Evidence against a role for insulin-signaling proteins PI 3-kinase and Akt in insulin resistance in human skeletal muscle induced by short-term GH infusion

Niels Jessen,1 Christian B. Djurhuus,1 Jens O. L. Jørgensen,1 Lasse S. Jensen,1 Niels Møller,1 Sten Lund,1 and Ole Schmitz1,2

1Medical Research Laboratory and Medical Department M (Endocrinology and Diabetes), University Hospital of Aarhus, and 2Department of Clinical Pharmacology, University of Aarhus, Aarhus, Denmark

Submitted 31 March 2004 ; accepted in final form 24 August 2004


    ABSTRACT
 TOP
 ABSTRACT
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Prolonged growth hormone (GH) excess is known to be associated with insulin resistance, but the underlying mechanisms remain unknown. The aim of this study was to assess the impact of GH on insulin-stimulated glucose metabolism and insulin signaling in human skeletal muscle. In a cross-over design, eight healthy male subjects (age 26.0 ± 0.8 yr and body mass index 24.1 ± 0.5 kg/m2) were infused for 360 min with either GH (Norditropin, 45 ng·kg–1·min–1) or saline. During the final 180 min of the infusion, a hyperinsulinemic euglycemic clamp was performed (insulin infusion rate: 1.2 mU·kg–1·min–1). Muscle biopsies from vastus lateralis were taken before GH/saline administration and after 60 min of hyperinsulinemia. GLUT4 content and insulin signaling, as assessed by insulin receptor substrate (IRS)-1-associated phosphatidylinositol 3-kinase and Akt activity were determined. GH levels increased to a mean (±SE) level of 20.0 ± 2.3 vs. 0.5 ± 0.2 µg/l after saline infusion (P < 0.01). During GH infusion, the glucose infusion rate during hyperinsulinemia was reduced by 38% (P < 0.01). In both conditions, free fatty acids were markedly suppressed during hyperinsulinemia. Despite skeletal muscle insulin resistance, insulin still induced a similar ~3-fold rise in IRS-1-associated PI 3-kinase activity (269 ± 105 and 311 ± 71% compared with baseline, GH vs. saline). GH infusion did not change Akt protein expression, and insulin caused an ~13-fold increase in Akt activity (1,309 ± 327 and 1,287 ± 173%) after both GH and saline infusion. No difference in total GLUT4 content was noted (114.7 ± 7.4 and 107.6 ± 16.7 arbitrary units, GH vs. saline, compared with baseline). In conclusion, insulin resistance in skeletal muscle induced by short-term GH administration is not associated with detectable changes in the upstream insulin-signaling cascade or reduction in total GLUT4. Yet unknown mechanisms in insulin signaling downstream of Akt may be responsible.

glucose transport; growth hormone; phosphatidylinositol 3-kinase; euglycemic hyperinsulinemic clamp


CHRONICALLY ELEVATED LEVELS of circulating growth hormone (GH), as seen in patients with acromegaly, induce insulin resistance and impaired glucose tolerance (25), and similar effects are observed in children and adults with GH deficiency treated with recombinant GH (31, 32).

Insulin exerts its effects on skeletal muscle through binding to the insulin receptor. This triggers a cascade of intracellular signaling activity leading to translocation of glucose transporters (GLUT4) from intracellular vesicles to the cell surface, allowing glucose to enter the cell. The full extent of the insulin-signaling cascade is not yet known, but recent studies have shown that binding of insulin to its receptor leads to autophosphorylation of the intracellular domain of the receptor. It binds to the insulin receptor substrate (IRS), which subsequently is tyrosine phosphorylated. Phosphorylated IRS binds and activates the lipid kinase phosphatidylinositol (PI) 3-kinase, and inhibition of this step with the specific inhibitor wortmannin abrogates GLUT4 translocation and insulin-stimulated glucose uptake (10). The steps downstream of the PI 3-kinase are shown in many studies to involve the serine/threonine kinase Akt/PKB (1), but the link that leads to GLUT4 translocation is not identified. Interestingly, after binding to the GH receptor, GH has been shown to phosphorylate IRS-1 through activation of the Janus kinase JAK2 in skeletal muscle from fasted (36), but not fed, rats (9). The physiological relevance of this cross talk between GH and insulin signaling remains unclear.

