Decreased plasma adiponectin concentrations are closely related to hepatic fat content and hepatic insulin resistance in pioglitazone-treated type 2 diabetic patients

The effect of pioglitazone (PIO) on plasma adiponectin concentration, endogenous glucose production (EGP), and hepatic fat content (HFC) was studied in 11 type 2 diabetic patients (age, 52 +/- 2 yr; body mass index, 29.6 +/- 1.1 kg/m(2); HbA(1c), 7.8 +/- 0.4%). HFC (magnetic resonance spectroscopy) and basal plasma adiponectin concentration were quantitated before and after PIO (45 mg/d) for 16 wk. Subjects received a 3-h euglycemic insulin (100 mU/m(2).min) clamp combined with 3-[(3)H] glucose infusion to determine rates of EGP and tissue glucose disappearance (Rd) before and after PIO. PIO reduced fasting plasma glucose (10.0 +/- 0.7 to 7.2 +/- 0.6 mmol/liter, P < 0.01) and HbA(1c) (7.8 +/- 0.4 to 6.5 +/- 0.3%, P < 0.01) despite increased body weight (83.0 +/- 3.0 to 86.4 +/- 3.0 kg, P < 0.01). PIO improved Rd (6.6 +/- 0.6 vs. 5.2 +/- 0.5 mg/kg.min, P < 0.005) and reduced EGP (0.23 +/- 0.04 to 0.05 +/- 0.02 mg/kg.min, P < 0.01) during the 3-h insulin clamp. After PIO treatment, HFC decreased from 21.3 +/- 4.2 to 11.0 +/- 2.4% (P < 0.01), and plasma adiponectin increased from 7 +/- 1 to 21 +/- 2 micro g/ml (P < 0.0001). Plasma adiponectin concentration correlated negatively with HFC (r = -0.60, P < 0.05) and EGP (r = -0.80, P < 0.004) and positively with Rd before (r = 0.68, P < 0.02) pioglitazone treatment; similar correlations were observed between plasma adiponectin levels and HFC (r = -0.65, P < 0.03) and Rd after (r = 0.70, P = 0.01) pioglitazone treatment. EGP was almost completely suppressed after pioglitazone treatment; taken collectively, plasma adiponectin concentration, before and after pioglitazone treatment, still correlated negatively with EGP during the insulin clamp (r = -0.65, P < 0.001). In conclusion, PIO treatment in type 2 diabetes causes a 3-fold increase in plasma adiponectin concentration. The increase in plasma adiponectin is strongly associated with a decrease in hepatic fat content and improvements in hepatic and peripheral insulin sensitivity. The increase in plasma adiponectin concentration after thiazolidinedione therapy may play an important role in reversing the abnormality in hepatic fat mobilization and the hepatic/muscle insulin resistance in patients with type 2 diabetes.     

Plasma resistin concentration, hepatic fat content, and hepatic and peripheral insulin resistance in pioglitazone-treated type II diabetic patients

OBJECTIVES: To study the effect of pioglitazone (PIO) on plasma resistin concentration, endogenous glucose production (EGP), and hepatic fat content (HFC) in patients with type II diabetes (T2DM). SUBJECTS: A total of 13 T2DM patients (age=51+/-2 y, BMI=29.7+/-1.1 kg/m(2), HbA(1c)=8.0+/-0.5%). METHODS: HFC (magnetic resonance spectroscopy) and basal plasma resistin concentration were quantitated before and after PIO treatment (45 mg/day) for 16 weeks. Subjects received a 3 h euglycemic insulin (100 mU/m(2)/min) clamp with 3-[(3)H] glucose to determine rates of EGP and tissue glucose disappearance (Rd) before and after PIO. RESULTS: PIO reduced fasting plasma glucose (10.3+/-0.7 to 7.6+/-0.6 mmol/l, P<0.001) and HbA(1c) (8.0+/-0.4 to 6.8+/-0.3%, P<0.001) despite increased body weight (83.2+/-3.4 to 86.3+/-3.4 kg, P<0.001). PIO improved Rd (4.9+/-0.4 to 6.6+/-0.5 mg/kg/min, P<0.005) and reduced EGP (0.22+/-0.04 to 0.06+/-0.02 mg/kg/min, P<0.01) during the insulin clamp. Following PIO, HFC decreased from 21.1+/-3.5 to 11.2+/-2.1% (P<0.005), and plasma resistin decreased from 5.3+/-0.6 to 3.5+/-0.3 ng/ml (P<0.01). Plasma resistin concentration correlated positively with HFC before (r=0.58, P<0.05) and after (r=0.55, P<0.05) PIO treatment. Taken collectively, plasma resistin concentration, before and after PIO treatment, correlated positively with hepatic fat content (r=0.66, P<0.001) and EGP during the insulin clamp (r=0.41, P<0.05). However, the plasma resistin concentration did not correlate with whole body glucose disposal (Rd) during the insulin clamp either before (r=-0.18, P=NS) or after (r=-0.13, P=NS) PIO treatment. CONCLUSIONS: PIO treatment in T2DM causes a significant decrease in plasma resistin concentration. The decrease in plasma resistin is positively correlated with the decrease in hepatic fat content and improvement in hepatic insulin sensitivity.     

