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Endocrinology Vol. 144, No. 12 5293-5299
Copyright © 2003 by The Endocrine Society

Dual Effects of Pituitary Adenylate Cyclase-Activating Polypeptide and Isoproterenol on Lipid Metabolism and Signaling in Primary Rat Adipocytes

Lina Åkesson, Bo Ahrén, Vincent C. Manganiello, Lena Stenson Holst, Gudrun Edgren and Eva Degerman

Section for Molecular Signaling, Department of Cell and Molecular Biology (L.A., L.S.H., G.E., E.D.), Department of Medicine (B.A.), Lund University, SE-221 84 Lund, Sweden; and Pulmonary-Critical Care Medicine Branch (V.C.M.), National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892

Address all correspondence and requests for reprints to: Lina Åkesson, Biomedical Center C11, SE-221 84 Lund, Sweden. E-mail: lina.akesson{at}medkem.lu.se.


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Pituitary adenylate cyclase-activating peptide (PACAP) is a neuropeptide that exerts its effects throughout the body by elevating the intracellular amounts of cAMP. In adipocytes, an increased amount of cAMP is associated with increased lipolysis. In this work we evaluated the effects of PACAP38 on triglyceride metabolism in primary rat adipocytes. Stimulation of adipocytes with PACAP (0.1–100 nM) resulted in stimulation of lipolysis to the same extent as isoproterenol. Lipolysis was blocked by 25 µM of the protein kinase A inhibitor H-89 and potentiated in the presence of 10 µM OPC3911, a phosphodiesterase 3 inhibitor. In addition, PACAP38 induced activation of protein kinase A. Insulin efficiently inhibited PACAP38-induced lipolysis in a phosphatidyl inositol 3-kinase and phosphodiesterase 3-dependent manner. Interestingly, we also found that PACAP38, as well as isoproterenol, induced potentiation of lipogenesis in the presence of insulin. These results show that PACAP38 and isoproterenol mediate catabolic as well as anabolic effects in adipocytes, depending on the concentration of insulin present. We speculate that in the early postprandial state and during fasting, when insulin levels are low, PACAP and ß-adrenergic catecholamines induce lipolysis, whereas when higher levels of insulin are present, these agents potentiate the anabolic effect of insulin, i.e. storage of triglycerides.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
PITUITARY ADENYLATE CYCLASE-activating polypeptide (PACAP) is a neuropeptide belonging to the glucagon superfamily of hormones and was first identified in ovine hypothalamus (1, 2). It exists in two forms, PACAP27 and PACAP38, of which PACAP27 is an N-terminally truncated form of PACAP38 (3). PACAP is localized to the central nervous system as well as to peripheral nerves and exerts its effects through three different G protein-coupled receptors (GPCRs). One receptor is PACAP specific (PAC1), and the other two receptors, VPAC1 and VPAC2, have equal affinity for PACAP and another structurally related peptide, vasoactive intestinal peptide (4). PACAP mediates effects in several organs, generally by increasing the intracellular content of cAMP (5). Like glucagon-like peptide 1 (GLP-1), PACAP exerts a prominent effect on insulin secretion. Therefore PACAP is of interest in type 2 diabetes (6, 7). In the pancreas, PACAP is localized to nerves surrounding the blood vessels, the exocrine parenchyma and in conjunction with the endocrine islets (8, 9). It has been proposed that PACAP is released from parasympathetic nerves upon food intake (10, 11), and, by increasing the levels of cAMP in pancreatic ß-cells, PACAP potentiates glucose-stimulated insulin secretion (12, 13). Results from studies in PACAP-/- mice suggest a critical role for PACAP not only in insulin secretion but also through direct effects on metabolism of carbohydrates and lipids (14). Furthermore, PACAP has been shown to potentiate insulin-mediated glucose uptake in 3T3-L1 adipocytes (15) and to exert direct effects on the liver (16, 17). However, the direct effects of PACAP on adipose tissue and lipid metabolism are not known.

