scholarly journals Changes in the anti-lipolytic action and binding to plasma membranes of N6-L-phenylisopropyladenosine in adipocytes from starved and hypothyroid rats

1984 ◽  
Vol 223 (1) ◽  
pp. 53-59 ◽  
Author(s):  
P Chohan ◽  
C Carpenter ◽  
E D Saggerson
Keyword(s):  
Adipose Tissue ◽  
Adenosine Deaminase ◽  
Binding Sites ◽  
Plasma Membranes ◽  
High Concentration ◽  
Lipolytic Action ◽  
Increased Sensitivity ◽  
Adipose Tissue Lipolysis ◽  
Adenosine Analogue ◽  
Adipocyte Plasma Membranes

The anti-lipolytic effect of the adenosine analogue N6-L-phenylisopropyladenosine was studied with rat adipocytes incubated with a high concentration of adenosine deaminase (0.5 unit/ml, approx. 2.5 micrograms/ml) and concentrations of noradrenaline that were equieffective in different physiological states. These studies were performed to compare the fed and starved (24h) states and to compare a hypothyroid state (induced by feeding propylthiouracil + a low-iodine diet) with the euthyroid state. Starvation increased sensitivity of the cells to the lipolytic action of noradrenaline, while decreasing sensitivity to the antilipolytic action of phenylisopropyladenosine. Hypothyroidism resulted in decreased sensitivity to noradrenaline and increased sensitivity to phenylisopropyladenosine. Studies of the binding of [3H]phenylisopropyladenosine to adipocyte plasma membranes indicated heterogeneity of binding sites or negative co-operativity in the binding. Starvation did not change [3H]phenylisopropyladenosine binding to membranes, whereas hypothyroidism caused an unexpected decrease in both the number and affinity of the binding sites. These observations are discussed in terms of the dual regulation of adipose-tissue lipolysis by lipolytic and anti-lipolytic agents.

Stimulation of cAMP accumulation and lipolysis in hamster adipocytes with forskolin

1984 ◽  
Vol 246 (1) ◽  
pp. C63-C68 ◽  
Author(s):  
R. J. Schimmel
Keyword(s):  
Adipose Tissue ◽  
Adenosine Deaminase ◽  
Camp Accumulation ◽  
Camp Content ◽  
Lipolytic Action ◽  
White Adipocytes ◽  
Free Media ◽  
Phenylisopropyl Adenosine ◽  
Camp Levels ◽  
Stimulation Of

This study compares the effects of forskolin and isoproterenol on lipolysis and adenosine 3',5'-cyclic monophosphate (cAMP) accumulation in hamster white adipocytes. Rates of lipolysis in forskolin-stimulated cells were equivalent to those in cells incubated with isoproterenol, but cAMP levels were more than 10-fold greater in the presence of forskolin. The stimulatory effects of forskolin were partially inhibited by N6-phenylisopropyl adenosine but not by 2',5'-dideoxyadenosine. In other experiments, cells were exposed to forskolin in combination with either isoproterenol or adenosine deaminase. A concentration of forskolin that caused only a small increase in lipolysis was used. When isoproterenol or adenosine deaminase were added with forskolin, lipolysis increased dramatically, but cAMP content either did not change, as occurred with isoproterenol, or increased only slightly with adenosine deaminase. Isoproterenol potentiation of forskolin's lipolytic action persisted in the absence of extracellular K+, even though the lipolytic response to isoproterenol alone was absent in K+-free media. These data demonstrate that the lipolytic responses of adipose tissue are more complex than are responses simply in proportion to cellular concentration of cAMP. Such complexity could arise if lipolytic regulatory factors other than cAMP existed or if cAMP and protein kinase were functionally segregated within adipocytes.

scholarly journals Changes in the sensitivity to glucagon of lipolysis in adipocytes from pregnant and lactating rats

1988 ◽  
Vol 254 (3) ◽  
pp. 661-665 ◽  
Author(s):  
V A Zammit
Keyword(s):  
Adipose Tissue ◽  
The Other ◽  
High Concentration ◽  
Response Curves ◽  
Pregnant Rats ◽  
Adipose Tissue Lipolysis ◽  
The Right ◽  
Peak Lactation ◽  
Stimulation Of

