Uptake Of Triglyceride Fatty Acids Research Articles

Cholecystokinin is involved in triglyceride fatty acid uptake by rat adipose tissue.

The incorporation of plasma triglyceride (TG) fatty acids to white adipose tissue (WAT) depends on lipoprotein lipase (LPL), which is regulated by angiopoietin-like protein-4 (ANGPTL-4), an unfolding molecular chaperone that converts active LPL dimers into inactive monomers. The production of ANGPTL-4 is promoted by fasting and repressed by feeding. We hypothesized that the postprandial hormone cholecystokinin (CCK) facilitates the storage of dietary TG fatty acids in WAT by regulating the activity of the LPL/ANGPTL-4 axis and that it does so by acting directly on CCK receptors in adipocytes. We report that administration of CCK-8 (a bioactive fragment of CCK) to rats: (i) reduces plasma ANGTPL-4 levels; (ii) represses Angptl-4 expression in WAT and (iii) simultaneously enhances LPL activity in this tissue without inducing Lpl expression. In vivo CCK-8 effects are specifically antagonized by the CCK-2 receptor (CCK-2R) antagonist, L-365,260. Moreover, CCK-8 downregulates Angptl-4 expression in wild-type pre-adipocytes, an effect that is not observed in engineered pre-adipocytes lacking CCK-2R. These effects have functional consequences as CCK-8 was found to promote the uptake of dietary fatty acids by WAT, as demonstrated by means of proton nuclear magnetic resonance (1H-NMR). The efficacy of acute CCK-8 administration was not reduced after chronic CCK-8 treatment. Moreover, the effects of CCK-8 on WAT were not associated to the increase of circulating insulin. Our results show that cholecystokinin promotes lipid storage in WAT by acting on adipocyte CCK-2R, suggesting a pivotal role for CCK in TG homeostasis.

Splanchnic Spillover of Extracellular Lipase–Generated Fatty Acids in Overweight and Obese Humans

Triglyceride-rich lipoproteins, primarily chylomicrons, can contribute to plasma free fatty acid (FFA) concentrations via spillover of fatty acids during intravascular hydrolysis into the venous effluent of some tissues. The present study was undertaken to determine whether spillover occurs in the splanchnic bed of humans. Arterial and hepatic venous blood was sampled in postabsorptive (n = 6; study A) and postprandial (n = 5; study B) obese humans during infusion of carbon-labeled ((14)C or (13)C) oleate and (3)H triolein, the latter incorporated into a lipid emulsion as a surrogate for chylomicrons. Spillover was determined by measuring production of (3)H oleate. Splanchnic spillover was higher than nonsplanchnic systemic spillover in both study A (60 +/- 7 vs. 24 +/- 6%; P < 0.01) and study B (54 +/- 3 vs. 16 +/- 5%; P < 0.005). Because portal vein sampling is not feasible in humans, assumptions regarding actual spillover in nonhepatic splanchnic tissues were required for the spillover calculation. A mathematical model was developed and demonstrated that nonhepatic splanchnic spillover rates in study A and study B of 69 and 80%, respectively, provided the best fit with the data. There was preferential splanchnic uptake of triglyceride fatty acids compared with FFAs in study B (fractional extraction 61 +/- 3 vs. 33 +/- 2%; P < 0.005). These data confirm previous studies indicating that the transport of FFAs and triglyceride fatty acids are partitioned in tissues and indicate that splanchnic spillover from triglyceride-rich lipoproteins may be a significant source of both portal venous and systemic FFAs.

Fat transfer and energetics during lactation in the hooded seal: the roles of tissue lipoprotein lipase in milk fat secretion and pup blubber deposition.

