Management of muscle haematomas in patients with severe haemophilia in an evidence-poor world.

Treatment studies in haemophilia focus on joint bleeds; however, some 10-25% of bleeds occur in muscles. This review addresses management of muscle haematoma in severe haemophilia, defines gaps in the published evidence, and presents a combined clinician and physiotherapist perspective of treatment modalities. The following grade 2C recommendations were synthesized: (i) Sport and activity should be based on individual factor levels, bleeding history and physical characteristics, (ii) Musculoskeletal review aids the management of children and adults, (iii) 'Time to full recovery' should be realistic and based on known timelines from the healthy population, (iv) Diagnosis should be carried out by both a clinician and physiotherapist, (v) Severe muscle bleeds should be treated similarly to surgical patients: a 50% trough for 10-14 days followed by high-level prophylaxis, (vi) Protection, rest, ice, compression and elevation should be implemented in the acute stage, and (vii) Physiotherapy and rehabilitation should be divided into: control of haemorrhage (phase 1); restoration of Range of Movement (ROM) and strength (phase 2); functional rehabilitation and return to normal living (phase 3). Recommendations specifically for inhibitor patients include: (i) Minor to moderate bleeds should be managed by home-treatment within 1 h of bleed onset using either one injection of rFVIIa 270 µg kg(-1), or two to three injections of rFVIIa 90 µg kg(-1) (2-3 h intervals), or FEIBA 50-100 U kg(-1) (repeated at 12-hourly intervals, if necessary) and (ii) Severe muscle bleeds should be supervised by the treatment centre and include bypassing agents until clinical improvement is observed.

Optimization of a novel class of benzimidazole-based farnesoid X receptor (FXR) agonists to improve physicochemical and ADME properties.

Structure-guided lead optimization of recently described benzimidazolyl acetamides addressed the key liabilities of the previous lead compound 1. These efforts culminated in the discovery of 4-{(S)-2-[2-(4-chloro-phenyl)-5,6-difluoro-benzoimidazol-1-yl]-2-cyclohexyl-acetylamino}-3-fluoro-benzoic acid 7g, a highly potent and selective FXR agonist with excellent physicochemical and ADME properties and potent lipid lowering activity after oral administration to LDL receptor deficient mice.

The need for speed in the management of haemophilia patients with inhibitors.

Rapid control of bleeding is the key to reducing bleeding complications and thereby preserving joint and musculoskeletal function in haemophilia patients with inhibitors. However, this requires early diagnosis following the onset of bleeding and strategies for rapid treatment in an outpatient setting. Overarching themes on the need for speed in managing bleeds in haemophilia patients were examined by a panel of clinicians experienced in managing inhibitor patients and joint disease during the Third Zürich Haemophilia Forum on 8 May 2009. This report summarizes the opinions of the panel on how to achieve rapid bleeding control in inhibitor patients and areas that were identified by the panel for future research or as needing new consensus guidelines. The consensus was that home treatment should be established for haemophilia patients with inhibitors, as it is associated with a faster time to treatment, as well as improvements in the quality of life of patients and their carers. In addition, as improved haemostatic control now allows inhibitor patients to participate in a wider range of physical activities, specific guidelines are required on which types of sport and work are appropriate. It was agreed that clear, systematic approaches are needed for early diagnosis of joint and muscle bleeds in inhibitor patients, which could facilitate rapid treatment. There may be opportunities for exploiting new diagnostic techniques from osteoarthritis to enable earlier diagnosis of haemophilic arthropathy. Overall, it was concluded that greater emphasis should be placed on education and patients' psychological needs, to enable inhibitor patients to cope up more effectively with their disease.

Paediatric haemophilia with inhibitors: existing management options, treatment gaps and unmet needs.

Development of inhibitors is a severe complication of haemophilia posing many management challenges. While a long-term goal in inhibitor patients is eradication of inhibitors through immune tolerance induction, bypassing agents such as recombinant activated factor VII (rFVIIa) and activated prothrombin complex concentrate (aPCC) are essential for control of bleeding episodes. Paediatric patients with haemophilia and inhibitors are at particular risk of recurrent haemarthroses, and management of these patients should seek to avoid joint damage and support the child's full social and physical development. Current options for management of bleeding complications include on-demand treatment of acute bleeding episodes, secondary prophylaxis to avoid recurrent bleeds and surgery to treat affected joints. There is also a rationale for adopting prophylactic approaches to prevent bleeding in inhibitor patients, allowing this group similar opportunities for protection against arthropathy development as are given to non-inhibitor patients. This paper, based on a roundtable meeting of haematology experts at the first Zürich Haemophilia Forum in May 2008, reviews the current evidence supporting more intense and prophylactic approaches to manage bleeding risk in paediatric haemophilia patients with inhibitors, and highlights the need for investigations of primary prophylaxis in this vulnerable patient group, to support best long-term outcome.

