scholarly journals Fasting enhances glycogen synthase activation in hepatocytes from insulin-resistant genetically obese (fa/fa) rats

1990 ◽  
Vol 269 (3) ◽  
pp. 789-794 ◽  
Author(s):  
G van de Werve
Keyword(s):  
Dose Response ◽  
Time Course ◽  
Glycogen Synthase ◽  
Rat Hepatocytes ◽  
Insulin Resistant ◽  
Nutritional Conditions ◽  
Obese Rats ◽  
Elevated Glucose ◽  
Lean Group ◽  
In Cells

Glycogen synthase activation and phosphorylase inactivation by glucose were studied in hepatocytes isolated from fed or overnight-fasted lean or genetically obese (fa/fa) rats. In cells from fed animals, both the time course and dose-response to glucose of synthase activation were the same in both groups, despite higher levels of phosphorylase a in hepatocytes from obese animals. In contrast, in cells from fasted obese animals synthase activation with or without glucose was enhanced severalfold over that of lean controls, despite similar levels of phosphorylase a and of total (a + b) synthase activities. In both nutritional conditions glucose 6-phosphate concentrations were 2-3-fold higher in obese-rat hepatocytes than in lean-rat cells. In addition, synthase activation was transient in the fasted lean group, but was sustained in obese-rat hepatocytes. The rate of synthase activation was, however, comparable in lean- and obese-rat liver Sephadex G-25 filtrates, irrespective of the nutritional state of the donor rats. It is concluded that enhanced synthase activation in hepatocytes from starved obese rats might be due to an unbalanced synthase interconversion brought about by elevated glucose 6-phosphate concentrations and impaired kinase [van de Werve & Massillon (1990) Biochem. J. 269, 795-799], rather than to an intrinsic change in synthase phosphatase.

scholarly journals Glucose induces the translocation of glycogen synthase to the cell cortex in rat hepatocytes

1997 ◽  
Vol 321 (1) ◽  
pp. 227-231 ◽  
Author(s):  
Josep M. FERNÁNDEZ-NOVELL ◽  
David BELLIDO ◽  
Senen VILARÓ ◽  
Joan J. GUINOVART
Keyword(s):  
Laser Scanning ◽  
Glycogen Synthase ◽  
Protein A ◽  
Rat Hepatocytes ◽  
Laser Scanning Microscopy ◽  
Confocal Laser ◽  
Cell Cortex ◽  
Cell Periphery ◽  
Glycogen Deposition ◽  
In Cells

After incubation with glucose a dramatic change in the intracellular distribution of glycogen synthase was observed in rat hepatocytes. Confocal laser scanning microscopy showed that glycogen synthase existed diffusely in the cytosol of control cells, whereas in cells incubated with glucose it accumulated at the cell periphery. Colocalization analysis between glycogen synthase immunostaining and actin filaments showed that the change in glycogen synthase distribution induced by glucose correlated with a marked increase in the co-distribution of the two proteins, indicating that, in response to glucose, glycogen synthase moves to the actin-rich area close to the membrane. When glycogen synthase was immunostained with rabbit anti-(glycogen synthase) and Protein A–colloidal gold, few particles were observed close to the membrane in control cells. In contrast, in cells incubated with glucose most of the gold particles were found near the membrane, confirming that glycogen synthase had moved to the cell cortex. Furthermore, in agreement with the glycogen synthase distribution, glycogen deposition appeared to be more active at the periphery of the cell.

scholarly journals Evaluation of oxidative status in acetaminophen treated rat hepatocytes in culture

2009 ◽  
pp. 239-246
Author(s):  
T Roušar ◽  
O Kučera ◽  
P Křiváková ◽  
H Lotková ◽  
R Kanďár ◽  
...  
Keyword(s):  
Functional Capacity ◽  
Time Course ◽  
Rat Hepatocytes ◽  
Oxidative Status ◽  
Ros Production ◽  
Cellular Viability ◽  
Time Intervals ◽  
Leakage Test ◽  
Cultured Rat Hepatocytes ◽  
In Cells