The role of plasma fatty acid composition in endogenous glucose production in patients with type 2 diabetes mellitus

Hepatic insulin resistance and increased endogenous glucose production (EGP) are associated with increased plasma free fatty acids (FFA). However, the contribution of FFA composition to the regulation of EGP is not known. Six obese nondiabetic subjects and 6 patients with type 2 diabetes mellitus (DM2) were studied after an overnight and a 3-day fast. Plasma insulin concentrations after an overnight fast were similar in the DM2 and nondiabetic patients (88.8 +/- 26.4 v 57.6 +/- 12.6 pmol/L, not significant [NS]) despite increased plasma glucose (9.9 +/- 1.8 v 5.1 +/- 0.1 mmol/L, P <.01) and EGP (510.3 +/- 77.7 v 298.3 +/- 18.3 micromol x m(-2) x min(-1), P <.05) in the patients with DM2. Absolute rates of gluconeogenesis using the heavy water method were also increased in the patients with DM2 (346.8 +/- 74.9 v 198.8 +/- 16.4 micromol x m(-2). min(-1), P <.05). No differences were observed in plasma polyunsaturated fatty acids (PUFA) between the diabetic and nondiabetic subjects. However, total saturated fatty acid (SFA) concentrations (350 +/- 37.4 v 230.9 +/- 33.3 micromol/L, P <.02) were significantly increased in the diabetic subjects. Rates of EGP were correlated with total plasma FFA concentration (r =.71, P <.01) and the concentration of SFA (r =.71, P <.01), but not monounsaturated fatty acids or PUFA. Rates of gluconeogenesis were also correlated with plasma FFA (r =.64, P <.05) and SFA (r =.67, P <.05). We observed no relationship between EGP and either total FFA or fatty acid composition after a 3-day fast. We conclude that increases in EGP are associated with concentrations of plasma SFA after an overnight fast.     

Effect of pioglitazone on abdominal fat distribution and insulin sensitivity in type 2 diabetic patients

We examined the effect of pioglitazone on abdominal fat distribution to elucidate the mechanisms via which pioglitazone improves insulin resistance in patients with type 2 diabetes mellitus. Thirteen type 2 diabetic patients (nine men and four women; age, 52 +/- 3 yr; body mass index, 29.0 +/- 1.1 kg/m(2)), who were being treated with a stable dose of sulfonylurea (n = 7) or with diet alone (n = 6), received pioglitazone (45 mg/d) for 16 wk. Before and after pioglitazone treatment, subjects underwent a 75-g oral glucose tolerance test (OGTT) and two-step euglycemic insulin clamp (insulin infusion rates, 40 and 160 mU/m(2).min) with [(3)H]glucose. Abdominal fat distribution was evaluated using magnetic resonance imaging at L4-5. After 16 wk of pioglitazone treatment, fasting plasma glucose (179 +/- 10 to 140 +/- 10 mg/dl; P < 0.01), mean plasma glucose during OGTT (295 +/- 13 to 233 +/- 14 mg/dl; P < 0.01), and hemoglobin A(1c) (8.6 +/- 0.4% to 7.2 +/- 0.5%; P < 0.01) decreased without a change in fasting or post-OGTT insulin levels. Fasting plasma FFA (674 +/- 38 to 569 +/- 31 microEq/liter; P < 0.05) and mean plasma FFA (539 +/- 20 to 396 +/- 29 microEq/liter; P < 0.01) during OGTT decreased after pioglitazone. In the postabsorptive state, hepatic insulin resistance [basal endogenous glucose production (EGP) x basal plasma insulin concentration] decreased from 41 +/- 7 to 25 +/- 3 mg/kg fat-free mass (FFM).min x microU/ml; P < 0.05) and suppression of EGP during the first insulin clamp step (1.1 +/- 0.1 to 0.6 +/- 0.2 mg/kg FFM.min; P < 0.05) improved after pioglitazone treatment. The total body glucose MCR during the first and second insulin clamp steps increased after pioglitazone treatment [first MCR, 3.5 +/- 0.5 to 4.4 +/- 0.4 ml/kg FFM.min (P < 0.05); second MCR, 8.7 +/- 1.0 to 11.3 +/- 1.1 ml/kg FFM(.)min (P < 0.01)]. The improvement in hepatic and peripheral tissue insulin sensitivity occurred despite increases in body weight (82 +/- 4 to 85 +/- 4 kg; P < 0.05) and fat mass (27 +/- 2 to 30 +/- 3 kg; P < 0.05). After pioglitazone treatment, sc fat area at L4-5 (301 +/- 44 to 342 +/- 44 cm(2); P < 0.01) increased, whereas visceral fat area at L4-5 (144 +/- 13 to 131 +/- 16 cm(2); P < 0.05) and the ratio of visceral to sc fat (0.59 +/- 0.08 to 0.44 +/- 0.06; P < 0.01) decreased. In the postabsorptive state hepatic insulin resistance (basal EGP x basal immunoreactive insulin) correlated positively with visceral fat area (r = 0.55; P < 0.01). The glucose MCRs during the first (r = -0.45; P < 0.05) and second (r = -0.44; P < 0.05) insulin clamp steps were negatively correlated with the visceral fat area. These results demonstrate that a shift of fat distribution from visceral to sc adipose depots after pioglitazone treatment is associated with improvements in hepatic and peripheral tissue sensitivity to insulin.     