After 2–4 h of GH stimulation, an anti-insulin-like action of GH is observed, resulting in inhibited glucose utilization (13). The impaired glucose tolerance is mainly due to reduced glucose uptake in skeletal muscle (4, 20, 26), the predominant tissue for insulin-stimulated glucose disposal (14). In contrast, glucose uptake in heart muscle is unchanged (6). The mechanisms behind this impaired insulin action are still unknown, but infusion of GH to achieve physiological circulating concentrations has been shown to increase levels of free fatty acids (FFAs) (28), and this has been proposed as one possible mechanism (27). FFAs were originally proposed to induce insulin resistance by substrate competition (30), but more recent studies have shown that high levels of FFAs effectively inhibit the insulin-signaling cascade activity already at IRS-1 phosphorylation and IRS-1-associated PI 3-kinase activity (16, 18).

Animal studies of long-term GH stimulation using either GH treatment in rats (34, 35) or transgenic animals overexpressing bovine GH (15) have shown inhibition of the insulin-signaling cascade in skeletal muscles that mimics the changes induced by elevated FFAs. Because FFA levels were not reported, it is not clear whether this inhibition is due to a direct effect of GH stimulation or indirectly through GH-mediated lipolysis and elevated FFAs.

The present study was undertaken to gain further insight into the mechanisms behind the GH-induced insulin resistance by assessing the impact of short-term GH infusion on IRS-1-associated PI 3-kinase and Akt activity in skeletal muscle during concomitant insulin-induced suppression of FFA levels.


    SUBJECTS AND METHODS
 TOP
 ABSTRACT
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Subjects. Eight healthy male volunteers participated in the study. Their age was 26.0 ± 0.8 yr (means ± SE), and body mass index was 24.1 ± 0.5 kg/m2. None of them had a family history of diabetes, and none were receiving any form of medication. The Scientific Ethics Committee of Aarhus County approved the study protocol, and all study participants gave informed consent according to the second declaration of Helsinki.

Design. Each participant underwent two studies in random order with and without GH infusion ~4 wk apart. Intense physical exertion was avoided for 24 h before the examinations. The studies commenced at 8:00 AM after a 10-h overnight fast and were conducted in the supine position. A Venflon catheter was inserted in an antecubital vein for administration of the infusates. For blood sampling, a wrist vein of the contralateral hand was cannulated and kept in a heating box to provide arterialized blood. Before infusions, a "baseline" muscle biopsy was taken from vastus lateralis muscle with a Bergström biopsy needle under local anesthesia (1% lidocaine), a small incision having been made through the skin and muscle sheath 15–20 cm above the knee. A total amount of ~200 mg of muscle was aspirated; biopsies were cleaned for blood (within 15 s) and snap-frozen in liquid nitrogen. Muscle biopsies were stored at –80°C until analyzed. After baseline blood sampling at time 0, either saline or GH (Norditropin; Novo Nordisk, Gentofte, Denmark) was infused. GH was infused at a rate of 45 ng·kg–1·min–1 for 330 min. At 180 min, a hyperinsulinemic (insulin infusion rate: 1.2 mU·kg–1·min–1) euglycemic (plasma glucose ~5 mmol/l) clamp was commenced and continued for the next 150 min. At 240 min, a second muscle biopsy was obtained from the thigh at a distance of ~5 cm from the first incision. The glucose infusion rate (GIR) during this procedure was considered an estimate of insulin-stimulated glucose uptake, as the endogenous glucose release at this degree of hyperinsulinemia is presumed to be very close to zero.

Analytic methods. All samples were analyzed in duplicate. Plasma glucose was measured immediately by a glucose analyzer (Beckman Instruments, Palo Alto, CA). Serum insulin concentrations were measured in duplicate by a two-site immunospecific insulin enzyme-linked immunosorbent assay (2). Serum FFA concentrations were determined by a colorimetric method using a commercial kit (Wako Chemicals, Neuss, Germany). Serum GH and cortisol were measured with radioimmunoassays (DELFIA; Wallac Oy, Turku, Finland). Plasma glucagon concentrations were determined by radioimmunoassay, as described by Ørskov et al. (29) with modifications.

Muscle preparations for insulin-signaling assays. Muscles were homogenized as described by Wojtaszewski et al. (38). In brief, frozen muscles biopsies (~80 mg) were homogenized in ice-cold solubilization buffer {50 mM HEPES, 137 mM NaCl, 10 mM Na4P2O7, 10 mM NaF, 1 mM MgCl2, 1 mM CaCl2, 1% NP-40, 10% glycerol, 2 mM Na3VO4, 2 µg/ml aprotinin, 5 µg/ml leupeptin, 0.5 µg/ml pepstatin, 10 µg/ml anti-pain, 1.5 mg/ml benzamidine, and 100 µmol/l AEBSF [4-(-2-aminoethyl)benzenesulfonyl fluoride, hydrochloride], pH 7.4} and rotated for 1 h at 4°C. Insoluble materials were removed by centrifugation at 16,000 g for 60 min at 4°C, and protein content on the supernatant was determined with a bicinchoninic acid protein assay reagent (Pierce Chemical, Rockford, IL).