Hooded seals (Cystophora cristata) lactate for 3.6 days during which females simultaneously fast and transfer large amounts of energy to their pups through fat-rich milk. Pups grow rapidly, principally due to blubber deposition. Lipoprotein lipase (LPL), the primary enzyme responsible for tissue uptake of triglyceride fatty acids, may strongly influence both maternal milk fat secretion and pup blubber deposition. We measured the energetic costs of lactation (using hydrogen isotope dilution, 3H2O), milk composition, prolactin, and LPL activity (post-heparin plasma LPL [PH LPL], blubber, mammary gland and milk; U) in six females. PH LPL and blubber LPL were measured in their pups. Females depleted 216.3 MJ.day-1 of body energy and fat accounted for 59% of maternal mass loss and 90% of postpartum body energy loss, but maternal body composition changed little. Maternal blubber LPL was negligible (0.0-0.2 U), while mammary LPL was elevated (1.8-2.5 U) and was paralleled by changes in prolactin. Estimated total mammary LPL activity was high (up to 20,000 U.animal-1) effectively favoring the mammary gland for lipid uptake. Levels of total blubber LPL in pups increased seven-fold over lactation. Pups with higher PH LPL at birth had greater relative growth rates (P = 0.025). Pups with greater blubber stores and total blubber LPL activity had elevated rates of fat deposition (P = 0.035).

Postprandial leg and splanchnic fatty acid metabolism in nonobese men and women.

These studies were conducted to determine whether there are gender-specific regional differences in meal triglyceride fatty acid uptake. Systemic and regional oleate ([3H]oleate) kinetics were measured in nine nonobese men and eight nonobese women before and at the end of a 6-h meal, administered as small frequent feedings to achieve steady-state chylomicronemia. Chylomicron uptake in the splanchnic bed accounted for 71 +/- 15% of meal triglyceride disappearance in men and 20 +/- 7% in women (P < 0.01), whereas leg chylomicron uptake could only account for 12 +/- 2 and 8 +/- 4% (P not significant in men vs. women) of meal triglyceride disappearance. Meal ingestion suppressed (P < 0.05) systemic and regional free fatty acid release in both men and women. Splanchnic nonchylomicron triglyceride release and leg nonchylomicron triglyceride uptake were not significantly different in men and women. In summary, the largest quantitative difference between men and women in fatty acid kinetics during meal ingestion is a substantially greater splanchnic uptake of meal triglyceride fatty acids in men. This could represent greater meal fatty acid storage in visceral adipose tissue.

Spinal cord of the rat contains more lipoprotein lipase than other brain regions.

Lipoprotein lipase (LPL) is important for the delivery of triglyceride fatty acids (TGFA) to a variety of tissues. We have used measurements of heparin-releasable LPL activity, immunohistochemistry, in situ hybridization, and Northern analysis to more fully characterize the location of LPL within the entire central nervous system (CNS) of the rat. Surprisingly, the levels of LPL activity and mRNA in the caudal spinal cord were 5- to 10-times higher than those found in any other area of the brain, levels similar to those found in adipose tissue or skeletal muscle. A number of cell types including neurons in the hippocampus, Purkinje cells of the cerebellum, and cells deep within the cortex were identified as sources of LPL mRNA. LPL protein was found within many vascular structures throughout the CNS, and within Purkinje cells. The strongest immunostaining was around nerve rootlets associated with the caudal spinal cord. Feeding studies were carried out with [14C]oleic acid to see whether CNS LPL functioned in the uptake of TGFA. These studies demonstrated uptake of chylomicron triglyceride fatty acids throughout the CNS. The localization of LPL within these structures suggests that the uptake of triglyceride fatty acids is an integral part of normal lipid metabolism of the central nervous system and may be important in regulating feeding behavior and/or maintaining normal neuronal function.

Uptake of triglyceride fatty acids in adipose tissue in vivo in man

Currently available information on adipose tissue metabolism in man is mainly based on studies in vitro. In the present work adipose tissue lipid uptake was studied in vivo in man. 100 g glucose and 120 g milk fat with 10 microCi U-14C oleic acid were given in the overnight fasting state to eight women and 2 h after a carbohydrate-rich meal to eight women. After 4 h, 1-day, 1 week and 1 month radioactivity levels were determined in the lipids of adipose tissue in the femoral and abdominal regions and in plasma. At 4 h 30 and 20% of the oleic acid was estimated to remain in the extracellular space in the fasted and fed groups respectively, measured in plasma. Contents of oleic acid radioactivity was higher in the abdominal than femoral region. An estimated 27 and 46 g of fat was taken up in adipose tissue of the fasted and fed groups, constituting 1/3 and 1/2 of total tissue uptake respectively. After 1 day these figures were 43 and 60 g respectively. At 1 week and 1 month adipose tissue radioactivity was increasing slowly. Lipoprotein lipase (LPL) activity in adipose tissue at 4 h was higher in the femoral than abdominal adipose tissue and higher in the fed than fasted state in the abdominal region. A significant correlation was found between uptake and LPL in abdominal adipose tissue only. These results show that uptake of fat measured in vivo is probably not necessarily reflected by LPL measurements only, suggesting other regulatory factors.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of pregnancy on the uptake of lipoprotein triglyceride fatty acids by isolated adipocytes in the rat