Effect of pioglitazone on circulating adipocytokine levels and insulin sensitivity in type 2 diabetic patients

We examined the effect of pioglitazone (PIO) on circulating adipocytokine levels to elucidate the mechanisms by which thiazolidinediones improve insulin resistance in type 2 diabetes mellitus (T2DM). Twenty-three subjects with T2DM (age 54 +/- 2 yr, body mass index 29 +/- 1 kg/m(2)) were randomly assigned to receive placebo (n = 11) or PIO, 45 mg/d (n = 12), for 4 months. Before and after treatment, subjects received a 75-g oral glucose tolerance test (OGTT); euglycemic insulin clamp (40 mU/m(2).min) with 3-(3)H-glucose; determination of fat mass ((3)H(2)O); and measurement of fasting glucose, free fatty acids (FFAs), leptin, adiponectin, and TNFalpha concentrations. After 4 months of PIO, fasting plasma glucose concentration (Delta = -2.7 mol/liter), mean plasma glucose during OGTT (Delta = -3.8 mol/liter), and hemoglobin A(1c) (Delta = 1.7%) decreased (P < 0.05 vs. placebo) without change in fasting or post-OGTT plasma insulin levels. Fasting FFAs (Delta = 168 micromol/liter) and TNFalpha (Delta = 0.7 pg/ml) concentrations decreased (P < 0.05 vs. placebo), whereas adiponectin (Delta = 8.7 microg/ml) increased (P < 0.01 vs. placebo). Despite the increase in body fat mass (Delta = 3.4 kg) after PIO, plasma leptin concentration did not change significantly. No changes in plasma glucose, FFAs, or adipocytokine levels were observed in placebo-treated subjects. During the insulin clamp, endogenous (hepatic) glucose production decreased (Delta = -2.67 micromol/fat-free mass.min, P < 0.05 vs. placebo), whereas metabolic clearance rate of glucose (MCR) increased (Delta = 0.58 ml/fat-free mass.min, P < 0.05 vs. placebo) after PIO. In all subjects, before and after PIO, the decrease in plasma FFA concentration was correlated with the changes in both endogenous (hepatic) glucose production (r = 0.47, P < 0.05) and MCR (r = -0.41, P < 0.05), whereas the increase in plasma adiponectin concentration was correlated with the change in endogenous (hepatic) glucose production (r = -0.70, P < 0.01) and MCR (r = 0.49, P < 0.05). These results suggest that the direct effects of PIO on adipose tissue to decrease plasma FFA levels and increase plasma adiponectin contribute to the improvements in hepatic and peripheral insulin sensitivity and glucose tolerance in patients with T2DM.     

Relationship between hepatic/visceral fat and hepatic insulin resistance in nondiabetic and type 2 diabetic subjects

BACKGROUND AND AIMS: Abdominal fat accumulation (visceral/hepatic) has been associated with hepatic insulin resistance (IR) in obesity and type 2 diabetes (T2DM). We examined the relationship between visceral/hepatic fat accumulation and hepatic IR/accelerated gluconeogenesis (GNG). METHODS: In 14 normal glucose tolerant (NGT) (body mass index [BMI] = 25 +/- 1 kg/m(2)) and 43 T2DM (24 nonobese, BMI = 26 +/- 1; 19 obese, BMI = 32 +/- 1 kg/m(2)) subjects, we measured endogenous (hepatic) glucose production (3-(3)H-glucose) and GNG ((2)H(2)O) in the basal state and during 240 pmol/m(2)/min euglycemic-hyperinsulinemic clamp, and liver (LF) subcutaneous (SAT)/visceral (VAT) fat content by magnetic resonance spectroscopy/magnetic resonance imaging. RESULTS: LF was increased in lean T2DM compared with lean NGT (18% +/- 3% vs 9% +/- 2%, P < .03), but was similar in lean T2DM and obese T2DM (18% +/- 3% vs 22% +/- 3%; P = NS). Both VAT and SAT increased progressively from lean NGT to lean T2DM to obese T2DM. T2DM had increased basal endogenous glucose production (EGP) (NGT, 15.1 +/- 0.5; lean T2DM, 16.3 +/- 0.4; obese T2DM, 17.2 +/- 0.6 micromol/min/kg(ffm); P = .02) and basal GNG flux (NGT, 8.6 +/- 0.4; lean T2DM, 9.6 +/- 0.4; obese T2DM, 11.1 +/- 0.6 micromol/min/kg(ffm); P = .02). Basal hepatic IR index (EGP x fasting plasma insulin) was increased in T2DM (NGT, 816 +/- 54; lean T2DM, 1252 +/- 164; obese T2DM, 1810 +/- 210; P = .007). In T2DM, after accounting for age, sex, and BMI, both LF and VAT, but not SAT, were correlated significantly (P < .05) with basal hepatic IR and residual EGP during insulin clamp. Basal percentage of GNG and GNG flux were correlated positively with VAT (P < .05), but not with LF. LF, but not VAT, was correlated with fasting insulin, insulin-stimulated glucose disposal, and impaired FFA suppression by insulin (all P < .05). CONCLUSIONS: Abdominal adiposity significantly affects both lipid (FFA) and glucose metabolism. Excess VAT primarily increases GNG flux. Both VAT and LF are associated with hepatic IR.     

