Peripheral and hepatic insulin sensitivity in subjects with impaired glucose tolerance

Summary Recent evidence suggests that the post-prandial hyperglycaemia in impaired glucose tolerance is primarily due to impaired suppression of basal hepatic glucose output. This in turn appears to be secondary to decreased first phase insulin secretion, although decreased hepatic insulin sensitivity, which is a feature of non-insulin-dependent diabetes mellitus, might also play a role. Eight mildly overweight subjects with impaired glucose tolerance and eight closely matched control subjects with normal glucose tolerance underwent an intravenous glucose tolerance test to assess first phase insulin secretion. Insulin sensitivity was examined by a 150-min hyperinsulinaemic-euglycaemic clamp. Somatostatin was infused from 150 min to suppress endogenous insulin secretion, and glucagon and insulin were replaced by constant infusion. Glucose with added dideuterated glucose (labelled infusion technique) was infused to maintain euglycaemia. First phase insulin secretion ( 0–10 min insulin area ÷ 0–10 min glucose area) was significantly decreased in the subjects with impaired glucose tolerance (median [range]: 1.2 [0.2–19.4] vs 9.1 [2.6–14.5] mU·mmol^–1; p<0.01). During the clamp, circulating insulin (93±8 [mean±SEM] and 81±10 mU·l^–1) and glucagon (54±4 and 44±6 ng·l^–1) levels were comparable. Total glucose disposal was decreased in subjects with impaired glucose tolerance (2.78±0.27 vs 4.47±0.53 mg·kg^–1·min^–1; p<0.02), and was primarily due to decreased non-oxidative glucose disposal. However, hepatic glucose output rates were comparable during the clamp (0.38±0.10 and 0.30±0.18 mg·kg^–1·min^–1). Therefore, the main defects in subjects with impaired glucose tolerance are decreased first phase insulin secretion and peripheral non-oxidative glucose disposal, but hepatic glucose output shows normal responsiveness to insulin.Abbreviations FPIS First phase insulin secretion - PG plasma glucose - NIDDM non-insulin-dependent diabetes mellitus - IGT impaired glucose tolerance - HGO hepatic glucose output - IVGTT intravenous glucose tolerance test - OGTT oral glucose tolerance test     

Serum adiponectin levels predict the effect of short-term dietary interventions on insulin sensitivity in humans

Aims/hypothesis Fat-rich diets can acutely induce insulin resistance. Data from adiponectin knock-out mice suggest that this effect might be increased in the absence of adiponectin. In the present study we tested whether plasma adiponectin concentrations influence changes in insulin sensitivity induced by a short-term dietary intervention in humans.Methods We analysed data from 27 healthy, non-obese men with normal glucose tolerance. These men ate a diet high in fat and a diet high in carbohydrates for three days each.Results The high-fat diet induced a significant drop in insulin sensitivity (determined by euglycaemic–hyperinsulinaemic clamp) compared to baseline (0.100±0.009 vs 0.083±0.007 µmol·kg^–1·min^–1·(pmol·l^–1), p=0.01). The drop in insulin sensitivity was more pronounced in subjects with low serum adiponectin (0.094±0.011 vs 0.077±0.010 µmol·kg^–1·min^–1·(pmol·l^–1), p=0.02) than in subjects with high serum adiponectin (0.103±0.011 vs 0.090±0.040 µmol·kg^–1·min^–1·(pmol·l^–1), p=0.16). In the whole group the high-carbohydrate, low-fat diet did not cause an increase in insulin sensitivity (0.095±0.007 vs 0.102±0.009 µmol·kg^–1·min^–1·(pmol·l^–1), p=0.06). However, insulin sensitivity was significantly increased in the subgroup with low serum adiponectin levels (0.084±0.013 vs 0.099±0.018 µmol·kg^–1·min^–1·(pmol·l^–1), p=0.01). In an additional multivariate analysis post-intervention insulin sensitivity was predicted by pre-intervention insulin sensitivity (p<0.001) and adiponectin concentrations (p=0.001).Conclusions/interpretation These data indicate that the reduction in insulin sensitivity achieved by a short-term high-fat diet is more pronounced in non-obese subjects with low serum adiponectin. Thus it is possible that the restriction of dietary fat and a diet high in carbohydrates might be particularly effective in subjects with low adiponectin such as obese or Type 2 diabetic individuals.     

Effect of dexamethasone on insulin sensitivity,islet amyloid polypeptide and insulin secretion in humans

Summary The response of islet amyloid polypeptide and insulin and their molar ratios were investigated in eight healthy volunteers before and after treatment with dexamethasone by oral and frequently-sampled intravenous glucose tolerance tests. Following dexamethasone treatment the insulin sensitivity index decreased significantly from 6.5±1.3 to 4.1±1.0 (U·ml^–1·min^–1, p<0.05. The area under the curve representing above-basal levels of insulin during oral glucose tolerance test increased significantly following dexamethasone treatment from 48132±9736 to 82230±14846 pmol·l^–1·3 h^–1, p<0.05, the area under the curve of islet amyloid polypeptide increased from 1308±183 to 2448±501 pmol·l^–1·3h^–1, p<0.05. The overall insulin/islet amyloid polypeptide molar ratios calculated from the area under the curve during the 3-h period of the oral glucose tolerance test was not significantly different before and after dexamethasone treatment (42±5 vs 40±4). During the oral glucose tolerance test the insulin/islet amyloid polypeptide ratio increased significantly from baseline to 30 min (p<0.05), then declined towards initial values before and after dexamethasone treatment. In conclusion, dexamethasone induced a significant decrease in insulin sensivity and a significant increase in insulin secretion during the oral glucose tolerance test. However, in contrast to previous animal experiments we did not find a change in the insulin/islet amyloid polypeptide ratio before and after dexamethasone treatment.     

