Assessment of discomfort in gallstone-bearing mice: a practical example of the problems encountered in an attempt to recognize discomfort in laboratory animals

In order to obtain practical experience on the recognition, assessment and evaluation of discomfort in laboratory animals, the degree of discomfort was studied in gallstone-free and gallstone-bearing mice. Out of nine parameters to which scores were assigned per individual mouse, only the response to palpation of the right hypochondrium was found to score significantly higher in gallstone-bearing mice. That is, the incidence of squeaking and the magnitude of muscular contractions were significantly higher in these animals compared with the gallstone-free mice. The stance of the gallstone-bearing mice also tended to be abnormal, although the difference between gallstone-free and gallstone-bearing animals did not reach statistical significance. Although this study does not prove unequivocally that the induction of gallstones per se causes discomfort or pain in mice, we tentatively conclude that it does. We feel that this should be taken into account in any projected work in which gallstone induction in animals may occur. There was considerable between-assessor variation in the assignment of scores to the variables used to assess discomfort, including the response to palpation. It is concluded that the selection of parameters and the experience and/or attitude of the assessor are critically important when the magnitude of discomfort, if any, is assessed in experimental animals.

Hypo- and hyperresponders: individual differences in the response of serum cholesterol concentration to changes in diet

The feeding of cholesterol-rich diets to random-bred animals results in marked interindividual differences in the response of serum cholesterol. Certain animals show only small responses (hyporesponders), whereas others develop high degrees of hypercholesterolemia (hyperresponders). Inbred strains of rabbits, rats, and mice differing in their sensitivity to dietary cholesterol are available. In these animals, and also in monkeys, the responsiveness to high-cholesterol diets has a strong genetic basis. The existence of hyper- and hyporesponders also holds in humans, though not as pronounced as in laboratory animals. Repeated trials with the same subjects have shown that persons exist with a consistently low or high response to increased intakes of cholesterol. However, "spontaneous," diet-independent within-person variations in the level of serum cholesterol markedly inflate the between-person variation in the response of serum cholesterol; both variations are of the same order of magnitude. Hypo- and hyperresponsiveness to dietary cholesterol extends to other hypercholesterolemic components of the diet. In humans and rabbits hyperresponsiveness to dietary cholesterol is associated with responsiveness to dietary saturated fatty acids. The mechanisms underlying hypo- and hyperresponsiveness to dietary cholesterol have not yet been unraveled. On the basis of available data, we propose that in hyperresponders, compared with hyporesponders, there is a higher hepatic efflux of cholesterol in low-density lipoproteins (LDL), or its precursors, after cholesterol consumption. This may be caused by insufficient inhibition of cholesterol biosynthesis and/or the high capacity of cholesterol absorption in the hyperresponders. The stimulation of LDL production accounts for the increase in LDL cholesterol in serum. The number of hepatic LDL receptors, which may be already decreased in hyperresponders, will decrease further through down-regulation. The receptor-mediated LDL clearance decreases, but the absolute amount of LDL cholesterol taken up by the cells via the receptor and by the receptor-independent pathway increases because of the increased level of LDL cholesterol. In this way a new equilibrium is reached in which LDL production equals LDL catabolism. The phenomenon of hypo- and hyperresponsiveness may have implications for counseling subjects who attempt to lower their serum cholesterol by diet. However, identification of true hyper- and hyporesponders is greatly hampered by within-person fluctuations of the level of serum cholesterol. No simple test is available to discriminate hypo- from hyperresponders.(ABSTRACT TRUNCATED AT 400 WORDS)

Cholesterol metabolism and esterases in four strains of rats with differential cholesterolemic responses to a high-cholesterol, high-cholate diet

The increase in serum cholesterol after feeding a diet containing 2% (w/w) of cholesterol and 0.5% of cholate for 13 days was 200 and 800% in two hypo- and two hyper-responsive inbred strains of rats, respectively. While remaining on the high-cholesterol, high-cholate diet for longer periods, the level of serum cholesterol dropped in the hyper-responsive strains, and after 8 weeks on the diet one hyper-responsive strain had similar serum cholesterol concentrations as the two hypo-responsive strains. The feeding of a semipurified diet, containing 1% (w/w) of cholesterol and 20% of fat, did not discriminate between the two hypo- and hyper-responsive strains with respect to the response of serum cholesterol. The activities in plasma of the indicators for liver function, aspartate amino transferase and alkaline phosphatase, were significantly increased in all strains after feeding the high-cholesterol, high-cholate diet. Only alkaline phosphatase was increased by the semipurified diet. Evidence is presented that in the four inbred strains of rats the differential cholesterolemic response to the high-cholesterol, high-cholate diet is not related to the baseline serum lipoprotein profile, liver cholesterol accumulation, fecal bile acid excretion, and the total activities and patterns of esterases in serum, liver and small intestine.

