scholarly journals Mechanisms of leptin secretion from white adipocytes

2002 ◽  
Vol 283 (1) ◽  
pp. C244-C250 ◽  
Author(s):  
Philippe G. Cammisotto ◽  
Ludwik J. Bukowiecki
Keyword(s):  
Intracellular Camp ◽  
Adenylate Cyclase System ◽  
Inhibitory Effects ◽  
High Affinity ◽  
White Adipocytes ◽  
Selective Antagonists ◽  
Camp Levels ◽  
Lipolytic Hormones ◽  
Phosphodiesterase Iii ◽  
Stimulation Of

The mechanisms regulating leptin secretion were investigated in isolated rat white adipocytes. Insulin (1–100 nM) linearly stimulated leptin secretion from incubated adipocytes for at least 2 h. The adrenergic agonists norepinephrine, isoproterenol (two nonselective β-agonists), or CL-316243 (potent β3) all inhibited insulin (10 nM)-stimulated leptin release. The inhibitory effects of norepinephrine and isoproterenol could be reversed not only by the nonselective antagonist propranolol but also by the selective antagonists ICI-89406 (β1) or ICI-118551 (β2), the β2-antagonist being less effective than the β1. Insulin-stimulated leptin secretion could also be inhibited by a series of agents increasing intracellular cAMP levels, such as lipolytic hormones (ACTH and thyrotropin-stimulating hormone), various nonhydrolyzable cAMP analogs, pertussis toxin, forskolin, methylxanthines (caffeine, theophylline, IBMX), and specific inhibitors of phosphodiesterase III (imazodan, milrinone, and amrinone). Significantly, antilipolytic agents other than insulin (adenosine, nicotinic acid, acipimox, and orthovanadate) did not mimic the acute stimulatory effects of insulin on leptin secretion under these conditions. We conclude that norepinephrine specifically inhibits insulin-stimulated leptin secretion not only via the low-affinity β3-adrenoceptors but also via the high-affinity β1/β2-adrenoceptors. Moreover, it is suggested that 1) activation of phosphodiesterase III by insulin represents an important metabolic step in stimulation of leptin secretion, and 2) lipolytic hormones competitively counterregulate the stimulatory effects of insulin by activating the adenylate cyclase system.

Interaction of adenosine with vasopressin in the inner medullary collecting duct

1990 ◽  
Vol 259 (4) ◽  
pp. F679-F687 ◽  
Author(s):  
Y. Yagil
Keyword(s):  
Pertussis Toxin ◽  
Receptor Agonist ◽  
Collecting Duct ◽  
Phosphodiesterase Inhibitor ◽  
Inhibitory Effects ◽  
Inner Medullary Collecting Duct ◽  
Medullary Collecting Duct ◽  
Camp Levels ◽  
Dose Dependent ◽  
Stimulation Of

Administration of adenosine (Ado) into rat renal artery induces dose-dependent diuresis that is independent of changes in glomerular filtration rate or renal blood flow, suggesting a direct effect on tubule H2O reabsorption. To test the hypothesis that Ado modulates cellular action of arginine vasopressin (AVP) as a tubular mechanism for the diuretic effect of Ado, interaction of Ado with AVP was studied in primary cell culture of rat inner medullary collecting duct (IMCD) epithelium. Stimulation of cells with 10(-6) M AVP in presence of 0.1 mM Ro 20-1724, a nonmethylxanthine phosphodiesterase inhibitor that has no effect on Ado receptors, increased adenosine 3',5'-cyclic monophosphate (cAMP) levels twofold or more above baseline. Stimulation of cells with the A1 Ado-receptor agonist N6-cyclohexyladenosine (CHA), the A2-receptor agonist 5'-(N-ethylcarboxamido)-adenosine (NECA), or with the P-site agonist 2',5'-dideoxyadenosine (DDA) significantly inhibited the AVP-stimulated cAMP response. Preincubation with pertussis toxin abolished the inhibitory effects of CHA and NECA, but not of DDA. The data suggest that, in the rat IMCD, Ado modulates AVP action by interfering with its ability to stimulate formation of its second messenger, cAMP. This effect is mediated by the extracellular Ado receptors A1 and A2 and by the intracellular P-site. It occurs by at least two pathways, one sensitive and the other insensitive to pertussis toxin.

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.

The thienopyridine ticlopidine selectively prevents the inhibitory effects of ADP but not of adrenaline on cAMP levels raised by stimulation of the adenylate cyclase of human platelets by PGE1

1990 ◽  
Vol 40 (12) ◽  
pp. 2683-2687 ◽  
Author(s):  
Christian Gachet ◽  
Jean-Pierre Cazenave ◽  
Philippe Ohlmann ◽  
Cyrille Bouloux ◽  
Ghyslain Defreyn ◽  
...  
Keyword(s):  
Adenylate Cyclase ◽  
Human Platelets ◽  
Inhibitory Effects ◽  
Camp Levels ◽  
Stimulation Of

scholarly journals Changes in gene expression in the Ras/adenylate cyclase system of Saccharomyces cerevisiae: correlation with cAMP levels and growth arrest.

