Whole body and tissue cholesterol turnover in the baboon

Cholesterol turnover was studied in four baboons by injecting [14C]cholesterol 186 days and [3H]cholesterol 4 days before necropsy, and fitting a two- or three-pool model to the resulting specific activity-time data. At necropsy, cholesterol mass and specific activity were determined for the total body (minus the central nervous system) and for many tissues. A pool model permits the estimation, from the plasma specific activity-time curve alone, of total body cholesterol within a limited range, depending upon the extent of side pool synthesis. The principal aim of this study was to estimate the extent of cholesterol synthesis in the side pools of the model, by computing the amount of side pool synthesis needed to equal the measured total body cholesterol. Central pool synthesis varied from 61 to 89% of the total cholesterol production rate. Thus, approximately 25% (11 to 39%) of the production rate arose from peripheral (pool 3 for the three-pool, and pool 2 for the two-pool model) cholesterol synthesis. Moreover, the finding that the measured total body cholesterol fell within the range obtained from the kinetic analysis by using reasonable assumptions (namely, that zero or that half the production rate occurred in the side pools), provides evidence for the physiological validity of the model. A second aim of this study was to explore cholesterol turnover in various tissues. A pool model predicts that rapidly turning over tissues will have higher specific activities at early times and lower specific activities at later times after injection of tracer relative to slowly turning over tissues, except where significant synthesis occurs. Tissues were ranked 1 to 17 for 3H and 17 to 1 for 14C cholesterol specific activity values. Except for the GI tract and testis, the tissues had similar ranks for both 3H and 14C, further validating model predictions. Results in all four baboons were similar. Turnover rates for the different tissues loosely fell into three groups which were turning over at fast, intermediate, and slow rates. Finally, the magnitude of variation of cholesterol specific activity was moderate for several distributed tissues (fat, muscle, arteries, and the alimentary tract), but was small for liver. Cholesterol turnover in serial biopsies of skin, muscle, and fat could, however, be fitted with a single pool to estimate tissue turnover rates.     

The effect of fasting and physical exercise on plasma leptin concentrations in high-fat fed rats.

The aim of our study was to estimate the effect of fasting and physical exercise on a treadmill on plasma leptin concentrations in high-fat fed rats. Male Wistar rats were injected a low dose of streptozotocin (STZ) or buffer at 2 days of age and later fed a standard or high-fat diet (HFD). Plasma leptin was measured by RIA method in all the groups studied in basal conditions, after 48h fasting, a single bout of exhaustive exercise, and 4 weeks of exercise training. Plasma leptin concentrations were markedly elevated in the HFD and STZ/HFD groups compared to the control group. The significant correlation between plasma leptin and body weight was noted. Fasting and exercise training decreased plasma leptin in similar percentage in all the groups studied. The observed decrease was greater than expected from changes in body weight. We conclude that high-fat feeding results in an increase in plasma leptin levels in rats independently of plasma insulin or daily calorie intake. High-fat fed rats have maintained leptin response to fasting and exercise training. The reduction in plasma leptin after exercise training is partly independent on changes in body weight or plasma insulin.     

Effect of diet composition on coenzyme A and its thioester pools in various rat tissues

Three coenzyme A (CoA) molecular species, i.e., acetyl-CoA, malonyl-CoA, and nonesterified CoA (CoASH), in 13 types of fasted rat tissue were analyzed. A relatively larger pool size of total CoA, consisting of acetyl-CoA, malonyl-CoA, and CoASH, was observed in the medulla oblongata, liver, heart, and brown adipose tissue. Focusing on changes in the CoA pool size in response to the nutrient composition of the diet given, total CoA pools in rats continuously fed a high-fat diet for 4 weeks were significantly higher in the hypothalamus, cerebellum, and kidney, and significantly lower in the liver and skeletal muscle than those of rats fed a high-carbohydrate or high-protein diet. In particular, reductions in the liver were remarkable and were caused by decreased CoASH levels. Consequently, the total CoA pool size was reduced by approximately one-fifth of the hepatic contents of rats fed the other diets. In the hypothalamus, which monitors energy balance, all three CoA molecular species measured were at higher levels when rats were fed the high-fat diet. Thus, it was of interest that feeding rats a high-fat diet affected the behaviors of CoA pools in the hypothalamus, liver, and skeletal muscle, suggesting a significant relationship between CoA pools, especially malonyl-CoA and/or CoASH pools, and lipid metabolism in vivo.     

