Adenylyl cyclase inhibitory pathway is differentially modified in rat white and brown fat by high-energy diets

1997 ◽  
Vol 272 (6) ◽  
pp. E1043-E1049 ◽  
Author(s):  
Y. Kenan ◽  
M. Levinson ◽  
M. Pines ◽  
M. Naim
Keyword(s):  
Adipose Tissue ◽  
Adenylyl Cyclase ◽  
High Energy ◽  
Inhibitory Pathway ◽  
Balanced Diet ◽  
Brown Adipose ◽  
Gs Alpha ◽  
Phenylisopropyl Adenosine ◽  
Camp Levels ◽  
Camp Formation

Incubation of white adipose tissue (WAT) adipocytes from rats fed a high-energy diet (Exp group) with antilipolytic Gi-coupled adenylyl cyclase inhibitory agonists, nicotinic acid (Nic) and N8-(L-2-phenylisopropyl)adenosine (PIA), resulted in lower cellular adenosine 3',5'-cyclic monophosphate (cAMP) levels than in stimulated adipocytes from rats fed a nutritionally balanced diet (Con group). In contrast to WAT, incubation of brown adipose tissue (BAT) adipocytes with Nic yielded higher cAMP levels in the Exp vs. Con rats. In both WAT and BAT adipocytes, pertussis toxin treatment abolished the differences in Nic- and PIA-inhibited cAMP formation between Exp and Con animals. Immunoblotting of adipocyte membranes indicated a lower content of Gi alpha but not Gs alpha in BAT membranes of Exp vs. Con animals after 6 and 10 wk of feeding. No such differences were found in the Gs alpha or Gi alpha contents of WAT membranes. Thus the inhibitory pathway of adenylyl cyclase is proposed to be sensitized in WAT and desensitized in BAT of rats fed high-energy diets. These modifications in sensitivity are in line with reduced cAMP and lipolysis in WAT and increased cAMP and thermogenesis in BAT during obesity.

Perinatal expression of adenylyl cyclase subtypes in rat brown adipose tissue

1996 ◽  
Vol 270 (4) ◽  
pp. R755-R760 ◽  
Author(s):  
A. Chaudhry ◽  
L. A. Muffler ◽  
R. Yao ◽  
J. G. Granneman
Keyword(s):  
Adipose Tissue ◽  
Brown Adipose Tissue ◽  
Adenylyl Cyclase ◽  
Perinatal Period ◽  
Mrna Levels ◽  
Protection Assay ◽  
Brown Adipose ◽  
Nuclease Protection Assay ◽  
6 Hydroxydopamine ◽  
Gs Alpha

The ability of norepinephrine to stimulate adenylyl cyclase (AC) activity increases during the perinatal period in rat brown adipose tissue (BAT), and this increase is associated with changes in the activities of both GS alpha and AC. The purpose of this study was to determine which AC subtypes are present in neonatal BAT and to examine whether the perinatal increase in AC activity corresponds to an increase in the expression of a particular AC subtype. Analysis of AC mRNAs by nuclease protection assay demonstrated the presence of mRNAs encoding AC-III, AC-IV, AC-VI, and AC-IX in embryonic and postnatal BAT. Of the subtypes detected, only AC-III mRNA levels increased substantially during the perinatal period. The increase in AC-III expression was paralleled by an increase in isoproterenol-stimulated AC activity. Treatment of neonates was the sympathetic neurotoxin 6-hydroxydopamine abolished the perinatal increase in both AC activity and AC-III mRNA levels but had no effect on the expression of other AC subtypes. These results strongly indicate that the increase in AC activity during the perinatal period is due to an increase in the expression of AC-III.

Effect of hypothyroidism on adenylyl cyclase activity and subtype gene expression in brown adipose tissue

1997 ◽  
Vol 273 (2) ◽  
pp. R762-R767 ◽  
Author(s):  
A. Chaudhry ◽  
J. G. Granneman
Keyword(s):  
Gene Expression ◽  
Adipose Tissue ◽  
Brown Adipose Tissue ◽  
Adenylyl Cyclase ◽  
Regulation Of Gene Expression ◽  
Mrna Levels ◽  
Adrenergic Stimulation ◽  
Functional Responses ◽  
Synergistic Interactions ◽  
Brown Adipose