Assessment of insulin sensitivity and secretion with the labelled intravenous glucose tolerance test: improved modelling analysis

Summary A new modelling analysis was developed to assess insulin sensitivity with a tracer-modified intravenous glucose tolerance test (IVGTT). IVGTTs were performed in 5 normal (NGT) and 7 non-insulin-dependent diabetic (NIDDM) subjects. A 300 mg/kg glucose bolus containing [6,6-²H₂]glucose was given at time 0. After 20 min, insulin was infused for 5 min (NGT, 0.03; NIDDM, 0.05 U/kg). Concentrations of tracer, glucose, insulin and C-peptide were measured for 240 min. A circulatory model for glucose kinetics was used. Glucose clearance was assumed to depend linearly on plasma insulin concentration delayed. Model parameters were: basal glucose clearance (Cl_b), glucose clearance at 600 pmol/l insulin concentration (Cl₆₀₀), basal glucose production (P_b), basal insulin sensitivity index (BSI = Cl_b/basal insulin concentration); incremental insulin sensitivity index (ISI = slope of the relationship between insulin concentration and glucose clearance). Insulin secretion was calculated by deconvolution of C-peptide data. Indices of basal pancreatic sensitivity (PSI_b) and first (PSI₁) and second-phase (PSI₂) sensitivity were calculated by normalizing insulin secretion to the prevailing glucose levels. Diabetic subjects were found to be insulin resistant (BSI: 2.3 ± 0.6 vs 0.76 ± 0.18 ml · min^–1· m^–2· pmol/l^–1, p < 0.02; ISI: 0.40 ± 0.06 vs 0.13 ± 0.05 ml · min^–1· m^–2· pmol/l^–1, p < 0.02; Cl₆₀₀: 333 ± 47 vs 137 ± 26 ml · min^–1· m^–2, p < 0.01; NGT vs NIDDM). P_b was not elevated in NIDDM (588 ± 169 vs 606 ± 123 μmol · min^–1· m^–2, NGT vs NIDDM). Hepatic insulin resistance was however present as basal glucose and insulin were higher. PSI₁ was impaired in NIDDM (67 ± 15 vs 12 ± 7 pmol · min^–1· m^–2· mmol/l^–1, p < 0.02; NGT vs NIDDM). In NGT and in a subset of NIDDM subjects (n = 4), PSI_b was inversely correlated with BSI (r = 0.95, p < 0.0001, log transformation). This suggests the existence of a compensatory mechanism that increases pancreatic sensitivity in the presence of insulin resistance, which is normal in some NIDDM subjects and impaired in others. In conclusion, using a simple test the present analysis provides a rich set of parameters characterizing glucose metabolism and insulin secretion, agrees with the literature, and provides some new information on the relationship between insulin sensitivity and secretion. [Diabetologia (1998) 41: 1029–1039] Received: 17 September 1997 and in final revised form: 28 April 1998     

Contribution of glucose/glucose 6-phosphate cycle activity to insulin resistance in Type 2 (non-insulin-dependent) diabetes mellitus

Summary It has been suggested that increased glucose/glucose 6-phosphate substrate cycling impairs net hepatic glucose uptake in Type 2 (non-insulin-dependent) diabetes mellitus and contributes to hyperglycaemia. To investigate glucose/glucose 6-phosphate cycle activity and insulin action in Type 2 diabetes we studied eight patients and eight healthy control subjects, using the euglycaemic glucose clamp and isotope dilution techniques with purified [2-³H]- and [6-³H] glucose tracers, in the post-absorptive state and eight patients and five healthy control subjects during consecutive insulin infusions at rates of 0.4 and 2.0 mU·kg^–1·min^–1. [2-³H]glucose and [6-³H]glucose radioactivity in plasma samples were determined using selective enzymatic detritiation, allowing calculation of glucose turnover rates for each isotope, the difference being glucose/glucose 6-phosphate cycling. Endogenous glucose production ([6-³H]glucose) was greater in diabetic than control subjects in the post-absorptive state (15.6±1.5 vs 11.3±0.4 mol·kg^–1·min^–1, p<0.05) and during the 0.4 mU insulin infusion (10.1±1.3 vs 5.2±0.3 mol·kg^–1·min^–1, p<0.01) indicating hepatic insulin resistance. Glucose/glucose 6-phosphate cycling was significantly greater in diabetic than in control subjects in the post-absorptive state (2.6±0.4 vs 1.6±0.2 mol·kg^–1·min^–1, p<0.05) but not during the 0.4 mU insulin infusion (2.0±0.4 vs 2.0±0.3 mol·kg^–1·min^–1). During the 2.0 mU insulin infusion endogenous glucose production was suppressed to a similar degree in both groups (2.6±0.5 vs 3.4±0.7 mol · kg^–1·min^–1) but glucose disappearance was lower in the diabetic subjects (30.8±2.0 vs 52.4±4.6 mol·kg^–1·min^–1, p<0.01). During the 2.0 mU insulin infusion glucose/glucose 6-phosphate cycling was greater in the diabetic subjects (3.8±0.7 vs 0.8±0.6 mol·kg^–1·min^–1, p<0.05). In conclusion, both hepatic and peripheral insulin action are impaired in Type 2 diabetes. Increased glucose/glucose 6-phosphate cycling is seen in the post-absorptive state and also during marked hyperinsulinaemia, when insulin resistance is predominantly due to reduced peripheral tissue glucose uptake.     