Cholesterol turnover and metabolism in two patients with abetalipoproteinemia

Total body turnover of cholesterol was studied in two patients with abetalipoproteinemia, a 32-year-old man and a 31-year-old woman. The patients received [14C]cholesterol intravenously, and the resulting specific activity-time curves (for 40 and 30 weeks, respectively) were fitted with a three-pool model. Parameters were compared with those from studies of cholesterol turnover in 82 normal and hyperlipidemic subjects. A three-pool model gave the best fit for the abetalipoproteinemic patients, as well as for the 82 previously studied subjects, suggesting general applicability of this model. Cholesterol production rates in the two abetalipoproteinemic subjects (0.82 and 0.89 g/day) were close to values predicted for persons of their body weight. Thus, total body turnover rate of cholesterol was quite normal in abetalipoproteinemia, confirming previous reports. Very low values (9.2 and 8.4 g) were found for M1, the size of the rapidly exchanging compartment pool 1, in the two abetalipoproteinemic subjects. These values were well below the values predicted (from the comparison study population) for normal persons of this size with low plasma cholesterol levels. For one patient, total body exchangeable cholesterol was very low, although not significantly below the predicted values for a person of his size. In the second patient, the observed estimate for total body exchangeable cholesterol was well within the range of values predicted for persons of her size with low to extremely low cholesterol levels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Purification of adenylosuccinate lyase from rat skeletal muscle by a novel affinity column. Stabilization of the enzyme, and effects of anions and fluoro analogues of the substrate.

The turnover of prothrombin and of factor X was investigated in rabbits fed on a 1%-cholesterol-supplemented or a standard diet by studying the evolution of radioactivity in blood and in plasma from these animals after the intravenous injection of either 125I-rabbit factor X or 125I-bovine prothrombin. For factor X, half-lives and fractional pool sizes were similar for the two groups of rabbits in the extravascular, intravascular and plasma compartments. However, the equivalent plasma fractional pool size for the two groups of rabbits was only 73% of that in the intravascular compartment. The fractional catabolic rate for the hypercholesterolaemic rabbits [0.064 +/- 0.007 (of the intravascular pool)/h] was not significantly different from that in the rabbits fed on the standard diet (0.074 +/- 0.008/h). However, the absolute catabolic rate, and therefore the rate of synthesis, was significantly higher (1.261 +/- 0.141 mg/day per kg body wt. of rabbit) in the rabbits fed on the cholesterol-supplemented than that in the rabbits fed on the standard diet (0.705 +/- 0.019 mg/day per kg). The prothrombin half-lives and fractional pool sizes were similar for the two groups of rabbits in the extravascular and the intravascular compartments. The fractional catabolic rate for the hypercholesterolaemic rabbits [0.041 +/- 0.003 (of the plasma pool)/h] was not significantly different from that in the rabbits fed on the standard diet (0.035 +/- 0.003/h). However, the absolute catabolic rate and therefore the rate of prothrombin synthesis was significantly higher (3.96 +/- 0.48 mg/day per kg body wt.) in the rabbits fed on the cholesterol-supplemented than that in the rabbits fed on the standard diet (2.24 +/- 0.12 mg/day per kg).     

Plasma lipids and other factors in the LA/N corpulent rat in the presence of chronic exercise and food restriction

The effects of regular exercise and food restriction were studied in the LA/N corpulent rat up to age 9 months. This congenic strain of the Lister and Albany rat is normotensive, corpulent, and hyperlipidemic when homozygous for the corpulent (cp) gene derived from the Koletsky strain. Food restriction of corpulent animals to the intake of matched lean rats caused body weight to be significantly lower, although not as low as that of the lean animals. Plasma total cholesterol in freely eating sedentary corpulent animals was significantly higher (210 mg/100 mL) than in food-restricted rats (165 mg/100 mL), in which plasma cholesterol was considerably elevated compared with lean rats (80 mg/100 mL). Exercise caused a modest but significant increase in both total and high density lipoprotein cholesterol in both corpulent and lean rats. The rise was greater in corpulent rats and, in food-restricted exercising corpulent rats, the cholesterol concentrations were equivalent to those of freely eating corpulent animals. Systolic blood pressure in lean rats fell slowly from 146 mmHg at 8 weeks to 132 mmHg at 36 weeks and was not affected by exercise. Sedentary corpulent rats showed a rapid rise in systolic pressure from 107 mmHg at 7 weeks to 128 mmHg at 11 weeks. This rise was reduced by food restriction and completely prevented by the combination of food restriction and exercise. Thus, in this strain of rats exercise was associated with higher plasma cholesterol concentrations, while food restriction had limited effects.     

