Ghrelin enhances glucose-induced insulin secretion in scheduled meal-fed sheep

The purpose of this study was to investigate the effects of physiologic levels of ghrelin on insulin secretion and insulin sensitivity (glucose disposal) in scheduled fed-sheep, using the hyperglycemic clamp and hyperinsulinemic euglycemic clamp respectively. Twelve castrated Suffolk rams (69.8 +/- 0.6 kg) were conditioned to be fed alfalfa hay cubes (2% of body weight) once a day. Three hours after the feeding, synthetic ovine ghrelin was intravenously administered to the animals at a rate of 0.025 and 0.05 mug/kg body weight (BW) per min for 3 h. Concomitantly, the hyperglycemic clamp or the hyperinsulinemic euglycemic clamp was carried out. In the hyperglycemic clamp, a target glucose concentration was clamped at 100 mg/100 ml above the initial level. In the hyperinsulinemic euglycemic clamp, insulin was intravenously administered to the animals for 3 h at a rate of 2 mU/kg BW per min. Basal glucose concentrations (44+/- 1 mg/dl) were maintained by variably infusing 100 mg/dl glucose solution. In both clamps, plasma ghrelin concentrations were dose-dependently elevated and maintained at a constant level within the physiologic range. Ghrelin infusions induced a significant (ANOVA; P < 0.01) increase in plasma GH concentrations. In the hyperglycemic clamp, plasma insulin levels were increased by glucose infusion and were significantly (P < 0.05) greater in ghrelin-infused animals. In the hyperinsulinemic euglycemic clamp, glucose infusion rate, an index of insulin sensitivity, was not affected by ghrelin infusion. In conclusion, the present study has demonstrated for the first time that ghrelin enhances glucose-induced insulin secretion in the ruminant animal.     

Effects of hyperinsulinemia and hyperglycemia on insulin receptor function and glycogen synthase activation in skeletal muscle of normal man

Insulin receptor function, glycogen synthase activity, and activation by phosphatases were studied in biopsies of human skeletal muscle under conditions of hyperglycemia and/or hyperinsulinemia for 150 minutes. Twenty-one healthy volunteers underwent either (A) a hyperinsulinemic, euglycemic clamp (serum insulin, 160.0 +/- 7.7 mU/L; plasma glucose, 4.9 +/- 0.1 mmol/L; n = 9), (B) a hyperglycemic clamp during normoinsulinemia (serum insulin, 18.1 +/- 3.3 mU/L; plasma glucose, 12.9 +/- 0.2 mmol/L; n = 6), or (C) a combined hyperinsulinemic, hyperglycemic clamp (serum insulin, 158.3 +/- 15.0 mU/L; plasma glucose, 11.4 +/- 0.8 mmol/L; n = 6). During all studies, the endogenous insulin secretion was inhibited with somatostatin. Insulin binding and kinase activity of insulin receptors solubilized from vastus lateralis muscle biopsies were unaffected by hyperglycemia and/or hyperinsulinemia. Hyperinsulinemia activated the muscle glycogen synthase with a decrease in the half-maximal activation constant (A0.5) for glucose-6-phosphate (G6P) from 0.53 +/- 0.04 to 0.21 +/- 0.02 mmol/L (study A, P less than .02) and from 0.53 +/- 0.06 to 0.19 +/- 0.05 mmol/L (study C, P less than .03). In addition, the rate of glycogen synthase activation by phosphatases increased from 0.078 +/- 0.017 to 0.134 +/- 0.029 U/min/mg protein (study A, P less than .03) and from 0.082 +/- 0.013 to 0.145 +/- 0.033 U/min/mg protein (study C, P = .05). Hyperglycemia during normoinsulinemia did not affect A0.5 or phosphatase activity. In conclusion, (1) hyperinsulinemia for 2 1/2 hours increases glycogen synthase activity and activation by phosphatases independently on the glycemia; and (2) insulin receptor binding and basal and insulin-stimulated receptor kinase activity are not modified during short-term hyperinsulinemia and/or hyperglycemia.     