Mechanisms of glucose intolerance in cystic fibrosis

Aims Although cystic fibrosis‐related diabetes (CFRD), a poor prognostic factor in cystic fibrosis (CF), is characterized by insulinopenia, the role of insulin resistance is unclear. Using a prospective study design, we measured insulin resistance, pancreatic β‐cell function and correlated glycaemic status with clinical parameters. Methods Oral glucose tolerance test was performed in 60 stable adult CF patients. Insulin sensitivity and β‐cell function were measured using the homeostatic model assessment (HOMA2), Stumvoll and oral glucose insulin sensitivity (OGIS) indices. Results Forty‐two (70%) had normal glucose tolerance (NGT), 10 (17%) impaired glucose tolerance (IGT) and eight (13%) CFRD. There was no difference in insulin sensitivity among the three groups (HOMA2: NGT 280, IGT 250, CFRD 339, P = 0.42; Stumvoll: NGT 0.128, IGT 0.126, CFRD 0.129, P = 0.76; and OGIS: NGT 515, IGT 472, CFRD 472, P = 0.12). Pancreatic β‐cell function (CFRD 50% vs. NGT 67%; P < 0.05) and first‐phase insulin secretion were reduced in CFRD (250 vs. NGT 509; P = 0.004). First‐phase insulin secretion was inversely correlated with 1‐h (r = ?0.74; P < 0.0001) and 2‐h glucose levels (r = ?0.34; P < 0.05). There was no difference in body mass index or poor lung function (forced expiratory volume in 1 s: CFRD 54% vs. NGT 65%; P = 0.43). However, there were more hospital admissions in the CFRD group (three vs. NGT one per patient per year; P < 0.05). Conclusions CFRD is characterized by qualitative and quantitative defects in insulin secretion, but not insulin resistance, and is associated with increased hospital admissions for pulmonary exacerbations.     

Insulin resistance in Type 2 (non-insulin-dependent) diabetic patients with hypertriglyceridaemia

Summary Hypertriglyceridaemia, which is frequently seen in Type 2 (non-insulin-dependent) diabetes mellitus, is associated with insulin resistance. The connection between hypertriglyceridaemia and insulin resistance is not clear, but could be due to substrate competition between glucose and lipids. To address this question we measured glucose and lipid metabolism in 39 Type 2 diabetic patients with hypertriglyceridaemia, i. e. mean fasting serum triglyceride level equal to or above 2 mmol/l (age 59±1 years, BMI 27.4±0.5 kg/m², HbA_1c8.0±0.2%, serum triglycerides 3.2±0.2 mmol/l) and 41 Type 2 diabetic patients with normotriglyceridaemia, i. e. mean fasting serum triglyceride level below 2 mmol/l (age 58±1 years, BMI 27.0±0.7 kg/m², HbA_1c7.8±0.2 %, serum triglycerides 1.4±0.1 mmol/l). Insulin sensitivity was assessed using a 340 pmol·(m²)^–1· min^–1 euglycaemic insulin clamp. Substrate oxidation rates were measured with indirect calorimetry and hepatic glucose production was estimated using a primed (25 Ci)-constant (0.25 Ci/min) infusion of [3-³H]-glucose. Suppression of lipid oxidation by insulin was impaired in patients with hypertriglyceridaemia vs patients with normal triglyceride levels (3.5±0.2 vs 3.0±0.2mol·kg^–1· min^–1; p<0.05). Stimulation of glucose disposal by insulin was reduced in hypertriglyceridaemic vs normotriglyceridaemic patients (27.0±1.3 vs 31.9±1.6 mol·kg^–1·min^–1; p<0.05) primarily due to impaired glucose storage (9.8±1.0 vs 14.6±1.4mol·kg^–1·min^–1; p<0.01). In contrast, insulinstimulated glucose oxidation was similar in patients with hypertriglyceridaemia and in patients with normal triglyceride concentrations (16.9±0.8 vs 17.2±0.7mol·kg^–1·min^–1). Hepatic glucose production in the basal state and during the clamp did not differ between the two groups. We conclude therefore that oxidative substrate competition between glucose and lipids does not explain insulin resistance associated with hypertriglyceridaemia in Type 2 diabetes. The question remains whether the reduced nonoxidative glucose disposal observed in the patients with hypertriglyceridaemia is genetically determined or a consequence of increased lipid oxidation.     

Acetyl-salicylic acid impairs insulin-mediated glucose utilization and reduces insulin clearance in healthy and non-insulin-dependent diabetic man

Summary The effect of acetyl-salicylic acid (ASA, 3 g per day for 3 days) on glucose utilization and insulin secretion was studied in healthy volunteers and Type 2 diabetic patients using the hyperglycaemic and euglycaemic insulin clamp technique. When in healthy subjects arterial plasma glucose was acutely raised and maintained at +7 mmol/l above fasting level, the plasma insulin response was enhanced by ASA (70±7 vs. 52±7mU/l), whereas the plasma C-peptide response was identical. Despite higher insulin concentrations, glucose utilization was not significantly altered (control, 61±7; ASA, 65±6mol·kg^–1·min^–1) indicating impairment of tissue sensitivity to insulin by ASA. Inhibition of prostaglandin synthesis was not likely to be involved in the effect of ASA, since insulin response and glucose utilization were unchanged following treatment with indomethacin. In the euglycaemic insulin (1 mU·kg^–1·min^–1) clamp studies, glucose utilization was unaltered by ASA despite higher insulin concentrations achieved during constant insulin infusion (103±4vs. 89±4mU/l). In Type 2 diabetic patients, fasting hyperglycaemia (10.6 ±1.1 mmol/l) and hepatic glucose production (15±2 mol·kg^–1·min^–1) fell upon ASA treatment (8.6±0.7 mmol/l; 13±1 mol·kg^–1· min^–1). During the hyperglycaemic clamp study, the plasma response of insulin, but not of C-peptide, was enhanced by ASA, whereas tissue sensitivity to insulin was reduced by 30 percent. It is concluded that in healthy and Type 2 diabetic man, ASA impairs tissue sensitivity to the action of insulin. This effect is counterbalanced by an augmented plasma insulin response to glucose, which results from a reduced insulin clearance rate. In Type 2 diabetic patients, the reduction in hepatic glucose production may be responsible for the amelioration of hyperglycaemia following ASA treatment.     