Cholesterol metabolism and sterol carrier protein-2 (non-specific lipid transfer protein)

Hepatic sterol carrier protein-2 significantly enhances the microsomal conversion of cholesterol to 7 alpha-hydroxy-cholesterol. In the present work we have attempted to correlate the hepatic content of sterol carrier protein-2 with bile acid formation. We have determined the amount of this protein in a variety of physiological and experimental conditions, in which the rate of bile acid synthesis varies over a wide range, viz. during fetal development, in inbred strains of rats with different rates of bile acid synthesis, and in rats fed diets containing drugs which modify the rate of bile acid synthesis. The outcome of these experiments does not support the idea that sterol carrier protein-2 has any association with bile acid synthesis. From our data we further conclude that hepatic sterol carrier protein-2 is an adaptable protein because its level increases during development from the fetal to the post-weaning stage of the rat and since it can be modulated by oral administration of certain drugs. Furthermore, it is demonstrated that the level of sterol carrier protein-2 varies between six inbred strains of rats.

Endogenous cholesterol synthesis, fecal steroid excretion and serum lanosterol in subjects with high or low response of serum cholesterol to dietary cholesterol

In this study we addressed the question whether hypo- and hyper-responders to dietary cholesterol differ with regard to the flexibility of endogenous cholesterol synthesis after changes in cholesterol intake. Whole-body cholesterol synthesis was measured as faecal excretion of neutral steroids and bile acids minus cholesterol intake. In addition, we determined serum concentrations of lanosterol, a precursor of cholesterol and a possible indicator of cholesterol biosynthetic activity. The study was carried out with 2 hyper- and 4 hypo-responders; these subjects had shown a consistently high or low response of serum cholesterol to a decrease in dietary cholesterol in two previous experiments. The subjects received controlled high- (on average 697 mg of cholesterol per day) and low-cholesterol (109 mg/day) diets for periods of 4 weeks in succession; cholesterol was the only dietary variable. The two hyper-responders again showed a significant decrease in serum cholesterol. There was essentially no decrease in serum cholesterol in three of the four hypo-responders. The decrease in cholesterol intake caused an increase in cholesterol synthesis in five out of the six subjects. There was no association between the individual change in serum cholesterol and the change in cholesterol synthesis. Transfer from the high- to low-cholesterol diet caused an increase in serum lanosterol in all subjects. The increase was 3- to 4-fold higher in three out of the four hypo-responders than in the two hyper-responders. We tentatively suggest that this study provides some evidence that the flexibility of cholesterol synthesis is involved in the responsiveness to dietary cholesterol.

Fecal steroid excretion in relation to the development of casein-induced hypercholesterolemia in rabbits

Two groups of nine rabbits fed a purified diet containing soy protein were injected intravenously with [4-14C]cholesterol. One group was fed the same diet for 78 d while the other group was fed a diet containing casein. The feces of the rabbits were collected and analyzed for radioactivity present in the neutral steroid and bile acid fractions. The excretion of neutral steroids and bile acids was lowered within 3 d after soy protein was replaced by casein and before the serum cholesterol concentration was increased. However, in the casein-fed rabbits the specific radioactivity of the bile acids was greater, whereas the amount of excreted bile acids was lower than in the soy protein-fed rabbits. After the serum cholesterol level in the casein-fed animals became constant (d 35), a further injection of [4-14C]cholesterol was given to all animals. Kinetic parameters of cholesterol metabolism according to a two-pool model were estimated from the die-away curve of [4-14C]cholesterol in serum. The size of the rapidly exchangeable pool (pool A) was greater in the casein-fed rabbits than in the soy protein-fed rabbits, whereas the size of pool B was similar in the two groups. The partial turnover rate of pool A was lower, as was the partial turnover of the slowly exchangeable pool (pool B), and the production rate of cholesterol was significantly lower on the casein-fed rabbits than in the soy protein-fed rabbits. This study suggests that the reduced excretion of steroids in casein-fed rabbits could be the cause of the hypercholesterolemia and is not the result of it.

Long-term effects of partial ileal bypass on the health status of rabbits

Partial ileal bypass (PIB) surgery is a method for the treatment of familial hypercholesterolaemia in man. Since the rabbit is frequently used as an animal model in experimental studies on PIB, we have investigated the long-term effects of this surgical procedure on the health status of rabbits. Forty-eight weeks after surgery plasma and liver cholesterol levels were decreased by about 40%. The inner diameter of the bypassed ileum was drastically reduced, unlike its length. The bypassed segment did not show clear histological abnormalities. The microflora of the caecum was similar in control and PIB rabbits. PIB did not influence liver histology. The bile of the rabbits with PIB was less lithogenic than that of control animals. Blood haemoglobin levels, haematocrit values and plasma concentrations of alkaline phosphatase, alanine aminotransferase, gamma-glutamyl transferase and lactate dehydrogenase were not changed after PIB. Plasma levels of albumin, creatinine, calcium, phosphorus, vitamin B12 and folic acid were not significantly affected by PIB. Rabbits with PIB had significantly higher plasma levels of bilirubin and zinc than control rabbits, but plasma vitamin E concentrations were significantly lower. These results may be of importance for further studies on the effects of PIB in rabbits.