Elevated production of cAMP in adipocytes results in increased activity of protein kinase A (PKA). Activation of PKA is mainly induced by ß-adrenergic catecholamines and results in phosphorylation and activation of hormone-sensitive lipase (18). Activation of hormone-sensitive lipase leads to increased hydrolysis of stored triglycerides (lipolysis) and a subsequent release of glycerol and free fatty acids into the circulation (18). Lipolysis is efficiently inhibited by insulin, which under most conditions is mediated by the lowering of cAMP levels, leading to the inhibition of PKA (19, 20). The decreased cAMP is mainly the result of insulin-mediated phosphorylation and activation of phosphodiesterase 3B (PDE3B), the main cAMP-hydrolyzing enzyme in adipocytes (21, 22). Insulin-induced activation of PDE3B is a process dependent on active phosphatidyl inositol 3-kinase (PI3-K) and is suggested to include phosphorylation by protein kinase B (23, 24, 25, 26). It is possible that PACAP can modulate lipolysis because the PACAP receptors are expressed on adipocytes (27) and PACAP stimulation is linked to increased formation of cAMP in other cells (5).

In this study we used PACAP38 to analyze its effects on lipid metabolism in adipocytes. As a model we used primary adipocytes isolated from rat. We show that PACAP38 can mediate catabolic as well as anabolic effects in adipose cells. In the absence of insulin, PACAP38 increased lipolysis by activating PKA. However, in the presence of insulin, PACAP38-induced lipolysis was inhibited, and an ability of PACAP38 to potentiate lipogenesis was demonstrated. Interestingly, we found that isoproterenol, which is well characterized as a cAMP-increasing and lipolytic agent, also resulted in potentiation of insulin-induced lipogenesis.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Materials
OPC3911 was a kind gift from Otsuka Pharmaceutical Corp. (Tokyo, Japan). H-89 was purchased from BioMol (Helsingborg, Sweden). Wortmannin, protein kinase inhibitor, ATP, 2,5-diphenyl oxazole, 1,4-bis[5-phenyl-2-oxazolyl]benzene; 2,2'-p-phenylen-bis[5-phenyloxazole], kemptide phosphate acceptor peptide (Leu-Arg-Arg-Ala-Ser-Leu-Gly), 3-isobutyl-1-isobutylxanthine, and PACAP38 were from Sigma (Stockholm, Sweden). Glycerol-3-phosphate dehydrogenase, glycerokinase and nicotinamide adenine dinucleotide were all purchased from Roche (Stockholm, Sweden). 6-[3H]Glucose and [32P] were from Amersham Biosciences (Buckinghamshire, UK).

Animals
Male Sprague Dawley rats, 36 d of age, were obtained from B&K Universal (Stockholm, Sweden). The rats were maintained in a facility with controlled temperature and 12-h light, 12-h dark cycle. The rats were given free access to food and water. All experiments were approved by the Ethical Committee of Lund University.

Preparation of adipocytes
Epididymal fat pads were isolated and digested in collagenase and washed as described previously (28). Packed cell volume was determined by centrifuging adipocyte suspensions in hematocrit tubes. The adipocytes were resuspended in wash buffer [Krebs Ringers HEPES (KRH)] containing 25 mM HEPES (pH 7.5), 120 mM NaCl, 4.74 mM KCl, 1.19 mM KH2PO4, 1.19 mM MgSO4, 2.54 mM CaCl2, 1% BSA, 2 mM glucose, and 200 nM adenosine. In experiments in which H-89, OPC3911, or wortmannin was used, the cells were pretreated with 25 µM H-89, 10 µM OPC3911, or 100 nM wortmannin for 30 min before proceeding with the stimulations.

Lipolysis measurements
Glycerol release was measured as previously described (29). Briefly, a 5% cell suspension (in KRH) was incubated with agents as indicated in the figure legends. Incubations were stopped after 30 min of shaking (150 rpm, 37 C) and put on ice for 20 min. One milliliter of hydrazine buffer containing 50 mM glycine (pH 9.8), 0.05% hydrazine hydrate, 1 mM MgCl2 supplemented with 0.75 mg/ml ATP, 0.375 mg/ml nicotinamide adenine dinucleotide, 25 µg/ml glycerol-3-phosphate dehydrogenase, and 0.5 µg/ml glycerokinase was added to 200 µl of collected media. After incubation for 40 min in room temperature, OD340 was measured and glycerol release was calculated.