1. Rates of lipolysis were measured at different concentrations of glucagon in adipocytes prepared from parametrial adipose tissue of fed or starved rats in different reproductive states. All experiments were performed in the presence of a high concentration of adenosine deaminase (1 unit/ml). 2. Maximal rates of lipolysis (elicited by 25 nM-glucagon in each instance) were higher in adipocytes from peak-lactating rats than those from pregnant animals in both the fed and starved states. 3. Of adipocytes from fed animals, those from peak-lactating rats were the most sensitive to glucagon, whereas those from late-pregnant and early-lactating rats were 1-2 orders of magnitude less sensitive. 4. Adipocytes from 24 h-starved rats showed a much smaller stimulation of lipolysis by glucagon, making the assessment of sensitivity difficult. Therefore, rates of lipolysis were also measured in the presence of a maximally anti-lipolytic dose of insulin. The presence of insulin did not alter the relative sensitivities to glucagon of adipocytes from fed animals in different reproductive states, although all dose-response curves were shifted to the right. When lipolysis in adipocytes from starved animals was measured in the presence of insulin, it became evident that starvation for 24 h markedly increased the sensitivity of adipocytes from late-pregnant rats to glucagon, but did not affect that of cells from animals in the other reproductive states. 5. It is concluded that the large changes in sensitivity to glucagon that occurred during the reproductive cycle may enable the modulation of adipose-tissue lipolysis in vivo to satisfy the different metabolic requirements of the animal in the transition from pregnancy to peak lactation.

Selective uptake of cholesteryl ester from high density lipoproteins by plasma membranes of adipose tissue

1990 ◽  
Vol 68 (5) ◽  
pp. 870-879 ◽  
Author(s):  
Joel G. Parkes ◽  
Aubie Angel
Keyword(s):  
Adipose Tissue ◽  
Cholesteryl Ester ◽  
Plasma Membranes ◽  
Divalent Cations ◽  
High Density ◽  
Metabolic Energy ◽  
High Density Lipoproteins ◽  
High Affinity ◽  
Lipoprotein Binding ◽  
Adipocyte Plasma Membranes

The interaction between high density lipoproteins (HDL) and adipose tissue is an important pathway for cholesterol and cholesteryl ester flux. In intact fat cells, a disproportionately greater net uptake of cholesteryl ester occurs subsequent to lipoprotein binding than would have been predicted from a consideration of holoparticle uptake alone. To characterize the early events in this process, cholesteryl hexadecyl ether, a nonmetabolizable, accumulative marker of cholesteryl ester, was incorporated into canine HDL2, and its uptake by omental adipocyte plasma membranes was measured in relation to the binding of HDL2, which in this animal species is enriched in apolipoprotein A-I and free of apolipoprotein E. The dose–response profile for HDL2 binding was consistent with a single lipoprotein binding site at all concentrations of HDL2, whereas uptake of cholesteryl ester from HDL2 was biphasic, suggesting a high affinity site at low HDL2 concentrations and a low affinity site at high lipoprotein concentrations. Pronase treatment stimulated binding twofold and this was accompanied by a parallel twofold stimulation of cholesteryl ester uptake. EDTA, on the other hand, reduced binding and uptake of cholesteryl ester by 20%, indicating partial dependence upon divalent cations. The proportion of HDL2 cholesteryl ester accumulated by plasma membranes relative to HDL2 protein bound was not altered by either pronase or EDTA, despite the fact that these agents had opposite effects upon binding. In dissociation studies, a portion of membrane-associated HDL2 did not equilibrate with exogenous HDL2 and a greater proportion of the cholesteryl ester failed to dissociate. A stepwise mechanism for cholesteryl ester uptake, involving (i) saturable, high affinity HDL2 binding to cell surface sites, (ii) vectoral, HDL2 concentration-dependent delivery of cholesteryl ester to the membrane, and (iii) cholesteryl ester sequestration into a nonexchangeable membrane compartment, appears to be independent of metabolic energy or cell processing.Key words: cholesteryl ester transport, high density lipoprotein receptor, cholesterol storage.

scholarly journals Sensitivity of glucose uptake and lipolysis of white adipocytes of the rat to insulin and effects of some metabolites

1979 ◽  
Vol 180 (2) ◽  
pp. 365-370 ◽  
Author(s):  
A Green ◽  
E A Newsholme
Keyword(s):  
Adipose Tissue ◽  
Glucose Uptake ◽  
Adenosine Deaminase ◽  
Blood Lactate ◽  
Incubation Medium ◽  
Glucose Utilization ◽  
Lactate Concentration ◽  
Blood Lactate Concentration ◽  
White Adipocytes ◽  
Increased Sensitivity

