A hyperinsulinaemic, sequentially eu- and hypoglycaemic clamp test to characterize autonomous insulin secretion in patients with insulinoma

To better characterize autonomous insulin secretory behaviour in insulinoma patients and to establish diagnostic criteria with high accuracy, hyperinsulinaemic, sequentially eu- and hypoglycaemic clamp tests were performed in insulinoma patients and control subjects. Ten patients with insulinoma (benign in nine, histologically proven in nine) and 10 patients with suspected episodes of hypoglycaemia, in whom thorough clinical evaluation excluded an insulinoma, were examined. Five insulinoma patients were restudied after successful extirpation of the tumour. Suppression of C-peptide during low-dose [2 pmol kg^–1 min^–1 (20 mU kg^–1h^–1) for 90 min, plasma insulin approximately 120 pmol L^–1 (20 mU L^–1)] and high-dose [8 pmol kg^–1 h^–1 (80 mU kg^–1 h^–1) for 90 min, plasma insulin approximately 450 pmol L^–1 (75 mU L^–1)] insulin infusion under euglycaemic conditions [plasma glucose 4.4–5.0 mmol L^–1 (80–90 mg dL^–1)]) and during high-dose insulin infusion under hypoglycaemic conditions [glucose 2–2.2 mmol L^–1 (40–45 mg dL^–1)] was evaluated by radioimmunoassay (RIA). Euglycaemic hyperinsulinaemia suppressed C-peptide in control subjects (P < 0.0001), whereas in insulinoma patients apparently irregular changes in C-peptide concentrations (with spontaneous or paradoxical increments, P = 0.0006 vs. controls) were observed. The combination of hyperinsulinaemia and controlled hypoglycaemia led to a nearly complete suppression of C-peptide in normal subjects (from basal, 0.76 ± 0.08–0.06 ± 0.01 nmol L^–1; maximum observed value 0.10 nmol L^–1), which was more pronounced than at the point of discontinuation of prolonged fasting (> 48 h; 0.26 ± 0.16 nmol L^–1; P = 0.005). In insulinoma patients, C-peptide remained elevated under all conditions (P = 0.51 vs. prolonged fasting). All these findings were reversible after successful surgical removal of the insulinoma. Insulinoma patients could be identified as abnormal by (a) non-suppression of C-peptide even under hyperinsulinaemic/hypoglycaemic conditions (10 out of 10 patients) and (b) irregular increments in C-peptide under conditions that led to at least partial suppression in all normal subjects (9 out of 10 patients) and/or by an apparent shift to the left of insulin secretion relative to glucose concentrations (7 out of 10 patients). Controlled exposure to hyperinsulinaemic/hypoglycaemic conditions can help to characterize autonomous secretion in insulinoma patients and may be used as a diagnostic procedure when conventional methods yield equivocal results.     

Hepatic balances of glucose and insulin in response to physiological increments of endogenous insulin during glucose infusions in dogs.

Hepatic glucose uptake was measured in dogs in relation to physiological increments of plasma insulin levels under steady state conditions. Endogenous insulin secretion was stimulated by the infusion of small glucose loads, achieving normoglycaemia or mild hyperglycaemia. The measurement of hepatic arterial and portal venous blood flows allowed calculation of the relationships between net hepatic balances of insulin and glucose, the magnitude of insulin extraction by the liver and the hepatic sensitivity to physiological levels of insulin. During normoglycaemia, small glucose loads (2 and 4.5 mg/min. kg) reduced hepatic glucose output without a concomitant increase of the estimated total glucose utilization. No changes in arterial or hepatic venous plasma insulin levels occurred. Portal venous plasma insulin alone rose under the influence of the glucose stimulus. In the presence of hyperglycaemia, the liver further reduced its glucose output. Infusions of 11.3 mg/min. kg glucose resulted in reversal of hepatic glucose output to a net uptake of glucose. However, due to the large amounts of insulin emerging from the liver, peripheral tissue glucose utilization was significantly increased. A strong inverse correlation existed between arterial glucose concentration and hepatic glucose output as well as between portal venous plasma insulin level and hepatic glucose output. The net hepatic balance of insulin was promptly raised in response to the glucose perfusions, even when normoglycaemia was maintained. A highly significant, inverse correlation was demonstrated between net hepatic balance of insulin (i.e. net uptake of insulin by the liver) and hepatic glucose output. Hepatic insulin extraction ratio and hepatic plasma insulin clearance increased during glucose administration but no evident relationship to portal venous plasma insulin levels was found. These data suggest that insulin rather than glucose is the primary agent responsible for the reversal of the hepatic gradient of glucose in vivo.     