PKA assay
Adipocytes were suspended in KRH and diluted to 6% cell suspension. Stimulations were carried out as indicated in figure legends and stopped by adding 250 µl of ice-cold homogenization buffer containing 50 mM Tris (pH 7.4), 50 mM EDTA, 2 mM 3-isobutyl-1-isobutylxanthine, 50 µM OPC3911, 10 µg/ml antipain, 10 µg/ml leupeptin, and 1 µg/ml pepstatin. Samples were immediately homogenized on ice and subsequently centrifuged at 13,000 rpm for 10 min at 4 C. The fat cake and pellet were discarded, and 10 µl of the infranatants were incubated for 20 min at 30 C with 5 µl phosphorylation mix containing 20 mM Tris-EDTA-sucrose (pH 7.4), 50 mM MgSO4, 0.2 mM ATP, 5 mM dithioerythriol, 4 mg/ml substrate peptide (kemptide), and 5 µCi [{gamma}-32P]ATP with or without 10 µM protein kinase inhibitor (to correct for non-PKA activity). Sixteen micromoles per liter cAMP were used as a positive control to achieve maximal activation of PKA. The reactions were stopped by the addition of 10 µl 1% BSA and 1 mM ATP (pH 3.0) and precipitated with 10 µl of 31% trichloroacetic acid. Samples were left to precipitate for 15 min and then centrifuged at 10,000 rpm for 3 min at 4 C. Ten-microliter aliquots were then put on p81-membranes, and after drying they were washed three times with 75 mM H3PO4 and once with acetone. The amount of 32P incorporated was determined by scintillation counting.

Lipogenesis measurements
Adipocytes were prepared as described above but washed in KRH containing 0.55 mM glucose and 3.5% BSA but without adenosine. A 2% cell suspension was stimulated as indicated for 30 min with 0.4 µCi 6-[3H]glucose and stopped with a scintillation fluid containing 3 g/liter POPOP, 5 g/liter 2,5-diphenyl oxazole in toluol. The amount of 3H incorporated into the lipid-based fraction was determined by scintillation counting (30).

Statistical analysis
All data are presented as means ± SEM. The statistical analysis was carried out with unpaired Student’s t test. Statistical significance was defined as P < 0.05.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
The effect of PACAP38 on lipolysis and PKA activity
To study the effect of PACAP38 on lipolysis, freshly isolated adipocytes were incubated with 0.1–100 nM PACAP38 for 30 min. As a measure of lipolysis, glycerol accumulation in the medium was determined. Figure 1AGo shows that PACAP38 increased glycerol release in a dose-dependent manner. PACAP38 had no effect on lipolysis at 0.1 nM, whereas 1 nM PACAP38 induced an approximately 2-fold increase of lipolysis, compared with nonstimulated cells. At 10–100 nM PACAP38, glycerol release was increased approximately 6-fold, i.e. almost to the same extent as with the maximal dose of isoproterenol (30 nM). Over the same concentration range, the functionally related peptide GLP-1 had no effect on lipolysis (Fig. 1BGo). Next we examined whether PACAP38 stimulation of adipocytes results in activation of PKA. Figure 2Go shows that 100 nM PACAP38 activated PKA to the same extent as 30 nM isoproterenol, i.e. approximately 2-fold, compared with nonstimulated cells. We also investigated the role of PKA activation in PACAP38-mediated lipolysis by using the PKA inhibitor H-89. When pretreating adipocytes with 25 µM H-89, we found that PACAP38-induced lipolysis was completely abolished (Fig. 3Go).



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  		FIG. 1. Effect of PACAP38 and GLP-1 on lipolysis in adipocytes. Adipocytes were stimulated for 30 min with PACAP38 (A) or GLP-1 (B) both at 0.1, 1, 10, or 100 nM. Glycerol release was calculated and expressed as fold increase, compared with unstimulated cells. Data were presented as means ± SEM. Each condition was performed in triplicate in three independent experiments.

 


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  		FIG. 2. Effect of PACAP38 on PKA activity. Adipocytes were stimulated with 100 nM PACAP or 30 nM isoproterenol (Iso) for 1 min. PKA activity calculated and expressed as fold increase in PKA activity, compared with unstimulated cells (control). Statistical significance was assessed by Student’s t test and expressed as ***, P < 0.001. Data were presented as means ± SEM. Each condition was performed in duplicate in five independent experiments.

 


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  		FIG. 3. Effect of H-89 on PACAP38-induced lipolysis. Adipocytes were pretreated (open bars) or not (black bars) for 30 min with 25 µM H-89. The adipocytes were then stimulated as indicated for 30 min. Glycerol release was calculated and expressed as fold increase, compared with unstimulated cells (control). Data were presented as means ± SEM. Each condition was performed in triplicate in three independent experiments.

