scholarly journals Interrelationship and control of glucose metabolism and lipogenesis in isolated fat-cells. Control of pentose phosphate-cycle activity by cellular requirement for reduced nicotinamide adenine dinucleotide phosphate

1972 ◽  
Vol 128 (5) ◽  
pp. 1097-1102 ◽  
Author(s):  
H. Kather ◽  
M. Rivera ◽  
K. Brand
Keyword(s):  
Fatty Acid ◽  
Glucose Metabolism ◽  
Fatty Acid Synthesis ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Acid Synthesis ◽  
Pentose Phosphate ◽  
Fat Cells ◽  
Isolated Fat Cells ◽  
Pentose Phosphate Cycle ◽  
Phenazine Methosulphate

By using inhibitors and stimulators of different metabolic pathways the interdependence of the pentose phosphate cycle and lipogenesis in isolated fat-cells was studied. Rotenone, which is known to inhibit electron transport in the respiratory chain, blocked glucose breakdown at the site of pyruvate dehydrogenase. Consequently, because of the lack of acetyl-CoA, fatty acid synthesis was almost abolished. A concomitant decrease in pentose phosphate-cycle activity was observed. Phenazine methosulphate stimulated pentose phosphate-cycle activity about five- to ten-fold without a considerable effect on fatty acid synthesis. The influence of rotenone on both the pentose phosphate cycle and lipogenesis could be overcome by addition of phenazine methosulphate, indicating that rotenone has no direct effect on these pathways. The decreased rate of the pentose phosphate cycle in the presence of rotenone therefore has to be considered as a consequence of decreased fatty acid synthesis. The rate of glucose catabolism via the pentose phosphate cycle in adipocytes appears to be determined by the requirement of NADPH for lipogenesis. Treatment of cells with 6-aminonicotinamide caused an accumulation of 6-phosphogluconate, indicating an inhibition of 6-phosphogluconate dehydrogenase. The rate of glucose metabolism via the pentose phosphate cycle as well as the rate of fatty acid synthesis, however, was not affected by 6-aminonicotinamide treatment and could still be stimulated by addition of insulin. Since even in cells from starved animals, in which the pentose phosphate-cycle activity is extremely low, no accumulation of 6-phosphogluconate was observed, it is concluded that the control of this pathway is achieved by the rate of regeneration of NADP at the site of glucose 6-phosphate dehydrogenase.

scholarly journals Interrelationship and control of glucose metabolism and lipogenesis in isolated fat-cells. Effect of the amount of glucose uptake on the rates of the pentose phosphate cycle and of fatty acid synthesis

1972 ◽  
Vol 128 (5) ◽  
pp. 1089-1096 ◽  
Author(s):  
H. Kather ◽  
M. Rivera ◽  
K. Brand
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Glucose Metabolism ◽  
Glucose Uptake ◽  
Fatty Acid Synthesis ◽  
Acid Synthesis ◽  
Pentose Phosphate ◽  
Fat Cells ◽  
Pentose Phosphate Cycle ◽  
Wide Range

In order to study the quantitative relationship between fatty acid synthesis and pentose phosphate-cycle activity under different hormonal and dietary conditions affecting the extent of glucose uptake, cells isolated from rat epididymal adipose tissue were incubated in bicarbonate buffer containing [U-14C]-, [1-14C]- or [6-14C]-glucose. From the amount of glucose taken up, the production of lactate and pyruvate, and the incorporation of 14C from differently labelled [14C]glucose into CO2, fatty acids and glyceride glycerol, the rates of glucose metabolism via different pathways and the extent of lipogenesis under various experimental conditions were determined. The contribution of the pentose phosphate-cycle to glucose metabolism under normal conditions was calculated to be 8%. Starvation and re-feeding, and the presence of insulin, caused an enhancement of glucose uptake, pentose phosphate-cycle activity and fatty acid synthesis. Plots of both pentose phosphate-cycle activity and fatty acid synthesis versus glucose uptake revealed that the extent of glucose uptake, over a wide range, determines the rates of fatty acid synthesis and glucose metabolism via the pentose phosphate cycle. A balance of formation and production of nicotinamide nucleotides in the cytoplasm was established. The total amount of cytoplasmic NADH and NADPH formed was only in slight excess over the hydrogen equivalents required for the synthesis of fatty acids, glyceride glycerol and lactate. Except in cells from starved animals, the pentose phosphate cycle was found to provide only about 60% of the NADPH required for fatty acid synthesis. The results are discussed with respect to an overall control of the different metabolic and biosynthetic reactions in the fat-cells by the amount of glucose transported into the cell.

