Nonesterified Fatty Acid Uptake Research Articles

Hepatocellular uptake of oleate is energy dependent, sodium linked, and inhibited by an antibody to a hepatocyte plasma membrane fatty acid binding protein.

Several studies suggest that a portion of hepatocellular nonesterified fatty acid uptake may be carrier mediated. To further investigate this process, initial rates (Vo) of [14C]oleate uptake into rat hepatocytes, isolated by collagenase perfusion and incubated at 37 degrees C with oleate in the presence of bovine serum albumin, were studied as a function of the concentration of unbound [14C]oleate in the medium. Vo was saturable with increasing unbound oleate concentration (Km = 8.3 X 10(-8) M; Vmax = 197 pmol per min per 5 X 10(4) hepatocytes) and was not inhibited by up to 40 microM sulfobromophthalein, taurocholate, or cholic acid. Oleate uptake was sodium dependent. Vo was significantly diminished when Li+, K+, choline, or sucrose were substituted for Na+ in the incubation medium and was reduced 46% by 1 mM ouabain. Uptake was also markedly reduced after exposure of cells to metabolic inhibitors (e.g., 2,4-dinitrophenol, carbonyl cyanide m-chlorophenylhydrazone, antimycin, KCN). To evaluate the physiologic significance of the previously isolated rat liver plasma membrane fatty acid-binding protein, the effect of an antibody directed against this protein on hepatocellular [14C]oleate uptake was examined. Preincubation of hepatocytes with the IgG fraction of this antiserum inhibited Vo of [14C]oleate by up to 65% in dose-related fashion, without altering Vo for [35S]sulfobromophthalein, [14C]taurocholate, or [3H]cholate. These data indicate that at least a portion of hepatocellular oleate uptake is energy dependent, sodium linked, and mediated by a specific liver plasma membrane-fatty acid-binding protein.

Inhibitory effects of the D(−) isomer of 3-hydroxybutyrate on cardiac non-esterified fatty acid uptake and oxygen demand induced by norepinephrine in the intact dog

The effects of ketosis on the norepinephrine-induced high rates of cardiac uptake of non-esterified fatty acids (NEFA = free fatty acids = FFA) and oxygen consumption were studied in anesthetized intact dogs. After a control infusion of norepinephrine (500 ng/kg.min into the left ventricle), the D(-) isomer or natural form of 3-hydroxybutyrate was infused intravenously as the arginine salt at rates of 20 mumol/kg.min in group A (10 dogs) and 80 mumol/kg.min in group B (10 dogs) and a second norepinephrine infusion was superimposed on the ketone treatment. At the time the effects of the second catecholamine infusion were measured, the arterial 3-hydroxybutyrate concentration averaged 1.2 +/- 0.1 mM in group A and 8.3 +/- 0.4 mM in group B, and the cardiac uptake of the ketone amounted to 17.4 +/- 0.6 and 35.8 +/- 5.3 mumol/min.100 g, respectively. Relative to the control norepinephrine infusion, the arterial NEFA concentration was reduced to 88 +/- 4% in group A and to 62 +/- 8% in group B, but the cardiac uptake of NEFA was significantly more depressed, to 65 +/- 7% in group A and to 35 +/- 8% in group B. These changes were not observed in ten non-ketotic animals under repeated norepinephrine infusion. Thus, ketosis inhibited the norepinephrine-stimulated uptake of NEFA, presumably through (1) a lowered availability of NEFA from arterial blood, attributable to a reduction of extracardiac lipolysis, and (2) competition of 3-hydroxybutyrate with NEFA for metabolism by the myocardium in the face of still high arterial NEFA concentrations, 1.7 +/- 0.1 mM in group A and 1.1 +/- 0.2 mM in group B. In both groups, the lowering of the contribution of NEFA to cardiac metabolism was associated with a reduction of the estimated oxygen demand per beat (ratio of cardiac oxygen consumption/min to the pressure-rate product), while the pressure response to norepinephrine was not modified. There was no evidence for abnormal cardiac function.