 
In agreement with previous results (31), we found that isoproterenol-induced stimulation of lipolysis was potentiated in the presence of a specific PDE3-inhibitor, OPC3911. Pretreatment of adipocytes with 10 µM OPC3911 followed by stimulation with 30 nM isoproterenol resulted in potentiation of lipolysis by about 30% (Fig. 4AGo). As shown in Fig. 4BGo, PACAP38-induced lipolysis was potentiated as well by about 30%, in the presence of OPC3911. This indicates that there is a functional coupling between degradation of cAMP by PDE3B, which is the PDE3 isoform present in adipocytes (21, 22), and PACAP38-induced formation of cAMP.



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  		FIG. 4. Effect of OPC3911 on isoproterenol- (A) and PACAP38-induced (B) lipolysis. Adipocytes were pretreated (open bars) or not (black bars) with 10 µM OPC3911 for 30 min. The adipocytes were then stimulated as indicated for 30 min. Glycerol release was calculated and expressed as fold increase, compared with unstimulated cells. Statistical significance of differences between samples treated or untreated with OPC3911 was assessed by Student’s t test and indicated as * (P < 0.05), ** (P < 0.01), or *** (P < 0.001). Data were presented as means ± SEM. Each condition was performed in triplicate in three independent experiments.

 
The effect of insulin on PACAP38-induced lipolysis
We also wanted to study the effects of insulin on PACAP38-induced lipolysis. Therefore, adipocytes were incubated for 30 min with 100 nM PACAP38 in the absence or presence of insulin (0.0017–1.7 nM), and glycerol accumulation was measured. As shown in Fig. 5Go, treatment of adipocytes with 0.17 nM insulin completely abolished lipolysis induced by 100 nM PACAP38.



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  		FIG. 5. Effects of insulin on PACAP38-induced lipolysis. Adipocytes were stimulated for 30 min with 100 nM PACAP38 and 0, 0.0017, 0.017, 0.170, or 1700 nM insulin (black bars). Glycerol release was calculated and expressed as fold increase, compared with unstimulated cells (ctrl, open bar). Data were presented as means ± SEM. Each condition was performed in triplicate in three independent experiments.

 
To determine whether the inhibitory effect of insulin on PACAP38-induced lipolysis was dependent on PI3-K, adipocytes were pretreated with 100 nM of the PI3-K inhibitor wortmannin for 30 min before stimulating cells with 100 nM PACAP and 1.7 nM insulin. As shown in Fig. 6AGo, the ability of insulin to antagonize PACAP-induced lipolysis was inhibited when cells were pretreated with wortmannin. No effect of wortmannin was detected on basal lipolysis or PACAP38-induced lipolysis (Fig. 6BGo). The critical role of PI3-K in insulin-mediated inhibition of PACAP-induced lipolysis was further established using another PI3-K inhibitor, LY294002. We found that 100 µM LY294002 completely prevented the ability of 1.7 nM insulin to inhibit lipolysis induced by 100 nM PACAP or 30 nM isoproterenol (Fig. 6CGo). To further evaluate the mechanism underlying the inhibitory effect of insulin on PACAP-induced lipolysis, adipocytes were preincubated for 20 min with 10 µM of PDE3 inhibitor OPC3911. As shown in Fig. 6DGo, OPC3911 was able to restore lipolysis inhibited by insulin.



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  		FIG. 6. Effects of wortmannin, LY294002, or OPC3911 on insulin inhibition of PACAP38-induced lipolysis. A, Adipocytes were stimulated with 100 nM PACAP38 (black bar), PACAP38 together with 1.7 nM insulin (open bar), or preincubated with 100 nM wortmannin for 30 min followed by stimulation with 100 nM PACAP38 and 1.7 nM insulin (striped bar). B, Adipocytes were preincubated with 100 nM wortmannin for 30 min (black bars) or not (open bars) followed by stimulation with 0.1–100 nM PACAP38. C, Adipocytes were incubated with 100 nM PACAP38 or 30 nM isoproterenol (black bars) for 30 min, PACAP38 or isoproterenol together with 1.7 nM insulin for (open bars), or preincubated with 100 µM LY294002 for 30 min followed by stimulation with 100 nM PACAP or 30 nM isoproterenol together with 1.7 nM insulin (striped bars). D, Adipocytes were treated with 100 nM PACAP38 (black bar), PACAP38 together with 1.7 nM insulin (open bar), or preincubated with 10 µM OPC3911 for 30 min followed by stimulation with 1.7 nM insulin and 100 nM PACAP38 (striped bar). Control cells were left unstimulated (black bar), treated with 1.7 nM insulin (open bar), or preincubated with 10 µM OPC3911 for 30 min followed by stimulation with 1.7 nM insulin (striped bar). In A–D, glycerol release was calculated and expressed as fold increase, compared with unstimulated cells (control, black bar). Statistical analysis was assessed with Student’s t test and indicated as ***, P < 0.001, and nonsignificant differences were indicated as NS. Data were presented as means ± SEM. Each condition was performed in triplicate in three independent experiments.