Vanadyl sulfate improves hepatic and muscle insulin sensitivity in type 2 diabetes

Vanadyl sulfate (VOSO(4)) is an oxidative form of vanadium that in vitro and in animal models of diabetes has been shown to reduce hyperglycemia and insulin resistance. Small clinical studies of 2- to 4-week duration in type 2 diabetes (T2DM) have led to inconsistent results. To define its efficacy and mechanism of action, 11 type 2 diabetic patients were treated with VOSO(4) at a higher dose (150 mg/day) and for a longer period of time (6 weeks) than in previous studies. Before and after treatment we measured insulin secretion during an oral glucose tolerance test, and endogenous glucose production (EGP) and whole body insulin-mediated glucose disposal using the euglycemic insulin clamp technique combined [3-(3)H]glucose infusion. Treatment significantly improved glycemic control: fasting plasma glucose (FPG) decreased from 194 +/- 16 to 155 +/- 15 mg/dL, hemoglobin A(1c) decreased from 8.1 +/- 0.4 to 7.6 +/- 0.4%, and fructosamine decreased from 348 +/- 26 to 293 +/- 12 micromol/L (all P < 0.01) without any change in body weight. Diabetics had an increased rate of EGP compared with nondiabetic controls (4.1 +/- 0.2 vs. 2.7 +/- 0.2 mg/kg lean body mass.min; P< 0.001), which was closely correlated with FPG (r = 0.56; P< 0.006). Vanadyl sulfate reduced EGP by about 20% (P< 0.01), and the decline in EGP was correlated with the reduction in FPG (r = 0.60; P< 0.05). Vanadyl sulfate also caused a modest increase in insulin-mediated glucose disposal (from 4.3 +/- 0.4 to 5.1 +/- 0.6 mg/kg lean body mass x min; P< 0.03), although the improvement in insulin sensitivity did not correlate with the decline in FPG after treatment (r = -0.16; P = NS). Vanadyl sulfate treatment lowered the plasma total cholesterol (223 +/- 14 vs. 202 +/- 16 mg/dL; P < 0.01) and low density lipoprotein cholesterol (141 +/- 14 vs. 129 +/- 14 mg/dL; P < 0.05), whereas 24-h ambulatory blood pressure was unaltered. We conclude that VOSO(4) at maximal tolerated doses for 6 weeks improves hepatic and muscle insulin sensitivity in T2DM. The glucose-lowering effect of VOSO(4) correlated well with the reduction in EGP, but not with insulin-mediated glucose disposal, suggesting that liver, rather than muscle, is the primary target of VOSO(4) action at therapeutic doses in T2DM.     

Tumor necrosis factor alpha and insulin resistance in obese type 2 diabetic patients

The relationship between basal serum tumor necrosis factor alpha (TNFalpha) levels and peripheral tissue (muscle) sensitivity to insulin was examined in 63 subjects with normal glucose tolerance (NGT), 18 subjects with impaired glucose tolerance (IGT), and 123 patients with type 2 diabetes mellitus (T2DM). The BMI was similar in NGT (28.8+/-0.7 kg/m(2)), IGT (31.1+/-1.0), and T2DM (30.0+/-0.4) groups. The fasting serum TNFalpha concentration in T2DM (4.4+/-0.2 pg/ml) was significantly higher than in NGT (3.1+/-0.2) and IGT (3.4+/-0.2; both P<0.05). In T2DM the fasting plasma glucose (FPG=183+/-5 mg/dl) and insulin (FPI=17+/-1 micro U/ml) concentrations were significantly higher than in NGT (FPG=95+/-1; FPI=10+/-1) and IGT (FPG=100+/-2; FPI=13+/-1; all P<0.01). The rate of total body insulin-mediated glucose disposal (Rd; 40 mU/m(2) min euglycemic insulin clamp in combination with (3)H-glucose) was reduced in T2DM (102+/-3 mg/m(2) min) compared with NGT (177+/-10) and IGT (151+/-14; both P<0.01). The serum TNFalpha concentration was inversely correlated with Rd (r=-0.47, P<0.0001) and positively correlated with both FPG (r=0.32, P=0.004) and FPI (r=0.32, P=0.004) in NGT plus IGT. No correlation was observed between serum TNFalpha and Rd (r=-0.02), FPG (r=0.15), or FPI (r=0.15) in T2DM. In stepwise multiple regression analysis using age, sex, BMI, FPG, FPI and serum TNFalpha concentration as independent variables, only BMI and serum TNFalpha concentration were significant and independent predictors of Rd (r(2)=0.29, P<0.0001) in the NGT plus IGT group, while FPG and FPI were significant and independent predictors of Rd (r(2)=0.13, P<0.0001) in T2DM. These results suggest that: (i) an increase in circulating TNFalpha concentration is associated with peripheral insulin resistance and increased plasma glucose and insulin levels prior to the onset of type 2 diabetes; and (ii) the further deterioration in peripheral insulin resistance in T2DM (compared with NGT and IGT) is unrelated to the increase in serum TNFalpha concentration.     

Brain-derived neurotrophic factor ameliorates hepatic insulin resistance in Zucker fatty rats

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophins, has been reported to ameliorate hyperglycemia in obese diabetic animal models. To elucidate the mechanism of BDNF on glucose metabolism, we determined the glucose turnover under basal and euglycemic hyperinsulinemic (insulin infusion rate, 54 pmol. kg(-1). min(-1)) clamp conditions in obese insulin-resistant rats, male Zucker fatty rats, which had been acutely administered a subcutaneous injection of BDNF (20 mg/kg) (n = 9, BDNF) or vehicle (n = 8, vehicle). Under the basal condition, acute administration of BDNF did not affect the blood glucose level, plasma insulin level, rate of glucose disappearance (Rd), and endogenous glucose production (EGP). Under the clamp condition, the glucose infusion rate (GIR) was significantly higher in BDNF than in vehicle (mean +/- SD, 61.4 +/- 19.1 v 41.4 +/- 4.9 micromol. kg(-1). min(-1), P <.05). There was no significant difference in Rd and EGP between the 2 groups under the clamp condition, but the insulin-mediated suppression ratio of endogenous glucose production in BDNF was significantly greater than in vehicle (48.9 +/- 22.2 v 22.4% +/- 20.6%, P <.05). In BDNF, mRNA expressions of hepatic phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) were comparable to those of vehicle, while hepatic glucokinase (GK) mRNA expression was significantly higher (1.57 +/- 0.33 v 1.03 +/- 0.17, P <.05). We conclude that BDNF mainly improves hepatic insulin resistance in obese insulin-resistant rats, probably by affecting the hepatic GK flux. Copyright 2003, Elsevier Science (USA). All rights reserved.     