Rates of sterol synthesis in the liver and extrahepatic tissues of the SHR/N-corpulent rat, an animal with hyperlipidemia and insulin-independent diabetes

The SHR/N-corpulent rat is a new genetically obese strain that exhibits both insulin-independent diabetes and hyperlipidemia. The present studies were undertaken to characterize various parameters of cholesterol metabolism in this model. At 11 weeks of age, the obese animals had markedly elevated plasma cholesterol, triglyceride, glucose, and insulin concentrations and elevated hepatic triglyceride concentrations compared to their lean littermates. The additional cholesterol in plasma was carried in the fractions of density less than 1.006, 1.020-1.055, 1.055-1.095, and 1.095-1.21 g/ml. In the obese rats the level of free cholesterol in the liver was decreased significantly while that of cholesteryl ester showed little change. Hepatic sterol synthesis was markedly suppressed in the obese animals. However, the rate of sterol synthesis in the small intestine and other extrahepatic tissues generally remained unchanged. Although hepatic synthesis was suppressed, whole animal sterol synthesis in the obese rats was similar to that in the lean controls. This resulted because, in the obese animals, not only was the reduced rate of hepatic synthesis partly balanced by a greater than 70% increase in liver mass, but the mass of the small intestine and adipose tissue was also increased more than 30% and 4-fold, respectively, thereby making these tissues quantitatively more important sites of sterol synthesis. When obese rats were pair-fed to the intake of their lean littermates for 10 weeks, there was only a modest reduction in body weight and plasma cholesterol concentration, and the rate of hepatic sterol synthesis remained very low. The suppression of synthesis in the liver also persisted when the obese rats were fed surfomer, a drug that specifically blocks cholesterol absorption. In contrast, feeding cholestyramine restored the rate of hepatic sterol synthesis to that found in lean animals. Bile acid pool size in the obese males and females was 2.5-fold greater than in their lean controls. The suppression of hepatic sterol synthesis in this model may be due to a change in the entero-hepatic circulation of bile acids arising from an expanded pool or, alternatively, it may represent a compensatory response to overproduction of sterol and its precursors in the intestinal and adipose compartments.     

Efflux of cholesterol from different cellular pools

Free cholesterol is very efficiently removed from cells by 2-hydroxypropyl-beta-cyclodextrins. The efflux of cholesterol occurs from two distinct kinetic pools: the half-times (t(1/2)) for the two pools in CHO-K1 cells are 15 +/- 5 s and 21 +/- 6 min and they represent 25% +/- 5% and 75% +/- 5% of the readily exchangeable cell cholesterol, respectively. In this study we have determined that the fast pool and the majority of the slow kinetic pool for cholesterol efflux are apparently present in the plasma membrane. Numerous agents that inhibit intracellular cholesterol trafficking are unable to affect either the size or the t(1/2) for efflux of either kinetic pool. In contrast, treatment of the cells with N-ethylmaleimide (NEM), exogenous lipases such as sphingomyelinase and phospholipase C, calcium ionophore A23187, or heat resulted in the dramatic increase in the size of the fast kinetic pool of cholesterol. These changes in the kinetics of cholesterol efflux are not specific to the nature of the extracellular acceptor indicating that they are a consequence of changes in the cell plasma membrane. The above treatments disrupt the normal organization of the lipids in the plasma membrane via either hydrolysis or randomization. The phosphatidylcholine and sphingomyelin present in the plasma membrane are critical for maintaining the two kinetic pools of cholesterol; any alteration in the amount or the location of these phospholipids results in an enhancement of efflux by redistributing cholesterol into the fast kinetic pool.     