 
The effect of PACAP38 on lipogenesis
Previous reports show an anabolic effect of PACAP38 on 3T3-L1 adipocytes in the presence of insulin (15). Therefore, we studied the effect of PACAP38 and isoproterenol on lipogenesis in adipocytes. Adipocytes were incubated for 30 min with 100 nM PACAP38 or 30 nM isoproterenol in the presence or absence of 1.7 nM insulin. Figure 7AGo demonstrates that lipogenesis was not affected by PACAP38 or isoproterenol alone. However, in the presence of insulin, both PACAP38 and isoproterenol potentiated lipogenesis by 30% and 45%, respectively.



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  		FIG. 7. Effect of PACAP38 and isoproterenol on lipogenesis. Adipocytes were stimulated with 1.7 nM insulin (open bars) or without insulin (black bars). In addition, samples were treated with 30 nM isoproterenol (iso) or 100 nM PACAP38 for 30 min as indicated. The amount of 6-[3H]glucose incorporated into lipids was determined by scintillation counting. Incorporation is expressed as fold increased lipogenesis, compared with unstimulated cells (control, black bar). Statistical analysis was assessed using Student’s t test where **, P < 0.03, and nonsignificant differences were indicated as NS. Data were presented as means ± SEM. Each condition was performed in triplicate in three independent experiments.

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
It has previously been shown that disruption of the PACAP gene in mice results in early postnatal death and abnormal regulation of insulin secretion (14). The same study suggested a role for PACAP in carbohydrate and lipid metabolism. Although a few studies have shown that PACAP can directly regulate carbohydrate metabolism in 3T3-L1 adipocytes and liver, very little is known regarding direct effects of PACAP on carbohydrate and lipid metabolism (15, 16, 17). PACAP is known to increase cAMP levels in several tissues (5). Because cAMP has a critical role in the regulation of adipocyte lipolysis (19, 20), stimulation of PACAP receptors on adipocytes (27) is expected to lead to increased lipolysis. In agreement with this hypothesis, we found that PACAP38 was able to stimulate lipolysis in a dose-dependent manner in primary rat adipocytes. Our findings that PACAP38 activated PKA and that the PKA-inhibitor H-89 blocked the PACAP38-induced lipolysis support an important role for PKA in this lipolytic process.

The inhibiting effect of insulin on isoproterenol-induced lipolysis has previously been shown to involve PI3-K and PDE3B (22, 23). We found that also PACAP38-induced lipolysis was efficiently inhibited by insulin in a PI3-K- and PDE3B-dependent manner. Based on the finding that inhibition of PDE3B resulted in potentiated lipolysis, PDE3B appears to be directly involved in PACAP38-induced signaling, apart from participating in insulin-induced inhibition of lipolysis. It has been reported that PDE3B is activated by PKA following isoproterenol stimulation and thereby involved in negative feedback regulation of cAMP and lipolysis (32). Thus, our data support that PACAP38-mediated cAMP production is subject to such feedback regulation.