Ageing impairs insulin-mediated vasodilatation but not forearm glucose uptake

BACKGROUND: It is unclear if insulin-mediated vasodilatation is altered by ageing and if this affects insulin-mediated glucose uptake. MATERIAL AND METHODS: A 2-h euglycaemic hyperinsulinaemic clamp (56 mU m(-2) min(-1)) was performed in 10 healthy, nonobese elderly men (70-75 years) and 13 young men (23-28 years). Forearm blood flow (FBF) was measured by venous occlusion plethysmography and forearm glucose uptake was calculated by arterial and venous serum glucose determinations in the forearm. RESULTS: Insulin induced an increase in FBF in the younger men (from 3.9 +/- 1.1 SD to 5.9 +/- 2.2 mL min(-1) 100(-1)mL tissue, P < 0.001), but this insulin-mediated vasodilatation was completely blunted in the elderly subjects. Glucose extraction during the clamp was significantly higher in the elderly subjects (1.2 +/- 0.76 vs. 0.82 +/- 0.37 mmol L(-1) at 120 min, P < 0.01), resulting in a similar forearm glucose uptake in the two groups. On the other hand, whole-body glucose uptake was significantly decreased in the elderly subjects (5.3 +/- 1.8 vs. 8.0 +/- 1.1 mg kg(-1) min(-1), P < 0.001). CONCLUSION: The present study showed that the ability of insulin to induce vasodilatation is blunted in the forearm in healthy, nonobese elderly subjects. However, the elderly compensate for this impairment with an increased glucose extraction from arterial blood to maintain an unaltered forearm glucose uptake.     

High dose insulin does not increase glucose transfer across the blood–brain barrier in humans: a re-evaluation

BACKGROUND: This study re-evaluates previously published data on blood-brain barrier transfer coefficients in humans exposed to high insulin levels. DESIGN: In this study of seven volunteers, global blood-brain barrier permeability to glucose and phenylalanine was measured by means of the intracarotid double-indicator method before, during, and after an insulin-glucose clamp. Data were reanalyzed by means of a mathematical model that takes capillary heterogeneity and labelled glucose backflux from the brain into account. RESULTS: The permeability-surface area product (PS) for glucose transport from the blood into the brain, PS1, was 0.145 (0.102-0.211) (median and quartiles), 0.146 (0.113-0.259), and 0.157 (0.133-0.181) ml g-1 min-1 before, during, and after insulin challenge, respectively. In six of the subjects, PS for transport from brain to blood over the brain glucose distribution volume, PS2/Ve decreased under hyperinsulinemia, from a baseline value of 6.56 (3.0-14.9) to 3.86 (1.41-5.32), and restored to a value of 3.8 (2.8-12.1) min-1 after insulin challenge. This decrease in PS2/Ve is probably due to an increase in the brain glucose distribution volume induced by an insulin induced increased intracellular glucose uptake during the experiment. For phenylalanine (n = 5), PS1 was unchanged before, during, and after insulin challenge. In hyperinsulinemia, PS3/Ve for phenylalanine decreased in all subjects. CONCLUSION: We conclude that acutely elevated high plasma insulin levels in humans does not alter the brain uptake of glucose or phenylalanine from the blood. It seems, however, that high plasma insulin levels induce an increase in the movement of D-glucose and L-phenylalanine from the brain interstitial fluid into the intracellular compartment.     

