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C Lutton

Publications and source records attributed to C Lutton.

At least 91 records · Page 5Linked to original sources
PubMed1985

Origin and fate of cholesterol in rat plasma lipoproteins in vivo. I. Qualitative analysis.

Rats were conditioned to ingest a 15-gram dietary mixture, in a single daily meal, between 6:00 and 9:00 a.m. Labeled cholesterol was introduced into the organism through four different physiological routes: ingestion of 14C-cholesterol, injection of 14C-acetate, injection of red cells or plasma whose cholesterol was tritium-labeled. The specific radioactivities of free and esterified cholesterol, in the different plasma lipoproteins and in the major organs, were measured at various time spans after the introduction. The results revealed a different source of cholesterol in chylomicrons and VLDL discharged by the intestine: the chylomicrons would principally carry esterified cholesterol coming from the intestinal contents, while esterified cholesterol coming from the intestinal wall was found mainly in VLDL. The free cholesterol of these lipoproteins would initially have the same origin as esterified cholesterol but rapid free cholesterol exchanges would introduce precociously cholesterol coming from other structures. The results demonstrated the significant role of the intestine in cholesterol synthesis and revealed that of VLDL in the internal secretion of cholesterol by the intestine. Chylomicrons also appeared to play a significant role in this secretion, by way of exchanges between intestinal cells and chylomicrons in the process of formation. Finally, the results suggested the existence of esterified cholesterol transfers from HDL to lower density lipoproteins (chylomicrons, VLDL and possibly LDL).

Animals↗
PubMed1985

Origin and fate of cholesterol in rat plasma lipoproteins in vivo. II. Modelling of cholesterol absorption and its release into plasma lipoproteins.

After a single ingestion of a diet containing 14C-cholesterol, cholesterol radioactivity in the stomachal and intestinal contents, in the different organs and in the very low density lipoproteins (VLDL) and chylomicrons was measured at different times during 2 days. Based on the results, a quantitative model of cholesterol absorption and of its release into the VLDL and chylomicrons has been elaborated. This model takes into account the different processes implied in the turnover of intestinal cholesterol and that of the entire organism. It constitutes a coherent whole (satisfactory simulations for the variables studied, suitable mass balances for each compartment and the absence of major contradictions with preexisting quantitative data). Once again the model demonstrates the important part played by the intestine in rat cholesterol system dynamics. It takes into account the existence of two related exogenous and endogenous cholesterol pools from which the cholesterol released by the intestine into the chylomicrons and VLDL originates. The results suggest the existence of an important esterified cholesterol uptake from other plasma lipoproteins by the chylomicrons.

Animals↗
PubMed1985

Cholesterol metabolism in lean and obese Zucker rats: effects of portacaval anastomosis.

The effects of portacaval anastomosis (PCA) on cholesterol biodynamics of male adult (fa/fa) Zucker rats and their lean littermates were studied with an isotopic equilibrium method. Animals were fed with a sucrose-rich semi-purified diet. Obese rats were hypercholesterolemic (2.03 +/- 0.14 vs 1.06 +/- 0.7 mg/ml), had a cholesterol-enriched liver (135.3 +/- 14.5 vs 40.0 +/- 2.6 mg/liver) and accumulated cholesterol in body pools. However no difference in the rates of cholesterol absorption, synthesis, fecal elimination or transformation into bile acids distinguished obese from lean Zucker rats. In both lean and obese rats, PCA decreased cholesterolemia by about 28 per cent and liver weight by 40 per cent while the total cholesterol content of the liver was not affected. Input of synthesized cholesterol (internal secretion) was strikingly decreased by the shunt (from 13.2 +/- 0.6 and 12.6 +/- 0.7 mg/day/rat before PCA, to 8.9 +/- 0.8 and 8.6 +/- 1.0 mg/day/rat after PCA) in lean and obese rats respectively. A similar decrease was observed in the cholesterol transformation into bile acids. Since the activity of the gut for cholesterol synthesis, as shown by the fecal external secretion (cholesterol synthesized by the gut and directly eliminated in the gut and feces) was probably not modified, the reduction of internal secretion induced by PCA resulted from decreased hepatic cholesterogenesis. It is suggested that this decrease may be one of the factors involved in the lowering effect of PCA on plasma cholesterol level.

