Serum Levels of Copeptin are Decreased in Gestational Diabetes Mellitus.

OBJECTIVE: Copeptin, the c-terminal part of pro-Arginine vasopressin, has recently been introduced as a novel risk factor to develop facets of the metabolic syndrome. However, regulation of copeptin in pregnancy-associated metabolic disease, i. e., gestational diabetes mellitus (GDM), has not been fully understood, so far. PATIENTS AND MEASUREMENTS: For this study, 74 GDM patients and 74 healthy, pregnant, age-, body mass index-, and gestational age-matched controls were recruited. Serum levels of copeptin were quantified by an illuminometric assay. Furthermore, copeptin concentrations were correlated to biochemical and anthropometric markers of obesity, glucose and lipid metabolism, renal function, and inflammation. RESULTS: Median [interquartile range] serum copeptin levels were significantly lower in subjects with GDM (3.5 [2.0] pmol/l) as compared to controls (4.4 [3.2] pmol/l) (p<0.05). Furthermore, GDM remained an independent predictor of circulating copeptin in multivariate regression analysis (p<0.05). Moreover, copeptin was independently associated with gestational age at blood sampling (p<0.05). CONCLUSIONS: Copeptin serum levels are significantly lower in GDM as compared to healthy pregnant controls. Further studies are needed to better clarify the pathophysiological role of copeptin in GDM.

Circulating angiopoietin-like protein 8 is independently associated with fasting plasma glucose and type 2 diabetes mellitus.

OBJECTIVE: Angiopoietin-like protein 8 (Angptl8) has recently been introduced as a novel adipokine/hepatokine that promotes pancreatic ß-cell proliferation and improves glucose tolerance in mouse models of insulin resistance. However, regulation of Angptl8 in human type 2 diabetes mellitus (T2DM) and renal dysfunction has not been determined. RESEARCH DESIGN AND METHODS: Serum Angptl8 levels were quantified by ELISA in 62 patients with T2DM as compared with 58 nondiabetic subjects in vivo. Within both groups, about half of the patients were on chronic hemodialysis or had an estimated glomerular filtration rate above 50 mL/min/1.73 m(2). Furthermore, we investigated the effect of insulin and differentiation on Angptl8 mRNA expression in 3T3-L1 adipocytes in vitro. RESULTS: Median [interquartile range] serum Angptl8 levels were higher in patients with T2DM (1.19 [0.37] µg/L) as compared with nondiabetic subjects (1.03 [0.47] µg/L) (P = .005). Furthermore, the adipokine/hepatokine was significantly higher in women (1.21 [0.47] µg/L) as compared with men (1.05 [0.44] µg/L]) (P = .013). In multivariate analysis, fasting glucose and T2DM but not renal function remained independent and positive predictors of circulating Angptl8 even after adjustment for markers of obesity, lipid status, and inflammation (P < .05). Furthermore, Angptl8 mRNA expression was induced by insulin and during adipogenesis in 3T3-L1 adipocytes in vitro. CONCLUSIONS: Circulating Angptl8 is positively and independently associated with T2DM and fasting glucose in vivo. Furthermore, Angptl8 mRNA expression is induced by insulin and during adipogenesis in 3T3-L1 adipocytes in vitro.

Circulating adipocyte fatty acid binding protein is increased in chronic and acute renal dysfunction.

BACKGROUND AND AIMS: The adipokine adipocyte fatty acid binding protein (AFABP) is positively associated with the development of the metabolic syndrome, diabetes mellitus, and cardiovascular disease. We hypothesized that AFABP also increases with deteriorating renal function. METHODS AND RESULTS: Serum AFABP levels were quantified by enzyme linked immunosorbent assay in 532 patients with chronic kidney disease (CKD) covering the whole spectrum of estimated glomerular filtration rate (eGFR) categories from G1 to G5 (study population 1). Furthermore, AFABP was measured in 32 patients before and within 30 h after elective unilateral nephrectomy, a model of acute kidney dysfunction (AKD) (study population 2). Moreover, circulating AFABP was investigated in rats undergoing bilateral nephrectomy (BNE) as compared to sham-operated animals. Median serum AFABP levels adjusted for age, gender, and body mass index significantly increased with increasing eGFR category (G1: 22.0 µg/l; G2: 34.6 µg/l; G3: 56.7 µg/l; G4: 95.2 µg/l; and G5: 173.9 µg/l). Furthermore, renal dysfunction remained positively associated with AFABP in multivariate analysis in this cohort. In patients undergoing unilateral nephrectomy, AFABP increased significantly after surgery (42.1 µg/l) as compared to pre-surgical values (29.3 µg/l). Furthermore, relative changes of post-to-pre-surgical AFABP levels were independently associated with relative changes of post-to-pre-surgical creatinine concentrations. After BNE in rats, AFABP increased significantly as compared to sham-operated animals. CONCLUSIONS: We show that AFABP is significantly elevated in CKD and AKD patients. Furthermore, measures of renal function are associated with circulating AFABP. Moreover, animal experiments indicate that AFABP levels strongly depend on renal function.