Restoration of normal glucose tolerance in severely obese patients after bilio-pancreatic diversion: role of insulin sensitivity and beta cell function

Aims/hypothesis The aim of this study was to analyse the mechanisms underlying the improvement in glucose tolerance seen in morbidly obese patients undergoing bilio-pancreatic diversion (BPD).Subjects and methods We evaluated glucose tolerance (by OGTT), insulin sensitivity (euglycaemic–hyperinsulinaemic clamp and the OGTT index OGIS) and beta cell function (OGTT modelling analysis) in 32 morbidly obese (BMI=52±7 kg/m², mean±SD) patients (12 with NGT, 9 with IGT and 11 with type 2 diabetes), before and after BPD, and in 22 lean control subjects. Patients were studied before and from 7 days to 60 months after surgery.Results BPD improved glucose tolerance in all subjects, who after surgery all had normal glucose tolerance. Insulin sensitivity was restored to normal levels in all subjects (pre-BPD 341±79 ml min⁻¹ m⁻², post-BPD 511±57 ml min⁻¹ m⁻², lean 478±49 ml min⁻¹ m⁻²). The insulin sensitivity change was detectable within 10 days of BPD. At baseline, beta cell sensitivity to glucose was impaired in diabetic subjects (25 [18] pmol min⁻¹ m⁻² l mmol⁻¹, median [interquartile range]) compared with lean subjects (82 [98]; p≤0.05). After BPD, beta cell glucose sensitivity showed a tendency towards improvement but remained impaired in diabetic subjects (30 [62]; p<0.01 vs lean). Total insulin output decreased in parallel with the insulin sensitivity increase in all groups. In the whole patient group, mean OGTT glucose levels were inversely related to both insulin sensitivity and beta cell glucose sensitivity (r ²=0.67, partial r=−0.76 and −0.41, respectively). NEFAs, leptin and adiponectin were related to insulin sensitivity but could not explain the early improvement.Conclusions/interpretation Following BPD, glucose tolerance was restored mainly as a result of a rapid and large improvement in insulin sensitivity.     

In vivo insulin action and muscle glycogen synthase activity in Type 2 (non-insulin-dependent) diabetes mellitus: effects of diet treatment

Summary Insulin resistant glucose metabolism is a key element in the pathogenesis of Type 2 (non-insulin-dependent) diabetes mellitus. Insulin resistance may be of both primary (genetic) and secondary (metabolic) origin. Before and after diet-induced improvement of glycaemic control seven obese patients with newly-diagnosed Type 2 diabetes were studied with the euglycaemic clamp technique in combination with indirect calorimetry and forearm glucose balance. Muscle biopsies were obtained in the basal state and again after 3 h of hyperinsulinaemia (200 mU/l) for studies of insulin receptor and glycogen synthase activities. Similar studies were performed in seven matched control subjects. Insulin-stimulated glucose utilization improved from 110±11 to 183±23 mg·m^–2·min^–1 (p<0.03); control subjects: 219+23 mg·m^–2·min^–1 (p=NS, vs post-diet Type 2 diabetes). Nonoxidative glucose disposal increased from 74±17 to 138+19 mg·m^–2·min^–1 (p<0.03), control subjects: 159±22 mg· m^–2·m^–1 (p=NS, vs post-diet Type 2 diabetic patients). Forearm blood glucose uptake during hyperinsulinaemia increased from 1.58±0.54 to 3.35±0.23 mol·l^–1·min^–1 (p<0.05), control subjects: 2.99±0.86 mol·l^–1·min^–1 (p=NS, vs post-diet Type 2 diabetes). After diet therapy the increase in insulin sensitivity correlated with reductions in fasting plasma glucose levels (r=0.97, p<0.001), reductions in serum fructosamine (r=0.77, p<0.05), and weight loss (r=0.78, p<0.05). Values of muscle glycogen synthase sensitivity to glucose 6-phosphate (A_0.5 for glucose 6-phosphate) were similar in the basal state. However, insulin stimulation of glycogen synthase was more pronounced after diet treatment (A_0.5: 0.43±0.06 (before) vs 0.30±0.04 mmol/l (after); p<0.03; control subjects: 0.22±0.03 mmol/l). Muscle insulin receptor binding and kinase activity were similar before and after diet treatment and comparable to values in the control group. The data suggest that impaired insulin stimulation of in vivo glucose turn-over and muscle glycogen synthase activity tend to be restored during successful diet treatment of patients with Type 2 diabetes.     

