In vivo activity of 11beta-hydroxysteroid dehydrogenase type 1 and free fatty acid-induced insulin resistance

INTRODUCTION: Free fatty acids (FFAs) induce hepatic insulin resistance and enhance hepatic gluconeogenesis. Glucocorticoids (GCs) also stimulate hepatic gluconeogenesis. The aim of this study was to investigate whether the FFA-induced hepatic insulin resistance is mediated by increased activity of hepatic 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1), accompanied by elevated hepatic cortisol levels. METHODS: Following a 10-h overnight fast, six healthy male volunteers were investigated. A euglycaemic hyperinsulinaemic clamp was performed during lipid or saline infusion. To assess hepatic 11beta-HSD1 activity, plasma cortisol levels were measured after oral administration of cortisone acetate during lipid or saline infusion. In addition, 11beta-HSD activities were determined in vivo by calculating the urinary ratios of GC metabolites. RESULTS: Lipid infusion increased FFAs (5.41 +/- 1.00 vs. 0.48 +/- 0.20 mmol/l; P < 0.005) and significantly increased insulin resistance [glucose infusion rate (GIR) 6.02 +/- 2.60 vs. 4.08 +/- 2.15 mg/kg/min; P < 0.005]. After lipid and saline infusions no changes in 11beta-HSD1 activity were found, neither by changes in cortisone acetate to cortisol conversion nor by differences in urinary free cortisol (UFF) or cortisone (UFE), 5beta-tetrahydrocortisol (THF), 5alpha-THF, cortisone (THE), UFF/UFE and (5alpha-THF + THF)/THE ratios. CONCLUSIONS: We found no change in hepatic and whole-body 11beta-HSD1 activity during acute FFA-induced insulin resistance. Further studies are necessary to clarify whether 11beta-HSD1 in muscle and adipose tissue is influenced by FFAs and whether 11beta-HSD1 is involved in other conditions of insulin resistance.     

Rosiglitazone prevents free fatty acid-induced vascular endothelial dysfunction

CONTEXT: Free fatty acids (FFAs) cause insulin resistance and vascular endothelial dysfunction. The peroxisome proliferator-activated receptor gamma agonist rosiglitazone acts as insulin sensitizer and could exert vasoprotective properties by preservation of endothelium-dependent vasodilation. OBJECTIVE: We tested the effect of rosiglitazone on FFA-induced endothelial dysfunction of the forearm resistance vessels, insulin sensitivity, asymmetric dimethylarginine (ADMA), and high-sensitivity C-reactive protein concentrations in humans. DESIGN AND SETTING: We conducted a double-blind, randomized, placebo-controlled parallel-group study at a university hospital. PATIENTS AND INTERVENTIONS: Rosiglitazone 8 mg daily or placebo was administered to 16 healthy male subjects for 21 d. On the last day, triglycerides and heparin were infused iv to increase FFA plasma concentrations. MAIN OUTCOME MEASURES: Forearm blood flow responses to the endothelium-dependent vasodilator acetylcholine and the endothelium-independent vasodilator nitroglycerine were assessed using strain-gauge plethysmography at baseline, and on d 21 before and after 5 h of triglyceride/heparin infusion. RESULTS: Forearm blood flow reactivity was not affected by rosiglitazone or placebo. Infusion of triglyceride/heparin substantially increased FFA concentrations (P < 0.001) and reduced endothelium-dependent vasodilation by 38 +/- 17% (P = 0.024). In the face of lower FFA elevation (P = 0.047 vs. controls), endothelium-dependent vasodilation was preserved in subjects receiving rosiglitazone (P = 0.016 vs. placebo). Endothelium-independent vasodilation and C-reactive protein were unchanged, whereas insulin sensitivity and plasma ADMA similarly decreased in both study groups after FFA elevation (both P < 0.05 vs. baseline). CONCLUSIONS: Rosiglitazone mitigates the increase in FFA after infusion of triglyceride/heparin and prevents FFA-induced endothelial dysfunction. These effects are independent and possibly occur before any changes in insulin sensitivity and ADMA plasma concentrations in healthy subjects.     

Influence of rosiglitazone treatment on beta-cell function in type 2 diabetes: evidence of an increased ability of glucose to entrain high-frequency insulin pulsatility

Thiazolidinediones have well-established insulin-sensitizing effects. Their impact on insulin secretion is less clarified. Consequently, we sought to determine potential effects of a thiazolidinedione (rosiglitazone) on the beta-cell function. Twenty type 2 diabetic individuals were randomized to receive rosiglitazone (rosi) 4 mg twice daily or placebo (pla) for 13 wk. Before treatment and at the end of the treatment period, the patients underwent an iv glucose tolerance test (0.3 g/kg), a hyperglycemic (15 mmol/liter) clamp with arginine (5 g) stimulation, assessment of baseline high-frequency insulin pulsatility, and glucose-entrained insulin pulsatility (6 mg/kg.min every 10 min), and a hyperinsulinemic euglycemic clamp. Fasting plasma glucose was reduced (pla, 8.2 +/- 2.1 vs. 8.8 +/- 2.6 mmol/liter; rosi, 8.6 +/- 7.1 vs. 7.1 +/- 1.2 mmol/liter; P < 0.01), and insulin sensitivity was increased by rosiglitazone treatment (M value: pla, 5.3 +/- 1.8 vs. 5.4 +/- 1.6 mg/kg.min; rosi, 5.9 +/- 2.2 vs. 7.4 +/- 1.3 mg/kg.min; P = 0.05). First-phase insulin secretion and insulin secretory capacity were unaffected. Glucose-entrained insulin secretion was increased as assessed by spectral power analysis (P = 0.05). In conclusion, rosiglitazone treatment for 3 months in type 2 diabetic patients exerts no action on insulin secretion per se. Improved glucose-entrained high-frequency insulin pulsatility suggests an increased ability of the beta-cell to sense and respond to glucose changes within the physiological range.     