Serum levels of fractalkine are associated with markers of insulin resistance in gestational diabetes.

AIMS: Fractalkine has recently been introduced as an adipokine that improves glucose tolerance. Regulation of fractalkine in gestational diabetes, as well as its association with markers of obesity, glucose and lipid metabolism, inflammation and renal function, has not been elucidated. METHODS: Circulating fractalkine was quantified by enzyme-linked immunosorbent assay in 74 women with gestational diabetes and 74 healthy, pregnant control subjects matched for age, BMI, and gestational age. RESULTS: Median (interquartile range) levels of fractalkine were not significantly different between the two groups [gestational diabetes: 2.24 (2.16) µg/l; control: 2.45 (1.38) µg/l] (P = 0.461). In multivariate linear regression analysis, fractalkine remained independently associated with homeostasis model assessment of insulin resistance (ß = -0.253, P = 0.002) and the proinflammatory adipokine progranulin (ß = 0.218, P = 0.007). CONCLUSIONS: Circulating fractalkine is not different between women with gestational diabetes and control subjects, but the adipokine is independently associated with markers of insulin resistance and proinflammatory progranulin in pregnancy.

Adipocyte fatty acid-binding protein is released from adipocytes by a non-conventional mechanism.

Adipocyte fatty acid-binding protein (AFABP) is an adipokine, which induces insulin resistance. However, AFABP does not possess any secretion-directed signals and the mechanisms for AFABP release have not been thoroughly assessed so far. In the current study, mechanisms for AFABP secretion were elucidated in 3T3-L1 adipocytes in vitro in the presence or absence of hormonal stimulation, calcium ionophore and secretion inhibitors by cell fractionation experiments, immunoblotting and ELISAs. We demonstrate that AFABP secretion is upregulated during adipocyte differentiation. AFABP secretion is not influenced by treatment with protein secretion inhibitors that block vesicular traffic at the endoplasmic reticulum and the Golgi apparatus. AFABP is secreted partially by adipocyte-derived microvesicles (ADMs), an established mechanism for unconventional secretion from adipocytes. Both total and ADM-secreted AFABP are downregulated by insulin and upregulated by the calcium ionophore ionomycin. Furthermore, murine RAW 264.7 macrophages secrete AFABP and AFABP release from these cells is upregulated by lipopolysaccharide treatment. Taken together, these results suggest that AFABP is actively released by unconventional mechanisms and by ADMs from 3T3-L1 adipocytes. Furthermore, AFABP secretion from fat cells is regulated by insulin and intracellular calcium.

Different associations of adipokines in lean and healthy adults.

Regulation of adipokines in lean adults without metabolic disease and without eating disorders has not been comprehensively elucidated. We hypothesized that some of the established associations of these adipocyte-secreted proteins with anthropometric and biochemical measures of glucose homeostasis, lipid metabolism, renal function, as well as inflammation, differ in healthy and low weight adults as compared to overweight/obese patients. Eighty-one subjects with a body mass-index below 22.0 kg/m2 and without malnutrition or eating disorders, as well as fifty overweight/obese patients, were recruited for the study. Serum concentrations of seven adipokines (adiponectin, leptin, adipocyte fatty acid-binding protein [AFABP], chemerin, fibroblast growth factor [FGF]-21, resistin, retinol-binding protein [RBP]-4) were measured by enzyme-linked immunosorbent assays. Lean probands had significantly higher levels of adiponectin and resistin, as well as lower levels of leptin, AFABP, and RBP-4, as compared to overweight/obese subjects. Serum concentrations of adiponectin, leptin, AFABP, chemerin, and resistin were significantly higher in lean women as compared to men (p<0.05). In lean subjects, fasting insulin independently predicted leptin and resistin concentrations. Furthermore, C-reactive protein was independently associated with circulating AFABP and chemerin. Moreover, lean body mass was an independent predictor of leptin, fat mass predicted AFABP levels, whereas RBP-4 was independently correlated to age and triglycerides. In addition, high density lipoprotein cholesterol predicted AFABP. Our results support the notion that several of these adipokines are regulated in a different manner in lean adults as compared to overweight/obese subjects and patients with eating disorders.

