triiodobenzoic acid]), the radiographic contrast material used for intravenous cholangiography, is a potent choleretic. Experiments were performed in unanesthetized dogs to determine if the increased bile flow produced by iodipamide is canalicular or ductular in origin, to quantitate the choleresis associated with iodipamide and taurocholate excretion, and to correlate these findings with the results of in vitro studies in which the osmotic activities of iodipamide and taurocholate in both isotonic saline and bile were determined. The plasma erythritol clearance increase linearly with the excretion of iodipamide, indicating that iodipamide stimulates canalicular bile flow. The choleretic potency of iodipamide (22 ml/mmol) is approximately 3 times that of taurocholate (7.8 ml/mmol), yet the osmotic activity of iodipamide in bile (1.5 mosmol/mmol) is only twice as great as that of taurocholate in bile (0.8 mosmol/mmol). It therefore appears that, per unit of effective osmotic solute secreted, iodipamide carries more water into the bile canaliculi than does taurocholate.

Effect of phenobarbital, spironolactone and pregnenolone-16 alpha-carbonitrile on bile formation in the rat

The effects of pretreatment for 4 days with the hepatic microsomal enzyme inducers phenobarbital (8 mg/100 g body weight), spironolactone (20 mg/100 g body weight) and pregnenolone-16alpha-carbonitrile (7 mg/100 g body weight) on bile flow and bile pipid secretion have been compared in rats. Similar to phenobarbital, spironolactone and pregnenolone-16alph-carbonitrile increased bile flow but did not alter bile salt excretion, indicating that these agents increased bile salt independent bile formation. This finding could be substantiated for spironolactone by studies of the relationship between bile salt excretion and bile flow during bile salt infusions. Whereas phenobarbital decreased cholesterol and phospholipid secretion to 39 and 49 per cent, respectively, spironolactone and pregnenolone-16alpha-carbonitrile more than doubled cholesterol excretion without influencing phospholipid output. As a consequence, marked differences in the effect on cholesterol saturation were observed: a decrease by phenobarbital and an increase following spironolactone and pregnenolone-16alpha-carbonitrile. The present studies demonstrate that different types of enzyme inducers may share certain effects on bile formation and differ in others.

Pathogenesis of human cholesterol cholelithiasis

The pathogenesis of cholesterol cholelithiasis in humans has been studied by means of three techniques. The cholesterol-solubilizing capacity of bile may be determined by estimation of the relative composition of the three major lipid constituents of bile. Consistent reduction in the cholesterol-carrying capacity of gallbladder bile of persons with gallstones when compared with normal subjects has not been shown. Normal subjects frequently have supersaturated bile. Secretion rates of biliary lipids have been estimated by two methods; with the method that appears to be more physiologic no change in lipid secretion rates was found in gallstone patients. Bile acid pool size has been measured by isotope dilution techniques; it is reduced in patients with gallstones. It is not clear whether this reduction is important in the pathogenesis of cholesterol cholelithiasis, for the bile acid secretion rate is normal because of an increased rate of cycling of the pool through the enterohepatic circulation. The role of the gallbladder in the genesis of cholesterol cholelithiasis may be more important than has been realized.

Effects of meals and interruption of enterohepatic circulation on flow, lipid composition, and cholesterol saturation of bile in man after cholecystectomy

In 4 patients studied after cholecystectomy and common-duct exploration for cholesterol gallstones, bile salt (BS) and phospholipid (PL) output and bile flow increased significantly in response to breakfast, but cholesterol (Ch) output was unaltered. Simultaneously, Ch concentration decreased while PL and BS concentrations did not change. The degree of Ch saturation of bile, [BS PLUS PL]/[ch], decreased in each study, whether or not the original ratio indicated Ch supersaturation; in 3 of 5 studies, an initially super-saturated bile became unsaturated with Ch in response to breakfast. No significant changes were noted after lunch. During interruption of enterohepatic circulation (EHC), studies with radiolabeled bile acids indicated that the increased bile acid output in response to meals was secondary to increased recirculation of intestinal bile acids rather than to de novo bile acid synthesis. This mechanism may account for the adequate delivery of BS and for the decreased degree of Ch saturation of bile postprandially in cholecystectomized patients.