Free phytosterols facilitate excretion of endogenous cholesterol in gerbils

To determine whether phytosterols (PST) facilitate excretion of whole body cholesterol and whether dietary fat or enhancing gallbladder contraction with curcumin might influence this process, four experiments were conducted in gerbils. In Experiment 1, naive gerbils received cholesterol-free purified diets with 30% energy from fat and 0% or 0.75% free PST from tall oil for 4 weeks. In Experiment 2, body cholesterol pools were expanded by feeding a diet containing 0.3% cholesterol for 3 weeks. Subsequently, PST was provided in either fat-free or normal-fat diets without cholesterol for only 2 h each morning, followed by a low-fat diet for the rest of the day and food restriction overnight. In Experiment 3, gerbils were preloaded with cholesterol, followed by either PST alone or PST+curcumin to enhance gallbladder contraction. In Experiment 4, curcumin or curcumin+PST were fed with 30% as fat and 0.15% cholesterol throughout the study. Because of the small whole body cholesterol pool in Experiment 1, the impact of PST was limited. When whole body cholesterol was expanded in Experiments 2 and 3, subsequent reductions of liver esterified cholesterol by PST were significant. In the presence of dietary fat, PST caused a greater reduction (23%) than in a fat-free diet (8%) compared to respective controls. Curcumin (Experiments 3 and 4) proved ineffective in reducing liver or plasma cholesterol pools, and the 3:1 ratio between PST/diet cholesterol was less effective at blocking cholesterol absorption than a 5:1 ratio previously employed. Thus, free PST removed whole body cholesterol, which was enhanced by concomitant fat intake, but was unaffected by a gallbladder contracting agent.     

有氧运动同时补充玉米肽对肥胖大鼠脂肪分解关键酶的影响

目的：研究有氧运动同时补充玉米肽对高脂饮食诱导的肥胖大鼠减脂的作用及其与脂肪分解关键酶甘油三酯脂肪酶（ATGL）和脂蛋白酯酶（LPL）关系。方法：4周龄健康雄性SD大鼠150只,体重160~180 g,随机选取15只作为普通膳食不运动组,给予普通饲料喂养。剩余135只大鼠进行8周的高脂饲料喂养建立肥胖大鼠模型,以体重超过普通膳食不运动组大鼠平均体重的20%作为肥胖大鼠建模成功的标准。将建模成功的肥胖大鼠40只随机分为5组（n=8）：肥胖对照组、酪蛋白组、玉米肽组、运动组和运动+玉米肽组。除酪蛋白组、玉米肽组喂养自制饲料外,其余各组均用普通饲料喂养,运动组每天进行15 m/min,持续时间60 min的跑台运动,每周6天。4周运动和玉米肽干预后取血,检测大鼠血浆中TG、TC、HDL、LDL的含量;取大鼠肾周、附睾脂肪和肝,检测肾周和附睾脂肪的重量,Western blot检测大鼠肝ATGL、脂肪LPL的蛋白表达水平。结果：与肥胖对照组大鼠相比：①运动组、运动+玉米肽组大鼠的体重、附睾和肾周脂肪含量明显降低（P<0.05）,且运动+玉米肽组比运动组下降得更明显（P<0.05）,而其它组大鼠无显著差异。②运动组大鼠血浆TG显著降低,运动+玉米肽组的血浆TG、TC显著降低（P<0.05）,其它组大鼠的TG、TC无显著差异;血浆HDL和LDL各组间均无显著性差异。③运动组和运动+玉米肽组大鼠的肝ATGL、脂肪组织LPL的蛋白水平明显增加（P<0.01）,且运动+玉米肽组比运动组的更显著（P<0.05）;其他两组无显著差异。结论：有氧运动、有氧运动同时补充玉米肽都可以明显降低大鼠的体脂和血脂水平,且后者的作用更强,这可能与其更显著地增加肥胖大鼠肝ATGL和脂肪LPL的蛋白水平有关。而仅仅补充玉米肽不能降低大鼠的体脂和血脂水平。     

Physiological basis for effect of physical conditioning on chronic ethanol-induced hypertension in a rat model