Insulin detemir under steady-state conditions: no accumulation and constant metabolic effect over time with twice daily administration in subjects with Type 1 diabetes.

AIMS: This study investigated the pharmacodynamic and pharmacokinetic characteristics of the novel long-acting insulin analogue insulin detemir (IDet) under single-dose and steady-state conditions in comparison with those of NPH insulin at steady state. METHODS: Twenty-five subjects with Type 1 diabetes [seven females, 18 males, mean age (+/- sd) 39 +/- 12 years, body mass index 24 +/- 3 kg/m(2)] participated in three 24-h glucose clamps. IDet or NPH were given at 12-h intervals in fixed, individualized doses. The first clamp assessed the metabolic effect of NPH at steady state, the second investigated the effect of two single injections of IDet. Subjects continued IDet treatment for 7-14 days, after which the third clamp was performed to investigate IDet at steady state. RESULTS: At steady state, the metabolic effect of IDet was constant over 24 h while a clear peak in the metabolic effect [expressed as glucose infusion rates (GIR)] was observed with NPH after each injection. The fluctuation in the metabolic effect (maximum GIR divided by the average of the GIR values at the interval ends) was significantly lower in the second 12 h of the experiments with IDet under steady-state conditions compared with NPH (fluctuation(12-24 h) 1.27 +/- 0.17 vs. 1.56 +/- 0.72, P < 0.05). The overall metabolic effect of IDet at steady state was comparable with that of NPH [GIR-area under curve (AUC)(0-24 h): 5697 +/- 1861 vs. 5929 +/- 1965 mg/kg] whereas a significantly lower effect (5187 +/- 1784 mg/kg, P = 0.01 vs. steady state) was observed following the first two IDet injections. GIR values at the end of clamp day 2 (first doses) and clamp day 3 (steady state) were comparable [GIR(trough 24 h) 3.7 +/- 1.7 vs. 3.8 +/- 1.6 mg/(kg x min) NS], indicating that IDet had reached steady state after the first two injections. CONCLUSIONS: IDet administered twice daily reached steady state after the second injection and showed a constant metabolic effect over time under steady-state conditions. This should facilitate basal insulin substitution and decrease the risk of hypoglycaemia in insulin-treated subjects.     

Slower activation of insulin action in upper body obesity

To determine the influence of body fat distribution on kinetic aspects of insulin action, we have monitored the rate of increase of glucose infusion during 6-hour hyperinsulinemic (40 mU/m2/min) euglycemic clamps in 10 patients with upper body obesity (body mass index [BMI], 41 +/- 3 kg/m2; waist-to-hip ratio [WHR], > 1.00 for men and > 0.85 for women), 12 patients with lower body obesity (BMI, 40 +/- 2 kg/m2; WHR, < 1.00 for men and < 0.85 for women), and 5 control subjects (BMI, < 30 kg/m2; WHR, < 1.00 for men and < 0.85 for women). In all subjects, glucose infusion rate (GIR) to maintain euglycemia increased during the clamp studies to achieve maximal, steady state values after the fourth to fifth hour. During the first 2 hours of clamp, mean GIR (GIR20-120min) (traditional approach to assess insulin sensitivity) was lower (P < 0.05) in the upper body obesity group than in the lower body obesity group (2.12 +/- 0.14 and 3.03 +/- 0.33 mg/kg per min, respectively). In contrast, the maximal steady-state GIR (GIRMAX) (calculated as mean GIR during the sixth hour of clamp) was similar in the upper body and in the lower body obesity groups (4.48 +/- 0.45 and 4.57 +/- 0.36 mg/kg per min, respectively). Control subjects exhibited higher values of both GIR20-120min and GIRMAX (5.57 +/- 0.67 and 7.05 +/- 0.59 mg/kg per min, respectively) than those of both groups of obese patients. The time to reach half-maximal GIR (T1/2) was greater (P < .05) in the upper body obesity (94 +/- 12 min) than that in the lower body obesity (41 +/- 5 min) and in the control group (30 +/- 5 min). In pooled subjects, BMI correlated with GIRMAX (n = 27, R = -.75, P < .001), but not with T1/2 (R = .21). Similarly, whole body percent fat mass, as assessed by bioelectrical impedance analysis, correlated with GIRMAX (n = 16, R = -.79, P < .001), but not with T1/2 (R = .10). In contrast, WHR closely correlated with T1/2 (n = 27, R = .78, P < .001), but not with GIRMAX (R = .11). We conclude that upper body obesity is associated with a slower rate of activation of insulin action on glucose metabolism, whereas total body adiposity selectively affects the maximal, steady-state insulin effect.     