To determine whether the reduced lipoprotein lipase activity in adipose tissue in late pregnancy corresponds to parallel changes in the uptake of triglyceride fatty acids, isolated adipocytes from 19- and 21-day pregnant rats and virgin controls were incubated for different periods in the presence of rat plasma triglyceride-rich lipoproteins with their esterified fatty acids of neutral glycerides (triglycerides) labelled with 3H. The hydrolysis of triglycerides and uptake of fatty acids by the adipocytes increased linearly and parabolically with respect to the incubation time and were always lower in cells from pregnant animals than from controls. Addition of heparin to the incubation medium produced similar increases in hydrolysis and uptake in all groups. Results indicate that the diminished uptake of triglyceride fatty acids by adipose tissue contributes to hypertriglyceridemia in late pregnancy which is counteracted by lipogenesis increase to maintain the mother's augmented body fat.

Effect of dexamethasone on lipoprotein lipase activity of fetal rat lung.

Dexamethasone was administered by continuous subcutaneous infusions (16 microgram/kg/h) to pregnant rats from day 16 of gestation. Administration of the hormone markedly affected maternal and fetal weight gain, fetal lung:body weight ratio and lipoprotein lipase activity of the lung. Cumulative maternal weight gain from days 15-21 of gestation was 80 +/- 4.0 g in control and 30 +/- 10 g in dexamethasone-treated rats. Fetal weight at 22 days of gestation and 1 day after birth was 5.5 +/- 0.39 and 8.6 +/- 0.30 in control and 4.65 +/- 0.26 and 5.9 +/- 0.34 in dexamethasone-treated rats. The ratio of lung weight to body weight was lower throughout the last 5 days of gestation in dexamethasone-treated than in control rats. Dexamethasone administration led to a 2- to 3-fold increase in lipoprotein lipase activity levels in fetal rat lung at 19 and 20 days' gestation and prevented the decline in enzyme activity shortly before birth. Stimulation of fetal lung lipoprotein lipase activity suggests that increased uptake of triglyceride-fatty acids by the lung could be a contributory factor to corticosteroid-enhanced surfactant synthesis.

Effect of nutritional status on rat adipose tissue, muscle and post-heparin plasma clearing factor lipase activities: their relationship to triglyceride fatty acid uptake by fat-cells and to plasma insulin concentrations.

1. In rats in a variety of nutritional states, the adipose tissue clearing factor lipase activity is strongly, positively correlated with fat-cell triglyceride fatty acid uptake. 2. In the same animals, muscle clearing factor lipase activity is inversely correlated with the activity of the enzyme in adipose tissue and with the plasma insulin concentration. 3. In starved animals that are given glucose, adipose tissue clearing factor lipase activity is positively correlated with the plasma insulin concentration. 4. The effect of changes in nutritional status on the activity of clearing factor lipase in rat post-heparin plasma depends on the heparin dosage used. The administration of glucose, but not of fructose or sucrose, to starved rats alters the response to heparin injection towards that found in rats in the fed state.

Genesis of fatty liver and hyperlipemia in the fetal guinea pig.

