Dietary fat and cholesterol modulate the plasma lipoprotein distribution and production of pigment or cholesterol gallstones in hamsters

To evaluate the impact of key dietary factors on plasma lipoproteins and gallstone induction, male Syrian hamsters were fed either cholesterol and fat-supplemented purified diets containing glucose or lactose, or cholesterol and fat-free diets with or without fiber, for 13 wk. Fat-supplemented hamsters were hyperlipidemic in comparison to those fed fat-free diets. The former group revealed a greatly expanded VLDL fraction, whereas a normal HDL2 pool predominated in the latter group. Plasma fatty acids indicated that hamsters fed the fat-free diet were essential fatty acid deficient whilst the hamsters fed the fat-supplemented diet were subnormal in essential fatty acids. Ninety-three percent of the hamsters fed the fat-supplemented diet had gallstones (mostly cholesterol), whereas 62% of hamsters fed the fat-free diet had gallstones (almost all pigmented). Lactose increased cecal weight and prevented pigment stone formation in the fat-supplemented hamsters, whereas adding fiber to the fat-free diet contributed essential fatty acids, eliminated cholesterol stones and enhanced pigment stone formation. Thus, diets containing casein, rice flour, glucose and fiber with minimal essential fatty acids but no cholesterol promoted pigment stones (associated with a normal lipoprotein profile); a low fat diet limited in essential fatty acids but containing cholesterol and lactose, promoted cholesterol gallstones (associated with an expanded VLDL pool).

Indomethacin and postprandial gallbladder emptying

Patients with gallstone disease commonly have impaired gallbladder emptying. To see whether non-steroidal anti-inflammatory drugs (NSAIDs) prevent gallstone formation by improving gallbladder emptying, we assessed the effect of indomethacin on postprandial emptying in healthy subjects and in patients with gallstone disease. Subjects received indomethacin 25 mg three times a day for a week and matching placebo for another week. Compared with placebo, indomethacin improved postprandial gallbladder emptying in all 7 patients with gallstone disease. This finding was not recorded in healthy subjects with normal gallbladders. The prevention of gallstone formation associated with ingestion of NSAIDs may be due mainly to a prokinetic effect on the gallbladder since there is no evidence to suggest that these drugs affect cholesterol crystal nucleation at ordinary therapeutic doses in man or animals.

Inhibitory effects of pravastatin, a competitive inhibitor of hydroxymethylglutaryl coenzyme A reductase, on cholesterol gallstone formation in prairie dogs

The effects of pravastatin on cholesterol gallstone formation were determined in prairie dogs. We fed 10 prairie dogs 1% cholesterol with or without 0.05% (w/w) pravastatin (n = 5, each) for 4 weeks. In addition, another 5 prairie dogs were fed a standard rodent chow as a control. Only the animals fed 1% cholesterol without pravastatin treatment formed cholesterol gallstones. Gallbladder bile from cholesterol-fed animals contained cholesterol monohydrate crystals, whereas those treated with pravastatin contained no crystal. Furthermore, marked increases in tissue cholesterol levels (serum, liver and bile), and in biliary mucous glycoprotein levels were evident in cholesterol-fed animals, whereas pravastatin treatment normalized these levels. These findings raise the possibility that such inhibitors might have a future role to play in the prevention of cholesterol gallstone formation and/or recurrence.

Aspirin does not inhibit cholesterol cholelithiasis in two established animal models

The effect of aspirin on cholesterol cholelithiasis was examined in the hamster and the prairie dog. In the prairie dog, diets were composed of semipurified components of chow, plus cholesterol (1.2%), with and without aspirin. Animals were studied for either 2 weeks or 4 weeks. Cholesterol gallstones were present in all groups at the end of each period; aspirin did not alter the incidence of cholelithiasis. All animals studied had cholesterol crystals in the bile when they were killed. Liver cholesterol levels in prairie dogs with and without aspirin tended to be lower in animals fed chow than in animals fed semipurified diets. There were no significant differences in cholesterol levels in the plasma or bile. The cholesterol saturation index of all biles approached unity when animals were fed chow with aspirin; animals fed the semipurified diets had cholesterol saturation indices of less than 1.0. The prairie dogs fed aspirin plus cholesterol in the semipurified diet showed increased levels of biliary chenodeoxycholic acid amidates and concomitant decreased levels of cholic acid amidates compared with animals fed the same diet without aspirin. Hamsters fed aspirin plus cholesterol in a semipurified diet tended to have a greater incidence of gallstones than animals given no aspirin (80% vs. 55%). Liver and bile cholesterol levels were similar with and without aspirin; plasma cholesterol levels increased significantly with aspirin [14.20 vs. 7.80 mmol/L (549 vs. 301 mg/dL)]. Lithogenic indices in all hamsters were above unity; biliary lipids, total lipid concentration, and biliary bile acid composition were similar. These results show that the addition of aspirin to a lithogenic diet does not reduce the incidence of cholelithiasis.