The present study describes the estimation of acetaminophen (AAP) toxicity in cultured rat hepatocytes. We used different concentrations of AAP – 1, 2.5, 5, 10 and 20 mM, to test influence of AAP on cellular viability, functional capacity and oxidative status at given time intervals. WST-1 test showed decrease of dehydrogenase activity in 5, 10 and 20 mM AAP to 75 % of control values after 1 hour of incubation. At 12 h of treatment, all AAP concentrations decreased WST-1 signal; no enzyme activity was found since 18 h in cells treated with 20 mM AAP according to LDH leakage test performed at 24 h of incubation. Functional capacity was tested by albumin assay where the decrease was strictly related to AAP dose. Intracellular oxidative status was assessed by analysis of GSH/GSSG levels and time course of ROS production and glutathione reductase (GR) activity. Increased ROS production was found already after 3 h of incubation in 2.5, 5, 10 and 20 mM AAP, respectively. The highest ROS production was measured after 12 h treatment. GR activity was decreased already after 3 h of incubation and remained also decreased in cells treated with 2.5, 5, 10 and 20 mM AAP during further incubation.

scholarly journals Fructose-induced increase in intracellular free Mg2+ ion concentration in rat hepatocytes: relation with the enzymes of glycogen metabolism

1997 ◽  
Vol 326 (3) ◽  
pp. 823-827 ◽  
Author(s):  
Vinciane GAUSSIN ◽  
Philippe GAILLY ◽  
Jean-Marie GILLIS ◽  
Louis HUE
Keyword(s):  
Glycogen Phosphorylase ◽  
Time Course ◽  
Buffer Capacity ◽  
Glycogen Synthase ◽  
Glycogen Synthesis ◽  
Rat Hepatocytes ◽  
Glycogen Metabolism ◽  
Dose Dependence ◽  
Ion Concentration ◽  
Extracellular Medium

In rat hepatocytes subjected to a fructose load, ATP content decreased from 3.8 to 2.6 μmol/g of cells. Under these conditions, the intracellular free Mg2+ ion concentration, as measured with mag-fura 2, increased from 0.25 to 0.43 μmol/g of cells and 0.35 μmol of Mg2+ ions were released per g of cells in the extracellular medium. Therefore the increase in the intracellular free Mg2+ ion concentration was less than expected from the decrease in ATP, indicating that approx. 80% of the Mg2+ ions released from MgATP2- were buffered inside the cells. When this buffer capacity was challenged with an extra Mg2+ ion load by blocking the fructose-induced Mg2+ efflux, again approx. 80% of the extra Mg2+ ion load was buffered. The remaining 20% appearing as free Mg2+ ions in fructose-treated hepatocytes could act as second messenger for enzymes having a Km for Mg2+ in the millimolar range. Fructose activated glycogen synthase and glycogen phosphorylase, although both the time course and the dose-dependence of activation were different. This was reflected in a stimulation of glycogen synthesis with concentrations of fructose below 5 mM. Indeed, activation of glycogen synthase reached a maximum at 30 min of incubation and was observed with small (5 mM or less) concentrations of fructose, whereas the activation of glycogen phosphorylase was almost immediate (within 5 min) and maximal with large doses of fructose. The fructose-induced activation of glycogen phosphorylase, but not that of glycogen synthase, could be related to an increase in free Mg2+ ion concentration.

scholarly journals Altered regulation of glycogen metabolism by vasopressin and phenylephrine in hepatocytes from insulin-resistant obese (fa/fa) rats. Role of protein kinase C

1990 ◽  
Vol 269 (3) ◽  
pp. 795-799 ◽  
Author(s):  
G van de Werve ◽  
D Massillon
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Glycogen Synthase ◽  
Rat Hepatocytes ◽  
Glycogen Metabolism ◽  
Hormonal Control ◽  
Maximal Response ◽  
Insulin Resistant ◽  
Kinase C

The hormonal control of glycogen synthase and phosphorylase interconversion was investigated in hepatocytes isolated from lean and genetically obese (fa/fa) rats. In cells from obese animals, the inactivation of synthase by 4 β-phorbol 12 β-myristate 13 alpha-acetate (PMA), phospholipase C, vasopressin and the alpha 1-adrenergic agonist phenylephrine was markedly impaired, and the property of PMA to counteract phosphorylase activation by phenylephrine was attenuated. The maximal response of phosphorylase activation to phenylephrine and vasopressin was increased in obese-rat hepatocytes, but the sensitivity to these hormones was similar to that in lean-rat hepatocytes. These observations indicate that the defect in protein kinase C that we reported previously in heart of insulin-resistant fa/fa rats [van de Werve, Zaninetti, Lang, Vallotton & Jeanrenaud (1987) Diabetes 36, 310-319] is probably also expressed in liver.

scholarly journals Effects of lithium ions on glycogen synthase and phosphorylase in rat hepatocytes.