Effects of polyunsaturated fats on lipid metabolism in patients with hypertriglyceridemia

Studies were carried out on the effects of polyunsaturated fats on lipid metabolism in 11 patients with hypertriglyceridemia. During cholesterol balance studies performed in eight patients, the feeding of polyunsaturated fats, as compared with saturated fats, caused an increased excretion of endogenous neutral steroids, acidic steroids, or both in most patients. Increases in steroid excretions were marked in some patients and generally exceeded the decrement of cholesterol in the plasma compartment. The finding of a greater excretion of fecal steroids on polyunsaturated fats in hypertriglyceridemic patients contrasts to the lack of change in sterol balance previously reported for patients with familial hypercholesterolemia; however, other workers have found that polyunsaturated fats also enhance steroid excretion in normal subjects. In most of the patients, simultaneous studies were carried out on biliary lipid composition, hourly outputs of biliary lipids, and pool sizes of bile acids. In several but not all patients, fasting gallbladder bile became more lithogenic after institution of polyunsaturated fats. This increased lithogenicity was not due to a decrease in bile acid pools; in no case was the pool decreased by polyunsaturated fats. On the other hand, two patients showed an increased output of biliary cholesterol, and frequently there was an increase in fecal neutral steroids that were derived from cholesterol; thus, polyunsaturated fats may increase bile lithogenicity in some patients through mobilization of cholesterol into bile. Reductions in plasma cholesterol during the feeding of polyunsaturated fats was seen in most patients, and these changes were usually associated with a decrease in concentration of plasma triglycerides. In fact, the degree of cholesterol lowering was closely correlated with the extent of triglyceride reduction. Therefore, in hypertriglyceridimec patients polyunsaturated fats may contribute to cholesterol reduction by changing the metabolism of triglycerides or very low density lipoproteins. The findings of changes in the metabolism of cholesterol, bile acids, and triglycerides in the patients of this study suggests that polyunsaturated fats may cause a lowering of cholesterol through multiple mechanisms, and it seems unlikely that a single action can explain all the effects of these fats on the plasma lipids.

Cholelithiasis and ileal pathology in childhood

Primary cholelithiasis is rare in childhood. A particular etiology has appeared over the last few years in connection with unusual physiological situations. Three cases of cholelithiasis after ileal atresia or resection are presented in children of 1, 1, and 7 yr. Another case is presented after abdominal irradiation for Wilms' tumor and ileal resection in a child of 7. The pathogenesis is discussed, raising the question of the interruption of the enterohepatic circulation of bile salts.

Analysis of gallbladder bile in morbid obesity

Thirty-seven per cent of our grossly obese patients selected for gastric bypass had cholesterol gallstones. To document the composition of the biliary lipids prior to weight loss, the bile taken from eleven obese patients at the time of gastric bypass was analyzed and the results compared with those in eleven nonobese patients undergoing elective surgery. There was extreme supersaturation of both gallbladder and hepatic bile in all obese patients. The gallbladder bile of all obese patients fell well outside the micellar zone whereas the bile from all but one of the controls fell within the micellar zone. These data provide biochemical support for the clinical association of obesity and cholesterol gallstone formation and are evidence against the possibility that gastric bypass is a lithogenic operation.

Mechanism of secretion of biliary lipids. I. Role of bile canalicular and microsomal membranes in the synthesis and transport of biliary lecithin and cholesterol