Effect of partial ileal bypass on ileum morphology in cholesterol-fed pigs

We have studied ileum morphology in pigs 3.5 months after partial ileal bypass (PIB) surgery. PIB caused a reduction in the length of the bypassed ileum by 60%, while the circumference was decreased by about 70%. We did not find evidence for dilatation of the functional, neo-terminal ileum. These results in pigs are contrary to those found earlier in rabbits. This may be of importance concerning the choice of animal model to study the effects of PIB.

Existence of consistent hypo- and hyperresponders to dietary cholesterol in man

Hyper- and hyporesponsiveness of serum cholesterol to dietary cholesterol is an established concept in animals but not in man. The authors studied the stability of the individual response of serum cholesterol to dietary cholesterol in three controlled experiments in 1982. The subjects were volunteers from the general population living in or near Wageningen, the Netherlands. Each experiment had a low-cholesterol baseline period (121, 106, and 129 mg/day in experiments 1, 2, and 3, respectively) and a high-cholesterol test period (625, 673, and 989 mg/day). Duplicate portion analysis showed that dietary cholesterol was the only variable. The 94 healthy men and women who completed experiment 1 showed an increase (mean +/- standard deviation (SD] in serum cholesterol of 0.50 +/- 0.39 mmol/liter (19 +/- 15 mg/dl). Seventeen putative hyperresponders, defined by their response in experiment 1, were retested in experiments 2 and 3; they showed responses of 0.28 +/- 0.38 mmol/liter (11 +/- 15 mg/dl) and 0.82 +/- 0.35 mmol/liter (32 +/- 14 mg/dl), respectively. Fifteen hyporesponders, selected in experiment 1, showed responses in experiments 2 and 3 of 0.06 +/- 0.35 mmol/liter (2 +/- 14 mg/dl) and 0.47 +/- 0.26 mmol/liter (18 +/- 10 mg/dl), significantly lower than the corresponding values for hyperresponders. The standardized regression coefficient for individual responses in experiment 2 on those in experiment 1 was beta = 0.34 (p = 0.03, n = 32); the corresponding regression coefficient for experiment 3 and experiment 1 was 0.53 (p less than 0.01). After correction for intraindividual fluctuations the true responsiveness distribution was found to have a between-subject standard deviation of about 0.29 mmol/liter (11 mg/dl). This implies that if the mean response to a certain dietary cholesterol load amounts to e.g., 0.58 mmol/liter (22 mg/dl), then the 16% of subjects least susceptible to diet will experience a rise of only 0.29 mmol/liter (11 mg/dl) or less, while in the 16% of subjects most susceptible to diet, serum cholesterol will rise by 0.87 mmol/liter (34 mg/dl) or more. The authors conclude that modest differences in responsiveness of serum cholesterol to dietary cholesterol do exist in man, and that the wide scatter of responses observed in single experiments is largely due to chance fluctuations.

The lipid composition of serum lipoproteins in the harbour seal, Phoca vitulina

The density profile of serum lipoproteins and their lipid composition was studied in 12 adult, female harbour seals. The animals were sampled after an approximate 20 hr fast. The density profile of lipoproteins showed that the harbour seals displayed a distinct VLDL (density less than 1.006 g/ml) and HDL band (density about 1.125 g/ml), but no clear LDL band. There was a rather diffuse population of lipoproteins in the density range of 1.019-1.100 g/ml. Mean serum total cholesterol concentration was 5.7 mmol/l; about 60% of this cholesterol was located in the HDL fraction (density greater than 1.063 g/ml). The fasted seals were found to carry 4% of serum total lipids in chylomicrons. These lipoproteins consisted of 51% of triaclyglycerols (on the basis of total chylomicron lipids). The LDL (defined as heparin-manganese precipitable lipoproteins in VLDL and chylomicron-deficient serum) contained 49% of cholesterol and 43% of phospholipids (on the basis of total LDL lipids). The HDL (defined as heparin-manganese soluble lipoproteins in VLDL and chylomicron-deficient serum) contained 36% of cholesterol and 58% of phospholipids (on the basis of total HDL lipids).

Treatment of young rats with cholestyramine or a hypercholesterolemic diet does not influence the response of serum cholesterol to dietary cholesterol in later life

Groups of 10 female Wistar rats (aged 4 weeks) were fed for 29 days either a low-cholesterol commercial diet, a commercial diet containing 2% (w/w) cholesterol, 0.5% cholate and 5% olive oil or a diet containing 2% cholestyramine. The rats were then fed the low-cholesterol commercial diet for the next 91 days and the high-cholesterol diet for another 29 days. There was no significant difference between the groups in the increase of cholesterol in serum and liver during the last period of cholesterol feeding. A fourth group of 10 animals was fed the diet containing cholesterol and cholate during the entire experimental period of 149 days. By the end of the experiment serum cholesterol in these animals was lower and liver cholesterol was higher than in the 3 groups fed the high-cholesterol diet during days 120-149 of the experiment. This study does not present evidence for imprinting effects of early diet manipulation on the later cholesterolemic response to a high cholesterol diet.