Hyperglycemia per se can reduce plasma free fatty acid and glycerol levels in the acutely insulin-deficient dog

To evaluate the in vivo effect of hyperglycemia per se on plasma free fatty acid (FFA) and glycerol concentrations, euglycemic and hyperglycemic clamp studies were performed in six overnight fasted dogs in the state of insulin deficiency produced by somatostatin (SRIF) infusion. The mean blood glucose concentrations during the steady-state (the second hour of each study) averaged 4.65 +/- 0.10 mmol/L in euglycemic clamp and 14.11 +/- 0.10 mmol/L in hyperglycemic clamp. During the SRIF infusion, plasma FFA concentrations increased from 0.32 +/- 0.05 mumol/mL at the basal state to 0.76 +/- 0.04 mumol/mL at the steady-state in euglycemic clamp and from 0.26 +/- 0.04 mumol/mL to 0.43 +/- 0.02 mumol/mL in hyperglycemic clamp. Plasma glycerol concentrations increased from the basal value of 0.07 +/- 0.01 mumol/mL to 0.15 +/- 0.01 mumol/mL during the steady-state in euglycemic clamp and from 0.06 +/- 0.01 mumol/mL to 0.08 +/- 0.01 mumol/mL in hyperglycemic clamp. The steady-state concentrations of plasma FFA and glycerol in hyperglycemic clamp were significantly lower than those in euglycemic clamp (P less than .001; respectively). These results suggest that hyperglycemia per se might decrease plasma FFA and glycerol concentrations at least in part by decreasing lipolysis in the acutely insulin-deficient dog.     

Time-dependent effect of hyperglycemia and hyperinsulinemia on oxidative and non-oxidative glucose metabolism in patients with NIDDM.

The present study was undertaken to compare the effect of hyperglycemia and euglycemia during identical hyperinsulinemic conditions on glucose metabolism in NIDDM subjects. Eight NIDDM subjects participated in a 4 h hyperglycemic (12.1 +/- 0.7 mmol/l), hyperinsulinemic (475 +/- 43 pmol/l) and in a 4 h euglycemic (5.5 +/- 0.5 mmol/l), hyperinsulinemic (468 +/- 36 pmol/l) insulin clamp in combination with indirect calorimetry and [3H]-3-glucose. Six non-diabetic subjects were studied during euglycemia (5.1 +/- 0.2 mmol/l) and hyperinsulinemia (474 +/- 35 pmol/l) and served as controls. In NIDDM patients the rate of insulin-stimulated glucose disposal was 57% greater during hyperglycemia compared with euglycemia throughout the 4 h clamp (p less than 0.01). The major part of the increase in glucose metabolism during hyperglycemia was due to an increase in the non-oxidative glucose metabolism (89%). Whereas glucose metabolism could not be normalized during the prolonged euglycemic hyperinsulinemic clamp in NIDDM patients (49.9 +/- 6.8 vs 57.5 +/- 5.4 mumol.(kgLBM)-1.min-1 in controls) the addition of hyperglycemia resulted in complete normalization of the glucose disposal rates (78.3 +/- 5.8 mumol.(kgLBM)-1.min-1). The effect of hyperglycemia was apparent already at 60 min of the clamp. The data thus suggest that glucose metabolism in NIDDM is insulin resistant, but that the defect in insulin-stimulated glucose uptake can be overcome by increasing the glucose concentration.     

Possible novel index determined by the glucose clamp test for selection of a suitable therapy for each type 2 diabetic patient

The hallmark of type 2 diabetes is insulin resistance and insufficient insulin secretion, and appropriate therapy should be selected for each patient. In this study, to establish some index to select suitable therapy for each patient, we evaluated insulin sensitivity and insulin secretion with euglycemic hyperinsulinemic clamp and hyperglycemic clamp tests, respectively, and found that specific GIR index (GIRxIRI (90)) could be a useful marker to select suitable therapy for each type 2 diabetic patient (GIR: glucose infusion rate in euglycemic hyperinsulinemic clamp test; IRI (90): plasma insulin level 90 min after starting the hyperglycemic clamp test).     