PI 3-kinase assay. PI 3-kinase activity was assessed as previously described (38), with minor modifications. Briefly, aliquots of protein were immunoprecipitated overnight with protein A-agarose-coupled anti-IRS-1 antibody (Upstate Biotechnology, Lake Placid, NY). The immune complexes were washed thoroughly, and IRS-1-associated PI 3-kinase activity was assessed directly on the protein A-agarose complex in a buffer containing 10 mM Tris·HCl, 1 mM EDTA, 1 mM MgCl2, 75 µM ATP, 50 mM NaCl, and 6 µCi [{gamma}-32P]ATP (NEN, Boston, MA). Reaction products were resolved by thin-layer chromatography and were quantified using a phosphorimager (Packard BioScience, Meriden, CT).

Akt/PKB protein expression. Aliquots of protein were resolved by SDS-PAGE using the Bio-Rad Mini Protean II system (10% polyacrylamide gels), transferred to nitrocellulose, blocked with 5% nonfat milk in TBST (10 mM Tris, 150 mM NaCl, pH 8.0, and 0.1% Tween 20) and incubated with anti-PKB/Akt antibody (New England BioLabs, Beverly, MA). The membranes were then washed and incubated with secondary horseradish peroxidase-conjugated goat anti-rabbit IgG antibody (Pierce Chemical) as secondary antibody, and proteins were visualized by BioWest enhanced chemiluminescence (UVP, Upland, CA) and quantified by UVP BioImaging System.

Akt/PKB activity assay. Aliquots of protein were immunoprecipitated overnight with protein G-agarose-coupled anti-Akt/PKB antibody, which reacts with both the {alpha}- and {beta}-subunits (Upstate Biotechnology, Lake Placid, NY). The activity was assessed as described by Sherwood et al. (33), with minor modifications. The complex was washed, and Akt/PKB activity was assessed in buffer containing 50 mM Tris·HCl (pH 7.4), 10 mM MgCl2, 1 mM DTT, 0.01 mM PKA inhibitor peptide (Upstate Biotechnology), 0.1 mM PKB/serum- and glucocorticoid-induced kinase (SGK)-specific peptide (Upstate Biotechnology), 3 µCi [{gamma}-32P]ATP (NEN), and 5 mM ATP at a final volume of 30 µl at 30°C for 30 min. At the end of the reaction, a 20-ml aliquot was removed and spotted on Whatman P81 paper. The papers were washed six times for 20 min each in 1% phosphoric acid and once with acetone, and radioactivity was quantified by scintillation countering (Wallac 1409; Wallac).

Total muscle GLUT4 content. Total crude membranes were prepared from ~20 mg of skeletal muscles, and aliquots of protein were resolved as previously described (7) by use of a polyclonal anti-COOH-terminal peptide GLUT4 antibody (23). Proteins were visualized by chemiluminescence (Pierce Super Signal) and quantified with the UVP BioImaging System.

Statistics. All data are presented as means ± SE. Statistical analysis was performed using SPSS for Windows (v. 11.0; SPSS, Chicago, IL). Normality of the data was tested with the Kolmogorov-Smirnov test of normal distribution. Where P > 0.20 the data was considered to be normally distributed. Statistical evaluation of differences between normally distributed data was done with a paired t-test. Differences between groups were considered statistically significant if P < 0.05.