Brown adipose tissue (BAT) expresses several adenylyl cyclase (AC) subtypes, and adrenergic stimulation selectively upregulates AC-III gene expression. Previous studies have described synergistic interactions between the sympathetic nervous system (SNS) and 3,5,3'-triiodothyronine (T3) on the regulation of gene expression in BAT. Because adrenergic stimulation also increases the activity of BAT type II thyroxine 5'-deiodinase (DII) and local T3 generation is important for many functional responses in BAT, we examined the effects of thyroid hormone status on the expression of various AC subtypes. Hypothyroidism selectively increased AC-III mRNA levels in BAT but not in white adipose tissue. Of the other subtypes examined, hypothyroidism did not alter AC-VI mRNA levels and slightly reduced AC-IX mRNA levels in BAT. The increase in AC-III expression was paralleled by an increase in forskolin-stimulated AC activity in BAT membranes. Sympathetic denervation of BAT abolished the increase in both AC activity and AC-III mRNA expression produced by hypothyroidism, but did not affect the expression of other subtypes. Surgical denervation also prevented the induction of AC-III in the cold-stressed euthyroid rat, but injections of T3 failed to alter AC-III expression in intact or denervated BAT. Our results indicate that T3 does not directly affect expression of AC-III. Rather, hypothyroidism increases BAT AC-III expression indirectly via an increase in sympathetic stimulation. Furthermore, our results strongly indicate that the increase in AC activity in hypothyroid BAT is due to increased expression of AC-III.

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.

Effects of triiodothyronine administration on the adenylyl cyclase system in brown adipose tissue of rat

1997 ◽  
Vol 273 (2) ◽  
pp. E247-E253
Author(s):  
H. Adli ◽  
R. Bazin ◽  
R. Vassy ◽  
G. Y. Perret
Keyword(s):  
Adipose Tissue ◽  
Brown Adipose Tissue ◽  
Adenylyl Cyclase ◽  
Protein Concentration ◽  
Response Curves ◽  
Fourfold Increase ◽  
Brown Adipose ◽  
Cgp 12177 ◽  
Polymerase Chain ◽  
Gamma S

This study was undertaken to investigate the effect of triiodothyronine (T3) administration to euthyroid rats on beta 3-adrenoceptor (beta 3-AR) expression and on the different components of the adenylyl cyclase (AC) system in brown adipose tissue (BAT). In rats treated with T3, the beta 3-AR density (assessed by the binding of [3H]CGP-12177) showed a decrease of 50%, as did their mRNA, as analyzed by reverse transcriptase-polymerase chain reaction. In hyperthyroid rats, compared with control rats, there was a 40% increase in G alpha s activity (stimulated by NaF or GTP gamma S) and a fourfold increase in the protein concentration (Western blotting). In contrast, the level of the pertussis toxin substrate Gi declined by 35% in response to T3. Analysis of dose-response curves for isoproterenol and CGP-12177 revealed that neither basal nor stimulated AC activities nor 50% stimulatory concentration for these agonists was changed by T3 administration. In conclusion, these results suggest that downregulation of the beta 3-AR by T3 was counter-balanced by changes in other components of the AC cascade (i.e., Gs and Gi), so no change occurred in the capacity of BAT to generate adenosine 3',5'-cyclic monophosphate.

Control of glyceroneogenic activity in rat brown adipose tissue

2003 ◽  
Vol 285 (1) ◽  
pp. R177-R182 ◽  
Author(s):  
W. T. L. Festuccia ◽  
N. H. Kawashita ◽  
M. A. R. Garofalo ◽  
M. A. F. Moura ◽  
S. R. C. Brito ◽  
...  
Keyword(s):  
Adipose Tissue ◽  
Brown Adipose Tissue ◽  
Glucose Utilization ◽  
Streptozotocin Diabetes ◽  
Sympathetic Control ◽  
Balanced Diet ◽  
Threefold Increase ◽  
Brown Adipose

Brown adipose tissue (BAT) glyceroneogenesis was evaluated in rats either fasted for 48 h or with streptozotocin-diabetes induced 3 days previously or adapted for 20 days to a high-protein, carbohydrate-free (HP) diet, conditions in which BAT glucose utilization is reduced. The three treatments induced an increase in BAT glyceroneogenic activity, evidenced by increased rates of incorporation of [1-14C]pyruvate into triacylglycerol (TAG)-glycerol in vitro and a marked, threefold increase in the activity of BAT phospho enolpyruvate carboxykinase (PEPCK). BAT glycerokinase activity was not significantly affected by fasting or diabetes. After unilateral BAT denervation of rats fed either the HP or a balanced diet, glyceroneogenesis activity increased in denervated pads, evidenced by increased rates of nonglucose carbon incorporation into TAG-glycerol in vivo (difference between 3H2O and [14C]glucose incorporations) and of [1-14C]pyruvate in vitro. PEPCK activity was not significantly affected by denervation. The data suggest that BAT glyceroneogenesis is not under sympathetic control but is sensitive to hormonal/metabolic factors. In situations of reduced glucose use there is an increase in BAT glyceroneogenesis that may compensate the decreased generation of glycerol-3-phosphate from the hexose.