Incomplete suppression of hepatic glucose production in non-insulin dependent diabetes mellitus measured with [6,6-2H2]glucose enriched glucose infusion during hyperinsulinaemic euglycaemic clamps

We have minimized methodological errors in the isotope dilution technique by using stable isotope, [6,6-2H2]glucose, thus avoiding the problem of contamination of tritiated glucose tracers and, by maintaining a constant plasma tracer enrichment have reduced error due to mixing transients. Using these modifications we have calculated hepatic glucose production in 20 patients with non-insulin-dependent diabetes mellitus during low (1 mU kg-1 min-1) and high (8 mU kg-1 min-1) dose insulin infusions. Mean fasting hepatic glucose production was 14.2 +/- 0.8 mumol kg-1 min-1. This suppressed by only 68% to 4.6 +/- 0.8 mumol kg-1 min-1 during the low-dose insulin infusion (plasma insulin 0.85 +/- 0.05 nmol l-1) and did not suppress further during the high-dose insulin infusion (plasma insulin 14.55 +/- 0.83 nmol l-1). Hepatic glucose production was significantly higher than zero throughout the study. Thus, we have found that minimization of known errors in the isotope dilution technique results in physiologically plausible and significantly positive values for hepatic glucose production indicating that the liver is resistant to insulin in patients with non-insulin-dependent diabetes mellitus.     

Suppression of lipolysis in normal man does not inhibit recovery from insuIin-induced hypoglycaemia

Abstract. Pharmacological suppression of lipolysis is being increasingly used in the treatment of diabetic hyperlipidaemia. Although theoretical hazard of such treatment is that recovery from hypoglycaemia might be impaired. Seven normal subjects were theretore studied on two occasions, following treatment with a single dose of either acipimox 250 mg or placebo. Hypoglycaemic recovery was unaffected, despite effective suppression of plasma non-esterified fatty acid levels with acipimox. The results suggest that under these conditions activation of lipolysis may not be essential to recovery from hypoglycaemia.     

Assessment of beta-cell function during the oral glucose tolerance test by a minimal model of insulin secretion

OBJECTIVE: To characterise the performance of beta-cell during a standard oral glucose tolerance test (OGTT). DESIGN: Fifty-six subjects were studied. A minimal analogic model of beta-cell secretion during the OGTT was applied to all OGTTs (see below). The amount of insulin secreted over 120' in response to oral glucose (OGTT-ISR; Insulin Units 120'-1 m-2 BSA) and an index of beta-cell secretory 'force' (beta-Index; pmol.min-2.m-2 BSA) were computed with the aid of the model. In protocol A, 10 healthy subjects underwent two repeat 75 g OGTT with frequent (every 10'-15') blood sampling for glucose and C-peptide to test the reproducibility of OGTT-ISR and beta-Index with a complete or a reduced data set. In protocol B, 7 healthy subjects underwent three OGTTs (50, 100 or 150 g), to test the stability of the beta-Index under different glucose loads. In protocol C, 29 subjects (15 with normal glucose tolerance, 7 with impaired glucose tolerance and 7 with newly diagnosed type 2 diabetes) underwent two repeat 75 g OGTT with reduced (every 30' for 120') blood sampling to compare the reproducibility and the discriminant ratio (DR) of OGTT-ISR and beta-index with the insulinogenic index (IG-Index: Delta Insulin 30' - Basal/Delta Glucose 30' - Basal). In protocol D, 20 subjects (14 with normal glucose tolerance, 5 with impaired glucose tolerance and 1 with newly-diagnosed type 2 diabetes) underwent a 75 g OGTT and an intravenous glucose tolerance test (IVGTT) on separate days to explore the relationships between acute (0'-10') insulin response (AIR) during the IVGTT and beta-index and OGTT-ISR during the OGTT. RESULTS: In all protocols, the minimal analogic model of C-peptide secretion achieved a reasonable fit of the experimental data. In protocol A, a good reproducibility of both beta-index and OGTT-ISR was observed with both complete and reduced (every 30') data sets. In protocol B, increasing the oral glucose load caused progressive increases in OGTT-ISR (from 2.63 +/- 0.70 to 5.11 +/- 0.91 Units.120'-1.m-2 BSA; P < 0.01), but the beta-index stayed the same (4.14 +/- 0.35 vs. 4.29 +/- 0.30 vs. 4.30 +/- 0.33 pmol.min-2.m-2 BSA). In protocol C, both OGTT-ISR and beta-index had lower day-to-day CVs (17.6 +/- 2.2 and 12.4 +/- 2.4%, respectively) and higher DRs (2.57 and 1.74, respectively) than the IG-index (CV: 35.5 +/- 6.3%; DR: 0.934). OGTT-ISR was positively correlated to BMI (P < 0.03), whereas beta-index was inversely related to both fasting and 2 h plasma glucose (P < 0.01 for both). In protocol D, beta-index, but not OGTT-ISR, was significantly correlated to AIR (r = 0.542, P < 0.02). CONCLUSIONS: Analogically modelling beta-cell function during the OGTT provides a simple, useful tool for the physiological assessment of beta-cell function.     