Circulating levels of the chemokines JE and KC in female C3H apolipoprotein-E-deficient and C57BL apolipoprotein-E-deficient mice as potential markers of atherosclerosis development.

We have investigated serum chemokines for their suitability as markers of atherosclerosis development in apoE (apolipoprotein E)-deficient ((-/-)) mice. Female C3H apoE(-/-) and C57BL apoE(-/-) mice were fed on either diet W (Western diet; 6 weeks) or normal rodent diet (12 weeks). Serum lipids (0, 6 and 12 weeks) and terminal chemokine levels were measured using commercially available assays, whereas the lesion area was determined using Oil-Red O-stained aortic sections. Serum lipids were higher in C3H apoE(-/-) mice for both diets throughout the study; however, lesions were significantly larger in C57BL apoE(-/-) mice fed on either diet. Chemokine levels were significantly lower in C3H apoE(-/-) mice fed on the normal diet, but no difference was observed between the two groups fed on diet W. We conclude that serum chemokine levels are potential markers for atherosclerosis susceptibility in C3H and C57BL apoE(-/-) mice fed on a normal rodent diet.

C3H apoE(-/-) mice have less atherosclerosis than C57BL apoE(-/-) mice despite having a more atherogenic serum lipid profile.

Wild-type C57BL mice are known to be susceptible to diet-induced atherosclerosis, whilst C3H mice are resistant. We investigated the effect of these background strains on the hyperlipidaemia and atherosclerosis that develops in mice deficient in apolipoprotein E (apoE(-/-)). Male and female apoE(-/-) mice on C3H/HeNHsd (C3H) and C57BL/6J (C57) backgrounds were fed atherogenic Western diet for 12 weeks. Serum cholesterol and triglyceride concentrations were measured and atherosclerosis quantified in the aortic sinus. C3H apoE(-/-) mice fed normal diet had 1.5 2 fold higher serum cholesterol levels than C57 apoE(-/-) mice and 4-5 fold higher serum triglyceride concentrations. Feeding Western diet caused a 4-5 fold increase in serum cholesterol in all mice, but levels of triglyceride were either attenuated or were unaffected in C3H apoE(-/-) and C57 apoE(-/-) mice, respectively. C3H apoE(-/-) mice had approximately 2 fold higher serum cholesterol and 4 fold higher triglyceride concentrations than the C57 apoE(-/-) mice throughout the study. Serum triglyceride concentrations were 35-108% higher in male C3H apoE(-/-) than female C3H apoE(-/-) mice. Most of the lipids were present in the very low density lipoprotein (VLDL)/chylomicron fraction in both strains of mice whether they were fed normal or Western diet. Notwithstanding the lower plasma lipid concentrations, atherosclerotic lesion areas were more than 2-fold larger in C57 apoE(-/-) than in C3H apoE(-/-) mice (males 68 +/- 11 x 10(3) vs 30 +/- 6 x 10(3) females 102 +/- 12 x 10(3) vs 41 +/- 8 x 10(3) microm2. mean +/- SEM).

Phenotyping apolipoprotein E*3-leiden transgenic mice by two-dimensional polyacrylamide gel electrophoresis and mass spectrometric identification.

Apolipoprotein E (ApoE) plays an important role in cholesterol and triglyceride metabolism, being one of the major structural components of chylomicrons and very low density lipoprotein (VLDL) remnants. ApoE functions as a ligand in the receptor-mediated uptake of these remnants from the blood by the liver. A variant form of ApoE, apolipoprotein E*3-Leiden, shows reduced affinity for the low density lipoprotein (LDL) receptor, and results in the dominant expression of type III hyperlipoproteinemia. Two-dimensional electrophoresis (2-DE) has been used to characterise protein expression in serum samples from control and transgenic mice expressing the human ApoE*3-Leiden mutation, fed a cholesterol-rich diet, and transgenic mice fed a normal diet. For the identification of proteins, single silver-stained spots were excised from the 2-DE gels and subjected to in-gel enzymatic digestion. Extracted peptides were analysed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). This proteomic approach has enabled the ApoE*3-Leiden variant to be positioned in a 2-DE separation of serum proteins, and has identified changes in the expression of haptoglobin, indicating that this protein may provide a marker for the potential onset of atherosclerosis.