Metabolic and genetic predictors of circulating adipocyte fatty acid-binding protein.

BACKGROUND: Adipocyte fatty acid-binding protein (AFABP) was recently introduced as a novel adipokine playing an important role in glucose homeostasis. In this study, we investigated the relationship between serum AFABP levels and metabolic, as well as cardiovascular parameters, in the self-contained population of Sorbs. Furthermore, we conducted a genome-wide association study on serum AFABP concentrations in the Sorbs and we separately analyzed the effects of two common variants in the FABP4 gene on AFABP serum concentration. METHODS: Serum AFABP concentrations were quantified by enzyme-linked immunosorbent assay and correlated with metabolic and cardiovascular parameters, as well as inflammatory markers and renal function, in 868 well-characterized non-diabetic Sorbs from Germany. RESULTS: Median AFABP serum concentrations were 1.5-fold higher in female subjects (23.03 µg l(-1)) as compared to male subjects (15.86 µg l(-1)). Waist-to-height ratio and glomerular filtration rate were independently associated with AFABP concentrations in multiple regression analysis in both female and male subjects. The genome-wide scan for association of single-nucleotide polymorphisms with serum AFABP levels in the Sorbs revealed 39 loci reaching P-values <10(-4). Two single-nucleotide polymorphisms, rs16909187 and rs10808846, representing common genetic variation in FABP4 did not show any effect on serum AFABP concentrations in our study cohort. CONCLUSION: AFABP serum concentrations are determined by parameters of fat distribution, renal function and gender.

Serum levels of the adipokine zinc-α2-glycoprotein are increased in preeclampsia.

BACKGROUND: Preeclampsia (PE) is associated with facets of the metabolic syndrome and an increased future metabolic and cardiovascular risk for mother and newborn. Recently, zinc-α2-glycoprotein (ZAG) has been proposed as a new adipokine involved in the pathogenesis of obesity. AIM: In the current study, we investigated ZAG serum levels in PE patients as compared to healthy gestational age-matched controls. SUBJECTS AND METHODS: We quantified serum concentrations of ZAG in patients with PE (no.=37) as compared to healthy gestational age-matched controls (no.=37) by enzyme-linked immunosorbent assay. Furthermore, association of this adipokine with renal function, glucose and lipid metabolism, as well as inflammation was studied. RESULTS: Median serum ZAG levels were 1.4-fold higher in PE patients (58.8 mg/l) as compared to controls (41.9 mg/l) (p<0.01). Furthermore, circulating ZAG was positively correlated to systolic and diastolic blood pressure, creatinine, triglycerides, and leptin in univariate analyses. In multiple regression analysis, creatinine remained independently associated with ZAG. CONCLUSIONS: We demonstrate that maternal ZAG serum concentrations are significantly increased in PE. Furthermore, renal function is an independent predictor of circulating ZAG.

Serum levels of the adipokine fasting-induced adipose factor/angiopoietin-like protein 4 depend on renal function.

Fasting-induced adipose factor/angiopoietin-like protein 4 (FIAF/Angptl4) was recently introduced as a novel adipokine influencing glucose and lipid homeostasis. In the current study, we quantified circulating FIAF/Angtl4 levels in patients on chronic hemodialysis (CD) as compared to controls with a glomerular filtration rate above 50 ml/min. FIAF/Angptl4 was determined by ELISA in control (n=60) and CD (n=60) patients and correlated to clinical and biochemical measures of renal function, glucose and lipid metabolism, as well as inflammation, in both groups. Median serum FIAF/Angptl4 levels were more than 5-fold higher in CD patients (48.3 µg/l) as compared to control subjects (8.4 µg/l) (p<0.001). Furthermore, serum creatinine independently predicted FIAF/Angptl4 concentrations in multiple regression analyses in control subjects (p<0.01). In CD patients, C-reactive protein was independently and positively associated with circulating FIAF/Angptl4 (p<0.01). Taken together, we show that serum FIAF/Angptl4 levels are significantly increased in end-stage renal disease and independently associated with markers of renal function in control subjects.

Serum levels of the adipokine lipocalin-2 are increased in preeclampsia.