    RESULTS
 TOP
 ABSTRACT
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Circulating hormones, substrates, and GIRs. Serum GH increased gradually during the GH infusion, eventually reaching a plateau of 20.2 ± 2.3 µg/l during the final 30 min of the exposure compared with 0.8 ± 0.4 µg/l during saline infusion (P < 0.01; Fig. 1). Plasma glucose levels were stable before and during the clamp (5.2 ± 0.07 and 5.1 ± 0.04 mM from 0–180 min and 5.2 ± 0.2 and 5.1 ± 0.2 mM from 180–330 min, GH vs. saline infusion). Average serum insulin was identical in the two conditions before the hyperinsulinemic clamp (43.7 ± 2.1 and 44.7 ± 2.0 pM, GH vs. saline). During insulin infusion, circulating insulin rose sharply, ~10-fold, to levels that were comparable in the GH and saline condition. Average serum insulin during the last 30 min of the clamp was 485.9 ± 16.8 and 509.4 ± 16.5 pM (GH vs. saline), and at 240 min, i.e., when the second biopsy was taken, serum insulin was 478.9 ± 20.6 and 473.3 ± 13.8 pM (GH vs. saline). During GH administration, serum FFA increased from 0.53 ± 0.08 mM at 0 min to a peak concentration of 0.98 ± 0.10 mM just before initiation of hyperinsulinemia compared with a peak concentration of 0.51 ± 0.10 mM during saline infusion (P < 0.01). During insulin infusion, serum FFA was markedly suppressed to 0.15 ± 0.01 and 0.05 ± 0.01 mM (GH vs. saline infusion, P < 0.01) at 240 min and was further reduced to 0.10 ± 0.02 and 0.03 ± 0.00 mM (GH vs. saline) during the final 30 min of the clamp period. The latter reduction amounted to 81 and 92%, respectively, of the basal FFA concentrations.



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Fig. 1. Circulation levels of growth hormone (GH), glucose, insulin, and free fatty acids (FFAs) and glucose infusion rates (GIR) during GH ({circ}) and saline infusions ({bullet}). Values are means ± SE. *P < 0.01 during GH vs. saline infusion.

 
GIR was considerably reduced after GH exposure, both during the last 30 min of the hyperinsulinemic euglycemic clamp (5.0 ± 0.9 and 8.1 ± 0.9 mg·kg–1·min–1, GH vs. saline, P < 0.01) and from 230 to 240 min (4.7 ± 0.5 and 7.7 ± 1.1 mg·kg–1·min–1, GH vs. saline, P < 0.01).

No differences were observed in circulating glucagon or cortisol in the two conditions (data not shown).

IRS-1-associated PI 3-kinase activity. Insulin stimulation caused an approximately threefold rise in IRS-1-associated PI 3-kinase activity (Fig. 2). There was no difference in the insulin-stimulated activities during GH and saline infusion (269 ± 105 and 311 ± 71% compared with baseline, GH vs. saline).



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Fig. 2. Insulin receptor substrate (IRS)-1-associated phosphatidylinositol (PI) 3-kinase (top) and Akt/PKB activity (bottom) at baseline (open bars) and under insulin stimulation during GH (filled bars) and saline infusions (gray bars). Values are means ± SE. IRS-1-associated PI 3-kinase activity is expressed in arbitrary units and Akt/PKB activity as pmol incorporated ATP·mg protein–1·min–1.

 
Akt/PKB activity protein expression. Expression of Akt/PKB did not change from baseline during either GH or saline infusion (data not shown).

Akt/PKB activity. To further investigate any potential involvement of the insulin-signaling cascade, the activity of the downstream kinase Akt/PKB was assessed. Insulin caused a substantial increase in activity (~13-fold) under both GH and saline infusions compared with basal, but no difference was observed in the two conditions (1,309 ± 327 and 1,287 ± 173% compared with baseline, GH vs. saline; Fig. 2).

Muscle GLUT4 protein content. Infusion of GH did not alter total GLUT4 protein content (114.7 ± 7.4 and 107.6 ± 16.7% of baseline level, GH vs. saline; Fig. 3).



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Fig. 3. Total crude membrane GLUT4 content at baseline (open bars) and under insulin stimulation during GH (filled bar) and saline infusions (gray bar). Values are means ± SE and are expressed in arbitrary units.

 

    DISCUSSION
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 ABSTRACT
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
The present study shows that hypersomatotropinemia induces insulin resistance even though FFA levels are substantially suppressed, indicating that GH also perturbs insulin-stimulated glucose uptake in a non-FFA-dependent manner. Apparently, the GH-induced insulin resistance was not associated with detectable changes in PI 3-kinase or Akt activity or the total expression of GLUT4.

In this study, the second muscle biopsy was performed after 60 min of hyperinsulinemia because it has been established that insulin-signaling activity at this time point has reached maximal levels (37). It should be emphasized that, already at this time point, insulin sensitivity was considerably reduced during GH exposure. Furthermore, we wanted to minimize the role of GH-induced lipolysis in the signaling process. To that end, we used an insulin infusion rate leading to supraphysiological levels of circulating insulin. Although FFA levels were slightly higher under GH administration than during saline, serum FFA was suppressed to very low levels during both conditions (~15% of baseline levels).

