The catabolism of human and rat very low density lipoproteins by perfused rat hearts

Dory, Ladislav; Pocock, Dorothy M.-E.; Rubinstein, David

doi:10.1016/0005-2760(78)90191-1

Cited by 21 publications

(7 citation statements)

References 46 publications

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“…It appears therefore that peak-III radioactivity, presumably apo C-protein radioactivity, is lost from the circulation. The report by Dory et al (1978) that, when labelled VLD lipoproteins are perfused through the rat heart, their degradation is accompanied by the uptake of over 40% of the radioactivity by the heart tissue, would be consistent with this.…”

supporting

confidence: 64%

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

Suri¹,

Targ²,

Robinson³

1979

Biochemical Journal

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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-lowdensity lipoproteins, d< 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 370C. 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. This transfer mainly involved the peak-II (arginine-rich and/or apo A-I) and peak-Ill (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. This 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-Il 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.

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confidence: 64%

“…Furthermore, the iodination of lipoproteins causes very different degrees of labelling of the distinct apoprotein species (Fidge & Poulis, 1974) and results in considerable incorporation of radioactivity into the lipid moiety. Both these factors can complicate the interpretation of the results obtained (Shepherd et al, 1976;Dory et al, 1978).…”

mentioning

confidence: 99%

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

Suri¹,

Targ²,

Robinson³

1979

Biochemical Journal

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“…A number of in vitro studies using either human postheparin plasma LPL activity, purified postheparin plasma LPL, or pertused isolated rat heart systems have demonstrated an interconversion of VLDL to "LDL-like" particles in the presence of LPL activity. 13 " 16 Studies in which LPL was immunochemically inhibited in vivo have shown VLDL catabolism to be blocked with the inactivation of the enzyme. At the same time, LDL formation was stopped, illustrating the requirement, in vivo, for LPL activity in VLDL catabolism to LDL.…”

Section: Discussionmentioning

confidence: 99%

Roles of lipoprotein lipase and hepatic triglyceride lipase in the catabolism in vivo of triglyceride-rich lipoproteins.

Reardon¹,

Sakai²,

Steiner³

1982

Arteriosclerosis

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“…Synthesis of apoB is the rate-limiting step in this process (18). VLDL is then transformed into LDL particles by delipidation of its lipid core by lipoprotein lipase (27)(28)(29)(30). Thus, down-regulation of apoB synthesis may explain the reduction of VLDL, as well as of LDL, in response to ACTH.…”

Section: Figmentioning

confidence: 99%

ACTH Decreases the Expression and Secretion of Apolipoprotein B in HepG2 Cell Cultures

Xu¹,

Ekström²,

Nilsson‐Ehle³

2001

Journal of Biological Chemistry

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Administration of adrenocorticotropic hormone (ACTH)has been shown to decrease plasma concentrations of apolipoprotein B (apoB) containing lipoproteins, including lipoprotein(a), in man. However, the mechanism behind this hypolipidemic effect is unknown. This study aimed at distinguishing between the main possibilities (increased elimination or decreased production of lipoproteins) using HepG2 cell cultures. Addition of ACTH to the cell culture medium selectively downregulated apoB mRNA expression and apoB secretion in a dose-dependent manner. At 100 pmol/liter ACTH, the apoB mRNA level was about 40% lower than in the untreated cells, and the secretion of apoB into the medium was decreased to a similar extent. The expression and secretion of other apolipoproteins (apoA-I, apoE, and apoM), however, were not affected by ACTH. Under normal culture conditions the level of secretion of apoB from HepG2 cells is quite low. In the presence of 0.4 mmol/liter oleic acid secretion of apoB increased 3-fold, but this phenomenon was not seen in ACTH-treated cells. Binding and internalization of radiolabeled low density lipoprotein (LDL) by HepG2 cell, as well as LDLreceptor mRNA and scavenger receptor B-I mRNA levels, were not influenced by ACTH. In conclusion, ACTH directly and selectively down-regulated the production and secretion of apoB in HepG2 cell cultures, suggesting that a principal mechanism behind the cholesterollowering effect of ACTH in vivo may be a decreased production rate of apoB-containing lipoproteins from the liver. It is well documented that adrenocorticotropic hormone (ACTH)1 regulates important aspects of lipid metabolism in the adrenal gland, especially those related to steroid hormone homeostasis (1). ACTH has also been shown to influence plasma lipid and lipoprotein metabolism (2-7). Thus, we have demonstrated previously that ACTH treatment markedly and consistently lowers plasma concentrations of low density lipoproteins (LDL), very low density lipoprotein (VLDL), and lipoprotein(a) (Lp(a)) in healthy individuals (2, 7), in steroid-treated patients with renal disease, and in uremic patients treated by hemodialysis (3, 4). In some of the studies, an increased high density lipoprotein (HDL) cholesterol concentration was also observed (4, 6). The effects of ACTH on LDL and Lp(a) levels seem attributable to ACTH as such, because they are clearly distinct from the effects of equipotent doses of corticosteroids (6).The mechanisms behind the lipid-lowering effects of ACTH are not known. Previous data indicated that ACTH could increase LDL receptor (LDL-R) activity in HepG2 cells (6), suggesting that an increased elimination rate of LDL might be involved. It has also been reported that ACTH increased the receptor-mediated uptake of native LDL but not of oxidized LDL or of LP(a) in HepG2 cells. However, because the elimination of LDL and Lp(a) from the circulation occurs via distinctly different routes (i.e. Lp(a) does not utilize the LDL-R pathway), the parallel decrease in plasma LDL and Lp(a) concentrati...

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The catabolism of human and rat very low density lipoproteins by perfused rat hearts

Cited by 21 publications

References 46 publications

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

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

Roles of lipoprotein lipase and hepatic triglyceride lipase in the catabolism in vivo of triglyceride-rich lipoproteins.

ACTH Decreases the Expression and Secretion of Apolipoprotein B in HepG2 Cell Cultures

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