Insulin and glucagon secretion are suppressed equally during both hyper- and euglycemia by moderate hyperinsulinemia in patients with diabetes mellitus

Hyper- and euglycemic clamp studies were performed in patients with noninsulin-dependent diabetes mellitus to examine the effects of exogenous insulin administration on insulin and glucagon secretion. Plasma glucose was kept at the fasting level [mean, 10.0 +/- 0.2 (+/- SE) mmol/L; hyperglycemic clamp], and graded doses of insulin (1, 3, and 10 mU/kg.min, each for 50 min) were infused. The plasma C-peptide level gradually decreased from 523 +/- 66 to 291 +/- 43 pmol/L (n = 13; P less than 0.005) by the end of the hyperglycemic clamp study. After 90 min of equilibration with euglycemia (5.4 +/- 0.1 mmol/L; euglycemic clamp), the same insulin infusion protocol caused a similar decrease in the plasma C-peptide level. With the same glucose clamp protocol, physiological hyperinsulinemia for 150 min (676 +/- 40 pmol/L), obtained by the infusion of 2 mU/kg.min insulin, caused suppression of the plasma C-peptide level from 536 +/- 119 to 273 +/- 65 pmol/L during hyperglycemia and from 268 +/- 41 to 151 +/- 23 pmol/L during euglycemia (n = 9; P less than 0.005 in each clamp). Plasma glucagon was suppressed to a similar degree in both glycemic states. These results demonstrate that 1) insulin secretion in non-insulin-dependent diabetes mellitus is suppressed by high physiological doses of exogenous insulin in both the hyper- and euglycemic states, the degree of inhibition being independent of the plasma glucose level; and 2) glucagon secretion is also inhibited by such doses of exogenous insulin.     

Obesity and insulin resistance in humans: a dose-response study

Insulin-mediated glucose metabolism (euglycemic insulin clamp at plasma insulin concentration of 100 microU/mL) and glucose-stimulated insulin secretion (hyperglycemic clamp) were examined in 42 obese subjects (ideal body weight [IBW], 158 +/- 4%) with normal glucose tolerance and in 36 normal weight (IBW, 102% +/- 1%) age-matched controls. In 10 obese and eight control subjects, insulin was infused at six rates to increase plasma insulin concentration by approximately 10, 20, 40, 80, 2,000, and 20,000 microU/mL. Throughout the physiologic range of plasma insulin concentrations, both the increase in total body glucose uptake and the suppression of hepatic glucose production (HGP) were significantly impaired in the obese group (P less than .001 to .01). At the two highest plasma insulin concentrations, inhibition of HGP and the stimulation of glucose disposal were similar in both the obese and control groups. Insulin secretion during the hyperglycemic (+/- 125 mg/dL) clamp was twofold greater in obese subjects than in controls (P less than .01) and was inversely related to the rate of glucose uptake during the insulin clamp (r = -.438, P less than .05), but was still unable to normalize glucose disposal (P less than .05). In conclusion, our results indicate that insulin resistance is a common accompaniment of obesity and can be overcome at supraphysiological insulin concentrations. Both in the basal state and following a hyperglycemic stimulus obese people display hyperinsulinemia, which correlates with the degree of insulin resistance. However, endogenous hyperinsulinemia fails to fully compensate for the insulin resistance.     

Acute hyperglycemia and acute hyperinsulinemia decrease plasma fibrinolytic activity and increase plasminogen activator inhibitor type 1 in the rat

Decreased plasma fibrinolysis may contribute to accelerated atherothrombosis in diabetes. To observe whether hyperglycemia and hyperinsulinemia, common findings in type 2 diabetes, acutely affect plasma fibrinolysis in vivo, we evaluated plasma fibrinolysis (lysis of fibrin plates, free PAI-1 activity and t-PA activity) in the rat after a hyperglycemic euinsulinemic clamp (n=8), an euglycemic hyperinsulinemic clamp (n=7) or a saline infusion (n=15). Plasma fibrinolytic activity was sharply reduced after both the hyperglycemic and hyperinsulinemic clamps as compared to the respective controls (mean lysis areas on the fibrin plate, 139+/-21 vs. 323+/-30 mm2, p<0.001; 78+/-27 vs. 312+/-27 mm2 p<0.001, respectively). Plasma PAI-1 activity was greater after both hyperglycemic and hyperinsulinemic clamps as compared to saline infusion (6.6+/-2.6 vs. 1.6+/-0.6 IU/ml, p<0.001; 26+/-4 vs. 1.3+/-0.7 IU/ml, p<0.0001, respectively). Plasma t-PA activity was significantly reduced both after the hyperglycemic (0.36+/-0.15 vs. 2.17+/-0.18 IU/ml in controls, p<0.001) and the hyperinsulinemic (0.3+/-0.1 vs. 2.3+/-0.3 IU/ml in control, p<0.001) clamps. These data show that in vivo both acute hyperglycemia and acute hyperinsulinemia can decrease plasma fibrinolytic potential and that this is due to increased plasma PAI-1 and decreased free t-PA activities.     