Apolipoprotein B overproduction by the perfused liver of the St. Thomas' mixed hyperlipidemic (SMHL) rabbit.

The St. Thomas' mixed hyperlipidemic (SMHL) rabbit (previously St. Thomas' Hospital rabbit) is a putative model of familial combined hyperlipidemia (FCH). When fed a low (0.08%) cholesterol diet, it exhibits elevations in both plasma cholesterol and triglyceride compared to New Zealand White (NZW) controls. To determine the mechanism for this hyperlipidemia we studied the secretion of apolipoprotein B (apoB)-containing lipoproteins from perfused livers of both young and mature rabbits. During a 3-h perfusion we measured the total cholesterol and triglyceride content of the medium and the cholesterol, triglyceride, and apoB content of very low density lipoprotein (VLDL)(1) (S(f) 60;-400), VLDL(2) (S(f) 20;-60), intermediate (S(f) 12;-20), and low (S(f) 0;-12) density lipoproteins (IDL, LDL). Lipoprotein concentrations increased linearly throughout the perfusion period. The rate of cholesterol output was 3-fold higher (459 vs. 137 ng/g liver/min, P = 0.003) in SMHL versus NZW rabbits whilst that of triglyceride was similar (841 vs. 662 ng/g liver/min, NS). VLDL(1) cholesterol output was elevated 2-fold (232 vs. 123 ng/g liver/min, P < 0.05) and VLDL(2) + IDL + LDL cholesterol output, 4.5-fold (106 vs. 23 ng/g liver/min, P < 0. 005) in SMHL versus NZW rabbits. ApoB output in VLDL1 was 38 ng/g liver per min in SMHL and 14 ng/g liver per min in NZW (NS). In SMHL VLDL(2) + IDL + LDL apoB was increased 9-fold at 53 versus 6 ng/g liver per min in NZW (P < 0.001). We conclude that the SMHL rabbit overproduces apoB-containing lipoproteins particularly in the VLDL(2) + IDL + LDL fraction, a characteristic consistent with its use as a model of FCH.

Modulation of the regression of atherosclerosis in the hamster by dietary lipids: comparison of coconut oil and olive oil.

The Golden Syrian hamster (Mesocricetus auratus) has been shown to be a useful model of both human lipoprotein metabolism and the development of atherosclerosis. We report the effects of dietary lipids on the progression and regression of atherosclerosis in this model. In the first study, hamsters fed on coconut oil (150 g/kg diet) and cholesterol (30 g/kg diet) developed lipid-rich lesions in the ascending aorta (0.28 (SD 0.14) mm2) and aortic arch (0.01 (SD 0.01) mm2) after 4 weeks that continued to progress over the next 8 weeks (0.75 (SD 0.41) mm2 and 0.12 (SD 0.11) mm2 for the ascending aorta and aortic arch respectively). Removal of cholesterol from the diet halted this progression. Furthermore, in animals fed on olive oil in the absence of added cholesterol, plasma LDL-cholesterol concentrations were lower (P < 0.05) and the extent of atherosclerotic lesions was reduced (P < 0.001 for both regions of the aorta) compared with animals fed on coconut oil (with no added cholesterol). In a second study, animals were fed on the atherogenic diet for 10 weeks, transferred to diets containing either coconut oil (150 g/kg diet) or olive oil (150 g/kg diet) without added cholesterol and monitored for up to 16 weeks. In the ascending aorta, lesion size doubled in animals fed on coconut oil but stabilized in those fed on olive oil. In the aortic arch, lesion size decreased linearly (P < 0.05, P < 0.001 for coconut oil and olive oil respectively) with the greatest reduction being seen in the olive-oil-fed animals (P < 0.05). Again, progression and regression of atherosclerosis appeared to reflect the relative concentrations of LDL-cholesterol and HDL-cholesterol in the plasma. We conclude that the male Golden Syrian hamster represents a useful model of dietary induced regression as well as progression of atherosclerosis.

Effect of probucol on serum lipids, atherosclerosis and toxicology in fat-fed LDL receptor deficient mice.

