In Vivo and In Vitro Effect of Phthalazinol (EG 626) on Lipolytic Enzyme Activities of The Aorta and Epididymal Adipose Tissue in The Rat

Rat adipose tissue from different body sites was shown to contain uridine diphosphoglucose (UDPG)-transglucosylase activity, which on the basis of protein content was comparable to or higher than that reported for muscle or liver. In epididymal adipose tissue, the activity of UDPG-glycogen transglucosylase and phosphorylase, as well as the content of glycogen per wet weight, decreased with increasing age of the animals in parallel with the decrease of tissue protein content. On prolonged fast the activity of UDPG-glycogen transglucosylase and phosphorylase per milligram protein dropped by 25–50% of the control value. On refeeding, the extent of changes was variable but, in general, at 24 hr control or higher levels of activity were reached and at 48 hr the activities were elevated. The ratio of glucose 6-phosphate independent activity of UDPG-glycogen transglucosylase to total activity was not affected by fasting and refeeding or by the administration of glucose with insulin. In adrenalectomized rats, with high adipose tissue glycogen, no change in UDPG-glycogen transglucosylase was found, whereas the levels of phosphorylase were elevated. Epinephrine in vivo and in vitro did not affect the activity of UDPG-glycogen transglucosylase of adipose tissue.

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The effect of insulin and glucocorticoids on the synthesis and degradation of phosphoenolpyruvate carboxykinase (GTP) in rat adipose tissue cultured in vitro

Biochemical Journal ◽

10.1042/bj1580009 ◽

1976 ◽

Vol 158 (1) ◽

pp. 9-16 ◽

Cited By ~ 19

Author(s):

O Meyuhas ◽

L Reshef ◽

F J Ballard ◽

R W Hanson

Keyword(s):

Protein Synthesis ◽

Adipose Tissue ◽

Phosphoenolpyruvate Carboxykinase ◽

Epididymal Adipose Tissue ◽

Large Size ◽

A Value ◽

Rat Adipose Tissue ◽

Synthesis And Degradation

1. Epididymal adipose tissue from the rat was maintained in culture for periods of up to 96h. 2. After an initial decrease in protein synthesis during the first 24h of culture, the adipose tissue recovered its capacity to synthesize and accumulate proteins of a relatively large size. 3. The activity of phosphoenolpyruvate carboxykinase decreased in a parallel manner, but increased again after 24h of incubation of the tissue in culture, to a value twice that noted in the tissue in vivo. This increase in enzyme activity was due to an increase in its rate of synthesis. 4. Both insulin and dexamethasone (9alpha-fluoro-16alpha-methyl-11beta,17,-21-trihydroxypregna-1,4-diene-3,20-dione) inhibited phosphoenolpyruvate carboxykinase synthesis, but dexamethasone also decreased total protein synthesis. 5. The half-life of phosphoenolpyruvate carboxykinase in adipose tissue cultured in vitro was 5-7h and was not altered by insulin or dexamethasone. 6. It is concluded that both insulin and glucocroticoids lower the activity of phosphoenolpyruvate carboxykinase in rat adipose tissue by decreasing its rate of synthesis.

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Regulation of lipoprotein lipase activity and mRNA content in rat epididymal adipose tissue in vitro by recombinant tumour necrosis factor

Biochemical Journal ◽

10.1042/bj2690123 ◽

1990 ◽

Vol 269 (1) ◽

pp. 123-126 ◽

Cited By ~ 20

Author(s):

A G Mackay ◽

J D Oliver ◽

M P Rogers

Keyword(s):

Adipose Tissue ◽

Tumour Necrosis Factor ◽

Lipoprotein Lipase ◽

Tumour Necrosis ◽

Epididymal Adipose Tissue ◽

Mrna Levels ◽

Isolated Adipocytes ◽

Necrosis Factor

Tumour necrosis factor (TNF) has previously been shown to decrease lipoprotein lipase (LPL) activity and mRNA levels in 3T3-L1 cells and in adipose tissue from rats and guinea pigs when injected in vivo, but not to alter LPL activity in human adipocytes incubated in vitro. The effect of recombinant human TNF on LPL activity and mRNA levels in rat epididymal adipose tissue incubated in vitro was examined. LPL activity and mRNA levels fell in adipose tissue taken from fed rats and incubated in Krebs-Henseleit bicarbonate medium with glucose. The addition of insulin and dexamethasone prevented these falls. TNF (400 ng/ml) produced a fall of approx. 50% in LPL activity after 2 h of incubation and of approx. 30% in LPL mRNA levels after 3 h. TNF did not decrease LPL activity in isolated adipocytes. These results demonstrate that rat adipose tissue incubated in vitro is responsive to TNF whereas isolated adipocytes are not.