Sclerotherapy of the gallbladder in pigs. Development of a balloon catheter for a single-step procedure

Gallbladder sclerotherapy after permanent cystic duct occlusion, to prevent gallstone recurrence in nonsurgical gallstone therapy, is at least a two-stage procedure. A balloon catheter was developed to perform gallbladder sclerotherapy with only temporary occlusion of the cystic duct, and the efficacy and safety of this method was subsequently investigated. Twenty pigs underwent cholecystostomy for positioning of a 7-Fr triple-lumen balloon catheter with proximal side holes. Sclerotherapy with 96% ethanol and 3% sodium tetradecyl sulfate for 20 minutes was performed. The animals were killed 24 hours, two, six, and 12 weeks after the procedure. The balloon catheter functioned well and seems suitable for procedures in which a temporary occlusion of the cystic duct is required. Although gallbladders after six and 12 weeks were shrunken and fibrotic, a single treatment of gallbladder sclerotherapy with subsequent catheter removal and no permanent cystic duct occlusion, as performed in this experiment, did not produce complete gallbladder ablation. In this study, sclerotherapy proved safe in the short term, but long-term effects remain to be assessed.

Comparative evaluation of chenodeoxycholic and ursodeoxycholic acids in obese patients. Effects on biliary lipid metabolism during weight maintenance and weight reduction

Obesity is a condition associated with an increased frequency of gallstone disease. This study attempted to evaluate the comparative effects of two gallstone-dissolving agents, chenodeoxycholic acid and ursodeoxycholic acid, on bile acid metabolism and biliary lipid secretion in obese subjects in order to identify the bile acid of choice in preventing and treating gallstone disease in obesity. Twenty obese subjects (greater than 120% ideal body wt) were randomly treated with ursodeoxycholic acid (10 mg.kg-1.day-1.1 mo-1) and then with chenodeoxycholic acid (15 mg.kg-1.day-1.1 mo-1) or with chenodeoxycholic acid first and then with ursodeoxycholic acid. Patients 1-10 were studied while eating an unrestricted weight-maintenance diet, whereas patients 11-20 were eating a 1080-kcal/d hypocaloric diet. Biliary lipid composition, cholesterol saturation index, and biliary bile acid pattern were evaluated in all subjects before and after each treatment period; in subjects 6-10 and 16-20, biliary lipid secretion rates and bile acid pool size were also evaluated. Both ursodeoxycholic acid and chenodeoxycholic acid decreased cholesterol outputs and cholesterol saturation index. However, during the weight-maintenance period the decrease induced by chenodeoxycholic acid was not significant. Biliary cholesterol outputs and cholesterol saturation index were always lower during ursodeoxycholic acid administration than during chenodeoxycholic acid therapy. Ursodeoxycholic acid levels during ursodeoxycholic acid administration and chenodeoxycholic acid levels during chenodeoxycholic acid administration increased in bile to 50% and 77%, respectively, of total bile acid levels. Bile acid pool size remained unchanged during chenodeoxycholic acid administration and was significantly reduced by ursodeoxycholic acid administration during the weight-reduction period. In conclusion, ursodeoxycholic acid in obese subjects seems more effective than chenodeoxycholic acid, at least during weight maintenance, in reducing cholesterol saturation of bile. This effect is related to a significant decrease of biliary cholesterol output.

One gram of aspirin per day does not reduce risk of hospitalization for gallstone disease

Data from 4524 patients in a randomized, controlled trial of aspirin were analyzed to determine if aspirin reduced the risk for hospitalization for gallstone disease. Aspirin at a dose of 1000 mg/day did not reduce the risk of hospitalization for gallstones. Hospitalization rates for gallstone disease were consistent with national rates, and the data confirmed previous associations of gallstone disease with age, elevated serum triglycerides, obesity, and female gender.