scholarly journals Attenuation of Gs α coupling efficiency in brown-adipose-tissue plasma membranes from cold-acclimated hamsters

1993 ◽  
Vol 295 (3) ◽  
pp. 655-661 ◽  
Author(s):  
P Svoboda ◽  
L Unelius ◽  
B Cannon ◽  
J Nedergaard
Keyword(s):  
Adipose Tissue ◽  
Adenylate Cyclase ◽  
Plasma Membranes ◽  
Coupling Efficiency ◽  
Ouabain Binding ◽  
Beta Adrenergic ◽  
Brown Adipose ◽  
Density Band ◽  
Gs Protein ◽  
Gs Alpha

In order to localize site(s) of beta-adrenergic desensitization found in brown adipocytes from cold-acclimated animals, total brown-adipose-tissue homogenates (postnuclear supernatant) were obtained from control or cold-acclimated hamsters and were fractionated on discontinuous sucrose gradients. A low-density band (cytosolic proteins) and a high-density band (mitochondria) were obtained; in the middle fractions only low levels of protein were recovered. However, these fractions displayed a high level of specific [3H]ouabain binding, indicating that they represented fractions enriched in plasma membranes. The level of [3H]ouabain binding was significantly higher in plasma membranes from cold-acclimated animals, indicating an increased density of Na,K-ATPase units. The maximal activity of adenylate cyclase, as estimated with forskolin, was not changed by cold acclimation. However, the levels of cyclase activity observed after Gs-protein-mediated activation (with guanosine 5′-[gamma-thio]triphosphate, isoprenaline, both of these, or fluoride) were decreased, indicating a decreased coupling efficiency. Notably, a significant decrease was observed in the functional activity of the Gs protein, as directly measured by estimation of the ability of cholate extracts of brown-fat plasma membranes to reconstitute Gs-protein-mediated stimulation of adenylate cyclase in cyc- membranes. Further, a functionally significant decrease (to 72%) was observed in the ratio between the amount of functional Gs proteins and adenylate cyclase units. The total content of Gs alpha protein was decreased to the same extent as the coupling efficiency of the membranes, indicating that a lower content of functionally equivalent Gs alpha molecules could explain the decreased coupling. It could therefore be concluded that a decrease in Gs-protein-mediated coupling efficiency, owing to a decrease in the amount of Gs alpha, is at least one site of beta-adrenergic desensitization in cold-acclimated animals. This may, at least in part, explain that desensitization takes place despite the fact that the beta 3-adrenoceptor itself apparently lacks some of the sites known to be involved in the desensitization process in other beta-adrenergic receptors.

Glycerokinase activity in brown adipose tissue: a sympathetic regulation?

2002 ◽  
Vol 282 (4) ◽  
pp. R1185-R1190 ◽  
Author(s):  
N. H. Kawashita ◽  
W. T. L. Festuccia ◽  
M. N. Brito ◽  
M. A. F. Moura ◽  
S. R. C. Brito ◽  
...  
Keyword(s):  
Adipose Tissue ◽  
Brown Adipose Tissue ◽  
Cold Acclimation ◽  
Cold Exposure ◽  
Turnover Rates ◽  
Physiological Conditions ◽  
Balanced Diet ◽  
Norepinephrine Turnover ◽  
Brown Adipose ◽  
Sympathetic Regulation

The effect of brown adipose tissue (BAT) sympathetic hemidenervation on the activity of glycerokinase (GyK) was investigated in different physiological conditions. In rats fed a balanced diet, the activity of the enzyme was ∼50% lower in BAT-denervated pads than in intact, innervated pads. In rats adapted to a high-protein, carbohydrate-free diet, norepinephrine turnover rates and BAT GyK activity were already reduced, and BAT denervation resulted in a further decrease in the activity of the enzyme. Cold acclimation of normally fed rats at 4°C for 10 days markedly increased the activity of the enzyme. Cold exposure (4°C) for 6 h was insufficient to stimulate BAT GyK, but the activity of the enzyme was already increased after 12 h of cold exposure. The cold-induced BAT GyK stimulation was completely blocked in BAT-denervated pads. The data indicate that an adequate sympathetic flow to BAT is required for the maintenance of normal levels of GyK activity and for the enzyme response to situations, such as cold exposure, which markedly increase BAT sympathetic flow.

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