动态血糖监测联合胰岛素泵强化治疗2型糖尿病疗效及安全性评价

目的分析动态血糖监测联合胰岛素泵强化治疗2型糖尿病（T2DM）的临床疗效及安全性。方法将88例T2DM患者随机分为观察组和对照组,每组44例。观察组采用动态血糖监测系统（CGMS）联合胰岛素泵持续皮下输注（CSII）,即＂双C＂疗法进行治疗,对照组仅采用CSII进行治疗,比较2组患者治疗前后血糖水平的变化、血糖达标时间、胰岛素用量及低血糖事件的发生情况。结果治疗后,2组患者的空腹血糖（FBG）和2h餐后血糖（2hPG）均较治疗前明显降低;观察组患者胰岛素用量及血糖达标时间均显著低于对照组,差异有统计学意义;治疗期间,观察组有8例患者出现低血糖,均无其他伴随症状,对照组有18例患者出现低血糖,均伴有冷汗、心慌等症状,2组低血糖发生率比较差异显著。结论 ＂双C＂疗法可有效降低T2DM患者的血糖水平,减少胰岛素用量及缩短血糖达标时间,降低低血糖发生率,值得在临床推广应用。     

实时动态血糖监测系统在危重症胰岛素强化治疗中作用的荟萃分析

目的 评价实时动态血糖监测系统(RT-CGMS)与传统间断血糖监测方法(IGM)在危重症胰岛素强化治疗(ⅡT)中的作用是否存在差异,以探讨RT-CGMS在危重症强化降低血糖治疗中的意义.方法 系统性检索中文、西文文献数据库中的相关临床随机对照试验(RCT),应用Review Manager 5.2软件进行荟萃分析.评价指标包括:低血糖事件发生率、平均血糖水平、血糖达标时间比例、短期病死率等.结果 共有6篇文献,总计531例患者纳入本次研究.平均血糖水平合并SMD=-0.21(95％ SMD:-0.43 ～0.01,P=0.07);血糖达标比例时间合并SMD=0.20(95％ SMD:-0.09～0.49,P=0.18);低血糖事件发生率合并OR=0.20 (95％ CI:0.09～0.43,P＜0.01);短期病死率合并OR=0.35 (95％ CI:0.14～0.89,P=0.03).结论 危重症强化胰岛素治疗(ⅡT)过程中应用RT-CGMS可明显减少低血糖事件的发生率,但RT-CGMS在保持血糖于理想水平方面比较传统间断血糖监测(IGM)未见明显优势.     