Reproducibility of the variations between humans in the response of serum cholesterol to cessation of egg consumption

To find out whether the variable response of serum cholesterol levels to changes in cholesterol intake in man is due to constitutional differences in responsiveness, we have reinvestigated in 1982 34 healthy men and women, who habitually consumed at least 1 egg/day and had participated in a trial in 1976. Serum cholesterol was measured on the habitual diet (about 800 mg cholesterol/day), and after 3 weeks during which no eggs or egg-containing products were consumed (about 300 mg cholesterol/day). Serum cholesterol decreased by 0.16 +/- 0.42 mmol/1 (6 +/- 16 mg/dl) in 1976 and by 0.31 +/- 0.35 mmol/l (12 +/- 14 mg/dl) in 1982 (mean +/- SD). Individual responses varied from -1.0 to +0.5 mmol/l (-39 to +19 mg/dl). The correlation between the responses in 1976 and 1982 was r = 0.32 (P less than 0.05). The decrease in serum cholesterol was most pronounced for subjects with a low body mass index and a high level of HDL-cholesterol. In men, the increase in serum cholesterol with age was correlated with the mean decrease in the trials (r = 0.42, n = 16, P = 0.11). In a controlled trial, 4 hypo- and 2 hyperresponders were given 11 mg cholesterol/MJ (11 mg/240 kcal; 116 mg/day) for 4 weeks followed by 72 mg/MJ for another 4 weeks; all other nutrients were kept constant. Almost all food was supplied and intakes were rigidly controlled. The 2 hyperresponders and 3 of the 4 hyporesponders were also hyper- and hyporesponsive under the controlled conditions. We conclude that part of the cholesterolemic response to dietary cholesterol in man is individually determined and stable for at least 6 years.

[Corneal opacity]

A case with bilateral corneal opacification in the form of a half-ring is described. Routine laboratory tests revealed no abnormalities, and serum lipoprotein composition was normal. The authors suspect that this was a case of primary lipoidal keratopathy.

Why do polyunsaturated fatty acids lower serum cholesterol?

Replacement of saturated by polyunsaturated fatty acids in the diet may lower serum very low-density and low-density lipoprotein concentrations because the liver preferentially converts polyunsaturated fatty acids into ketone bodies instead of into very low-density lipoprotein triglycerides. Thus unlike saturated fatty acids, polyunsaturated fatty acids are transported to the tissues for oxidation without leaving a trail of lipoprotein remnants in the form of low-density lipoproteins.

Rapid sampling and long-term storage of subcutaneous adipose-tissue biopsies for determination of fatty acid composition

The fatty acid composition of fat tissue is a valid indicator of the fatty acid composition of the diet over the preceding 1 to 3 yr. Here we describe a rapid method for sampling of buttock fat without anesthesia. On average, 35 mg can be obtained using a common blood-sampling system. Sampling of 40 subjects takes about 3 h. The procedure caused no more anxiety or discomfort than a routine venipuncture. Application in about 500 subjects has as yet yielded no infectious or other complications. With regard to the fatty acid composition of the biopsy, sampling site (left versus right buttock) was not found to be a source of error. The biopsies could be stored for periods up to 1.5 yr without changes in the fatty acid profile. With this method one can obtain biopsies from a large number of subjects and determine objectively the long-term fatty acid composition of their diet.

Serum lipoproteins in cholesterol-fed pigs after partial ileal bypass

Partial ileal bypass (PIB) surgery was performed in hypercholesterolaemic mini-pigs and Yorkshire pigs fed a semipurified diet containing 1% (W/W) of cholesterol. PIB drastically reduced serum total cholesterol and phospholipid concentrations and the cholesterol: phospholipid ratio in spite of continuation of cholesterol feeding. The relative distribution of cholesterol between serum lipoproteins was affected by PIB; the surgical treatment caused an increase in the ratio of high-density lipoprotein (HDL) to low-density lipoprotein (LDL) cholesterol. Serum apo B and apo A levels were rapidly decreased by PIB. The operation induced a decrease in the cholesterol: apo B and cholesterol: apo A ratios. It is suggested that the pig is a suitable animal model to study PIB-induced changes in lipoprotein metabolism.

Effect of egg yolk feeding on the concentration and composition of serum lipoproteins in man

The effect of egg yolk consumption on the composition of LDL and on the concentration of HDL subclasses was studied in healthy subjects. Six volunteers consumed a diet low in cholesterol for 10 days and then daily added 6 egg yolks to their diet for another 10 days; the experiment was repeated 1 year later with the same subjects. Egg yolk consumption caused the cholesterol intake to increase by 1600 mg/day, and the fat intake by 7 energy % at the expense of carbohydrates; this increase was due almost exclusively to monounsaturated fatty acids. Upon egg yolk feeding the mean level of serum total cholesterol rose by 13%; the bulk of this rise was due to LDL cholesterol, which increased by 21%. VLDL and IDL cholesterol decreased by 19 and 11%, and serum total triglycerides by 17%. Marked relative increases of 35 and 36% were seen in the cholesterol level of the HDL subfractions with densities of 1.055-1.075 g/ml (HDL1) and 1.075-1.100 g/ml (HDL2), respectively. The HDL2/LDL cholesterol ratio increased by 16%. No change in cholesterol in HDL3 (d greater than 1.100 g/ml) was observed. The increase in cholesterol in HDL isolated by density gradient ultracentrifugation significantly exceeded the increase in cholesterol in heparin-Mn2+ soluble HDL. This suggests the formation of apo E-containing HDL, i.e. HDLc, which has HDL density but is not soluble in heparin-Mn2+. The composition of the LDL particles was significantly altered; the core became enriched in esterified cholesterol at the expense of triglycerides, and the ratio of core components to surface components increased by 7%.