Free fatty acids decrease circulating ghrelin concentrations in humans

OBJECTIVE: Concentrations of the orexigenic peptide ghrelin is affected by a number of hormones, which also affect circulating levels of free fatty acids (FFAs). The present study was therefore designed to determine the direct effect of FFAs on circulating ghrelin. DESIGN: Eight lean, healthy men were examined for 8 h on four occasions using variable infusion rates (0, 3, 6 and 12 microl/kg per min) of intralipid to create different plasma FFA concentrations. Constant levels of insulin and GH were obtained by administration of acipimox (250 mg) and somatostatin (300 microg/h). At the end of each study day a hyperinsulinaemic-euglycaemic clamp was performed. RESULTS: Four distinct levels of FFAs were obtained at the end of the lipid infusion period (FFA(LIPID): 0.03 +/- 0.00 vs: 0.49 +/- 0.04, 0.92 +/- 0.08 and 2.09 +/- 0.38 mmol/l; ANOVA P < 0.0001) and during hyperinsulinaemia (FFA(LIPID+INSULIN): 0.02 +/- 0.00 vs: 0.34 +/- 0.03, 0.68 +/- 0.09 and 1.78 +/- 0.32 mmol/l; ANOVA P < 0.0001). Whereas, somatostatin infusion alone reduced ghrelin concentration by approximately 67%, concomitant administration of increasing amounts of intralipid reduced circulating ghrelin by a further 14, 19 and 19% respectively (change in ghrelin: 0.52 +/- 0.05 vs: 0.62 +/- 0.06, 0.72 +/- 0.09 and 0.71 +/- 0.05 microg/l; ANOVA P = 0.04). No further reduction in ghrelin concentration was observed during hyperinsulinaemia. CONCLUSION: FFA exposure between 0 and 1 mmol/l significantly suppresses ghrelin levels independent of ambient GH and insulin levels.     

No effect of free fatty acids on adrenocorticotropin and cortisol secretion in healthy young men

Free fatty acids (FFAs) affect anterior pituitary function. However, the effect of FFAs on corticotropin (ACTH) and cortisol in humans is controversial. Thus, we assessed the effect of a pronounced increase in circulating FFA levels induced by infusion of lipid/heparin on ACTH and cortisol secretion in young men. Eight healthy male volunteers who underwent a 10-hour overnight fast were investigated. A 20% lipid/heparin or saline/heparin infusion was given at a rate of 1.5 mL/min for 6 hours. A euglycemic hyperinsulinemic clamp was performed in 6 subjects 4 hours after the start of infusion. To assess steroid metabolism, we measured ACTH, cortisol, FFAs, and urinary steroids. Lipid infusion increased FFAs (6.06 +/- 0.52 vs 0.70 +/- 0.23 mmol/L; P < .005) and induced insulin resistance (glucose infusion rate, 4.08 +/- 2.15 vs 6.02 +/- 2.60 mg/kg per minute; P < .005). Serum cortisol and plasma ACTH decreased independent of lipid/heparin or saline/heparin infusion. In addition, we found no effect of hyperinsulinemia on ACTH and cortisol levels. There were no differences in urinary free cortisol, urinary free cortisone, 5beta-tetrahydrocortisol, 5alpha-tetrahydrocortisol, and tetrahydrocortisone. In conclusion, FFAs had no effect on basal ACTH and cortisol secretion in normal-weight young men. In addition, no alterations in urinary glucocorticoid metabolites were detected, suggesting unchanged cortisol metabolism during lipid infusion.     

The insulin-sensitizing effect of rosiglitazone in type 2 diabetes mellitus patients does not require improved in vivo muscle mitochondrial function

AIMS: Our objective was to investigate whether improved in vivo mitochondrial function in skeletal muscle and intramyocellular lipids (IMCLs) contribute to the insulin-sensitizing effect of rosiglitazone. METHODS: Eight overweight type 2 diabetic patients (body mass index = 29.3 +/- 1.1 kg/m(2)) were treated with rosiglitazone for 8 wk. Before and after treatment, insulin sensitivity was determined by a hyperinsulinemic euglycemic clamp. Muscular mitochondrial function (half-time of phosphocreatine recovery after exercise) and IMCL content were measured by magnetic resonance spectroscopy. RESULTS: Insulin sensitivity improved after rosiglitazone (glucose infusion rate: 19.9 +/- 2.8 to 24.8 +/- 2.1 micromol/kg.min; P < 0.05). In vivo mitochondrial function (phosphocreatine recovery half-time: 23.8 +/- 3.5 to 20.0 +/- 1.7 sec; P = 0.23) and IMCL content (0.93 +/- 0.18% to 1.37 +/- 0.40%; P = 0.34) did not change. Interestingly, the changes in PCr half-time correlated/tended to correlate with changes in fasting insulin (R(2) = 0.50; P = 0.05) and glucose (R(2) = 0.43; P = 0.08) levels. Changes in PCr half-time did not correlate with changes in glucose infusion rate (R(2) = 0.08; P = 0.49). CONCLUSION: The rosiglitazone-enhanced insulin sensitivity does not require improved muscular mitochondrial function.     