Evaluation of insulin sensitivity in patients with Klinefelter's syndrome: a hyperinsulinemic euglycemic clamp study

Patients with Klinefelter’s syndrome have a higher incidence of diabetes mellitus and the percentage of insulin resistance was reported to be high in these patients. However, little is known about the insulin sensitivity assessed by the hyperinsulinemic euglycemic clamp in these patients. In the present study, subjects included 13 newly diagnosed patients with Klinefelter’s syndrome, and 9 age- and body mass index-matched healthy males. The hyperinsulinemic euglycemic clamp was performed in all patients and controls. Insulin resistance was present in five (38.5%) patients with Klinefelter’s syndrome. Compared with control subjects, patients with Klinefelter’s syndrome had elevated plasma concentrations of fasting insulin, follicle-stimulating hormone, luteinizing hormone, estradiol, and sex hormone-binding globulin, whereas they had reduced plasma free testosterone and total testosterone concentrations. The multivariate linear regression analysis showed that fasting glucose, fasting insulin, free testosterone, and total testosterone were independently associated with M-value. In conclusion, the present study by using hyperinsulinemic euglycemic clamp indicates the high prevalence of insulin resistance in Klinefelter’s syndrome patients. However, these patients did not have reduced mean M-values compared with the controls, although their plasma insulin levels were significantly elevated. It is possible that hyperinsulinemia may be the primary metabolic abnormality rather than insulin resistance.     

Chronic hyperinsulinemia decreases insulin action but not insulin sensitivity

Hyperinsulinemia and insulin resistance are commonly seen in obese and non-insulin-dependent diabetes mellitus (NIDDM) patients, suggesting a causal link exists between hyperinsulinemia and insulin resistance. In a previous study, we demonstrated that chronic (28 days) intraportal hyperinsulinemia (50% increase in basal insulin levels) resulted in a decrease in insulin action as assessed by a one-step euglycemic hyperinsulinemic clamp. Since only one dose of insulin was used during the clamp, it was not possible to determine if the decrease in insulin action was due to a change in insulin sensitivity and/or maximal insulin responsiveness. In the present study, insulin resistance was induced as before, but insulin action was assessed in overnight fasted conscious dogs using a four-step euglycemic hyperinsulinemic clamp (1, 2, 10, and 15 mU/kg/min). Insulin responsiveness was assessed before the induction of chronic hyperinsulinemia (day 0), and after 28 days of hyperinsulinemia (day 28). Transhepatic glucose balance and whole-body glucose utilization were measured to allow assessment of both the hepatic and peripheral effects of insulin. Chronic hyperinsulinemia increased basal insulin levels from 13 +/- 2 to 21 +/- 4 microU/mL. After 4 weeks of chronic hyperinsulinemia, maximal insulin-stimulated glucose utilization was decreased 23% +/- 4% (P less than .05) and insulin sensitivity (ED50) was not significantly altered. During the four-step clamp, the liver was a major site of glucose utilization. The liver was responsible for 13% of the total glucose disposal rate on day 0 (2.9 mg/kg/min) at the highest insulin infusion rate (15 mU/kg/min; 2,000 microU/mL).(ABSTRACT TRUNCATED AT 250 WORDS)     

Leucine kinetics and the effects of hyperinsulinemia in patients with Cushing's syndrome