In an earlier study, utilizing the isotope dilution technique in combination with the hyperinsulinemic clamp in an experimental design in many respects comparable to the present one, we demonstrated that GIRs were almost identical to the isotopically determined insulin-stimulated glucose disposal in healthy people after short-term GH exposure (4). This indicates that the endogeneous glucose release in the present study is restrained to insignificant values and, consequently, that the reduced rates of glucose infusion reflect insulin resistance in peripheral tissues. Furthermore, of note, insulin infusion rates were almost twofold higher in the present study, further minimizing the endogenous glucose release.

Recent studies have demonstrated that FFAs severely blunt insulin signaling already at the levels of IRS-1 phosphorylation and IRS-1-associated PI 3-kinase activity (16, 18). This impairment cannot be overcome by high levels of insulin, but insulin signaling returns to normal when the FFA level is normalized (40). Moreover, studies of skeletal muscle from obese subjects (17) and type 2 diabetic patients (5, 22) have shown reduced activity in the insulin-signaling cascade, indicating that impairment of the insulin-signaling cascade can be at least partly responsible for the reduced glucose uptake in skeletal muscle observed with elevated FFAs and/or type 2 diabetes.

Studies of the effects of short-term GH exposure in humans (4) and rodents (21) have shown insulin resistance combined with a reduced activity in the downstream target of insulin action glycogen synthase. These findings have been supported by animal studies of long-term GH exposure where a reduced activity in the proximal insulin-signaling cascade in skeletal muscle was found. The impairment was observed at the IRS-1 level (34) and on the downstream target PI 3-kinase (15, 35). These alterations are very similar to what has been observed after FFA exposure, and, as none of the animal studies focusing on the upstream insulin-signaling cascade include measurements of FFAs, the isolated role of GH on proximal insulin signaling in skeletal muscles cannot be evaluated.

The direct effect of GH on IRS-1 phosphorylation in skeletal muscle has been observed in fasted (36) but not fed rats (9), whereas insulin induces phosphorylation in both situations. This indicates that the phosphorylation of IRS-1 induced by the relatively low levels of insulin in the fed rat obliterates the effects of GH stimulation. Similarly, GH has been shown to induce Akt/PKB phosphorylation in vitro in 3T3-L1 adipocytes (39) when incubated with GH at concentrations ~25 times higher than the plasma concentrations reached in this study. Given these observations, it cannot be completely excluded that the insulin-signaling phosphorylation was slightly elevated at the initiation of the clamp. However, it has been established that the muscle biopsy procedure per se induces insulin resistance (19); consequently, to include an extra muscle biopsy immediately before the hyperinsulinemic clamp may have a destructive effect on interpretation of the data.

In the present study, insulin stimulation resulted in a threefold rise in IRS-1-associated PI 3-kinase activity during both GH and saline infusions; thus no effect of GH infusion was noted. To further investigate the insulin-signaling cascade, insulin-stimulated Akt/PKB activity and protein expression were assessed. Insulin promotes glycogen synthase by inhibiting glycogen synthase kinase-3 through activation of Akt/PKB (12). We have previously shown that GH infusion inhibits glycogen synthase activity (4). In the present study, we failed to demonstrate any difference in insulin-stimulated Akt/PKB expression or activity or that the reduced glycogen synthase activity may be due to reduced glucose availability in the cell. The finding of normal activity in the insulin-signaling cascade, despite significantly reduced insulin sensitivity, emphasizes that GH and FFAs might inhibit insulin-stimulated glucose transport in distinct manners, and this finding is in line with a previous study that shows that GH infusion imposes insulin resistance before any changes in lipolysis are observed (24). Clearly, we cannot rule out that chronic elevation of GH, as present in acromegaly, may affect the insulin-signaling cascade in a different manner.

During physiological conditions, translocation of the insulin-sensitive GLUT4 to the cell surface has been shown to be the limiting factor for insulin-stimulated glucose transport (11). Total GLUT4 content is not affected in insulin-resistant states like type 2 diabetes mellitus (3), and animals receiving long-term GH treatment show normal GLUT4 expression (8). This is consistent with the present data that demonstrate that short-term GH infusion does not affect expression of GLUT4 in human skeletal muscles.

In conclusion, the present study shows that GH infusion is able to induce profound insulin resistance in the presence of suppressed circulating FFA levels. The underlying molecular mechanisms do not appear to involve impairment of IRS-1-associated PI 3-kinase or PKB/Akt activity or changes in total GLUT4 content, and we therefore speculate whether yet-unknown mechanisms in insulin signaling downstream of Akt are responsible.