Impact of particle size and aerosolization time on the metabolic effect of an inhaled insulin aerosol

The effects were compared of varying aerosol particle size and aerosolization time within each breath on the metabolic effect elicited by inhalation of a liquid insulin aerosol in comparison with that after subcutaneous injection (s.c.) of regular insulin. In this single-center, open-label euglycemic glucose clamp study, 13 healthy non-smoking subjects received five administrations of insulin in randomized order on separate study days, once by s.c. (0.15 U/kg of regular insulin) and four times by inhalation. Subjects inhaled 1.5 U/kg of liquid insulin aerosol administered by the Aerodose Insulin Inhaler (Aerogen Inc., Mountain View, CA) configured to deliver two aerosol particle sizes--fine [F, 4.4 +/- 0.3 microm (mean +/- SD)] or very fine (VF, 3.5 +/- 0.2 microm)--and two aerosolization times (aerosol released for the first 2 or 4 s after the start of each 5-s inhalation). Glucose infusion rate (GIR) values necessary to keep blood glucose concentrations constant at 5.0 mmol/L were determined over a 6-h period following insulin administration. After inhalation of insulin, the onset of action was substantially more rapid on all four inhalation study days than after s.c. insulin, and the time to maximal action [t(GIRmax) (min)] was reached earlier: F/2 s, 127 +/- 54; F/4 s, 128 +/- 55; VF/2 s, 158 +/- 91; VF/4 s, 132 +/- 72; s.c., 175 +/- 69 (P < 0.0001). The longer aerosolization time (4 vs. 2 s) resulted in higher maximal metabolic action [GIR(max) (mg/kg/min), F/4 s 8.1 +/- 3.6, VF/4 s 8.4 +/- 2.7 vs. F/2 s 6.6 +/- 2.4, VF/2 s 7.2 +/- 2.4 (P = 0.01 for 4 s vs. 2 s, grouped data)], total metabolic activity [area under the curve of GIR 0-6 h (g/kg), F/4 s 1.97 +/- 0.92, VF/4 s 2.14 +/- 0.86 vs. F/2 s 1.56 +/- 0.68, VF/2 s 1.78 +/- 0.60 (P = 0.01)], and relative biopotency [F/4 s 10.6 +/- 4.0%, VF/4 s 11.7% +/- 4.1% vs. F/2 s 8.5 +/- 3.2%, VF/2 s 9.7 +/- 2.4% (P = 0.01)]. None of these summary measures was significantly affected by particle size. No drug- or device-related adverse events were observed. This study shows that aerosolization time, but not particle size, in the ranges studied, had an impact on the metabolic effect elicited by inhaled insulin, allowing rational selection of delivery parameters for further clinical testing. Based on the observed biopotency and the rapid onset of action, inhalation of a liquid insulin aerosol generated by the Aerodose Insulin Inhaler shows promise for covering prandial insulin requirements.     

Chronic physiologic hyperinsulinemia impairs suppression of plasma free fatty acids and increases de novo lipogenesis but does not cause dyslipidemia in conscious normal rats

Type 2 diabetes mellitus and obesity are characterized by fasting hyperinsulinemia, insulin resistance with respect to glucose metabolism, elevated plasma free fatty acid (FFA) levels, hypertriglyceridemia, and decreased high-density lipoprotein (HDL) cholesterol. An association between hyperinsulinemia and dyslipidemia has been suggested, but the causality of the relationship remains uncertain. Therefore, we infused eight 12-week-old male catheterized conscious normal rats with insulin (1 mU/min) for 7 days while maintaining euglycemia using a modification of the glucose clamp technique. Control rats (n = 8) received vehicle infusion. Baseline FFAs were 1.07+/-0.13 mmol/L, decreased to 0.57+/-0.10 (P < .05) upon initiation of the insulin infusion, and gradually increased to 0.95+/-0.12 by day 7 (P = NS vbaseline). On day 7 after a 6-hour fast, plasma insulin, glucose, and FFA levels in control and chronically hyperinsulinemic rats were 32+/-5 versus 116+/-21 mU/L (P < .005), 122+/-4 versus 129+/-8 mg/dL (P = NS), and 1.13+/-0.18 versus 0.95+/-0.12 mmol/L (P = NS); total plasma triglyceride and cholesterol levels were 78+/-7 versus 66+/-9 mg/dL (P = NS) and 50+/-3 versus 47+/-2 mg/dL (P = NS), respectively. Very-low-density lipoprotein (VLDL) + intermediate-density lipoprotein (IDL), low-density lipoprotein (LDL), and HDL2 and HDL3 subfractions of plasma triglyceride and cholesterol were similar in control and hyperinsulinemic rats. Plasma FFA correlated positively with total (r = .61, P < .005) triglycerides. On day 7 after an 8-hour fast, hyperinsulinemic-euglycemic clamps with 3-3H-glucose infusion were performed in all rats. Chronically hyperinsulinemic rats showed peripheral insulin resistance (glucose uptake, 15.8+/-0.8 v 19.3+/-1.4 mg/kg x min, P < .02) but normal suppression of hepatic glucose production (HGP) compared with control rats (4.3+/-1.0 v 5.6+/-1.4 mg/kg x min, P = NS). De novo tissue lipogenesis (3-3H-glucose incorporation into lipids) was increased in chronically hyperinsulinemic versus control rats (0.90+/-0.10 v 0.44+/-0.08 mg/kg x min, P < .005). In conclusion, chronic physiologic hyperinsulinemia (1) causes insulin resistance with regard to the suppression of plasma FFA levels and increases lipogenesis; (2) induces peripheral but not hepatic insulin resistance with respect to glucose metabolism; and (3) does not cause an elevation in VLDL-triglyceride or a reduction in HDL-cholesterol.     