Cholesterol metabolism in two strains of rats with high or low response of serum cholesterol to a cholesterol-rich diet

Transfer from a low cholesterol commercial diet to a high cholesterol diet, containing 2% (wt/wt) cholesterol and 0.5% cholate, caused an increase in serum cholesterol from about 2.5 mmol/L in two inbred rat strains to 5 mmol/L in the hyporesponsive strain and to 20 mmol/L in the hyperresponsive strain. In both strains the excess of cholesterol in the serum was exclusively located in the very low density lipoproteins. Cholesterol feeding caused a sevenfold increase in the amount of cholesterol in the liver, the increase tending to be greater in the hyporesponders. On the commercial diet, the decay of specific radioactivity of serum cholesterol after the intravenous administration of labeled cholesterol was faster in the hyporesponsive rats. The rate of fecal excretion of radioactive bile acids on this diet was higher in the hyporesponders when compared with the hyperresponders, whereas there was no strain difference with regard to the output of fecal neutral steroids. Sterol balance data showed that whole-body cholesterol synthesis on the low cholesterol diet was about twofold higher in the hypo- than in the hyperresponders. When fed the high cholesterol diet the half-life in the serum of injected radioactive cholesterol was about six times shorter in the hyporesponders. In absolute amounts, the hypo- and hyperresponders excreted similar amounts of endogenous (radioactive) bile acids and fecal steroids with the feces on this diet.

Studies on the assay, activity and sedimentation behaviour of acetyl-CoA carboxylase from isolated hepatocytes incubated with insulin or glucagon

The activity of acetyl-CoA carboxylase, measured in various ways, was studied in 15000g extracts of rat liver hepatocytes and compared with the rate of fatty acid synthesis in intact hepatocytes incubated with insulin or glucagon. Hepatocyte extracts were prepared by disruption of cells with a Dounce homogenizer or by solubilization with 1.5% (v/v) Triton X-100. Sucrose-density-gradient centrifugation demonstrated that the sedimentation coefficient of acetyl-CoA carboxylase from cell extracts was 30-35S, regardless of the conditions of incubation or disruption of hepatocytes. Solubilization of cells with 1.5% Triton X-100 yielded twice as much enzyme activity (measured by [14C]bicarbonate fixation) in the sucrose-gradient fractions as did cell disruption by the Dounce homogenizer. Analysis by high-performance liquid chromatography of acetyl-CoA carboxylase reaction mixtures showed that [14C]malonyl-CoA accounted for 10-60% of the total acid-stable radioactivity, depending on the method for disrupting hepatocytes and on the preincubation of the 15000g extract, with or without citrate, before assay. Under conditions in which incubation of cells with insulin or glucagon caused an activation or inhibition, respectively, of acetyl-CoA carboxylase, only 25% of the acid-stable radioactivity was [14C]malonyl-CoA and enzyme activity was only 13% (control), 16% (insulin), and 57% (glucagon) of the rate of fatty acid synthesis. Under conditions when up to 60% of the acid-stable radioactivity was [14C]malonyl-CoA and acetyl-CoA carboxylase activity was comparable with the rate of fatty acid synthesis, there was no effect of insulin or glucagon on enzyme activity.

The effect of dietary saturated fat versus polyunsaturated fat on serum cholesterol and phospholipid concentrations in rabbits with partial ileal bypass

Rabbits were fed semipurified diets containing either corn oil or coconut fat. Dietary coconut fat significantly elevated serum total cholesterol and phospholipid concentrations. Rabbits with partial ileal bypass (PIB) had significantly lower serum cholesterol and phospholipid values, irrespective of whether the diet contained corn oil or coconut fat. The effect on serum lipids of the type of fat was similar in control and PIB animals. Since PIB rabbits are known to excrete extremely high amounts of steroids with the feces, we suggest that our data point to a lack of interaction of the type of dietary fat with the fecal excretion of steroids.

Plasma lipoprotein profiles and arylesterase activities in two inbred strains of rabbits with high or low response of plasma cholesterol to dietary cholesterol

Cholesterol feeding for 4 weeks of female and male rabbits of two inbred strains increased plasma cholesterol concentrations by about 11 and 48 mmole/1 in the hypo- and hyperresponsive strain, respectively. On the low-cholesterol pre-experimental diet, the hyporesponsive animals had significantly higher plasma HDL (high density protein) cholesterol levels than hyperresponders. In both strains, cholesterol feeding caused elevations of cholesterol in all lipoprotein classes, the difference between the hypo- and hyperresponsive strains in essence only being observed in the VLDL (very low density lipoprotein) fraction. Basal plasma total arylesterase activity was significantly higher in the hypo- than in the hyperresponsive rabbits. Dietary cholesterol caused an increase in plasma esterase activity in both We suggest that in rabbits a low plasma arylesterase activity and a low concentration of HDL cholesterol are associated with an increased sensitivity to dietary cholesterol.