10 to 20% of [1-14C] palmitate injected into pregnant guinea pigs was recovered in lipids of their fetuses. From these data and the rate of transport of palmitate in maternal blood, it appears that placental transport of free fatty acids can account for the accumulation of lipids in late gestational fetuses. About 80% of the labeled palmitate in the fetus appeared initially in lipids of the liver. 14C appeared in plasma triglyceride fatty acids after a few minutes and subsequently accumulated in lipids of white and brown adipose tissue, suggesting that much of the palmitate deposited in adipose tissue were derived from hepatogenous triglyceride fatty acids. By contrast, 14C was usually maximal in heart and carcass lipids before it appeared in plasma triglyceride fatty acids. Lipoprotein lipase activity in fetal adipose tissue was low, and activity of cofactor protein of lipoprotein lipase in fetal blood plasma was much lower than that observed in other mammalian species. On the basis of these and earlier observations, it is concluded that the accumulation of triglycerides in liver and blood plasma of fetal guinea pigs during late gestation is at least partly the result of the large uptake of maternally derived free fatty acids by the fetal liver accompanied by rapid synthesis and secretion of triglyceride-rich very low density lipoproteins into the blood. However, limited uptake of triglyceride fatty acids in adipose tissue may contribute to the fatty liver and hyperlipemia.

A case of massive hypertriglyceridaemia and impaired fatty acid incorporation into adipose tissue glycerides (FIAT), both corrected by nicotinic acid.

Abstract. A case of massive chylomicronaemia with fasting plasma triglyceride levels around 100 mmol/1 and normal postheparin lipoprotein lipase activity (LLA) has been studied. To investigate other possible mechanisms for the hypertriglyceridaemia than reduced LLA, we have attempted to evaluate the capacity of adipose tissue to assimilate fatty acids split off from plasma triglycerides by LLA by studying the incorporation rate of fatty acids into adipose tissue (FIAT). Adipose tissue incubated in vitro showed a lowered FIAT. Also the incorporation of medium glucose into glyceride glycerol (GLIAT) was low compared to control subjects. After two months' treatment with nicotinic acid, when plasma triglyceride levels had fallen to nearly normal levels, FIAT and GLIAT had increased about 3–6‐fold and were then in the range of the control subjects. The role of the capacity of adipose tissue for assimilation of fatty acids split off from plasma triglycerides in regulating uptake of triglyceride fatty acids from the blood is discussed.

Uptake and metabolism of circulating chylomicron triglyceride by rabbit aorta

To determine if chylomicron triglycerides are taken up and metabolized by the arterial wall, rabbit abdominal aortas were perfused in situ for various times up to 2 hr with blood-buffer containing isotopically labeled substrates. Labeled chylomicrons were obtained by feeding [(3)H]palmitic acid or [(3)H]glyceryl trioleate to rats and rabbits with cannulated thoracic ducts. After aortic perfusion with these chylomicrons, more than 85% of aortic lipid ester radioactivity was in triglyceride; when labeled glycerol or palmitic acid was perfused, most aortic ester lipid radioactivity was in diglycerides and phospholipids. This indicated that, during perfusion with chylomicrons, intact triglyceride molecules were taken up by aorta. The rate of triglyceride fatty acid uptake by the inner avascular segment approached maximal values at low concentrations of perfusate triglyceride fatty acids (2 mm), whereas uptake in the outer capillary perfused segment increased with increasing triglyceride fatty acid concentration (0.4-25 mm). By double-radioisotope techniques it was shown that aortic free fatty acid was derived from both perfusate free fatty acids and from hydrolysis of lipoprotein glycerides within the aortic wall. Uptake of chylomicron triglyceride by perfused aorta was independent of triglyceride hydrolysis, which was quantitatively small.

Response of rat tissue lipases to physical training and exercise.

SummaryThe results of this study indicate that physical training causes an adaptive increase in epinephrine-stimulated fatty acid mobilization potential in adipose tissue of rested animals. Exhaustion caused an increase in ESL activity of similar magnitude in untrained animals. The exercise effect was not additive with the training effect when trained animals were exercised or exhausted.Lipoprotein lipase was unaffected by training and increased in heart and muscle of untrained animals following exhaustion. Trained animals exhibited a similar but smaller trend toward increased LPL activity with exercise or exhaustion.Taken together, the results of this study are compatible with the concept that exercise increases lipolysis in adipose tissue and LPL mediated triglyceride fatty acid uptake by muscular tissues. Physical training appeared to increase the responsiveness of adipose tissue to adrenergic stimulation. An increased adipokinetic response by adipose tissue of trained animals would be compatible with ...