scholarly journals A modified perifused incubation system for isolated fat-cells. Investigation of intermediary metabolism by perifusion

1984 ◽  
Vol 224 (1) ◽  
pp. 235-239
Author(s):  
R D Harper
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Fatty Acid Synthesis ◽  
Acid Synthesis ◽  
Fat Cells ◽  
Isolated Fat Cells ◽  
Glycerol Synthesis ◽  
Perifusion System ◽  
Net Release

Perifused fat-cells showed similar values for acylglycerol glycerol synthesis from glucose with insulin and for the effects of added palmitate to those in normal incubations and those reported in the literature. Fatty acid synthesis was lower in perifused cells compared with normal incubations, and there was a net release of fatty acids only with the perifused fat-cells. Hence fluxes of metabolites were different in the two incubation systems, and the perifusion system enables the investigation of the flux of metabolites under conditions which may more closely resemble those in vivo.

Glucose metabolism in the female rat adipocyte: lipid synthesis from glucose during pregnancy and progesterone treatment

1983 ◽  
Vol 97 (2) ◽  
pp. 207-212 ◽  
Author(s):  
M.-Th Sutter-Dub ◽  
A. Sfaxi ◽  
P. Strozza
Keyword(s):  
Fatty Acid ◽  
Glucose Metabolism ◽  
Fatty Acid Synthesis ◽  
Pentose Phosphate Pathway ◽  
Lipid Synthesis ◽  
Acid Synthesis ◽  
Pentose Phosphate ◽  
Ovariectomized Rats ◽  
Female Rat ◽  
Progesterone Treatment

Pregnancy and progesterone treatment of ovariectomized rats decrease glucose metabolism through the pentose-phosphate pathway in isolated female rat adipocytes. As demonstrated in previous studies, progesterone directly decreases [1-14C]glucose oxidation through the pentose-phosphate pathway and lipogenesis from [6-14C]glucose; the present study therefore compared glucose-induced lipid synthesis during pregnancy (10, 16 and 20 days of pregnancy) with the effect of progesterone treatment (5 mg/rat per day for 14 days) to shed more light on the role of this steroid in glucose metabolism during pregnancy. The inhibition of [6-14C]glucose incorporation into triacylglycerols in the progesterone-treated rats was comparable to that which occurs during late (20 days) and mid-pregnancy (16 days) but not during early pregnancy (10 days). The inhibition of fatty acid synthesis was more important as pregnancy advanced and was different from the decrease in fatty acid synthesis induced by progesterone treatment. The sensitivity to insulin was comparable in virgin, ovariectomized and progesterone-treated ovariectomized rats but not in pregnant rats. This implies that progesterone and insulin affect glucose-induced lipid synthesis by distinct processes and that the impaired glucose metabolism is characterized by a reduction in basal glucose utilization rather than by an impaired insulin response.

scholarly journals The regulation of glyceride synthesis in isolated white-fat cells. The effects of palmitate and lipolytic agents

1972 ◽  
Vol 128 (5) ◽  
pp. 1057-1067 ◽  
Author(s):  
E. D Saggerson
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Free Fatty Acids ◽  
Fatty Acid Synthesis ◽  
Acid Synthesis ◽  
Fat Cells ◽  
Glyceride Synthesis ◽  
Glucose Incorporation ◽  
High Concentrations ◽  
Stimulation Of

1. 0.5mm-Palmitate stimulated incorporation of [U-14C]glucose into glyceride glycerol and fatty acids in normal fat cells in a manner dependent upon the glucose concentration. 2. In the presence of insulin the incorporation of 5mm-glucose into glyceride fatty acids was increased by concentrations of palmitate, adrenaline and 6-N-2′-O-dibutyryladenosine 3′:5′-cyclic monophosphate up to 0.5mm, 0.5μm and 0.5mm respectively. Higher concentrations of these agents produced progressive decreases in the rate of glucose incorporation into fatty acids. 3. The effects of palmitate and lipolytic agents upon the measured parameters of glucose utilization were similar, suggesting that the effects of lipolytic agents are mediated through increased concentrations of free fatty acids. 4. In fat cells from 24h-starved rats, maximal stimulation of glucose incorporation into fatty acids was achieved with 0.25mm-palmitate. Higher concentrations of palmitate were inhibitory. In fat cells from 72h-starved rats, palmitate only stimulated glucose incorporation into fatty acids at high concentrations of palmitate (1mm and above). 5. The ability of fat cells to incorporate glucose into glyceride glycerol in the presence of palmitate decreased with increasing periods of starvation. 6. It is suggested that low concentrations of free fatty acids stimulate fatty acid synthesis from glucose by increasing the utilization of ATP and cytoplasmic NADH for esterification of these free fatty acids. When esterification of free fatty acids does not keep pace with their provision, inhibition of fatty acid synthesis occurs. Provision of free fatty acids far in excess of the esterification capacity of the cells leads to uncoupling of oxidative phosphorylation and a secondary stimulation of fatty acid synthesis from glucose.