1993 ◽  
Vol 4 (7) ◽  
pp. 757-765 ◽  
Author(s):  
M Russell ◽  
J Bradshaw-Rouse ◽  
D Markwardt ◽  
W Heideman
Keyword(s):  
Gene Expression ◽  
Saccharomyces Cerevisiae ◽  
Adenylate Cyclase ◽  
Oxidative Metabolism ◽  
Growth Arrest ◽  
Intracellular Camp ◽  
Adenylate Cyclase System ◽  
Diauxic Shift ◽  
Yeast Saccharomyces Cerevisiae ◽  
Camp Levels

Levels of cyclic 3',5'-cyclic monophosphate (cAMP) play an important role in the decision to enter the mitotic cycle in the yeast, Saccharomyces cerevisiae. In addition to growth arrest at stationary phase, S. cerevisiae transiently arrest growth as they shift from fermentative to oxidative metabolism (the diauxic shift). Experiments examining the role of cAMP in growth arrest at the diauxic shift show the following: 1) yeast lower cAMP levels as they exhaust their glucose supply and shift to oxidative metabolism of ethanol, 2) a reduction in cAMP is essential for traversing the diauxic shift, 3) the decrease in adenylate cyclase activity is associated with a decrease in the expression of CYR1 and CDC25, two positive regulators of cAMP levels and an increase in the expression of IRA1 and IRA2, two negative regulators of intracellular cAMP, 4) mutants carrying disruptions in IRA1 and IRA2 were unable to arrest cell division at the diauxic shift and were unable to progress into the oxidative phase of growth. These results indicate that changes cAMP levels are important in regulation of growth arrest at the diauxic shift and that changes in gene expression plays a role in the regulation of the Ras/adenylate cyclase system.

scholarly journals Adenosine 3':5'-monophosphate content and actions in the division cycle of synchronized HeLa cells.

1976 ◽  
Vol 71 (2) ◽  
pp. 515-534 ◽  
Author(s):  
C E Zeilig ◽  
R A Johnson ◽  
E W Sutherland ◽  
D L Friedman
Keyword(s):  
Cell Cycle ◽  
Cyclic Amp ◽  
Hela Cells ◽  
S Phase ◽  
Intracellular Camp ◽  
Specific Effects ◽  
Low Concentrations ◽  
High Concentrations ◽  
Camp Levels ◽  
Stimulation Of

The involvement of adenosine 3':5'-monophosphate (cAMP) in the regulation of the cell cycle was studied by determining intracellular fluctuations in cAMP levels in synchronized HeLa cells and by testing the effects of experimentally altered levels on cell cycle traverse. Cyclic AMP levels were lowest during mitosis and were highest during late G-1 or early S phase. These findings were supported by results obtained when cells were accumulated at these points with Colcemid or high levels of thymidine. Additional fluctuations in cAMP levels were observed during S phase. Two specific effects of cAMP on cell cycle traverse were found. Elevation of cAMP levels in S phase or G-2 caused arrest of cells in G-2 for as long as 10 h and lengthened M. However, once cells reached metaphase, elevation of cAMP accelerated the completion of mitosis. Stimulation of mitosis was also observed after addition of CaCl2. The specificity of the effects of cAMP was verified by demonstrating that: (a) intracellular cAMP was increased after exposure to methylisobutylxanthine (MIX) before any observed effects on cycle traverse; (b) submaximal concentrations of MIX potentiated the effects of isoproterenol; and (c) effects of MIX and isoproterenol were mimicked by 8-Br-cAMP. MIX at high concentrations inhibited G-1 traverse, but this effect did not appear to be mediated by cAMP. Isoproterenol slightly stimulated G-1 traverse and partially prevented the MIX-induced delay. Moreover, low concentrations of 8-Br-cAMP (0.10-100 muM) stimulated G-1 traverse, whereas high concentrations (1 mM) inhibited. Both of these effects were also observed with the control, Br-5'-AMP, at 10-fold lower concentrations.