1986 ◽  
Vol 261 (36) ◽  
pp. 16927-16931
Author(s):  
F Bosch ◽  
A M Gómez-Foix ◽  
J Ariño ◽  
J J Guinovart
Keyword(s):  
Glycogen Synthase ◽  
Rat Hepatocytes ◽  
Lithium Ions

Time course of insulin resistance associated with feeding dogs a high-fat diet

1997 ◽  
Vol 272 (1) ◽  
pp. E147-E154 ◽  
Author(s):  
A. P. Rocchini ◽  
P. Marker ◽  
T. Cervenka
Keyword(s):  
Insulin Resistance ◽  
Blood Pressure ◽  
Glucose Uptake ◽  
Dose Response ◽  
High Fat Diet ◽  
Time Course ◽  
Rapid Development ◽  
Diet Group ◽  
Whole Body ◽  
High Fat

The current study evaluated both the time course of insulin resistance associated with feeding dogs a high-fat diet and the relationship between the development of insulin resistance and the increase in blood pressure that also occurs. Twelve adult mongrel dogs were chronically instrumented and randomly assigned to either a control diet group (n = 4) or a high-fat diet group (n = 8). Insulin resistance was assessed by a weekly, single-dose (2 mU.kg-1.min-1) euglycemic-hyperinsulinemic clamp on all dogs. Feeding dogs a high-fat diet was associated with a 3.7 +/- 0.5 kg increase in body weight, a 20 +/- 4 mmHg increase in mean blood pressure, a reduction in insulin-mediated glucose uptake [(in mumol-kg-1.min-1) decreasing from 72 +/- 6 before to 49 +/- 7 at 1 wk, 29 +/- 3 at 3 wk, and 30 +/- 2 at 6 wk of the high-fat diet, P < 0.01]. and a reduced insulin-mediated increase in cardiac output. In eight dogs (4 high fat and 4 control), the dose-response relationship of insulin-induced glucose uptake also was studied. The whole body glucose uptake dose-response curve was shifted to the right, and the rate of maximal whole body glucose uptake was significantly decreased (P < 0.001). Finally, we observed a direct relationship between the high-fat diet-induced weekly increase in mean arterial pressure and the degree to which insulin resistance developed. In summary, the current study documents that feeding dogs a high-fat diet causes the rapid development of insulin resistance that is the result of both a reduced sensitivity and a reduced responsiveness to insulin.

scholarly journals Control of glycogen synthase phosphorylation in isolated rat hepatocytes by epinephrine, vasopressin and glucagon

1984 ◽  
Vol 142 (3) ◽  
pp. 511-520 ◽  
Author(s):  
Carlos CIUDAD ◽  
Marcella CAMICI ◽  
Zafeer AHMAD ◽  
Yuhuan WANG ◽  
Anna A. DePAOLI-ROACH ◽  
...  
Keyword(s):  
Glycogen Synthase ◽  
Rat Hepatocytes ◽  
Isolated Rat Hepatocytes ◽  
Isolated Rat

rhIGF-I Enhances Functional Recovery from Sciatic Crush Time-Course and Dose-Response Study

1993 ◽  
Vol 692 (1 The Role of I) ◽  
pp. 314-316 ◽  
Author(s):  
PATRICIA C. CONTRERAS ◽  
CATHY STEFFLER ◽  
JEFFRY L. VAUGHT
Keyword(s):  
Functional Recovery ◽  
Dose Response ◽  
Time Course ◽  
Dose Response Study

scholarly journals Calcium metabolism in rat hepatocytes

1978 ◽  
Vol 170 (3) ◽  
pp. 615-625 ◽  
Author(s):  
S Foden ◽  
P J Randle
Keyword(s):  
Cyclic Amp ◽  
Time Course ◽  
Rat Hepatocytes ◽  
Ionophore A23187 ◽  
Total Calcium ◽  
Free Medium ◽  
Adrenergic Agonists ◽  
Calcium Efflux ◽  
Similar Time ◽  
Carbonyl Cyanide