Although numerous transgenic mouse models for atherosclerosis have been developed recently, little is known about their response to hypolipidaemic or anti-atherosclerotic agents. We investigated the effect of the known hypocholesterolaemic and anti-atherosclerotic drug probucol on serum lipids, lipoproteins and atherosclerosis in fat-fed low density lipoprotein (LDL) receptor deficient mice. Probucol at doses of 0.2 and 1% in the diet which are similar to those used in the mouse by other investigators reduced serum cholesterol by 26 and 37%, respectively. Probucol also reduced serum triglyceride levels by 33 and 47% at doses of 0.2 and 1%, respectively. The decrease in serum cholesterol and triglycerides was mainly due to a decrease of these lipids in VLDL and or chylomicrons. Despite these potentially beneficial changes in serum lipids atherosclerotic lesion areas in the aortic root were unchanged in the probucol treated mice. After 12 weeks treatment most of the mice receiving probucol had swollen feet and tails due to oedema. Histological examination of the base of the hearts from the probucol treated mice revealed lipid droplets within the reticuloendothelial and other interstitial cells. There was also an interstitial subacute inflammatory cell infiltration associated with the lipid deposition. The oedema induced by probucol could be the result of cardiac insufficiency due to interstitial lipidosis and inflammation in the base of the heart together with the extensive atherosclerotic lesions in the aortic sinus.

SK&F 97426-A: a novel bile acid sequestrant with higher affinities and slower dissociation rates for bile acids in vitro than cholestyramine.

SK&F 97426-A is a novel bile acid sequestrant that is threefold more potent than cholestyramine at increasing bile acid excretion in the hamster. SK&F 97426-A is a quaternary alkylammonium polymethacrylate that was selected for comparison with cholestyramine in vivo because of its superior in vitro bile acid binding properties. Association, dissociation, affinity, and capacity experiments were performed under physiologically relevant conditions with the most abundant bile acids found in human bile. The bile acids came to equilibrium with SK&F 97426-A and cholestyramine within approximately 30 min and 6 min, respectively. SK&F 97426-A and cholestyramine had similar capacities for all the bile acids (between 2.5 and 4 mmol/g) and both had similar, very high affinities and slow dissociation rates for the dihydroxy bile acids. However, SK&F 97426-A had much higher affinities for the trihydroxy bile acids glycocholic acid and taurocholic acid than did cholestyramine. Dissociation of glycocholic acid and taurocholic acid from SK&F 97426-A was also much slower (27 and 25%, respectively, dissociated after 60 min) than from cholestyramine (89 and 84%, respectively, dissociated after 60 min). The higher affinities and slower dissociation rates of the trihydroxy bile acids for and from SK&F 97426-A probably account for the increased potency of SK&F 97426-A over cholestyramine in vivo.

Quantitative assessment of aortic atherosclerosis in APOE*3 Leiden transgenic mice and its relationship to serum cholesterol exposure.

Transgenic mice overexpressing the human dysfunctional apolipoprotein E variant, APOE*3 Leiden, develop hyperlipidemia and are highly susceptible to diet-induced atherosclerosis. In the present study, we investigated the effects of diet composition and feeding period on serum cholesterol exposure and the amount of atherosclerosis in the aortic sinus in these mice, using quantitative image analysis. On each of the three diets tested--a low-fat diet, a high-saturated-fat/cholesterol diet, and a high saturated-fat/high-cholesterol/0.5%-cholate diet--transgenic animals showed a marked hyperlipidemia compared with nontransgenic littermates. Measurement of the atherosclerotic lesion areas in cross sections of the aortic sinus in animals exposed to these three diets for up to 6 months showed a 5 to 10 times greater lesion area in transgenic mice compared with nontransgenic controls. Highly significant positive correlations were found between the log-transformed data on lesion area and serum cholesterol exposure (r = .82 to .85 for the 1-, 2-, and 3-month treatment groups), indicating that the hyperlipidemia is likely to be a major determinant in lesion formation. On the basis of these findings, we suggest that the APOE*3 Leiden mouse represents a promising model for intervention studies with hypolipidemic and antiatherosclerotic drugs.

Polydeoxycholate in human and hamster feces: a major product of cholate metabolism.