The contribution of hyperglycaemia and hypoinsulinaemia to the insulin resistance of streptozotocin-diabetic rats

Summary The relative contribution of hyperglycaemia and hypoinsulinaemia was evaluated in rats made diabetic by streptozotocin administration. Four groups of rats were studied: untreated normal rats; streptozotocin-diabetic; streptozotocin-diabetic treated with phlorizin (0.4 mg/kg body weight per day); streptozotocin-diabetic mildly treated with insulin (0.7 IU/day). In all groups, insulin action (responsiveness) was assessed with the euglycaemic (5.3 mmol/l) hyperinsulinaemic (524 mU/l) clamp technique combined with ³H-2-deoxy-D-glucose method, enabling determination of the glucose utilization index in various tissues. Responsiveness of the overall glucose utilization process to insulin was reduced by 28% in streptozotocin-diabetic rats (12.0±1.2 vs 16.5±0.6 mg·kg^–1·min^–1, p<0.001). This was associated with a significant reduction (p<0.05) in the glucose utilization index in all muscles studied (average=17.0 vs 32.1 ng·mg of tissue^–1·min^–1), in the heart (19.6 vs 39.5 ng·mg^–1·min^–1), brown adipose tissue (98.9 vs 178.0 ng·mg^–1·min^–1), skin (6.4 vs 13.1 ng·mg^–1·min^–1). Phlorizin treatment normalized plasma glucose levels without affecting those of insulin, and restored overall glucose utilization to normal (16.6±1.0mg·kg^–1·min^–1). This normalization was accompanied by a normalization of the glucose utilization index in all muscle types studied (29.2 ng·mg^–1·min^–1), in the heart (50.0ng·mg^–1·min^–1), brown adipose tissue (157.2 ng·mg^–1·min^–1), and skin (10.0 ng·mg^–1·min^–1). White adipose tissue, brain and gut were not affected. Mild insulin treatment with persistent hyperglycaemia was not able to significantly ameliorate glucose disposal (14.5±0.9 mg·kg^–1·min^–1) or the glucose utilization index of most individual tissues (muscle=18.4; heart=36.2; brown adipose tissue=148.0; skin=7.7 ng· mg^–1· min^–1). These data show that correction of hyperglycaemia in streptozotocin-diabetic rats normalizes insulin action, while partial correction of the hypoinsulinaemia fails to do so.     

Effects of islet amyloid polypeptide on hepatic insulin resistance and glucose production in the isolated perfused rat liver

Summary The impact of (pancreatic) islet amyloid polypeptide on glucose metabolism and insulin sensitivity was examined in isolated rat livers perfused in a non-recirculating system. Continuous infusion of 10^–7mol/l islet amyloid polypeptide affected neither basal nor glucagon (10^–9 mol/l)-stimulated glucose output by livers from fed rats, but it did increase the hepatic cyclic AMP release within 44 min (7.91±12.07 vs control: 0.07±0.03 pmol·100 g body weight^–1). The effect of the peptide on the ability of insulin to inhibit glucagon-induced hepatic glycogenolysis was measured in three experimental groups (n = 6). As expected glucagon (7×10^–11 mol/l) increased integral hepatic glucose release within 84 min (763.4±161.7 vs –25.7±73.2 mol · 100 g body weight^–1 in the control group, p<0.001), while insulin (100 mU/l) decreased the glucagon-stimulated glucose production (395.2±180.0 mol·100 g body weight^–1, p<0.01). Simultaneous infusion of 10^–7 mol/l islet amyloid polypeptide however, was not able to reverse insulin-dependent inhibition of glucagon-stimulated hepatic glucose output (370.0±102.5 mol·100 g body weight^–1, NS) or to enhance lactate-induced gluconeogenesis of livers from 24 h fasted rats (n = 8). The glucose production stimulated by 10^–9 mol/l glucagon was slightly greater in islet amyloid polypeptide-pre-treated livers than in a control group without addition of islet amyloid polypeptide (5 min: 3.60±3.36 vs 1.67±1.28 mol·min^–1·100 g body weight^–1). These results suggest that islet amyloid polypeptide neither directly affects hepatic glycogenolysis nor causes insulin resistance to hormone-sensitive glucose production, but may increase the size of the hepatic glycogen pool by enhancing gluconeogenesis.     

Characterisation of beta-cell dysfunction of impaired glucose tolerance: Evidence for impairment of incretin-induced insulin secretion

Aims/hypothesis. Our studies were undertaken to characterise the defective insulin secretion of impaired glucose tolerance (IGT).¶Methods. We studied 13 normal glucose tolerant subjects (NGT) and 12 subjects with IGT carefully matched for age, sex, BMI and waist-to-hip ratio. A modified hyperglycaemic clamp (10 mmol/l) with a standard 2-h square-wave hyperglycaemia, an additional glucagon-like-peptide (GLP)-1 phase (1.5 pmol · kg^–1· min^–1 over 80 min) and a final arginine bolus (5 g) was used to assess various phases of insulin secretion rate.¶Results. Insulin sensitivity during the second phase of the hyperglycaemic clamp was low in both groups but not significantly different (0.12 ± 0.021 in NGT vs 0.11 ± 0.013 μmol · kg^–1· min^–1· pmol^–1 in IGT, p = 0.61). First-phase insulin secretion was lower in IGT (1467 ± 252 vs 3198 ± 527 pmol · min^–1, p = 0.008) whereas the second phase was not (677 ± 61 vs 878 ± 117 pmol · min^–1, p = 0.15). The acute insulin secretory peak in response to GLP-1 was absent in IGT subjects who only produced a late phase of GLP-1-induced insulin secretion rate which was lower (2228 ± 188 pmol · min^–1) than in NGT subjects (3056 ± 327 pmol · min^–1, p = 0.043). Insulin secretion in response to arginine was considerably although not significantly lower in IGT subjects. The relative impairment (per cent of the mean rate for NGT subjects) was greatest for the GLP-1 peak (19 ± 9 %).¶Conclusion/interpretation. In this Caucasian cohort a defective insulin secretion rate is essential for the development of IGT. The variable degrees of impairment of different phases of the insulin secretion rate indicate that several defects contribute to its abnormality in IGT. Defects in the incretin signalling pathway of the beta cell could contribute to the pathogenesis of beta-cell dysfunction of IGT and thus Type II (non-insulin-dependent) diabetes mellitus. [Diabetologia (2000) 43: 852–858]     

