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Our previous work established that hypocholesterolemic agents altered K-ras intracellular localization in lung. Here, we examined K-ras activity to define further its potential importance in lung carcinogenesis. K-ras activity in lungs from male A/J, Swiss and C57BL/6 mice was examined. For three weeks, mice consumed either 2 or 4% cholestyramine (CS), 1% niacin, 5% konjac mannan (KM), or were injected with lovastatin 25 mg/kg three or five times weekly (Lov-3X and Lov-5X). A pair-fed (PF) group was fed the same quantity of diet consumed by the Lov-5X mice to control for lower body weights in Lov-5X mice. After three weeks, serum cholesterol was assayed with a commercial kit. Activated K-ras protein from lung was affinity precipitated with a Raf-1 ras binding domain-glutathione-S-transferase fusion protein bound to glutathione-agarose beads, followed by Western blotting, K-ras antibody treatment, and chemiluminescent detection. Only KM reduced serum cholesterol (in 2 of 3 mouse strains). In C56BL/6 mice treated with Lov-3X, lung K-ras activity increased 1.8-fold versus control (p = 0.009). In normal lung with wild-type K-ras, this would be expected to be associated with maintenance of differentiation. In A/J mice fed 4% CS, K-ras activity increased 2.1-fold (p = 0.02), which might be responsible for the reported enhancement of carcinogenesis in carcinogen-treated rats fed CS. KM feeding and PF treatment had no significant effects on K-ras activity. These data are consistent with the concept that K-ras in lung has an oncogenic function when mutated, but may act as a tumor suppressor when wild-type.

Hypocholesterolemic drugs may themselves increase (cholestyramine, CS) or decrease (lovastatin, Lov) peripheral tissue de novo cholesterol biosynthesis. This will alter the abundance of prenyl groups and potentially increase (CS) or decrease (Lov) K-ras membrane localization, with possible pro- or anti-carcinogenic effects (K- ras is a proto-oncogene frequently mutated in lung cancer). Female A/J, Swiss, and C57BL/6 mice were fed 2 or 4% CS, 1% niacin, or injected with Lov three (Lov-3×) or five (Lov-5×) times per week. After three weeks, serum cholesterol and triglycerides were determined enzymatically. Total, membrane, and cytoplasmic K-ras proteins were determined in lung homogenates by immunoprecipitation followed by Western blotting with a K-ras specific antibody. CS feeding increased membrane K-ras as hypothesized in A/J and C57BL/6 mice, but had no effect in Swiss mice. Lov failed in all three strains to reduce membrane K-ras, and resulted in an increase in total K-ras in A/J and C57BL/6 mice, while again lacking effect in Swiss mice. Niacin had no effect on K-ras protein in any mouse strain. These results differ from our published results for male mice of the same strains, particularly for A/J mice. Increased amounts of K-ras protein in the membrane fraction of A/J females (but not males) treated with either Lov or CS imply that if K-ras were to become mutated, CS could result in increased lung tumorigenesis and Lov would be less likely to be protective in females. In the light of these data, both sexes should be included in future animal and human chemoprevention trials.

Agents that either increase (cholestyramine, CS) or decrease (lovastatin, Lov) de novo peripheral cholesterol synthesis may increase (CS) or decrease (Lov) ras protein membrane localization by altering protein prenylation, and potentially have pro- or anti-carcinogenic effects. Male A/J, Swiss, and C57/BL6 mice were treated with 2 or 4% CS, 1% dietary niacin, or 25 mg/kg of Lov three times per week (Lov-3X) or five times per week (Lov-5X). After 3 weeks, serum cholesterol and triglycerides were determined enzymatically. Membrane and cytoplasmic K-ras proteins in lung were determined by immunoprecipitation followed by western blotting with a K-ras specific antibody. Results confirmed the hypothesis only in isolated instances. A/J mice had a significant 30% increase in cytoplasmic K-ras and a 40% decrease in membrane K-ras from Lov treatment, as predicted. C57/BL6 mice had a significant 77% increase in membrane K-ras, as expected from CS feeding. At variance with the hypothesis, Swiss mice had increased levels (3–28%) of membrane K-ras with all treatments (including Lov), and C57/BL6 mice treated with Lov had a 58–78% increase in cytoplasmic K-ras without any reduction in the levels of membrane K-ras. Niacin, predicted to have no effect on ras membrane localization, decreased cytoplasmic K-ras in A/J mice, increased both membrane and cytoplasmic K-ras in Swiss mice, and had no effect in C57/BL6 mice. Results may have differed from those predicted because of strain-dependent differences in response to the cholesterol-lowering agents. A difference in response among the mouse strains suggests that individual genetic differences may alter the effect of hypocholesterolemic agents on K-ras membrane localization, and potentially the risk of ras-dependent cancer.