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Comparative in vivo and in vitro Effect of Mono- and Disaccharides on Intestinal Brush Border Enzyme Activities in Suckling Rats

Neonatology ◽

10.1159/000241437 ◽

1981 ◽

Vol 39 (3-4) ◽

pp. 200-207 ◽

Cited By ~ 13

Author(s):

Francis Raul ◽

Michèle Kedinger ◽

Patricia M. Simon ◽

Jacques F. Grenier ◽

Katy Haffen

Keyword(s):

Brush Border ◽

Enzyme Activities ◽

Suckling Rats ◽

Intestinal Brush Border ◽

Brush Border Enzyme ◽

Vitro Effect

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Adaptable hexokinase activity in epididymal adipose tissue studied in vivo and in vitro

Biochimica et Biophysica Acta (BBA) - General Subjects ◽

10.1016/0304-4165(67)90095-5 ◽

1967 ◽

Vol 141 (2) ◽

pp. 221-230 ◽

Cited By ~ 21

Author(s):

B. Borrebaek

Keyword(s):

Adipose Tissue ◽

Epididymal Adipose Tissue ◽

Hexokinase Activity

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Potential role of leucine metabolism in the leucine-signaling pathway involving mTOR

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00153.2003 ◽

2003 ◽

Vol 285 (4) ◽

pp. E854-E863 ◽

Cited By ~ 78

Author(s):

Christopher J. Lynch ◽

Beth Halle ◽

Hisao Fujii ◽

Thomas C. Vary ◽

Reidar Wallin ◽

...

Keyword(s):

Protein Synthesis ◽

Adipose Tissue ◽

Phosphorylation Site ◽

Epididymal Adipose Tissue ◽

Keto Acid ◽

Leucine Metabolism ◽

Leucine Oxidation ◽

Plasma Leucine

Leucine has been shown to stimulate adipose tissue protein synthesis in vivo as well as leptin secretion, protein synthesis, hyper-plastic growth, and tissue morphogenesis in in vitro experiments using freshly isolated adipocytes. Recently, others have proposed that leucine oxidation in the mitochondria may be required to activate the mammalian target of rapamycin (mTOR), the cytosolic Ser/Thr protein kinase that appears to mediate some of these effects. The first irreversible and rate-limiting step in leucine oxidation is catalyzed by the branched-chain α-keto acid dehydrogenase (BCKD) complex. The activity of this complex is regulated acutely by phosphorylation of the E1α-subunit at Ser293 (S293), which inactivates the complex. Because the α-keto acid of leucine regulates the activity of BCKD kinase, it has been suggested as a potential target for leucine regulation of mTOR. To study the regulation of BCKD phosphorylation and its potential link to mTOR activation, a phosphopeptide-specific antibody recognizing this site was developed and characterized. Phospho-S293 (pS293) immunoreactivity in liver corresponded closely to diet-induced changes in BCKD activity state. Immunoreactivity was also increased in TREMK-4 cells after the induction of BCKD kinase by a drug-inducible promoter. BCKD S293 phosphorylations in adipose tissue and gastrocnemius (which is mostly inactive in vivo) were similar. This suggests that BCKD complex in epididymal adipose tissue from food-deprived rats is mostly inactive (unable to oxidize leucine), as is the case in muscle. To begin to test the leucine oxidation hypothesis of mTOR activation, the dose-dependent effects of orally administered leucine on acute activation of S6K1 (an mTOR substrate) and BCKD were compared using the pS293 antibodies. Increasing doses of leucine directly correlated with increases in plasma leucine concentration. Phosphorylation of S6K1 (Thr389, the phosphorylation site leading to activation) in adipose tissue was maximal at a dose of leucine that increased plasma leucine approximately threefold. Changes in BCKD phosphorylation state required higher plasma leucine concentrations. The results seem more consistent with a role for BCKD and BCKD kinase in the activation of leucine metabolism/oxidation than in the activation of the leucine signal to mTOR.

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