The study aim was to investigate the interaction of physical conditioning and chronic ethanol ingestion on blood pressure (BP), heart rate (HR), nitric oxide (NO) and oxidants/antioxidants balance in the plasma of rats. Male Fisher rats were divided into four groups of seven animals each and treated as follows: (1) Control (5% sucrose, orally) daily for 12 weeks; (2) ethanol (4 g kg⁻¹, orally) daily for 12 weeks; (3) exercise training on treadmill plus sucrose daily for 12 weeks and (4) exercise training on treadmill followed by ethanol (4 g kg⁻¹, orally) daily for 12 weeks. The body weight, BP and HR were recorded every week. The animals were sacrificed under ether anesthesia after 12 weeks, blood collected in heparinzed vials, plasma isolated and analyzed. The results show that exercise training significantly lowered the weight gain 6–12 weeks in ethanol treated rats compared to ethanol alone or control rats. The mean arterial BP was significantly elevated 6–12 weeks after ethanol ingestion without significant alterations in HR. Exercise training lowered the BP close to the normal control values in ethanol fed rats. Ethanol significantly decreased the plasma NO levels, reduced to oxidized glutathione ratio (GSH/GSSG) and antioxidant enzymes-superoxide dismutase (CuZn-SOD, and Mn-SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) activities while plasma NADPH oxidase activity and malondialdehyde (MDA) levels were significantly elevated compared to control. Exercise training significantly restored the depletion of plasma NO levels, GSH/GSSG ratio, and antioxidant enzyme activities and normalized the MDA levels and NADPH oxidase activity in the plasma of ethanol treated rats. The study concluded that physical conditioning attenuates the chronic ethanol-induced hypertension by augmenting the NO bioavailability and reducing the oxidative stress response in the plasma of rats.     

Isomers of conjugated linoleic acid decrease plasma lipids and stimulate adipose tissue lipogenesis without changing adipose weight in post-prandial adult sedentary or trained Wistar rat

The respective effects and interactions of supplementation with two conjugated linoleic acid (CLA) isomers and exercise on plasma metabolic profile, activity of lipogenic enzymes and cellularity in two adipose tissue sites, those of the liver and heart, were examined in adult Wistar rats. Rats that were either sedentary or exercise-trained by treadmill running were fed one of four diets: a diet without CLA; a diet with either 1% cis 9, trans 11 CLA or 1% trans 10, cis 12 CLA; or a mixture of both isomers (1% of each) for 6 weeks. We observed that the exercise decreased lipogenic enzyme activities in epididymal and perirenal adipose tissue. Plasma cholesterol, insulin, and leptin concentrations were lower in exercise-trained rats than in sedentary rats. The ingestion of either CLA mixture or the trans 10, cis 12 CLA increased lipogenic enzyme activities in epididymal tissue and more markedly in perirenal adipose tissue, especially in sedentary rats, and without affecting adipose tissue weight or cellularity. A similar effect of trans 10, cis 12 CLA was observed in regard to malic enzyme activity in the liver. In addition, this isomer decreased plasma lipid and urea concentrations and increased plasma 3-hydroxybutyrate levels. The ingestion of cis 9, trans 11 CLA increased fatty acid synthase activity in perirenal adipose tissue in sedentary rats and decreased plasma cholesterol and leptin concentrations. These results show that isomers of CLA decrease plasma lipids and stimulate adipose tissue lipogenesis without changing adipose weight in adult sedentary or exercise-trained rat, thus suggesting a stimulation of adipose tissue turnover.     

Studies on the regulation of plasma cholesterol levels in squirrel monkeys of two genotypes

Certain individual squirrel monkeys ("hypo-responders") are able to remain normocholesterolemic when fed diets containing cholesterol (0.5 mg/kcal). Other squirrel monkeys ("hyperresponders") when fed the same diet become hypercholesterolemic. The purpose of these studies was to identify the mechanisms which allow hyporesponders to compensate for dietary cholesterol. Using formula diets and sterol balance techniques, we have compared cholesterol absorption, synthesis, excretion, and turnover in hypo- and hyperresponding monkeys. Cholesterol absorption was essentially identical in the two groups (about 55 mg/day). Cholesterol synthesis was likewise similar in the two groups (about 35 mg/day) and there was no evidence of feedback inhibition at the level of cholesterol fed. Hyporesponders had faster turnover rates and smaller body cholesterol pools than did hyperresponders. Excretion of neutral steroids was similar for hypo- and hyperresponders and did not change with cholesterol feeding. In contrast, hyporesponders increased bile acid excretion shortly after cholesterol feeding was begun. Hyperresponders responded more slowly and to a lesser degree. It is concluded that, in this species, the mechanism of control of plasma cholesterol levels is related to the rate of conversion of cholesterol to bile acids.     