BACKGROUND: Preeclampsia (PE) is a serious complication in pregnancy which increases the future risk for vascular and metabolic disease in both mother and newborn. Recently, lipocalin-2 has been introduced as a novel adipokine which contributes to obesity, insulin resistance, and vascular disease. AIM: In the current study, we investigated lipocalin-2 serum levels in PE patients as compared to healthy gestational age-matched controls. SUBJECTS AND METHODS: Lipocalin-2 serum concentrations were quantified by enzyme-linked immunosorbent assay in control (no.=22) and PE (no.=22) patients. Furthermore, lipocalin-2 levels were correlated to clinical and biochemical measures of renal function, glucose, and lipid metabolism, as well as inflammation. RESULTS: Median maternal lipocalin-2 concentrations were significantly increased in PE (121.3 µg/l) as compared to control subjects (99.8 µg/l) (p<0.05). Furthermore, circulating lipocalin 2 correlated positively with diastolic blood pressure, creatinine, and C reactive protein. In multivariate analyses, creatinine and C reactive protein remained independently associated with lipocalin-2 levels. CONCLUSIONS: We demonstrate that maternal lipocalin-2 concentrations are significantly increased in PE. Furthermore, markers of renal function and inflammation independently predict circulating lipocalin-2.

Fibroblast growth factor 19 serum levels: relation to renal function and metabolic parameters.

Fibroblast growth factor 19 (FGF19) was recently introduced as a novel metabolic regulator reversing diabetes mellitus, hepatic steatosis, hyperlipidemia, and adiposity. In the current study, we determined circulating FGF19 levels in patients on chronic hemodialysis (CD) as compared to controls with a glomerular filtration rate (GFR) above 50 ml/min. FGF19 was measured by ELISA in control (n=60) and CD (n=60) patients and correlated to clinical and biochemical measures of renal function, glucose, and lipid metabolism, as well as inflammation, in both groups. Median serum FGF19 levels were 1.5-fold higher in CD patients (266.7 microg/l) as compared to subjects with a GFR above 50 ml/min (178.1 microg/l) (p=0.001). Furthermore, fasting glucose negatively and independently predicted circulating FGF19 in controls (p<0.05). Moreover, adiponectin was a positive and C-reactive protein was a negative independent predictor of FGF19 serum concentrations in CD patients. Taken together, we have demonstrated that circulating FGF19 levels are significantly increased in end-stage renal disease. Furthermore, FGF19 is associated with a beneficial metabolic profile in both control and CD patients.

Tissue inhibitor of metalloproteinase 1 expression and secretion are induced by beta-adrenergic stimulation in 3T3-L1 adipocytes.

Tissue inhibitor of metalloproteinase (TIMP)-1 is an adipocytokine upregulated in obesity which might promote adipose tissue development. In the current study, the impact of the beta-adrenergic agonist isoproterenol on TIMP-1 gene expression and secretion was determined in 3T3-L1 adipocytes. Interestingly, isoproterenol increased TIMP-1 secretion 2.7-fold. Furthermore, isoproterenol induced TIMP-1 mRNA in a time- and dose-dependent fashion with significant effects observed as early as 1 h after effector addition and at concentrations as low as 1 microM isoproterenol. Significant isoproterenol-induced upregulation of TIMP-1 mRNA could also be found in immortalized brown adipocytes. Inhibitor experiments confirmed that the positive effect of isoproterenol on TIMP-1 is mediated via beta-adrenergic receptors and protein kinase A. Moreover, increasing cAMP levels with forskolin or dibutyryl-cAMP was sufficient to stimulate TIMP-1 synthesis. Insulin induced basal TIMP-1 mRNA, but did not significantly influence forskolin-induced TIMP-1 expression. Taken together, we demonstrate that TIMP-1 expression and secretion are selectively upregulated in adipocytes by beta-adrenergic agonists via a classic Gs-protein-coupled pathway.

Insulin resistance-inducing cytokines differentially regulate SOCS mRNA expression via growth factor- and Jak/Stat-signaling pathways in 3T3-L1 adipocytes.