Fecal bile acid excretion is one of the two major routes by which cholesterol is eliminated from the body, fecal cholesterol being the other. During their enterohepatic circulation, bile acids are secreted into the duodenum, pass down the jejunum and into the ileum where more than 95% is reabsorbed by the gut. Bile acids that escape reabsorption in the small intestine are metabolized by microorganisms in the large intestine. The major routes of metabolism are reported to be deconjugation, dehydroxylation, especially at the 7 alpha-hydroxy position, and dehydrogenation of the hydroxyl moieties. There are also some reports that saponifiable metabolites containing mostly deoxycholic acid form a major component of the bile acids found in human feces. We have identified a novel metabolite of cholic acid, 3 alpha-hydroxy polydeoxycholate, in both human and hamster feces that is the major constituent of these saponifiable metabolites. Furthermore, we have shown in hamsters that the animals that excreted more bile acid were excreting the additional bile acid as polydeoxycholate. As expected, there was a negative correlation between bile acid excretion in the feces and plasma cholesterol concentrations in these animals. We speculate that polydeoxycholate is formed in the lower gut of both humans and hamsters and that, by its formation, bile acid will be sequestered in an insoluble form, thus inhibiting its reabsorption by the gut. This process may help to reduce plasma cholesterol concentrations and coronary heart disease in humans.

Bile acid synthesis in hamster hepatocytes in primary culture: sources of cholesterol and comparison with other species.

The synthesis of bile acids by primary hamster hepatocytes in culture has been studied. Measurable rates of bile acid synthesis were obtained from cells prepared from livers of animals fed 2% w/w cholestyramine to induce the synthesis of bile acids through the rate-limiting enzyme cholesterol 7 alpha-hydroxylase. The effects of various sources of substrate for bile acid synthesis in these cultured cells were examined over a period of 24 h and the results compared with published or parallel studies in primary rat hepatocytes or in the human hepatoma cell line, HepG2. In all the cells, bile acid synthesis was stimulated by the addition of 7 alpha-hydroxycholesterol, indicating the rate-limiting role of the cholesterol 7 alpha-hydroxylase. Bile acid synthesis in the hamster hepatocytes was also stimulated by a variety of sources of cholesterol as substrate, mevalonic acid (increasing the production of newly-synthesised cholesterol in the cell), and as an exogenous source, hamster LDL. Similarly, if cholesterol was diverted from intracellular esterification using the ACAT inhibitor Dup128, a further increase in bile acid synthesis could be demonstrated. These results show that hepatocytes obtained from cholestyramine-treated hamsters are deficient in substrate cholesterol for bile acid synthesis. A similar conclusion can be drawn from the published work with rat hepatocytes and is further supported by experiments on the regulation of cholesterol 7 alpha-hydroxylase activity at the mRNA and the protein level, although some in vivo studies in animals and studies in man have led authors to suggest that cholesterol 7 alpha-hydroxylase is saturated with substrate.

SK&F 97426-A a more potent bile acid sequestrant and hypocholesterolaemic agent than cholestyramine in the hamster.

SK&F 97426-A is a novel bile acid sequestrant which was selected for comparison with cholestyramine in vivo because of its superior in vitro bile acid binding properties. The effects of the two sequestrants on faecal bile acid excretion, plasma total cholesterol, VLDL + LDL and HDL cholesterol and triglyceride concentrations and on liver enzymes involved in the synthesis and metabolism of cholesterol were investigated in normocholesterolaemic hamsters. Four studies were conducted to determine the relative potencies of the two resins using a range of doses of the sequestrants over treatment periods of up to 2 weeks. Curves fitted to the resulting data allowed common maximum responses and separate ED50s to be calculated for each sequestrant. The maximum response of both sequestrants was to increase bile acid excretion by 352% and lower plasma total cholesterol by 37-58%. LDL + VLDL and HDL cholesterol were reduced by 56-75% and 25-41%, respectively. SK&F 97426-A was 3 times more potent than cholestyramine at increasing the excretion of bile acids in the faeces and 2.1-3.4-fold and 2.3-3.2-fold more potent at lowering total plasma cholesterol and LDL plus VLDL cholesterol, respectively. In some of the experiments SK&F 97426-A was also more potent than cholestyramine at lowering HDL cholesterol. Plasma triglycerides were also lowered by both sequestrants by up to 31% after 1 week but the relative potency could not be determined. These HDL cholesterol and total triglyceride lowering effects of bile acid sequestrants in the hamster are known not to occur in people treated with cholestyramine. There were minimal differences between hamsters treated for 1 or 2 weeks in the relative potencies or ED50s calculated for the total plasma cholesterol, LDL + VLDL and HDL cholesterol. Both sequestrants may have been slightly more efficacious on these parameters after 2 weeks of treatment. Liver weights were reduced by about 15% by both sequestrants at 2% (w/w) in the diet for 1 week. The activities of the liver HMG-CoA reductase and cholesterol 7 alpha-hydroxylase were increased as expected, whilst the activity of the acyl-CoA:cholesterol acyltransferase was reduced by both sequestrants at this dose. SK&F 97426-A was, therefore, 2-3-fold more potent as a bile acid sequestrant and hypocholesterolaemic agent than cholestyramine when tested in the hamster.