REGULATION OF CYCLIC NUCLEOTIDE PHOSPHODIESTERASE ACTIVITY IN PLATELETS BY PHOSPHORYLATION

1987 ◽  
Author(s):  
P G Grant ◽  
A F Mannarino ◽  
R W Colman
Keyword(s):  
Protein Kinase ◽  
Cyclic Nucleotide ◽  
Kinase Inhibitor ◽  
Specific Activity ◽  
Intracellular Camp ◽  
Blue Dextran ◽  
Dependent Protein ◽  
Camp Levels ◽  
Hydrolysis Of ◽  
Stimulation Of

Cyclic nucleotide phosphodiesterases (PDE) provide the only known pathway for the hydrolysis of cyclic nucleotides in cells and thus have the potential for modulating the effects of cAMP and cGMP on cells. In platelets a rise in intracellular cAMP levels inhibits platelet aggregation and secretion. Since cAMP exerts many of its effects through a cAMP-dependent kinase we questioned whether phosphorylation of cAMP PDE might be a mode for regulation of PDE activity in platelets. When platelets were incubated for 10 min with forskolin (100 μM) the level of cAMP rose at least 10-fold.When the low Km cyclic nucleotide PDE was isolated from freeze-thaw lysates of forskolin treated platelets by chromatography on blue dextran-Sepharose, the specific activity of this enzyme was increased 3 to 13-fold over similarly processed control platelets. The specific activity of a second PDE, the cGMP-stimulated cAMP PDE, was increased 1.5 to 3-fold by forskolin treatment of platelets. Forskolin had no direct effect on either purified PDE. The stimulation of the low Km cAMP PDE activity by exposure of platelets to forskolin was blocked when the platelets were simultaneously treated with the protein kinase inhibitor H-8 (100 μM) which is most potent toward cAMP dependent protein kinase indicating that this kinase may be responsible for the stimulation. When platelets which had been prelabeled with 32P inorganic phosphate were treated with forskolin and the low Km cAMP PDE isolated by blue dextran-Sepharose chromatography, a protein migrating in SDS gels at Mr=110,000, the molecular weight of the low Km cAMP PDE, was labeled indicating that phosphorylation of the PDE occurred coincident with stimulation of activity. These results suggest that phosphorylation of the low Km cAMP PDE by protein kinase may be an important regulatory mechanism for cAMP PDE activity and cyclic nucleotide levels in platelets.

Forskolin and thyrotrophin stimulation of rat FRTL-5 thyroid cell growth: the role of cyclic AMP

1987 ◽  
Vol 114 (2) ◽  
pp. 199-205 ◽  
Author(s):  
P. A. Ealey ◽  
C. A. Ahene ◽  
J. M. Emmerson ◽  
N. J. Marshall
Keyword(s):  
Cyclic Amp ◽  
Dose Range ◽  
Phosphodiesterase Inhibitor ◽  
Lag Phase ◽  
Thyroid Cell ◽  
Intracellular Camp ◽  
Camp Levels ◽  
Tsh Stimulation ◽  
Stimulation Of

ABSTRACT The adenylate cyclase stimulator forskolin increases intracellular cyclic AMP (cAMP) in rat FRTL-5 cells within minutes and, after a lag phase of 20–24 h, an increase of cells in metaphase is seen. The dose– response relationships were similar in both systems, with significant increases in the number of metaphases observed at ∼0·1 μmol/l and a doubling of cAMP levels at 1 μmol/l, whilst doses of 0·1 mmol/l and above proved cytotoxic. An involvement of intracellular cAMP as a positive intermediate in cell division was further suggested by the finding that a low dose of forskolin (0·1 μmol/l) potentiated TSH stimulation of mitosis. Isobutyl methyl xanthine (IBMX), a phosphodiesterase inhibitor, also acted as a mitogen and potentiated TSH action. Moreover, the simultaneous inclusion of low doses of IBMX and forskolin additionally potentiated TSH stimulation of mitosis. An analogue of cAMP, dibutyryl cAMP, also stimulated mitosis and acted over a restricted dose range, with maximal stimulation at 1 mmol/l. We conclude that cAMP may act as a positive signal for FRTL-5 thyroid cell proliferation. J. Endocr. (1987) 114, 199–205

Stimulation of glucose transport in rat adipocytes by calcium

1979 ◽  
Vol 57 (6) ◽  
pp. 692-699 ◽  
Author(s):  
Wayne M. Taylor ◽  
Lena Hau ◽  
Mitchell L. Halperin
Keyword(s):  
Glucose Transport ◽  
Maximum Velocity ◽  
Pentose Phosphate ◽  
Calcium Flux ◽  
Intracellular Camp ◽  
Rat Adipocytes ◽  
Phosphorylation Mechanism ◽  
Rate Limiting ◽  
Camp Levels ◽  
Stimulation Of