Kinetic analysis of myocardial fatty acid oxidation suggesting an albumin receptor mediated uptake process

The relationship between extracellular albumin and non-esterified fatty acid (NEFA) concentrations and the rate of fatty acid oxidation was studied. The data were obtained from tests performed on a working rat heart. When NEFA concentration was increased the rate of fatty acid oxidation showed a saturation curve at a constant NEFA/albumin ratio. Keeping constant the albumin concentration, a rise in NEFA concentration resulted in a linear increase of fatty acid oxidation. No correlation, however, was found between fatty acid oxidation and the unbound fraction of fatty acids. These results suggest an albumin receptor mediated NEFA uptake. With this assumption the following rate law of the NEFA uptake was derived: UPT = UPT0 X [FA]/(Km + [ALB] ) where [FA] and [ALB] are the total NEFA- and albumin concentrations, UPT0 and Km are constants. The rates of oxidation computed with this equation show a very good congruence to the values obtained experimentally. The validity of the rate law is confirmed by the fact that it is shown to be in agreement to the results of other investigators.

The 75-g oral glucose tolerance test: effect on splanchnic metabolism of substrates and pancreatic hormone release in healthy man.

To determine the effect of the 75 g oral glucose tolerance test on carbohydrate and lipid metabolism, the splanchnic exchange of glucose, lactate, pyruvate, non-esterified fatty acids, beta-hydroxybutyrate and acetoacetate as well as the release of insulin, C-peptide, glucagon and pancreatic polypeptide were evaluated in eight healthy male volunteers in the basal state and for 150 min following glucose ingestion. Oral glucose loading was followed by a rapid rise in splanchnic output of glucose (mean +/- SEM; 154 +/- 12 mmol/150 min), pyruvate (1.2 +/- 1.2 mmol/150 min) and lactate (8.6 +/- 2.0 mmol/150 min), whereas there were reductions in the splanchnic uptake of non-esterified fatty acids (-10.7 +/- 4.4 mmol/150 min) and the splanchnic output of beta-hydroxybutyrate (-4.8 +/- 3.3 mmol/150 min) and acetoacetate (-3.0 +/- 1.2 mmol/150 min). In parallel, splanchnic output of insulin (12.3 +/- 2.7 nmol/150 min), C-peptide (36.1 +/- 5.0 nmol/150 min) and transiently of pancreatic polypeptide rose, whereas that of glucagon fell (-0.58 +/- 0.21 nmol/150 min). Even at 150 min after glucose ingestion, splanchnic output and arterial concentrations of glucose, lactate, insulin and C-peptide were still above their respective basal values while those of non-esterified fatty acids and glucagon were reduced. Taking into account the partial suppression of endogenous glucose production by ingested glucose it is concluded that, in normal postabsortive man, only 49-63% of a 75 g oral glucose load is retained by the splanchnic bed during the first 150 min, the rest being available for non-hepatic tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of 3-hydroxybutyrate formation and secretion of very-low-density-lipoprotein triacylglycerol by perfused livers from fed and starved rats.

Acetoacetate was the sole ketone body formed when livers from starved rats were perfused with minimal concentrations of non-esterified fatty acid. Absence of 3-hydroxybutyrate was related to a low substrate potential, which caused a more oxidized redox state and a decreased [ATP]/[ADP] ratio. Only under conditions of comparable non-esterified fatty acid uptake was lipoprotein triacylglycerol production inversely related to ketogenesis.

Uptake and tissue content of fatty acids in dog myocardium under normoxic and ischemic conditions.

The effect of ischemia on the myocardial content of nonesterified fatty acids (NEFA), triacylglycerol, cholesteryl esters, and phospholipids assayed with gas-liquid chromatography was studied in an open-chest dog preparation. Ischemia was induced by partial occlusion of the left interventricular coronary artery during 120 minutes (n = 20). Tissue content of the lipid classes was assessed in biopsies taken from ischemic and normoxic areas of the left ventricular free wall. Local venous blood from the concomitant vein of the left interventricular coronary artery was collected to determine myocardial extraction of lipids. In eight other dogs, no ischemia was induced (control group). Under normoxic conditions, NEFA appeared to be present in trace amounts: about 25 nmol/g wet weight of tissue, representing less than 0.1% of total myocardial fatty acids. During ischemia, NEFA increased in the affected area. This accumulation was most pronounced in the least perfused layer: the subendocardium (up to 172 nmol/g). Blood flow, estimated with radioactively labeled microspheres fell from 0.55 to 0.06 ml/min per g in this particular layer. The uptake of NEFA by the ischemic myocardium was decreased, indicating that enhanced lipolysis of endogenous lipids or reduced combustion may be held responsible for the accumulation of NEFA in ischemic tissue. Since arachidonic and linoleic acids showed the highest relative increase, lipolysis of endogenous phospholipids, rich in these fatty acids, seems to be reasonable. Ischemia had no significant effect on the content of triacylglycerol and cholesteryl esters. Phospholipids tended to decrease in the affected subendocardial layers.