In vitro studies to investigate the reasons for the low potency of cholestyramine and colestipol.

The association rates, dissociation rates, and equilibrium binding of bile acids with cholestyramine and colestipol were measured under physiological conditions with the most abundant bile acids found in humans. Cholestyramine and colestipol equilibrated with the bile acids (5 mM) within 1 h and they bound > 58% and > 17% of the bile acid, respectively, when at equilibrium with physiological concentrations of bile acid (4.3-10.1 mM). However, the conjugated trihydroxy bile acids taurocholic acid and glycocholic acid dissociated rapidly from both cholestyramine and colestipol when the sequestrants, preloaded with the bile acid, were washed with the Krebs-Henseleit buffer. The taurine-conjugated and dihydroxy bile acids dissociated more slowly from cholestyramine and colestipol than the glycine-conjugated and trihydroxy bile acids and, therefore, would be expected to avoid reabsorption to a greater extent by the terminal ileum and colon in vivo. We predict from these results that the reasons for the low potency of cholestyramine and colestipol are that they bind a relatively small proportion of the trihydroxy bile acids in the duodenum and jejunum and that all of the bile acids dissociate to varying extents from the sequestrants in the terminal ileum where the unbound bile acids are reabsorbed by the gut.

Precipitation and 13C-NMR relaxation enhancement measurements of the interactions of bile acids with synthetic cationic bile acid derivatives, and with spin labelled fatty acids.

In an investigation of novel potential bile acid sequestrants, the affinities of the sodium salts of the glycine and taurine conjugates of naturally occurring bile acids (cholate, deoxycholate, chenodeoxycholate and lithocholate) for several cationic ammonium bile acid derivatives have been investigated by measurements of the extent to which the derivatives are able to precipitate the bile acids. This is roughly proportional to the lipophilicity of the interacting species. Thus, amino and ammonium derivatives of cholic acid do not precipitate taurocholate or glycocholate to any great extent, whereas ammonium derivatives of deoxycholate and lithocholate are much more effective. To complement the precipitation measurements, high resolution 13C-NMR has been applied to investigate the weaker interactions between the ammonium cholate derivative and glycocholate, glycodeoxycholate and glycochenodeoxycholate. Addition of either of the latter two bile acids to the cationic ammonium compound results in considerable broadening of the 13C resonances of both species, indicating the formation of relatively rigid structures. In addition, we have used T2 relaxation enhancement induced by spin-labelled fatty acids to examine the mechanism of interaction with bile acids of amphiphilic anions, which might compete with bile acids for sites on bile acid sequestrants. Low concentrations of 16-DOXY L-Stearate dramatically broaden the 13C-NMR resonances of deoxycholate carbons 19, 18 and 7 in particular, while 5-DOXY L-Stearate exerts much less specific effects. These results have been incorporated into a snapshot model of bile acid-fatty acid interactions.

Cholesterol lowering and bile acid excretion in the hamster with cholestyramine treatment.

Cholestyramine was administered to hamsters at 6 doses in the diet for 1 week. Plasma cholesterol, LDL + VLDL cholesterol and HDL cholesterol were measured after this period. Bile acid excretion was measured in faeces collected over the final 24 h of the experiment. A dose-response curve for each parameter measured was constructed using data from individual hamsters. For the bile acid and the cholesterol measurements a maximum response was observed at the highest doses. A correlation between the bile acids excreted over 24 h and the LDL + VLDL cholesterol showed that the maximum effect of cholestyramine on lowering plasma and lipoprotein cholesterol occurred at a submaximal excretion level of bile acids. Comparison of the efficiency of cholestyramine in reducing plasma cholesterol in the hamster with limited data in the dog and in man suggest that a greater lowering of plasma cholesterol is achieved in the dog and in man for an equivalent increase in bile acid excretion caused by the sequestrant. As is already known, cholestyramine treatment caused an increase in hepatic cholesterol 7 alpha-hydroxylase and HMG-CoA reductase activity. Interestingly in this study the novel observation was made that the bile acid sequestrant reduced the activity of hepatic acyl-CoA: cholesterol acyltransferase.