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 SUBJECTS AND METHODS
 RESULTS
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This study was supported by the Novo Nordisk Foundation and the Institute of Experimental Clinical Research, University of Aarhus, Denmark.


    ACKNOWLEDGMENTS
 
E. Carstensen, E. Hornemann, A. Mengel, and H. Petersen are thanked for excellent technical assistance. L. Goodyear, Joslin Diabetes Center, Harvard Medical School, Boston, MA, is thanked for stimulating discussions.

N. Jessen is currently a fellow at the Joslin Diabetes Center, Boston, MA.


    FOOTNOTES
 

Address for reprint requests and other correspondence: N. Jessen, Joslin Diabetes Center, Metabolism, One Joslin Pl., Boston, MA 02215 (E-mail: Niels.Jessen{at}Joslin.Harvard.edu)

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.


    REFERENCES
 TOP
 ABSTRACT
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 

  1. Alessi DR and Cohen P. Mechanism of activation and function of protein kinase B. Curr Opin Genet Dev 8: 55–62, 1998.[CrossRef][ISI][Medline]
  2. Andersen L, Dinesen B, Jørgensen PN, Poulsen F, and Roder ME. Enzyme immunoassay for intact human insulin in serum or plasma. Clin Chem 39: 578–582, 1993.[Abstract/Free Full Text]
  3. Andersen PH, Lund S, Vestergaard H, Junker S, Kahn BB, and Pedersen O. Expression of the major insulin regulatable glucose transporter (GLUT4) in skeletal muscle of noninsulin-dependent diabetic patients and healthy subjects before and after insulin infusion. J Clin Endocrinol Metab 77: 27–32, 1993.[Abstract]
  4. Bak JF, Møller N, and Schmitz O. Effects of growth hormone on fuel utilization and muscle glycogen synthase activity in normal humans. Am J Physiol Endocrinol Metab 260: E736–E742, 1991.[Abstract/Free Full Text]
  5. Bjørnholm M, Kawano Y, Lehtihet M, and Zierath JR. Insulin receptor substrate-1 phosphorylation and phosphatidylinositol 3-kinase activity in skeletal muscle from NIDDM subjects after in vivo insulin stimulation. Diabetes 46: 524–527, 1997.[Abstract]
  6. Bøtker HE, Wiggers H, Bøttcher M, Christiansen JS, Nielsen TT, Gjedde A, and Schmitz O. Short-term effects of growth hormone on myocardial glucose uptake in healthy humans. Am J Physiol Endocrinol Metab 278: E1053–E1059, 2000.[Abstract/Free Full Text]
  7. Buhl ES, Jessen N, Schmitz O, Pedersen SB, Pedersen O, Holman GD, and Lund S. Chronic treatment with 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside increases insulin-stimulated glucose uptake and GLUT4 translocation in rat skeletal muscles in a fiber type-specific manner. Diabetes 50: 12–17, 2001.[Abstract/Free Full Text]
  8. Cartee GD and Bohn EE. Growth hormone reduces glucose transport but not GLUT-1 or GLUT-4 in adult and old rats. Am J Physiol Endocrinol Metab 268: E902–E909, 1995.[Abstract/Free Full Text]
  9. Chow JC, Ling PR, Qu Z, Laviola L, Ciccarone A, Bistrian BR, and Smith RJ. Growth hormone stimulates tyrosine phosphorylation of JAK2 and STAT5, but not insulin receptor substrate-1 or SHC proteins in liver and skeletal muscle of normal rats in vivo. Endocrinology 137: 2880–2886, 1996.[Abstract]
  10. Clarke JF, Young PW, Yonezawa K, Kasuga M, and Holman GD. Inhibition of the translocation of GLUT1 and GLUT4 in 3T3-L1 cells by the phosphatidylinositol 3-kinase inhibitor, wortmannin. Biochem J 300: 631–635, 1994.[ISI][Medline]
  11. Cline GW, Petersen KF, Krssak M, Shen J, Hundal RS, Trajanoski Z, Inzucchi S, Dresner A, Rothman DL, and Shulman GI. Impaired glucose transport as a cause of decreased insulin-stimulated muscle glycogen synthesis in type 2 diabetes. N Engl J Med 341: 240–246, 1999.[Abstract/Free Full Text]