As muscle wasting and resistance to insulin-mediated glucose utilization are features of Cushing's syndrome (CS), we examined glucose and amino acid metabolism in six patients with CS and six normal subjects before and during euglycemic hyperinsulinemic clamp studies (plasma insulin concentrations, approximately 0.36, approximately 0.65, and approximately 10.05 mmol/L). The two groups had similar body mass index values. In the postabsorptive state, leucine and alpha-ketoisocaproate (KIC) rates of appearance (Ra), KIC oxidation, and nonoxidized leucine-carbon flux, an index of leucine entering protein (Leu----P), were comparable in CS patients [2.38 +/- 0.14 (+/- SE), 0.22 +/- 0.04, and 2.16 +/- 0.12 mumol/kg.min) and in normal subjects (2.73 +/- 0.25, 0.17 +/- 0.02, and 2.59 +/- 0.22 mumol/kg.min). During the euglycemic clamp studies the leucine and KIC Ra values, KIC oxidation, and Leu----P decreased to a similar extent in both groups. In contrast, insulin-mediated glucose utilization was impaired in the CS patients at each clamp step (P less than 0.05). In summary, postabsorptive whole body leucine metabolism is normal in patients with CS and is normally suppressed by hyperinsulinemia, indicating a dissociation in insulin sensitivity with respect to glucose and amino acid metabolism.     

Simultaneous assessment of insulin secretion and insulin sensitivity using a hyperglycemia clamp.

A hyperglycemic clamp is an established method to assess insulin secretion and is generally used only for this purpose. To determine whether it could also be used to assess insulin sensitivity, we compared insulin sensitivity indices (ISI) obtained during euglycemic and hyperglycemic clamp experiments in 22 nonobese volunteers (body mass index, 23.9 +/- 0.6 kg/m2) and in 20 obese individuals (body mass index, 30.8 +/- 1.3 kg/m2) matched for age and gender. The ISI values (micromoles per kg.min/pmol) of the obese group assessed during hyperglycemic (0.088 +/- 0.011) and euglycemic (0.050 +/- 0.005) clamp experiments were both significantly lower than the ISI of the nonobese group assessed in hyperglycemic and euglycemic clamp experiments (0.179 +/- 0.024 and 0.096 +/- 0.009, respectively; both P less than 0.01). Although the ISI values obtained with hyperglycemic clamps were consistently greater than those obtained with euglycemic clamp (0.137 +/- 0.016 vs. 0.075 +/- 0.007; P less than 0.001), they were highly correlated (r = 0.84; P less than 0.0001). Moreover, when these indices were converted to clearance rates, thereby correcting for the mass action effects of glucose on glucose disposal, the values obtained with the hyperglycemic clamp (0.0137 +/- 0.0016 mL/kg.min/pmol) were statistically identical to those obtained with the euglycemic clamp (0.0142 +/- 0.0013 mL/kg.min/pmol), as indicated by a regression equation having an intercept of 0 and a slope (1.03) not different from 1. We, therefore, conclude that the hyperglycemic clamp and the euglycemic clamp yield comparable estimates of insulin sensitivity and that, under appropriate conditions, the hyperglycemic clamp technique may be used to assess both insulin sensitivity and insulin secretion in the same individual in a single experiment.     

Feedback inhibition of insulin secretion is altered in cirrhosis

Hyperinsulinemia in human cirrhosis is generally considered an expression of reduced hepatic insulin degradation. To determine whether hyperinsulinemia may also depend on an altered feedback inhibition of insulin secretion, we performed euglycemic hyperinsulinemic clamp studies, infusing 40, 372, or 1280 mU/m2 X min biosynthetic human insulin in 30 compensated cirrhotic patients with portal hypertension and impaired glucose tolerance and 25 normal subjects, matched for age, sex, and weight. Mean fasting plasma insulin was significantly higher in cirrhotic patients [26.1 +/- 2.3 vs. 12.4 +/- 0.6 (+/- SE) microU/ml; P less than 0.001], while fasting plasma glucose levels were similar in the 2 groups. The mean plasma C-peptide level was significantly higher in cirrhotic patients, both basally (2.7 +/- 0.1 vs. 1.7 +/- 0.1 ng/ml; P less than 0.001) and during the clamp studies. Suppression of C-peptide at 120 min of the clamp was significantly less in cirrhotic patients (37 +/- 7% vs. 79 +/- 4%, 52 +/- 9% vs. approximately 100%, and 54 +/- 4% vs. approximately 100% during the 40, 372, and 1280 mU/m2 X min insulin infusions, respectively). The fasting C-peptide to insulin molar ratio was significantly lower in cirrhotic patients (5.4 +/- 0.3 vs. 6.4 +/- 0.3; P less than 0.005). The MCR of insulin at the three steady states was not significantly different between the 2 groups, whereas the basal systemic delivery rate of insulin was significantly higher in cirrhotic patients (14.7 +/- 1.7 vs. 6.5 +/- 0.4 mU/m2 X min; P less than 0.001). These results suggest that reduced feedback inhibition of insulin secretion may contribute to the hyperinsulinemia associated with cirrhosis.     