Relationship between insulin responses tod-glucose and tol-arginine in women with a history of gestational diabetes

The relationship between insulin responses to glucose and to arginine was studied in non-obese women with previous gestational diabetes (PGD). One group,n=10, had normal glucose tolerance (NGT) by WHO criteria and another,n=8, had impaired glucose tolerance (IGT). A third group of women without PGD,n=12, was also studied. A hyperglycaemic clamp (blood glucose level 11 mM) and an arginine stimulation test (150 mg/kgl-arginine followed by 10 mg/kg · min) were performed on separate days. The ratios of arginine to glucose responses 0–10 min differed: they were 1.00 for non-PGD, 1.29 for NGT and 1.46 for IGT (P<0.02 vs non-PGD). A further difference between groups was the ratio between first- and second-phase glucose-induced insulin secretion, which was significantly decreased in IGT, 0.72, compared with NGT, 0.98 (P<0.01), and non-PGD, 1.05 (P<0.005). However, within each group insulin responses 0–10 min to glucose and arginine were strongly correlated: for NGT (r=0.75,P<0.05), for IGT (r=0.85,P<0.01) and for women without PGD (r=0.69,P<0.05). Insulin sensitivity, as assessed by the M/I ratio, was non-significantly decreased in IGT (0.18±0.03 mg/kg·min per mU/l vs 0.26 ±0.03 in NGT and 0.28±0.03 in non-PGD,P<0.1). Conclusions are: (1) insulin responses to glucose and arginine are linked both in PGD and non-PGD women, but (2) the relative potency of these secretagogues as well as the time-dynamics of glucose-induced insulin secretion may be altered in PGD with IGT.     

Effect of insulin on renal sodium handling in hyperinsulinaemic Type 2 (non-insulin-dependent) diabetic patients with peripheral insulin resistance

Summary The sodium retaining effect of insulin was studied in ten Type 2 (non-insulin-dependent) diabetic patients (mean age 56 (43–73) years, mean body mass index 29.5 (24.2–33.7) kg/m²) and eight age-matched control subjects (mean age 57 (43–68) years, mean body mass index 23.4 (20.8–26.6) kg/m²). The renal clearances of ^99mTc-DTPA, lithium, sodium and potassium were measured over a basal period of 90 min. Then insulin was infused at a rate of 40 mU·mirr^–1·m^–2. After an equilibration period of 90 min, the clearance measurements were repeated during a new 90 min period. Blood glucose was clamped at the basal level (diabetic patients: 9.9±3.5, control subjects: 5.3±0.5 mmol/l) by a variable glucose infusion. Basal plasma insulin concentration was elevated in the diabetic patients (0.12±0.05 vs 0.05±0.02 pmol/ml, p<0.01). Insulin infusion resulted in comparable absolute increments in plasma insulin concentrations in the diabetic group and in the control group (0.44±0.13 vs 0.36±0.07 pmol/ml, NS). The metabolic clearance rate of glucose during the last 30 min of insulin infusion was lower in the diabetic patients (155±62 vs 320±69 ml·min^–1·m², p<0.01), reflecting peripheral insulin resistance. The decline in sodium clearance during insulin infusion was similar in diabetic subjects (1.8±1.1 vs 0.7±0.4 ml·min^–1·1.73 m^–2, p< 0.01) and in control subjects (1.7±0.3 vs 0.8±0.3 ml · min^–1 · 1.73 m^–2, p<0.01). The glomerular filtration rate and lithium clearance was unchanged, consequently calculated distal tubular fractional sodium reabsorption increased (diabetic patients: 92.9±4.1 vs 97.1±1.5, p<0.01, control subjects: 93.1±1.1 vs 96.5±0.6%, p< 0.01). Estimated extracellular fluid volume was 10% higher in the diabetic subjects (16.3±2.1 vs 14.8±2.01·1.73 m^–2, NS). In conclusion, the sodium retaining effect of insulin is preserved in Type 2 diabetic patients with peripheral insulin resistance. Insulin may contribute to sodium and fluid retention and thus to the increased frequency of hypertension in hyperinsulinaemic Type 2 diabetic patients.     