Lovastatin inhibits gallstone formation in the cholesterol-fed prairie dog

The efficacy of lovastatin, an inhibitor of hepatic cholesterol synthesis in the prevention of cholesterol gallstone formation, was evaluated in the prairie dog model. Two groups of animals were maintained on either nonlithogenic or 1.2% cholesterol-enriched chow for 21 days. Seven of the animals in each group received lovastatin, and the remaining six received only distilled water. All of the cholesterol-fed/water-treated animals had crystals and 83% had gallstones, but none of the cholesterol-fed/lovastatin-treated animals had gallstones and only three had microscopic crystals. These data indicate that lovastatin inhibits cholesterol gallstone formation in a diet-induced model of gallstone disease.

Effect of bile diversion and sphincterotomy on gallbladder muscle contractility and gallstone formation

Feeding prairie dogs a diet rich in cholesterol induces gallstone formation that is preceded by a sustained decrease in gallbladder smooth muscle contractility. Sphincterotomy is known to prevent gallstone formation in cholesterol-fed prairie dogs. Experiments were designed to determine whether the effect of sphincterotomy is a consequence of hepatic bile diversion, and whether bile diversion prevents the altered contractility. Following sham operation, surgical biliary enteric bypass, or sphincterotomy, prairie dogs were fed a high-cholesterol or a regular diet. Gallbladder muscle contractility and the presence of crystals and stones were determined. In sham-operated animals, the cholesterol diet induced a decrease in gallbladder muscle contractility and caused the formation of cholesterol gallstones. In animals with bile diversion and sphincterotomy, the effects of cholesterol feeding were reduced or prevented. Thus, these procedures may prevent stone formation by preventing a reduction in gallbladder contractility. Contractility was depressed in animals with bile diversion fed a regular diet, compared with animals with a sham operation fed a regular diet. The mechanism for this depression may differ from that induced by the cholesterol diet. Diversion, and perhaps sphincterotomy, impairs gallbladder filling. Thus, gallbladder muscle is not stretched and does not contract against a load. This could result in a "disuse atrophy." If the results from our study apply to humans, sphincterotomy may reduce stone formation by preventing the effects of lithogenic bile on gallbladder muscle contractility and by enhancing the ability of the muscle to empty the lithogenic bile.

Differential effects of ursodeoxycholic acid and ursocholic acid on the formation of biliary cholesterol crystals in mice

The preventive effect of 3 alpha, 7 beta, 12 alpha-trihydroxy-5 beta-cholanoic acid (ursocholic acid) and ursodeoxycholic acid on the formation of biliary cholesterol crystals was studied in mice. Cholesterol crystals developed with 80% incidence after feeding for five weeks a lithogenic diet containing 0.5% cholesterol and 0.25% sodium cholate. When 0.25% ursocholic acid or ursodeoxycholic acid was added to the lithogenic diet, the incidence as well as the grade (severity) of the gallstones were reduced. Plasma and liver cholesterol levels were decreased by ursodeoxycholic acid but not by ursocholic acid. Gallbladder cholesterol and phospholipid levels were decreased by both bile acids. The biliary bile acid level was decreased by ursocholic acid but not by ursodeoxycholic acid. After feeding ursocholic acid, its level in the bile was about 25% and the levels of cholic acid and beta-muricholic acid decreased. Fecal sterol excretion was not changed by ursocholic acid, but was increased by ursodeoxycholic acid. After feeding ursocholic acid, fecal excretion of deoxycholic acid, cholic acid, and ursocholic acid increased. No differences were found between mice, with or without gallstones, in plasma and liver cholesterol levels, biliary phospholipid and bile acid levels, fecal sterol and bile acid levels, and biliary and fecal bile acid composition. The results suggest that the lower incidence of crystal formation after treatment with ursocholic acid is probably by a different mechanism than with ursodeoxycholic acid. In the mouse model, ursodeoxycholic acid exerts its effect at least partially, by decreasing cholesterol absorption. Ursocholic acid is well absorbed and excreted into bile and transformed into deoxycholic acid by the intestinal microflora in mice.

[Prevention of recurrence after successful gallstone dissolution]

Gallstone recurrence is a major problem in the medical treatment of gallstones (treatment with UDCA/CDCA, ESWL, local MTBE lysis). The probability of gallstone recurrence is higher in subjects with multiple stones before dissolution treatment and in older subjects (greater than 50 years). The present knowledge on factors predictive of gallstone recurrence and the results of clinical trials for preventing recurrence are given. The different effects of diet and drugs on cholesterol saturation of bile, on nucleation of bile, on mucus production of gallbladder and on gallbladder contractility are discussed and recommendations for a rational approach for prevention of gallstone recurrence are given. Preventable risk factors for gallstone disease have to be eliminated. In general, continuous post-dissolution treatment seems not justified. Regular follow-up ultrasound examinations should be started to detect renewed of gallstones at an early stage.