Acute elevation of free fatty acids impairs hepatic glucose uptake in conscious rats

To investigate the dose-dependent effect of free fatty acid (FFA) on the hepatic glucose uptake (HGU), we determined hepatic glucose fluxes by a dual tracer technique during the basal state and euglycemic hyperinsulinemic clamp combined with a portal glucose load in three groups of rats given saline (saline), low-dose lipid (lipid-L), or high-dose lipid infusion (lipid-H). In the basal state, lipid infusion dose-dependently increased plasma FFA (saline, 400 +/- 50; lipid-L, 550 +/- 30; lipid-H, 1700 +/- 270 micromol l(-1); mean +/- S.E). Endogenous glucose production (EGP) in lipid-H was 63.5 +/- 5.5 micromol kg(-1) min(-1) and significantly higher than in the saline and lipid-L (40.2 +/- 2.9, 47.6 +/- 3.1 micromol kg(-1) min(-1), respectively). During euglycemic hyperinsulinemic clamp, plasma FFA decreased to 130 +/- 30 micromol l(-1) in saline, but remained at basal levels in lipid-L and lipid-H (470 +/- 30 and 1110 +/- 180 micromol l(-1), respectively). Insulin-suppressed EGP was complete in saline and lipid-L, but impaired in lipid-H (38.0 +/- 6.4 micromol kg(-1) min(-1)). Elevated FFA dose-dependently reduced HGU (saline, 12.2 +/- 0.9; lipid-L, 8.6 +/- 0.6; lipid-H, 4.7 +/- 1.4 micromol kg(-1) min(-1)). In conclusion, acutely elevated FFA impairs HGU as well as insulin-mediated suppression of EGP during hyperinsulinemic clamp with portal glucose loading. Impaired hepatic glucose uptake associated with elevated FFA may contribute to the development of insulin resistance in obesity and type 2 diabetes.     

Fasting hyperglycemia impairs glucose- but not insulin-mediated suppression of glucagon secretion

AIM: Our aim was to assess the effect of chronic hyperglycemia on glucose- and insulin-mediated suppression of glucagon secretion by the alpha-cell. METHODS: Thirty subjects with normal glucose tolerance, 27 with impaired fasting glucose and/or impaired glucose tolerance, and 32 type 2 diabetic subjects were studied with oral glucose tolerance test (OGTT) and euglycemic hyperinsulinemic clamp. Fasting plasma glucagon concentration and plasma glucagon concentration during the OGTT and insulin clamp were measured. RESULTS: During the OGTT, the decrement in the plasma glucagon concentration (area under the curve) was correlated inversely with the fasting plasma glucose concentration (r = -0.35; P < 0.001). As the fasting glucose level increased, the suppression of plasma glucagon progressively diminished. In contrast, during the euglycemic insulin clamp, the suppression of plasma glucagon was not correlated with the fasting plasma glucose concentration and was similar in subjects with normal glucose tolerance, subjects with impaired fasting glucose/impaired glucose tolerance, and diabetic subjects: 18, 23, and 18%, respectively. CONCLUSION: Insulin-mediated suppression of glucagon secretion is unrelated to the fasting plasma glucose concentration and is not impaired by chronic hyperglycemia. Thus, the defect in plasma glucagon suppression during the OGTT most likely results from impaired glucose-mediated glucagon suppression. The close correlation between fasting plasma glucose concentration and reduced glucagon suppression suggests a glucotoxic effect on alpha-cell function.     

Somatostatin does not alter insulin-mediated glucose disposal

We examined the effect of somatostatin (SRIH) infusion on insulin-mediated glucose disposal (Rd) in normal young subjects (n = 8) to determine the influence of SRIH on insulin action. Paired 3-h euglycemic insulin clamp studies were performed in random order employing insulin alone (25 mU/m2 X min) or insulin with SRIH (250 micrograms/h) and replacement of basal glucagon (0.4 ng/kg X min). Basal plasma glucose, insulin, glucagon (IRG), and GH concentrations, hepatic glucose production, and Rd were similar on each occasion. Steady state (10-180 min) plasma insulin insulin alone, 283 +/- 10 (+/- SEM); insulin, IRG, and SRIH, 284 +/- 10 pmol/L) and glucagon levels (insulin alone, 84 +/- 7; insulin, IRG, and SRIH, 82 +/- 7 ng/L) were similar. Hepatic glucose production (insulin alone, 0.66 +/- 0.12; insulin, IRG, and SRIH, 0.78 +/- 0.48 mg/kg X min) and Rd (insulin alone, 8.16 +/- 0.62; insulin, IRG, and SRIH, 8.17 +/- 0.61 mg/kg X min) were not different at steady state. We conclude that SRIH infusion with glucagon replacement does not augment insulin-mediated glucose disposal in normal young subjects at physiological insulin levels.     