A strain of hyperlipidaemic Sprague-Dawley (HSD) rat was compared with normal Sprague-Dawley (SD) rats for expression of cholesterol 7alpha-hydroxylase activity (CYP7A1) and other cytochrome P450 (P450) enzymes in liver. Hepatic microsomal CYP7A1 activity in male HSD rats was 2-3-fold lower than in male SD rats with CYP7A1 apoprotein levels being similarly reduced. CYP7A1 expression was subject to diurnal variation in HSD rats as found in SD rats. Treatment of HSD rats with cholestyramine caused an increase in hepatic microsomal cholesterol 7alpha-hydroxylase activity of 3.3-fold compared with a 3.5-fold increase in SD rats with similar changes in apoprotein levels. These results indicate that the lower activity in HSD rats is not due to a defect in the catalytic activity of the enzyme, regulation affecting diurnal variation or regulation through bile acid feedback inhibition. No difference between hepatic microsomal methoxyresorufin-O-demethylase, benzoxyresorufin-O-debenzylase or chlorzoxazone 6-hydroxylase activities in SD and HSD rats was found, nor was there any difference in the levels of CYP1A2, CYP2D1, CYP2E1, CYP3A1, CYP3A2 or NADPH cytochrome P450 reductase determined by immunoblotting using specific anti-peptide antibodies. However, unlike in male SD rats, CYP2C13 was absent in male HSD rats and this was associated with a two-fold reduction in testosterone 6beta-hydroxylase activity. In conclusion, while HSD rats do not have a general reduction in P450 levels, they do lack CYP2C13 and have lowered cholesterol 7alpha-hydroxylase activity, as a result of a reduced level of expression of the enzyme.

Agents that inhibit hepatic cholesterol biosynthesis reduce circulating cholesterol levels in experimental animals and humans, and may be of pharmacological importance in the prevention of atherosclerosis. Azalanstat (RS-21607), a synthetic imidazole, has been shown to inhibit cholesterol synthesis in HepG2 cells, human fibroblasts, hamster hepatocytes and hamster liver, by inhibiting the cytochrome P450 enzyme lanosterol 14 alpha-demethylase. When administered orally to hamsters fed regular chow, RS-21607 (50 mg/kg/day) lowered serum cholesterol in a dose-dependent manner (ED50 = 62 mg/kg) in a period of 1 week. It preferentially lowered low density lipoprotein (LDL) cholesterol and apo B relative to high density lipoprotein (HDL) cholesterol and apo A-1. It also lowered plasma cholesterol levels in hamsters fed a high saturated fat and cholesterol diet. RS-21607 inhibited hepatic microsomal hydroxymethylglutaryl-CoA (HMG-CoA) reductase activity in hamsters in a dose-dependent manner (ED50 = 31 mg/kg), and this was highly correlated with serum cholesterol lowering (r = 0.97). Cholesterol lowering by azalanstat and cholestyramine was additive, and the increase in HMG-CoA reductase brought about by cholestyramine was attenuated significantly by azalanstat. In vitro studies with HepG2 cells indicated that this modulation of reductase activity was indirect, occurring at a post-transcriptional step, and it is proposed that a regulatory oxysterol derived from dihydrolanosterol (or lanosterol) may be responsible for this regulation. Azalanstat does not appear to lower circulating cholesterol in the hamster by up-regulation of the hepatic LDL receptor, suggesting that other mechanisms are involved. Orally administered azalanstat (50-75 mg/kg) stimulated hepatic microsomal cholesterol 7 alpha-hydroxylase activity by 50-400% in hamsters, and it is postulated that this may result from modified cholesterol absorption and bile acid synthesis.