[Clinical and experimental studies on stone detectability of cholangiography and choledochoscopy. Prevention of retained biliary-tract stones]

Preoperative diagnostic accuracy was significantly improved following a recent development of diagnostic imaging techniques. However, the incidence of retained biliary tract stones is far from satisfactory low. Retrospective studies on operative and postoperative cholangiography, and choledochoscopy were carried out to determine the limitation of each modality in preventing the retained biliary tract stones. The effectiveness of postoperative stone extraction technique for retained biliary tract stones was reevaluated by a follow up study of 213 cases with retained biliary tract stones in which complete removal of the stones was considered to be successful. Finally, a radiological experimental study concerning stone detectability was carried out using phantom system.

CONCLUSION

1) In the retrospective study of operative cholangiography, stones were not demonstrated on cholangiograms in 78 out of 167 cases, although they were detected and extracted by postoperative choledochoscopy. The main causes of the failure of cholangiography were the administration of highly concentrated contrast material (47.4%) and incomplete filling of whole ducts (26.9%). Therefore, the further development for the detection of these stones by operative cholangiography should be desired. 2) In the experimental study, it was clarified that complete filling of the ducts with 30% or 20% contrast materials was essential in normal size or dilated ducts respectively in order to detect small size stones. Moreover, the author emphasized that it is important to take two photographs, one is taken at proper voltage and the other at voltage 10 kVp. Higher in order to demonstrate whole stones whose sizes are varied. 3) Stone detectability was improved to 87.1% by using both operative cholangiogram and choledochoscopy. 4) Routine use of postoperative choledochoscopy at the time of T-tube removal is essential, because stone not detected by T-tube cholangiography were found endoscopically in 2.2% of cases with retained stones. 5) In the follow-up study, a good result was obtained in the cases in which complete stone extraction was considered to be successful by postoperative choledochoscopy. However, reoperation was found to have been performed in 13 cases, because of recurrent or retained stones. Of them three cases were judged to be recurrence. In the other 10 cases, the stones were defined as overlooked stones by postoperative choledochoscopy.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of dietary ethanol on gallbladder absorption and cholesterol gallstone formation in the prairie dog

Dietary ethanol has been reported to protect against cholesterol gallstone formation. Because enhanced gallbladder absorption of water is important in cholesterol cholelithiasis, we examined the hypothesis that ethanol acts by inhibiting the absorptive function of the gallbladder. Eighteen adult male prairie dogs were fed a lithogenic liquid diet containing 0.4% cholesterol. Half of the animals received 30% of total calories as ethanol, whereas their pair-fed controls received equicaloric amounts of maltose-dextrin. After 3 months, the gallbladders were inspected for gallstones and crystals, and gallbladder and hepatic bile were analyzed. Cholesterol stones and crystals were present in all nine controls. None of the alcohol-fed animals had stones, but four had cholesterol crystals. Gallbladder cholesterol, phospholipids, and total calcium were significantly decreased in alcohol-fed animals. In both gallbladder and hepatic bile, the cholesterol saturation index was significantly lower in alcohol-fed animals, as was the ratio of trihydroxy to dihydroxy bile salts. The ethanol-supplemented diet produced a significant decrease in the absorption of water by the gallbladder as indicated by changes in the gallbladder bile to hepatic bile ratios of the total bile salt concentration (7.29 +/- 1.25 versus 3.84 +/- 0.56; p less than 0.05) and the total calcium (3.37 +/- 0.24 versus 2.43 +/- 0.29; p less than 0.05). These findings indicate that the protective effect of ethanol may be related to its ability both to inhibit gallbladder absorption of water and to alter the composition of biliary lipids.

