scholarly journals Very-low-density-lipoprotein secretion by isolated hepatocytes of fat-fed rats

1981 ◽  
Vol 198 (2) ◽  
pp. 373-377 ◽  
Author(s):  
A D Kalopissis ◽  
S Griglio ◽  
M I Malewiak ◽  
R Rozen ◽  
X L Liepvre
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Isolated Hepatocytes ◽  
Low Density Lipoproteins ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Lipoprotein Secretion ◽  
Fat Feeding

The very-low-density-lipoprotein secretion rate of isolated hepatocytes obtained from rats fed a high-fat diet was half that of cells from control animals. In fat-fed rats, the initial cellular uptake of [l-14C]oleate in vitro was decreased by 25%, its esterification to triacylglycerols and phospholipids by 50% and its incorporation into very-low-density-lipoprotein triacylglycerols by 70%. Exogenous oleate was not the main precursor of very-low-density lipoproteins in these animals. Lipogenesis, a minor source of very-low-density lipoproteins with the control diet in our experimental conditions, was inhibited by 84% after fat-feeding. A short-term inhibition of lipogenesis in vitro did not result in a decrease in very-low-density-lipoprotein secretion rate. The results suggest that fat-feeding decreased availability of exogenous as well as endogenous fatty acids for synthesis of very-low-density lipoproteins.

scholarly journals Stimulation of triacylglycerol synthesis in rat adipocytes by plasma very-low-density lipoproteins

1978 ◽  
Vol 176 (1) ◽  
pp. 169-174 ◽  
Author(s):  
P Thomopoulos ◽  
M Berthelier ◽  
D Lagrange ◽  
M J Chapman ◽  
M H Laudat
Keyword(s):  
Fatty Acids ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Low Density Lipoproteins ◽  
High Density Lipoproteins ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Rat Adipocytes ◽  
Triacylglycerol Synthesis

The effect of human plasma lipoproteins on lipogenesis from glucose has been studied in isolated rat adipocytes. The very-low-density lipoproteins increased lipogenesis specifically, whereas low-density lipoproteins and high-density lipoproteins were without effect. Such stimulation could be reproduced with partially delipidated very-low-density lipoproteins. Nod-esterified fatty acids and glycerol were also without effect. Pretreatment of the adipocytes with trypsin did not alter the effect of very-low-density lipoprotein. The presence of Ca2+ was required for the full activation of lipogenesis. The synthesis of acylglycerol fatty acids and of acylglycerol glycerol were equally increased. The effect of very-low-density lipoprotein was not additive to that of insulin. It is suggested that very-low-density lipoprotein may directly stimulate lipogenesis in fat-cells, particularly in states when the lipoproteins are present at high concentration in the circulation.

scholarly journals The effects of monensin on secretion of very-low-density lipoprotein and metabolism of asialofetuin by cultured rat hepatocytes

1985 ◽  
Vol 227 (2) ◽  
pp. 529-536 ◽  
Author(s):  
A C Rustan ◽  
J ∅ Nossen ◽  
T Berg ◽  
C A Drevon
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Rat Hepatocytes ◽  
Low Density Lipoproteins ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Dependent Manner ◽  
Very Low Density Lipoproteins ◽  
Low Concentrations ◽  
Maximum Inhibition

Primary cultures of rat hepatocytes were used to study secretion of very-low-density lipoproteins and metabolism of asialofetuin. The ionophore monensin inhibited both secretion of very-low-density lipoproteins and binding and degradation of asialofetuin in a concentration-dependent manner. Secretion as well as receptor binding were markedly decreased after 15 min treatment with monensin. The inhibitory effect of the ionophore was fully reversible, and no effect on protein synthesis was observed at concentrations up to 50 microM. The secretion of apoproteins (B-small, B-large and E) and that of albumin were inhibited to the same extent as was triacylglycerol secretion. Secretion of very-low-density lipoproteins was more sensitive to low concentrations of monensin than was the metabolism of asialofetuin. Maximum inhibition of very-low-density-lipoprotein secretion was obtained at 5-10 microM-monensin, whereas 25 microM was required to obtain maximum inhibition of binding and degradation of asialofetuin. The number of surface receptors for asialofetuin decreased to about half when the cells were exposed to 25 microM-monensin. It is possible that monensin inhibits endo- and exo-cytosis via a similar mechanism, e.g. by disturbing proton gradients. Since secretion of very-low-density lipoproteins was more sensitive to low concentrations of monensin, it is likely that monensin independently inhibits endocytic and secretory functions in cultured hepatocytes.

Composition and metabolism of very low density lipoproteins in dog cardiaclymph

1981 ◽  
Vol 59 (8) ◽  
pp. 709-714 ◽  
Author(s):  
P. Julien ◽  
A. Angel
Keyword(s):  
Activity Ratio ◽  
Specific Activity ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Low Density Lipoproteins ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Protein Ratio ◽  
Vldl Triglyceride