Relations between fatty acid synthesis, pyruvate concentration and cell concentration of suspensions of isolated rat hepatocytes

The cell concentration of suspensions of isolated rat hepatocytes affects both the rate of pyruvate accumulation in the incubation medium and the rate of fatty acid synthesis. At low cell concentrations pyruvate accumulation is directly related to the cell concentration but levels off at higher concentrations even when maximum pyruvate concentrations in the medium are not yet reached. The rate of fatty acid synthesis in the 30-60-min incubation interval is proportional to the cell concentration. In contrast, the rate of fatty acid synthesis during the 0-30-min incubation period decreases with increasing cell concentrations and subsequently becomes independent of the cell concentration.

Treatment of dietary casein with formaldehyde reduces its hypercholesterolemic effect in rabbits

Rabbits were fed cholesterol-free, semipurified diets containing 42% (wt/wt) casein or 21% casein plus one of the following nitrogen sources: soy isolate, amino acid mixture simulating casein, amino acid mixture simulating soy isolate, formaldehyde-treated casein or formaldehyde-treated soy isolate. Two additional groups of rabbits were fed the 42% casein diet and the diet containing casein plus soy isolate to which 0.4% (wt/wt) pure formaldehyde was added, this amount being identical to the amount of formaldehyde present in the diets with formaldehyde-treated proteins. Growth was somewhat reduced on the three diets containing 42% casein. The diet containing 42% casein to which no formaldehyde had been added induced severe hypercholesterolemia, the level of serum cholesterol after 8 weeks being about 10 mmol/L. The hypercholesterolemia was markedly reduced by the replacement of half of the casein by soy isolate, formaldehyde-treated soy isolate or formaldehyde-treated casein. No significant reduction of the concentration of serum cholesterol was seen when half of the 42% casein was replaced by an amino acid mixture imitating either casein or soy isolate. Formaldehyde per se did not significantly influence the level of serum cholesterol. We conclude that the differential tertiary structure of intact casein and soy isolate is an important factor in determining the cholesterolemic responses in rabbits to these proteins.

Arylesterase activities in the plasma of rats, rabbits and humans on low- and high-cholesterol diets

Arylesterase activities were measured with beta-naphthylpropionate and/or alpha-naphthylacetate as substrate in the plasma of rats, rabbits and humans on low- and high-cholesterol diets. The plasma esterase activities measured with alpha-naphthylacetate were similar in rats, rabbits and humans. With beta-naphthylpropionate as a substrate, rabbits were found to have a markedly higher esterase activity than rats and humans. Basal plasma esterase activity was significantly higher in an inbred rat strain which is hyporesponsive to dietary cholesterol than in a hyperresponsive strain. In rats, but not in humans and rabbits, plasma esterase activity was significantly increased by a high-cholesterol diet. In individual humans and random-bred rabbits and rats there was no association between initial plasma total esterase activity and the subsequent plasma cholesterol response to cholesterol feeding. We suggest that arylesterases are associated with cholesterol metabolism and with the response to dietary cholesterol in rats; evidence for such a role in rabbits and humans is, however, inconclusive.

Density profile and cholesterol concentration of serum lipoproteins in experimental animals and human subjects on hypercholesterolaemic diets

The density profile of Sudan black stained serum lipoproteins was studied in human subjects and various animal species on diets supplemented with cholesterol. In the animals studied (rabbits, calves, mice, chickens, rats and guinea-pigs), the feeding of cholesterol resulted in an elevation of serum cholesterol levels together with marked changes in the density profile and the cholesterol concentration of the serum lipoproteins. Large differences between animal species in their response to dietary cholesterol were found. In a human subject, an increased concentration of serum cholesterol due to the consumption of a diet supplemented with six egg yolks per day was reflected in an elevated level of LDL cholesterol, while changes in the density profile of stained serum lipoproteins were not observed. In subjects with familial type III and type IV hyperlipoproteinaemia, marked differences in the density profile of lipoproteins were found when compared with that of normolipoproteinaemic subjects. The density profile of stained lipoproteins in the type III patients was remarkably similar to that in cholesterol-fed chickens and lean Zucker rats.

Relationship between the fatty acid composition of the diet and that of the subcutaneous adipose tissue in individual human subjects

The fatty acid composition of the diet, measured by means of a two-day record, was compared with the fatty acid composition of subcutaneous body fat in 321 free-living adults. In spite of the known imprecision of dietary survey methods, highly significant correlations (r = 0.5) were found between the polyunsaturated fatty acid content or the polyunsaturated-to-saturated fatty acid ratio of the adipose tissue and the corresponding variable in the diet. It was estimated that complete elimination of the noise inherent in the measurement of an individual's fatty acid intake might have resulted in correlation coefficients of the order of 0.8. Analysis of subcutaneous fat biopsies merits consideration as a simple and reproducible measure of the dietary fatty acid composition of free-living individuals.