Animals↗
PubMed1983

[Effect of short- or medium-chain fatty acids on cholesterol dynamics in the rat].

The effects of a diet consisting of 10% medium-chain triglycerides (C8:0, C10:0) or 10% homogeneous triglycerides of 6- to 14-carbon chain saturated fatty acids on cholesterol turnover processes were studied in rats using the isotope equilibrium method. Cholesterol absorption was not significantly affected by the type of dietary fatty acid ingested. In contrast, lengthening of the fatty acid chain caused a moderate increase in the rates of cholesterol secretion (internal and external) and of transformation into bile acids. Thus, cholesterol synthesis was 80% higher in rats fed trimyristin (25.7 mg/day) than in those receiving tricaproin (14.6 mg/day). This increase seems essentially due to stimulated liver cholesterogenesis, as shown by in vivo incorporation of 14C-acetate.

Animals↗
PubMed1981

Identification and origins of neutral fecal sterols in adult Large White sows: occurrence of externally-secreted intestinal cholesterol.

Cholesterol, the main neutral fecal sterol (54-84 p. 100) in adult Large White sows fed a controlled semi-purified diet containing 0.08 p. 100 cholesterol (500 g twice a day; 3 510 kcal/day), was partially converted into coprostanol (10-44 p. 100). Exceptionally, epicoprostanol was present, indicating a second pathway of bacterial cholesterol degradation. In this paper, the term "fecal cholesterol" is restricted to the sum of cholesterol + coprostanol. The contribution of fecal cholesterol to the bulk of neutral fecal sterols eliminated daily, averaged 97 +/- 1 p. 100. For a given dietary cholesterol intake of 80 mg per day, eliminated fecal cholesterol was estimated to be 392 +/- 47 mg/day and mean fecal cholesterol concentration 1.88 +/- 0.12 mg/g of stools. The various sources of fecal cholesterol were unabsorbed ingested cholesterol, cholesterol excreted from the plasma, and externally-secreted intestinal cholesterol, synthesized by the digestive tract, discharged into the lumen and not absorbed. The respective contributions of these different sources were as follows: unabsorbed dietary cholesterol 34 +/- 2 mg/day, excreted cholesterol 234 +/- 28 mg/day and externally-secreted cholesterol 125 +/- 23 mg/day.

Animals↗
PubMed1981

New views on intestinal absorption of lipids in teleostean fishes: an ultrastructural and biochemical study in the rainbow trout.

Lipid absorption in rainbow trout was studied after gastric administration of [1-14C]linoleic and [1-14C]-palmitic acids. The intestinal epithelial cells were isolated at various times of absorption and the major lipid classes were isolated. Radioactivity was found primarily in the triglycerides. Blood radioactivity was measured at different times after administration of the labeled acids. It was very low until after 6 hr. After 4 hr when it was detectable, it was located essentially in the triglyceride fraction. At various times after feeding (a meal with 60% of unsaturated long chain fatty acids) the absorptive epithelium of the anterior intestine and pyloric caeca were examined by electron microscopy. Surprisingly, the esterification of fatty acids corresponded to the formation of VLDL-like particles, seen in SER, RER, Golgi apparatus, lamellar structures, intercellular space, interstitial space of lamina propria and lumen of lymphatic vessels. The respective roles of endoplasmic reticulum and Golgi apparatus in the lipoprotein synthesis are discussed. The particles are delivered in the intercellular spaces by way of the lamellar structures, whose role until now was unknown. Though the absorption of dietary triglycerides is much slower than in mammals, the mechanism does not differ fundamentally. The long chain fatty acids are esterified by the intestinal cells and transferred as VLDL-like particles to lymph. X

Animals↗
PubMed1980

Effect of dietary long-chain fatty acids on the rates of cholesterol turnover processes, cholesterol origin and distribution in the rat intestinal lumen.