scholarly journals Studies on the role of insulin in the regulation of glyceride synthesis in rat epididymal adipose tissue

1975 ◽  
Vol 150 (3) ◽  
pp. 441-451 ◽  
Author(s):  
S R Sooranna ◽  
E D Saggerson
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Fatty Acid Synthesis ◽  
Acid Synthesis ◽  
Synthesis Process ◽  
Epididymal Adipose Tissue ◽  
Fat Cells ◽  
Fat Cell ◽  
Glyceride Synthesis

1. When rat isolated fat-cells were incubated with fructose and palmitate, insulin significantly stimulated glyceride synthesis as measured by either [14C]fructose incorporation into the glycerol moiety or of [3H]palmitate incorporation into the acyl moiety of tissue glycerides. Under certain conditions the effect of insulin on glyceride synthesis was greater than the effect of insulin on fructose uptake. 2. In the presence of palmitate, insulin slightly stimulated (a) [14C]pyruvate incorporation into glyceride glycerol of fat-cells and (b) 3H2O incorporation into glyceride glycerol of incubated fat-pads. 3. At low extracellular total concentrations of fatty acids (in the presence of albumin), insulin stimulated [14C]fructose, [14C]pyruvate and 3H2O incorporation into fat-cell fatty acids. Increasing the extracellular fatty acid concentration greatly inhibited fatty acid synthesis from these precursors and also greatly decreased the extent of apparent stimulation of fatty acid synthesis by insulin. 4. These results are discussed in relation to the suggestion [A.P. Halestrap & R.M Denton (1974) Biochem. J. 142, 365-377] that the tissue may contain a specific acyl-binding protein which is subject to regulation. It is suggested that an insulin-sensitive enzyme component of the glyceride-synthesis process may play such a role.

scholarly journals The regulation of glyceride synthesis in isolated white-fat cells. The effects of acetate, pyruvate, lactate, palmitate, electron-acceptors, uncoupling agents and oligomycin

1972 ◽  
Vol 128 (5) ◽  
pp. 1069-1078 ◽  
Author(s):  
E. D Saggerson
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Fatty Acid Synthesis ◽  
Acid Synthesis ◽  
Fat Cells ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Normal Cells ◽  
Glyceride Synthesis ◽  
Glucose Incorporation

1. The incorporation of 5mm-[U-14C]glucose into glyceride fatty acids by fat cells from normal rats incubated in the presence of 20munits of insulin/ml was increased by acetate, pyruvate, palmitate, NNN′N′-tetramethyl-p-phenylenediamine, phenazine methosulphate, dinitrophenol, tetrachlorotrifluoromethyl benzimidazole and oligomycin. Lactate did not stimulate glucose incorporation into fatty acids. The effects of these agents were concentration-dependent. 2. In the presence of 5mm-glucose+insulin, [U-14C]acetate, [U-14C]pyruvate and [U-14C]lactate were incorporated into fatty acids in a concentration-dependent manner, thereby further increasing the total rate of fatty acid synthesis. 3. NNN′N′-tetramethyl-p-phenylenediamine decreased the incorporation of [U-14C]pyruvate into fatty acids in normal cells and increased the incorporation of [U-14C]lactate into fatty acids. 4. In fact cells from 72h-starved rats the stimulatory effects of NNN′N′-tetramethyl-p-phenylenediamine upon glucose and lactate incorporation into fatty acids were totally and partially abolished respectively whereas the stimulatory effects of acetate upon glucose incorporation were retained. 5. Combinations of the optimum concentrations of the substances that stimulate glucose incorporation into fatty acids were tested and compared. The effects of acetate+NNN′N′-tetramethyl-p-phenylenediamine and acetate+palmitate upon normal cells were additive. The effects of NNN′N′-tetramethyl-p-phenylenediamine+palmitate were not additive. It was found that total fatty acid synthesis in the presence of glucose was most effectively increased by raising the concentration of pyruvate in the incubation system. 6. The significance of these results in supporting the proposal that fatty acid synthesis from glucose in adipose tissue is a ‘self-limiting process’ is discussed.

scholarly journals Alternative substrates for triacylglycerol synthesis in isolated adipocytes of different size from the rat