Overnutrition induced decrease in insulin action for glucose storage: in vivo and in vitro in man

The effect of short-term overnutrition on insulin action for glucose disposal was assessed in 15 Southwest American Indians (mean wt = 74 +/- 6 kg). After two weeks of weight maintenance and again after two weeks of 62% greater caloric intake (constant ratio of fat:carbohydrate:protein), insulin action for glucose disposal was measured using the euglycemic clamp technique with plasma insulin concentrations of about 110 and 1800 uU/mL. Simultaneous indirect calorimetry was used to estimate carbohydrate oxidation and storage rates. Following overnutrition, mean weight gain was 3.0 +/- 0.2 kg, P less than 0.01. Overnutrition induced a decrease in glucose storage at the low and high insulin concentrations: 1.2 +/- 0.3 to 0.2 +/- 0.3, P less than 0.01, and 6.4 +/- 0.3 to 4.3 +/- 0.5, mg/kg FFM min, P less than 0.001. Carbohydrate oxidation was significantly increased at both insulin concentrations. The mean total insulin mediated glucose disposal rate decreased from 11.6 +/- 0.5 to 10.3 +/- 0.7, P less than 0.01, at the high insulin concentration. This decrease was due entirely to the reduction in carbohydrate storage and was correlated with increased fasting insulin concentration (r = 0.7, P less than 0.01). Overnutrition also induced a significant decrease in the percent muscle glycogen synthase active measured fasting and at the end of the high-dose insulin infusion. The results indicate that short-term overnutrition results in reduced insulin action for glucose storage and disposal which is correlated with increased fasting insulin concentrations. Reduced glycogen synthase activity may contribute to the effect of overnutrition on in vivo insulin-mediated glucose storage.     

The relationship between glucose disposal in response to physiological hyperinsulinemia and basal glucose and free fatty acid concentrations in healthy volunteers

This study was initiated to see if defects in the ability of physiological hyperinsulinemia (approximately 60 microU/mL) to stimulate glucose uptake in healthy, nondiabetic volunteers are associated with increases in concentrations of plasma glucose and free fatty acid (FFA) when measured at basal insulin concentrations (approximately 10 microU/mL). We recruited 22 volunteers (12 women and 10 men) for these studies, with a (mean +/- SEM) body mass index of 24.8 +/- 0.5 kg/m2. Resistance to insulin-mediated glucose disposal during physiological hyperinsulinemia was determined by suppressing endogenous insulin and determining the steady-state plasma glucose (SSPG) and steady-state plasma insulin (SSPI) concentrations at the end of a 3-h infusion, period during which glucose (267 mg/m2 x min) and insulin (32 mU/m2 x min) were infused at a constant rate. Glucose, insulin and FFA concentrations were also measured in response to infusion rates of glucose (50 mg/m2 x min) and insulin (6 mU/m2 x min). The SSPI concentration (mean +/- SEM) during physiological hyperinsulinemia was 64 +/- 3 microU/mL), in contrast to 12 +/- 0.4 microU/mL during the basal insulin study. The results demonstrated a significant relationship between SSPG concentration in response to physiological hyperinsulinemia (SSPG60) and SSPG(Basal) (r = 0.57, P < 0.01) and FFA(Basal) (r = 0.73, P < 0.001). Furthermore, FFA(Basal) and SSPG(Basal) were significantly correlated (r = 0.47, P < 0.05). Comparison of the seven most insulin-resistant and seven most insulin sensitive individuals (SSPG60 values of 209 +/- 16 vs. 64 +/- 8 mg/dL) revealed that the insulin-resistant group also had significantly higher SSPG(Basal) (105 +/- 5 vs. 78 +/- 7 mg/dL, P < 0.01) and FFA(Basal) (394 +/- 91 vs. 104 +/- 41, P < 0.02) concentrations. However, random fasting plasma glucose and FFA concentrations of the two groups were not different. The results presented demonstrate that individual differences in the ability of elevated insulin concentrations to stimulate muscle glucose disposal are significantly correlated with variations in insulin regulation of plasma glucose and FFA concentrations at basal insulin concentrations.     

Associations between regional body fat distribution, fasting plasma free fatty acid levels and glucose tolerance in premenopausal women

The associations between total adiposity, body fat distribution measured by computed tomography (CT) and estimated by the waist-to-hip ratio (WHR), regional fat cell morphology, fasting plasma free fatty acid (FFA) levels and glucose tolerance were studied in a sample of 37 premenopausal women aged 35.3 +/- 4.6 years (mean +/- s.d.). Body fat mass, CT-derived abdominal and femoral fat areas, as well as the abdominal fat cell weight were all significantly associated with fasting plasma FFA levels (0.34 less than r less than 0.49, 0.005 less than P less than 0.05), and with the glucose and insulin areas during the oral glucose tolerance test (OGTT) (0.36 less than r less than 0.70, 0.0001 less than P less than 0.05). No associations were found between the WHR, the femoral fat cell weight and fasting plasma FFA levels or glucose area during the OGTT. However, the WHR and the femoral fat cell weight were positively associated with insulin area. Plasma FFA levels were positively correlated with the glucose area during the OGTT, whereas no association was found between plasma FFA levels and the insulin area. Covariance analysis indicated that this effect of plasma FFA levels on the magnitude of glucose response to OGTT was independent from that of total adiposity or regional body fat distribution variables. These results emphasize the importance of plasma FFA levels as a correlate of glucose tolerance and suggest that the associations previously reported between obesity, regional body fat distribution, fat cell size and glucose tolerance are, at least partly, mediated by variations in plasma FFA levels.     