Regulation of Gluconeogenesis and Ketogenesis during Rest and Exercise in Diabetic Subjects and Normal Men

The splanchnic-hepatic metabolism of glucose, lactate, pyruvate, alanine, glycerol, non-esterified fatty acids (NEFA), ketone bodies and oxygen were investigated in five normal men and six juvenile diabetic subjects at rest and during exercise after an overnight fast. A linear relationship was found between load (arterial concentration multiplied by hepatic blood flow) and splanchnic-hepatic uptake of lactate, pyruvate, glycerol and NEFA. The uptake of alanine was highly sensitive to load, but was also regulated by the concentration of hepatic venous glucagon. The uptake of pyruvate was high in exercising diabetic subjects, who had a high lactate/pyruvate concentration ratio in hepatic venous blood. The rate of uptake of the total measured gluconeogenic precursors was significantly higher in the diabetic group at a given load. The rate of ketogenesis was linearly related to the NEFA load in both groups; however, the rate of ketogenesis was twofold at a given load in the diabetic group. The highest rates of ketogenesis were found coincident with the highest concentrations of glucagon in hepatic venous blood. The observed antiketogenic effect of exercise was due to a decreased load of NEFA, mainly caused by a decrease in the hepatic blood flow.

Mechanical and metabolic effects of insulin on newborn lamb myocardium

The effects of insulin on myocardial contractility (MC) and metabolism were studied in 18 newborn lambs. Cardiac work and rate were kept constant. Following insulin (80 units, intravenously), contractility increased and remained elevated for 1 hour. This was not prevented by beta blockade or glucose infusion. Myocardial extraction and uptake of glucose and nonesterified fatty acid (NEFA) increased, the arterial concentration of both decreased. But after glucose fell to less than 20 per cent of control, uptake of both glucose and NEFA declined as did MC. It is concluded that in the neonate insulin increases MC as well as substrate uptake.

Relationship of epicardial ST segment elevation to the plasma free fatty acid/albumin ratio during coronary occlusion in dogs.

1. Intravenous infusions of lipid-free albumin were used to lower the arterial non-esterified fatty acids (NEFA)/albumin ratio during coronary occlusion in dogs. 2. Reduction of the NEFA/albumin ratio was accompanied by proportionate reductions in myocardical uptake of NEFA and the degree of ST segment elevation in epicardial electrocardiographic recordings from the ischaemic zone. Aortic pressure and heart rate were unchanged. 3. Infusions of control albumin preparations had no effect on the NEFA/albumin ratio or ST segment elevation. 4. These observations support the proposition that the disturbance of cellular function during myocardial ischaemia is influenced by the degree of saturation of albumin-binding sites with NEFA and by their availability.

Demonstration of two pools of albumin-bound fatty acids

The uptakes of albumin-bound nonesterified fatty acids and of [1-14C]palmitic acid complexed to albumin by the isolated perfused rat liver were compared. During perfusion, the rate of uptake of nonesterified fatty acids decreased and became zero when the fatty acid:albumin molar ratio reached 0.3, but the rate of uptake of radioactive palmitic acid remained constant. This finding suggests the existence of two pools of fatty acids bound to albumin with different fractional turnover rates. This view was supported by the fact that when delipidated albumin complexed in vitro to radioactive and nonradioactive fatty acids was used no difference was observed between the uptakes of nonesterified fatty acids and radioactive fatty acids by perfused liver. Similar results were found with albumin-bound radioactive fatty acid in vivo (obtained from rats fed radioactive palmitic acid), showing a homogeneous distribution of the label in both pools. The existence of two nonesterified fatty acid pools in plasma would arise from the differences in the nature of bonds between fatty acid and albumin molecules, which could determine the rate of exchange of fatty acids between the albumin-bound and soluble forms preceding their uptake by the cells.