Effects of clozapine administration on body weight, glucose tolerance, blood glucose concentrations, plasma lipids, and insulin in male C57BL/6 mice: A parallel controlled study

Background: Clozapine has been associated with metabolic adverse events (AEs) (eg, elevated body weight, blood glucose concentrations, cholesterol, triglycerides [TG]), all of which have deleterious effects on health and medication compliance. However, little focus has been directed toward finding a suitable experimental model to study the metabolic AEs associated with clozapine.Objective: The aim of this study was to assess the effects of clozapine administration for 28 days on body weight, glucose tolerance, blood glucose concentrations, plasma lipids, and insulin in C57BL/6 mice.Methods: C57BL/6 mice were grouped and treated with clozapine 2 or 10 mg/kg or vehicle intraperitoneally QD for 28 days. Body weight was assessed on days 0 (baseline), 7, 14, 21, and 28, and glucose tolerance, blood glucose concentrations, insulin (calculated by insulin resistance index [IRI]), and plasma lipids (including total cholesterol, TG, high-density lipoprotein cholesterol [HDL-C], and low-density lipoprotein cholesterol) were assessed on day 29.Results: Sixty 10-week-old, male C57BL/6 mice were included in the study and were divided into 3 groups (20 mice per group). The body weight significantly decreased in the clozapine 10-mg-treated group on days 14, 21, and 28 compared with the vehicle group (mean [SD] body weight: 21.61 [1.05] vs 22.79 [1.11], 22.53 [1.05] vs 24.17 [1.24], and 22.21 [1.07] vs 24.99 [1.39] g, respectively; all, P < 0.05). In the clozapine 10-mg/kg group, blood glucose concentrations significantly increased 0, 30, 60, and 120 minutes after glucose administration compared with the vehicle group (mean [SD]: 6.67 [1.25], 25.34 [5.85], 12.68 [3.39], and 7.52 [1.45] mmol/L, respectively, vs 4.61 [0.78], 21.54 [6.55], 11.46 [3.46], and 6.55 [1.42] mmol/L, respectively; all P < 0.05). The clozapine 10-mg/kg group also had significant increases in plasma insulin concentrations compared with the vehicle group (12.70 [5.27] vs 7.62 [4.54] μIU/mL; P < 0.05) and IRI (3.01 [1.26] vs 1.51 [0.96]; P < 0.05). Plasma HDL-C concentration also significantly decreased in the clozapine 10-mg/kg group compared with the vehicle group (1.23 [0.25] vs 1.47 [0.16]; P < 0.05).Conclusion: Clozapine 10 mg/kg was associated with significant decreases in body weight and significant increases in fasting blood glucose and glucose tolerance in these male C57BL/6 mice.     

Quantitative study of starving platelets in a minimal medium: maintenance by acetate or plasma but not by glucose

Summary. The requirement of donor platelets for fuels, plasma and calcium were studied using platelets washed, filtered to remove leucocytes and resuspended in a new glucose-free minimal platelet storage medium with low citrate (3 mmol/1), low buffer capacity and no calcium. This is the first study of platelets stored without plasma, glucose or calcium and it was shown that platelets continued to aggregate with collagen plus adrenaline for 48 h and showed only a 50% fall in 'swirl index', an objective morphology score, after 3 days, showing that by these criteria human platelets do not require glucose. Sodium acetate extended the storage time by between 2 and 4 days, depending on the index parameter. This is the first evidence showing that failure of platelets in these conditions is at least partly due to exhaustion of fuel, and the first evidence that acetate prolongs in vitro survival. As little as 10% low-glucose plasma extended the storage time, but it was no better than acetate. New observations using this system included a very rapid fall in pH during resuspension of the washed platelet pellet, a rising pH in the absence of added fuel and an increased pH with added acetate.     

Resuscitation of severe but brief haemorrhagic shock with PFC in rabbits restores skeletal muscle oxygen delivery and does not alter skeletal muscle metabolism