Acute effects of ghrelin administration on glucose and lipid metabolism

CONTEXT: Ghrelin infusion increases plasma glucose and nonesterified fatty acids, but it is uncertain whether this is secondary to the concomitant release of GH. OBJECTIVE: Our objective was to study direct effects of ghrelin on substrate metabolism. DESIGN: This was a randomized, single-blind, placebo-controlled two-period crossover study. SETTING: The study was performed in a university clinical research laboratory. PARTICIPANTS: Eight healthy men aged 27.2 +/- 0.9 yr with a body mass index of 23.4 +/- 0.5 kg/m(2) were included in the study. INTERVENTION: Subjects received infusion of ghrelin (5 pmol x kg(-1) x min(-1)) or placebo for 5 h together with a pancreatic clamp (somatostatin 330 microg x h(-1), insulin 0.1 mU x kg(-1) x min(-1), GH 2 ng x kg(-1) x min(-1), and glucagon 0.5 ng.kg(-1) x min(-1)). A hyperinsulinemic (0.6 mU x kg(-1) x min(-1)) euglycemic clamp was performed during the final 2 h of each infusion. RESULTS: Basal and insulin-stimulated glucose disposal decreased with ghrelin [basal: 1.9 +/- 0.1 (ghrelin) vs. 2.3 +/- 0.1 mg x kg(-1) x min(-1), P = 0.03; clamp: 3.9 +/- 0.6 (ghrelin) vs. 6.1 +/- 0.5 mg x kg(-1) x min(-1), P = 0.02], whereas endogenous glucose production was similar. Glucose infusion rate during the clamp was reduced by ghrelin [4.0 +/- 0.7 (ghrelin) vs. 6.9 +/- 0.9 mg.kg(-1) x min(-1); P = 0.007], whereas nonesterified fatty acid flux increased [131 +/- 26 (ghrelin) vs. 69 +/- 5 micromol/min; P = 0.048] in the basal period. Regional lipolysis (skeletal muscle, sc fat) increased insignificantly with ghrelin infusion. Energy expenditure during the clamp decreased after ghrelin infusion [1539 +/- 28 (ghrelin) vs. 1608 +/- 32 kcal/24 h; P = 0.048], but the respiratory quotient did not differ. Minor but significant elevations in serum levels of GH and cortisol were observed after ghrelin infusion. CONCLUSIONS: Administration of exogenous ghrelin causes insulin resistance in muscle and stimulates lipolysis; these effects are likely to be direct, although a small contribution of GH and cortisol cannot be excluded.     

Acute hyperglycemia reduces myocardial blood flow reserve and the magnitude of reduction is associated with insulin resistance: a study in nondiabetic humans using contrast echocardiography

The effect of acute hyperglycemia per se on coronary perfusion in humans is undefined. We evaluated the effects of short-term hyperglycemia on myocardial blood flow reserve (MBFR) in healthy nondiabetic volunteers. Twenty-one nondiabetic volunteers (76 % females, mean ± SD, age 48 ± 5 years) had noninvasive MBFR assessment while exposed to pancreatic clamp with somatostatin and replacement glucagon and growth hormone infusions, with frequent interval plasma glucose (PG) monitoring. Insulin was infused at 0.75 mU/kg/min to mimic postprandial plasma insulin concentrations, and glucose was infused to maintain euglycemia (PG 93.9 ± 7.3 mg/dl) followed by hyperglycemia (PG 231.5 ± 18.1 mg/dl). Myocardial contrast echocardiography (MCE) was performed during each glycemic steady state using continuous infusion of Definity at rest and during regadenoson (Lexiscan 5 ml (400 μg) intravenous bolus) infusion to quantify myocardial blood flow (MBF) and determine MBFR. Insulin resistance (IR) was assessed by glucose infusion rate (GIR; mg/kg/min) at euglycemia. Median stress MBF, MBFR, and β reserve were significantly reduced during acute hyperglycemia versus euglycemia (stress MBF 3.9 vs 5.4, P = 0.02; MBFR 2.0 vs 2.7, P < 0.0001; β reserve 1.45 vs 2.4, P = 0.007). Using a median threshold GIR of 5 mg/kg/min, there was a correlation between GIR and hyperglycemic MBFR (r = 0.506, P = 0.019). MBFR, as determined noninvasively by MCE, is significantly decreased during acute hyperglycemia in nondiabetic volunteers, and the magnitude of this reduction is modulated by IR.     

Insulin sensitivity regulates autonomic control of heart rate variation independent of body weight in normal subjects