Various cytokines, including tumor necrosis factor (TNF) alpha, growth hormone (GH) and interleukin (IL)-6, induce insulin resistance. Recently, it was demonstrated that induction of suppressor of cytokine signaling (SOCS)-3 by TNFalpha and GH is an important mechanism by which these cytokines impair insulin sensitivity. The current study investigated in 3T3-L1 adipocytes whether TNFalpha and GH also upregulate SOCS-1 and SOCS-6, which have both been shown to inhibit insulin signaling potently, and whether IL-6 might alter synthesis of SOCS-1, -3 and -6. Interestingly, 10 ng/ml TNFalpha, 500 ng/ml GH and 30 ng/ml IL-6 induced SOCS-1 mRNA time-dependently with maximal stimulation detectable after 8 h of TNFalpha and 1 h of GH and IL-6 addition respectively. Furthermore, TNFalpha and GH caused sustained upregulation of SOCS-1 for up to 24 h, whereas stimulation by IL-6 was only transient, with SOCS-1 mRNA returning to basal levels 2 h after effector addition. Induction of SOCS-1 was dose-dependent, and significant stimulation was detectable at concentrations as low as 3 ng/ml TNFalpha, 50 ng/ml GH and 10 ng/ml IL-6. Furthermore, stimulation experiments and studies using pharmacologic inhibitors suggested that the positive effect of TNFalpha, GH and IL-6 on SOCS-1 mRNA is, at least in part, mediated by Janus kinase (Jak) 2. Finally, SOCS-3 expression was dose- and time-dependently induced by IL-6, at least in part via Jak2, but none of the cytokines affected SOCS-6 expression. Taken together, our results show a differential regulation of SOCS mRNA by insulin resistance-inducing hormones, and suggest that SOCS-1, as well as SOCS-3, may be an important intracellular mediator of insulin resistance in fat cells and a potential pharmacologic target for the treatment of impaired insulin sensitivity.

GH is a positive regulator of tumor necrosis factor alpha-induced adipose related protein in 3T3-L1 adipocytes.

Tumor necrosis factor (TNF) alpha-induced adipose-related protein (TIARP) has recently been cloned as a TNFalpha-stimulated protein expressed in adipocytes. Its expression is differentiation-dependent and potentially involved in mediating TNFalpha-induced insulin resistance. To further characterize regulation of TIARP gene expression, 3T3-L1 adipocytes were treated with key hormones modulating insulin sensitivity and influencing adipocyte metabolism, and TIARP gene expression was determined by quantitative real-time RT-PCR. Interestingly, TIARP mRNA expression was stimulated almost 9-fold after 500 ng/ml GH were added for 16 h whereas addition of 10 microM isoproterenol, 100 nM insulin and 100 nM dexamethasone for 16 h significantly decreased TIARP gene expression to between 35 and 50% of control levels. In contrast, angiotensin 2 (10 microM) and triiodothyronine (1 microM) did not have any effect. The stimulatory effect of GH was time- and dose-dependent with stimulation occurring as early as 1 h after effector addition and at concentrations as low as 5 ng/ml GH. Moreover, pharmacological inhibition of Janus kinase 2 and p42/44 mitogen-activated protein kinase reversed the stimulatory effect of GH, suggesting that both signaling molecules are involved in activation of TIARP gene expression by GH. Furthermore, an increase of TIARP mRNA could be completely reversed to control levels by withdrawal of GH for 24 h. Taken together, these results show that TIARP is not only responsive to TNFalpha but also to important other hormones influencing glucose homeostasis and adipocyte metabolism. Thus, this factor may play an integrative role in the pathogenesis of insulin resistance and its link to obesity.

Suppression of aquaporin adipose gene expression by isoproterenol, TNFalpha, and dexamethasone.

Aquaporin adipose (AQPap) is a putative glycerol channel in adipocytes. It has recently been shown to be upregulated in insulin resistance stimulated by thiazolidinediones and inhibited by insulin. To further clarify regulation of AQPap gene expression, 3T3-L1 adipocytes were chronically treated with various hormones known to influence insulin sensitivity and adipocyte metabolism, and AQPap mRNA was measured by quantitative real-time reverse transcription-polymerase chain reaction. Interestingly, treatment of 3T3-Ll adipocytes with 10 micro M isoproterenol, 10 ng/ml TNFalpha, and 100 nM dexamethasone for 16 h inhibited AQPap gene expression by 62 %, 60 %, and 39 %, respectively; angiotensin 2, growth hormone, and triiodothyronine did not have any effect. The inhibitory effects were dose-dependent with significant suppression detectable at concentrations as low as 1 nM isoproterenol, 1 ng/ml TNFalpha, and 10 nM dexamethasone. Furthermore, inhibition of AQPap gene expression could be almost completely reversed by pretreating 3T3-L1 adipocytes with the beta-adrenoceptor antagonist propranolol. Moreover, stimulation of Gs-proteins with cholera toxin and adenylyl cyclase with forskolin and dibutyryl-cAMP dramatically downregulated AQPap mRNA. Taken together, our results suggest that AQPap is an adipocyte-expressed glycerol channel selectively regulated and profoundly downregulated by hormones implicated in the pathogenesis of insulin resistance and dyslipidemia.