In the present study, very low density lipoprotein (VLDL, d < 1.006) in cardiac lymph was characterized to determine its role as a metabolic substrate in the interstitial compartment. A major efferent cardiac lymph trunk was cannulated in fasting (18 h) dogs (20–27 kg). Three to five millilitres of lymph were collected over 3–4 h at 4 °C. Cardiac lymph VLDL concentration was 1.7 ± 0.7 mg protein∙100 mL−1 compared with 1.8 ± 0.8 mg protein∙100 mL−1 in plasma. The VLDL triglyceride concentration in lymph was 1.0 ± 0.3 mg triglyceride∙100 mL−1 with triglyceride/protein ratio of 0.9 compared with plasma VLDL triglyceride of 5.0 ± 1.6 mg∙100 mL−1 with a triglyceride/protein ratio of 5.5. Electron microscopy of VLDL revealed globular particles with a mean diameter of 388 Å in lymph and 661 Å in plasma. Thus, cardiac lymph VLDL are smaller and contain less triglyceride per particle than plasma VLDL. Following i.v. administration of human 125I-labelled low density lipoprotein ([125I]LDL, d 1.025–1.045), cardiac lymph/plasma LDL specific activity ratio was 0.52 ± 0.15 (n = 3) and 0.55 ± 0.15 (n = 4) at 3 and 27 h, respectively. The fact that the specific activity ratio did not reach 1 at plateau suggests continuous addition of unlabelled LDL in the cardiac interstitium, presumably from VLDL precursors. These findings demonstrate that on a protein basis the concentration of VLDL in cardiac lymph equals that of plasma, and also suggests that VLDL degradation and LDL production occur in the cardiac interstitial space.

scholarly journals The metabolic conversion of very-low-density lipoprotein into low-density lipoprotein by the extrahepatic tissues of the rat

1979 ◽  
Vol 178 (2) ◽  
pp. 455-466 ◽  
Author(s):  
B S Suri ◽  
M E Targ ◽  
D S Robinson
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Quantitative Information ◽  
Low Density Lipoproteins ◽  
High Density Lipoproteins ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Apo B ◽  
Extrahepatic Tissues

1. The work reported was designed to provide quantitative information about the capacity of the extrahepatic tissues of the rat to degrade injected VLD lipoproteins (very-low-density lipoproteins, d less than 1.006) to LD lipoproteins (low-density lipoproteins, d 1.006–1.063) and to study the fate of the different VLD-lipoprotein apoproteins during the degradative process. 2. Rat liver VLD lipoproteins, radioactively labelled in their protein moieties, were produced by the perfusion of the organ and were either injected into the circulation of the supradiaphragmatic rats or incubated in rat plasma at 37 degrees C. At a time (75 min) when approx. 90% of the triacylglycerol of the VLD lipoproteins had been hydrolysed the supradiaphragmatic rats were bled and VLD lipoproteins, LD lipoproteins and HD lipoproteins (high-density lipoproteins, d 1.063–1.21) were separated from their plasma and from the plasma incubated in vitro. The apoproteins of each of the lipoprotein classes were resolved by gel-filtration chromatography into three main fractions, designated peaks I, II and III. 3. Incubation of the liver VLD lipoproteins in plasma in vitro led to the transfer of about 30% of the total protein radioactivity to the HD lipoproteins. The transfer mainly involved the peak-II (arginine-rich and/or apo A-I) and peak-III (apo C) proteins. There was also a small transfer of radioactivity (about 5% of the total) to the LD lipoproteins. 4. Injection of the liver VLD lipoproteins into the circulation of the supradiaphragmatic rat resulted in the transfer of about 15% of the total VLD-lipoprotein radioactivity to the LD lipoproteins. The transfer involved mainly the peak-I (apo B) proteins and accounted for about 20% of the total apo B protein radioactivity of the injected VLD lipoproteins. When the endogenous plasma VLD lipoprotein was taken into account the transfer of apo B protein was about 35%. 5. The transfer of peak-II protein radioactivity from the VLD to the HD lipoproteins was greater in the plasma of the supradiaphragmatic rat than in the incubated plasma suggesting that there was a net transfer of peak-II apoproteins during the VLD lipoprotein degradation. The transfer of peak-III protein radioactivity was not greater in the plasma of the supradiaphragmatic rat, but there was a loss of this radioactivity from the circulation.

Transfer of newly made triglyceride from hepatocytes to preexisting extracellular very low density lipoproteins

1987 ◽  
Vol 65 (3) ◽  
pp. 337-343
Author(s):  
Gen Yoshino ◽  
George Steiner
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Liver Cells ◽  
Low Density Lipoproteins ◽  
In Vivo Studies ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Apoprotein B

Previous in vivo studies suggested a new model to describe the metabolism of very low density lipoproteins (VLDL). It was hypothesized that some of the lipoprotein triglyceride was transferred directly from hepatocytes and intestinal mucosal cells into preexisting extracellular VLDL particles. These studies employ an in vitro system to test this hypothesis. Isolated rat liver cells containing newly made radioactive triglyceride were prepared. These cells were incubated in medium to which exogenous VLDL had or had not been added. The presence of extracellular VLDL (rat or human) stimulated the transfer of labeled triglyceride out of the liver cells. This triglyceride was recovered in the medium's VLDL (as determined by its density and its precipitability by MnCl2–heparin or by anti-apoprotein B). Although these studies focussed on VLDL, preliminary data showed that similar triglyceride transfer occurred in the presence of the other apoprotein B containing lipoprotein, low density lipoprotein (LDL). However, in the presence of equivalent amounts of LDL, this triglyceride transfer was less than that seen in the presence of exogenous VLDL. Furthermore, the increased triglyceride released in the presence of LDL occurred entirely in the d < 1.006 fraction of the medium. That released in the presence of VLDL was recovered in the d > 1.006 fraction. Hence, we conclude that the transfer of the newly made triglyceride was from the cell to the extracellular lipoprotein that had been added to the medium. The transfer of triglyceride to VLDL did not depend on the synthesis and release of new VLDL particles because it was not accompanied by a change in the production of [14C]leucine VLDL protein, it was not blocked by chloroquine, and the LDL induced triglyceride release occurred into the d > 1.006 fraction. This transfer did not depend on the previously described triglyceride-transfer factor. The present in vitro studies support the model suggested by our earlier in vivo studies. The VLDL particle does not appear to be metabolized as a complete intact unit. Rather, some of its major lipid component, triglyceride, can move directly into and out of already existing extracellular lipoproteins.

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