1. The total calcium concentration in rat hepatocytes was 7.9 microgram-atoms/g dry wt.; 77% of this was mitochondrial. Approx. 20% of cell calcium exchanged with 45Ca within 2 min. Thereafter incorporation proceeded at a low rate to reach 28% of total calcium after 60 min. Incorporation into mitochondria showed a similar time course and accounted for 20% of mitochondrial total calcium after 60 min. 2. The alpha-adrenergic agonists phenylephrine and adrenaline + propranolol stimulated incorporation of 45Ca into hepatocytes. Phenylephrine was shown to increase total calcium in hepatocytes. Phenylephrine inhibited efflux fo 45Ca from hepatocytes perifused with calcium-free medium. 3. Glucagon, dibutryl cyclic AMP and beta-adrenergic agonists adrenaline and 3-isobutyl-1-methyl-xanthine stimulated calcium efflux from hepatocytes perifused with calcium-free medium. The effect of glucagon was blocked by insulin. Insulin itself had no effect on calcium efflux and it did not affect the response to dibutyryl cyclic AMP. 4. Incorporation of 45Ca into mitochondria in hepatocytes was stimulated by phenylephrine and inhibited by glucagon and by carbonyl cyanide p-trifluoromethoxyphenylhydrazone. The effect of glucagon was blocked by insulin. 5. Ionophore A23187 stimulated hepatocyte uptake of 45Ca, uptake of 45Ca into mitochondria in hepatocytes and efflux of 45Ca into a calcium-free medium.

scholarly journals Rat uterine microbiochemistry: metabolic enzyme activities stimulated by 17-beta-estradiol are localized in epithelial cells.

1987 ◽  
Vol 35 (6) ◽  
pp. 657-662 ◽  
Author(s):  
J P Holt ◽  
E Rhe
Keyword(s):  
Enzyme Activity ◽  
Smooth Muscle ◽  
Epithelial Cells ◽  
Dose Response ◽  
Enzyme Activities ◽  
Time Course ◽  
Citrate Synthase ◽  
Ovariectomized Rats ◽  
Similar Response ◽  
Estradiol Treatment

Lactate dehydrogenase (LDH; EC 1.1.1.27), citrate synthase (CS; EC 4.1.3.7), and beta-hydroxyacyl-CoA-dehydrogenase (beta-OH-acyl-CoA-DH; EC 1.1.1.35) activities were determined in each of the three major cell types of rat uterus, i.e., epithelial, stromal, and smooth muscle, using quantitative microanalytical techniques. Adult ovariectomized rats were treated with 17-beta-estradiol to determine the time course and dose response (0.025-50 micrograms/300-g rat) effect of estrogen on enzyme activity of each type of uterine cell. The use of "oil well" and enzyme-cycling microtechniques to determine the time course and the dose responses of enzyme activity changes required microassays involving 1595 microdissected single cell specimens. Estradiol treatment increased epithelial LDH, CS and beta-OH-acyl-CoA-DH activity but had no effect on these enzymes in the stroma or in smooth muscle cells. The estradiol-stimulated peak enzyme activities on Day 4 in the intervention group are compared with those in the ovariectomized rat controls as follows: LDH, 44.5 +/- 3.5 vs 22.3 +/- 3.9; CS, 3.5 +/- 0.2 vs 1.5 +/- 0.6; beta-OH-acyl-CoA-H, 3.5 +/- 0.32 vs 2.2 +/- 0.2 (mean +/- standard deviation; mol/kg/hr). Stromal cell activities (LDH, 7.4 +/- 1.0; CS, 1.2 +/- 0.2; beta-OH-acyl-CoA-DH, 0.9 +/- 0.1) were significantly lower than epithelial cell levels and were similar to smooth muscle levels. Therefore, even in the ovariectomized animal epithelial cells have markedly higher metabolic activity compared with adjacent cells. The enzyme activities are expressed as moles of substrate reacting per kilogram of dry weight per hour. All three enzymes exhibited a 17-beta-estradiol-induced dose response between 0.025-0.15 micrograms/300-g rat. The three enzymes studied all had similar response patterns to estrogen. The effect of estradiol was restricted to epithelial cells, with enzyme activities increasing to maximal levels after approximately 96 hr of hormone treatment. This study therefore not only confirms the specific and differential metabolic responses of uterine cells to estradiol treatment, but clearly demonstrates that marked metabolic differences exist between epithelial cells and stromal or smooth muscle uterine cells.

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