Quantitative studies of the metabolism of chylomicron triglycerides and cholesterol by liver and extrahepatic tissues of sheep and dogs.

Unanesthetized sheep and dogs, previously fitted with indwelling catheters in the aorta, lower vena cava, mesenteric, portal, left hepatic and jugular veins, were given constant intravenous infusions of lymph in which the chylomicron lipids were variously labeled with (3)H or (14)C. Para-aminohippuric acid was infused into the mesenteric venous catheter for measurement of portal and hepatic venous blood flow. In some animals, alternately labeled free fatty acids bound to albumin were mixed with the lymph to be infused. In both species, chylomicron triglyceride fatty acids were taken up in the region drained by the lower vena cava and portal vein and free fatty acids derived from hydrolysis of these triglycerides were extensively recycled in the blood. Direct uptake of triglyceride fatty acids also occurred in liver and accounted for about 10% of the total triglyceride fatty acids removed from the blood in sheep and 22% in dogs. In sheep, 10% and, in dogs, about 40% of these triglyceride-fatty acids were released into the blood as free fatty acids. The free fatty acids recycled from various regions accounted for a substantial fraction of the chylomicron fat eventually deposited in each tissue. Uptake of chylomicron cholesterol from the blood of sheep occurred primarily in liver and to a small extent in certain tissues drained by the portal vein. The results obtained, together with other available data, demonstrate that chylomicron triglycerides are removed primarily in extrahepatic tissues of both species, while the liver removes cholesterol contained in chylomicron "skeletons" from which most of the triglycerides have been removed. The quantitative differences between transport of chylomicron lipid in sheep and dogs may be related to known differences in the structure of their hepatic sinusoids.

Lipoprotein lipase content and triglyceride fatty acid uptake in adipose tissue of rats of differing body weights

Increasing body weight appears to alter lipid metabolism in adipose tissue. We have measured the content of lipoprotein lipase and the uptake of chylomicron triglyceride fatty acids in epididymal fat pads of rats of different weights. In order that the results might be expressed in terms of cell numbers, the relationship between the weights of fat pads and the numbers and volumes of fat cells isolated from them was determined. Highly significant correlations were found between fat pad weight and both the number and the volume of the individual adipocytes. In rats weighing from 140 to 350 g, the increase in the size of fat pads was attributable almost equally to increases in cell size and in cell number. Lipoprotein lipase activity was measured in acetone powders of whole fat pads and of isolated fat cell preparations. With both, lipoprotein lipase activity per cell diminished significantly as the weight of fat tissue increased, i.e., larger fat cells contained less enzyme per cell than smaller cells. The uptake of triglyceride fatty acid radioactivity was measured after incubation of fat pads with radiolabeled rat lymph chylomicrons in flasks containing either buffer alone or with added glucose or glucose plus insulin. The addition of glucose and insulin led to a mean increase of 70% in the uptake of radioactivity, but larger adipocytes were stimulated less than smaller cells. This resulted in a significant negative correlation between the weights of fat pads and the uptake of radioactivity. Enlargement of fat cells also led to a diminution in their capacity to esterify fatty acids.

Clearing-factor lipase in adipose tissue. Distinction of different states of the enzyme and the possible role of the fat cell in the maintenance of tissue activity.

1. Incubation of intact epididymal adipose tissue from fed rats at 37 degrees in an albumin solution at pH7.4 in vitro results in rapid loss of clearing-factor lipase activity until a low activity, stable to prolonged incubation, is attained. The clearing-factor lipase activity of intact tissue from starved rats, which is initially much less than that of tissue from fed rats, is mainly stable to incubation at 37 degrees . 2. Much of the clearing-factor lipase activity of intact epididymal adipose tissue from fed rats is inactivated by collagenase. The enzyme activity of intact tissue from starved rats is not inactivated by collagenase. 3. The clearing-factor lipase activity of fat cells isolated from the epididymal adipose tissue of fed rats is stable to prolonged incubation at 37 degrees . It represents only a small proportion of the total activity of the intact tissue. In starved rats, the isolated fat cells contain a much higher proportion of the activity of the intact tissue. Their activity is also stable at 37 degrees . 4. Incubation of isolated fat cells in a serum-based medium leads to a progressive rise in clearing-factor lipase activity. Actinomycin increases the extent of this rise in activity. No rise in clearing-factor lipase activity occurs when stromal-vascular cells isolated from epididymal adipose tissue are incubated in the medium. 5. The findings indicate that less than 20% of the activity of intact adipose tissue from fed rats is retained when fat cells are isolated from the tissue by collagenase treatment. The activity that is lost could be that which normally functions in the uptake of triglyceride fatty acids by the tissue.