  12. Cross DA, Alessi DR, Cohen P, Andjelkovich M, and Hemmings BA. Inhibition of glycogen synthase kinase-3 by insulin mediated by protein kinase B. Nature 378: 785–789, 1995.[CrossRef][ISI][Medline]
  13. Davidson MB. Effect of growth hormone on carbohydrate and lipid metabolism. Endocr Rev 8: 115–131, 1987.[ISI][Medline]
  14. DeFronzo RA, Jacot E, Jequier E, Maeder E, Wahren J, and Felber JP. The effect of insulin on the disposal of intravenous glucose. Results from indirect calorimetry and hepatic and femoral venous catheterization. Diabetes 30: 1000–1007, 1981.[ISI][Medline]
  15. Dominici FP, Cifone D, Bartke A, and Turyn D. Alterations in the early steps of the insulin-signaling system in skeletal muscle of GH-transgenic mice. Am J Physiol Endocrinol Metab 277: E447–E454, 1999.[Abstract/Free Full Text]
  16. Dresner A, Laurent D, Marcucci M, Griffin ME, Dufour S, Cline GW, Slezak LA, Andersen DK, Hundal RS, Rothman DL, Petersen KF, and Shulman GI. Effects of free fatty acids on glucose transport and IRS-1-associated phosphatidylinositol 3-kinase activity. J Clin Invest 103: 253–259, 1999.[Abstract/Free Full Text]
  17. Goodyear LJ, Giorgino F, Sherman LA, Carey J, Smith RJ, and Dohm GL. Insulin receptor phosphorylation, insulin receptor substrate-1 phosphorylation, and phosphatidylinositol 3-kinase activity are decreased in intact skeletal muscle strips from obese subjects. J Clin Invest 95: 2195–2204, 1995.[ISI][Medline]
  18. Griffin ME, Marcucci MJ, Cline GW, Bell K, Barucci N, Lee D, Goodyear LJ, Kraegen EW, White MF, and Shulman GI. Free fatty acid-induced insulin resistance is associated with activation of protein kinase C theta and alterations in the insulin signaling cascade. Diabetes 48: 1270–1274, 1999.[Abstract]
  19. Holck P, Pørksen N, Nielsen MF, Nyholm B, Bak JF, Andreasen F, Møller N, and Schmitz O. Effect of needle biopsy from the vastus lateralis muscle on insulin-stimulated glucose metabolism in humans. Am J Physiol Endocrinol Metab 267: E544–E548, 1994.[Abstract/Free Full Text]
  20. Jørgensen JO, Møller J, Alberti KG, Schmitz O, Christiansen JS, Ørskov H, and Møller N. Marked effects of sustained low growth hormone (GH) levels on day-to-day fuel metabolism: studies in GH-deficient patients and healthy untreated subjects. J Clin Endocrinol Metab 77: 1589–1596, 1993.[Abstract]
  21. Kim JK, Choi CS, and Youn JH. Acute effect of growth hormone to induce peripheral insulin resistance is independent of FFA and insulin levels in rats. Am J Physiol Endocrinol Metab 277: E742–E749, 1999.[Abstract/Free Full Text]
  22. Krook A, Roth RA, Jiang XJ, Zierath JR, and Wallberg-Henriksson H. Insulin-stimulated Akt kinase activity is reduced in skeletal muscle from NIDDM subjects. Diabetes 47: 1281–1286, 1998.[Abstract]
  23. Lund S, Flyvbjerg A, Holman GD, Larsen FS, Pedersen O, and Schmitz O. Comparative effects of IGF-I and insulin on the glucose transporter system in rat muscle. Am J Physiol Endocrinol Metab 267: E461–E466, 1994.[Abstract/Free Full Text]
  24. Moller N, Butler PC, Antsiferov MA, and Alberti KG. Effects of growth hormone on insulin sensitivity and forearm metabolism in normal man. Diabetologia 32: 105–110, 1989.[ISI][Medline]
  25. Møller N, Jørgensen JO, Abildgard N, Ørskov L, Schmitz O, and Christiansen JS. Effects of growth hormone on glucose metabolism. Horm Res 36, Suppl 1: 32–35, 1991.
  26. Møller N, Schmitz O, Jørgensen JO, Astrup J, Bak JF, Christensen SE, Alberti KG, and Weeke J. Basal and insulin-stimulated substrate metabolism in patients with active acromegaly before and after adenomectomy. J Clin Endocrinol Metab 74: 1012–1019, 1992.[Abstract]