Adult male rats were fed a semi-purified diet containing 20 p. 100 of lard or homogeneous triglycerides (tripalmitin, tristearin, triolein, trierucin) for 4 months. The rates of the processes (absorption, synthesis, degradation into bile acids, fecal and urinary excretion) involved in cholesterol turnover were measured using the isotope equilibrium method. The absorption coefficient of dietary cholesterol attained 71 +/- 3 p. 100 in rats fed the lard diet. It was unchanged in rats eating the triolein (73 +/- 3 p. 100) or tripalmitin (75 +/- 4 p. 100) diet but was drastically reduced in those receiving trierucin (45 +/- 1 p. 100) or tristearin (34 +/- 1 p. 100). Some functional and topological aspects of cholesterol absorption are discussed. Four to 6 times more endogenous cholesterol was found in the intestinal lumen of rats fed trierucin than in that of rats receiving a normolipid diet. Micelle cholesterol increase was also proportionally less. There was no direct relationship between the quantity of cholesterol found in the micelles and that absorbed. Dietary cholesterol was absorbed in the second as well as in the first half of the intestine, while the proportions of micellar cholesterol decreased continuously from the jejunum to the ileum. The rates of fecal excretion and fecal external secretion were inversely correlated to the absorption coefficient of dietary cholesterol, as has been previously described. The internal secretion was stimulated two to threefold in rats fed tristearin (22.3 +/- 0.7 mg/d), tripalmitin (28.4 +/- 4.6 mg/d) and trierucin (33.2 +/- 2.8 mg/d) as compared to rats fed lard (12.5 +/- 0.6 mg/d) or triolein (14.4 +/- 1.2 mg/d). Feeding a tripalmitin or a trierucin diet greatly increased cholesterogenesis (probably in the liver), while tristearin stimulated non-hepatic cholesterogenesis. The variations in daily bile acid elimination may be seen as an adaptive parameter, modulating its rate according to the cholesterol supply (absorption and synthesis).

Animals↗
PubMed1980

In vivo plasma cholesterol exchanges in the digestive tract of the rat: effect of L-thyroxine.

Cholesterol exchanges between plasma and digestive organs (stomach, small intestine divided into jejunum and ileum, cecum plus colon) were studied in control and in L-thyroxine-fed rats receiving a constant venous infusion of (3H)-cholesterol for 3 or for 6 h and in unoperated rats by use of the isotopic equilibrium method. In control rats, total cholesterol radioactivity in the walls of stomach, intestine and cecumcolon averaged 0.50% of infused (3H)-cholesterol at the end of 6 h; between 70 and 75% of this radioactivity was located in the intestine. However, the relative transfer rates into these walls, expressed as tissue radioactivity for the same free cholesterol specific activity in the plasma at the moment of sacrifice, are nearly the same when expressed per gram of tissue (walls) or per milligram of DNA in the epithelial cells of the jejunum and the ileum. In thyroxine-fed rats, total cholesterol radioactivity in the walls reached 1.27% of infused (3H)-cholesterol after 6 h, the intestine still containing the major part of radioactivity (80%). The relative cholesterol transfer rates into the walls are unchanged in stomach, ileum and cecum-colon when compared to the controls. But in the jejunum, L-thyroxine causes a twofold increase in plasma cholesterol exchanges through the wall and through the epithelial cell membrane. Moreover, in the epithelial cell of the jejunum, this hormone increases the percentage of plasma cholesterol, as estimated by the isotopic equilibrium method. Plasma cholesterol radioactivity enters the lumen mainly through the jejunal mucosa L-Thyroxyine strongly enhances jejunal excretion of plasma cholesterol explaining the twofold increase of fecal cholesterol excretion.

Animals↗
PubMed1980

Comparison of isotopic equilibrium and dual isotope blood ratio methods for measurement of cholesterol absorption in rats.

The dual isotope plasma ratio method (IRM) was applied to eight 3-month-old rats fed a semipurified diet. 1 month later, the isotopic equilibrium method (IEM) was substituted and was continued for 2 months. The animals were therfore 6 months old at the end of the isotope experiment. The IRM was then applied to a second group of eight 6-month-old rats. No difference was seen between the absorption coefficient of cholesterol measured by the IRM in rats of the first (73 +/- 2%) and of the second groups (72 +/- 4%) or by the IEM (69 +/- 1%). A critical discussion of both techniques is presented.