Plasma free fatty acid concentration during hyperglycemic glucose clamp with and without somatostatin infusion in obese subjects with normal glucose tolerance

In the present study we evaluated the regulation of plasma free fatty acid (FFA) concentration by glucose and insulin in human obesity. To this purpose we measured plasma FFA concentration in normoglycemic, normoinsulinemic obese (n = 8) and nonobese (n = 8) healthy subjects during 240 min of exogenous hyperglycemia (hyperglycemic glucose clamp) in presence of both glucose-stimulated (0-120 min and 180-240 min) and somatostatin-inhibited (120-180 min) insulin secretion. We found that plasma FFA curves were roughly parallel in the 0-120 min period and FFA values of obese subjects were constantly higher throughout the experimental period. Moreover, the difference between the two groups was significant when individual data were expressed as a percent of fasting FFA value (P less than 0.0001 from 0 to 120 min). Plasma insulin levels were similar in the two groups during the entire study. The amount of glucose metabolized during the 80-120 min period was significantly lower in obese than in nonobese subjects (172 +/- 7 v. 341 +/- 11 mg/m2.min, P less than 0.01; means +/- s.e.). During the somatostatin period (120-180 min) plasma insulin was lowered close to basal values in both groups (116 +/- 15 and 109 +/- 11 pmol/l) and plasma FFA concentrations rose in a linear fashion. Our data suggest that suppression of plasma FFA concentrations by glucose and insulin is qualitatively similar in healthy nonobese and obese subjects, the latter having higher FFA values. Insulin action on FFA metabolism isn ot grossly impaired in obese subjects who are clearly insulin resistant as far as glucose metabolism is concerned.     

The effect of rosiglitazone on the liver: decreased gluconeogenesis in patients with type 2 diabetes

AIMS/HYPOTHESIS: Diabetic hyperglycemia results from insulin resistance of peripheral tissues and glucose overproduction due to increased gluconeogenesis (GNG). Thiazolidinediones have been shown to improve glycemic control and increase peripheral insulin sensitivity. Whether chronic thiazolidinedione treatment is associated with a decrease in GNG has not been determined. MATERIALS AND METHODS: We studied 26 diet-treated type 2 diabetic patients randomly assigned to rosiglitazone (RSG; 8 mg/d; n = 13) or placebo (n = 13) for 12 wk. At baseline and 12 wk, we measured endogenous glucose production (by [3H]glucose infusion) and GNG (by the [2H]2O technique) after a 15-h fast. Peripheral insulin sensitivity was evaluated by a two-step (240 and 960 pmol/min/m(-2)) euglycemic insulin clamp. RESULTS: Compared with placebo, RSG reduced fasting plasma glucose (9.7 +/- 0.7 to 7.4 +/- 0.3 mmol/liter; P < 0.001), fasting fractional GNG (-15 +/- 4%; P = 0.002), and fasting GNG flux (-3.9 +/- 1.2 micromol/min/kg fat-free mass; P = 0.004), with no effect on glycogenolytic flux. Changes in GNG flux and fasting glucose were tightly correlated (r = 0.83; P < 0.0001). During both clamp steps, RSG enhanced insulin-mediated glucose clearance (by 26% and 31%; P = 0.01 and P < 0.02, respectively). In a subgroup of patients studied with magnetic resonance imaging, the reduction in GNG flux was correlated (r = 0.65; P < 0.02) with the reduction in visceral fat area. CONCLUSION/INTERPRETATION: RSG increases peripheral tissue insulin sensitivity and decreases endogenous glucose release via an inhibition of gluconeogenesis.     

Recombinant human insulin-like growth factor I treatment for 1 week improves metabolic control in type 2 diabetes by ameliorating hepatic and muscle insulin resistance

The administration of recombinant human insulin-like growth factor I (rhIGF-I) reduces hyperglycemia and insulin requirements in subjects with severe insulin resistance syndromes and in patients with type 2 diabetes mellitus (T2DM). However, the mechanisms responsible for the improved metabolic control are incompletely understood. One proposed mechanism is that rhIGF-I therapy in T2DM may bypass early defects in insulin action (i.e. signal transduction), leading to improved hepatic and/or peripheral insulin sensitivity. To test this hypothesis, we used the euglycemic insulin clamp to measure the response to 7 days of rhIGF-I therapy (80 microg/kg, sc, twice daily) in eight poorly controlled T2DM subjects. rhIGF-I significantly improved fasting (203 +/- 12 vs. 134 +/- 14 mg/dL; P < 0.01) and day-long (0800-1700 h; 234 +/- 11 vs. 153 +/- 10 mg/dL; P < 0.01) plasma glucose levels. Basal endogenous glucose production decreased from 3.2 +/- 0.2 to 2.7 +/- 0.2 mg/kg lean body mass x min (P < 0.03) despite a concomitant decline in the fasting plasma insulin concentration from 13 +/- 5 to 5 +/- 1 microU/mL (P < 0.01). The decrement in basal endogenous glucose production was closely correlated with the decrement in fasting plasma glucose concentration (r = 0.78; P < 0.01). Whole body insulin-stimulated glucose disposal increased by 27% (from 5.6 +/- 0.8 to 7.1 +/- 0.8 mg/kg lean body mass x min; P < 0.01), but remained well below that observed in age- and weight-matched healthy subjects. The effects of rhIGF-I on endogenous glucose production and peripheral insulin sensitivity resemble those observed with intensified insulin regimens in T2DM. We conclude that 7 days of sc rhIGF-I improves glucose control by improving hepatic and muscle insulin sensitivity, but it remains markedly abnormal. This indicates that an intrinsic defect(s) responsible for insulin resistance in T2DM cannot be overcome by rhIGF-I treatment.     