  27. Nielsen S, Møller N, Christiansen JS, and Jørgensen JO. Pharmacological antilipolysis restores insulin sensitivity during growth hormone exposure. Diabetes 50: 2301–2308, 2001.[Abstract/Free Full Text]
  28. Nørrelund H, Nair KS, Jørgensen JO, Christiansen JS, and Møller N. The protein-retaining effects of growth hormone during fasting involve inhibition of muscle-protein breakdown. Diabetes 50: 96–104, 2001.[Abstract/Free Full Text]
  29. Ørskov H, Thomsen HG, and Yde H. Wick chromatography for rapid and reliable immunoassay of insulin, glucagon and growth hormone. Nature 219: 193–195, 1968.[ISI][Medline]
  30. Randle PJ, Garland PB, Hales CN, and Newsholme EA. The glucose fatty-acid cycle. Its role in insulin sensitivity and the metabolic disturbances of diabetes mellitus. Lancet 1: 785–789, 1963.[ISI][Medline]
  31. Rosenfalck AM, Maghsoudi S, Fisker S, Jørgensen JO, Christiansen JS, Hilsted J, Volund AA, and Madsbad S. The effect of 30 months of low-dose replacement therapy with recombinant human growth hormone (rhGH) on insulin and C-peptide kinetics, insulin secretion, insulin sensitivity, glucose effectiveness, and body composition in GH-deficient adults. J Clin Endocrinol Metab 85: 4173–4181, 2000.[Abstract/Free Full Text]
  32. Seminara S, Merello G, Masi S, Filpo A, La Cauza F, D'Onghia G, Martelli E, and Loche S. Effect of long-term growth hormone treatment on carbohydrate metabolism in children with growth hormone deficiency. Clin Endocrinol (Oxf) 49: 125–130, 1998.[CrossRef][ISI][Medline]
  33. Sherwood DJ, Dufresne SD, Markuns JF, Cheatham B, Moller DE, Aronson D, and Goodyear LJ. Differential regulation of MAP kinase, p70S6K, and Akt by contraction and insulin in rat skeletal muscle. Am J Physiol Endocrinol Metab 276: E870–E878, 1999.[Abstract/Free Full Text]
  34. Smith TR, Elmendorf JS, David TS, and Turinsky J. Growth hormone-induced insulin resistance: role of the insulin receptor, IRS-1, GLUT-1, and GLUT-4. Am J Physiol Endocrinol Metab 272: E1071–E1079, 1997.[Abstract/Free Full Text]
  35. Thirone AC, Carvalho CR, Brenelli SL, Velloso LA, and Saad MJ. Effect of chronic growth hormone treatment on insulin signal transduction in rat tissues. Mol Cell Endocrinol 130: 33–42, 1997.[CrossRef][ISI][Medline]
  36. Thirone AC, Carvalho CR, and Saad MJ. Growth hormone stimulates the tyrosine kinase activity of JAK2 and induces tyrosine phosphorylation of insulin receptor substrates and Shc in rat tissues. Endocrinology 140: 55–62, 1999.[Abstract/Free Full Text]
  37. Wojtaszewski JF, Hansen BF, Kiens B, and Richter EA. Insulin signaling in human skeletal muscle: time course and effect of exercise. Diabetes 46: 1775–1781, 1997.[Abstract]
  38. Wojtaszewski JF, Hansen BF, Urso B, and Richter EA. Wortmannin inhibits both insulin- and contraction-stimulated glucose uptake and transport in rat skeletal muscle. J Appl Physiol 81: 1501–1509, 1996.[Abstract/Free Full Text]
  39. Yamauchi T, Kaburagi Y, Ueki K, Tsuji Y, Stark GR, Kerr IM, Tsushima T, Akanuma Y, Komuro I, Tobe K, Yazaki Y, and Kadowaki T. Growth hormone and prolactin stimulate tyrosine phosphorylation of insulin receptor substrate-1, -2, and -3, their association with p85 phosphatidylinositol 3-kinase (PI3-kinase), and concomitantly PI3-kinase activation via JAK2 kinase. J Biol Chem 273: 15719–15726, 1998.[Abstract/Free Full Text]
  40. Yu C, Chen Y, Cline GW, Zhang D, Zong H, Wang Y, Bergeron R, Kim JK, Cushman SW, Cooney GJ, Atcheson B, White MF, Kraegen EW, and Shulman GI. Mechanism by which fatty acids inhibit insulin activation of insulin receptor substrate-1 (IRS-1)-associated phosphatidylinositol 3-kinase activity in muscle. J Biol Chem 277: 50230–50236, 2002.[Abstract/Free Full Text]




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