Animals↗
PubMed1979

Coronary care.

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Coronary Disease↗
PubMed1979

Biliary cholesterol absorption in normal and L-thyroxin-fed rats.

Infusion of bile containing labeled cholesterol into bile fistula rats has permitted an in vivo study of the movements and of the absorption of biliary cholesterol in the digestive tract. The specific activities of cholesterol were similar in the micelles and the sediment of the luminal content after a 6 hr infusion, indicating rapid exchange of cholesterol between these fractions. In animals fed a basal diet, the biliary cholesterol absorption was higher (83%) than that of dietary cholesterol (70%). Bile cholesterol is essentially absorbed in the jejunum while the absorption of cholesterol from the diet takes place all along the small intestine but preferentially in its second and third quarters. Both alimentary cholesterol and bile cholesterol enter the top cells of the villi in preference to those of the crypts. In L-thyroxin-fed rats, a parallel decrease in biliary and dietary cholesterol absorption was observed. The increase in the intestinal transit of cholesterol and epithelium cell renewal of the jejunum accounted for this observation.

Animals↗
PubMed1978

Diet and sterol biohydrogenation in the rat: occurrence of epicoprostanol.

The fecal sterols from rats fed several types of semipurified or commercial diets were analyzed by a combination of thin layer and gas liquid chromatography. In rats fed semipurified diets with lard, sucrose, and casein, increasing proportions of lard (0, 8, 20, 65%) enhanced the fecal coprostanol/coprostanol + cholesterol ratio (from 0.50 to 0.85). This ratio was reduced by replacing lard with triolein or a mixture of calcium oleate and linoleate (1:1) and did not change when trierucin was substituted. No coprostanol formation was observed in rats fed a diet with tripalmitin or tristearin. The addition of sodium hyodeoxycholate (0.5%) or cholestyramine (2%) to the basal diet was without effect on the coprostanol/coprostanol + cholesterol ratio in the feces. The addition of sodium taurocholate (0.2, 0.75, and 4%) strongly reduced coprostanol formation, while a chronic bile duct ligation led to an enhancement. Cholesterol feeding (0.05, 0.2, and 0.5% in the diet) slightly increased (from 51 to 66%) coprostanol formation. Trace amounts of epicoprostanol were generally found in the feces. However, in some cases a very high proportion (up to 60%) of this sterol was observed. Possible relationships between the presence of epicoprostanol and the nature of the diet are discussed.

Animals↗
PubMed1977

Effects of dietary fiber and salt mixtures on the cholesterol metabolism of rats.

The isotopic dilution method, which permits the in vivo measurements of the rates of the processes involved in cholesterol turnover, has been applied to rats fed a commercial stock diet or a basal semipurified diet in which either the nature and proportions of the source of dietary fiber or the salt mixture were changed. The cholesterolemia was about 100 mg/100 g in rats fed agar-agar, cellulose, bran or the stock diet. Pectin addition (5%) lowered significantly the plasma concentration of cholesterol (70 mg/100 g). Changes in the source of dietary fiber or salt mixture have moderate effects on the absorption coefficient of dietary cholesterol (range 58.2%-82%). In comparison to agar-agar, cellulose at 2.3% in the diet significantly lowered this coefficient, but larger amounts of cellulose (6.8% or 12.3%), or pectin (5%) were without effect, while bran addition (10%) tended to slightly decrease cholesterol absorption. Hence, high levels of cellulose in the diet increased the absorption coefficient in comparison to a low cellulose diet. A decrease of this coefficient was also observed when the calcium content of the diet was increased. Cholesterol biosynthesis and fecal excretion were inversely correlated to the absorption coefficient of dietary cholesterol in rats fed all of the semipurified diets indicating, as previously shown, that the intestine was the major source of biosynthesized cholesterol diverted into the plasma. However, feeding a commercial stock diet greatly increased the cholesterogenesis and the fecal elimination of bile acids, suggesting a high hepatic cholesterogenesis.