Orally active inhibitors of acyl CoA:cholesterol acyl transferase (ACAT), such as Lederle CL277082 (LE), are known to reduce plasma and hepatic cholesteryl ester levels, although the mechanisms are not well understood. Several groups have reported the inhibition of cholesterol absorption upon oral ACAT inhibitor administration. In this study, we used 7-day dietary and drug treatments of hamsters to examine the possible effects of LE on hepatic ACAT. ACAT assays were performed using liver homogenates in the absence and presence of a saturating level of exogenously added cholesterol. LE (100 mg/kg/day) treatment of chow or 0.5% cholesterol-fed animals caused reductions in ACAT activity without additional cholesterol as compared with non-treated animals. When a saturating level of cholesterol was added to the assays, reductions in ACAT activity upon LE treatment of chow- or cholesterol-fed animals were also observed. Treatment of cholesterol-fed animals with cholestyramine in the diet reduced ACAT activity in the absence of added cholesterol. However, ACAT activities similar to those of non-treated animals were observed at a saturating level of cholesterol. This latter effect demonstrates that inhibition of cholesterol absorption reduces cholesterol delivery to the liver but does not reduce cholesterol esterifying capacity since cholestyramine is not absorbed and has no direct effect on the liver. The decreased ACAT activity in homogenates from LE-treated animals could also be mimicked in a dose-dependent manner by the addition of exogenous LE to liver homogenates from non-treated animals. These results indicate that hepatic ACAT activity is regulated by the availability of free cholesterol, and that orally administered LE has a direct effect on hepatic ACAT activity in the liver. In addition, the data are consistent with LE activity in the liver as being responsible, in part, for the reduced hepatic and plasma cholesteryl esters in treated animals.

Novel bile salts (quaternary ammonium conjugates) inhibited cholic acid binding and transport in everted ileal sacs in vitro . The cationic piperazine conjugate of lithocholic acid (di-iodide salt, compound 8, BRL 39924A) appeared most active, inhibiting binding by 29% and transport by 59% in guinea-pig ileum (200 μM). BRL 39924A also inhibited taurocholate uptake into guinea-pig ileal sacs and cholate uptake into rat ileal sacs and was selected for further study in vivo . In hyperlipidaemic rats, BRL 39924A significantly raised cholesterol 7α-hydroxylase activity and decreased hepatic accumulation of exogenous cholic acid. HDL cholesterol concentration in the serum increased and the level of VLDL plus LDL cholesterol decreased. In hyperlipidaemic guinea-pigs, BRL 39924A lowered serum total cholesterol and triglyceride levels. Although metabolic changes were less than those achieved with the bile acid sequestrant, cholestyramine, the doses of BRL 39924A used were much lower (100–500 mg/kg body wt). Selective inhibition of receptor mediated bile acid uptake may be associated with local side-effects but these novel bile salts are useful pharmacological tools to examine the effects of receptor blockade on lipoprotein metabolism.

In order to investigate the physiological role of acetoacetyl-CoA synthetase (acetoacetate-CoA ligase, EC 6.2.1.16), a cytosolic acetoacetate-activating enzyme, effects of streptozotocin (STZ)-induced diabetes on the enzyme activity was investigated in rats. At 72 hr of the STZ administration (80 mg/kg body weight, injected intravenously), hepatic enzyme specific activity decreased to 23% of its initial activity. However, the enzyme activities in non-hepatic tissues were not significantly affected by the STZ treatment. Feeding of rats with both 4% cholestyramine and 0.4% pravastatin for 3 days remarkably increased the hepatic acetoacetyl-CoA synthetase activity and decreased the plasma ketone bodies level in the diabetic rats. These results suggest that acetoacetyl-CoA synthetase has important roles in the regulation of ketone body utilization in rat liver and that these hypocholesterolemic agents have the ability to remedy the impaired utilization of ketone bodies under the diabetic condition.