The role of bile canalicular and microsomal membranes in the synthesis and transport of biliary lipids was investigated by using the isolated perfused rat liver model. Labeled lecithin precursors ((3H)-palmitic acid, (14C)linoleic acid, (3H)choline, and 32PO4) and a cholesterol precursor ((3H)mevalonic acid) were administered with and without sodium taurocholate. The incorporation pattern of these labeled precursors into linoleyl and arachidonyl lecithins and cholesterol fractions of microsomes, bile canaliculi, and bile were examined at 30-min intervals up to 90 min. Marker enzymes and electron microscopy indicated that isolated subfractions of plasma membranes were enriched with bile canaliculi (less than 10 percent microsomal contamination). Taurocholate significantly stimulated the incorporation of 32PO4, (3H)choline, (3H)palmitic acid, and (14C)linoleic acid into linoleyl and arachidonyl lecithin with parallel incorporation curves for microsomal and bile canalicular membranes throughout the 90-min study period. During the 30-60-min period, however, these same lecithin fractions in bile significantly exceeded the specific activity of the membrane lecithins. The enzyme CDP-choline diglyceride transferase was virtually absent from canaliculi relative to microsomes, indicating that canaliculi lack the capacity for de novo lecithin synthesis. Incorporation of (3H)mevalonic acid into membranous and biliary cholesterol followed a pattern similar to that for lecithin. These data provide evidence that (a) biliary lecithin and cholesterol are derived from a microsomal subpool regulated by the flux of enterohepatic bile acids, (b) the role of the bile canalicular membranes with respect to biliary lipids is primarily transport rather than synthesis, and (c) lecithin and cholesterol are transported together from microsomes to bile. The findings are consistent with the existence of a cytoplasmic lipid complex within the hepatocyte which is actively involved in the intermembrane transport of biliary lipid.

Biliary lipid output during three meals and an overnight fast. II. Effect of chenodeoxycholic acid treatment in gallstone subjects

Oral treatment with chenodeoxycholic acid causes dissolution of cholesterol gallstones in man. In order to determine the mechanism of this effect, we have measured 24-hour biliary lipid output, lipid composition of fasting gallbladder bile, and bile acid pool sizes before and during such treatment in six patients with radiolucent gallstones in functioning gallbladders. In all six patients, the degree of cholesterol saturation of fasting-state gallbladder bile was decreased during treatment to a level below the thermodynamic solubility line. This effect was due to a decrease in biliary cholesterol output, associated with conversion of more than 90% of the total bile acid pool to chenodeoxycholic acid. It could not be attributed to an increase in total bile acid pool size nor to an increase in biliary bile acid or phospholipid output.

Biliary lipid output during three meals and an overnight fast. I. Relationship to bile acid pool size and cholesterol saturation of bile in gallstone and control subjects

Using a duodenal perfusion technique, the biliary output of bile acids, phospholipid, and cholesterol was measured hourly during three meals and an overnight fast in seven Caucasians with radiolucent gallstones in a functioning gallbladder, and in seven health controls without gallstones, closely matched for age, sex, and weight. Before the perfusion, bile acid kinetics were defined by an isotope dilution procedure, and the biliary lipid composition of fasting gallbladder bile was determined. Total daily biliary lipid output was similar in gallstone and control subjects, and was unrelated to cholesterol saturation of fasting gallbladder bile and to bile acid pool size. There was an inverse relationship between the size and recycling frequency of the bile acid pool, so that secretion rate and hepatic return of bile acids remained constant, despite a wide range of pool sizes. The finding of a normal bile acid synthesis rate in subjects with a small pool size therefore indicated normal feedback regulation of bile acid synthesis. Hourly measurements of biliary lipid output showed a linear relationship between bile acid and cholesterol output, with a similar regression line for gallstone and control subjects, but a non-linear relationship between bile acid and phospholipid output. Consequently, samples from all subjects were consistently supersaturated with cholesterol at low bile acid outputs, especially during overnight fasting, but not at high bile acid outputs. These findings indicate that hepatic secretion of bile supersaturated with cholesterol is physiological in man at low bile acid outputs, that bile acid pool size is probably determined in part by its recycling frequency, and that cholesterol cholelithiasis in some Caucasians may be due to an underlying extrahepatic abnormality.

Variation in hepatic bile composition following cholecystectomy in patients with previous gallstones

The composition of fasting hepatic bile was analyzed in 63 samples from 8 patients following cholecystectomy to determine if bile was lithogenic in patients with previous cholesterol gallstones after removal of the gallbladder. Bile specimens were obtained from t-tubes over a 7-20 day study period following re-establishment of the enterohepatic circulation. Bile composition varied on a day to day basis in each patient. 18 of 63 samples were lithogenic according to criteria of Admirand and Small while 35 of 63 samples were lithogenic according to criteria of Hegardt and Dam. Variations in the composition of hepatic bile appeared related to changes in the excretion rate of bile acids. These studies demonstrate that hepatic bile may be lithogenic after cholecystectomy and indicate that factors other than sequestration of the bile acid pool in the gallbladder influence the enterohepatic circulation of bile acids and the lithogenicity of bile.