A practical guide to the nonsurgical treatment of gallstones

Until recently, cholecystectomy was the only treatment available for symptomatic gallstone disease. During the past 20 years, better understanding of the pathogenesis of cholesterol gallstone disease has led to alternative nonsurgical methods for treating gallstones in selected groups of patients. Use of 2 naturally occurring bile acids, chenodeoxycholic acid (CDCA) and ursodeoxycholic acid (UDCA), was reported in 1972 and 1975, respectively, for successful dissolution of cholesterol gallstones in humans. Both these bile acids act by reducing cholesterol secretion in bile, thus enabling it to solubilise more cholesterol from the stone surface. Micellar solubilisation is involved, together with liquid crystal formation in the case of UDCA. Having been extensively studied in clinical trials to assess efficacy and safety, both these compounds are now available for general use. The efficacy of CDCA can be enhanced by single bedtime dose administration and by taking a low cholesterol diet. Bedtime administration also enhances the effect of a suboptimal dose of UDCA. CDCA induces dose-related diarrhoea and hypertransaminaemia, and UDCA can induce calcification of gallstones, thus rendering them resistant to medical dissolution. A combination of the 2 bile acids at half the recommended dose for each has become an accepted practice for reducing adverse effects, and this may also enhance efficacy. One of the main problems of bile acid therapy is that dissolution of gallstones is a very slow process. Use of extracorporeal shockwave lithotripsy (ESWL) to break the stones into smaller fragments, with concurrent use of bile acids, has been shown to speed dissolution rate and to achieve complete gallstone dissolution in 78% of selected cases within 12 months.(ABSTRACT TRUNCATED AT 250 WORDS)

The prevention of cholelithiasis with infused sodium chenodeoxycholate in the prairie dog (Cynomys ludovicianus)

1. This study examines the efficacy of infused sodium chenodeoxycholate to prevent cholesterol gallstone formation in the prairie dog when fed a high cholesterol diet. 2. Three experimental groups were designed to examine this. The first group (N = 5) was fed a normal rat chow diet, the second group (N = 5) was fed a high cholesterol diet (0.4% cholesterol by weight), and the third group (N = 5) was fed a high cholesterol diet plus given a daily injection of intravenous sodium chenodeoxycholate (15 mg/kg). 3. All of the animals in the second group had cholesterol crystals and cholesterol gallstones. In the third group, none of the animals had gallstones, and all but one lacked cholesterol crystals. 4. Statistical analysis showed that the first and third groups were statistically identical in their lithogenic indices and biliary lipid composition. 5. We concluded that infused sodium chenodeoxycholate is effective in preventing cholesterol gallstone formation in the prairie dog when fed a high cholesterol diet.

[Changes in bile components during the formation and prevention of black pigment gallstone in a guinea pig model]

Black pigment gallstones were found in 22 out of 23 guinea pigs one week after the common bile ducts were partially ligated (S group). The incidence decreased to 11/20 (P less than 0.01) if the animals were fed with a chow containing bile salt mixture, glucurolactone, ane aspirin (S+M group). Three weeks after the ligation the incidence of gallstone in S group and S+M group was 17/18, and 9/10, respectively (P greater than 0.05). Glucuronidase (beta-G) activity in the bile of S group was not higher than that of control group (C group, P greater than 0.05), and all the bile samples were sterile. The biliary concentrations of ionized calcium (ICa), unconjugated bilirubin (UCB), total calcium (TCa), total bilirubin (TBr), glycoprotein (GIy. P), and PH significantly fluctuated among guinea pig groups and were parallel to gallstone incidence. The results of this study could hardly be explained by Maki beta-G theory, but were consistent with the assumption that the precipitation-dissolution equilibrium of calcium bilirubinate is the key of pigment gallstone formation, thus the increases of the above mentioned bile components, including beta-G activity, would bias this equilibrium towards calcium bilirubinate precipitation and therefore promote gallstone formation. On the contrary, stone formation would be prevented.

[The effect of proglumide on gallstone formation in guinea pigs]

In this study, the chronic effects of proglumide (PGM, a cholecystokinin/gastrin receptor antagonist) on gallstone formation and hepatic bile secretion were investigated as follows: Group 1: Fed with low protein (14%) lithogenic diet. Group 2: Fed with the same lithogenic diet and was given PGM (250 mg/kg, bid, p. o.). Group 3: Fed with commercial guinea pig chow (protein content 22%). Eight weeks later the animals were operated under urethane anesthesia, the gallbladders were removed and examined for gallstones. Meanwhile, by bile duct cannulation, the hepatic bile flow and bile contents were measured. It was found that: (1) the animal model was valid for the purpose specified; (2) the rate of gallstone formation was significantly lower in PGM group than in the controls (17.5% vs 56.8%, P less than 0.01); and (3) PGM significantly enhanced the flow rates and electrolyte contents and decreased the unconjugated bilirubin content of the hepatic bile. It is concluded that PGM may suppress gallstone formation in guinea pigs on lithogenic diet, and this may be related to its stimulatory effect on hepatic bile secretion and to its ability to induce a decrease in unconjugated bilirubin in the hepatic bile.