1981 ◽  
Vol 194 (2) ◽  
pp. 377-384 ◽  
Author(s):  
A A Francendese ◽  
M Digirolamo
Keyword(s):  
Fatty Acid ◽  
Fatty Acid Synthesis ◽  
Glucose Utilization ◽  
De Novo ◽  
Acid Synthesis ◽  
The Other ◽  
Fat Cells ◽  
Triacylglycerol Synthesis ◽  
Isolated Adipocytes ◽  
Metabolic Deficiency

The metabolic utilization of 14C-labelled acetate, pyruvate, lactate and glucose by isolated epididymal fat-cells was compared in two groups of rats fed ad libitum, one group young and lean (150-200 g body wt.), the other older and spontaneously obese (500-650 g body wt.). The influence of unlabelled glucose (6 mM) and insulin on substrate utilization by adipocytes was also studied. (1) Pyruvate and lactate were found to be good precursors for fatty-acid synthesis in small fat-cells, but not in larger fat-cells. On the other hand, lactate conversion into CO2 and the glycerol moiety of acylglycerols proceeded activity in both types of cells, and in some cases, it even exceeded the rates of glucose utilization. (2) The addition of glucose or glucose plus insulin, but not insulin alone, enhanced the metabolism of acetate, pyruvate and lactate in both types of fat-cells. (3) Fatty-acid synthesis de novo in large fat-cells was markedly decreased regardless of the substrate utilized. These findings point to lactate as a significant precursor for triacylglycerol synthesis in adipocytes. Furthermore, decreased fatty-acid synthesis de novo appears to be an acquired metabolic deficiency of enlarging adipocytes, independent of precursor substrate availability.

The role of phosphorylation in the regulation of fatty acid synthesis by insulin and other hormones

1983 ◽  
Vol 302 (1108) ◽  
pp. 33-45 ◽  
Keyword(s):  
Fatty Acid ◽  
Fatty Acid Synthesis ◽  
Pyruvate Dehydrogenase ◽  
Kinase Activity ◽  
Acid Synthesis ◽  
Fat Cells ◽  
Acetyl Coa Carboxylase ◽  
Atp Citrate Lyase ◽  
Acetyl Coa ◽  
Citrate Lyase

Insulin stimulates fatty acid synthesis in white and brown fat cells as well as in liver and mammary tissue. Hormones that increase cellular cyclic AMP concentrations inhibit fatty acid synthesis, at least in white adipose tissue and liver. These changes in fatty acid synthesis occur within minutes. In white fat cells, they are brought about not only by changes in glucose transport but also changes in the activities of pyruvate kinase, pyruvate dehydrogenase and acetyl-CoA carboxylase. The basis of the alterations in pyruvate kinase activity in fat cells is not understood. Unlike the liver isoenzyme, the isoenzyme present in fat cells does not appear to be phosphorylated either in the absence or presence of hormones. The changes in pyruvate dehydrogenase activity in fat cells are undoubtedly due to changes in phosphorylation of the α subunits. Insulin appears to act by causing the parallel dephosphorylation of all three sites. The persistence of the effect of insulin during the preparation and subsequent incubation of mitochondria has allowed the demonstration that insulin acts mainly by stimulating pyruvate dehydrogenase phosphatase rather than inhibiting the kinase. Acetyl-CoA carboxylase within fat cells is phosphorylated on a number of different sites. The exposure of cells to insulin leads to activation of the enzyme and this is associated with increased phosphorylation of a specific site on the enzyme. Exposure to adrenalin, which results in a marked diminution in activity, also causes a small increase in the overall level of phosphorylation, but this increase is due to an enhanced phosphorylation of different sites; probably those phosphorylated by cyclic-AMP-dependent protein kinase. Acetyl-CoA carboxylase is one of a number of proteins in fat cells that exhibit increased phosphorylation with insulin. Others include ATP-citrate lyase, the ribosomal protein S 6 , the β subunit of the insulin receptor and a heat and acid stable protein of M r 22 000. Changes in phosphorylation of ATP-citrate lyase do not appear to result in any appreciable changes in catalytic activity. A central aspect of insulin action may be the activation and perhaps release of a membrane-associated protein kinase. Plasma membranes from fat cells have been shown to contain a cyclicnucleotide-independent kinase able to phosphorylate and activate acetyl-CoA carboxylase. Furthermore, high-speed supernatant fractions from cells previously exposed to insulin contain elevated levels of the same or similar kinase activity capable of phosphorylating both ATP-citrate lyase and acetyl-CoA carboxylase.

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