Comparison of insulin sensitivity,clearance, and secretion estimates using euglycemic and hyperglycemic clamps in children

The euglycemic clamp is the gold standard for estimating insulin sensitivity. The hyperglycemic clamp is easier to perform and is the gold standard for estimating beta-cell secretion. Reports in adults suggest that hyperglycemic clamps can estimate insulin sensitivity with results equivalent to euglycemic clamps. We investigated whether insulin sensitivity measures from both clamps are equivalent in children. Thirty-one lean and obese children (mean body mass index, 25.1 +/- 4.9 kg/m(2); mean age, 8.7 +/- 1.4 yr; 15 girls and 16 boys; 12 black and 19 white) were studied. All subjects underwent hyperglycemic clamps, then euglycemic clamps 2-6 wk later. Body composition was estimated by dual energy x-ray absorptiometry. Visceral and sc abdominal fat was estimated by abdominal magnetic resonance imaging. Whole-body glucose disposal and insulin sensitivity (SI clamp) derived from both clamps and normalized for total or visceral fat and lean mass were significantly correlated (r, 0.45-0.65; P < 0.05). However, absolute SI clamp values were not equivalent. Bland-Altman comparisons found that SI clamp estimates from hyperglycemic clamps became less precise as SI clamp increased. There were significant correlations between indices of beta-cell secretion from the hyperglycemic clamp and mean C-peptide values from the euglycemic clamp (P < 0.05). However, no correlation was found between measures of total insulin clearance (derived from the euglycemic clamp) and surrogates of hepatic insulin clearance (derived from the hyperglycemic clamp). In this cohort of diverse children, SI clamp values from euglycemic and hyperglycemic clamps were significantly correlated but were not equivalent, whereas the insulin clearance measures were not correlated. It cannot be assumed that the hyperglycemic clamp obviates the need for euglycemic clamp studies to accurately estimate insulin sensitivity in children.     

Effects of ketone bodies on basal and insulin-stimulated glucose utilization in man

Using the euglycemic clamp technique, we investigated the effects of high ketone body levels on basal and insulin-stimulated glucose utilization in normal subjects. Infusion of sodium acetoacetate in the postabsorptive state raised ketone body levels from 150 +/- 20 (+/- SE) mumol/liter to more than 1 mmol/liter. Endogenous glucose production declined from 2.71 +/- 0.20 mg kg-1 min-1 to 1.75 + 0.26 (P less than 0.01) and glucose utilization from 2.71 +/- 0.20 to 1.98 +/- 0.17 mg kg-1 min-1 (P less than 0.01), while blood glucose was maintained at the initial level by the infusion of glucose. There were no changes in plasma glucagon, insulin, or C-peptide. Plasma nonesterified fatty acids (P less than 0.01) and blood glycerol (P less than 0.01) and alanine (P less than 0.05) decreased, while blood lactate increased (P less than 0.01). Infusion of sodium bicarbonate had no effect on glucose kinetics. The decreases in glucose utilization and endogenous glucose production during the infusion of acetoacetate were not modified when the fall of plasma nonesterified fatty acids was prevented by iv heparin injection. During control euglycemic hyperinsulinemic clamps (1 and 10 mU kg-1 min-1 insulin infusion), endogenous glucose production was suppressed at the lowest insulin infusion rate; glucose utilization increased first to 7.32 +/- 0.96 mg kg-1 min-1 and then to 16.5 +/- 1.27 mg kg-1 min-1. During euglycemic hyperinsulinemic clamps with simultaneous sodium acetoacetate infusion, similar insulin levels were attained; endogenous glucose production was also suppressed at the lowest insulin infusion rate, and insulin-stimulated glucose utilization rates (7.93 +/- 1.70 and 15.80 +/- 1.30 mg kg-1 min-1) were not modified. In conclusion, acetoacetate infusion decreased basal, but not insulin-stimulated, glucose utilization. The increase in lactate during acetoacetate infusion in the postabsorptive state suggests that ketone body acted by decreasing pyruvate oxidation.     