Insulin regulation of glucose and lipid metabolism in massive obesity

Summary Eight obese patients and 12 normal individuals underwent a euglycaemic insulin clamp (20 and 40 mU · m^2–1 · min^–1) along with continuous infusion of 3-³H-glucose and 1-¹⁴C-palmitate and indirect calorimetry. Basal plasma glucose concentration (4.7±0.3 vs 4.4±0.2 mmol/l) was similar in the two groups, whereas hepatic glucose production was slightly higher in obese individuals (1.11±0.06 vs 0.84±0.05 mmol/min) in spite of higher plasma insulin levels (17±2 vs 6±1 mU/l; p<0.01). Insulin inhibition of hepatic glucose production was impaired in obese subjects. Glucose disposal by lean body mass was markedly reduced both at baseline (11.7±1.1 vs 15.6±0.6 mol · kg^–1 · min^–1; p<0.05) and during clamp (15.0±1.1 vs 34.4±2.8 and 26.7±3.9 vs 62.2±2.8 mol · kg^–1 · min^–1; p<0.01) Oxidative (12.2±1.1 vs 17.8±1 and 16.1±1.1 vs 51.1±1.7 mol · kg^–1 · min^–1; p<0.05–0.002) and non-oxidative glucose metabolism (3.9±1.1 vs 15.0±2.8 and 12.8±3.3 vs 38.3±2.2 mol · kg^–1 · min^–1; p<0.01–0.001) were impaired. Basal plasma concentrations of non-esterified fatty acids (635±75 vs 510±71 mol/l) and blood glycerol (129±17 vs 56±5 mol/l; p<0.01) were increased in obese patients. Following hyperinsulinaemia, plasma non-esterified fatty acids (244±79 vs 69±16 and 140±2 vs 36±10 mol/l; p<0.01) and blood glycerol levels (79±20 vs 34±6 and 73±22 vs 29±5 mol/l; p<0.01) remained higher in obese subjects. Baseline non-esterified fatty acid production rate per kg of fat body mass was significantly larger in normal weight subjects (37.7±6.7 vs 14.0±1.8 mol/l; p<0.01) and insulin inhibition was reduced in obese patients (–41±9 vs –74±3 and –53±11 vs –82±3%; p<0.05). Basal plasma non-esterified fatty acid utilization by lean body mass was similar in the two groups (9.8±0.9 vs 8.8±2.0 mol · kg^–1 · min^–1), whereas during clamp it remained higher in obese patients (6.0±1.2 vs 2.8±2.5 and 4.9±1.3 vs 1.5±0.6 mol · kg^–1 · min^–1; p<0.1–0.05). Lipid oxidation was higher in obese individuals in spite of hyperinsulinaemia (3.7±0.3 vs 2.4±0.4 and 2.3±0.4 vs 0.9±0.3 mol · kg^–1 · min^–1; p<0.05– 0.02). An inverse correlation was found between lipid oxidation and glucose oxidation (r=0.82 and 0.93; p<0.001) and glucose utilization (r=0.54 and 0.83; p<0.05–0.001) both in obese and control subjects. A correlation between lipid oxidation and non-oxidative glucose metabolism was present only in normal weight individuals (r=0.75; p<0.01). We conclude that in obesity all tissues (muscles, liver, and adipose tissue) are resistant to insulin action. Insulin resistance involves glucose as well as lipid metabolism.     

Assessment of insulin sensitivity in glucokinase-deficient subjects

Summary The chronic hyperglycaemia of glucokinase-deficient diabetes results from a glucose-sensing defect in pancreatic beta cells and abnormal hepatic glucose phosphorylation. We have evaluated the contribution of insulin resistance to this form of chronic hyperglycaemia. Insulin sensitivity, assessed by the homeostasis model assessment (HOMA) method in 35 kindreds with glucokinase mutations, was found to be significantly decreased in 125 glucokinase-deficient subjects as compared to 141 unaffected first-degree relatives. Logistic regression analysis showed that in glucokinase-deficient subjects a decrease in insulin sensitivity was associated with deterioration of the glucose tolerance status. A euglycaemic hyperin-sulinaemic clamp was performed in 14 glucokinase-deficient subjects and 12 unrelated control subjects. In six patients and six control subjects the clamp was coupled to dideutero-glucose infusion to measure glucose turnover. Average glucose infusion rates (GIR) at 1 and 5 mU · kg body weight · min^–1 insulin infusion rates were significantly lower in (the glucokinase-deficient) patients than in control subjects. Although heterogeneous results were observed, in 8 out of the 14 patients GIRs throughout the experiment were lower than 1 SD below the mean of the control subjects. Hepatic glucose production at 1 mU · kg body weight^–1 · min^–1 insulin-infusion rate was significantly higher in patients than in control subjects. In conclusion, insulin resistance correlates with the deterioration of glucose tolerance and contributes to the hyperglycaemia of glucokinase-deficient diabetes. Taken together, our results are most consistent with insulin resistance being considered secondary to the chronic hyperglycaemia and/or hypoinsulinaemia of glucokinase-deficiency. Insulin resistance might also result from interactions between the unbalanced glucose metabolism and susceptibility gene(s) to low insulin sensitivity likely to be present in this population.Abbreviations NIDDM Non-insulin-dependent diabetes mellitus - HGP hepatic glucose production - GCK glucokinase - IIR insulin infusion rate - GIR glucose infusion rate - MFH mild fasting hyperglycaemia - NGT normal glucose tolerance - IGT impaired glucose tolerance - HOMA homeostasis model assessment - ANOVA analysis of variance - MODY maturity-onset diabetes of the young     

Multiple defects of both hepatic and peripheral intracellular glucose processing contribute to the hyperglycaemia of NIDDM