Relationship between acid-soluble carnitine and coenzyme A pools in vivo

The relationship between the acid-soluble carnitine and coenzyme A pools was studied in fed and 24-h-starved rats after carnitine administration. Carnitine given by intravenous injection at a dose of 60μmol/100g body wt. was integrated into the animal's endogenous carnitine pool. Large amounts of acylcarnitines appeared in the plasma and liver within 5min of carnitine injection. Differences in acid-soluble acylcarnitine concentrations were observed between fed and starved rats after injection and reflected the acylcarnitine/carnitine relationship seen in the endogenous carnitine pool of the two metabolic states. Thus, a larger acylcarnitine production was seen in starved animals and indicated a greater source of accessible acyl-CoA molecules. In addition to changes in the amount of acylcarnitines present, the specific acyl groups present also varied between groups of animals. Acetylcarnitine made up 37 and 53% of liver acid-soluble acylcarnitines in uninjected fed and starved animals respectively. At 5min after carnitine injection hepatic acid-soluble acylcarnitines were 41 and 73% in the form of acetylcarnitine in fed and starved rats respectively. Despite these large changes in carnitine and acylcarnitines, no changes were observed in plasma non-esterified fatty acid or β-hydroxybutyrate concentrations in either fed or starved rats. Additionally, measurement of acetyl-CoA, coenzyme A, total acid-soluble CoA and acid-insoluble CoA demonstrated that the hepatic CoA pool was resistant to carnitine-induced changes. This lack of change in the hepatic CoA pool or ketone-body production while acyl groups are shunted from acyl-CoA molecules to acylcarnitines suggests a low flux through the carnitine pool compared with the CoA pool. These results support the concept that the carnitine/acid-soluble acylcarnitine pool reflects changes in, rather than inducing changes in, the hepatic CoA/acyl-CoA pool.     

Dynamics of lysosomal cholesterol in Niemann-Pick type C and normal human fibroblasts

The dynamics of endolysosomal cholesterol were investigated in Niemann-Pick type C (NPC) cells and in human fibroblasts treated with class 2 amphiphiles to mimic NPC cells. We showed through new approaches that the massive pools of endolysosomal cholesterol in these cells are not trapped but, rather, circulate to the cell surface at about the normal rate. This flux spared NPC and amphiphile-treated cells from disruption by the extraction of their plasma membrane cholesterol with cyclodextrin. Nocodazole, a microtubule-depolymerizing agent, reversed the resistance of NPC and U18666A-treated cells to cholesterol depletion, apparently by reducing the flux of endolysosomal cholesterol to the plasma membrane. Neither nocodazole nor bafilomycin A1 (an inhibitor of the vacuolar proton pump) acted in the same way as the NPC mutation or class 2 amphiphiles: both agents decreased plasma membrane cholesterol at the expense of the endolysosomal pool and both blocked the actions of the amphiphile, U18666A. Finally, the resistance of NPC cells to lysis by amphotericin B was shown not to reflect a reduction in plasma membrane cholesterol arising from a block in lysosomal cholesterol export but rather the diversion of the amphotericin B to cholesterol-rich endolysosomes. We conclude that the large pool of endolysosomal cholesterol in NPC and amphiphile-treated fibroblasts is dynamic and that its turnover, as in normal cells, is dependent on microtubules.     

Intravascular metabolism of lipoprotein cholesteryl esters in African green monkeys: differential fate of doubly labeled cholesteryl oleate

High density lipoproteins (HDL), doubly labeled with [3H]cholesteryl oleate and cholesteryl [14C]oleate, were reinjected to study HDL cholesteryl ester metabolism in African green monkeys. The transfer of labeled HDL cholesteryl ester to low density lipoprotein (LDL) was rapid and equilibration of the [3H]cholesteryl oleate and cholesteryl [14C]oleate specific activities in LDL and HDL occurred within 90 min after reinjection. The apparent rates of disappearance from the circulation of the two moieties of the cholesteryl ester were different. In the same four animals, the residence time for the turnover of plasma [3H]cholesterol averaged 6.1 days while the residence time for the removal of cholesteryl [14C]oleate from plasma was approximately 2.1 days. These results suggest that for some lipoprotein cholesteryl esters removed from plasma, the cholesterol moiety subsequently reappeared in plasma. The difference between the rate of decay of the 14C-labeled fatty acid moiety, which represents all of the cholesteryl ester removed from plasma (0.48 pools/day) and the decay of the 3H-labeled cholesterol moiety, which represents the sum of cholesteryl ester removal and cholesterol reappearance (0.16 pools/day), is the fraction of the cholesteryl ester pool recycled per day (0.32 pools/day or 22.5 mg/kg per day). In other words, approximately 68% of the cholesterol moiety that was removed from plasma as cholesteryl oleate reappeared in the plasma cholesterol pool. These studies support the concept that an efficient reutilization cycle for plasma cholesterol occurs, i.e., the cholesteryl ester molecule can exit and the cholesterol moiety can re-enter plasma without effective equilibration of the cholesterol moiety with extravascular cholesterol pools.     