Interleukin (IL)-6 mRNA expression is stimulated by insulin, isoproterenol, tumour necrosis factor alpha, growth hormone, and IL-6 in 3T3-L1 adipocytes.

Interleukin (IL)-6 has recently been shown to be an adipocyte-expressed cytokine. Its serum concentrations are elevated in insulin resistance and obesity. For further evaluation of IL-6 gene expression regulation, fully differentiated 3T3-L1 adipocytes were treated with various hormones known to induce insulin resistance. IL-6 mRNA content was measured by quantitative real-time reverse transcription-polymerase chain reaction. Interestingly, treatment of adipocytes with 100 nM insulin, 10 micro M isoproterenol, 10 ng/ml tumour necrosis factor alpha (TNFalpha), and 500 ng/ml growth hormone (GH) for 16 h stimulated IL-6 mRNA expression 2.3-fold, 47-fold, 74-fold, and 1.4-fold, respectively (p < 0.01). In contrast, treatment with 100 nM dexamethasone significantly decreased IL-6 expression to 32 % of control levels (p < 0.01), whereas triiodothyronine and angiotensin 2 did not have any effect. Furthermore, stimulation of IL-6 expression was time-dependent with maximal stimulatory effects detectable after 1 h of insulin, isoproterenol, and GH addition and 12 h of TNFalpha, respectively. Moreover, isoproterenol's effect could be almost completely reversed by pretreatment of 3T3-L1 cells with the beta-adrenergic antagonist propranolol and mimicked by stimulation of G S -proteins with cholera toxin and adenylyl cyclase with forskolin and dibutyryl cAMP, respectively. Finally, IL-6 strongly induced its own expression in a time-dependent fashion. Taken together, our results demonstrate that IL-6 expression in adipocytes is governed by an autocrine positive feedback loop and upregulated by insulin, isoproterenol, TNFalpha, and GH. In concert with this adipocytokine's upregulation in states of decreased insulin sensitivity such as obesity and diabetes, the data support a possible role of IL-6 as a selectively regulated mediator of insulin resistance.

Isoproterenol is a positive regulator of the suppressor of cytokine signaling-3 gene expression in 3T3-L1 adipocytes.

SOCS (suppressor of cytokine signaling)-3 has recently been shown to be an insulin- and tumor necrosis factor (TNF)-alpha-induced negative regulator of insulin signaling. To further clarify a potential involvement of SOCS-3 in the development of insulin resistance, we measured differentiation-dependent SOCS-3 mRNA expression in 3T3-L1 adipocytes and studied its regulation by various hormones known to impair insulin signaling using quantitative real-time RT-PCR. There was a differentiation-dependent downregulation of SOCS-3 mRNA by 50% over the 9 day adipocyte differentiation course. Interestingly, besides insulin and TNF-alpha, chronic treatment of differentiated 3T3-L1 cells with 10 microM isoproterenol for 16 h stimulated SOCS-3 gene expression by about 3.5-fold. Furthermore, isoproterenol stimulated SOCS-3 mRNA expression in a dose-dependent manner with significant activation detectable at concentrations as low as 10 nM isoproterenol. Moreover, a strong 27- and 47-fold activation of SOCS-3 mRNA expression could be seen after 1 h of isoproterenol and GH treatment respectively. The stimulatory effect of isoproterenol could be almost completely reversed by pretreatment of 3T3-L1 cells with the beta-adrenergic antagonist propranolol. Finally, isoproterenol's action could be mimicked by stimulation of G(S)-proteins with cholera toxin and of adenylyl cyclase with forskolin and dibutyryl cAMP. Taken together, our results demonstrate a differentiation-dependent downregulation of SOCS-3 in adipocytes and suggest that SOCS-3 gene expression is stimulated by beta-adrenergic agents via activation of a G(S)-protein-adenylyl cyclase-dependent pathway. As SOCS-3 is a novel inhibitor of insulin signaling, the data support a possible role of this protein as a selectively regulated mediator of catecholamine-induced insulin resistance.