Summary Non-insulin-dependent diabetic (NIDDM) patients were studied during a modified euglycaemic state when fasting hyperglycaemia was normalized by a prior (–210 to –150 min) — and later withdrawn (–150–0 min) — intravenous insulin infusion. Glucose metabolism was assessed in NIDDM patients (n=10) and matched control subjects (n=10) using tritiated glucose turnover rates, indirect calorimetry and skeletal muscle glycogen synthase activity determinations. Total and non-oxidative exogenous glycolytic flux rates were measured using appearance rates of tritiated water. A+180 min euglycaemic hyperinsulinaemic (40 mU·m^–2·min^–1) clamp was performed to determine the insulin responsiveness of the various metabolic pathways. Plasma glucose concentration increased spontaneously during baseline measurements in the NIDDM patients (–120 to 0 min: 4.8±0.3 to 7.0±0.3 mmol/l; p<0.01), and was primarily due to an elevated rate of hepatic glucose production (3.16±0.13 vs 2.51±0.16 mg·kg FFM^–1·min^–1; p<0.01). In the NIDDM subjects baseline glucose oxidation was decreased (0.92±0.17 vs 1.33±0.14 mg·kg FFM^–1·min^–1; p<0.01) in the presence of a normal rate of total exogenous glycolytic flux and skeletal muscle glycogen synthase activity. The simultaneous finding of an increased lipid oxidation rate (1.95±0.13 vs 1.61±0.07 mg·kg FFM^–1·min^–1; p=0.05) and increased plasma lactate concentrations (0.86±0.05 vs 0.66±0.03 mmol/l; p=0.01) are consistent with a role for both the glucose-fatty acid cycle and the Cori cycle in the maintenance and development of fasting hyperglycaemia in NIDDM during decompensation. Insulin resistance was demonstrated during the hyperinsulinaemic clamp in the NIDDM patients with a decrease in the major peripheral pathways of intracellular glucose metabolism (oxidation, storage and muscle glycogen synthase activity), but not in the pathway of non-oxidative glycolytic flux which was not completely suppressed during insulin infusion in the NIDDM patients (0.55±0.15 mg·kg FFM^–1·min^–1; p<0.05 vs 0; control subjects: 0.17±0.29; NS vs 0). Thus, these data also indicate that the defect(s) of peripheral (skeletal muscle) glucose processing in NIDDM goes beyond the site of glucose transport across the cell membrane.Abbreviations NIDDM Non-insulin-dependent diabetes mellitus - FFM fat free mass - HGP hepatic glucose production - R_d peripheral glucose disposal (uptake) rate - G6P glucose 6-phosphate - UDPG uridine diphosphate glucose - FV fractional velocity     

Failure to adequately adapt reduced insulin sensitivity with increased insulin secretion in women with impaired glucose tolerance

Summary To study the islet adaptation to reduced insulin sensitivity in normal and glucose intolerant post-menopausal women, we performed a euglycaemic, hyperinsulinaemic clamp in 108 randomly selected women, aged 58–59 years. Of the 20 women with the lowest insulin sensitivity, 11 had impaired glucose tolerance (IGT) whereas 9 had normal glucose tolerance (NGT). These women together with 15 women with medium insulin sensitivity and 16 women with high insulin sensitivity and NGT were further examined with arginine stimulation at three glucose levels (fasting, 14 and >25 mmol/l). In NGT, the acute insulin response (AIR) to 5 g i. v. arginine at all three glucose levels and the slope_AIR, i. e. the glucose potentiation of insulin secretion, were markedly increased in the women with the lowest insulin sensitivity and NGT compared to those with medium or high insulin sensitivity. In contrast, in low insulin sensitivity, AIR was significantly lower in IGT than in NGT (at glucose 14 mmol/l p=0.015, and at >25 mmol/l p=0.048). The potentiation of AIR induced by low insulin sensitivity in women with NGT was reduced by 74% (AIR at 14 mmol/l glucose) and 57% (AIR at >25 mmol/l glucose), respectively, in women with IGT. Also the slope_AIR was lower in IGT than in NGT (p=0.025); the increase in slope_AIR due to low insulin sensitivity was abolished in IGT. In contrast, glucagon secretion was not different between women with IGT as opposed to NGT. We conclude that as long as there is an adequate beta-cell adaptation to low insulin sensitivity with increased insulin secretory capacity and glucose potentiation of insulin secretion, NGT persists.Abbreviations NIDDM Non-insulin-dependent diabetes mellitus - AIR acute insulin response - AGR acute glucagon response     

Normal insulin sensitivity during the phase of glucose intolerance but insulin resistance at the onset of diabetes in the spontaneously diabetic BB rat

Summary In diabetes-prone BB rats, 30 to 50% of animals undergo autoimmune destruction of the pancreatic B-cells leading to a short period of glucose intolerance, followed by an abrupt onset of diabetes. We have examined whether the glucose intolerance period and the onset of diabetes are associated with changes in insulin sensitivity, using the euglycaemic hyperinsulinaemic clamp coupled with [3-³H] glucose infusion. Glucose intolerant rats were detected by a transient glycosuria one hour after an oral glucose load performed every four days. Insulin sensitivity studied in these rats the day following their detection was normal. Other diabetes-prone BB rats were tested daily and studied on the first day of glycosuria. In the basal state, glucose production was increased in diabetic rats (11.3±1.1 vs 7.1±0.8mg·min^–1·kg^–1, p<0.05). Tissue glucose utilization was similar in diabetic and control rats (8.3±0.5 vs 7.1±0.8mg·min^–1·kg^–1) despite a three fold higher glycaemia in the diabetic rats. During the hyperinsulinaemic clamps, glycaemia was clamped at 6.1–6.6 mmol/l in diabetic and control rats. A decreased insulin sensitivity was observed in diabetic rats at submaximal (200 U/ml) and maximal (1500 U/ml) insulin concentrations for both inhibition of hepatic glucose production and stimulation of glucose utilization. No autoantibodies against insulin could be detected in the plasma of diabetic rats. Plasma concentrations of glucagon, catecholamines, ketone bodies and fatty acids were similar in control and diabetic rats during the clamp studies. Our results suggest that the decrease of basal insulin concentration is responsible for the insulin resistance in the diabetic BB rat at onset of diabetes, either directly or through the increased glycaemia.