Animals↗
PubMed1976

[Regulation of cholesterol levels in plasma and liver of adult rats].

The dynamics of cholesterol-system in the plasma is characterized by a parameter which is a linear function of the internal secretion of cholesterol. So, the level of plasma cholesterol from synthesis is a low as its flow is high. Moreover, the level of plasma cholesterol from diet is simultaneously proportional to the flow of cholesterol intestinal absorption and dependent on the dynamics controlled by the internal secretion. The laws of the cholesterolemia cumulate these partial laws. Similar relations concern the esterified cholesterol in the liver.

Animals↗
PubMed1976

A new rat liver phospholipid exchange protein.

The soluble fraction from several mammalian tissue homogenates is known to stimulate phospholipid exchange between cell membrane fractions or artificial vesicles. All phospholipid exchange proteins purified to data exhibit an acidic isoelectric point. Using an assay that measures the transfer of [32P] phosphatidylcholine from liposomes to beef heart mitochondria, we report the presence of a new phospholipid exchange protein with a basic isoelectric point (8.4) in rat liver cytosol. A purification procedure, consisting of pH adjustment to 5.1, gel filtrations on Sephadex G 75 and DE 52 cellulose, isoelectric focusing between a pH of 5 and 10, and gel filtration on Sephadex G-50, yielded a fraction with high phosphatidylcholine exchange activity per mg of protein. This fraction exhibits a major band and two minor bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The molecular weight of the major band (18 700) is close to that for basic exchange protein fraction obtained by gel filtration (17 000). The distribution of basic and acidic exchange proteins differs markedly in various tissues and animal species. About 50 and 35% of phosphatidylcholine exchange activity from rat liver and rat intestine respectively are due to basic phospholipid exchange proteins. In contrast, no basic exchange protein was found in beef heart and only a small amount in beef liver. In the latter organ, less than 10% of phosphatidylcholine exchange activity was due to a basic phospholipid exchange protein fraction.

Animals↗
PubMed1976

Elongation of (omega-14C)oleic acid and (omega-14C)nervonic acid.

During feeding experiments with [omega-14C]oleic acid and [omega-14c]nervonic acid to adult rats, 14C-labelled C26, C28 and C30 fatty acids were recovered from the intestinal mucosa, liver, plasma, kidney and stools. The structures of these fatty acids were determined by g.l.c., radio-g.l.c. and mass spectrometry. The Schmidt and Ginger degradation methods indicated that most of the 14C found in these extra-long fatty acids remained in the omega position. These radioactive extra-long fatty acids were found mainly in the polar lipids of rats killed 3 or 15 h after being fed on labelled oleic acid or nervonic acid. Rats killed 63 h later yielded only traces of these extra-long fatty acids. When the rats were given antibiotics or received the same radioactive fatty acids by intravenous injection, the labelled extra-long fatty acids could not be detected in any of the tissues. We conclude that they were probably synthesized by elongation of oleic acid and nervonic acid by intestinal micro-organisms (probably yeasts) and then absorbed by the intestinal mucosa.

Animals↗
PubMed1976

Phospholipid exchange proteins in rat intestine.

The 105,000 g supernatant and pH 5.1 supernatant fractions from rat intestinal homogenates stimulate phosphatidylcholine exchange between [32P] phosphatidylcholine liposomes and beef heart mitochondria. This active fraction shows the characteristics of a protein. Isoelectric focusing of the intestinal pH 5.1 fraction shows two peaks of phosphatidylcholine exchange activity: one at an acidic pH (4.5-5.3), the other in a basic pH range (8-9). The second peak of activity appears to be a new phospholipid exchange protein. The anatomic distribution of phosphatidylcholine exchange activity in intestine has been investigated. Expressed per mg of protein, phosphatidylcholine exchange activity is higher in mucosa than in the intestinal wall. No significant differences have been found between villi and crypts cells or between jejunal and ileal villi. Futhermore, exchange activity per mg of protein in mucosa is unaffected by fasting or by feeding a high fat or high cholesterol diet. This suggests that phospholipid exchange activity in the absorptive cells is not a rate limiting step in the process of fat absorption.

Animals↗