The influence of barley fibre on bile composition, gallstone formation, serum cholesterol and intestinal morphology in hamsters

Frequency of gallstones, concentration of bile acids and cholesterol in bile, concentration of cholesterol in serum, and structure of the small intestinal mucosa were analyzed in male Syrian Golden hamsters fed a stone provoking fibre-free diet with or without supplementation of brewer's spent grain (BSG), a concentrated barley fibre source from the by-product of brewing. A significantly lower frequency of gallstones was found in the animals with 10% BSG dietary supplementation. Addition of 30% BSG after an initial 6-week period with a fibre-free, stone provoking diet seemed to dissolve previously formed gallstones. Total bile acid concentration was higher in bile from animals given a diet supplemented with 10% BSG. In addition, the cholesterol concentration in both serum and bile was lower in the 30% BSG supplemented group. Structurally, a 10% BSG supplementation decreased ileal epithelium height whereas a high supplementation (30%) of BSG induced a decrease in epithelial height both of jejunal and ileal mucosa. The results show that BSG has significant effects on the metabolism of bile acids and cholesterol as well as on the morphology of the small intestinal mucosa.

Biliary D-glucaric acid: its quantitation and preventive role in gallstone formation

A method for quantitation of D-glucaric acid in bile has been developed involving extraction with tetrahexylammonium chloride, boiling for 40-60 min, and determination of the percentage inhibition of beta-glucuronidase activity at 56 degrees C and pH 4. D-glucaric acid, bilirubin, bile acid, and protein were determined in 106 human gallbladder biles obtained at autopsy, including 20 with gallstones. The mean D-glucaric acid content was 1125 +/- 159 microM (mean +/- SE). Biliary beta-glucuronidase activity was not affected by D-glucaric acid because of 1) no difference in biliary D-glucaric acid content, either absolute or corrected for per unit of bilirubin, bile acid, or protein, between those with and those without gallstones; 2) no negative correlation between D-glucaric acid content and beta-glucuronidase activity in the bile; and 3) minimal conversion of D-glucaric acid to D-glucaro-1,4-lactone at the usual pH of bile. We conclude that biliary D-glucaric acid plays no role in the prevention of gallstone formation.

Synthetic low and high fat diets for the study of atherosclerosis in the mouse

Diets currently used to produce atherosclerotic lesions in mice are often undefined and cause accumulation of fat in the liver and gallstone formation. Therefore, synthetic low and high fat diets of known composition were formulated in this study. A synthetic diet containing 50% sucrose, 15% cocoa butter, 1% cholesterol, and 0.5% sodium cholate was found to produce a depression in high density lipoprotein cholesterol (HDL-C) and an elevation of very low density lipoprotein (VLDL) and low density lipoprotein cholesterol (LDL-C) in the atherosclerosis-susceptible strain, C57BL/6J. This diet was able to consistently produce aortic lesions and led to a decrease in liver damage and gallstone formation. The synthetic low fat diet did not produce HDL-C levels as high as those found in mice fed chow, but resulted in similar VLDL/LDL-C levels. Lipoprotein and apolipoprotein parameters were compared in C57BL/6J and the atherosclerosis-resistant strain, C3H/HeJ, consuming the synthetic low fat or high fat diets. As reported earlier, when consuming a high fat diet C57BL/6J mice have significantly lower HDL-C and apoA-I levels than C3H/HeJ mice. Further analysis shows that the molar ratio of plasma HDL-C to apoA-I is significantly lower in C57BL/6J mice, suggesting that HDL in the susceptible strain has a lower cholesterol-carrying capacity. This conclusion is consistent with the observation that the HDL particle size is smaller for C57BL/6J mice than for C3H/HeJ. Both strains increased their apoE levels when fed the synthetic high fat diet, but C3H/HeJ mice had higher levels of apoE on both diets. The major response to consumption of the high fat diet for both strains was an increase in apoB-48 from 5 micrograms/ml on a low fat diet to 54 and 109 micrograms/ml for C57BL/6J and C3H/HeJ, respectively. ApoB-100 showed minimal response to the high fat diet. The defined high fat diet can be used to study atherosclerosis in the mouse since it produces aortic lesions but reduces or eliminates other pathological changes such as gallstone formation and liver damage.