Glucose transport in rat adipocytes was studied by monitoring the conversion of [1-14C]-glucose to 14CO2 in a system where glucose transport was made rate-limiting by increasing the flux through the pentose phosphate pathway with phenazine methosulphate, an agent which rapidly reoxidizes NADPH. Calcium increased both basal and insulin-stimulated apparent rates of glucose transport by approximately 40%. The maximum velocity of the apparent rate of glucose transport was increased by extracellular calcium both in the presence or absence of insulin. There was no change in the glucose concentration required for half-maximal rates of 14CO2 production. Calcium also enhanced the stimulation of apparent rates of glucose transport by insulin when examined over a range of hormone concentrations. Adipocyte cAMP concentrations were significantly lowered by calcium under conditions which led to increased apparent rates of glucose transport. In contrast, cobalt and nickel, antagonists of calcium action, elevated adipocyte cAMP levels and inhibited apparent rates of glucose transport. Agents which inhibit transmembrane calcium flux (verapamil, tetracaine, and procaine) inhibited apparent rates of glucose transport despite a reduction in adipocyte cAMP concentration.On the basis of the above data we suggest that calcium may increase apparent rates of glucose transport in rat adipocytes both by lowering intracellular cAMP concentration and by a further mechanism independent of changes in the level of cAMP. These results are consistent with the hypothesis that glucose transport in rat adipocytes may be controlled, in part, by a cAMP-induced phosphorylation mechanism.

Xanthine derivatives without PDE effect stimulate voltage-activated chloride conductance of toad skin

2003 ◽  
Vol 284 (2) ◽  
pp. C521-C527 ◽  
Author(s):  
Wolfram Nagel ◽  
Uri Katz
Keyword(s):  
Intracellular Camp ◽  
Voltage Sensitivity ◽  
Inhibitory Effects ◽  
Amphibian Skin ◽  
Toad Skin ◽  
Camp Content ◽  
Xanthine Derivatives ◽  
X 32 ◽  
Intracellular Camp Content ◽  
Stimulation Of

The effect of xanthine derivatives on the voltage-activated Cl− conductance ( G Cl) of amphibian skin was analyzed. 3-Isobutyl-1-methylxanthine (IBMX) and the recently synthesized xanthine derivatives 3,7-dimethyl-1-propyl xanthine (X-32) and 3,7-dimethyl-1-isobutyl xanthine (X-33), which lack inhibitory effects on phosphodiesterases in CHO and Calu-3 cells, increased voltage-activated G Cl without effect on baseline conductance at inactivating voltage. Half-maximal stimulation of G Cl occurred at 108 ± 9 μM for X-32 and X-33 after apical or basolateral application. The stimulation of G Cl, which occurs only in the presence of Cl− in the mucosal solution, is caused by a shift of the voltage sensitivity to lower clamp potentials and an increase of the maximally activated level. Furosemide reversed both the shift of sensitivity and the increase in magnitude. These patterns are fundamentally different from those seen after application of membrane-permeant, nonmetabolized analogs of cAMP, and they indicate that the xanthines stimulate G Cl directly. This notion is strengthened by the lack of influence on intracellular cAMP content, which is consistent with the observations in CHO and Calu-3 cells. We propose that the xanthine derivatives increase the voltage sensitivity of a regulative component in the conductive Cl− pathway across amphibian skin.

scholarly journals Phosphorylation of the Receptor for PTH and PTHrP Is Required for Internalization and Regulates Receptor Signaling

2002 ◽  
Vol 16 (1) ◽  
pp. 1-13 ◽  
Author(s):  
Hesham A. W. Tawfeek ◽  
Fang Qian ◽  
Abdul B. Abou-Samra
Keyword(s):  
Direct Sequencing ◽  
Site Directed Mutagenesis ◽  
Intracellular Camp ◽  
Serine Residue ◽  
Increased Sensitivity ◽  
Carboxyl Terminal ◽  
Phosphopeptide Mapping ◽  
Pthrp Receptor ◽  
Camp Levels ◽  
Stimulation Of

Abstract We have previously shown that agonist-dependent phosphorylation of the PTH/PTHrP receptor occurs on its carboxyl-terminal tail. Using site- directed mutagenesis, phosphopeptide mapping, and direct sequencing of cyanogen bromide-cleaved fragments of phosphoreceptors, we report here that PTH-dependent phosphorylation occurs on the serine residues at positions 491, 492, 493, 495, 501, and 504, and that the serine residue at position 489 is required for phosphorylation. When these seven sites were mutated to alanine residues, the mutant receptor was no longer phosphorylated after PTH stimulation. The phosphorylation-deficient receptor, stably expressed in LLCPK-1 cells, was impaired in PTH-dependent internalization and showed an increased sensitivity to PTH stimulation; the EC50 for PTH-stimulated cAMP accumulation was decreased by 7-fold. Furthermore, PTH stimulation of the phosphorylation-deficient PTH/PTHrP receptor caused a sustained elevation in intracellular cAMP levels. These data indicate that agonist-dependent phosphorylation of the PTH/PTHrP receptor plays an important role in receptor function.

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