Studies have demonstrated that perfluorocarbon (PFC) emulsions associated with hyperoxia improved whole body oxygen delivery during resuscitation of acute haemorrhagic shock (HS). Nevertheless the microcirculatory effects of PFC and the potential deleterious effects of hyperoxic reperfusion are still of concern. We investigated (i) the ability of a newly formulated, small sized and highly stable PFC emulsion to increase skeletal muscle oxygen delivery and (ii) the effect of hyperoxic reperfusion on skeletal muscle metabolism after a brief period of ischaemia using an original, microdialysis-based method that allowed simultaneous measurement tissue oxygen pressure (PtiO2) and interstitial lactate and pyruvate. These measurements were carried out in anaesthetised and ventilated (FiO2 = 1) rabbits subjected to acute HS (50% of blood volume withdrawal) and either resuscitated with a PFC emulsion diluted with a 5% albumin solution (16.2 g PFC per kg body weight) (n = 10) or with a modified fluid gelatin solution (Gelofusine) (n = 10). We found no difference between the two groups for the haemodynamic and haematological variables (except for the venous oxygen partial pressure). However, a significant difference was observed in the slope of the regression linear relationship exhibited between the mean arterial pressure (MAP) and the PtiO2, PFC group showing a much steeper slope than Gelofusine group. In addition, PtiO2 values increased linearly with decreasing haematocrit (Hct) values in PFC-resuscitated animals and decreased linearly with decreasing Hct values in Gelofusine-resuscitated animals. There were no differences between the two groups concerning the blood and interstitial lactate/pyruvate ratios suggesting no deleterious effect of hyperoxic resuscitation in skeletal muscle. In conclusion these results suggest that resuscitation of severe, but brief, HS with PFC increased skeletal muscle oxygen delivery without measurable deleterious effects.     

The effect of insulin in combination with selenium on blood glucose and GLUT4 expression in the cardiac muscle of streptozotocin‐induced diabetic rats

We evaluated the effect of a combination of low doses of insulin (1 U/kg/day) and selenium (180 μg/kg/day) on general physiological parameters and the level of glucose transporter (GLUT4) in the cardiac muscle of streptozotocin‐induced diabetic rats. Diabetic rats were treated with insulin, selenium and a combination of insulin and selenium for 4 weeks. The levels of blood glucose and hemoglobin A1c were estimated; the level of the GLUT4 in the cardiac muscle was examined by immunoblotting and immunohistochemistry. Insulin in combination with selenium could significantly lower blood glucose and HbA1c levels and could restore disturbances in GLUT4 level in the cardiac muscle. The treatment with insulin was only partially effective in the restoration of diabetic alterations. We conclude that there was cooperation between insulin and selenium, and that the treatment of diabetic rats with combined doses of insulin and selenium was effective in the control of blood glucose and correction of altered GLUT4 distribution in diabetic rat hearts.     

QT dispersion from body surface ECG does not reflect the spatial dispersion of ventricular repolarization in sheep

The correlation between the QT dispersion on body surface ECG and the dispersion in ventricular repolarization from the cardiac surface was studied in six sheep anesthetized with pentobarbital. The standard 12-lead body surface ECG and multiple ventricular epicardial ECGs were simultaneously recorded. The activation-recovery interval (ARI) was measured from the unipolar epicardial ECGs. The pooled QT dispersion from the six animals was significantly smaller than the pooled ARI dispersion (22.7 +/- 2.6 vs 33.0 +/- 6.9 ms, P < 0.01). There was no correlation between the QT and ARI dispersion. The unipolar epicardial ECGs were then converted into bipolar ECGs and epicardial QT intervals were subsequently acquired from these ECGs. The average value of epicardial QT dispersion from the six animals was similar to that of body surface ECG, but was less than the ARI dispersion (27.5 +/- 6.8 vs 33.0 +/- 6.9, P < 0.01). A good correlation between the epicardial QT dispersion and ARI dispersion was identified (r = 0.84, P < 0.05). In addition, a prolongation in ventricular repolarization, induced by an increase in coronary flow, elicited a pooled ARI dispersion of 62.3 +/- 6.2 ms (n = 6), which was larger than the simultaneously recorded body surface QT dispersion (28.3 +/- 9.8 ms, n = 6, P < 0.01). No correlation between the ARI and QT dispersion was found in the presence of the prolonged ventricular repolarization. In conclusion, QT dispersion from a 12-lead body surface ECG seems to underestimate the spatial dispersion of ventricular repolarization acquired from sheep epicardium.