It is unclear whether insulin sensitivity independent of body weight regulates control of heart rate variation (HRV) by the autonomic nervous system. Insulin action on whole-body glucose uptake (M-value) and heart rate variability were measured in 21 normal men. The subjects were divided into 2 groups [normally insulin sensitive (IS, 8.0 +/- 0.4 mg/kg.min) and less insulin sensitive (IR, 5.1 +/- 0.3 mg/kg.min)] based on their median M-value (6.2 mg/kg x min). Spectral power analysis of heart rate variability was performed in the basal state and every 30 min during the insulin infusion. The IS and IR groups were comparable, with respect to age (27 +/- 2 vs. 26 +/- 2 yr), body mass index (22 +/- 1 vs. 23 +/- 1 kg/m(2)), body fat (13 +/- 1 vs. 13 +/- 1%), systolic (121 +/- 16 vs. 117 +/- 14 mm Hg) and diastolic (74 +/- 11 vs. 73 +/- 11 mm Hg) blood pressures, and fasting plasma glucose (5.4 +/- 0.1 vs. 5.5 +/- 0.1 mmol/L) concentrations. Fasting plasma insulin was significantly higher in the IR (30 +/- 4 pmol/L) than in the IS (17 +/- 3 pmol/L, P < 0.05) group. In the IS group, insulin significantly increased the normalized low-frequency (LFn) component, a measure of predominantly sympathetic nervous system activity, from 36 +/- 5 to 48 +/- 4 normalized units (nu; 0 vs. 30-120 min, P < 0.001); whereas the normalized high-frequency (HFn) component, a measure of vagal control of HRV, decreased from 66 +/- 9 to 48 +/- 5 nu (P < 0.001). No changes were observed in either the normalized LF component [35 +/- 5 vs. 36 +/- 2 nu, not significant (NS)] or the normalized HF component (52 +/- 6 vs. 51 +/- 4 nu, NS) in the IR group. The ratio LF/HF, a measure of sympathovagal balance, increased significantly in the IS group (0.92 +/- 0.04 vs. 1.01 +/- 0.04, P < 0.01) but remained unchanged in the IR group (0.91 +/- 0.04 vs. 0.92 +/- 0.03, NS). Heart rate and systolic and diastolic blood pressures remained unchanged during the insulin infusion in both groups. We conclude that insulin acutely shifts sympathovagal control of HRV toward sympathetic dominance in insulin-sensitive, but not in resistant, subjects. These data suggest that sympathetic overactivity is not a consequence of hyperinsulinemia.     

Time-action profile of the soluble, fatty acid acylated, long-acting insulin analogue NN304.

AIMS: To compare the pharmacokinetic and pharmacodynamic properties of subcutaneously injected NN304, a novel long-acting insulin analogue, to NPH-insulin during euglycaemic glucose clamps in 11 healthy volunteers. METHODS: On three study days NN304 was injected in three different doses (0.15, 0.3, 0.6 U/kg body weight), while NPH-insulin (0.3 U/kg) was injected in identical dose on two other days. RESULTS: Injection of NN304 resulted in a linear and proportional increase in total NN304 concentrations (AUC0-1440 min: 0.15 U/kg: 344+/-43, 0.3 U/kg: 666+/-82, 0.6 U/kg: 1295+/-210 nmol/l; P<0.001). Maximal concentrations (609+/-140, 1046+/-283, 2033+/-460 pmol/l; P<0.001) were reached after 4-6 h. The metabolic response (expressed as maximal glucose infusion rates (GIR)) induced by subcutaneous injection of NN304 did not show the pronounced peak seen with NPH-insulin in an identical dose: GIRmax 3.2+/-1.1 vs. 4.4+/-1.8 mg/kg/min (P<0.05 for 0.3 U/kg NN304 vs. NPH-insulin; mean of both study days with NPH-insulin, all others not significant). NN304 also showed a slower onset of action, as indicated by a significantly higher tmax (446+/-162 vs. 359+/-175 min) and lower AUC0-240min (0.5+/-0.3 vs. 0.8+/-0.4 g/kg/240min; P<0.05, respectively). The three different doses of NN304 induced a significantly different glucose consumption in the first 720 min after injection (AUC0-720 min 1.1+/-0.6, 1.9+/-0.8, 1.7+/-0.8 g/kg; P<0.05 for 0.15 U/kg), but not over the whole study period (AUC0-1440 min 1.8+/-1.1, 3.1+/-1.3, 2.8+/-1.4 g/kg). CONCLUSIONS: Injection of NN304 at different doses resulted in an increase in total NN304 concentration in a linear dose-response effect and a more even metabolic effect than NPH-insulin. However, we found no clear dose-response in its metabolic effect.     

胰岛素肠溶胶丸人体药代动力学、药效动力学及生物利用度研究

目的 以正规胰岛素皮下注射制剂为参比,进行胰岛素肠溶胶丸人体药代动力学、药效动力学及相对生物利用度研究。方法 20例健康受试者,男14例,女6例,年龄21～41（28．64-5．2）岁,BMI18．0～22．0（21．24-1．1）kg／m^2,在正常血糖葡萄糖钳夹技术平台上,按随机顺序分别接受受试制剂（50IU）和参比制剂（15IU）两次试验。每个试验日经2h平衡后给药,采29个时点血样测血清胰岛素水平,同时记录12h中每5分钟的葡萄糖输注率,以计算药代动力学和药效动力学参数。结果 受试制剂与参比制剂的血药浓度峰值分别为（22．1±8．0）m／U／L和（118．6±25．2）mlU／L,达峰时间分别为（255．8±142．2）min和（115．5±43．4）min。葡萄糖处置率峰值（GIRmax）分别为（3．56±0．85）mg·kg^-1·min^-1和（4．87±1．26）mg·kg^-1·min^-1,GIRmax达峰时间分别为（166．3±75．9）min和（148．0＋40．8）min。受试制剂相对生物利用度为（7．42±3．25）％,相对有效性为（24．78±0．08）％。结论 胰岛素肠溶胶丸可经胃肠道吸收入血,相对生物利用度与相对有效性差别大,充分体现了口服胰岛素制剂模拟内源胰岛素分泌生理过程所带来的益处。其药代、药效特点为进一步临床研究提供可靠的依据。     

Rats that are made insulin resistant by glucosamine treatment have impaired skeletal muscle insulin receptor phosphorylation