The hydroxylation of cholesterol by cholesterol 7 alpha-hydroxylase (CYP7) to 7 alpha-hydroxycholesterol is the rate-limiting step in the production of bile acids. An anti-peptide antibody targeted to the C-terminus of CYP7 was produced by immunising rabbits with the synthetic peptide Tyr-Lys-Leu-Lys-His. The antibody bound to a single band of 54 kDa from rat hepatic microsomal fractions. The intensity of the band was subject to a diurnal variation and showed a significant increase (P < 0.01) in apoprotein at night. Treatment of rats with cholestyramine increased CYP7 apoprotein in the morning (P < 0.005) and at night (P < 0.005), but diurnal variation was maintained. CYP7 catalytic activity, measured using a specific gas chromatography/mass spectrometry assay, showed similar changes in the pattern of diurnal variation and induction. The distribution of CYP7 in rat liver tissue sections was investigated by immunocytochemistry. In sections from rats treated with cholestyramine, there was an even distribution of immunoreactivity, except in the proximal perivenous hepatocytes where immunoreactivity was slightly more intense. A similar distribution was found in sections from untreated rat liver, except immunoreactivity was overall slightly less intense. This study shows that the C-terminus of CYP7 is a useful epitope for the targeting of anti-peptide antibodies.

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

The disposition of 1-[14C]clofibrate (0.4 mmolekg) was studied in rats after acute (single dose) and chronic (b.i.d., for 14 days) administration. With a single dose (orally or by intraperitoneal injection) of clofibrate, most (~90 per cent) of the 14C-dose appeared in the urine within 24 hr and the recovery of 14C from the urine and feces was nearly quantitative within 72 hr. Little fecal excretion of 14C (< 5 per cent) occurred after a single or chronic clofibrate administration. Clofibrate was readily absorbed and eliminated, as evidenced by a rapid increase in plasma 14C level within 90 min and a calculated biological half-life of 4.1 hr. The pharmacokinetic profile of 14C-elimination in rats was unaffected by pretreatment with cholestyramine. Clofibric acid [2-(4-chlorophenoxy)-2-methylpropionic acid] was identified as the major metabolite in plasma (~97 per cent) whereas the glucuronide of clofibric acid was the main urinary and biliary metabolite (~96 per cent). Clofibric acid, as the free acid and glucuronide form, accounted for 99 per cent of the total 14C-dose in rats, and unchanged clofibrate was not detected in any of the biological samples. Two unidentified, minor urinary metabolites were also detected. In cannulated bile duct studies, it was found that [14C]clofibrate, as clofibric acid, was rapidly and efficiently excreted in the bile. The biliary excretion rates of 14C and of the glucuronide of clofibric acid were also not altered by phenobarbital pretreatment. Chronic treatment with [14C]clofibrate did not alter the qualitative or quantitative nature of biotransformation in vivo. An increased rate of urinary 14C-elimination was observed following chronic 1-[14C]clofibrate treatment, with concomitant reductions in blood and heart 14C-content and an elevation in 14C-content of epididymal fat tissue. Subcellular fractionation of liver, from rats given [14C]clofibrate chronically, indicated an increased distribution of 14C into mitochondria and peroxisomes. Tissue 14C-levels, achieved in these in vivo studies, were an order of magnitude lower than those required for the pharmacological activities of clofibrate and clofibric acid in vitro.

The interrelationship of microsomal 7α-hydroxylation and drug oxidation reactions was studied in liver microsomes obtained from the male Wistar rat. When several compounds were administered to rats, a variety of changes ensued concerning the rate of cholesterol 7α-hydroxylation, ethylmorphine N -demethylase activity, and alterations in electron transport components. Cholestyramine and d -thyroxine administration resulted in significant increases in cholesterol 7α-hydroxylase activity. Both phenobarbital (PB) and spironolactone pretreatment did not produce an elevation of cholesterol 7α-hydroxylation, but significant increases in ethylmorphine N -demethylation over controls were realized. There was a lack of congruence with the rate of cholesterol 7α-hydroxylation and the content or activity of electron transport components whereas there was a demonstrable dependency of ethylmorphine N -demethylation on the monitored electron transport components for PB- and spironolactone-treated rats. Along with an elevation of cytochrome P448 content, 3-methylcholanthrene (3-MC) pretreatment reduced cholesterol 7α-hydroxylase activity and the rate of ethylmorphine N -demethylation. Concomitant treatment with 3-MC and cholestyramine caused no alteration of cholesterol 7α-hydroxylase activity. The inhibitory action of 3-MC on cholesterol 7α-hydroxylase activity was not due to competition for reducing equivalents in liver microsomes. The inhibitory phenomenon caused by NADH on microsomal cholesterol 7α-hydroxylase activity was reproducible and was dose-dependent at both subsaturating and saturating levels of NADPH. In conclusion, the results of this study indicate that the cholesterol 7α-hydroxylase enzyme system is distinctly different from that which catalyzes drug oxidations.