Nicotinic Acid Treatment of Bovine Ketosis I. Effects on Circulatory Metabolites and Interrelationships

Blood metabolite changes were measured in six subclinically and seven clinically ketotic cows following treatment with four 40-g doses of nicotinic acid given orally at 2-hr intervals. Subclinical ketosis was characterized by hyperketonemia, elevated nonesterified fatty acid (NEFA) and acetate, and depressed triglycerides, cholesterols, and phospholipids. Clinically ketotic cows displayed hypolactia, hypophagia, hypoglycemia, hyperketonemia, elevated NEFA and acetate, and depression of other lipids. Glucose and triglyceride utilization by the mammary gland was not apparently impaired during ketosis, although marked NEFA uptake may have had a sparing action on triglyceride fatty acids. Appetite returned within 18 hr after treatment. At 48 hr after treatment, NEFA and ketone bodies were further elevated and appetite was again depressed. Blood metabolites and appetite began to return to normal immediately after the rebound phase. Glucose had returned to normal by Day 7, while ketone body concentrations were normal by Day 14. By Day 21, all blood metabolites were within accepted ranges.

MYOCARDIAL METABOLISM AND DYNAMICS AFTER PRACTOLOL DURING LIGHT HALOTHANE ANAESTHESIA

SUMMARY In intact, steady-state, closed chest dogs, the effect of 0.625 and 1.25 mg/kg of the selective cardiac beta-adrenergic blocking drug, practolol, was tested during 1.2 m.a.c. halothane anaesthesia. Increases in the rate of rise of left ventricular pressure (dp/dt), left ventricular stroke work, mean aortic pressure, heart rate, and myocardial blood flow were observed. Myocardial oxygen, lactate and non-esterified fatty acid uptake increased also. In contrast to the effect of propranolol 0.25 mg/kg in a similar study, no evidence of cardiac depression was seen with practolol. It would appear that practolol is a more suitable beta-adrenergic blocking drug for use during halothane anaesthesia.

Blood Metabolite Interrelationships and Changes in Mammary Gland Metabolism During Subclinical Ketosis

Comparisons were from tail and mammary-vein blood samples from 20 cows, both when the milk acetone test was positive and after the test had become negative. The transition from subclinical ketosis to normal was marked by increasing glucose and triglycerides and decreasing acetate, ketone bodies, and nonesterified fatty acids. Also noted were increasing arteriovenous differences in glucose and triglycerides and a decreasing arteriovenous difference in nonesterified fatty acids. Negative arteriovenous differences (–.7 mg/100ml)in acetoacetate plus acetone were consistently noted during subclinical ketosis, thus suggesting mammary ketogenesis. Within cow correlations between arteriovenous acetoacetate plus acetone and arteriovenous nonesterified fatty acids (–.69**) indicated that conditions favoring increased uptake of nonesterified fatty acid's also favored increased mammary ketogenesis. A similar type of correlation between arteriovenous nonesterified fatty acids and arteriovenous triglycerides (–.58**) indicated a possible substitution of nonesterified for triglycerides-fatty acids for milk fat synthesis. Within cow correlations between arterial levels and arteriovenous differences were .77**, .82**, and .83** for glucose, nonesterified fatty acids, and triglycerides.

Quantitative evaluation of plasma free fatty acid uptake by the isolated perfused rat liver influence of hypoxia

1. 1. The uptake of non-esterified fatty acids by the liver was quantitatively evaluated using the isolated rat liver perfused with diluted blood containing a radioactive albumin-complexed fatty acid. The influence of the pO 2 in the perfusate on fatty acid uptake and oxygen consumption by the liver has been studied. 2. 2. Fatty acid uptake progressively decreased during the perfusion depending on the fatty acid concentration and the fatty acid/albumin molar ratio in the perfusate. 3. 3. Uptake values obtained by arteriovenous radioactivity difference are significantly higher than those obtained simultaneously by arteriovenous mass difference. Our experiments suggest that in vitro complexed fatty acids follow a different behaviour than the pre-existing fatty acids bound to the albumin in vivo. 4. 4. Hypoxia did not modify the fatty acids uptake by the liver. 5. 5. Oxygen consumption by the liver closely depends on the partial pressure of O 2 in the perfusate and is not affected by the amount of non-esterified fatty acids taken up by the liver.