1. Insulin increased glucose uptake and inhibited lipolysis in white adipocytes of the rat over the same concentration range of the hormone: the half-maximal effects were observed at approx. 10 microunits of insulin/ml. Thus, contrary to previous reports, no difference in sensitivity of the two processes to insulin could be found, which suggests that both these effects of insulin are important in increasing the rate of glucose utilization after a meal. 2. Adenosine deaminase, which lowers the concentration of adenosine in the incubation medium, decreased the sensitivity of both processes (lipolysis and glucose uptake) to insulin: this suggests that adenosine increases the sensitivity of both processes. Similarly, lactate and 3-hydroxybutyrate increased the sensitivity of both processes (to the same extent) to insulin. It is suggested that this increased sensitivity will improve the response (of adipose tissue) to insulin on refeeding after a prolonged period of starvation (when the hydroxybutyrate concentration is high), and after a short burst of exercise, when the blood lactate concentration is high and when large amounts of glucose are produced from lactate via gluconeogenesis in the liver.

Characterization of high-density lipoprotein binding to rat adipocytes and adipocyte plasma membranes

1988 ◽  
Vol 66 (9) ◽  
pp. 986-997 ◽  
Author(s):  
Eva Zsigmond ◽  
Bessie Fong ◽  
Aubie Angel
Keyword(s):  
Adipose Tissue ◽  
Plasma Membranes ◽  
Density Lipoprotein ◽  
Membrane System ◽  
Rat Plasma ◽  
High Density ◽  
High Density Lipoproteins ◽  
Binding Characteristics ◽  
Isolated Adipocytes ◽  
Adipocyte Plasma Membranes

The interaction of high-density lipoproteins (HDL) with adipocytes is important in the regulation of cellular cholesterol flux. To study the mechanisms of HDL binding and cellular processing, we incubated adipocytes isolated from epididymal and perirenal adipose tissue of male Wistar rats (300 g) with HDL1 (1.07–1.10 g/mL) and HDL2 (1.10–1.14 g/mL) fractions separated from rat plasma by gradient ultracentrifugation. Freshly isolated adipocytes were incubated with 125I-labeled HDL for 2 h at 37 °C to determine cell-associated uptake and degradation. Adipocytes from both fat regions showed significant cell-associated HDL1 and HDL2 uptake and very high medium degradation (2- to 6-fold higher than uptake). To assess 125I-labeled HDL binding independent of cellular metabolism, we purified adipocyte plasma membranes from isolated adipocytes and used them in binding assays. Binding of HDL1 and HDL2 in the membrane system was 85–95% specific, sensitive to high NaCl concentrations, and abolished by pronase treatment. In contrast to HDL2 binding, the maximum HDL1 binding to perirenal plasma membranes was significantly higher than its binding to epididymal membranes (7.2 ± 1.3 vs. 4.4 ± 0.2 μg/mg, n = 6, p < 0.05). This increment in HDL1 binding to perirenal membranes represented an EDTA- sensitive, calcium-dependent component. These results indicate that HDL binding to adipocyte plasma membranes depends on both adipose tissue region and HDL subtype. The membrane binding characteristics, taken together with the cellular uptake results, suggest that adipocytes bind and metabolize HDL and that this interaction may involve a protein receptor.

scholarly journals Adenosine and the control of lipolysis in rat adipocytes during pregnancy and lactation

1983 ◽  
Vol 216 (1) ◽  
pp. 121-128 ◽  
Author(s):  
R G Vernon ◽  
E Finley ◽  
E Taylor
Keyword(s):  
Adipose Tissue ◽  
Cell Volume ◽  
Adenosine Deaminase ◽  
Stromal Cells ◽  
Male Rats ◽  
Fat Cells ◽  
Pregnant Rats ◽  
Mean Cell Volume ◽  
Pregnancy And Lactation ◽  
Adenosine Analogue

The rate of noradrenaline-stimulated lipolysis is lower in fat-cells from lactating than from pregnant rats; this difference is eliminated by the addition of adenosine deaminase [Aitchison, Clegg & Vernon (1982) Biochem. J. 202, 243-247]. The activity of 5′-nucleotidase, and hence the capacity of the cells to synthesize adenosine, was the same in fat-cells and also stromal cells of adipose tissue from pregnant, lactating and male rats. The response and sensitivity of fat-cells to the anti-lipolytic effects of adenosine were measured by incubating cells in the presence of noradrenaline, adenosine deaminase (to remove endogenous adenosine) and various concentrations of the adenosine analogue N6-phenylisopropyladenosine (PIA). PIA caused a greater inhibition of the rate of noradrenaline-stimulated lipolysis in adipocytes from lactating than from pregnant rats. The concentration of PIA required to inhibit by 50% the rate of noradrenaline-stimulated lipolysis fell from over 100 nM for fat-cells from pregnant rats to 30 nM for fat-cells from lactating rats. The decreased rate of noradrenaline-stimulated lipolysis during lactation was not due to the smaller mean cell volume of adipocytes during this state.