The prevention of a fatty liver by adding test substances to a 1 per cent orotic acid diet was used to obtain assay curves for various hypolipidemic drugs. The following drugs had approximately the same activity in this test: ethyl p -chlorophenoxyisobutyric acid (PCIB); p -phenoxyphenyl methanesulfonate and N , N -dimethyl- N ′-(4-phenoxy-phenyl) sulfamide (Upjohn U 22105 and U 25030); and 2,2′-[(1-methyl-4,4′-diphenyl- butylidine)-bis-( p -phenyleneoxy)] bis-triethylamine-citrate (Squibb SQ 11071). 1- Methyl-4-piperidyl-bis-( p -chloro-phenoxy) acetate (Sandoz Salt 42348) was two to three times as active, and 2-methyl-2-( p -1,2,3,4-tetrahydro-1-napthylphenoxy) propionic acid (Ciba Su 13437) was ten times as active as CPIB. On the same weight basis, choloxon ( D -thyroxine; D-T 4 ) was 80–90 times as active. Dilantin, L -thyropine (L-T 4 ), Dow DH 581, nicotinic acid, and cholestyramine had little or no effect. Adenine, allopurinol [4-hydroxytyrazolo (3,4- d ) pyrimidine] and 5,5′-diphenyl-2-thiohydantoin (DPTH) were as active as most of the drugs in preventing triglyceride deposition. The only substances which increased liver α-glycerophosphate dehydrogenase were : CPIB, Su 13437, SaH 42348, D-T 4 and L-T 4 . The lipotropic effect of these drugs was not mediated through this enzyme. Feeding orotic acid alone practically eliminated the pre-β and β-lipoprotein (βLP) band from the serum gel electrophoresis, but the intensity of the β band was restored by the active drugs in proportion to their dosages; inactive substances did not restore the βLP band. A quick screening procedure was developed for substances which intensify the serum βLP band.

Male Wistar rats were given 200 mg/kg/day nicotinic acid or 1000 mg/kg/day cholestyramine by stomach tube for ten days. Peroxisomal palmitoyl-CoA oxidation (cyanide-insensitive) and the activities of palmitoyl-CoA hydrolase and urate oxidase were significantly increased in the total liver homogenate. Subcellular fractionation showed enhanced enzyme activities after drug treatment mainly in the peroxisome-containing fractions. The increase in urate oxidase activity and its subcellular distribution suggest that the tested drugs induce core-containing peroxisomes. The findings are similar to those previously reported with low doses of peroxisome-proliferating hypolipidemic drugs and with acetylsalicylic acid, a drug which is structurally similar to nicotinic acid. Since cholestyramine is not absorbed, its influence on hepatic enzymes probably occurs indirectly as a consequence of enhanced catabolism of cholesterol.

Administration of SKF-525A to rats fed on a stock diet specifically decreased the serum concentration of low-density lipoprotein. SKF-525A and cholestryamine also reversed the rise in circulating concentration of both very-low-density and low-density lipoprotein that was observed in rats given a sucrose-based, cholesterol-supplemented diet. The enhancement of hepatic cholesterol 7α-hydroxylase by SKF-525A or by cholestyramine is accompanied by homeostatic responses by the liver which include induction of low-density lipoprotein clearance and increased cholesterogenesis to attempt to replenish sterol pools. These compensatory mechanisms are separately controlled.