Renal uptake of [formula omitted] acid in vitro effects of palmitate and l-carnitine

1. 1. The uptake of p- aminohippuric acid by rat renal cortical slices and its relationship to the renal uptake of non-esterified fatty acids was studied. 2. 2. 1 mM palmitate competitively inhibits renal p- aminohippuric acid uptake. 3. 3. 1 mM carnitine stimulates renal p- aminohippuric acid uptake at low palmitate concentration but has no effect when 1 mM palmitate is present in the incubation media. 4. 4. It is suggested that the renal organic acid transport system participates in the uptake of palmitate by renal cells. Furthermore, palmitate and p- aminohippuric acid may share common intracellular binding sites in renal cortical cells. 5. 5. Factors affecting the affinity of intracellular binding sites, may regulate uptake of p- aminohippuric acid and uptake and metabolism of non-esterified fatty acids in renal cortical cells.

Nonesterified fatty acid uptake by dog kidney: effects of probenecid and chlorothiazide.

Nonesterified fatty acid uptake by dog kidney: effects of probenecid and chlorothiazide.

Hepatic lipid metabolism in experimental diabetes: I. release and uptake of triglycerides by perfused livers from normal and alloxan-diabetic rats

The uptake of nonesterified fatty acids was accelerated and the net release of triglyceride by the isolated perfused rat liver was depressed in alloxan diabetes. Triglyceride release by livers from either normal or diabetic rats was proportional to the palmitate presented to the liver; triglyceride release, however, was depressed in livers from diabetic rats at all concentrations of perfusate fatty acid. Uptake of triglyceride from chylomicra was more rapid by livers from diabetic animals than by livers from normal fed rats. Ketone-body formation and urea production were both accelerated by diabetes and restored to normal levels by treatment with insulin of the animal from which the liver was obtained. Ketone-body output remained constant regardless of the quantity of palmitate added to the perfusion medium. Since the uptake by liver of triglycerides from chylomicra, or from a neutral fat emulsion as reported previously, was accelerated in alloxan diabetes, it was of interest to compare the rates of disappearance of a neutral fat emulsion from the blood stream of normal or diabetic rats. It was observed that the disappearance of neutral fat from the plasma of diabetic rats was delayed considerably in comparison to the normal. Insulin therapy of the animals, moreover, increased the rate of disappearance of esterified fatty acid from the blood. The uptake and release of triglyceride by the isolated perfused rat liver were discussed with reference to a mechanism for the occurrence of fatty liver and hyperlipemia in experimental diabetes.

METABOLISM OF ISOLATED RAT RETINA. THE ROLE OF NON-ESTERIFIED FATTY ACID

1. Retina in vitro showed progressive uptake of non-esterified fatty acid, given in the form of complexes with bovine serum albumin. The rate of influx was related linearly to the concentration of non-esterified fatty acid in the incubation medium and was enhanced by glucose. 2. There was some exchange between medium and tissue non-esterified fatty acid, particularly in the early stages of incubation, and this probably corresponded to the rapid labelling of one component of the tissue non-esterified fatty acid pool. A much slower exchange with tissue non-esterified fatty acid was also evident, not reaching equilibrium even after 7(1/2) hr. incubation. Within the tissue, non-esterified fatty acid also found its way into the fat esters, and about 10% of the uptake was oxidized to carbon dioxide. 3. At high concentrations of non-esterified fatty acid in the medium, disproportionately more of the ingoing non-esterified fatty acid was found in the fat esters of the tissue, whereas the proportion in the tissue non-esterified fatty acid pool or oxidized to carbon dioxide did not change. 4. The role of non-esterified fatty acid as an energy-producing oxidizable substrate is discussed and the regulating influence of glucose on the metabolism of non-esterified fatty acid considered.

Effect of fasting, epinephrine and glucose and insulin on hepatic uptake of nonesterified fatty acids.

Catheters placed in the portal and hepatic veins of dogs were maintained in position for 2–4 weeks, and experiments were performed in the unanesthetized state no less than 3 days after the operative procedure. Hepatic uptake of nonesterified fatty acids (NEFA) was determined from the portal-hepatic NEFA difference and the hepatic blood flow. Hepatic NEFA uptake was found to increase with fasting and after administration of epinephrine. It was found to decrease after the administration of glucose and insulin. It was concluded that these factors did not directly influence the liver to alter its NEFA uptake but that the liver responded primarily to the concentration of NEFA in the blood entering it.