The current study sought to verify whether glucosamine (GlcN)-induced insulin resistance is associated with impaired insulin receptor (IR) autophosphorylation. Rats were given either saline or primed continuous GlcN infusion (5 micromol x kg(-1) x min(-1)) 10 minutes prior to and during euglycemic hyperinsulinemic clamp (primed continuous infusion of 20 mU x kg(-1) x min(-1) insulin for 2 hours). IR autophosphorylation was measured in skeletal muscle after in vivo insulin stimulation (ie, during clamp) by Western blot and then retested after subsequent in vitro 0.1 to 100 nmol/L insulin stimulation (by enzyme-linked immunosorbent assay [ELISA]). Tissue PC-1 enzymatic activity was also measured. In vivo, insulin/GlcN rats had decreased (P <.01) whole body glucose uptake (37.7 +/- 2.1 v 49.7 +/- 2.7 mg x kg(-1) x min(-1) in respect to insulin/saline), receptor autophosphorylation (37 +/- 5 v 82 +/-.0 arbitrary units/mg protein), and insulin receptor substrate-1 (IRS-1) phosphorylation (112% +/- 15% v 198% +/- 23% of saline infusion rats). Receptor autophosphorylation was correlated with whole body glucose uptake (r = 0.62, P <.05). Skeletal muscle PC-1 activity (58.8 +/- 10.7 v 55.7 +/- 5.8 nmol x mg(-1) x min(-1)) was not different in the 2 groups. Our data show that GlcN-induced insulin resistance is mediated, at least in part, by impaired skeletal muscle IR autophosphorylation.     

The impact of pegvisomant treatment on substrate metabolism and insulin sensitivity in patients with acromegaly

CONTEXT: Pegvisomant is a specific GH receptor antagonist that is able to normalize serum IGF-I concentrations in most patients with acromegaly. The impact of pegvisomant on insulin sensitivity and substrate metabolism is less well described. PATIENTS AND METHODS: We assessed basal and insulin-stimulated (euglycemic clamp) substrate metabolism in seven patients with active acromegaly before and after 4-wk pegvisomant treatment (15 mg/d) in an open design. RESULTS: After pegvisomant, IGF-I decreased, whereas GH increased (IGF-I, 621 +/- 82 vs. 247 +/- 33 microg/liter, P = 0.02; GH, 5.3 +/- 1.5 vs. 10.8 +/- 3.3 microg/liter, P = 0.02). Basal serum insulin and plasma glucose levels decreased after treatment (insulin, 54 +/- 5.9 vs. 42 +/- 5.3 pmol/liter, P = 0.001; glucose, 5.7 +/- 0.1 vs. 5.3 +/- 0.0 mmol/liter, not significant), whereas palmitate kinetics were unaltered. During the clamp, the glucose infusion rate increased after pegvisomant (3.1 +/- 0.5 vs. 4.4 +/- 0.6 mg/kg.min, P = 0.02), whereas the suppression of endogenous glucose production tended to increase (0.7 +/- 0.0 vs. 0.5 +/- 0.1 mg/kg.min, not significant). Total resting energy expenditure decreased after pegvisomant treatment (1703 +/- 109 vs. 1563 +/- 101 kcal/24 h, P = 0.03), but the rate of lipid oxidation did not change significantly. CONCLUSIONS: 1) Pegvisomant treatment for 4 wk improves peripheral and hepatic insulin sensitivity in acromegaly. 2) This is associated with a decrease in resting energy expenditure, whereas free fatty acid metabolism is unaltered. 3) The data support the important direct effects of GH on glucose metabolism and add additional benefits to pegvisomant treatment for acromegaly.     

Association of insulin resistance with hyperglycemia in streptozotocin-diabetic pigs: effects of metformin at isoenergetic feeding in a type 2-like diabetic pig model

Insulin-mediated glucose metabolism was investigated in streptozotocin (STZ)-treated diabetic pigs to explore if the STZ-diabetic pig can be a suitable model for insulin-resistant, type 2 diabetes mellitus. Pigs (approximately 40 kg) were meal-fed with a low-fat (5%) diet. Hyperinsulinemic (1, 2, and 8 mU kg(-1) min(-1)) clamps and/or 6,6-(2)H-glucose infusion studies were performed in 36 pigs. Diabetic (slow, 30-minute infusion of 130 mg STZ/kg) vs normal pigs were nonketotic, showed fasting hyperglycemia (21.7 +/- 1.1 vs 5.3 +/- 0.2 mmol/L), comparable plasma insulin (9 +/- 7 vs 5 +/- 1 mU/L), and elevated triglyceride concentrations (1.0 +/- 0.3 vs 0.2 +/- 0.1 mmol/L). After a standard meal, plasma triglycerides, cholesterol, and nonesterified fatty acid concentrations were significantly higher in diabetic vs normal pigs (1.2 +/- 0.3 vs 0.3 +/- 0.1, 2.3 +/- 0.2 vs 1.7 +/- 0.1, and 1.5 +/- 0.5 vs 0.2 +/- 0.1 mmol/L, respectively, P < .05). Fasting whole-body glucose uptake, hepatic glucose production, and urinary glucose excretion were increased (P < .01) in diabetic vs normal pigs (9.1 +/- 0.6 vs 4.8 +/- 0.4, 11.4 +/- 0.6 vs 4.8 +/- 0.4, and 2.3 +/- 0.2 vs 0.0 +/- 0.0 mg kg(-1) min(-1)). During hyperinsulinemic euglycemia (approximately 6 mmol/L), whole-body glucose uptake was severely reduced (P < .01) and hepatic glucose production was moderately increased (P < .05) in diabetic vs normal pigs (6.7 +/- 1.3 vs 21.1 +/- 2.2 and 1.7 +/- 0.5 vs 0.8 +/- 0.3 mg kg(-1) min(-1)) despite plasma insulin concentrations of 45 +/- 5 vs 24 +/- 5 mU/L, respectively. Metformin vs placebo treatment of diabetic pigs (twice 1.5 g/d) for 2 weeks during isoenergetic feeding (1045 kJ/kg body weight(0.75)) resulted in a reduction in both fasting and postprandial hyperglycemia (14.7 +/- 1.5 vs 19.4 +/- 0.6 and 24.9 +/- 2.2 vs 35.5 +/- 4.9 mmol/L), a reduction in daily urinary glucose excretion (approximately 250 vs approximately 350 g/kg food), and an increase in insulin-stimulated glucose disposal (9.4 +/- 2.2 vs 5.8 +/- 1.7 mg kg(-1) min(-1); P < .05), respectively. In conclusion, a slow infusion of STZ (130 mg/kg) in pigs on a low-fat diet induces the characteristic metabolic abnormalities of type 2 diabetes mellitus and its sensitivity to oral metformin therapy. It is therefore a suitable humanoid animal model for studying different aspects of metabolic changes in type 2 diabetes mellitus. Insulin resistance in STZ-diabetic pigs is most likely secondary to hyperglycemia and/or hyperlipidemia and therefore of metabolic origin.     