scholarly journals Guanosine nucleotides regulate hormone binding of insulin receptors

1992 ◽  
Vol 281 (3) ◽  
pp. 735-743 ◽  
Author(s):  
E R Mortensen ◽  
J Drachman ◽  
G Guidotti
Keyword(s):  
Binding Sites ◽  
Plasma Membranes ◽  
Insulin Receptors ◽  
Insulin Binding ◽  
Scatchard Analysis ◽  
Hormone Binding ◽  
Temperature Dependent ◽  
High Affinity ◽  
Mild Reduction ◽  
Adipocyte Plasma Membranes

Insulin receptors in turkey erythrocyte and rat adipocyte plasma membranes display non-linear hormone binding by Scatchard analysis. This result is consistent with evidence that the insulin-binding sites are heterogeneous and have at least two affinities for the hormone. Mild reduction of plasma membranes with dithiothreitol, before insulin binding, increased the fraction of hormone binding with high affinity without significantly changing the total number of receptor-binding sites. In the presence of guanosine 5′-[gamma-thio]triphosphate, the amount of receptor with high affinity for insulin in the reduced membranes decreased to that present in the absence of reduction; the effect of the nucleotide was concentration- and temperature-dependent. This decrease in insulin binding was specific for guanine nucleotides.

scholarly journals Increased sensitivity of diabetic rat adipose tissue towards the lipolytic action of epinephrine

Diabetologia ◽  
1975 ◽  
Vol 11 (6) ◽  
pp. 509-516 ◽  
Author(s):  
J. Zapf ◽  
D. Feuerlein ◽  
M. Waldvogel ◽  
E. R. Froesch
Keyword(s):  
Adipose Tissue ◽  
Diabetic Rat ◽  
Lipolytic Action ◽  
Increased Sensitivity ◽  
Rat Adipose Tissue

scholarly journals The decrease in the short variant of gsalpha protein is associated with an increase in [3H]CGP12177 binding, [3H]ouabain binding and Na, K-ATPase activity in brown adipose tissue plasma membranes of cold-acclimated hamsters

1999 ◽  
Vol 22 (1) ◽  
pp. 55-64 ◽  
Author(s):  
L Bourova ◽  
J Novotn ◽  
P Svoboda
Keyword(s):  
Adipose Tissue ◽  
Plasma Membrane ◽  
Atpase Activity ◽  
Brown Adipose Tissue ◽  
Binding Sites ◽  
Plasma Membranes ◽  
Immunoblot Analysis ◽  
Ouabain Binding ◽  
Brown Adipose ◽  
Sds Page

Sucrose density gradient purified plasma membranes isolated from brown adipose tissue of cold-acclimated hamsters (4-10 weeks at 0-4 degreesC) were analysed for the content of the short (GsalphaS) and long (GsalphaL) variants of Gsalpha protein (the alpha subunit of the stimulatory G protein) and compared with the membranes isolated from control animals. The relative ratio between the two variants (GsalphaS/GsalphaL) decreased from 0.48 to 0.24 (P<0.01). This result, obtained by electrophoretic resolution of membrane proteins by standard SDS-PAGE and an immunoblot analysis with an antiserum oriented against an internal sequence of Gsalpha, was verified by resolution on urea-containing gels and an antiserum oriented against the C-terminus decapeptide of Gsalpha. Under these conditions, the GsalphaS/GsalphaL ratio was decreased from 0.41 to 0.31 (P<0.05). The total amount of both isoforms (GsalphaS plus GsalphaL) decreased to 83% (P<0.05) or 68% (P<0.01) by standard or urea SDS-PAGE respectively. These data demonstrate that cold-acclimation of hamster brown adipose tissue is associated with preferential decrease in the plasma membrane density of the short variant of the Gsalpha protein.%This decrease was paralleled by an increase in the other plasma membrane constituents, [3H]CGP12177 binding sites, [3H]ouabain binding sites and Na,K-ATPase activity to 147%, 212% and 191% respectively.

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