Regression of casein and cholesterol-induced hypercholesterolaemia in rabbits

Hypercholesterolaemia was induced in rabbits by feeding semipurified diets containing soy protein plus cholesterol (0.8 g/kg) or casein for four weeks. Subsequently for a period of six weeks, some of the rabbits were transferred to diets containing soy protein while others continued to receive the hypercholesterolaemic diets to which was added a mixture of amino acids (g/kg feed; glycine, 3.9; arginine, 6.9 and alanine, 1.6). Such additions increased the concentration of these amino acids in the casein diet to that in the hypocholesterolaemic soy protein diet. The cholesterol levels in the serum of the rabbits transferred to the soy protein diets declined rapidly, becoming significantly different from animals remaining on the hypercholesterolaemic diets after only three days. Serum cholesterol levels comparable to those in rabbits fed soy protein throughout the entire experiment were reached after about two weeks. The addition of the amino acids tended to reduce the concentration of cholesterol in the serum of the rabbits made hypercholesterolaemic by feeding the diets containing either casein or cholesterol. However, the effect reached significance only with the diet containing casein to which amino acids were added and then only at one time point. Six weeks after the cholesterol-fed animals were transferred to the cholesterol-free soy protein diet or to the diet containing the additional amino acids, apo E disappeared from the IDL1 (1.006 less than d less than 1.012 g/ml) and IDL2 (1.012 less than d less than 1.019 g/ml) fractions, but not from the VLDL fraction. Both with the cholesterol-free soy protein diet and the cholesterol diet fortified with amino acids, cholesterol in the VLDL fraction was reduced to values seen in animals fed the soy protein diet throughout the entire experimental period. The amount of cholesterol in the IDL and LDL fractions was decreased only in the soy protein group. Replacement of casein by soy protein, or the addition of amino acids to the casein diet did not induce the disappearance of apo E from the IDL or VLDL fractions. Only the soy protein diet lowered the amount of cholesterol in the VLDL and LDL fractions appreciably. It is concluded that the amount of apo E present in both IDL and VLDL does not invariably correlate with the level of serum cholesterol in rabbits. This study also indicates that the hypercholesterolaemic nature of casein resides only partially in the fact that it contains relatively low proportions of glycine, alanine and arginine compared with soy protein.

Correlation between the cholesterolemic responses produced by dietary cholesterol and casein in rabbits

Rabbits were fed three semipurified diets, namely a cholesterol-free soy protein diet, a cholesterol-free casein diet or a diet containing soy protein plus cholesterol (2 g/kg). One group (Chol-Cas) of 24 rabbits was fed successively the diet containing soy protein plus cholesterol (25 days), the soy protein diet (36 days) and the casein diet (20 days). Another group (Cas-Chol) consisting of 25 animals received consecutively the diet containing casein, soy protein and soy protein supplemented with cholesterol. Hypercholesterolemia was induced by the diets containing cholesterol or casein, whereas regression was seen on the soy protein diet. Within the Chol-Cas or Cas-Chol group the cholesterolemic response to casein and that to cholesterol was significantly correlated, the correlation coefficient being as high as 0.66. This correlation was still observed when calculated for animals either hypo- or hyperresponsive to dietary casein or cholesterol. When all animals were pooled, the correlation coefficient for the cholesterolemic response to casein and to cholesterol was only 0.33. The mean response to dietary cholesterol and to casein was significantly higher in the last dietary period than in the first period.

Cholesterol concentration and lipoprotein pattern in the serum of veal calves fed milk replacers with various levels of cholesterol

Veal calves, aged about 1 week, were fed for 146 days milk replacement diets supplemented with various levels of cholesterol. Four groups consisting of 11 or 12 animals received diets to which 0, 0.19, 0.56 or 0.93% (on the basis of air-dry matter) cholesterol was added at the expense of fat. Cholesterol feeding significantly increased the level of serum cholesterol. This increase was either linear or S-shaped over the entire range of cholesterol feeding, depending on the time during which the calves were fed the diets. In the calves fed cholesterol, the ratio of free to esterified cholesterol in the serum was significantly increased. The ingestion of cholesterol markedly increased the cholesterol content of the VLDL, IDL and LDL fractions in the serum. When compared to the 0.56%-cholesterol diet, the inclusion of 0.93% cholesterol in the diet did not further increase the cholesterol concentrations in the IDL and LDL fractions. Upon density gradient ultracentrifugation of serum prestained for lipid with Sudan Black, it was observed that dietary cholesterol caused the HDL1 particles (1.063 less than d less than 1.092) to to shift towards a lower density range. Cholesterol feeding effected an increase in the level of serum triglycerides, the increase being already maximal with 0.19% cholesterol in the diet. Dietary cholesterol induced elevated concentrations of serum phospholipids, the elevation being proportional to the amount of cholesterol in the diet.