The effects of dietary fat and cholesterol on the metabolism of plasma low density lipoprotein apoproteins in squirrel monkeys.

Low density lipoprotein apoproteins from squirrel monkeys (Saimiri sciureus) had characteristic 2-phase die-away curves in plasma. The kinetic constants were similar with three methods of labeling: in vitro with 125I by the iodine monochloride or the Bolton-Hunter methods or in vivo by the injection of [3H]-leucine into a donor animal. Dietary cholesterol and the type of dietary fat influenced the concentration of plasma cholesterol and low density lipoproteins. The fractional turnover of low density lipoprotein apoprotein was greaterin monkeys fed semipurified diets with safflower oil than in those on butter but was not influenced by dietary cholesterol. The total low density lipoprotein apoprotein turnover (the product of fractional turnover and plasma lipoprotein concentration) was highest in monkeys fed butter plus added cholesterol and lowest in those on safflower oil without cholesterol. Dietary safflower oil resulted in a smaller proportion of the total low density lipoprotein pool in the intravascular compartment than did butter, regardless of whether cholesterol was added.     

Effects of fructose loading in streptozotocin-diabetic and nondiabetic rats.

The present study compares the cardiovascular consequences of a 6-week fructose feeding in nondiabetic and streptozotocin-diabetic rats. Myocardial performance of these animals was determined using the isolated perfused working heart preparation. Systolic blood pressure, pulse rate, ventricular weight/body weight ratio, and plasma levels of glucose, insulin, triglycerides, and cholesterol were measured. In nondiabetic rats, fructose drinking caused significant increases in blood pressure, pulse rate, and plasma concentrations of insulin and triglycerides. Streptozotocin-diabetic animals exhibited significantly less body weight growth, slower pulse rate, higher plasma levels of cholesterol and triglycerides, ventricular enlargement, and functional impairment of the myocardium. The fructose-loaded diabetic rats had larger increases in plasma cholesterol and triglycerides than did control fructose-fed rats, but the fructose-induced increases in blood pressure and pulse rate were attenuated significantly. However, plasma levels of glucose and insulin and the degree of ventricular enlargement and myocardial dysfunction were not significantly different from those of control diabetic rats. These results show that fructose loading for 6 weeks can cause increases in blood pressure, pulse rate, and plasma lipids in both nondiabetic and diabetic rats. However, fructose ingestion does not significantly alter glycemic control or affect the development of myocardial dysfunction in streptozotocin-diabetic rats.     

Isotopomer spectral analysis of intermediates of cholesterol synthesis in human subjects and hepatic cells

Steroid intermediates of the cholesterol synthesis pathway are characterized by rapid turnover rates relative to cholesterol due to their small pool size. Because the small pools will label rapidly, these intermediates may provide valuable information about the incorporation of isotopes in de novo synthesis of cholesterol and related compounds. The labeling of cholesterol synthesis intermediates from [1-(13)C]acetate was investigated in human subjects and in liver cell models by means of isotopomer spectral analysis (ISA). In human subjects, infusing [1-(13)C]acetate into the duodenum for 12 h demonstrated that approximately 50% of the plasma lathosterol pool was derived from de novo synthesis during this interval. The lipogenic acetyl-CoA precursor pool enrichment reached a constant value within 3 h of the start of the infusion. In vitro studies indicated that liver cell models decrease de novo lathosterol synthesis when cholesterol synthesis is inhibited by statins or cholesterol-containing serum. We propose a new calculation to increase the accuracy and precision of cholesterol synthesis estimates in vivo combining the ISA of lathosterol and cholesterol.