A meal model in which rats were trained to consume within 2 hr a high fat meal containing glycerol tri[1- 14 C]oleate and [ 3 H]cholesterol was compared to the corn oil bolus model. In the meal model, dietary triglyceride was absorbed from the small intestine faster during the first 6–8 hr and more completely than intubated corn oil, as determined by analysis of intestinal contents, serum radioactivity, serum triglycerides, adipose tissue and liver lipids. The effects of Cholestyramine, Colestipol and Pluronic L-101 (1% dietary admixes) on these variables were evaluated for 5 days in the meal model. Lipid absorption during a 72-hr period was reduced by all compounds. The per cent excretion of glycerol tri[1- 14 C]oleate was increased significantly by Pluronic L-101 (10-fold), Cholestyramine (5.7-fold) and Colestipol (2.7-fold). The excretion of [ 3 H]cholesterol was enhanced significantly by Cholestyramine (1.6-fold) and Colestipol (1.3-fold). The following observations were made 4hr after the initiation of the meal. Pluronic L-101 increased significantly the retention of glycerol tri[1- 14 C]oleate and [ 3 H]cholesterol in stomach (380 and 375 per cent, respectively), and of glycerol tri[1- 14 C]oleate in the small intestine (1100 per cent). The percent of intestinal lipid remaining as triglyce-ride from the intestinal lumen was increased significantly by Pluronic L-101 (160 per cent). Pluronic L-101 reduced significantly [ 14 C]lipid and [ 3 H]cholesterol in liver; Cholestyramine and Colestipol suppressed only [ 3 H]cholesterol. In adipose tissue, Pluronic L-101 treatment reduced significantly [ 14 C]lipid content only; Cholestyramine and Colestipol suppressed selectively [ 3 H]cholesterol. After 5 days of treatment, only Pluronic L-101 treatment resulted in significantly reduced serum triglycerides (32 per cent), cholesterol (21 per cent) and glucose (15 per cent). These data suggest that this in vivo meal-feeding model provides a physiological technique for evaluating agents affecting lipid absorption.

The hyperlipemia of puromycin aminonucleoside induced nephrotic syndrome (nephrosis) was found to provide a model for testing antilipemic drugs in the rat. Increased serum concentrations of cholesterol, triglycerides, phospholipids (mainly lecithin) and alpha and beta-lipoprotein lipids were effectively controlled in acute studies by two drugs—ethyl chlorophenoxyisobutyrate(Atromid-S)and sodium betabenzalbutyrate (Kata-Lipid)—after 7 days' treatment. Moderate hepatomegaly occurred with nephrosis, and was further increased by chlorophenoxyisobutyrate but not bybetabenzalbutyrate, adding indirect support to the hypothesis that these drugs may have different modes of action. Cholestyramine, d -thyroxine and 13,437-Su had no effect on nephrotic hyperlipemia in this acute study, although hepatomegaly was caused by 13,437-Su. Nephrotic hyperlipemia in man usually remains untreated although accelerated atherosclerosis with increased morbidity and mortality is a feature of the disease. Methods successful in controlling nephrotic hyperlipemia in the rat should be put to clinical trial in man.

Dogs were given clofibrate, 50 mg/kg of body weight/day for 6 days or 50 mg/kg of body weight/day for 2 days, followed by 40 mg/kg of body weight every 30–36 hr over an additional 9-day period. Cholestyramine, 0.7 g/kg of body weight/day, was administered to an additional group of dogs over an 11-day period. Plasma cholesterol concentrations in dogs treated with clofibrate for either 6 or 11 days decreased 24 per cent and decreased 16 per cent in dogs given cholestyramine. 14 C incorporation into bicarbonate from 3- 14 C-pyruvate, from [U- 14 C]-L-alanine and from [1- 14 C]glucose was significantly increased by liver slices from clofibrate-treated dogs when compared with tissue from control animals, but cloflbrate did not result in any changes in [ 14 C]cholesterol or [ 14 C]fatty acid formation from either [3- 14 C]pyruvate or from [U- 14 C]alanine. [ 14 C]Cholesterol formation from 6-[ 14 C]glucose was virtually abolished in liver slices taken from dogs treated with clofibrate for 11 days. Liver slices from dogs treated with cholestyramine showed a 3.5- to 4.0-fold increase in 14 C incorporation into cholesterol from both [3- 14 C]pyruvate and [6- 14 C] glucose, and a significant increase in 14 C incorporation from [1- 14 C]glucose into bicarbonate. Clofibrate administration resulted in decreased liver glycogen concentrations and decreased 14 C incorporation into glycogen from [ 14 C]glucose, but 14 C incorporation into glycogen from [U- 14 C]L-alanine was unaffected. If the hypocholesterolemic effect of clofibrate in dogs results from decreased cholesterol synthesis, changes in glucose metabolism may form the metabolic basis rather than alterations in pyruvate (or acetyl CoA) metabolism.