In this work we present new data that both PACAP38 and isoproterenol potentiated insulin-induced lipogenesis. The fact that these effects are observed in the presence of insulin, a condition under which PACAP-induced lipolysis is inhibited, argues against the possibility that we measure increased triglyceride turnover instead of lipogenesis. Instead, it is more likely that the increased lipogenesis observed is a consequence of PACAP-induced potentiation of insulin-mediated glucose uptake (15). In addition, dual effects of isoproterenol have previously been observed in adipocytes (33). Isoproterenol alone was shown to decrease leptin secretion, whereas isoproterenol potentiated the ability of insulin to stimulate leptin secretion. The mechanisms underlying the potentiating effects of PACAP38 and isoproterenol on lipogenesis are unknown; however, the lipogenic effect of insulin in primary rat adipocytes has previously been shown to be mediated by PI3-K (34). Furthermore, PACAP has been shown to activate PI3-K in 3T3-L1 adipocytes in the presence of insulin (15). There are also reports showing that ß-adrenergic receptors can couple to tyrosine kinase signaling pathways normally activated by growth factors (35). According to previous studies performed in adipocytes, ß-adrenergic receptors have been shown to couple to different pathways. For instance, MAPK cascades have been shown to be activated in PKA-dependent as well as PKA-independent manners, in response to stimulation of ß-adrenergic receptors (36, 37). Thus, stimulation of such receptors with PACAP and isoproterenol leading to potentiation of insulin-induced lipogenesis may involve cross-talk with the PI3-K signaling pathway.

The potentiating effects of PACAP38 and isoproterenol on insulin-induced lipogenesis also suggest that these cAMP-increasing agents, in addition to their catabolic effect, have anabolic influences on adipocytes. These dual effects of PACAP38 could be of physiological importance during fasting and postprandial phases. Increased release of free fatty acids from adipose tissue, in response to a lipolytic effect of PACAP38, could help optimizing the glucose-stimulated insulin secretion when insulin levels are low (38). However, in the presence of insulin, the lipolytic effect of PACAP38 is blocked and PACAP38 could then participate in the stimulation of lipogenesis via activation of PI3-K. There are several insulinotropic peptides released after food intake that have been shown to have multiple effects on adipocytes. GLP-1 has been shown to induce glucose uptake and lipogenesis in adipocytes, although the results concerning the lipolytic effect of GLP-1 are conflicting. This study shows that GLP-1 has no lipolytic effect, which is in accordance with some previous studies (39, 40) but in contrast to others (41, 42). Furthermore, glucose-dependent insulinotropic polypeptide, another PACAP-related peptide released after food intake, has also been shown to have anabolic as well as catabolic effect on adipocytes (43, 44).

The effects of PACAP on adipocytes were obtained at rather high concentrations of the peptide. The lipolytic and lipogenic effects of PACAP in vitro were detected at concentrations approximately 1 nM and were maximal at 10 nM. It has been shown that circulating levels of PACAP are very low, most likely less than 10 pM (45), although local concentrations could be higher. Therefore, because PACAP is a neuropeptide present in peripheral nerves, it is conceivable that the physiological effects of PACAP on adipocytes are mediated via neuronal stimulation rather than circulation. However, it remains to be elucidated whether PACAP is present in nerve endings in adipose tissue.

In summary, we provide evidence that PACAP38 has a lipolytic effect in adipocytes that is inhibited by insulin in a PI3-K and PDE3B-dependent manner. We also report that PACAP38 and isoproterenol are able to potentiate insulin-induced lipogenesis. These results suggest an important role for PACAP38 and cAMP-elevating agents in the regulation of adipose tissue metabolism, exhibiting both catabolic effects by increasing lipolysis and anabolic effects by increasing fat storage. However, the physiological relevance of PACAP in vivo is subject for future evaluation.


   Footnotes
 
This work was supported by the Swedish Research Council Project 3362 (to E.D.) and 6834 (to B.A.); the Swedish Diabetes Association; the A. Påhlsson, M. Bergvall, and Å. Wiberg Foundations; Center of Excellence Grant from the Juvenile Diabetes Foundation; the Knut and Alice Wallenbergs Foundation; Novo Nordisk (Denmark); the Dr. P. Håkansson’s Foundation; and the Swedish Society of Medicine.

Abbreviations: GLP-1, Glucagon-like peptide 1; KRH, Krebs Ringers HEPES; PACAP, pituitary adenylate cyclase-activating polypeptide; PDE3B, phosphodiesterase 3B; PI3-K, phosphatidylinositol 3-kinase; PKA, protein kinase A.

Received March 25, 2003.

Accepted for publication August 18, 2003.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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L. Akesson, B. Ahren, G. Edgren, and E. Degerman
VPAC2-R Mediates the Lipolytic Effects of Pituitary Adenylate Cyclase-Activating Polypeptide/Vasoactive Intestinal Polypeptide in Primary Rat Adipocytes
Endocrinology, February 1, 2005; 146(2): 744 - 750.
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