Enhancement of blood glucose lowering effect of a sulfonylurea when coadministered with an ACE inhibitor: results of a glucose-clamp study

BACKGROUND: To investigate if coadministration of enalapril alters the metabolic effect of glibenclamide by employing an euglycemic glucose-clamp technique in healthy volunteers. METHODS: A double-blind crossover study with nine healthy normotensive volunteers (age 27 +/- 3 y, BMI 23.3 +/- 2.0 kg m(-2); mean +/- SD)-randomly assigned to a 3-day treatment of either 5 mg enalapril or placebo. In the morning of the fourth day, volunteers orally received 3.5 mg glibenclamide together with either 10 mg enalapril or placebo. Blood glucose levels of volunteers were allowed to fall by 10% from fasting levels and were kept constant thereafter by employing a Biostator-based euglycemic glucose clamp. RESULTS: Coadministration of enalapril-compared with placebo-resulted in a temporarily higher metabolic effect of glibenclamide (AUC GIR(0-120)229 +/- 173 vs 137 +/- 44 mg kg(-1), p < 0.01; mean +/- SD), which lasted from 120 min to 240 min after enalapril administration. In parallel, the maximal metabolic effect of glibenclamide tended to be higher with enalapril (GIR(max)5.2 +/- 1.9 vs 4.1 +/- 1.3 mg kg(-1) min(-1); p = 0.19). However, the total metabolic effect of glibenclamide was almost identical between volunteers taking enalapril or placebo (AUC GIR(0-600)1267 +/- 334 vs 1286 +/- 249 mg kg(-1), ns). In contrast, serum insulin levels, C-peptide levels, and serum glibenclamide profiles were not significantly different between enalapril and placebo. CONCLUSIONS: The results of this study may explain the higher incidence of hypoglycemic episodes observed in patients with type 2 diabetes when taking ACE inhibitors together with sulfonylureas or insulin. ACE inhibitors may cause a temporary increase of the insulin sensitivity, which leads to an increased risk of hypoglycemia under these conditions.     

Baseline and CRH-stimulated ACTH and cortisol levels after administration of the peroxisome proliferator-activated receptor-gamma ligand, rosiglitazone, in Cushing's disease

The ability of acute rosiglitazone administration in influencing ACTH/cortisol secretion in basal conditions and after CRH stimulation was studied in patients with Cushing's disease. Ten patients (8 women and 2 men, aged 18-65 yr) with Cushing's disease were enrolled in the study: 6 of them had previously undergone unsuccessful surgery and 4 were untreated. Plasma ACTH and serum cortisol levels were evaluated at serial time points for 3 h during saline infusion and after the administration of rosiglitazone (8 mg, po) and for 1 h after the injection of CRH (1 microg/kg iv) given alone or 30 min following rosiglitazone administration. The 4 tests were performed in all subjects in randomized order on different days. No significant difference was observed between the pattern of hormone secretion during saline alone and after rosiglitazone, as evaluated by two-way analysis of variance (ANOVA). The integrated areas under the curves (AUCs) were also not significantly different (ACTH: 5683 +/- 1038 vs 6111 +/- 1007 pg/ml/180 min; cortisol: 2333 +/- 267 vs 2902 +/- 486 microg/dl/180 min). In addition, there was no difference for ACTH and cortisol responses to CRH given either alone or after rosiglitazone, when evaluated as peak, increment or AUC; the pattern of the responses analyzed by two-way ANOVA was also similar. In conclusion: 1) the administration of a single dose of rosiglitazone did not decrease ACTH/cortisol levels or blunt their response after CRH injection; 2) the activation of PPAR-gamma receptors by rosiglitazone seems unable to affect ACTH and cortisol secretion, at least in acute conditions, in patients with ACTH-secreting pituitary adenomas.