The significance of changes in tissue clearing-factor lipase activity in relation to the lipaemia of pregnancy.

1. The concentration of triglyceride fatty acid in the plasma of the pregnant rat rises to a maximum 2-4 days before parturition. Thereafter there is a rapid decline in the concentration to near normal values at parturition. 2. A similar increase occurs in animals fed on a diet low in fat. There is no increase in food consumption at the time when the triglyceride fatty acid concentration in the plasma is at its peak. 3. Rates of entry of triglyceride fatty acid into the blood during pregnancy have been estimated from the rate of accumulation of triglyceride in the plasma of animals injected with a non-ionic detergent, Triton. A progressive increase occurs in the entry rate as the body weight increases throughout pregnancy. Expressed per constant body weight, the entry rate does not change significantly. 4. Adipose-tissue clearing-factor lipase activity is low at the time when the plasma triglyceride fatty acid concentration is raised. Activity of the enzyme in heart, lung and diaphragm is unchanged. 5. It is suggested that the ;lipaemia of pregnancy' may be due to diminished uptake of triglyceride fatty acids by adipose tissue, and, further, that the disappearance of the lipaemia may be due to increased uptake of triglyceride fatty acids by the mammary gland.

The effect of ethyl chlorophenoxyisobutyrate (CPIB) on the uptake of triglyceride fatty acids, activity of lipoprotein lipase and lipogenesis from glucose in fat tissue of rats

Summary Ethyl chlorophenoxyisobutyrate, fed to rats in a dose which lowered the plasma triglyceride concentration in vivo enhanced the in vitro uptake of labelled triglyceride fatty acids by adipose tissue. This was found not to be due to increased lipoprotein lipase activity but was probably related to the augmented esterifying capacity of the tissue. Lipogenesis from [U- 14 C]glucose was not significantly disturbed by CPIB, but a higher proportion of the newly synthesized fatty acids was found to be esterified in the CPIB-treated rats.

Metabolism of lipoprotein lipid in the isolated perfused rat heart

1. 1. The disappearance from the perfusate, localization within heart lipids, and oxidation of 14C-labeled lipid from three ultracentrifugally separated lipoprotein fractions were studied in the isolated perfused rat heart. 2. 2. With d < 1.006 lipoprotein there was a net disappearance of triglyceride fatty acid from the perfusate. Heart lipids, increased free fatty acids and CO 2 accounted for all triglyceride fatty acid uptake. CO 2 formation and restoration of heart lipids in the perfused tissue accounted for 90% of the expected respiration. A net increase of free fatty acids in the perfusate suggested lipoprotein lipase activity either at or near the myocardial cell membrane, or lipase release into the perfusate. 3. 3. With d 1.006−1.070 lipoprotein, 14CO 2 and 14C-label in the heart lipids accounted for all of the triglyceride fatty acid uptake. The final concentration of triglycerides in the perfusate was very low and no net increase in free fatty acid in the buffer was observed. The amount of triglyceride fatty acid recovered in CO 2 was less than, and that in heart lipids equal to, that observed with d < 1.006 lipoprotein. A larger fraction of heart lipid was recovered as phospholipid. 4. 4. With d 1.070−1.210 lipoprotein, the lack of change in concentration or specific activity of phospholipid with perfusion suggested that phospholipids were not extracted, or metabolized by the perfused heart. The 14C-labeled lipid extracted was primarily free fatty acid; the major non-oxidative fate of this free fatty acid was incorporation into tissue phospholipids.