Inhibition of lipolysis during acute GH exposure increases insulin sensitivity in previously untreated GH-deficient adults

OBJECTIVE: Previous studies evaluating the lipolytic effect of GH have in general been performed in subjects on chronic GH therapy. In this study we assessed the lipolytic effect of GH in previously untreated patients and examined whether the negative effect of enhanced lipolysis on glucose metabolism could be counteracted by acute antilipolysis achieved with acipimox. METHODS: Ten GH-deficient (GHD) adults participated in four experiments each, during which they received in a double-blind manner: placebo (A); GH (0.88+/-0.13 mg) (B); GH+acipimox 250 mg b.i.d. (C); and acipimox b.i.d. (no GH) (D), where GH was given the night before a 2 h euglycemic, hyperinsulinemic clamp combined with infusion of [3-(3)H]glucose and indirect calorimetry. RESULTS: GH increased basal free fatty acid (FFA) levels by 74% (P=0.0051) and insulin levels by 93% (P=0.0051). This resulted in a non-significant decrease in insulin-stimulated glucose uptakes (16.61+/-8.03 vs 12.74+/-5.50 micromol/kg per min (s.d.), P=0.07 for A vs B). The rates of insulin-stimulated glucose uptake correlated negatively with the FFA concentrations (r=-0.638, P<0.0001). However, acipimox caused a significant improvement in insulin-stimulated glucose uptake in the GH-treated patients (17.35+/-5.65 vs 12.74+/-5.50 micromol/kg per min, P=0.012 for C vs B). The acipimox-induced enhancement of insulin-stimulated glucose uptake was mainly due to an enhanced rate of glucose oxidation (8.32+/-3.00 vs 5.88+/-2.39 micromol/kg per min, P=0.07 for C vs B). The enhanced rates of glucose oxidation induced by acipimox correlated negatively with the rate of lipid oxidation in GH-treated subjects both in basal (r=-0.867, P=0.0093) and during insulin-stimulated (r=-0.927, P=0.0054) conditions. GH did not significantly impair non-oxidative glucose metabolism (6.86+/-5.22 vs 8.67+/-6.65 micromol/kg per min, P=NS for B vs A). The fasting rate of endogenous glucose production was unaffected by GH and acipimox administration (10.99+/-1.98 vs 11.73+/-2.38 micromol/kg per min, P=NS for B vs A and 11.55+/-2.7 vs 10.99+/-1.98 micromol/kg per min, P=NS for C vs B). On the other hand, acipimox alone improved glucose uptake in the untreated GHD patients (24.14+/-8.74 vs 16.61+/-8.03 micromol/kg per min, P=0.0077 for D vs A) and this was again due to enhanced fasting (7.90+/-2.68 vs 5.16+/-2.28 micromol/kg per min, P=0.01 for D vs A) and insulin-stimulated (9.78+/-3.68 vs 7.95+/-2.64 micromol/kg per min, P=0.07 for D vs A) glucose oxidation. CONCLUSION: The study of acute administration of GH to previously untreated GHD patients provides compelling evidence that (i) GH-induced insulin resistance is mainly due to induction of lipolysis by GH; and (ii) inhibition of lipolysis can prevent the deterioration of insulin sensitivity. The question remains whether GH replacement therapy should, at least at the beginning of therapy, be combined with means to prevent an excessive stimulation of lipolysis by GH.     

Insulin resistance is associated with impaired nitric oxide synthase activity in skeletal muscle of type 2 diabetic subjects

Type 2 diabetes is an insulin-resistant state characterized by hyperinsulinemia and accelerated atherosclerosis. In vitro and in vivo studies in rodents have suggested that nitric oxide generation plays an important role in glucose transport and insulin action. We determined nitric oxide synthase (NOS) activity in skeletal muscle of 10 type 2 diabetic (hemoglobin A(1C) = 6.8 +/- 0.1%) and 11 control subjects under basal conditions and during an 80 mU/m(2).min euglycemic insulin clamp performed with vastus lateralis muscle biopsies before and after 4 h of insulin. In diabetics, insulin-stimulated glucose disposal (Rd) was reduced by 50%, compared with controls (5.4 +/- 0.3 vs. 10.4 +/- 0.5 mg/kg.min, P < 0.01). Basal NOS activity was markedly reduced in the diabetic group (101 +/- 33 vs. 457 +/- 164 pmol/min.mg protein, P < 0.05). In response to insulin, NOS activity increased 2.5-fold in controls after 4 h (934 +/- 282 pmol/min.mg protein, P < 0.05 vs. basal), whereas insulin failed to stimulate NOS activity in diabetics (86 +/- 28 pmol/min.mg protein, P = NS from basal). Basal NOS protein content in muscle was similar in controls and diabetics and did not change following insulin. In controls, insulin-stimulated NOS activity correlated inversely with fasting plasma insulin concentration (r = -0.58, P = 0.05) and positively with Rd (r = 0.71, P = 0.03). In control and diabetic groups collectively, Rd correlated with insulin-stimulated NOS activity (r = 0.52, P = 0.02). We conclude that basal and insulin-stimulated muscle NOS activity is impaired in well-controlled type 2 diabetic subjects, and the defect in insulin-stimulated NOS activity correlates closely with the severity of insulin resistance. These results suggest that impaired NOS activity may play an important role in the insulin resistance in type 2 diabetic individuals.