Acute hyperinsulinemia is associated with increased circulating levels of adrenomedullin in patients with type 2 diabetes mellitus

OBJECTIVE: To investigate the effect of acute hyperinsulinemia on the plasma levels of adrenomedullin (AM) in patients with type 2 diabetes mellitus. DESIGN: We measured the plasma levels of AM in 18 patients with type 2 diabetes mellitus and in 19 normal subjects before and during a euglycemic hyperinsulinemic clamp study (the goal was for blood sugar levels of 5.24 mmol/l and insulin levels of 1200 pmol/l). Both plasma AM and serum insulin were measured by immunoradiometric assays. RESULTS: Before the glucose clamp study there was no significant difference in the plasma levels of AM between patients with type 2 diabetes mellitus and normal subjects. During the glucose clamp study, the serum levels of insulin significantly increased (from 33.0+/-3.6 to 1344.6+/-67.8 pmol/ml, P<0.001), as did the plasma levels of AM (from 12.8+/-0.7 to 14.2+/-0.9 fmol/ml, P<0.03) only in patients with type 2 diabetes mellitus. There was a significant correlation between the change in circulating levels of insulin and AM (r=0.755, P<0.01). CONCLUSIONS: Acute hyperinsulinemia induced a significant increase in the plasma levels of AM in patients with type 2 diabetes mellitus. Increased insulin may regulate circulating levels of AM in patients with type 2 diabetes mellitus.     

Intraportal hyperinsulinemia decreases insulin-stimulated glucose uptake in the dog

Hyperinsulinemia and insulin resistance are commonly seen in obese and non-insulin-dependent diabetes mellitis (NIDDM) patients. While it is known that chronic exposure to severe hyperinsulinemia can lead to an insulin-resistant state and mild hyperinsulinemia for rather short durations (20 to 40 hours) and can also lead to insulin resistance, it is less clear whether mild hyperinsulinemia for a more prolonged duration can lead to insulin resistance. In the present study we determined the effects of chronic (28 days) exposure to mild hyperinsulinemia on insulin-stimulated glucose use. Chronic hyperinsulinemia was produced by an intraportal infusion of porcine insulin (425 microU/kg/min), which raised the basal peripheral insulin levels by approximately 50%. Insulin responsiveness was assessed using the euglycemic hyperinsulinemic clamp (2 mU/kg/min) in dogs before the induction of chronic hyperinsulinemia (day 0), after 28 days of hyperinsulinemia (day 28), and 28 days after discontinuation of the chronic insulin infusion (day 56). The amount of glucose (M) required to maintain euglycemia during the euglycemic hyperinsulinemic clamp was decreased (relative to day 0) 39% +/- 3% on day 28 and 18% +/- 3% on day 56 (P less than .05). In control animals that received a chronic infusion of saline for the 28-day period the glucose infusion rate (M) was not changed significantly (decreasing 2% +/- 5% and 5% +/- 10% on days 28 and 56, respectively). In conclusion insulin resistance can be produced by a mild hypersecretion of insulin and discontinuation of the chronic insulin infusion tends to reverse the resistance.     

Beneficial effects of nateglinide on insulin resistance in type 2 diabetes

Nateglinide, a rapid insulin secretagogue, is known to facilitate the early phase of insulin secretion and has been used for the treatment of type 2 diabetic patients with postprandial hyperglycemia. The aim of this study is to evaluate the effect of nateglinide on insulin resistance as well as insulin secretory defects in type 2 diabetic patients. Insulin secretion ability was evaluated by the hyperglycemic clamp test, and insulin sensitivity was evaluated by the euglycemic hyperinsulinemic clamp test, using an artificial pancreas. The hyperglycemic clamp test showed that a 7-day treatment with nateglinide significantly increased insulin secretion in response to high glucose. Interestingly, although nateglinide is known to facilitate insulin secretion, daily urinary C-peptide excretion was decreased after nateglinide treatment. Moreover, in the euglycemic hyperinsulinemic clamp test, glucose infusion rate was significantly increased by nateglinide treatment, indicating that nateglinide functions to decrease insulin resistance. Nateglinide ameliorates insulin resistance as well as insulin secretory defects in type 2 diabetic patients.     