Postprandial changes in the levels of lipids, glucose, urea and nonprotein nitrogen in the serum of veal calves fed milk replacers containing either skim milk powder or soybean protein concentrate

Postprandiale Veränderungen in der Serumkonzentration an Fetten, Glucose, Harnstoff und NPN bei Kälbern nach Zufuhr von Milchaustauschern mit Magermilchpulver oder Sojaproteinkonzentrat

Kälber im Alter von 7 Wochen (5–6 Tiere je Gruppe) erhielten Milchaustauscher mit Magermilchpulver oder Sojaproteinkonzentrat über 14 Wochen. Die Gewichtsentwicklung der Tiere zeigt bei der Magermilchgruppe eine höhere Tendenz.

Am Ende der Versuchsperiode wurden Blutproben kurz vor der Fütterung und etwa 3 Stunden nach der Fütterung genommen. Die Proteinquellen hatten keinen signifikanten Einfluß auf den Serumgehalt an Glucose, Harnstoff, NPN, Triglyceriden, Cholesterin und Phospholipiden vor der Fütterung. Ca. 3 Stunden nach der Aufnahme des Milchaustauschers mit Sojaproteinkonzentrat waren die Konzentrationen an NPN, Triglyceriden, Phospholipiden und Cholesterin erhöht. Die Unterschiede im Phospholipidgehalt und Cholesteringehalt waren signifikant. In der Magermilchgruppe war die Glucosekonzentration erhöht.

Die Erhöhung des Cholesteringehaltes wird auf die Freisetzung von Cholesterin bei der Umwandlung von HDL in LDL bei Sojaprotein‐Milchaustauscher zurückgeführt. Es wird vermutet, daß ein Teil der aufgezeigten postprandialen Veränderungen darauf beruhten, daß das Kasein im Gegensatz zum Sojaproteinkonzentrat im Abomasum des Kalbes koaguliert.

Diurnal patterns of the concentrations of cholesterol, triglycerides, glucose, nonprotein nitrogen and urea in the serum of veal calves fed a milk replacer supplemented with cholesterol

Veal calves (aged about 9 weeks; three animals per group) were fed twice a day liquid diets containing 60% skim milk powder and 20% crude fat (w/w) for 7.5 weeks. Addition of 1% cholesterol to the diet, at the expense of fat, caused a 70% increase in the level of serum cholesterol. Both in the control and cholesterol-fed calves, no diurnal rhythm in the concentration of cholesterol in the serum was observed. Serum triglycerides were not clearly elevated after feeding, but a steady increase during the day was observed, the increase being similar in both dietary groups. Cholesterol feeding seemed to induce lower postprandial levels of urea and higher levels of amino acid nitrogen, but this was only observed after feeding in the morning (8.00 a.m.), but not after feeding in the evening (8.00 p.m.). Dietary cholesterol significantly elevated postprandial glucose levels in veal calves. It is suggested that hypercholesterolemia effects an impaired glucose tolerance, possibly also in man.

The effect of replacement of dietary soybean protein by casein on the fecal excretion of neutral steroids in rabbits

Der Einfluß des Ersatzes von Sojaprotein durch Kasein auf die Ausscheidung von Neutralfetten beim Kaninchen

Der Ersatz von Sojaprotein in einer halbsynthetischen Diät durch Kasein führte bei Kaninchen zu einem ständigen Anstieg von Cholesterin im Serum und zwar innerhalb von 15 Tagen um 75%. Gleichzeitig waren die Ausscheidung von Cholesterin und Coprostanol bei Kaseinfütterung signifikant erniedrigt und zwar bereits nach zwei Tagen um etwa 40%. Dieser Prozeß setzte sich in etwa 3 Wochen fort. Es wird vermutet, duß die herabgesetzte Ausscheidung von Neutralfetten mit dem Kot der Kausalfaktor ist für die Entwicklung einer Hypercholesterinämie des Kaninchens bei Kaseinfütterung.

Relationships between cholesterol and phospholipid concentrations in the serum of humans, calves, rabbits and chickens

In humans, calves and rabbits very strong correlations were found between the concentrations of serum total cholesterol and phospholipids; in these species more than 70% of the variance in the level of serum phospholipids is accounted for by the variance in the serum cholesterol concentration. The regression coefficients in the equations relating the concentration of serum cholesterol to that of phospholipids were almost identical in humans and rabbits, but differed from those observed in calves and chickens. It is suggested that the rabbit is a suitable model animal for studying the relation between cholesterol and phospholipids in human serum.

Casein-induced hypercholesterolemia in rabbits: distribution of cholesterol, triglycerides and phospholipids between serum and liver

Replacement of soy protein by casein in the cholesterol-free, semipurified diet of rabbits caused hypercholesterolemia within 7 days. After 36 days, the serum of casein-fed rabbits displayed elevated levels of free and esterified cholesterol and phospholipids, but not of triglycerides. Most of the excess of serum cholesterol in the casein group was localized in the LDL fraction, but there were marked variations in the density profile of the serum lipoproteins between individual rabbits. Dietary casein induced an increased content in liver of free and esterified cholesterol, but not of phospholipids and triglycerides. The molar ratio of free to esterified cholesterol in the liver was decreased by casein. In contrast, feeding casein resulted in an increase of this ratio in the serum.