Improvement of insulin sensitivity after adrenalectomy in patients with pheochromocytoma

OBJECTIVE: Decreased insulin secretion is considered to be the main cause for pheochromocytoma-associated diabetes mellitus. Data from animal and evidence from clinical studies suggest that catecholamines can induce insulin resistance. However, there is no study investigating the effect of catecholamine excess on insulin resistance in patients with pheochromocytopma by the euglycemic hyperinsulinaemic clamp technique. RESEARCH DESIGN AND METHODS: We characterized the effect of high catecholamine plasma concentrations on glucose metabolism and insulin resistance. Euglycemic hyperinsulinemic clamps were performed in 10 patients with pheochromocytoma with and without diabetes mellitus before and 5 wk after adrenalectomy. RESULTS: In five patients with diabetes mellitus, glucose infusion rate required to maintain euglycemia during the clamp (mean +/- SEM) significantly improved from 27.5 +/- 6.5 micro mol/kg.min before surgery to 44.6 +/- 12.3 micro mol/kg.min 5 wk after adrenalectomy (P < 0.05). In five individuals without diabetes, total glucose disposal improved from 105 +/- 13.6 to 130 +/- 11.2 (P < 0.05). Improved insulin sensitivity after surgery was confirmed by a decrease of fasting hyperinsulinemia from 210 +/- 74 pmol/liter (diabetes mellitus) and 69 +/- 9 pmol/liter (no diabetes) before to 134 +/- 56 pmol/liter and 54 +/- 8 after surgery respectively (P < 0.01). In three patients, diabetes and hyperinsulinemia were reversed by the surgical removal of the pheochromocytoma. CONCLUSION: Our data provide evidence that endogenous catecholamine excess in patients with pheochromocytoma can induce or aggravate insulin resistance both in patients with type 2 diabetes and patients with normal glucose tolerance.     

Total ghrelin levels during acute insulin infusion in patients with polycystic ovary syndrome

Controversial data were reported concerning fasting ghrelin (decreased, normal or elevated) in polycystic ovary syndrome (PCOS). The aim of our study was to clarify ghrelin levels in non-obese, overweight, and obese PCOS patients; to investigate the effect of acute insulin infusion on ghrelin in PCOS as a chronic insulin-resistant state, with and without the impact of obesity, and to examine ghrelin-androgen interaction. In that order, we evaluated 1) ghrelin levels among 8 nonobese patients with PCOS [body mass index (BMI): 20.52+/-1.31 kg/m2], 8 overweight and obese patients with PCOS (BMI: 34.36+/-6.53 kg/m2) and their respective controls, 2) ghrelin suppression during euglycemic hyperinsulinemic clamp, and 3) ghrelin-androgen interrelationship. After overnight fast, 2-h euglycemic hyperinsulinemic clamp, was performed in all investigated women. Fasting ghrelin was significantly lower in non-obese PCOS than in controls (64.74+/-25.69 vs 108.36+/-52.60; p<0.05) as well as in overweight and obese PCOS in comparison with controls (38.71+/-14.18 vs 98.77+/-40.49; p<0.05). Insulin infusion significantly suppressed ghrelin in all subgroups of investigated women. Analysis of variance for repeatable measures confirmed that there was no significant difference in pattern of response between PCOS and controls. In conclusion, women with PCOS had lower fasting ghrelin and decreased insulin sensitivity independently of their BMI, compared to the controls. In addition, there were no differences between fasting ghrelin levels among non-obese, overweight, and obese women with PCOS. During euglycemic hyperinsulinemic clamp, ghrelin decreased in all studied groups to a similar extent, implying that, compared to chronic hyperinsulinemia, acute hyperinsulinemia reduces ghrelin levels independently of the degree of insulin resistance.